Preparation method of substrate integrated, self-assembled and self-aligned micro lens group

Abstract

The invention relates to a preparation method of a substrate integrated, self-assembled and self-aligned micro lens group, and belongs to the technical field of micro-nano processing of optical chips. According to the method, after a front epitaxial structure is completed and thinning and polishing are carried out, secondary epitaxy is carried out on the back surface of a wafer, a seed layer is manufactured, an infiltration layer and a lens layer are sequentially grown through an S-K growth method, and finally N infiltration layers and N lens layers are alternately grown on the back surface of the wafer, so that the epitaxial structure is formed; etching the formed epitaxial structure from top to bottom until the etching depth covers all the infiltration layers, and forming an etching window; only the lens layer is left in the etching window formed by corrosion and the infiltration layer around the etching window, and transparent materials are filled between the lens layer and the etching window for reinforcement. Based on S-K growth, the actual preparation of the micro lens group is completed in one step in the epitaxial growth stage, adverse factors such as errors and pollution accumulated in multiple links in the production circulation process are omitted, and the precision and the yield are fully guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of micro-nano processing of optical chips, and in particular relates to a method for preparing a substrate-integrated, self-assembled and self-aligned microlens group. Background Art

[0002] Due to the advantages of high coaxial precision, low equipment requirements and cost, the manufacturing of optical chips has gradually developed from the previous discrete chips and micro-optical elements such as micro-lenses / arrays combined together by flip-chip bonding and glue injection curing to the current common direct preparation of integrated micro-lenses / arrays and photonic crystal structures with diffraction / reflection functions on the substrate through photolithography, hot melting and etching or corrosion to improve the external quantum efficiency of optical chips. The existing technical solutions have greatly improved production efficiency, but there are still the following defects that are difficult to overcome: 1. The hemispherical microlens based on pattern transfer has high requirements for etching process. In particular, the uniformity of the microlens array is closely related to factors such as process gas distribution and plasma distribution in the cavity. It often takes a lot of manpower and material resources to debug. The uniformity of the microlens array directly affects the uniformity of the photoelectric detection array, blind pixel rate and other key indicators; 2. For a spherical lens with a shallow focal length, its smaller radius of curvature means a larger etching thickness (>10μm) and etching time of several hours, which also means greater non-uniformity, which greatly affects the efficiency and yield of chip mass production; 3. The existing scheme can only produce single lenses, but it is powerless to meet the needs of lens groups. Compared with single lenses, the dynamic range of lens groups in terms of focal length and other aspects is significantly improved; 4. The difficulty of photonic crystal structure lies in design and lithography. The maximum line width of submicron level requires a lithography machine with precision capability above i-line, which also increases the entry threshold for players. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide a method for preparing a substrate-integrated, self-assembled and self-aligned microlens group. The method solves the problem of substrate-integrated microlens group by using a self-assembled quantum dot preparation method based on SK growth (the SK growth mode is the Stranski-Krastanow growth mode), and does not require additional equipment, meets low cost and productivity. The actual preparation of the microlens group is completed in one step during the epitaxial growth stage, eliminating the adverse factors such as errors and pollution accumulated in multiple links during the production process, and the accuracy and yield are fully guaranteed.

[0004] To achieve the above object, the technical solution of the present invention is: a method for preparing a substrate-integrated, self-assembled, self-aligned microlens group, comprising the following steps: S1, growing various functional layers of the optical chip epitaxy on the substrate; S2. After the front epitaxial structure is completed and thinned and polished, secondary epitaxy is performed on the back of the wafer and a seed layer is made. The position of the seed layer is coaxial with the designed active area of ​​the optical chip, that is, the position of each seed in the seed layer needs to be coaxial with the active area of ​​each optical chip; S3, sequentially growing a wetting layer and a lens layer through a mixed growth mode, the periphery of the lens layer is connected to the seed layer through pillars, and the rest of the lens layer follows a layered growth mode to uniformly deposit one or several layers of atoms in a two-dimensional manner on the wetting layer; when the deposition reaches a predetermined thickness, the growth mode is changed to an island growth mode, and at this time, a three-dimensional island is formed at a position corresponding to the corresponding seed in the seed layer; S4, repeating step S3, and finally growing N wetting layers and N lens layers alternately on the back side of the wafer to form an epitaxial structure; S5, etching the epitaxial structure formed in step S4 from top to bottom until the etching depth covers all the wetting layers to form an etching window; S6, etching the wetting layer in and around the etched window formed in step S5, leaving only the lens layer, and filling the etched part with transparent material for reinforcement.

