Method for forming reflective electrode of liquid crystal on silicon

Abstract

A method for forming a reflective electrode of a liquid crystal on silicon. The method comprises: providing a semiconductor structure (100) which comprises a first dielectric layer (110), a second dielectric layer (120) formed on the surface of the first dielectric layer (110), first trenches (130), first through holes (140) and second trenches (150), which are formed in the first dielectric layer (110), and second through holes (160) formed in the second dielectric layer (120); forming a third dielectric layer (200) on the surface of the second dielectric layer (120), and etching the third dielectric layer (200) to form first filling trenches (210) and second filling trenches (220), wherein the first filling trenches (210) are located above the second through holes (160) and are in communication with the second through holes (160), and the second filling trenches (220) are located above the first trenches (130) and are in communication with the first trenches (130); and filling the first filling trenches (210) and the second filling trenches (220) with a metal reflective layer (300), and performing chemical-mechanical polishing on the metal reflective layer (300). When an aluminum reflective layer is formed by means of the existing processes, a tungsten through hole is required to be formed below the aluminum reflective layer, and residues would be generated on an edge of a wafer after the tungsten through hole is formed, resulting in the problem of generating arcing risks. By means of the present application, such problem is solved.

Description

Method for forming liquid crystal on silicon reflective electrode Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and in particular to a method for forming a silicon-based liquid crystal reflective electrode. Background Art

[0002] LCOS (Liquid Crystal on Silicon) displays are reflective liquid crystal displays that use semiconductor silicon technology to control liquid crystals to project color images. LCOS displays are primarily used in projectors, AR / VR imaging devices, light modulators, and wavelength selective switches.

[0003] The LCOS display has an aluminum layer formed as a reflective layer and an electrode layer. The formation process is as follows:

[0004] As shown in FIG1 , a semiconductor structure 10 is provided, which includes a substrate 11, a first dielectric layer 12 formed on a surface of the substrate 11, a copper trench 13 formed in the first dielectric layer 12, and a tungsten via 14 located above the copper trench 13. The copper trench 13 is connected to the tungsten via 14, and the first dielectric layer 12 includes a bottom silicon oxide layer 12a, an NDC layer 12b formed on a surface of the bottom silicon oxide layer 12a, and a top silicon oxide layer 12c formed on a surface of the NDC layer 12b. The tungsten via 14 further includes a first Ti / TiN layer 15.

[0005] As shown in FIG1 , a plurality of spaced-apart metal aluminum structures 20 are formed on the surface of the first dielectric layer 12 . The metal aluminum structure 20 is a sandwich structure, which includes a first Ti / TiN layer 15 , a first aluminum layer 21 , a second Ti / TiN layer 22 , and a first SiON layer 23 , sequentially formed from bottom to top.

[0006] As shown in FIG2 , a second dielectric layer 30 is formed on the surface of the first dielectric layer 12 and the surface of the metal aluminum structure 20, and a reflective aluminum structure 40 is formed on the surface of the second dielectric layer 30. The reflective aluminum structure 40 includes, from bottom to top, a third Ti / TiN layer 41, a second aluminum layer 42, and a second SiON layer 43. The reflective aluminum structure 40 is formed above a portion of the metal aluminum structure 20. The second dielectric layer 30 has the same structure as the first dielectric layer 12, including a bottom silicon oxide layer 12a, an NDC layer 12b formed on the surface of the bottom silicon oxide layer 12a, and a top silicon oxide layer 12c formed on the surface of the NDC layer 12b. A tungsten through-hole 14 is also formed in the second dielectric layer 30, electrically connecting the second aluminum layer 42 with the first aluminum layer 21.

[0007] As shown in FIG3 , a third dielectric layer 50 is formed on the surface of the second dielectric layer 30 and the surface of the reflective aluminum structure 40 , and the height of the third dielectric layer 50 is at least flush with the height of the second SiON layer 43 in the reflective aluminum structure 40 ;

[0008] As shown in FIG4 , the third dielectric layer 50 and the reflective aluminum structure 40 are chemically mechanically polished until the second aluminum layer 42 is exposed;

[0009] As shown in FIG5 , the third dielectric layer 50 , the second dielectric layer 30 and the first dielectric layer 12 are etched until the first aluminum layer 21 is exposed to form a trench 60 . The exposed first aluminum layer 21 is the aluminum layer above which the reflective aluminum structure 40 is not formed.

