GB2251335A

GB2251335A - Colour filter and its manufacture

Info

Publication number: GB2251335A
Application number: GB9118971A
Authority: GB
Inventors: Sang Sik Kim; Han Su Park
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1990-12-31
Filing date: 1991-09-04
Publication date: 1992-07-01
Also published as: IT1251699B; ITMI912730A1; JPH04234707A; KR920013735A; ITMI912730A0; GB9118971D0; FR2671198A1; DE4129427A1

Abstract

A colour filter formed on a semiconductor substrate (31) with a matrix of pixels (32-34) comprises a smoothing layer (39) over the pixels. Respective condensing lenses (41) are formed above the pixels. Intermediate layers are associated with respective dyed layers (45, 49, 53) situated above respective pixels. The transmissivity of incident light and spectral resolution of the device are thereby improved. In a preferred embodiment, a lens support layer 57 has additional lenses 59, 60, 61 formed thereon. <IMAGE>

Description

COLOUR FILTER AND ITS MANUFACTURE The present invention relates to a colour filter and a method for its manufacture. The invention is aimed at improving the optical efficiency of a colour filter for a semiconductor device such as an image sensor and for more nearly obtaining a uniform spectral response in such a device.

Solid-state image sensing devices are emerging as replacements for conventional electron tubes, and so are likely to become the next generation of image sensors.

These semiconductor sensors achieve colour discrimitation by means of colour filters formed on the upper surface of an optical-to-electrical converter region.

Colour liquid crystal displays (LCD's) also often utilise colour filters on their electrical-to-optical conversion regions.

There are two basic types of such colour filters.

One is made by dyeing with organic materials such as casein and gelatine. The other type is an inorganic filter which utilises optical interference effects. Of these, the organic filter usually has the lower cost and so is more widely used.

Fig. 1 of the accompanying drawings shows a cross-sectional view of a known colour filter for a conventional Charge Coupled Device (CCD). As illustrated, a semiconductor substrate 1 has recessed or concave portions and raised or convex portions.

Photodiodes 2,3,4 are formed at the surfaces of the respective concave portions. A conducting layer 5 and an insulating layer 7 are formed on the convex surfaces. These regions constitute CCDs on which a smoothing layer 9 of a transparent material such as polyimide is formed.

Next, three intermediate layers 13, 17 and 21 are formed by depositing polyimide (the same composition as the smoothing layer) across the entire surface of the above-described structure. Dyed layers 11, 15 and 19 are formed on the respective intermediate layers above the photodiodes 2, 3 and 4 respectively.

The dyed layers are formed of an organic material such as casein or gelatine containing a predetermined amount of (NH4) 2Cr 207 and are dyed with respective appropriate colours such as magenta, cyan, and yellow, in order to obtain the desired spectral separation of incident light.

Also, a lens support layer 23 is formed across the entire surface of the structure, on which is formed lenses 25,26 and 27 above the photodiodes 2, 3 and 4 respectively.

The method of manufacturing this conventional colour filter will now be explained briefly.

First, the photodiodes 2-4 formed on the respective concave (recessed) surfaces of the semiconductor substrate 1. The metal conducting layer 5 and the insulating layer 7 formed next on the convex (raised) surfaces and then, the transparent smoothing layer 9 of a material such as polyimide is formed on top.

Then, the dyed layer 11 is formed on the smoothing layer 9 and dyed magenta, cyan, or yellow, above the photodiode 2. Next, the intermediate layer 13 is formed by depositing polyimide on the entire surface of the structure together with dyed layer 15 above the photodiode 3, followed by the second intermediate layer and dyed layer 19 above the photodiode 4, in the same manner.

The intermediate layers 13 and 17 prevent colour mixing between sequentially formed dyed layers. The highest intermediate layer 21 and the lens support layer 23 are formed sequentially on the entire surface of the structure. The highest intermediate layer 21 is formed of the same material as the first two intermediate layers 13 and 17. The lens support layer 23 is formed of an acrylic material.

The lenses 25-27 are formed last by photolithography and a thermal processes. In the colour filter described above, the height between the insulating layer 5 and the photodiodes 2-4 is as much as 2-5#m.

Thus, the smoothing layer 9 is needed to ensure perfect flatness and relative positioning of the dyed layers (nearly 100% planarization ratio). The smoothing layer 9 is formed by spin-coating at least three times, of a highly sticky photoresist on the semiconductor substrate. Also, the-light incident on the lenses is transmitted normal to the lens surfaces, onto the dyed layers 11, 15 and 19.

After filtering by the dyed layers, the light of different colours is detected by the respective photodiodes 2-4.

The smoothing layer has to be thick to ensure the required planarization ratio. However this degrades the transmission efficiency and sensitivity of the device.

Furthermore, since the dyed layers are flat, the angles of the light rays passing through the lenses are different from each other, resulting in diffused internal reflection. This degrades the spectral resolution of the device.

A first object of the present invention is to provide a colour filter for improving device sensitivity by improving the optical transmissivity and condensing ratio.