[0005] In one embodiment of the present invention, the substrate is a semi-insulating substrate.

[0006] In one embodiment of the present invention, the seed layer manufacturing method includes a nanoimprint method, a selective area growth method, and a holographic lithography method.

[0007] In one embodiment of the present invention, the seeds in the seed layer are arranged in a square or honeycomb shape.

[0008] In one embodiment of the present invention, the size of the three-dimensional islands is controlled by adjusting the deposition conditions of the thin film, including temperature, pressure, and the difference in lattice constants between materials.

[0009] In one embodiment of the present invention, the lens layer / wetting layer is InP / In 1-x Ga x As y P 1-y The lattice constant a of the wetting layer is calculated by Vegard's law, that is, a=0.58688-0.04176x+0.01896y+0.00125xy. When the composition is adjusted to make a smaller than the InP lattice constant, the SK growth mode is formed.

[0010] In one embodiment of the present invention, the size of the upper three-dimensional islands is greater than or equal to the size of the lower three-dimensional islands, and the size of the upper three-dimensional islands is adjusted by the accumulated strain effect, specifically by adjusting the thickness of the wetting layer to achieve control of the accumulated strain effect.

[0011] In one embodiment of the present invention, in step S5, a non-selective dry etching process is adopted.

[0012] In one embodiment of the present invention, a selective wet etching process is used to etch the wetting layer in and around the etching window formed in step S5.

[0013] In one embodiment of the present invention, the transparent material is optical adhesive or other materials that are transparent to the target wavelength.

[0014] Compared with the prior art, the present invention has the following beneficial effects: the method of the present invention uses a self-assembled quantum dot preparation method based on SK growth to solve the problem of substrate integrated microlens group, and no additional equipment is required, and low cost and productivity are met; the actual preparation of the microlens group is completed in one step during the epitaxial growth stage, eliminating the unfavorable factors such as errors and pollution accumulated in multiple links during the production flow process, and the accuracy and yield are fully guaranteed; the method of the present invention has the following advantages: 1. Prepare lenses by epitaxial growth and use strain effect to manipulate the target parameters of the lens group instead of traditional pattern transfer methods such as hot melting and etching; 2. The substrate directly integrates a lens group instead of a single lens; 3. Self-assembly and self-alignment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the preparation steps of the preparation method of the present invention, in which 1 is a functional layer, 2 is a substrate, 3 is a wetting layer, and 4 is a lens layer.

[0016] Figure 2 These are examples of two seed arrangements.

[0017] Figure 3 Top view after etching window. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0019] The present invention provides a method for preparing a substrate-integrated, self-assembled, and self-aligned microlens group, comprising the following steps: S1, growing various functional layers of the optical chip epitaxy on the substrate; S2. After the front epitaxial structure is completed and thinned and polished, secondary epitaxy is performed on the back of the wafer and a seed layer is made. The position of the seed layer is coaxial with the designed active area of ​​the optical chip, that is, the position of each seed in the seed layer needs to be coaxial with the active area of ​​each optical chip; S3. A wetting layer and a lens layer are grown in sequence through a mixed growth mode (SK growth mode). The periphery of the lens layer is connected to the seed layer through pillars. The rest of the lens layer follows a layered growth mode (F-vdM growth mode, i.e., Frank-Van der Merwe growth mode) to uniformly deposit one or several layers of atoms on the wetting layer in a two-dimensional manner. When the deposition reaches a predetermined thickness, the growth mode is transformed into an island growth mode (VW growth mode, i.e., Volmer-Weber growth mode). At this time, three-dimensional islands are formed at positions corresponding to the corresponding seeds in the seed layer. S4, repeating step S3, and finally growing N wetting layers and N lens layers alternately on the back side of the wafer to form an epitaxial structure; S5, etching the epitaxial structure formed in step S4 from top to bottom until the etching depth covers all the wetting layers to form an etching window; S6, etching the wetting layer in and around the etched window formed in step S5, leaving only the lens layer, and filling the etched part with transparent material for reinforcement.

