A microlens conical coefficient controllable method based on etching selection ratio continuous regulation

Abstract

The application discloses a kind of based on etching selection ratio continuous control micro-lens conical coefficient controllable method.The method comprises: establishing the quantitative theoretical model between selection ratio distribution and conical coefficient;According to target conical coefficient, the selection ratio distribution required is deduced;The continuous control of selection ratio is realized by accurately regulating etching gas flow, and the photoresist lens profile is transferred to the base by combining sub-region etching technology;Through error compensation mechanism, the control accuracy of conical coefficient is better than 0.01.The application expands the conical coefficient control range, realizes the continuous adjustable of conical coefficient in a large range, has high machining precision, good process compatibility, and is suitable for batch preparation of high-precision aspherical micro-lens.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optical manufacturing technology, and relates to a method for controlling the conic coefficient of microlenses based on continuous control of etching selectivity, and more particularly to a method for controlling the conic coefficient of aspherical microlenses based on continuous control of etching selectivity. Background Technology

[0002] Microlens arrays are key optical components in imaging, sensing, beam shaping, and optical communication systems. Traditional hot reflow is the mainstream technology for fabricating wafer-level microlenses, which melts and shapes a photoresist micropillar array. However, the conicity of the fabricated microlenses is fixed at 0 (i.e., a standard sphere), which is difficult to meet the higher requirements of modern optical systems for aspherical lenses in terms of aberration correction, field of view, and resolution.

[0003] Currently, the main methods for fabricating aspherical microlenses include grayscale lithography, multi-step overlay, and plasma modification. However, these methods all have significant drawbacks: grayscale lithography requires extremely high control over masks and exposure, and is very expensive; multi-step overlay is complex and prone to introducing alignment errors, resulting in large surface roughness (usually exceeding 10 nm); plasma modification may damage the pattern structure, resulting in poor uniformity and low consistency of curvature radius; some etching methods attempt to adjust the selectivity, but lack a quantitative theoretical model between the selectivity and the conic coefficient, leading to blindness in process design.

[0004] In the prior art, patent CN113419301A improved the surface roughness of microlenses by optimizing etching parameters (which can reduce it to below 5nm), but it did not solve the problem of continuous control of the conic coefficient; the process disclosed in patent CN113703081A is complex, and the conic coefficient control error is usually greater than 0.05, which is difficult to meet the requirements of high precision. In addition, the surface roughness of multi-step overlay technology generally exceeds 10nm, and the uniformity is poor. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for controlling the conic coefficient of microlenses based on continuous adjustment of etching selectivity. By establishing a quantitative relationship model between selectivity and conic coefficient, continuous and precise control of conic coefficient can be achieved, providing support for the mass production of high-precision aspherical microlenses.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a method for controllable conic coefficient of microlenses based on continuous adjustment of etching selectivity, comprising the following steps: S1. Basic Parameter Calibration and Theoretical Modeling: Determine the initial contour parameters of the photoresist microlens formed by the thermal reflow process, including the vertex radius of curvature R and radial dimension; determine the target conicity coefficient according to optical design requirements. ; A mathematical model of the microlens profile is established, where the ideal aspherical profile is described by the equation of a quadratic surface: Where R is the radius of curvature at the vertex of the microlens; Sag represents the sag of the microlens; K is the conic coefficient (=0 corresponds to a standard sphere, <0 corresponds to an ellipsoid, and >0 corresponds to a hyperboloid / parabola), r is the radial coordinate, and r is the axial etching depth; the conic coefficient K is a key parameter characterizing the degree of asphericity. S2. Target selection ratio distribution calculation: based on the target conic coefficient. Substituting the equation of the quadratic surface, the target base profile is solved. ; Based on the contour transfer relationship, the radial selectivity distribution required to achieve the target contour is deduced: make sure The radial transition is continuous and smooth, avoiding contour defects. S3, Selective ratio continuous control implementation: Etching selectivity (ER) is defined as the photoresist etching rate. With substrate etching rate The ratio: in, This represents the photoresist etching rate. To achieve continuous control of the selectivity ratio for the Si substrate etching rate, the etching process is carried out in an inductively coupled plasma (ICP) etching apparatus, maintaining stable ICP power and chamber pressure. S4. Regional Etching and Contour Verification: Using an inductively coupled plasma (ICP) etching apparatus, with fixed ICP power and cavity pressure, only the selectivity-related gas flow rate is adjusted; regional etching is performed in order from the lens edge to the center, which is consistent with the selectivity gradient direction; according to The distribution determines the etching time for each region: the etching time is inversely proportional to the selectivity. The substrate profile was measured using a white light interferometer after etching. Calculate the actual conic coefficient ; By introducing a selection ratio compensation factor Correct errors and ensure .

