WO1997006407A1

WO1997006407A1 - Lens scatterometer system

Info

Publication number: WO1997006407A1
Application number: PCT/US1996/012513
Authority: WO
Inventors: John R. Mcneil; S. Sohail H. Naqvi; Scott R. Wilson
Original assignee: Mcneil John R; Naqvi S Sohail H; Wilson Scott R
Priority date: 1995-08-03
Filing date: 1996-07-31
Publication date: 1997-02-20
Also published as: US5703692A; AU6684896A

Abstract

An optical scatterometer system enables ilumination of a sample material (120) at various angles of incidence with beams (100) without rotating or otherwise moving the sample material (120).

Description

LENS SCATTEROMETER SYSTEM Reference to Related Patents

This application is related to and incoφorates by reference the subject matter of

U.S. Patent Nos. 4,710,642, 5,164,790, and 5,241,369.

Background and Summary ofthe Invention

This invention relates generally to scatterometers and more particularly to a lens

scatterometer system that provides for illumination ofa sample at different angles of

incidence without the necessity of rotating, tilting or otherwise moving the sample during

the course ofa scatterometer measurement.

Scatterometer arrangements, like those described in the prior art patents cited above, have been used for characterizing the microstructure of microelectonic and

optoelectronic semiconductor materials, computer hard disks, optical disks, finely

polished optical components, and other materials having lateral dimensions in the range of tens of microns to less than one micron.

Exemplary ofthe prior art are two publications. The first is by Michael R.

Murnane, et.al., "Developed Photoresist Metrology Using Scatterometry", Proceedings of the SPIE, Integrated Circuit Metrology, Inspection, and Process Control VIII, Vol 2196, pp 47-59 (1994); the second is by Michael R. Murnane, et. al.. "Scatterometry for 0.24 μm - 0.70 μm Developed Photoresist Metrology ", Proceedings ofthe SPIE, Integrated Circuit Metrology, Inspection, and Process Control IX, Vol 2439, pp 427-436 (1995). This referenced prior art extends the capability ofthe scatterometer measurements to enable characterization of structure having lateral dimensions that are sub-tenth-micron. The prior art scatterometer arrangement discussed in the literature is disadvantageous in that it requires rotation ofthe sample while performing a scatterometer measurement. This requirement precludes their use in applications in which the sample must remain stationary. In addition, the two rotation stages employed in this prior art scatterometer

represents a mechanical complexity, which can result in undesirable optical and

mechanical misalignment. Finally, the sample rotation required in this prior art

scatterometer necessitates increased sample handling, thus increasing the risk of damage to the sample.

It is therefore the principle object ofthe present invention to provide a

scatterometer system that enables illumination of a sample at various angles of incidence

without rotating or otherwise moving the sample.

Brief Description ofthe Drawings

Figure 1 is a pictorial diagram illustrating a prior art scatterometer system

employing a single detector and two rotation stages to move both the sample and the

detector.

Figure 2 is a pictorial diagram ofa lens in accordance with the present invention, illustrating use ofthe lens to provide illumination ofa sample at different angles of

incidence and to collect the light that is diffracted from the sample, in accordance with

the present invention.

Figure 3a is a pictorial diagram ofa lens scatterometer system in accordance with

the present invention, illustrating the use ofa lens, beam splitter, rotating block, and light

detection system for characterizing the light that is diffracted from the sample.

Figure 3b is a pictorial diagram ofa lens scatterometer system in accordance with the present invention, iUustrating the use of a lens, beam splitter, rotating block, and light

Figure 3 c is a pictorial diagram ofa lens scatterometer system in accordance with the present invention, illustrating the use ofa lens, beam splitter, rotating block, and two light detection systems for characterizing the light that is diffracted from the sample.

Figure 4 is a pictorial diagram ofa lens scatterometer system in accordance with the present invention, illustrating the use of a lens, beam splitter, mirror assembly, and light detection system for characterizing the light that is diffracted from the sample. Figure 5 a is a pictorial diagram of a portion ofa lens scatterometer system in accordance with the present invention, illustrating a block that is rotated about two axes

that is used for characterizing light that is conically diffracted from the sample.

Figure 5b is a pictorial diagram in accordance with the present invention,

illustrating the geometry involved in illuminating the sample under separate control ofthe

angle of incidence, Θ, and Φ, the angle between the grating vector and the incident beam.

Figure 6a is a pictorial diagram ofa lens scatterometer system in accordance with

the present invention, illustrating the use ofa lens, beam splitter, fiber optic assembly,

and light detection assembly for characterizing light that is diffracted from the sample.

Figure 6b is a pictorial diagram of a portion ofa lens scatterometer system in accordance with the present invention, illustrating the use ofa two dimensional fiber optic assembly for characterizing light that is conically diffracted from the sample.

Figure 7a is a pictorial diagram ofa lens scatterometer system in accordance with the present invention, illustrating the use ofa lens, beam splitter, laser array, and light detection assembly for characterizing light that is diffracted from the sample.

Figure 7b is a pictorial diagram of a portion ofa lens scatterometer system in

accordance with the present invention, illustrating the use ofa two dimensional source array for characterizing light that is conically diffracted from the sample.

Figure 8a is a pictorial diagram ofa lens scatterometer system in accordance with the present invention, illustrating the use ofa lens, beam splitter, linear beam, and light detection assembly for characterizing light that is diffracted from a sample. Figure 8b is a pictorial diagram ofa lens scatterometer system in accordance with

the present invention, illustrating the use ofa lens, two beam splitters, two linear beams,

and light detection assembly for characterizing light that is conically diffracted from the

sample.

Figure 8c is a pictorial diagram of a portion ofa lens scatterometer system in

accordance with the present invention, illustrating the use ofa lens, beam splitter, two

linear beams comprising a cross, and light detection assembly for characterizing light that is conically diffracted from the sample.

Figure 9 is a pictorial diagram ofa lens scatterometer system in accordance with

the present invention, illustrating the use ofa lens, beam splitter, rotating block, light

detection system, and mirror for characterizing the intensity and phase of light that is diffracted from the sample.