[0020] The parts etched in steps S5 and S6 are filled with transparent materials; because they will be divided into individual chips in the end, filling and reinforcement are necessary to ensure the stability of the lens group.

[0021] The following are specific implementation examples of the present invention.

[0022] The present invention provides a method for preparing a substrate-integrated, self-assembled, self-aligned microlens group, the preparation steps are as follows: Figure 1 As shown: 1. Growing the epitaxial functional layers 1 of the optical chip (for example, taking a typical APD chip with a SAGCM structure as an example, the functional layer 1 generally includes an A absorption layer, a G gradient layer, a C charge layer, an M multiplication layer and a cap layer, etc.), preferably, the substrate 2 is a semi-insulating substrate; 2. After the front epitaxial structure is completed and thinned and polished, secondary epitaxy is performed on the back of the wafer to produce a seed layer, which is coaxial with the designed chip active area (the position of each seed in the seed layer needs to be coaxial with the active area of ​​each optical chip). Preferably, the production method can be selected from nanoimprint method, selective area growth method, and holographic lithography method. Nanoimprint method, selective area growth method and holographic lithography method can all be selected to produce a "seed layer" or a patterned substrate. The purpose is to enhance the in-plane orderliness and coaxiality of the subsequent lens self-assembly growth through a stress field. The specific method is not limited. The arrangement of the seeds can be square or honeycomb, such as Figure 2 As shown ( Figure 2 In (a), the seeds are arranged in a square. Figure 2 (b) The seeds are arranged in a honeycomb shape); 3. A wetting layer 3 (sacrificial layer) and a lens layer 4 are grown in sequence by the SK growth method. Except for the four sides connected to the seed layer by pillars, the rest of the lens layer 4 starts by uniformly depositing one or several layers of atoms in a two-dimensional manner on the wetting layer 3. This step follows the Frank-Van der Merwe growth mode. When the deposition reaches a certain thickness, since the lattice constant of the lens layer 4 material is greater than that of the wetting layer 3, due to the gradually accumulated strain effect, the growth mode will be transformed into the Volmer-Weber growth mode. At this time, three-dimensional islands begin to form at the position corresponding to the "seed" on the seed layer. The size of the three-dimensional island can be precisely controlled by adjusting the deposition conditions of the film, including temperature, pressure and the difference in lattice constants between materials. For example, the lens layer 4 / wetting layer 3 is InP / In 1-x Ga x As y P 1-y For example, the lattice constant a of the wetting layer 3 can be calculated by Vegard's law (a=0.58688-0.04176x+0.01896y+0.00125xy). When the composition is adjusted to make a smaller than the InP lattice constant of 0.587nm, the SK growth mode may be formed. Currently recognized epitaxial growth modes include the Frank-van der Merve growth mode, the Volmer-Weber growth mode, and the Stranski-Krastanow growth mode: (1) Layered growth (F-vdM) mode. When the interaction between adsorbed atoms and the substrate is stronger than the interaction between atoms, layered growth occurs. (2) Island growth (VW) mode. When the interaction between adsorbed atoms or molecules is stronger than the interaction between adsorbed atoms and the substrate, adsorbed atoms nucleate on the substrate surface in the form of atomic clusters, and three-dimensional island growth occurs. (3) Mixed growth (SK) mode. A process between the two, first layered growth, and then transformed into island growth after exceeding a critical value. The lens region growth process described in the present invention is the SK growth mode.

[0023] 4. Repeat step 3, and finally grow N wetting layers 3 (sacrificial layers) and N lens layers 4 alternately on the back of the wafer to form an epitaxial structure. The size of the upper three-dimensional island may be the same as that of the lower layer, or it may be larger than that of the lower layer due to the accumulated strain effect. Its size can be adjusted by adjusting the thickness of the wetting layer 3 (sacrificial layer) to achieve precise control of the strain accumulation effect; 5. Use a non-selective dry etching process to etch the epitaxial structure from top to bottom until the etching depth covers all the wetting layers 3 (sacrificial layers) to form etching windows. Optionally, the etching process can be ICP etching; the windows only exist in the gaps between the lenses, and there is a certain interval between the windows. The top view is as shown in FIG. Figure 3 As shown ( Figure 3 In (a), the seeds are arranged in a square. Figure 3 (b) The seeds are arranged in a honeycomb shape); 6. Use a selective wet etching process to etch the wetting layer 3 (sacrificial layer) in and around the etching window, leaving only the lens layer 4, and fill the space between them with optical glue or other materials transparent to the target wavelength for reinforcement. Optionally, in the above InP / InGaAsP example, the etching solution for selectively removing the wetting layer 3 (sacrificial layer) can be a mixed solution of H2SO4:H2O2:H2O.