[0010] However, when forming the aluminum layer serving as the reflective layer and electrode layer using the above method, a two-layer aluminum process is required. In this case, a large number of masks (6) are required. Moreover, tungsten through-holes need to be formed under the reflective aluminum structure and the metal aluminum structure. However, the tungsten through-holes will remain at the edge of the wafer, bringing a breakdown risk to subsequent steps. Therefore, a bevel etch process needs to be added to overcome the arcing risk. Summary of the Invention

[0011] In view of the shortcomings of the prior art described above, the present invention aims to provide a method for forming a reflective electrode for a liquid crystal on silicon (LCOS) film. This method solves the problem that, when forming an aluminum reflective layer using the existing process, tungsten through-holes need to be formed beneath the aluminum reflective layer. However, the formation of tungsten through-holes can leave residues at the wafer edge, leading to breakdown defects.

[0012] To achieve the above-mentioned and other related objectives, the present invention provides a method for forming a liquid crystal on silicon reflective electrode, the method comprising:

[0013] A semiconductor structure is provided, comprising a first dielectric layer, a second dielectric layer formed on a surface of the first dielectric layer, a first trench, a first through-hole, and a second trench formed in the first dielectric layer, and a second through-hole formed in the second dielectric layer, wherein the first through-hole is formed below and communicates with the first trench, the second through-hole is formed above and communicates with the second trench, and the first trench, the first through-hole, the second trench, and the second through-hole are all filled with metallic copper;

[0014] forming a third dielectric layer on the surface of the second dielectric layer, and etching the third dielectric layer to form a first filling trench and a second filling trench, wherein the first filling trench is located above the second through hole and communicates with the second through hole, and the second filling trench is located above the first trench and communicates with the first trench;

[0015] Filling the first filling trench and the second filling trench with a metal reflective layer, and performing chemical mechanical polishing on the metal reflective layer;

[0016] Optionally, the method of forming the first filling trench and the second filling trench includes:

[0017] forming a first mask layer on the surface of the third dielectric layer;

[0018] performing patterning on the first mask layer to expose the surface of the third dielectric layer in an area where the second through hole is located;

[0019] Etching the leaked third dielectric layer to form the first filling trench;

[0020] forming a second mask layer on the surface of the third dielectric layer where the first filling trench is formed;

[0021] performing patterning on the second mask layer to expose the surface of the third dielectric layer in the area where the first trench is located;

[0022] The third dielectric layer, the second dielectric layer and the first dielectric layer are etched to form the second filling trench.

[0023] Optionally, the material of the first mask layer and the second mask layer includes photoresist.

[0024] Optionally, both the first dielectric layer and the second dielectric layer include an NDC layer and a silicon oxide layer formed on a surface of the NDC layer.

[0025] Optionally, the third dielectric layer includes the NDC layer and the silicon oxide layer formed on the surface of the NDC layer.

[0026] Optionally, the semiconductor structure further includes a substrate, a device structure is formed in the substrate, and the first through hole is electrically connected to the device structure.

[0027] Optionally, the material of the metal reflective layer includes metal aluminum.

[0028] Optionally, the number of the first grooves and the second grooves is at least 2, and each of the first grooves and each of the second grooves are symmetrically arranged around the same center line.

[0029] Optionally, the method further includes the step of forming a protection layer on the surface of the area outside the first filling trench and the second filling trench.

[0030] Optionally, the material of the protective layer includes silicon oxide.

[0031] As described above, the method for forming a liquid crystal on silicon reflective electrode of the present invention avoids the formation of metal tungsten through-holes by simultaneously forming an aluminum reflective layer above the second through-holes and the first grooves. This further avoids the risk of breakdown caused by residual tungsten metal at the wafer edge and the additional cost of edge etching. Furthermore, the aluminum process, which originally required two separate production steps, is integrated into a single aluminum process, which not only meets the polishing requirements of the aluminum reflective layer but also reduces the number of required reticles (only four reticles are required), thereby achieving cost savings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 1 to 5 are schematic cross-sectional views of a conventional process for forming an aluminum reflective layer.

[0033] 6 to 13 are schematic cross-sectional views showing the process of forming an aluminum reflective layer according to the present invention.

[0034] FIG. 14 is a flow chart showing a method for forming a LCOS reflective electrode according to the present invention.

[0035] Description of Reference Numerals

[0036] 10, 100: semiconductor structure; 11, 101: substrate; 12, 110: first dielectric layer; 12a: bottom oxide layer; 12b, 111: NDC layer; 12c: top oxide layer; 13: copper trench; 14: tungsten via; 15: first Ti / TiN layer; 20: metal aluminum structure; 21: first aluminum layer; 22: second Ti / TiN layer; 23: first SiON layer; 30, 120: second dielectric layer; 40: reflective aluminum structure; 4 1: Third Ti / TiN layer; Second aluminum layer 42; 43: Second SiON layer; 50, 200: Third dielectric layer; 60: Trench; 1112: Silicon oxide layer; 130: First trench; 140: First through hole; 150: Second trench; 160: Second through hole; 170: Metal copper; 210: First filled trench; 220: Second filled trench; 300: Metal reflective layer; 310: First mask layer; 320: Second mask layer; 400: Protective layer DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0038] Please refer to Figures 1 to 14. It should be noted that the figures provided in this embodiment are merely schematic illustrations of the basic concept of the present invention. Although the figures only show components relevant to the present invention and are not drawn according to the number, shape, and size of components in actual implementation, the shape, number, and proportion of each component in actual implementation may be changed arbitrarily, and the component layout may also be more complex.

