WO2006074579A1

WO2006074579A1 - Oil immersion exposure method in chip photolithographic process

Info

Publication number: WO2006074579A1
Application number: PCT/CN2005/000121
Authority: WO
Inventors: Xiao Zhu
Original assignee: Xiao Zhu
Priority date: 2005-01-14
Filing date: 2005-01-28
Publication date: 2006-07-20
Also published as: CN1804724A

Abstract

An oil immersion exposure method in chip photolithographic process comprises the steps: (1) at first, the exposing medium is placed in photomask and lens system of the photolithographic device; (2) the exposing medium is applied on the chip before the ‘‘aligning and exposing’’ procedure in the exposing reaction chamberé (3) the exposing medium on the surface of the chip is leveled off so that the medium is homogeneous and no buble appearsé (4) the photomask is moved to above the chip and the lens system is finely adjusted downwards so that the lens can contact the exposing medium on the surface of the chip. The exposing medium is a vegetable oil and preferablz is a cedar oil. The Oil immersion exposure method using the oil as the medium of the present invention not only can make a pattern whose size is smaller than the exposure wavelength, but also can avoid expensive cost investment.

Description

Oil immersion exposure method in chip lithography process

The present invention relates to an optical engraving method for a chip, and more particularly to an exposure method in a chip lithography process. BACKGROUND OF THE INVENTION Chips belong to the field of microelectronics in high technology, and are mainly used in computers, communications, military, aerospace and manufacturing industries, and have been widely used in various fields closely linked to people's daily lives as the society develops. Moreover, with the wide application of chip technology, it has promoted its own rapid development. On the one hand, the performance and use functions of the chip are expanding, and the appearance characteristics of the chip are getting smaller and smaller, so that the chip gradually enters the micro or super Micro state. Regardless of how small the feature size of the chip is, it is necessary to first ensure the accuracy and sufficient resolution of the circuit pattern printed on the chip. For this reason, lithography manufacturing processing of chips is a key technology among them. For example, the replacement of integrated circuits depends on the development of lithography, and each generation of integrated circuit technology must develop a new generation of specific lithography.

The lithography method that has been used for a long time, the method of using air as the beam propagation medium, will encounter bottlenecks as the feature size is reduced to below 100 nm. It is generally believed that the use of optical lithography to print fine patterns is approaching the limit. At present, optical lithography methods have evolved from contact proximity, reflective projection, and step projection to scanning projection. Other new technologies that may replace optical lithography methods are being developed, such as: Electronic Projection Lithography (EPL), Ion Projection Lithography (IPL), X-ray lithography, and electron beam direct writing lithography (EBDW). And ultra-violet lithography (EUV).

In the conventional chip lithography method, after the chip is completed, the chip enters the chip processing and manufacturing stage. The process is briefly described as follows: (1) Making a photomask, generally using an electron beam to copy the Layout design of the chip onto the reticle, including the fabrication of the lithography master and mask; (2) Preparing the wafer The wafer is the basic material for chip manufacturing; (3) oxidation, using a special gas, the chip crystal is chemically reacted at a specific temperature to produce an oxide layer, a silicon nitride layer and a polysilicon layer, respectively; (4) development, in the previous step Each layer is coated with a photoresist, and then the layers are exposed by a photomask to form a protective layer, that is, a region to be retained; (5) etching, etching the unexposed non-protected region with a chemical substance (strong acid, strong alkali) To produce the desired structural appearance; (6) ion implantation, ion implantation to ionize specific areas; (7) metal sputtering, the surface of the wafer is covered with a layer of metal material, and then the photoresist is used and the next Layer reticle to make metal lines for transistor connection; (8) making next Layer, repeat steps (3) to (8), complete the structure of the chip layer by layer; (9) test.

The basic process for manufacturing a complete chip, generally has five lithography processes, each of which has a process of exposure and etching, and the key to actually making micro-printing more precise is what kind of medium the beam passes through and the application The method of the medium.

The imprinting in chip manufacturing is a thin layer of light-sensitive material on the surface of a semiconductor wafer (called photoresist, photoresist), printed with a geometric mold, and the patterns on different masks are imprinted on the crystal layer more than once. Upper to form a component pattern; and then etched to obtain different regions for implantation and diffusion. Photoresist compounds are sensitive to radiation and are classified into positive and negative gels. After the photoresist on the wafer is exposed to light, the positive gel in the exposed area is dissolved, washed, dried, and then etched to remove the insulating layer in the exposed area, and the photoresist in the unexposed area is not affected. Etching, and finally removing the photoresist. Through this procedure, the insulating layer molded image required for the design can be produced. The entire circuit system process typically requires repeated multiple printing and etching processes on the wafer surface.

The chip's feature pattern size, alignment tolerance, wafer surface condition, and number of lithography layers all affect the ease of a particular lithography process and the process at each step. At different chip factories, many lithography processes are tailored to specific process conditions, and various specific processes are variations or options for basic lithography 10-step methods.

