GB2301194A

GB2301194A - Manufacture of spatial light modulators

Info

Publication number: GB2301194A
Application number: GB9510579A
Authority: GB
Inventors: Michael Roy Worboys; Sharon Radcliffe; Gordon Neil Blackie; Roger Keith Barton; Stephen James Foster
Original assignee: GEC Marconi Ltd; Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1995-05-24
Filing date: 1995-05-24
Publication date: 1996-11-27
Also published as: GB9510579D0

Abstract

A spatial light modulator is manufactured by producing a series of application specific integrated circuits (11) on a silicon wafer (20) and securing a front glass electrode (10) over and in correct alignment with each integrated circuit (11). A peripheral seal is arranged between each front glass electrode (10) and its associated integrated circuit (11) to leave a space for liquid crystal which is introduced before the wafer (20) is severed by saw cuts to separate the light modulators.

Description

MANUFACTURE OF SPATIAL LIGHT MODULATORS This invention relates to a method of manufacturing spatial light modulators, to apparatus for achieving the method of manufacture, and to spatial light modulators produced by the method.

Spatial light modulators are currently manufactured by forming a plurality of application specific integrated circuits (ASIC) on a silicone wafer which is then divided by saw cuts so that all of the ASICs are separated. Each ASIC is then individually aligned with a front glass electrode which is secured to the ASIC by a peripheral glue seal which defines a space for liquid crystal between the front glass electrode and the ASIC. This process requires considerable skill and dexterity to align the front glass electrode with the ASIC and to ensure that the glue seal is effective whilst not masking the pixel array on the ASIC. The space between the front glass electrode and the ASIC is individually filled with liquid crystal introduced through a gap in the glue seal which is subsequently sealed.This process also requires careful manipulation of each spatial light modulator to ensure that the space is filled with liquid crystal and that the glue seal is subsequently completed.

It is an object of the present invention to provide an improved process, for the manufacture of spatial light modulators, which reduces the cost of their manufacture and provides a more uniform product thereby reducing wastage.

According to one aspect of the invention a method of manufacturing a spatial light modulator includes producing a series of application specific integrated circuits in predetermined positions on a silicone wafer, placing a front glass electrode over and in correct alignment with each integrated circuit, securing each front glass electrode to the wafer with a peripheral seal whilst leaving a space for liquid crystal between the front glass electrode and its associated integrated circuit, and subsequently severing the wafer between all adjacent front glass electrodes.

The method preferably includes leaving a gap in each peripheral seal, filling each space with liquid crystal, and subsequently sealing the gap before the wafer is severed. The space may be filled by injecting liquid crystal through each gap. However, the method may alternatively include immersing the wafer in a bath of iiquid crystal until each space is filled with liquid crystal, removing the wafer from the bath, and removing excess liquid crystal from the wafer before the gaps are sealed.

The method may include placing each front glass electrode individually over and in correct alignment with its associated integrated circuit. This may include producing alignment references on each front glass electrode and aligning these references with corresponding references on the wafer. The method preferably includes locating the wafer in a predetermined position relative to a pick and place machine, and operating the pick and place machine to pick up individual front glass electrodes and to place each in tum over and in correct alignment with its associated integrated circuit.

Alternatively the method may include loading a plurality of front glass electrodes into a jig corresponding with the positions and orientations of the integrated circuits on the wafer, and using the jig to place the front glass electrodes over and in correct alignment with their respective integrated circuits. The method preferably includes loading all of the front glass electrodes required to complete a wafer into a jig corresponding with the positions and orientations of all of the integrated circuits on the wafer, and using the jig to place all of the front glass electrodes simultaneously over and in correct alignment with their respective integrated circuits. The method preferably includes producing alignment references on the wafer and aligning the jig with the references before the front electrodes are placed on the wafer.

According to another aspect of the invention apparatus, for manufacturing a spatial light modulator is provided to perform the improved manufacturing method referred to above.

The invention is now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a transverse section through a spatial light modulator taken along the line 1-1 of Figure 2; Figure 2 is a plan view of a spatial light modulator; Figure 3 is a plan view of a silicon wafer and illustrates the general method taught by the present invention; Figure 4 illustrates the use of ajig for simultaneously placing front glass electrodes on all ASIC's of a silicon wafer. and Figure 5 illustrates the operation of a pick and place machine to place individual front glass electrodes onto every ASIC defined by a silicon wafer.