[0007] Preferably, in step S3, the photoresist etching rate is fixed. Continuous control of substrate etching rate Through linear / nonlinear control Flow rate (Si etching main gas) realization Continuous change, ensuring and match.

[0008] Preferred, The flow rate regulation range is 20–80 sccm, with a regulation accuracy of 0.01 sccm.

[0009] Preferably, in step S3, the substrate etching rate is fixed. Continuous control of photoresist etching rate Through linear / nonlinear control Flow rate (main gas for photoresist etching) realization Continuous change, ensuring and match.

[0010] Preferred, The flow rate regulation range is 5–50 sccm, with a regulation accuracy of 0.01 sccm.

[0011] Preferably, in step S4, the power of the inductively coupled plasma (ICP) is 600-800W.

[0012] Preferably, in step S4, the cavity pressure of the inductively coupled plasma (ICP) is 10–20 mTorr.

[0013] Preferably, the etching time is controlled between 4000 and 9000 seconds.

[0014] Compared with existing technologies, the present invention provides a method for controlling the conic coefficient of a microlens based on continuous adjustment of the etching selectivity, which achieves at least the following beneficial effects: 1. Wide range of conic coefficient adjustment: It realizes continuous adjustment of the conic coefficient within a very large range, covering various quadratic surface types such as elliptical surfaces and hyperboloids; 2. High machining accuracy: the conic coefficient control error is less than 0.01, the surface roughness Ra of the microlens is <5nm, and the uniformity of the radius of curvature is >97%; 3. Good process compatibility: Suitable for various substrate materials such as silicon, silicon dioxide, and sapphire, and compatible with AZ series and SU-8 series photoresists; 4. High production efficiency: The process steps are simplified, suitable for wafer-level mass production, no special equipment modification is required, and the yield is high. Attached Figure Description

[0015] Figure 1The diagram shows the overall process flow of the method of this invention, illustrating the complete process from parameter calibration to etching verification.

[0016] Figure 2 The curves show the variation of the conic coefficient K under different selection ratio distributions.

[0017] Figure 3 This is a schematic diagram comparing the microlens profiles. The red part represents the initial spherical profile of the photoresist, while the blue part represents the ellipsoidal microlens profile after transfer (K=−2).

[0018] Figure 4 This is a schematic diagram showing the selection of a ratio ER that gradually changes radially from the outside to the inside.

[0019] Figure 5 This is an example curve showing the linear relationship between SF6 gas flow rate and etching selectivity. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] A method for controlling the conic coefficient of a microlens based on continuous adjustment of the etching selectivity includes the following steps: S1. Basic Parameter Calibration and Theoretical Modeling: Determine the initial contour parameters of the photoresist microlens formed by the thermal reflow process, including the vertex radius of curvature R and radial dimension; determine the target conicity coefficient according to optical design requirements. ; A mathematical model of the microlens profile is established, where the ideal aspherical profile is described by the equation of a quadratic surface: Where R is the radius of curvature at the vertex of the microlens; Sag represents the sag of the microlens; K is the conic coefficient (=0 corresponds to a standard sphere, <0 corresponds to an ellipsoid, and >0 corresponds to a hyperboloid / parabola), r is the radial coordinate, and r is the axial etching depth; the conic coefficient K is a key parameter characterizing the degree of asphericity. S2. Target selection ratio distribution calculation: based on the target conic coefficient. Substituting the equation of the quadratic surface, the target base profile is solved. ; Based on the contour transfer relationship, the radial selectivity distribution required to achieve the target contour is deduced: make sure The radial transition is continuous and smooth, avoiding contour defects. S3, Selective ratio continuous control implementation: Etching selectivity (ER) is defined as the photoresist etching rate. With substrate etching rate The ratio: in, This represents the photoresist etching rate. To achieve continuous control of the selectivity ratio for the Si substrate etching rate, the etching process is carried out in an inductively coupled plasma (ICP) etching apparatus, maintaining stable ICP power and chamber pressure. S4. Regional Etching and Contour Verification: Using an inductively coupled plasma (ICP) etching apparatus, with fixed ICP power and cavity pressure, only the selectivity-related gas flow rate is adjusted; regional etching is performed in order from the lens edge to the center, which is consistent with the selectivity gradient direction; according to The distribution determines the etching time for each region: the etching time is inversely proportional to the selectivity. The substrate profile was measured using a white light interferometer after etching. Calculate the actual conic coefficient ; By introducing a selection ratio compensation factor Correct errors and ensure .