[0039] As shown in FIG14 , this embodiment provides a method for forming a liquid crystal on silicon reflective electrode, the method comprising:

[0040] Step 1) providing a semiconductor structure 100, comprising a first dielectric layer 110, a second dielectric layer 120 formed on a surface of the first dielectric layer 110, a first trench 130, a first through-hole 140, and a second trench 150 formed in the first dielectric layer 110, and a second through-hole 160 formed in the second dielectric layer 120, wherein the first through-hole 140 is formed below and communicates with the first trench 130, the second through-hole 160 is formed above and communicates with the second trench 150, and the first trench 130, the first through-hole 140, the second trench 150, and the second through-hole 160 are all filled with metallic copper 170;

[0041] Step 2) forming a third dielectric layer 200 on the surface of the second dielectric layer 120 and etching the third dielectric layer 200 to form a first filling trench 210 and a second filling trench 220, wherein the first filling trench 210 is located above the second through hole 160 and communicates with the second through hole 160, and the second filling trench 220 is located above the first trench 210 and communicates with the first trench 130;

[0042] Step 3) Fill the first filling trench 210 and the second filling trench 220 with a metal reflective layer 300 , and perform chemical mechanical polishing on the metal reflective layer 300 .

[0043] The method for forming the liquid crystal on silicon reflective electrode provided by this embodiment is described in detail below with reference to the accompanying drawings.

[0044] As shown in FIG6 , in step 1), a semiconductor structure 100 is provided, which includes a first dielectric layer 110, a second dielectric layer 120 formed on the surface of the first dielectric layer 110, a first trench 130, a first through-hole 140, and a second trench 150 formed in the first dielectric layer 110, and a second through-hole 160 formed in the second dielectric layer 120, wherein the first through-hole 140 is formed below the first trench 130 and communicates therewith, and the second through-hole 160 is formed above the second trench 150 and communicates therewith, and the first trench 130, the first through-hole 140, the second trench 150, and the second through-hole 160 are all filled with metal copper 170.

[0045] In this embodiment, before the first trench 130, the first through-hole 140, the second trench 150, and the second through-hole 160 are filled with the copper metal 170, a barrier layer is formed on the bottom and sidewalls of the first trench 130, the first through-hole 140, the second trench 150, and the second through-hole 160. The barrier layer includes a Ti layer and a TiN layer. It should be noted that the barrier layer is not shown in the figure.

[0046] Specifically, the semiconductor structure 100 further includes a substrate 101 , a device structure is formed in the substrate 101 , and the first through hole 140 is electrically connected to the device structure.

[0047] In this embodiment, the device structure is not shown in the figure.

[0048] Specifically, the first dielectric layer 110 and the second dielectric layer 120 both include an NDC layer 111 and a silicon oxide layer 112 formed on a surface of the NDC layer 111 .

[0049] In this embodiment, the thickness of the NDC layer in the first dielectric layer 110 is 500 angstroms, and the thickness of the silicon oxide layer in the first dielectric layer 110 is much greater than the thickness of the silicon oxide layer in the second dielectric layer 120 .

[0050] Specifically, the number of the first grooves 130 and the second grooves 150 is at least two, and each of the first grooves 130 and each of the second grooves 150 is symmetrically arranged about the same center line.

[0051] In this embodiment, the number of the first grooves 130 and the second grooves 150 is two, and two second grooves 150 are located between two first grooves 130 (the dotted line in FIG. 6 represents the symmetry center line).

[0052] As shown in Figures 7 to 10, in step 2), a third dielectric layer 200 is formed on the surface of the second dielectric layer 120 and is etched to form a first filling trench 210 and a second filling trench 220, wherein the first filling trench 210 is located above the second through hole 160 and is connected to the second through hole 160, and the second filling trench 220 is located above the first trench 130 and is connected to the first trench 130.

[0053] Specifically, the method of forming the first filling trench 210 and the second filling trench 220 includes:

[0054] forming a first mask layer 310 on the surface of the third dielectric layer 200;

[0055] Performing patterning on the first mask layer 310 to expose the surface of the third dielectric layer 200 in the area where the second through hole 160 is located;

[0056] Etching the leaked third dielectric layer 200 to form the first filling trench 210;

[0057] forming a second mask layer 320 on the surface of the third dielectric layer 200 where the first filling trench 210 is formed;

[0058] Performing patterning on the second mask layer 320 to expose the surface of the third dielectric layer 200 in the area where the first trench 130 is located;

[0059] The third dielectric layer 200 , the second dielectric layer 120 and the first dielectric layer 110 are etched to form the second filling trench 220 .