Figures 1 and 2 illustrate the construction of a typical spatial light modulator which is formed by securing a front glass electrode 10 to an ASIC 11 by using a peripheral glue seal 12 which leaves a space 13 for liquid crystal between the front glass electrode 10 and the ASIC 11.

The front glass electrode 10 defines a window through which a pixel array 14 is viewed.

The ASIC 11 is formed as a rectangular silicon chip of which the upper surface (as seen in Figure 1) carries the pixel array 14. The front glass electrode 10 has its bottom surface (as viewed in Figure 1) formed with a transparent electrode 15 formed of indium tin oxide.

As shown in Figure 2, the transparent electrode 15 is positioned within the peripheral seal 12 and overlaps the pixel array 14. The transparent electrode 15 is formed with a tab 16, as shown in Figure 2, which extends across the peripheral seal 12 to a position in which it is secured by a blob of conducting expoxy resin 17 to an unshown contact pad on the ASIC. The peripheral seal 12 is provided with a gap 18 for the introduction of liquid crystal. It is irnportant for the liquid crystal to occupy all of the space 13 between the pixel array 14 and the transparent electrode 15. Conventionally the liquid crystal is introduced manually, by tipping the ASIC 11 so that the gap 18 forms the uppermost part of the space 13, thereby allowing the liquid crystal to displace all of the air from the space 13.After filling with liquid crystal, the gap 18 is sealed by the manual application of further sealing glue.

In the production of spatial light modulators of this construction, it is essential for the peripheral seal 12 to be positioned very precisely so that it does not extend over either the pixel array 14 or the transparent electrode 15. It is also essential for the front glass electrode 10 to be positioned very accurately over the ASIC 11 so that the transparent electrode 15 overlaps the pixel array 14 as shown in Figure 2. All of this requires considerable manual dexterity by the assembler and is time consuming. Furthermore, the filling of the liquid crystal through the gap 18 is also time consuming and requires substantial skill to ensure that the gap 18 is properly sealed.

One of the primary features of the present invention is the concept of securing the front glass electrodes 10 directly to the silicon wafer 20, as illustrated in Figure 3, before the individual ASICs 11 are separated. As shown in Figure 3, five front glass electrodes 10 have been placed over the corresponding ASICs 11 formed on the wafer 20. As shown, the wafer 20 has 32 rectangular regions 21 which are bordered by dotted lines indicating the future position of intended saw cuts. The ASICs 11 are formed in predetermined positions within the rectangles 21 thereby facilitating the correct positioning and alignment of the front glass electrodes 10 over each ASIC 11.

Although only five front glass electrodes 10 are shown in Figure 3, it should be understood that each of the rectangles 21 would normally contain an ASIC 11, and that a front glass electrode 10 would be secured in position over each ASIC 11 before the wafer 20 is severed to separate the 32 spatial light modulators. The concept of assembling the spatial light modulators on the wafer 20 greatly facilitates the overall production process. In particular the predetermined spacing of the ASICs 11, whether regular or irregular, enables the alignment and attachment of each front glass electrode to its ASIC to be automated. Similarly, the peripheral seal 12 may be applied to the undersurface of the front glass electrode 10 by an automated process.Due to the precise positioning of the front glass electrodes 10 on their ASICs 11, it is also possible to use an automatic dispenser to deposit the blob 17 to provide electrical contact between the transparent electrode 15 and the contact point on the ASIC. Furthermore, the gaps 18 will all be oriented in the same direction and all of the ASICs can be filled with liquid crystal in a single operation involving manipulation of the entire wafer 20. Although a liquid crystal dispenser could be used for automatically filling each space 13 through its respective gap 18, it is preferred for the entire wafer 20 to be immersed in a bath of liquid crystal so that all of the spatial light modulators are filled with liquid crystal at the same time.This process can be enhanced by processing the wafer 20 under reduced ambient pressure thereby facilitating the displacernent of the residual gas in the spaces 13 via the liquid crystal. After filling with liquid crystal an automatic sealant dispenser can be used to seal each of the gaps 18 with much greater precision than has hitherto been possible.