[0022] Example 1 In step S3, the photoresist etching rate is fixed. Continuous control of substrate etching rate Through linear / nonlinear control Flow rate (Si etching main gas) realization Continuous variation, with a flow rate control range of 20–80 sccm and a control accuracy of 0.01 sccm, ensuring… and match.

[0023] Example 2 In step S3, the substrate etching rate is fixed. Continuous control of photoresist etching rate Through linear / nonlinear control Flow rate (main gas for photoresist etching) realization Continuous change, The flow rate control range is 5–50 sccm, with a control accuracy of 0.01 sccm, ensuring… and match.

[0024] The power of inductively coupled plasma (ICP) is 600–800 W and the cavity pressure is 10–20 mTorr; In summary, this invention offers several advantages: a wide range of conic coefficient control: continuously adjustable conic coefficients within a wide range (e.g., -5 to +5), covering various quadratic surface types such as elliptical and hyperboloid surfaces; high processing precision: conic coefficient control error less than 0.01, microlens surface roughness Ra < 5nm, and curvature radius consistency > 97%; good process compatibility: suitable for various substrate materials such as silicon, silicon dioxide, and sapphire, and compatible with AZ series and SU-8 series photoresists; and high production efficiency: simplified process steps, suitable for wafer-level mass production, requiring no special equipment modifications, and achieving a high yield.

[0025] The above embodiments are not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the technical solutions of the present invention are also within the protection scope of the present invention.

Claims

1. A method for controlling the conic coefficient of a microlens based on continuous adjustment of etching selectivity, characterized in that: Includes the following steps: S1. Basic parameter calibration and theoretical modeling: Determine the initial contour parameters of the photoresist microlens formed by the thermal reflow process, including the vertex radius of curvature R and radial dimension; Determine the target conic coefficient based on optical design requirements. ; A mathematical model of the microlens profile is established, where the ideal aspherical profile is described by the equation of a quadratic surface: Where R is the radius of curvature at the vertex of the microlens; Sag represents the sag of the microlens; K is the conic coefficient (=0 corresponds to a standard sphere, <0 corresponds to an ellipsoid, and >0 corresponds to a hyperboloid / parabola), r is the radial coordinate, and r is the axial etching depth; the conic coefficient K is a key parameter characterizing the degree of asphericity. S2. Target selection ratio distribution calculation: based on the target conic coefficient. Substituting the equation of the quadratic surface, the target base profile is solved. ; Based on the contour transfer relationship, the radial selectivity distribution required to achieve the target contour is deduced: make sure The radial transition is continuous and smooth, avoiding contour defects. S3, Selective ratio continuous control implementation: Etching selectivity (ER) is defined as the photoresist etching rate. With substrate etching rate The ratio: in, This represents the photoresist etching rate. To achieve continuous control of the selectivity ratio for the Si substrate etching rate, the etching process is carried out in an inductively coupled plasma (ICP) etching apparatus, maintaining stable ICP power and chamber pressure. S4. Regional Etching and Contour Verification: Using an inductively coupled plasma (ICP) etching apparatus, with fixed ICP power and cavity pressure, only the selectivity-related gas flow rate is adjusted; regional etching is performed in order from the lens edge to the center, which is consistent with the selectivity gradient direction; according to The distribution determines the etching time for each region: the etching time is inversely proportional to the selectivity. The substrate profile was measured using a white light interferometer after etching. Calculate the actual conic coefficient ; By introducing a selection ratio compensation factor Correct errors and ensure .

2. The method according to claim 1, characterized in that: In step S3, the photoresist etching rate is fixed. Continuous control of substrate etching rate Through linear / nonlinear control Flow rate (Si etching main gas) realization Continuous change, ensuring and match.

3. The method according to claim 2, characterized in that: The flow rate regulation range is 20–80 sccm, with a regulation accuracy of 0.01 sccm.

4. The method according to claim 1, characterized in that: In step S3, the substrate etching rate is fixed. Continuous control of photoresist etching rate Through linear / nonlinear control Flow rate (main gas for photoresist etching) realization Continuous change, ensuring and match.

5. The method according to claim 4, characterized in that: The flow rate regulation range is 5–50 sccm, with a regulation accuracy of 0.01 sccm.

6. The method according to claim 1, characterized in that: In step S4, the power of the inductively coupled plasma (ICP) is 600-800W.

7. The method according to claim 1, characterized in that: In step S4, the cavity pressure of the inductively coupled plasma (ICP) is 10-20 mTorr.

8. The method according to any one of claims 1-7, characterized in that: In step S4, the etching time is controlled between 4000 and 9000 seconds.

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