[0024] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions do not exceed the scope of the technical solution of the present invention, belong to the protection scope of the present invention.

Claims

1. A method for preparing a substrate-integrated, self-assembled, self-aligned microlens assembly, characterized in that: The steps include: S1, growing various functional layers of the optical chip epitaxy on the substrate; S2. After the front epitaxial structure is completed and thinned and polished, secondary epitaxy is performed on the back of the wafer and a seed layer is made. The position of the seed layer is coaxial with the designed active area of ​​the optical chip, that is, the position of each seed in the seed layer needs to be coaxial with the active area of ​​each optical chip; S3, sequentially growing a wetting layer and a lens layer through a mixed growth mode, the periphery of the lens layer is connected to the seed layer through pillars, and the rest of the lens layer follows a layered growth mode to uniformly deposit one or several layers of atoms in a two-dimensional manner on the wetting layer; when the deposition reaches a predetermined thickness, the growth mode is changed to an island growth mode, and at this time, a three-dimensional island is formed at a position corresponding to the corresponding seed in the seed layer; S4, repeating step S3, and finally growing N wetting layers and N lens layers alternately on the back side of the wafer to form an epitaxial structure; S5, etching the epitaxial structure formed in step S4 from top to bottom until the etching depth covers all the wetting layers to form an etching window; S6, etching the wetting layer in and around the etched window formed in step S5, leaving only the lens layer, and filling the etched part with transparent material for reinforcement.

2. The method for preparing a substrate-integrated, self-assembled, self-aligned microlens assembly according to claim 1, characterized in that: The substrate is a semi-insulating substrate.

3. The method for preparing a substrate-integrated, self-assembled, self-aligned microlens assembly according to claim 1, characterized in that: The seed layer production methods include nanoimprinting method, selective area growth method, and holographic lithography method.

4. The method for preparing a substrate-integrated, self-assembled, self-aligned microlens assembly according to claim 1, characterized in that: The seeds in the seed layer are arranged in a square or honeycomb shape.

5. The method for preparing a substrate-integrated, self-assembled, self-aligned microlens assembly according to claim 1, characterized in that: The size of the 3D islands is controlled by adjusting the film deposition conditions, including temperature, pressure, and the difference in lattice constants between the materials.

6. The method for preparing a substrate-integrated, self-assembled, self-aligned microlens assembly according to claim 5, characterized in that: For the lens layer / wetting layer, InP / In 1-x Ga x As y P 1-y The lattice constant a of the wetting layer is calculated by Vegard's law, that is, a=0.58688-0.04176x+0.01896y+0.00125xy. When the composition is adjusted to make a smaller than the InP lattice constant, the SK growth mode is formed.

7. The method for preparing a substrate-integrated, self-assembled, self-aligned microlens assembly according to claim 1, characterized in that: The size of the upper three-dimensional island is greater than or equal to that of the lower three-dimensional island. The size of the upper three-dimensional island is adjusted by the accumulated strain effect. Specifically, the accumulated strain effect is controlled by adjusting the thickness of the wetting layer.

8. The method for preparing a substrate-integrated, self-assembled, self-aligned microlens assembly according to claim 1, characterized in that: In step S5, a non-selective dry etching process is adopted.

9. The method for preparing a substrate-integrated, self-assembled, self-aligned microlens assembly according to claim 1, characterized in that: A selective wet etching process is used to etch the wetting layer in and around the etching window formed in step S5.

10. The method for preparing a substrate-integrated, self-assembled, self-aligned microlens assembly according to claim 1, characterized in that: The transparent material is optical adhesive or other materials that are transparent to the target wavelength.

Images