[0060] More specifically, the material of the first mask layer 310 and the second mask layer 320 includes photoresist.

[0061] Specifically, the third dielectric layer 200 includes the NDC layer 111 and a silicon oxide layer 112 formed on the surface of the NDC layer 111 .

[0062] As shown in FIG. 11 and FIG. 12 , in step 3), a metal reflective layer 300 is filled in the first filling trench 210 and the second filling trench 220 , and chemical mechanical polishing is performed thereon.

[0063] In this embodiment, the flatness and light reflectivity of the metal reflective layer are ensured by a chemical mechanical polishing process.

[0064] Specifically, the material of the metal reflective layer 300 includes metal aluminum.

[0065] As shown in FIG. 13 , specifically, the method further includes a step of forming a protection layer 400 on the surface of the area other than the first filling trench 210 and the second filling trench 220 .

[0066] More specifically, the material of the protection layer 400 includes silicon oxide.

[0067] In summary, the present invention's method for forming a LCOS reflective electrode avoids the formation of metal tungsten through-holes by simultaneously forming an aluminum reflective layer above the second through-holes and first trenches. This, in turn, reduces the risk of tungsten breakdown at the wafer edge and the additional cost of edge etching caused by residual tungsten metal at the wafer edge. Furthermore, the aluminum process, which originally required two separate steps, is integrated into a single process, meeting the polishing requirements for the aluminum reflective layer while reducing the number of required reticles (only four are required), thereby achieving cost savings. Therefore, the present invention effectively overcomes the shortcomings of the prior art and possesses high industrial value.

[0068] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for forming a reflective electrode of liquid crystal on silicon, characterized in that, The method includes: providing a semiconductor structure, which includes a first dielectric layer, a second dielectric layer formed on the surface of the first dielectric layer, a first trench, a first via hole and a second trench formed in the first dielectric layer, and a second via hole formed in the second dielectric layer, wherein the first via hole is formed below and communicated with the first trench, the second via hole is formed above and communicated with the second trench, and the first trench, the first via hole, the second trench and the second via hole are all filled with metallic copper; forming a third dielectric layer on the surface of the second dielectric layer and etching it to form a first filling trench and a second filling trench, wherein the first filling trench is located above the second via hole and communicated with the second via hole, and the second filling trench is located above the first trench and communicated with the first trench; filling a metallic reflective layer in the first filling trench and the second filling trench and performing chemical mechanical polishing on it.

2. The forming method of the silicon-based liquid crystal reflective electrode according to claim 1, wherein, The method for forming the first filling trench and the second filling trench includes: forming a first mask layer on the surface of the third dielectric layer; performing patterning on the first mask layer to expose the surface of the third dielectric layer in the area where the second via hole is located; etching the exposed third dielectric layer to form the first filling trench; forming a second mask layer on the surface of the third dielectric layer where the first filling trench is formed; performing patterning on the second mask layer to expose the surface of the third dielectric layer in the area where the first trench is located; etching the third dielectric layer, the second dielectric layer and the first dielectric layer to form the second filling trench.

3. The method for forming a silicon-based liquid crystal reflective electrode according to claim 2, wherein The materials of the first mask layer and the second mask layer include photoresist.

4. The forming method of the silicon-based liquid crystal reflective electrode according to claim 1, wherein Both the first dielectric layer and the second dielectric layer include an NDC layer and a silicon oxide layer formed on the surface of the NDC layer.

5. The method for forming a silicon-based liquid crystal reflective electrode according to claim 4, wherein, The third dielectric layer includes the NDC layer and the silicon oxide layer formed on the surface of the NDC layer.

6. The method for forming a silicon-based liquid crystal reflective electrode according to claim 1, wherein The semiconductor structure further includes a substrate, a device structure is formed in the substrate, and the first via hole is electrically connected to the device structure.

7. The method for forming a silicon-based liquid crystal reflective electrode according to claim 1, wherein, The material of the metallic reflective layer includes metallic aluminum.

8. The forming method of the silicon-based liquid crystal reflective electrode according to claim 1, characterized in that, The number of the first trenches and the second trenches is at least two, and each of the first trenches and each of the second trenches are symmetrically arranged with the same center line.

9. The method for forming a silicon-based liquid crystal reflective electrode according to claim 1, wherein, The method further includes the step of forming a protective layer on the surface of the area outside the first filling trench and the second filling trench.

10. The method for forming a silicon-based liquid crystal reflective electrode according to claim 9, characterized in that, The material of the protective layer includes silicon oxide.

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