Detailed Description ofthe Preferred Embodiments

The present invention may be understood by first referring to the prior art

scatterometer system illustrated in Figure 1, hereafter referred to as the 2-Θ scatterometer

arrangement. In this scatterometer arrangement two rotational stages are incoφorated. One stage, called the "sample stage" is utilized to rotate the sample, and one stage, called

the "detector stage" is utilized to rotate a detector. Typically in this 2-Θ scatterometer

arrangement the rotation axes ofthe two stages are coincident, although this is not

required. The sample is illuminated with a light beam that is incident on the sample at a point that is also on the rotation axis ofthe sample; in other words the front surface ofthe

sample contains the axis of rotation of this sample stage. In this manner the angle of incidence ofthe light illuminating the sample can be made to vary over a range in a desired manner, and this can be controlled, for example, by a computer that is connected to the sample stage. Further, as the angle of incidence is changed by activating the sample stage, the detector stage is activated to move the detector in a desired manner. The two stages are activated either simultaneously, or practically simultaneously.

As explained previously, the 2-Θ scatterometer arrangement is especially useful for characterizing the light scattered and diffracted from samples which are comprised of structure that is periodic. When monochromatic, plane wave light is incident upon the periodic structure, the light is diffracted into orders at angles governed by the simple grating equation, sin Θ + sin Θ' = nλ / d. In this expression, Θ is the angle of incidence ofthe light, Θ' is the angle made by the diffraction order, n is the order number, λ is the wavelength ofthe light, and d is the period or pitch ofthe structure that is illuminated. This relationship is well known and

discussed in text books on optics.

The 2-Θ scatterometer thus monitors the intensity ofa single diffraction order as a

function ofthe angle of incidence ofthe illuminating light beam. The intensity variation

ofthe 0-order as well as higher diffraction orders from the sample can be monitored in

this manner, and this provides information which is useful for determining the properties

ofthe sample which is illuminated. Because the properties of a sample are determined by

the process used to fabricate the sample, the information is also useful as an indirect

monitor ofthe process. This methodology is described in the literature of semiconductor

processing..

Note that the light beam used to illuminate the sample might be the output from a

laser or it might be some other appropriate beam of radiation that can be directed to illuminate the sample. Typically continuous, low power lasers such as He-Ne, Ar-ion, He-Cd and semiconductor diodes are used for the source ofthe light beam, although other

sources of radiation might be used equally well in the scatterometer arrangement described here. The wavelength ofthe sources might range from x-ray through the visible and microwave regions, to the long wavelength region which corresponds to frequencies of just a few Hz. Generally, larger wavelengths provide for characterizing samples that have structure of larger dimensions. The following discussion will use the terminology "beam" or "light beam" to refer to the radiation that illuminates the sample that is within this wavelength region. Similarly, it is understood that the different diffraction orders that result from illuminating the sample with the beam will also be

called "diffracted beams".

A shortcoming ofthe prior art 2-Θ scatterometer arrangement illustrated in Figure

1 is that the sample must be rotated in the process of performing a scatterometer

measurement. The angular range over which the sample is rotated in this prior art

configuration is typically 40 degrees or more, and in some applications ofthe 2-Θ

scatterometer arrangement the sample must be rotated ± 40 degrees or more (i.e. a total

of 80 degrees or more). Because the axis of rotation ofthe sample is parallel to, and

included in the surface ofthe sample, this rotation precludes application ofthe prior art 2-

Θ scatterometer arrangement in situations in which the sample must necessarily be stationary. This occurs practically at all steps in processing many materials, including semiconductor materials, storage media, and the like. For example, in processing semiconductor wafers in a vacuum environment, in which the wafer can not be moved

existing processing equipment and associated processing techniques would require extensive modification to accommodate wafer rotation. Such modifications would be impractical.

Additionally, the two rotation stages utilized in the prior art 2-Θ scatterometer arrangement represent mechanical complexity. Eliminating one or both of them would represent a significant simplification in maintaining optical and mechanical alignment.

Another shortcoming ofthe sample rotation in implementing the prior art 2-Θ scatterometer arrangement illustrated in Figure 1 is that the two stages involve mechanical motion, and this generates particulate contamination. Because the sample is located near to the stages, contamination levels on the sample can increase because of this.

Finally, sample rotation in the prior art configuration of Figure 1 requires

increased levels of sample handling, which in turn increases the risk of damaging the

sample. The sample must be fixed in a holder that will sufficiently secure the sample for rotation, and this involves more handling ofthe sample compared to an arrangement in

which the sample is stationary. Similarly, increased handling requires more time before

the sample can be examined.

Figure 2 illustrates how a beam (100) can be directed to different points ofthe

entrance aperture ofa lens (110) and be transmitted through the lens (110) to illuminate a

sample (120) at different angles of incidence. The angle of incidence depends upon the radial location ofthe beam in the entrance aperture ofthe lens. Only two beams (100) are shown in the Figure 2 for puφoses of illustration; these two beams (100) are labeled "\" and "2" in Figure 2. The invention would typically utilize many beams to illuminate the sample (120). For simplicity of illustration, the beams (100) are shown to travel in directions that are parallel to the axis ofthe lens (110) prior to entering the lens (1 10).

However, the beams are not required to travel parallel to the axis ofthe lens (110) prior to entering the lens (110), nor are the beams required to be parallel to each other prior to entering the lens. The portion of the sample (120) which is to be characterized is located in the image plane ofthe lens at the point where the beams are imaged to a common point. In the special case in which the beams travel parallel to each other prior to entering the lens, the sample (120) is placed in the back focal plane of the lens; the back focal plane is the same as the image plane in this situation. More specifically, in the case in

which the beams are all parallel to the lens axis, the sample (120) is located at the back

focal point ofthe lens.

It is understood that in application ofthe invention discussed herein, many beams

are directed to the entrance aperture ofthe lens (110) to subsequently provide

illumination ofthe sample (120) at many different angles of incidence. In one

embodiment ofthe present invention, the beams are individually activated in sequence, such that only one beam illuminates the sample (120) at one specific time and at one

specific angle of incidence. Alternatively, more than one ofthe beams can be activated

simultaneously, with each beam illuminating the sample (120) at a corresponding angle

of incidence. A third embodiment ofthe present invention utilizes a single beam that is translated across the entrance aperture ofthe lens (110). This achieves the effect of illuminating the sample (120) with many beams at many different angles of incidence

over a period of time. A fourth embodiment ofthe present invention utilizes a linear beam to illuminate the entrance aperture ofthe lens (110). This achieves the effect of illuminating the sample (120) with a large number of beams at a continuum of angles of incidence. The light detection configuration, in part, determines the sample illumination

arrangement that is utilized.

