WO2007023422A2

WO2007023422A2 - Inspection method and inspection device for substrates

Info

Publication number: WO2007023422A2
Application number: PCT/IB2006/052825
Authority: WO
Inventors: Ralf Dorscheid; Gereon Vogtmeier; Roger Steadman
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2005-08-26
Filing date: 2006-08-16
Publication date: 2007-03-01
Also published as: WO2007023422A3

Abstract

An inspection method for through- wafer interconnects of a through- wafer interconnects substrate (105) the substrate having a front-side and a back-side on which back-side at least one contact (218) is formed, comprises the steps of placing a multi-contact foil (108) on the back-side and contacting the multi-contact foil (108) with a contacting substrate (109). An inspection device (107) for a through-wafer interconnects substrate (105) comprising a multi-contact foil (108) contactable to a through-wafer interconnects substrate (105) and contacted to a contacting substrate (105).

Description

Inspection Method and Inspection Device for Substrates

The invention relates to the field of inspection methods, inspection devices and inspection systems for substrates. In particular, the invention relates to inspection methods, inspection devices and inspection systems for substrates having through wafer interconnects. From the prior art wafers, e.g. semiconductor chips, are known which are contacted by connection pads arranged at the side of the chips. This leads to the fact that the packing density of such chips are low since the connecting pads require space which cannot be used for active components of the chips. For increasing of the packing density of such chips the technology of Through Wafer Interconnects (TWI) is proposed which allows the 3D-interconnections of wafer/chips with interconnections from the active front side to the back- side on which the contacts to the front side can be defined. This option avoids connection pads at the side of the chip, which prevent an all side placement of these chips next to each other.

Such a TWI wafer can be, for example, a fluidic system having through- wafer fluid interconnects as described in "Fabrication of Through- Wafer Fluid Interconnects with Low Dead Volume and Integrated Back-Plane Fluid Jumpers" Kashan Shaikh et al., 7^th International Conference on Miniaturized Chemical and Biological Analysis Systems, October 5-9, 2003 Squaw Valley, California USA Page 1053-1056. Another field of interest for TWI are semiconductor chips, in particular CMOS-chips and CMOS imagers which can be used in digital cameras, for example. In such CMOS imagers the interconnections from the CMOS front side to bump balls on the backside are formed by through-wafer interconnects leading to a higher packing density by avoiding the use of connection pads placed next to the chip.

One drawback of such through-wafer interconnects substrates (TWI substrates) is that classical standard needle test equipment cannot be used. Because of the fact, that TWI substrates are not available on the market, also no special equipment and/or method has been devised to allow inspection, characterization and/or testing of such TWI substrates.

It is an object of the invention to provide an inspection method of through-wafer interconnects substrates, an inspection device and an inspection system for carry out the inspection method.

An exemplary embodiment of the invention provides an inspection method for through-wafer interconnects of a through-wafer interconnects substrate the substrate having a front-side and a back-side on which back-side at least one contact is formed. The method comprising the steps of placing a multi-contact foil on the backside of the through-wafer interconnects substrate and contacting the multi-contact foil with a contacting substrate.

Moreover, an exemplary embodiment of the invention provides an inspection device for a through-wafer interconnects substrate comprising a multi- contact foil contactable to a through-wafer interconnects substrate and contacted to a contacting substrate.

The present invention provides for a non-destructive, flexible inspection method for the inspection and/or characterization of substrates with through-wafer interconnects (TWI substrates). The characteristic features according to the invention may have particularly the advantage that a complex positioning of contacts, e.g. needles in common needle test equipment, is not necessary. In case of the present invention the positioning may be less critical compared to common needle test equipment while still providing reliable connections to the contacts on the back-side of the TWI substrate. A further advantage of the characteristic feature according to the invention may be that due to the use of multi-contact foil the inspection of through- wafer interconnects substrates of different geometries and heights is possible. In particular, different bump ball heights, e.g. between 10 μm and 20 μm, on the back-side of the through-wafer interconnects substrate can be handled. This can be achieved by choosing the geometry of the multi-contact foil depending on the geometry of the through- wafer interconnects of the interconnects substrate. Thus, it is still ensured that predetermined contacts/bump balls are contacted on the back-side of the TWI substrate. Also the pitch of the substrate could vary within tolerances r the design, because of the fact, that a bump ball will be contacted by more than one insulated conductive wire of the flexible contact foil.

By using the multi-contact foil together with a contacting substrate it could be obtained that a inspection/testing equipment can read-out and feed-in different signals from/to the TWI substrate at the same time. The multi-contact foil may allow to contact to any connection point at the back-side of the substrate.