A second object of the present invention is to provide a colour filter which improves spectral resolution by suppressing the generation of diffused reflection.

Also, a third object of the present invention is to provide a method of manufacturing an improved colour filter.

Thus a first aspect of the present invention provides a solid state device comprising a plurality of device elements and respective optical filter regions provided for filtering light incident on at least two of said elements, at least two condenser lenses being respectively situated between said filter regions and said elements.

According to a second aspect of the present invention, there is provided a colour filter which is formed on a semiconductor substrate with a matrix of pixels, comprising: a smoothing layer formed on the semiconductor substrate, of which portions corresponding to respective pixels are concave with a predetermined radius of curvature, condensing lenses formed at the concave portions of the smoothing layer, two or more interlayers formed on the smoothing layer and the condensing layer, two or more dyed layers formed beneath the inter-layers which are convex with a predetermined radius of curvature and have a constant thickness, a lens layer formed on the highest interlayer, and lenses formed on the lens layer with a predetermined radius of curvature correspondingly to each pixel.

A third aspect of the present invention provides a method of manufacturing a solid state device, the method comprising forming a plurality of device elements, forming at least two condenser lenses above respective elements and forming respective optical filter regions above said at least two condenser lenses.

According to a fourth aspect of the present invention, there is also provided a method of manufacturing a colour filter on a semiconductor substrate with a matrix of pixels, comprising the steps of: (a) forming a smoothing layer of which portions corresponding to each pixel are concave, having the predetermined radius of curvature, (b) forming condensing lenses on the concave portions of said flatting layer.

(c) forming dyed layers which have the same radius of curvature at upper and lower parts on the condensing lense and forming interlayers on said dyed layers, (d) repeating the step (c) at least twice, (e) forming a lens layer on the highest interlayer after a step (d), and (f) forming lenses corresponding to each pixel on the lens layer.

The present invention will now be explained in more detail by way of the following description of a preferred embodiment and with reference to the accompanying drawings, in which: Fig. 1 shows a cross-sectional view of a conventional colour filter structure; Fig. 2 shows a cross-sectional view of a colour filter structure according to the present invention; and Figs 3 (A)-3 (D) are cross-sectional views showing the method of manufacture of the structure shown in Fig.

2.

Referring now to Fig. 2, a semiconductor substrate 31 has concave (recessed) and convex (raised) surfaces.

At the concave regions, a matrix of first, second, and third photodiodes 32-34 are respectively formed. At the convex regions, a conducting layer 35 and an insulating layer 37 are formed.

Next, a first smoothing layer 39 is formed from a transparent material.

The first smoothing layer 39 is deliberately formed thin at the concave regions, depressed by a predetermined radius of curvature. In these depressed regions, condensing convex lenses 41 etc are formed of a high refractive index material such as an acrylic.

A second smoothing layer 43 of the same material as the first smoothing layer 39 is formed across the condensing lenses and the exposed regions of the first smoothing layer.

The second smoothing layer 43 is prominent in the regions above the condensing lenses 41. On this second smoothing layer, first, second, and third intermediate layers 47, 51 and 53 are formed, each with a predetermined radius of curvature, above each condensing lens.

The lower parts of the dyed layers 45, 49 and 53 have the same radius of curvature as the curved upper parts of the second smoothing layer, to ensure substantially constant transmission paths length for the incident light.

Beneath the respective intermediate layers, first, second, and third died layers 45, 49, and 53 formed of casein, or gelatin containing a predetermined amount of ammonium dichromate and dyed with magenta, cyan, and yellow, respectively. Similar to the situation with the conventional device, a lens support layer 57 of polyimide or acrylic, of which the surface is flat, is formed on the third intermediate layer 55.

On the lens support layer 57, first, second and third lenses 59-61 are formed above the first, second and third photodiodes 32-34 respectively. The lenses 59-61 are close to each other to obtain the maximum area of coverage.

Also, the curvature of the first, second and third lenses 59-61 is similar to that of the first, second and third dyed layers above the photodiodes, so that diffuse reflection at the dyed layers is minimized.

The condensing lenses 41 concentrate the light through the dyed layers 45, 49 and 53 onto the photodiodes.

Referring to Fig. 3(A) the method of manufacturing this structure is shown. The first, second and third photodiodes 32-34 are formed on the concave portions of the surface of the semiconductor substrate 31 and on the convex regions, the insulating layer 35 is formed of Al and the conducting layer 37 is formed of SiO2 to produce a CCD matrix. The first smoothing layer 39 is formed on top of the latter structure by spin-coating of polyimide. The polyimide layer is formed thin at the convex portions, depressed with the predetermined radius of curvature. The radius of curvature is controlled by speed of resolution during the coating process.

After acrylic deposition across the entire surface of the first smoothing layer, patterns are formed on the concave portions by conventional exposure and development (photolithography). Subsequent etching and reflow forms the condensing lenses 41. The condensing lenses 41 are convex, and their curvature is controlled by the temperature and time of the reflow process.