Typically the diameter ofthe beam (100) is much smaller than the aperture ofthe lens (110). For example, in one implementation the output ofa He-Ne laser is approximately 1 mm in diameter, and the lens entrance aperture is in the range of 25 mm to 100 mm. Both the beam diameter and the lens entrance aperture can be scaled larger or smaller by use of appropriate optical elements. In this manner, the beam that exits the

lens illuminates the sample at substantially a single angle of incidence.

The lens (110) that is utilized in the present invention substantially determines the

range over which the angle of incidence ofthe beam can be varied. Specifically, the f-

number (f/#) ofthe lens will determine the maximum angle of incidence the beam can have in illuminating the sample. For example, in the case of beams that enter the lens

parallel to the lens axis, the maximum angle of incidence, Θ, is given by sin^"'{l/(2f/#)}.

Lenses are commercially available that have an f/# of 0.74 and an aperture of 50 mm

diameter. A beam that enters this lens traveling parallel to the lens axis and 25 mm from the lens center illuminates the sample with an angle of incidence of approximately 42.5

degrees. Beams that pass through the lens at smaller radial positions, closer to the center

ofthe lens, exit the lens to illuminate the sample at smaller angles of incidence. The

relation between the location ofthe beam in the lens entrance aperture and the angle of incidence ofthe beam at the sample is determined by the lens design. Similar relations exist in the case ofthe lens being cylindrical as opposed to spherical.

The light that illuminates the sample is diffracted by the sample into two or more beams. There are two sets of diffracted beams: beams that are transmitted into the sample and beams that are reflected from the sample. The two so-called 0-order diffracted beams or orders, coπesponding to n = 0 in the simple grating equation, will always exist, with one transmitted into the sample and the other reflected from the sample. Higher order diffraction from the sample, e.g. the n = ± 1, ±2, etc. orders that are reflected and transmitted may or may not be present; the existence ofthese higher orders is governed by the simple grating equation. The intensity ofthe diffracted beams is extremely sensitive to the structure comprising the sample. Specifically, the pitch ofthe lines

comprising the diffracting structure, as well as their width, height, and sidewall curvature

in the case ofthe sample being a relief grating, are contributing factors that determine the

diffraction characteristics ofthe sample. Ifthe sample is comprised of a phase grating,

such as exposed, but undeveloped photoresist, the pitch and width ofthe latent image

structure determine the diffraction characteristics. Details ofthe diffraction

characteristics are described in the literature.

One or more ofthe diffracted beams which are reflected from the sample enter the

bottom ofthe lens. The reflected 0-order beams will enter the lens, as shown in Figure 2;

this is illustrated by beams 1-0 and 2-0 in the figure for the two beams 1 and 2,

respectively. The higher diffraction orders reflected beams will enter the lens provided their diffraction angle is within the acceptance angle ofthe lens. This is illustrated in Figure 2 by diffraction order 1-1 shown entering the lens, and diffraction order 2-1 shown not entering the lens (110). Diffraction order 1-1 corresponds to one ofthe lst-order diffracted beams from the incident beam 1, and diffraction order 2-1 corresponds to one ofthe lst-order diffracted beams from the incident beam 2. The beams which enter the lens transmit through the lens and exit the lens as illustrated in Figure 2. For simplicity, not all ofthe reflected diffraction orders, and none ofthe transmitted diffraction orders are illustrated in Figure 2.

It is understood that the construction details ofthe lens (110) ofthe invention vary

significantly, depending, for example, upon the performance requirements ofthe lens (110). For example, the wavelength ofthe beam (100) will determine the material

properties ofthe elements which comprise the lens (1 10). The lens (110) will typically be comprised of transparent glass for wavelengths ofthe beam (100) which are within the

visible region. For wavelengths which are significantly shorter than those ofthe visible

region, some or all ofthe elements which comprise the lens (110) will necessarily be

reflecting to the beam (100). It is further understood that other performance requirements

ofthe lens (110) will determine details ofthe construction and characteristics ofthe lens (110).

Figures 3a and 3b illustrate scatterometer aπangements that utilize a rotating

block (150) to provide a means of translating the beam from the source (105) to different points ofthe entrance aperture ofthe lens (110), and thus to illuminate the sample (120) at different angles of incidence, Θ. These arrangements comprise lens scatterometer

systems and represent an improvement over the 2-Θ scatterometer. The lens

scatterometer aπangements provide a means of changing the angle of incidence, Θ, ofthe beam at the sample (120) without moving the sample (120).

The lens system scatterometer aπangements illustrated in Figures 3a and 3 b are comprised ofthe lens system and sample anangement previously described, together with a detection anangement (130), a beam splitter anangement (140), and a rotating block (150) that rotates about a single axis. The x-y axes ofa coordinate system are illustrated in the figures. The beam (100) is in the x-y plane as it originates from the source. The rotating block is transparent at the wavelength ofthe beam. In the anangement the beam from the source (105) propagates through the rotating block to different points on the beam splitter. At the beam splitter the beam is partially reflected. A portion ofthe beam is directed to different points ofthe entrance aperture ofthe lens (110) to illuminate the

sample (120) at different angles of incidence, Θ.

In Figure 3a the portion ofthe beam (100) that is reflected from the beam splitter

is directed toward the lens; the portion ofthe beam (100) that is transmitted by the beam

splitter is called the beam portion (300). In general, the block (150) rotates about an axis

that is not necessarily parallel to the beam propagation direction. The specific

anangement ofthe invention illustrated in Figure 3a has the block rotation axis being peφendicular to the x-y plane. In addition, the beam splitter (140) is peφendicular to the x-y plane. The faces ofthe block (150) at which the beam enters and exits are parallel,

and they are also both parallel to the axis of rotation. Additionally, these faces ofthe

block as well as the surfaces ofthe beam splitter (140) are peφendicular to the x-y plane. Thus the beam (100) remains in the x-y plane after transmission through the block (150) and after reflection from the beam splitter. The beam is offset after transmission through the block, shown as OS in Figure 3 a, and the amount of offset is dependent upon the rotation angle, Δ, ofthe block about its axis of rotation. This relation is easily calculated and is described in optics text books. In the specific anangement illustrated in Figure 3a, the block rotation causes the beam to be offset from, and parallel to, the beam prior to transmitting through the block, thus remaining in the x-y plane. In addition, the axis of the lens (110) is in the x-y plane in the anangement illustrated in Figure 3 a. Thus the beam is translated to different points along a line in the entrance aperture ofthe lens, and the beam locations at different angles of incidence, Θ, at the sample (120) location also lie in the x-y plane. In the anangement illustrated in Figure 3a, the beam portion (300) is directed to a beam dump or other device and is not utilized.