Referring to the dependent claims, further preferred embodiments of the invention will be described in the following. Next, preferred exemplary embodiments of the method of the invention for inspection of through-wafer interconnects will be described. These embodiments may also be applied for the inspection device.

In a further exemplary embodiment the contacting substrate is a routing substrate which is contactable to a read-out electronic and/or a power supply for the through-wafer interconnects substrate.

By using a routing substrate as the contacting substrate an intelligent board design can be used allowing different inspection or test cycles for different tests and/or different through-wafer interconnects substrates. Thus, the flexibility of the method according to the present invention may be increased. In another exemplary embodiment the multi-contact foil and the contacting substrate are coupled to each other and/or the multi-contact foil and the contacting substrate are coupled to a moveable device.

By coupling the multi-contact foil and the contacting substrate to each other the set-up of the multi-contact foil and the contacting substrate, building a contacting element, only has to be performed once for one type of through-wafer interconnects substrate. Leading to an easier and faster performing of inspections, tests, and/or characterizations of the through-wafer interconnects substrate. In particular, when the multi-contact foil and the contacting substrate are coupled to a moveable device an easy way for exchanging the through-wafer interconnects substrate may be provided by lifting the moveable device whereby the TWI substrate is uncovered.

In yet another exemplary embodiment the force is detected with which the multi-contact foil is pressed to the back-side of the through-wafer substrate. By measuring the force with which the multi-contact foil is pressed to the back-side of the substrate and due to the flexibility of the multi-contact foil an efficient method may be provided to ensure that an electrical contact between contacts, e.g. bump balls or contact pads, on the back-side of the substrate and the multi-contact foil is achieved, even if the contacts of the TWI substrate have different heights. The preferred force may be different when using bump balls or contact pads for the contacts of the TWI substrate. Simultaneously, the force could be limited according to a predetermined threshold so that it can be ensured that the substrate, in particular the contacts on the back- side and/or the front side, and/or the multi-contact foil are not damaged by exceeding a specified force. That is, a force feedback to control the contact force could be provided.

Next, further exemplary embodiments of the inspection device according to the present invention are described. These embodiments may also be applied for the inspection method. In another exemplary embodiment of the inspection device the multi- contact foil comprises a plurality of pattern wires.

The plurality of wires are insulated from each other by insulating layers. Preferably, a multi-contact foil is a flexible foil, e.g. a plastic or silicon foil, which comprises a plurality of wires which are insulated from each other. In particular, the wires could be formed as patterned wires in such a way that each wire forms an electrical path from one main face of the multi-contact foil to the other main face of the multi-contact foil. Multi-contact foils which could be used for the present invention are, as such, commercially available from ShinEtsu, for example.

The wires could be formed of any suitable conducting material. Preferably, conducting materials having low contact resistance, like gold or a nickel- gold alloy, are used, since the contact surfaces are quite small. The individual wires are insulated from each other by any suitable insulating material, like the plastic material of the foil.

In yet another exemplary embodiment a pitch between the pattern wires is adapted to ensure that any contact on the back-side of the through-wafer interconnects substrate can be contacted. The pitch could be chosen depending on a distance between individual contacts of the TWI substrate which shall be contacted while inspecting the TWI substrate. A possible pitch is between 20 μm and 60 μm, preferably 40 μm. While choosing the pitch it also could be ensured that no unwanted shorts between individuals contacts of the TWI substrate develop. Preferably, the pitch may be chosen to be smaller than the size of the contacts, e.g. bump balls or contact pads, of the TWI substrate. Thus, every contact is typically in electrical contact with a plurality of wires leading to a reduced contact resistance, while a short between individual contacts are prevented. In still another embodiment the inspection device is adapted to inspect through-wafer interconnects substrates having a circular, an elliptical, a square, a rectangular, or a polygon form.

By using the inspection device according to an embodiment of the present invention it is possible to handle all these forms. Thus, the inspection device as well as the above mentioned inspection method can be adapted to handle/inspect virtually every thinkable form of the TWI substrate.

In another embodiment the inspection device is adapted to inspect a complete wafer or a part of the complete wafer, which wafer is provided as the through- wafer interconnects substrate. Due to the possibility to manufacture multi-contact foils of quite big size, it is possible to facilitate wafer level tests, i.e. the testing of a whole wafer. Thus, leading to a fast and efficient way to inspect a great number of through-wafer interconnects and/or chips simultaneously. The wafer can have a size from 4 inch to 12 inch or even more. In yet still another exemplary embodiment the through-wafer interconnects substrate is a sensor chip, like a Micro-Electro-Mechanical System, a CMOS imager, an X-ray detector or a pressure sensor.