The 10 steps of the lithography process are as follows (take the process of bright field mask and negative glue as an example):

1, surface preparation, cleaning and drying the surface of the wafer; 2, applying photoresist, evenly applying a thin layer of photoresist on the surface of the wafer; 3, soft baking, heating, partially evaporating the photoresist solvent;

4, alignment and exposure, precise alignment of the mask and graphics on the wafer and exposure of the photoresist, negative gel is polymer; 5, development, removal of non-polymerized photoresist; 6, hard baking, Continue evaporation of the solvent; 7, visual inspection, check the surface alignment and defects; 8, Eclipse | J, remove the top of the wafer through the opening of the photoresist; 9, photoresist removal, crystal The photoresist layer on the circle is removed; 10, final visual inspection.

In order to ensure the minimum loss of resolution and the optimum size of the pattern on the lithographic mask onto the wafer surface, how to control the loss of resolution and the size of the pattern is the key to the technology. If a new exposure method can be found to reduce the size of the circuit on the chip, the performance of the chip will continue to increase. However, there is currently no way to afford a much lower cost of research and development while miniaturizing microelectronic circuits.

In the experiments of biological microscopic observation, the observation of the conversion of optical path medium provides a new idea for the development of medium ideas in the field of chip manufacturing. For example, in the conventional observation that air is the light propagation medium, the microscopic multiple is 20 to 640 times; and in the observation of oil as the light propagation medium - that is, the oil immersion objective lens - the microscopic multiple can reach 500~1600 Times. Invention patent content

SUMMARY OF THE INVENTION An object of the present invention is to provide an oil immersion exposure method in a lithography process capable of significantly improving chip integration, which uses oil as a light propagation medium, that is, it can concentrate the light beam more accurately without expensive cost, thereby manufacturing A chip with a smaller size.

The invention is based on the principle that in the lens system of the reticle (selecting a high power lens suitable for oil immersion), the light propagation medium around the chip, which is neither water nor air, but oil, is sent through the oil medium. It is possible to concentrate the beam more precisely.

In order to achieve the object of the present invention, the following technical solutions are adopted: a method of oil immersion exposure in chip lithography processing, ω first placing an exposure medium in a reticle lens system of a lithography machine;

(2) in the exposure reaction chamber, the chip is coated with an exposure medium before the "alignment and exposure" process;

(3) Flatten the exposure medium on the surface of the chip so that it is uniform and free of air bubbles; (4) Move the mask onto the chip, fine-tune the lens system so that the lens lens touches the exposure medium on the chip; The squash is 1. 5 mm. The flat thickness of the cedar oil is 1. 5 mm. The flat thickness of the cedar oil is 1. 5 mm.

As mentioned above, the "exposure" in the lithography process is a key step to improve the integration of the chip. From the principle of lithographic exposure projection, the refractive index n of the "aligned and exposed" beam medium in the lithography process, Partially determines the various properties of the reticle and its lens, such as microscopic resolution, depth of focus, accuracy of the beam, and so on. Increasing the refractive index n of the beam medium can improve the performance and exposure of the mask and its lens, and increase the multiple and accuracy of the micron.

The minimum size on the wafer, or the minimum resolution distance of the lens, is defined by the physical properties of the projection optics. According to the optical Rayleigh criterion, there is a relationship:

σ = κ λ /Ν. Α. =0. 61 λ / (η· sin θ )

Where: σ is the minimum pattern size, κ is the Rayleigh constant, λ is the wavelength of the exposure source, η is the refractive index of the medium in which the wafer is located (ie, the medium through which the beam propagates), and θ is the radius of the contraction lens to the wafer. Angle, η· sin e is the numerical aperture of the lens (abbreviated as NA). The larger the numerical aperture η· sin Θ is, the smaller the σ is, and the higher the resolution of the lens. It is known that the clean air of the refractive index η=1 is expensive, and its microscopic limit is reached;

The generation and release of vacuum in the exposure reaction chamber is not only extremely high in investment and low in efficiency; while the water having a refractive index η=1.33, due to physical and chemical factors such as the influence of water-soluble photoresist, its application as a beam medium No; solids with a high refractive index are not suitable for damage caused by contact with the wafer. Only greases with refractive indices close to glass and photoresist may be the object of choice, for example, natural vegetable oils, natural animal oils, mineral oils and synthetic oils. The invention relates to a medium for light propagation, in particular a natural vegetable oil having a refractive index close to glass, inactive chemical properties, stable physical properties, and a single composition, by linking the experiments of biological microscopic observation with the technique of lithographic exposure method. It is proposed to use cedar oil (cedar oil, which is higher in refractive index than air and water, close to the photoresist (refractive index n=l. 45) and close to glass (refractive index n=l.40~2.0). Cinnamon oil) as an exposure medium in lithography. The cedar oil is a yellow liquid with a density of about 0.92, a refractive index of n=1. 515~1. 52, a low freezing point of fats and fatty acids, and is the best choice for beam medium in lithography.