It is understood that more generally the rotation axis ofthe block (150), the axis

ofthe lens (110), and the surfaces ofthe beam splitter (140) are not required to be

peφendicular or parallel to the x-y plane as described above, in which case the beam

locations at different angles of incidence Θ define a surface that is not necessarily located in the x-y plane. It is also understood that the block (150) can have a shape that is not

exactly as illustrated in Figure 3a. For example, the block (150) can be rectangular in two

of its dimensions, as opposed to the square shape illustrated in Figure 3 a. More

generally, the block (150) can be comprised of a shape that has a total number of faces different than four, as illustrated in Figure 3a.

The reflected diffraction orders pass through the lens (110) as previously described to the beam splitter (140); for simplicity, only the reflected 0-order is illustrated in Figure 3a. At the beam splitter the reflected diffraction orders are partially transmitted by the beam splitter (140) to the detection system (130) where their intensities are measured. Measurements ofthe diffraction order intensities are made for each of a number of values of Δ and conesponding beam (100) angles of incidence Θ. The primary

puφose ofthe invention illustrated in Figure 3a, namely to provide a means of illuminating the sample at different angles of incidence and measuring the intensities of the reflected diffraction orders, without requiring the sample to be moved is thereby

accomplished. Figure 3b illustrates essentially the same invention as illustrated in Figure 3a. In the anangement of Figure 3b, the portion ofthe beam (100) from the source that is

transmitted by the beam splitter (140) is directed toward the lens (110) to illuminate the

sample (120); the portion ofthe beam (100) that is reflected by the beam splitter is called

the beam portion (300). The reflected diffraction orders which pass through the lens to

the beam splitter are partially reflected to the detection system (1 0). In the anangement

illustrated in Figure 3b, the beam portion (300) is directed to a beam dump or other

device and is not utilized. Otherwise the invention is essentially the same as that

illustrated in Figure 3a, with the primary purpose of providing a means of illuminating

the sample at different angles of incidence Θ and measuring the intensities ofthe

reflected diffraction orders without moving the sample.

Figure 3c illustrates how an additional detection system (135) can be utilized with the invention of either Figure 3a or 3b. The additional detection system is shown used in the anangement of Figure 3a for illustrative puφoses. The additional detection system (135) is used on the side ofthe sample (120) opposite to the side which is illuminated; i.e., below the sample (120). In this manner the anangement can characterize the intensities of diffraction orders that are transmitted by the sample (120). This measurement can be performed over a range of incident angles ofthe beam without

requiring the sample (120) to be moved. Note that the additional detection system (135) below the sample (120) can be utilized independently ofthe detection system (130) located above the sample (120) that measures the intensities ofthe reflected diffraction orders; the scatterometer anangement can be configured to have either or both ofthe detection systems. The detection system (135) below the sample (120) is not required to be identical to the detection system (130) above the sample (120). For example, the

detection system (135) below the sample (120) might include lower quality optical

elements, such as lenses of lessor optical quality than the lens (110).

The light detection systems (130) and (135) of Figures 3a, 3b, and 3c contain a

detector device. The detector device can be comprised ofa simple, single element such

as a Si photodiode, a photomultiplier, or other element appropriate for detecting the

wavelength and intensities ofthe reflected or transmitted diffracted beams. A single element detector provides an integrated measurement of all the diffraction order

intensities. Alternatively, the detector device can be comprised of a one-dimensional or

two-dimensional detector anay, such as a ccd anay, a photodiode anay, or other one- dimensional or two-dimensional detector anay appropriate for the wavelength and intensities ofthe diffracted beams. Use of a detector array provides spatially resolved intensity measurements ofthe individual diffraction orders and thus provides additional information compared to that obtained in integrated measurement. Similarly, the detector

device can be a videcon, nuvecon, or other similar detection element that provides spatially resolved intensity measurements ofthe diffraction orders. The detection systems (130) and (135) might also contain additional elements, such as lenses. In some situations the detection systems(130) and (135) might be considered to be a camera that

utilizes either ofthe detector devices previously mentioned.

Figure 4 illustrates how the lens system scatterometer invention described in Figure 3 a can utilize a set of minors (160) in place ofthe rotating block (150) to direct the beam to different points ofthe entrance aperture ofthe lens (110), and thus to illuminate the sample (120) at different angles of incidence. In Figure 4 the set of minors

(160) is comprised of two or more minors. In the anangement, one or more minors of

the set of minors (160) translates in a manner to cause the beam at the beam splitter (140)

to be offset from the same beam prior to encountering the set of minors. The amount of beam offset is dependent upon the amount of minor translation. This, in turn, causes the

beam to pass through the lens entrance aperture at different locations, and thus to

illuminate the sample (120) at different angles of incidence, similar to the description of

the invention of Figure 3a, b, and c. Figure 4 illustrates just one manner of achieving this beam offset. In the anangement illustrated in Figure 4, this is achieved by translating minor 1 and keeping minor 2 fixed in position. In this configuration, the beam (100) is reflected from minor 1 to different points on minor 2, reflected from minor 2 to different

points on the beam splitter (140), and it subsequently passes through the lens (110) at

different aperture locations, to thereby illuminate the sample (120) at different angles of incidence. The angle of incidence, Θ, depends upon the position of minor 1. The same effect can be achieved by translating minor 2 and keeping minor 1 fixed in position. In this manner the set of minors provides a similar function as the rotating block (150) in the invention illustrated in Figures 3a, b, and c. Otherwise the inventions of Figures 3a and 4 are essentially the same. A set of minors can be similarly utilized in place ofthe rotating block ofthe inventions described in Figures 3 b and 3c. It is understood that more generally some or all the minors ofthe set of minors (160) can be non-planar, and that some or all can be made to rotate. Other manners of translating or rotating minors which comprise a set of minors (160) can be envisioned to provide a means of translating the beam to different points in the entrance aperture ofthe lens (110), and thus to provide

sample illumination at different angles of incidence Θ without requiring the sample (120)

to be moved.

Other means can be envisioned of directing the beam to different points ofthe

entrance aperture ofthe lens (110). The two methods previously discussed, which

involve the rotating block (150) and the set of minors (160) are but two means of

achieving this.