Next, the second smoothing layer 43 is formed by deposition of the same material as the first smoothing layer 39 across the entire surface of the structure.

Referring now to Fig. 3(B), after depositing a mixture of gelatin and casein containing (NH4)2Cr207 having thickness of 4000-70000A, the dyed layer pattern for the first photodiode 32 is formed by conventional photolithography. Subsequently, a first dyed layer 45 is formed by spreading a dyeing material across the entire surface of the structure. The dyeing material reacts with, and is retained by the dyed layer pattern, but it does not react with the second smoothing layer.

The unwanted dyeing material remaining on the second smoothing layer is then removed with deionized water.

The dyeing material used for the first dyed layer 45 is one of the colours of the magenta, cyan and yellow, say magenta.

Referring to Fig. 3(C), a first intermediate layer 47 of lFm thickness is then formed on the entire surface structure using the same material as for the first and second smoothing layers.

The second and third dyed layers 49 and 53 are formed at positions corresponding to the second and third photodiodes 33 and 34. They are dyed respectively with cyan and yellow. The second and third intermediate layers 51 and 55 are formed on the second and third dyed layers 49 and 53 using the same material as that of the first intermediate layer 47.

Referring to Fig. 3(D), the lens support layer 57 of polyimide or acrylic is formed on the third intermediate layer 55. Subsequently, the first, second, and third lenses 59-61 are formed on the lens support layer 57. The lenses are formed very close to each other to maximize the lens area. The portions of the second smoothing layer 43 and the first and second intermediate layers are prominent so that the dyed layers 41, 45 and 59 have the required curvature.

Thus, because the smoothing layer is formed with concave regions above the photodiodes and the condensing lenses having the predetermined radius of curvature, are formed within these concave regions, the light transmission of the dyed layers and concentration of light on the photodiodes are improved.

The diffuse reflection is inhibited by forming the dyed layers to have a curvature similar to that of the lenses. Thus, the present invention in this embodiment is able to improve the sensitivity of the photodiodes and also to improve spectral resolution.

Claims

1. A solid state device comprising a plurality of device elements and respective optical filter regions provided for filtering light incident on at least two of said elements, at least two condenser lenses being respectively situated between said filter regions and said elements.

2. A solid state device according to claim 1, wherein said elements are arranged as a matrix.

3. A solid state device according to claim 2, wherein said device is an image sensor.

4. A solid state device according to any preceding claim, wherein said condenser lenses are formed on a smoothing layer.

5. A solid state device according to claim 4, wherein said smoothing layer is provided with depressed regions in which respective condenser lenses are seated.

6. A solid state device according to claim 4 or claim 5, wherein a second smoothing layer is provided over said condenser lenses

7. A solid state device according to any preceding claim, wherein said optical filter regions are associated with respective intermediate layers.

8. A solid state device according to any preceding claim, wherein at least one layer or filter region above said condenser lenses is curved with approximately the same radius of curvature as the upper surface of said condenser lenses.

9. A colour filter formed on a semiconductor substrate with a matrix of pixels, comprising: a smoothing layer formed on said semiconductor substrate, of which portions corresponding to respective pixels are concaved by a predetermined radius of curvature; condensing lenses formed at the concave portions of said smoothing layer; at least two dyed layers formed beneath said interlayers which are convex by a radius of curvature and have a constant thickness; a lens layer formed on a highest interlayer; and lenses formed with a predetermined radius of curvature on said lens layer, corresponding to each pixel.

10. The colour filter according to claim 8, wherein another smoothing layer is further formed on said condensing lenses.

11. The colour filter according to claim 9, wherein said condensing lenses are convex lenses.

12. The colour filter according to claim 9, wherein the curvature of said dyed layers is substantially similar to that of said condensing lenses.

13. A method of manufacturing a solid state device, the method comprising forming a plurality of device elements, forming at least two condenser lenses above respective elements and forming respective optical filter regions above said at least two condenser lenses.

14. A method of manufacturing a colour filter on a semiconductor with a matrix of pixels, comprising the steps of: (a) forming a smoothing layer of which portions corresponding to respective pixels are concave by a predetermined radius of curvature; (b) forming condensing lenses on the concave portions of said smoothing layer; (c) forming dyed layers on said condensing lenses to have the same radius of curvature at upper and lower parts, lens and forming interlayers on said dyed layers; (d) repeating said step (c) at least two times; (e) forming a lens layer on a highest interlayer after said step (d); and (f) forming lenses corresponding to respective pixels on said lens layer.

15. The method according to claim 14, wherein other smoothing layers are more formed on said condensing lenses in said step (b).

16. The method according to claim 14, wherein the radius of curvature of said smoothing layers is controlled by the revolving speed of said semiconductor substrate.

17. The method according to claim 14, wherein said condensing lenses are convex lenses.

18. A solid state device substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

19. A colour filter substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

20. A method of manufacturing a solid state device, the method being substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

21. A method of manufacturing a colour filter, the method being substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.