For this reason, if the lens is immersed in the oil, the aforementioned value of 0.006 / (η· sin e ) can be as small as 0.5, that is, the minimum pattern size that can be resolved is about half of the exposure wavelength. The method of the present invention is: in a projection lithography machine, adding a medium oil between a lens system of a reticle (selecting a high power lens suitable for oil immersion, a magnification of more than 90 times) and a wafer; Differentiate the mask after the lens and before, as in (a) and (b) below:

(a) If the mask is between the lens and the chip (ie, the mask in the optical path is 1 : 1 after the lens), the size of the pattern on the mask is the same as the size required on the wafer. After the parallel beam emerges from the lens system, it passes through the dielectric oil, passes through the masked glass, and passes through the dielectric oil to reach the photoresist. The refractive index of the optical path from the lens to the photoresist is substantially the same, so as to ensure the accuracy of the beam and the resolution of the exposure.

(b) If the end lens is between the mask and the chip (ie, before the mask is placed in the optical path, such as a step-and-repeat reduction system), the size of the pattern on the mask is generally the final on the wafer. 5 to 10 times the size. The lens system is also filled with dielectric oil. The mask is immersed in the medium oil. After the beam is emitted from the concentrating lens system, it passes through the medium oil, passes through the reticle glass, passes through the medium oil, and then passes through the condensing image. The lens system then passes through the dielectric oil and finally reaches the photoresist; the refractive index of the optical path from the concentrating lens to the photoresist is substantially the same, so as to ensure the accuracy and microscopic resolution of the beam. If the lens oil is not injected into the lens system, the mask is placed in the air. Only the end of the shrink lens system is connected to the chip by the medium oil. The beam is emitted from the shrink lens system and passes through the medium oil to reach the photoresist. . The refractive index of the optical path from the collapsing lens to the photoresist is substantially the same, which also ensures the accuracy and microscopic resolution of the beam. DRAWINGS

1 is a schematic view of an exposure system according to an embodiment of the present invention;

2 is a schematic view of an exposure system according to another embodiment of the present invention. detailed description

The embodiments are further described in detail with reference to the accompanying drawings. Performing an exposure process on the chip 1 Previously, proceed as follows: (1) First place cedar oil 30 in the reticle lens system 2 of the lithography machine; (2) In the exposure reaction chamber, before the "alignment and exposure" process on the chip 1 Apply cedar oil 31; (3) cedar oil 31 on the surface of the flat chip 1 so that the thickness of the cedar oil is 1. 5mm (may also be 1 leg, 2 legs respectively) no air bubbles; (4) move the mask 2 Above the chip 1, the lens system is fine-tuned so that the condensed lens lens 20 touches the cedar oil 31 on the chip 1, and the light path of the light beam is formed, and then the "alignment and exposure" and subsequent cleaning can be performed according to the original process requirements. , development and etching processes.

In the embodiment shown in Fig. 2, the reticle lens system 2 is not filled with cedar oil, and only the cedar oil 31 is applied to the chip 1 (the thickness of the cedar oil can be 1 mm and 2 mm, respectively), so that the lens system of the lens system 20 touches the cedar oil 31, so that the light beam is emitted from the contract lens system, passes through the medium oil 31, reaches the chip 1, and is exposed in sequence. The "S" shown in the figure is the light source, "H" is the thickness of the medium oil, 21 is the mask (the white area is the glass substrate, the black area is the chrome layer), 10 is the wafer, 11 is the oxide layer, 12 It is a photoresist. Industrial Applicability In the lithography process of a chip, the oil-based exposure method of the present invention can produce a chip having a pattern smaller than the exposure wavelength. Applying the invention at a wavelength of 193 nm, the development and production of the chip can enter the 60 nm line width generation. If the aperture angle Θ of the wafer is further improved from the lens aperture (i.e., using a large aperture lens system), the minimum pattern size on the resulting chip can be further reduced by the method of the present invention.

Claims

Rights request

1 . An oil immersion exposure method in a chip lithography process, comprising the steps of: α) first placing an exposure medium in a reticle lens system of a lithography machine; (2) in an exposure reaction chamber, at “pair” Pre- and Exposure "The chip is coated with an exposure medium before the process; (3) The exposure medium on the surface of the chip is flattened so that it is uniform and free of bubbles; (4) Move the mask over the chip, fine-tune the falling lens system, The lens lens touches the exposure medium on the chip.

2. The method of oil immersion exposure in a chip lithography process according to claim 1, wherein the exposure medium is a grease.

3. An oil immersion exposure method in a chip lithography process according to claim 2, wherein the oil is vegetable oil.

4. The method of oil immersion exposure in a chip lithography process according to claim 2, wherein the grease is a synthetic oil.

5. An oil immersion exposure method in a chip lithography process according to claim 2 or 3, wherein the vegetable oil is preferably cedar oil.

6. The method of oil immersion exposure in a chip lithography process according to claim 5, wherein the cedar oil has a flat thickness of 1 to 2 legs.

7. The method of oil immersion exposure in a chip lithography process according to claim 6, wherein the cedar oil has a flattened thickness of 1. 5 mm.