Figure 5a illustrates a modified version ofthe rotating block (150) ofthe

inventions illustrated in Figures 3a, 3b, and 3c. The rotating block (170) is mounted in a

manner that provides rotation about two axes, shown as axis 1 and axis 2 in Figure 5a. A typical application would include the two axes being orthogonal. For example, mounting the rotating block (170) in a gimbals arrangement would provide such orthogonal axes of

rotation. Under this biaxial rotation, the beam (100) that transmits through the block is

offset in two directions relative to the beam (100) which enters the block. This is illustrated in Figure 5a by the two beam offsets labeled OSI and OS2, conesponding to offsets in the x-y plane and x-z plane, respectively. The magnitudes of OSI and OS2 are

dependent upon the respective rotation angles Δl and Δ2 ofthe rotating block (170). The rotating block (170) replaces the block (150) ofthe scatterometer configurations described previously in connection with Figures 3a, 3b, and 3c; otherwise these scatterometer configurations operate in essentially the same manner as previously

described. Figure 5b illustrates how the biaxial rotation ofthe block (170) causes the beam to be directed to different points in the plane ofthe entrance aperture ofthe lens (110). The

plane ofthe entrance aperture ofthe lens (110) is parallel to the plane defined by the y'-z'

axes, and the lens axis is in the x'-y¹ plane shown in Figure 5b. In turn, the beam that

illuminates the sample lies within a cone that is determined by the f/# ofthe lens (110).

The incident beam makes an angle Θ with the normal to the sample and angle Φ with the

grating vector, k (175), as illustrated in Figure 5b. The grating vector, k (175), is in the

plane ofthe sample (120) and in the direction normal to the lines of one ofthe sets of

periodic structure comprising the sample (120). This is the two-dimensional extension of the one-dimensional illumination anangements discussed in connection with Figures 3a, 3b, and 3c. More specifically, the nonzero value of Δ2 causes Φ to be nonzero.

Diffraction in the general case of Φ being nonzero is called "conical diffraction".

Measurements ofthe diffraction order intensities are made for one or more combinations of Δl and Δ2 to provide diffraction data over a range of values of© and Φ. Note that the x-y axes and the x'-y' axes lie in the same plane. The anangements illustrated in Figures 5a and 5b thus provide a means to investigate the conical diffraction characteristics ofa sample, with precise and independent control of© and Φ, that does not require moving the sample.

Figure 6a illustrates a lens scatterometer anangement which utilizes one or more fiber optic elements (180) to comprise an anay that provides beams of light. The anay of fiber optic elements (180) is appropriately configured to provide beams (100) that are directed to different points ofthe entrance aperture ofthe lens (110), such that the sample ( 120) is illuminated at one or more desired angles of incidence, Θ. For example, the lens

scatterometer anangement of Figure 6a is similar to that of Figure 3a, except that nine

fiber optic elements are arranged in a linear anay situated along the y-axis in place ofthe

block (150). This will in turn provide illumination ofthe sample (120) at nine different

angles of incidence, Θ, and the beams which illuminate the sample (120) also lie in the x-

y plane, consistent with the discussion related to the lens scatterometer anangement of Figure 3a. Figure 6b illustrates how the fiber optic elements (180) can be aπanged in a two-dimensional anay that is utilized in the lens scatterometer anangement; for

convenience the other elements ofthe lens scatterometer anangement are not included in

this Figure 6b. In the figure, the fiber optic elements (180) are ananged in two lines contained in the y-z plane, with an included angle of α. This anangement provides beams in a two-dimensional anay that are directed to the entrance aperture ofthe lens (110). This, in turn, produces illumination ofthe sample (120) with two sets of beams

(100), with the angle Φ of one set of beams different from Φ ofthe other set of beams by the same angle α, thus providing a means of characterizing the conical diffraction ofthe sample (120). The operation ofthe scatterometer configurations illustrated in Figures 6a and 6b is otherwise essentially the same as those described in connection with Figures 3a, 3b, and 3c.

The linear anangements of fiber optic elements (180) illustrated in Figures 6a and 6b were shown for illustration. Similarly, illustrating nine fiber optic elements (180) in each ofthe linear anangements illustrated in Figures 6a and 6b was for puφoses of illustration. Finally, showing the fiber optics elements (180) centered about the axis of the lens (110) was for puφoses of illustration. The fiber optic elements (180) can be

ananged an any desired manner, in curved or planar anays that contain fewer or greater

than nine fiber optic elements. Similarly, the anays of fiber optic elements (180) are not

required to be situated in the manner discussed previously, and they might be made to

rotate or move laterally to provide for illumination at desired angles Θ and Φ. Because of

their small size, many fiber optic elements can be ananged to provide high resolution of

Θ and Φ.

Each fiber optic element is appropriately finished to provide a beam that is either

collimated or focused a desired distance from the end ofthe element. This could consist ofa simple lens attached to the output end ofthe fiber. A gradient index (grin) lens could

also be utilized for this puφose. A lens anay can be used for this puφose when a large

number of fiber optics elements is utilized.

The fiber optic elements (180) can be illuminated, or activated, at their input ends in a number of manners. In one anangement ofthe invention, each fiber optic element

(180) is individually illuminated with the beam from the light source (105). In this anangement, either the beam is scanned, or the fibers are moved to couple the beam into each fiber element (180). For this anangement the diffraction order intensity measurements are performed in a sequential manner, as each fiber optic element is

illuminated. An alternative anangement involves illuminating the input ends of two or more fiber elements simultaneously. In this case, the diffraction order intensity measurements are performed simultaneously for those two or more fiber elements (180) that are illuminated. This is repeated, as necessary until all fiber elements (180) have been illuminated, and the coπesponding diffraction order intensity measurements have

been performed. The detector device necessarily provides the required spatial resolution

in this situation. Still another anangement ofthe invention involves use of individual

light sources coupled to the input ends of each ofthe fiber optic elements (180). The

most practical source for this application is a laser diode. Laser diodes are available

commercially in anays that can be utilized for this puφose. The light sources can be

individually controlled to illuminate the fibers in the desired manner that is consistent

with optimal diffraction order measurement; any combination of sequential/simultaneous illumination is possible. For the puφose of illustration, Figures 6a shows one fiber optic element being illuminated, and Figure 6b shows two fiber optic elements being

illuminated.