After completion of all the spatial light modulators on the wafer 20, they would be separated by sawing the wafer as before. However, as the spatial light modulators are arranged in orderly rows with a significant gap between them, it is much easier to sever the wafer 20 without the risk of damaging any of the individual ASICs.

With reference to Figure 4, a jig 40 defines thirty-two locations 41 each designed to locate an individual front glass electrode with its tab 60 and gap 18 arranged in a predetermined orientation. The jig 40 is provided with two reference marks 42 and is movable, as indicated by arrow 43. so that it will be superimposed on the wafer 20 with the reference marks 42 accurately aligned with reference marks 44 printed on the wafer 20. By arranging for the locations 41 to be in predetermined position co-ordinated with the predetermined positions of the ASICs 11 formed on the wafer 20, the simple alignment of the references 42 and 44 simultaneously ensures the correct alignment of every front glass electrode with its associated ASIC 11.The reference marks 42 and 44 can be aligned manually, or the jig 40 may have optical or other sensors fixed to it, for instance in the position of the reference marks 42, for identifying the reference marks 44 on the wafer 20 and ensuring correct alignment of the jig 40.

With reference to Figure 5, the wafer 20 is located in a holder 50 which is provided with a reference mark 51. Alignment of the reference mark 51 of the holder 50 with a reference mark 52 on the wafer 20 enables the wafer 20 to be positioned precisely within the holder 50. A pick and place machine comprises a jig 53 which is arranged to remove individual front glass electrodes 10 from a stack 54 and to place them sequentially on each of the ASICs 11 carried by the wafer 20. The jig 53 is mounted on an arm 55 which passes through an actuator 56 mounted on the edge of the holder 50 for transverse movement, as indicated by the arrows, to enable the jig 53 to be moved laterally to cover any of the ASICs 11. The actuator 56 is also arranged to reciprocate the arm 55 thereby allowing the jig 53 to move from a position over the stack 54 to a position covering any of the ASICs 11.

Although the pick and place machine illustrated diagrammatically in Figure 5 is arranged to move the jig 53 holding a single front glass electrode, it could instead operate ajig capable of accommodating two or more front glass electrodes.

Claims

1. A method of manufacturing a spatial light modulator including producing a series of application specific integrated circuits in predetermined positions on a silicon wafer, placing a front glass electrode over and in correct alignment with each integrated circuit, securing each front glass electrode to the wafer with a peripheral seal whilst leaving a space for liquid crystal between the front glass electrode and its associated integrated circuit, and subsequently severing the wafer between all adjacent front glass electrodes.

2. A method, as in Claim 1, including leaving a gap in each peripheral seal, filling each space with liquid crystal, and subsequently sealing the gap before the wafer is severed.

3. A method, as in Claim 2, including injecting liquid crystal through each gap.

4. A method, as in Claim 2, including immersing the wafer in a bath of liquid crystal until each space is filled with liquid crystal, removing the wafer from the bath, and removing excess liquid crystal from the wafer before the gaps are sealed.

5. A method, as in any preceding claim, including placing each front glass electrode individually over and in correct alignment with its associated integrated circuit.

6. A method, as in Claim 5, including producing alignment references on each front glass electrode and aligning these references with corresponding references on the wafer.

7. A method, as in Claim 5 or 6, including locating the wafer in a predetermined position relative to a pick and place machine, and operating the pick and place machine to pick up individual front glass electrodes and to place each in turn over and in correct alignment with its associated integrated circuit.

8. A method, as in any of Claims 1 to 4, including loading a plurality of front glass electrodes into a jig corresponding with the positions and orientations of the integrated circuits on the wafer, and using the jig to place the front glass electrodes over and in correct alignment with their respective integrated circuits.

9. A method, as in Claim 7, including loading all of the front glass electrodes required to complete a wafer into ajig corresponding with the positions and orientations of all of the integrated circuits on the wafer, and using the jig to place all of the front glass electrodes simultaneously over and in correct alignment with their respective integrated circuits.

10. A method, as in Claim 8 or 9, including producing alignment references on the wafer and aligning the jig with the references before the front electrodes are placed on the wafer.

11. A method of manufacturing a spatial light modulator substantially as described herein with reference to the accompanying drawings.

12. Apparatus for manufacturing a spatial light modulator in accordance with the method of any preceding claim.

13. A spatial light modulator produced by the method of any of Claims 1 to 11.