The inspection device is in particular advantageous for CMOS imagers, since such imagers need to be irradiated from the front side but have to be contacted from the back-side to prevent shadowing of the front side. Such a CMOS imager have a light/photo sensitive part on the so called active side and a conduct part on the rear side. An inspection system for inspecting a CMOS imager comprises a light source and a substantially transparent layer covering the light source. Further, the inspection system comprises an inspection device according to the present invention which inspection device is adapted to contact to a contacting back-side of a CMOS imager when the CMOS imager is held in the positioning mask.

By using the inspection system according to the present invention a system could provided which allows illumination of the CMOS imager surface, i.e. the active front side. Simultaneously, it may be possible to contact to any connection point at the back-side of the CMOS imager. Furthermore, the equipment, i.e. the inspection system could read-out and feed-in different signals from/to the CMOS imager at the same time.

In an exemplary embodiment the inspection system further comprises a processor adapted to receive and/or to analyze signals from a CMOS imager under inspection. In another exemplary embodiment the inspection system further comprises a positioning mask partially covering the substantially transparent layer and adapted to hold a CMOS imager

One aspect of the present invention can be seen in the use of a multi- contact foil in an inspection method and/or inspection device for through-wafer interconnects of a through-wafer interconnects substrate, like a chip or a CMOS imager.

In such an embodiment the multi-contact foil could be used to read out signals of the TWI substrate and also to power the TWI substrate. On top of the multi- contact foil a connecting substrate, like a routing substrate, can be placed, which is contacted to a read-out electronic and a power supply for the TWI substrate. The placement of the multi-contact foil on the TWI substrate has to be in a determined range because e.g. the supply to the TWI substrate has to be done while using a specific contact on the back-side of the TWI substrate. The placement could be done depending on the pitch between the individual wires of the multi-contact foil and the distance between individual contacts on the back-side of the TWI substrate. The multi-contact foil and the connecting substrate are mounted to a moveable device which could be lifted up easily to remove an actual TWI substrate under test and place the next one. Furthermore, the moveable device detects a force with which the multi-contact foil is pressed to the TWI substrate while carry out the test.

The present invention may be of particular interest in the field of semiconductors for measurement equipment to characterize TWIs and/or chips with TWI. A test-setup according to an embodiment of the present invention could be extended also for other sensor chips than CMOS imager. For example, this could be a pressure sensor in which the air is sent through a small hole in a front side protecting layer, which is in case of the optical sensor (CMOS imager) an optical filter, e.g. a simple glass plate. Other applications are also possible, e.g. in the Micro-Electro- Mechanical System (MEMS) technology or in the field of X-ray detectors in the field of computer tomography.

The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment.

The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Fig. 1 shows a schematic view of a principle set-up of an inspection system for a CMOS imager; Fig. 2 shows a detailed view of a first contact situation of the inspection device according to the embodiment of Fig. 1 ; and

Fig. 3 shows a detailed view of a second contact situation of the inspection device according to the embodiment of Fig. 1.

The illustration in the drawing is schematically. In different drawings, similar or identical elements are provided with the same or similar reference signs. In the following, referring to Fig. 1, an inspection system 100 for a processed chip, e.g. a CMOS imager, is described in more detail. The inspection system 100 comprises a light source 101, which is preferably a digital controlled light source, e.g. a light source comprising LEDs. The light source 101 is housed in a light source housing 102 and is arranged to illuminate a substantially transparent protecting layer 103, like a glass plate or an optical filter. The light beam of the light source is indicated in the figure by the arrows 111. Onto the protecting layer 103 a positioning mask 104 is placed. The positioning mask 104 covers the protecting layer 103 and comprises a structure in which the CMOS imager can be placed so that an optical surface, i.e. the active front side, of the CMOS imager 105 can be placed on the protecting layer 103. The positioning mask 104 can be adapted for different geometries of CMOS chips or wafers on which the CMOS chips are formed. For example wafers having circular, elliptical, square, rectangular, or polygon shaped form can be tested, by adapting the positioning mask to the same shape. Thereby, the multi-contact foil does not necessarily have to be adapted to the shape of the wafer, as long as the multi-contact foil is large enough to cover at least that part of the wafer which is tested.

The inspection system 100 further comprises a movable device 106 on which an inspection device 107 is mounted. The inspection device 107 comprises a multi-contact foil 108 to which a board 109 including a routing substrate is coupled. The inspection device 107 is shown in greater detail in Figs. 2 and 3. The movable device 106 can be moved up and down along support posts 110 which movement is indicated by the arrow 112.