Figure 7a illustrates a lens scatterometer anangement which utilizes more than

one light source (105) to comprise an anay that provides beams oflight. The anay of light sources (105) is appropriately configured to provide beams (100) that are directed to different points ofthe entrance aperture ofthe lens (110), such that the sample (120) is illuminated at more than one angle of incidence, Θ. Suitable light sources include diode lasers and light emitting diodes (LEDs). For example, the scatterometer anangement of Figure 7a is similar in operation to those illustrated in Figures 3a and 6a except that nine light sources are ananged in a linear aπay situated along the y-axis in place ofthe block (150). This will in turn provide illumination ofthe sample (120) at nine different angles

of incidence, Θ. The beams which illuminate the sample (120) also lie in the x-y plane, consistent with the discussion related to the lens scatterometer anangement of Figure 3a. Figure 7b illustrates how the light sources (105) can be ananged in a two-dimensional anay that is utilized in the lens scatterometer anangement; for convenience the other

elements ofthe lens scatterometer anangement are not included in this Figure 7b. In the

figure, the light sources (105) are ananged in two lines contained in the y-z plane, with an

included angle of α. This anangement provides beams in a two-dimensional anay that

are directed to the entrance aperture ofthe lens (110). This, in turn, produces

illumination ofthe sample (120) with two sets of beams (100), with the angle Φ of one

set of beams different from Φ ofthe other set of beams by the same angle α, thus

providing a means of characterizing the conical diffraction ofthe sample (120). The operation ofthe scatterometer configurations illustrated in Figures 6a and 6b is otherwise

essentially the same as those described in connection with Figures 3a, 3b, and 3c.

The linear aπangements oflight sources (105) illustrated in Figures 7a and 7b were shown for illustration. Similarly, illustrating nine light sources (105) in each ofthe linear aπangements illustrated in Figures 7a and 7b was for puφoses of illustration. Finally, showing the light sources (105) centered about the axis ofthe lens (110) was for puφoses of illustration. The light sources (105) can be ananged an any desired manner, in curved or planar anays that contain fewer or greater than nine light sources. Similarly, the anays of light sources (105) are not required to be situated in the manner discussed previously, and they might be made to rotate or move laterally to provide for illumination at desired angles Θ and Φ. Because of their small size, many light sources can be ananged to provide high resolution of Θ and Φ. Each light source (105) is appropriately finished to provide a beam that is either collimated or focused a desired distance from the end ofthe element. This could consist of a lens attached to the output ofthe light source. A lens anay can be used for this puφose when a large number of light sources is utilized.

It is understood that other forms of a plurality of sources can be utilized within the

bounds of this invention.

The light sources (105) of Figures 7a and 7b can be activated in a number of

manners, similar to the invention of Figures 6a and 6b. In one anangement ofthe

invention, each light source (105) is individually activated to provide a beam, and the

diffraction order intensity measurements are performed in a sequential manner. An

alternative anangement involves activating two or more light sources (105)

simultaneously to provide two or more beams to illuminate the sample (120)

simultaneously. In this case, the diffraction order intensity measurements are performed simultaneously for those two or more light sources that are activated. This is repeated, as necessary, until all light sources (105) have been activated, and the coπesponding diffraction order intensity measurements have been performed. The detector device necessarily provides the required spatial resolution in this situation.

Figure 8a illustrates a lens scatterometer anangement which utilizes one light source (105) in conjunction with optical elements (160) to provide a linear beam (180). The term "linear beam" in this invention is understood to refer to a collimated beam which when viewed in cross-section (i.e. observing the beam intensity in a plane that is orthogonal to the direction of propagation) forms a line. The linear beam (180) is distinguished from the beam (100) mentioned previously in that the cross-section ofthe linear beam (180) is a line, whereas the cross-section ofthe beam (100) is typically a circle or nearly a circle. The linear beam (180) is directed to the beam splitter (140) which directs the beam to the entrance aperture ofthe lens (110), in a manner similar to

that previously discussed in connection with the anangement illustrated in Figure 3a.

The linear beam (180) passes through the lens (110), and it becomes a converging, fan-

shaped beam (190) which is focused at the sample (120). This provides the equivalent of simultaneous illumination ofthe sample (120) with a large number of beams (100) at a

large number of angles of incidence, Θ. The fan-shaped beam (190) lies in the x-y plane

in Figure 8a, consistent with the discussion related to the lens scatterometer anangement

of Figure 3a. The detection system (130) necessarily provides the required spatial resolution in this situation, as previously discussed.

In the scatterometer implementation illustrated in Figure 8a, the optical elements

(160) are constructed to convert the circular or near-circular beam (100) from the source

(105) into a linear beam (180). The width ofthe linear beam (180) is typically the same or nearly the same as the diameter ofthe beam (100), and the height ofthe linear beam (180) is much greater than its width. For example, the beam (100) from a He-Ne or similar laser is approximately circular and 1 mm in diameter. The optical elements (160) can be configured to convert this beam (100) into a linear beam (180) which in cross¬ section is a line of 1 mm by 50 mm. This might be accomplished, for example, by utilizing cylindrical lenses in a simple telescope configuration, including such designs as Keplerian, Galilean, astronomical, or others. Other configurations of optical elements (160) can be envisioned. For example, a portion ofthe optical elements (160) can be

located adjacent to, or incoφorated within the source (105), as is the case for a simple diode laser equipped with line generating optics. The output of such a configuration is a

fan-shaped beam. Sometimes called diode laser line projectors, these devices are

commonly available from a number of manufacturers, including Melles Griot of Irvine,

California and Edmund Scientific of Barrington, New Jersey. In this configuration the

remainder ofthe optical elements (160) would be comprised ofa lens and possibly

additional elements to collimate, or nearly collimate the fan-shaped beam, thus forming a linear beam (180).

The linear beam (180) might also be utilized to examine the conical diffraction

characteristics ofthe sample as previously discussed in connection with Figures 5a and

5b. To accomplish this without moving the sample (120), the linear beam is rotated about an axis that is parallel to, or coincident with its direction of propagation (the x-axis shown in Figure 8a). This might be achieved, for example, by making the optical elements (160) capable of rotating the linear beam (180) about the x-axis and might be achieved by

simply rotating the optical elements (160). In this configuration it may also be desirable to rotate the source (105) in order to maintain the desired polarization ofthe light field of the linear beam (180).

Figure 8b illustrates how two light sources (105) and (106), two sets of associated optical elements (160) and (165), and two linear beams (180) and (185) can be utilized in the lens scatterometer anangement to examine the conical diffraction characteristics of the sample (120). The source (106) has the properties discussed previously in connection

with the source (105). The sources (105) and (106) might be identical, or they might differ in some aspect such as emitting radiation at different wavelengths. The beam (101) has the properties described previously in connection with beam (100). The beams (100) and (101) might differ in some aspect, such as being comprised of radiation of different

wavelengths. Similarly, the optical elements (165) have the same general properties as

the optical elements (160), and the linear beam (185) has the same general properties as

the linear beam (180). In Figure 8b, the linear beam (180) from the source (105) is shown contained in the x-y plane as previously discussed. The linear beam (185) from

the source (106) is shown peφendicular to the x-y plane and thus appears as a single line

in Figure 8b. Note that it is not a requirement that this linear beam be peφendicular to

the x-y plane; the linear beam (185) can be ananged to make any angle with the x-y plane.

Refening to Figure 8b, the beam splitter (200) directs portions of both linear beams (180) and (185) toward the beam splitter (140), and a portion of both linear beams (180) and (185) are reflected from the beam splitter (140) and directed to the entrance aperture ofthe lens (110). Two fan-shaped beams (190) and (195) are formed from the linear beams (180) and (185), respectively, and these fan-shaped beams (190) and (195) are focused on the sample. This provides the equivalent of illuminating the sample by

two sets of beams, with each set illuminating the sample at many angles of incidence, Θ. The two sets of beams illuminate the sample at two different angles Φ. For the configuration illustrated in Figure 8b, one value of Φ is 0°, and the other value of Φ is

90°. Note that in general that Φ can have values different from 0° and 90° by orienting the two linear beams (180) and (185) in a desired manner with respect to the x-y- plane. The operation ofthe scatterometer configurations illustrated in Figures 8a and 8b is otherwise essentially the same as those described in connection with Figures 3a, 3b. and 3c.

Figure 8c illustrates the use of one light source (105) and optical elements (160)

to provide two linear beams (180) and (185) for use in the lens scatterometer system. For

convenience, only the source (105) and optical elements (160) are illustrated in Figure 8c.

The two linear beams (180) and (185) intersect and together comprise a beam which in

cross-section forms a cross. This pattern is directed toward the beam splitter (140). A portion ofthe optical elements (160) can be located adjacent to, or incoφorated within the source (105), as is the case for a simple diode laser equipped with cross-generating

optics. Such a system is available commercially from Lasiris, Inc. of St. Laurent,

Quebec, Canada. The source (105) and associated optical elements (160)' illustrated in Figure 8c are utilized in the scatterometer system shown in Figure 8a to provide a measurement capability that is essentially the same as that ofthe scatterometer system illustrated in Figure 8b. The conical diffraction properties ofthe sample (120) are characterized utilizing this apparatus without moving the sample.

Beams of other cross-section patterns are envisioned for use in the lens scatterometer system illustrated in Figure 8a in essentially the same manner as the cross beam pattern described in connection with Figure 8c. For example, the optical elements (160) can provide an anay of beams that are directed toward beam splitter (140). Specifically, the cross-section pattern ofthe beam subsequent to exiting the optical

elements (160) can be comprised of a one-dimensional or two-dimensional aπay of dots, a circle, an aπay of concentric circles, or some other desired pattern. Such patterns of light beams are possible by utilizing optical elements commercially from Lasiris, Inc. of St. Laurent, Quebec, Canada in conjunction with additional optical elements to comprise

the optical elements ( 160).

Figure 9 illustrates an additional minor (200) that is added to the lens system

scatterometer of Figure 3a; the same modification can be made to the other systems discussed previously. The addition ofthe minor (200) provides a significant increase in

the information content ofthe measurements that are performed by providing a reference

beam (210). The reference beam (210) allows the phase ofthe diffracted beams to be

measured. The increased information that the anangement of Figure 9 provides is useful for determining additional properties ofthe diffracting sample (120).

In the anangement of Figure 9, the portion ofthe beam (100) from the source

which illuminates the beam splitter but which is not directed to the lens (110) is allowed to illuminate the minor (200) is termed the beam portion (300). For example, in Figure 3 a the beam from the rotating block that illuminates the beam splitter (140) and which is transmitted by said beam splitter (140) is the beam portion (300) which illuminates the minor (200). Similarly, in the anangement of Figure 3b, the beam portion (300) that illuminates minor (200) is that which comes from the rotating block and which is reflected by the beam splitter (140). The function ofthe minor (200) is similar for the other scatterometer anangements discussed previously. Continuing, the minor (200) reflects this beam portion (300) back to the beam splitter (140). A portion thereof is reflected by the beam splitter (140) and becomes the so-called reference beam (210). It is a reference beam because its amplitude and phase does not depend upon, nor change with, the properties ofthe sample which is illuminated. The reference beam (210) propagates to the detection anangement (130) where it is detected. As the angle of

incidence ofthe scatterometer is changed, whether by the rotating the block (150),

moving a minor ofthe set of minors (160), or by other mechanisms, the minor (200)

operates in the manner just described to furnish a reference beam (210) to the detection

anangement (130) for all angles of incidence at which the sample (120) is illuminated.

The anangement of Figure 9 is similar to the well-known Twyman-Green and

Michelson interferometer systems that are described in text books on optics. Teachings

from these references can be utilized to understand the manner in which the reference

beam (210) contributes additional information to the measurements performed in utilizing the lens system scatterometer. There are two significant differences between these interferometer systems and the lens scatterometer system of Figure 9 in the manner that the reference beam is utilized. The interferometers utilize the reference beam only in

conjunction with the 0-order diffracted (specularly reflected) beam from the sample (120), while the lens scatterometer system illustrated in Figure 9 utilizes the reference beam (210) for all diffraction orders (0-order, ± 1 -orders, etc.) which are detected. Second, interferometers do not involve changing the angle of incidence ofthe beam that illuminates the sample, whereas a primary function ofthe lens scatterometer is to vary the angle of incidence. As a result, interferometers utilize the reference beam for only one angle of incidence, typically 0 degrees, whereas the lens scatterometer utilizes the

reference beam over a range of incidence angles. Note that the minor (200) can be constructed to contain a phase-shifting element that shifts the phase ofthe reference beam (210). The phase can be changed a desired

amount with the application of an appropriate signal to the phase-shifting element. This

phase-shifting ofthe reference beam (210) can be utilized during a measurement

performed using the lens system scatterometer to contribute additional information

concerning the sample (120) under investigation. The teachings from well-known books

on optics can be utilized for understanding the way in which the phase-shifting technique

can increase the information obtained in performing measurements oflight diffracted

from the sample (120). The phase-shifting element can, for example, be comprised ofa

piezo-electric crystal that is attached to the back surface ofthe minor (200). An

appropriate voltage applied to the piezo-electric crystal will cause the minor (210) to be displaced toward the beam splitter (140), thus changing the phase ofthe reference beam (210).