In Fig. 1 a lightproof housing 113 is schematically shown, which allows an inspection/test under well defined conditions by shielding lights coming from the environment.

The inspection system 100 described above can be used for testing processed chips, like CMOS imager. For testing such a CMOS imager, the CMOS imager 105 is placed in the positioning mask 104 so that the optical surface (active side, front side) is faced downwards and is arranged on the transparent protecting layer 103. The movable device 106 is then moved down so that the inspection device 107 which is mounted to the movable device 106 gets into contact with the back- side of the CMOS imager. That is, the multi-contact foil 108 gets into electrical contact to at least some of the through- wafer interconnects of the CMOS imager 105. The multi-contact foil 108 is flexible and mainly consist of conductive pattern wires, e.g. gold wires, which are insulated from each other, e.g. with silicon. A pitch between the pattern wires is adapted to ensure that any contact on the back-side of the through-wafer interconnects substrate can be contacted. A typical pitch between the pattern wires is about 40 μm. According to this embodiment, the multi-contact foil could not only be used to read-out signals originated by the CMOS imager but also to power the CMOS imager.

While moving down the movable device 106 a force is measured with which the multi-contact foil is pressed to the back-side of the CMOS imager, wherein the pressure is limited between a minimal pressure to achieve a sufficient contact and a maximum pressure to assure that neither the CMOS imager nor the inspection device itself, i.e. the multi-contact foil 108, is damaged, e.g. by deformation and/or scratches on the optical side of the CMOS imager. After moving the movable device down, the light source 101 will be used to illuminate the CMOS imager 105 from below. Then the signals originated by the CMOS imager 105 are transmitted through the through- wafer interconnects to the back- side of the CMOS imager 105 and through the multi-contact foil 108 to the routing substrate 109, which is contacted to a read-out electronic and a power supply (both not shown) for the CMOS imager 105. The read-out electronic can comprise an processor which can also be used to control the digital controlled light source 101. The placement is done depending on the pitch between the individual wires of the multi-contact foil and the distance between individual contacts on the back- side of the TWI substrate. For example, by using a typical pitch of 40 μm the placement of the system has to be within about 50 μm for testing, because e.g. the supply to the CMOS imager has to be done while using a specific contact on the CMOS imager. The routing substrate 109 can be included into a board known in the field of semiconductors.

After the test of an individual CMOS imager is finished the movable device 106 is lifted from the CMOS imager 105 and the CMOS imager can be replaced by a next CMOS imager which is to be tested. In the following, referring to Fig. 2, a first contact situation of an inspection device according to the embodiment of Fig. 1 is described. In Fig. 2 the protective layer 103 is shown on which the positioning mask 104 is placed. The protective layer 103 can be formed as an optical filter. In a recess of the positioning mask 104 the processed chip, e.g. a CMOS imager 105, is placed. The CMOS imager 105 comprises a plurality of bump balls 218 on the back-side thereof building the terminals of the through-wafer interconnects. The bump balls 218 are contacted to the multi-contact foil 108. In the multi-contact foil 108 individual wires are schematically shown as vertical lines 214. As can be seen in Fig. 2 the pitch between the individual wires 214 is smaller than the seize of the bump balls 218. Therefore, an electrical contact between each bump ball 218 and several wires of the multi-contact foil 108 is ensured. Due to the flexibility of the contact foil a sufficient electrical contact between the multi-contact foil 108 and each bump ball is ensured even if the bump balls 218 have different heights. Further, the multi-contact foil 108 is coupled to a board which includes the routing substrate 109. The routing substrate 109 also comprises bump balls 215 which connect some of the pattern wire of the multi contact foil 108 with schematically shown conductors 216 formed in the routing substrate and which are connectable with a read-out electronic (not shown). Furthermore, an axis 217 along which the inspection device 107 can be moved is schematically shown in Fig. 2. The multi-contact foil 108 and the routing substrate 109 can be coupled together by clamping.

In the following, referring to Fig. 3, a second contact situation of an inspection device according to the embodiment of Fig. 1 is described. In Fig. 3 the protective layer 103 is shown on which the positioning mask 104 is placed. The protective layer 103 can be formed as an optical filter. In a recess of the positioning mask 104 the processed chip 105 is placed. According to Fig. 3 the processed ship 105 does not comprises bump balls but contact pads which cannot be seen in the figure. The contact pads are contacted to the multi-contact foil 108. In particular to the wires formed in the multi-contact foil 108 schematically shown as the lines 214. Further, the multi-contact foil 108 is coupled to a board which includes the routing substrate 109. The routing substrate 109 of Fig.3 also comprises contact pads instead of the bump balls of Fig. 2 which contact pads cannot be seen in Fig. 3 and which connect some of the pattern wire 214 of the multi contact foil 108 with conductors formed in the routing substrate and which are not shown in Fig. 3 and which are connectable with a read-out electronic (not shown). Furthermore, an axis 319 along which the inspection device 107 can be moved is schematically shown in Fig. 3.