Note that the lens scatterometer anangements discussed above can be used to characterize samples which are unpattemed. In this situation in which the sample has no periodic structure, only the 0-order diffracted beams are diffracted, with one reflected from the sample and one transmitted into the sample. The intensities of one or both of these beams is measured. This amounts to characterizing the reflectance and transmittance ofthe sample as a function of angle ofthe incident beam. Analysis of this information yields information concerning the optical properties ofthe sample, such as the thickness and refractive index of thin films which might be part ofthe sample. The elements ofthe lens scatterometer system are typically controlled by a simple computer, such as a so-called PC or workstation. This control includes rotation ofthe

block (150) or block (170), or motion ofthe minor ofthe minor set (160), as well as

sample positioning, beam source activation, collection of data from the detector

anangement, and overall system coordination. In addition, the computer can perform

analysis ofthe data that is collected.

Claims

Ciaims 1. An optical scatterometer system for characterizing the diffraction properties ofa

sample material by varying the angle of incidence ofa light beam from a source without

moving the sample material, the optical scatterometer comprising:

light source means for transmitting one or more source light beams; a beam splitter positioned to direct the one or more source light beams toward the

sample material and to direct one or more light beams diffracted by the sample material;

a lens positioned to receive the one or more source light beams directed by the beam splitter, to transmit the one or more source light beams to illuminate the sample material, to receive the one or more light beams diffracted by the sample material, and to transmit the one or more light beams diffracted by the sample material to the beam

splitter;

one or more detection systems positioned to receive and characterize the one or more light beams diffracted by the sample material; and beam direction means positioned between the light source means and the beam splitter for directing the one or more source light beams transmitted by the light source means to selected different points of an entrance aperture ofthe lens.

2. An optical scatterometer system as in claim 1 wherein the beam direction means comprises a rotatable block transparent at the wavelength ofthe source light beam.

3. An optical scatterometer system as in claim 2 wherein the rotatable block is aπanged for rotation about one axis.

4. An optical scatterometer system as in claim 2 wherein the rotatable block is ananged for rotation about two axes to enable characterization of conical diffraction characteristics ofthe sample material.

5. An optical scatterometer system as in claim 1 wherein the beam direction

means comprises a set of minors.

6. An optical scatterometer system as in claim 5 wherein one or more minors of the set of minors are movable in a predetermined manner.

7. An optical scatterometer system as in claim 1 wherein the beam direction

means comprises an aπay of fiber optic elements.

8. An optical scatterometer system as in claim 7 wherein the aπay of fiber optic

elements comprises a one-dimensional anay.

9. An optical scatterometer system as in claim 7 wherein the anay of fiber optic elements comprises a two-dimensional array.

10. An optical scatterometer system for characterizing the diffraction properties of a sample material by varying the angle of incidence ofa light beam from a source without moving the sample material, the optical scatterometer comprising: light source means for transmitting a source light beam having a desired cross- sectional pattern; a beam splitter positioned to direct the source light beam toward the sample material and to direct one or more light beams diffracted by the sample material; a lens positioned to receive the source light beam directed by the beam splitter, to transmit the source light beam to illuminate the sample material, to receive the one or more light beams diffracted by the sample material, and to transmit the one or more light

beams diffracted by the sample material; and

one or more detection systems positioned to receive and characterize the one or

more light beams diffracted by the sample material.

11. An optical scatterometer system as in claim 10 wherein the light source

means is operative for transmitting a light beam of linear cross-section.

12. An optical scatterometer system as in claim 10 wherein the light source

means is operative for transmitting two light beams of linear cross-section for enabling

characterization of conical diffraction characteristics ofthe sample material.

13. An optical scatterometer system as in claim 12 wherein the light source

means comprises at least one light source operative for transmitting two intersecting source light beams that are each of linear cross-section.

14. An optical scatterometer system as in claim 12 wherein the light source means comprises at least one light source operative for transmitting an anay of source light beams.

15. An optical scatterometer system as in claim 1 wherein each ofthe one or more detection systems includes a single detection element for providing an integrated characterization ofthe one or more light beams diffracted by the sample material.

16. An optical scatterometer system as in claim 1 wherein each ofthe one or more detection systems includes an aπay of detection elements for providing one- dimensional characterization ofthe one or more light beams diffracted by the sample material.

17. An optical scatterometer system as in claim 16 wherein the anay of detection

elements comprises a CCD anay.

18. An optical scatterometer system as in claim 16 wherein the anay of detection

elements comprises a photodiode anay.

19. An optical scatterometer system as in claim 16 wherein the anay of detection

elements comprises a camera.

20. An optical scatterometer system as in claim 1 wherein each ofthe one or

more detection systems includes an anay of detection elements for providing two-

dimensional characterization ofthe one or more light beams diffracted by the sample

material.

21. An optical scatterometer system as in claim 1 wherein the one or more detection systems comprises a videcon.

22. An optical scatterometer system as in claim 1 wherein the one or more detection systems comprises a nuvicon.

23. An optical scatterometer system as in claim 20 wherein the aπay of detection elements comprises a CCD anay.

24. An optical scatterometer system as in claim 20 wherein the anay of detection

elements comprises a photodiode aπay.

25. An optical scatterometer system as in claim 20 wherein the aπay of detection elements comprises a camera.

26. An optical scatterometer system as in claim 1, further comprising a minor for providing a reference light beam to in turn provide additional information regarding the

sample material.

27. An optical scatterometer system as in claim 10, further comprising a minor

for providing a reference light beam to in turn provide additional information regarding

the sample material.

28. An optical scatterometer system for characterizing the diffraction properties

ofa sample material by varying the angle of incidence ofa light beam from a source

without moving the sample material, the optical scatterometer comprising: light source means for transmitting a plurality of source light beams; a beam splitter positioned to direct the plurality of source light beams toward the

a lens positioned to receive the plurality of source light beams directed by the beam splitter, to transmit the plurality of source light beams to illuminate the sample material, to receive the one or more light beams diffracted by the sample material, and to transmit the one or more light beams diffracted by the sample material to the beam splitter; and one or more detection systems positioned to receive and characterize the one or more light beams diffracted by the sample material;

said light source means being operative directing the plurality of source light beams to selected different points of an entrance aperture ofthe lens.

29. An optical scatterometer system as in claim 28 wherein the light source means comprises a one-dimensional anay oflight sources.

30. An optical scatterometer system as in claim 28 wherein the light source

means comprises a two-dimensional anay oflight sources.