Thus, as described by the description of the preferred embodiments, one aspect of the present invention can be seen in the usage of a multi-contact foil in an inspection method and/or inspection device for through-wafer interconnects of a through-wafer interconnects substrate, like a chip or a CMOS imager. The usage of such a flexible multi-contact foil enables the execution of an easy and efficient method for testing of through-wafer interconnects wafer.

It should be noted that the term "comprising" does not exclude other elements or steps and the "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined.

It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

CLAIMS:

1. An inspection method for through-wafer interconnects of a through- wafer interconnects substrate (105), the substrate having a front-side and a back-side on which back-side at least one contact (218) is formed, comprising the steps of: placing a multi-contact foil (108) on the back-side, and - contacting the multi-contact foil (108) with a contacting substrate

(109).

2. The inspection method of claim 1, further comprising the step of: providing a routing substrate which is contactable to a read-out electronic and/or a power supply for the through-wafer interconnects substrate (105) as the contacting substrate (109).

3. The inspection method of claim 1 or 2, further comprising the step of: coupling the multi-contact foil (108) and the contacting substrate (109) to each other.

4. The inspection method of anyone of the claims 1 to 3, further comprising the step of: coupling the multi-contact foil and the contacting substrate to a moveable device (106).

5. The inspection method of anyone of the claims 1 to 4, further comprising the step of: detecting the force with which the multi-contact foil (108) is pressed to the back- side.

6. An inspection device (107) for a through-wafer interconnects substrate (105), the inspection device comprising: a multi-contact foil (108), and - a contacting substrate (109), wherein the multi-contact foil (108) is contactable to the through-wafer interconnects substrate (105) and contacted to the contacting substrate (109).

7. The inspection device (107) of claim 6, wherein the contacting substrate (109) is a routing substrate which is contactable to a read-out electronic and/or a power supply for the through-wafer interconnects substrate (105).

8. The inspection device (107) of claim 6 or 7, further comprising: a moveable device (106) to which the multi-contact foil (108) and the contacting substrate (109) are coupled.

9. The inspection device (107) of anyone of the claims 6 to 8, wherein the inspection device (107) is adapted to measure a pressure with which the multi-contact foil (108) is pressed to the through-wafer interconnects substrate (105).

10. The inspection device (107) of anyone of the claims 6 to 8, wherein the multi-contact foil (108) comprises a plurality of pattern wires.

11. The inspection device (107) of claim 10, wherein a pitch between the pattern wires is adapted to ensure that any contact on the back-side of the through-wafer interconnects substrate (105) can be contacted.

12. The inspection device (107) of anyone of the claims 6 to 11, wherein the inspection device is adapted to inspect through-wafer interconnects substrates having a circular, an elliptical, a square, a rectangular, or a polygon form.

13. The inspection device (107) of anyone of the claims 6 to 12, wherein the inspection device is adapted to inspect a complete wafer or a part of the complete wafer, which wafer is provided as the through-wafer interconnects substrate.

14. The inspection device (107) of anyone of the claims 6 to 13, wherein the through-wafer interconnects substrate (105) is a sensor chip.

15. The inspection device (107) of claim 14, wherein the sensor chip is a Micro-Electro-Mechanical System, a CMOS imager, an X-ray detector or a pressure sensor.

16. An inspection system (100) for inspecting a CMOS imager (105) the inspection system comprising: - a light source (101); a substantially transparent layer (103) covering the light source (101); and an inspection device (107) of anyone of the claims 6 to 12 which is adapted to contact to a contacting back-side of a CMOS imager (105) when the CMOS imager (105) is held in the positioning mask (104).

17. The inspection system (100) of claim 16 further comprising: a processor adapted to receive and/or to analyze signals from a CMOS imager (105) under inspection.

18. The inspection system (100) of claim 16 or 17 further comprising: a positioning mask (104) partially covering the substantially transparent layer (103) and adapted to hold a CMOS imager (105);

19. Using of a multi-contact foil (108) in an inspection method for through- wafer interconnects of a through-wafer interconnects substrate (105).