A method for dynamic optimization control of microlens surface shape

Abstract

The present invention discloses a method for dynamically adjusting and optimizing the microlens surface shape, which includes the following steps: inputting a target profile equation and an initial exposure dose; performing an exposure simulation to determine the dissolution rate distribution; performing a development process simulation to determine the optimal development time; judging whether the accuracy requirement is met, and if the accuracy requirement is not met, performing program optimization until the required accuracy is reached; repeating the above steps to find the minimum error at different focal points, outputting the optimal parameter combination, and realizing fine adjustment and control of the microlens three-dimensional surface shape. The present invention not only saves design time, but also improves the manufacturing accuracy and quality of the target structure.

Description

Technical Field

[0001] The invention relates to the technical field of three-dimensional microstructure manufacturing, and in particular to a method for dynamically regulating and optimizing a microlens surface shape. Background Art

[0002] Compared with binary lithography technology that only produces planar structures, 3D lithography technology can realize the rapid preparation of arbitrary 3D morphology structures. 3D lithography technology has become an important technology in the field of microelectromechanical systems (MEMS) and is also the main means of processing micro-nano structures.

[0003] At present, the three-dimensional micro-nano structure processing methods can be roughly divided into several categories according to their different processing methods, such as direct write lithography, moving mask lithography, grayscale mask lithography and DMD-based grayscale lithography. Direct-write lithography is a processing method that achieves point-by-point exposure of photoresist by precisely controlling the position of the beam focus. It has high processing accuracy, but because it adopts a point-by-point scanning processing method, the work efficiency is low and it is not suitable for mass production; the technical principle of grayscale mask lithography is basically the same as that of traditional two-dimensional mask lithography. The only difference is that the mask used in grayscale mask lithography has a certain grayscale change, but the mask cost is relatively high, and each mask can only process one three-dimensional structure, and the processing flexibility is also limited; mobile mask lithography is a technology that dynamically adjusts the mask during the exposure process to obtain the desired three-dimensional surface structure. It can usually only be used for the preparation of some simple periodic three-dimensional micro-nano structures, and it is difficult to produce some microstructure devices with complex structures and changeable shapes; DMD-based grayscale lithography technology avoids the introduction of physical masks, and can realize computer-controlled real-time arbitrary pattern maskless lithography. It has the advantages of flexible design, high efficiency and low cost, and has attracted much attention in the field of three-dimensional micro-nano structure processing.

[0004] In a DMD lithography system, when the DMD receives a signal from a computer (i.e., bitmap data, designed exposure dose), the micromirror in the DMD modulates the spatial distribution of ultraviolet light, thereby determining whether the light reflected by the unit can eventually reach the photoresist surface. Generally speaking, among the many process parameters of DMD-based thick-film positive photoresist grayscale lithography, three important parameters should be determined before production: (1) the exposure dose associated with the grayscale mask pattern, (2) the focal position in the photoresist, and (3) the development time. However, there is currently no effective optimization tool to determine these highly coupled process parameters, which poses a challenge to improving the accuracy of thicker photoresist structures; therefore, a method for dynamically regulating and optimizing the microlens surface shape is proposed to address the above issues. Summary of the invention

[0005] In order to make up for the deficiencies of the prior art and solve at least one of the above problems, the present invention proposes a method for dynamically adjusting and optimizing the microlens surface shape.

[0006] A method for dynamically adjusting and optimizing a microlens surface shape, the method comprising the following steps:

[0007] Step S1: input the target microlens structure profile equation and the exposure dose determined by the initial experiment to calculate the exposure dose distribution inside the photoresist;

[0008] Step S2: performing exposure simulation using initial parameters and combining with an empirical dissolution rate model to determine the dissolution rate distribution;

[0009] Step S3: using the fast marching algorithm to simulate the development process and determine the optimal development time under the current exposure dose;

[0010] Step S4: evaluating the error between the simulated microlens structure and the target profile, determining whether the accuracy requirement is met, and checking whether the stop conditions are met, such as the maximum program running time, the minimum exposure dose step length, etc.;

[0011] Step S5: If the accuracy requirement is not met, the exposure dose is adjusted using a steepest descent optimization procedure based on sensitivity analysis, and steps S1-S4 are repeated until the optimization reaches the required accuracy or a stop condition is reached;

[0012] Step S6: Repeat steps S1-S5 to find the minimum error at different focus positions, thereby obtaining the best parameter combination of exposure dose, focus position and development time.

[0013] Preferably, the step S1 requires fixing the target microlens at a focal position, and calculating the exposure dose distribution inside the photoresist through exposure simulation using grayscale lithography technology based on a digital micromirror device (DMD).

[0014] Preferably, the measurement of the dissolution rate in step S2 needs to determine the local dissolution rate from the local exposure dose according to an empirical dissolution rate model.

[0015] Preferably, during the development in step S3, the developer is an alkaline developer.

[0016] Preferably, there are two ways to evaluate the error in step S4: one is to evaluate the local height difference between the measured value and the target value; the other is to evaluate the mean square error from a global perspective.

[0017] Preferably, if the optimization reaches the stop condition in step S5, it indicates that the exposure dose and the development time have reached the optimal state.

[0018] The present invention is beneficial in that:

[0019] 1. The method for dynamically regulating and optimizing the microlens surface shape proposed by the present invention is based on the three-dimensional lithography simulation and sensitivity analysis of the grayscale lithography system of the DMD, and can optimize the parameter combination of the optimal exposure dose, focus position and development time of the positive photoresist. This single exposure optimization method has the characteristics of simple design, strong reliability and high simulation accuracy. Since the invention combines the DMD maskless grayscale lithography technology, it can realize the simulation and manufacture of three-dimensional microstructures quickly and economically, and can conveniently and quickly design the required lens mask graphics, saving costs and improving work efficiency. Since the optimal combination of the three important parameters in the invention is obtained through an automatic optimization process, it can significantly reduce a lot of design time, and the optimization result has high precision and good accuracy, which can make up for the defects of the current three-dimensional microstructure manufacturing technology with limited precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0021] Figure 1 It is a flow chart of the optimization steps of the present invention;

[0022] Figure 2 This is a structural diagram of the DMD maskless grayscale lithography equipment system of the present invention;

[0023] Figure 3 is an optimized parameter diagram of the microlens structure of the present invention;

[0024] Figure 4 This is a structural diagram of the microlens of the present invention.

[0025] In the figure: 1. 405nm ultraviolet light source; 2. homogenizing element; 3. collimating element; 4. reflector; 5. DMD chip; 6. computer; 7. imaging lens; 8. projection microscope lens; 9. sample; 10. platform; 11. PMER photoresist; 12. silicon wafer. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] A method for dynamically adjusting and optimizing a microlens surface shape, the method comprising the following steps:

[0028] Step S1: input the target microlens structure profile equation and the exposure dose determined by the initial experiment to calculate the exposure dose distribution inside the photoresist;

[0029] Step S2: performing exposure simulation using initial parameters and combining with an empirical dissolution rate model to determine the dissolution rate distribution;

[0030] Step S3: using the fast marching algorithm to simulate the development process and determine the optimal development time under the current exposure dose;

[0031] Step S4: evaluating the error between the simulated microlens structure and the target profile, determining whether the accuracy requirement is met, and checking whether the stop conditions are met, such as the maximum program running time, the minimum exposure dose step length, etc.;

[0032] Step S5: If the accuracy requirement is not met, the exposure dose is adjusted using a steepest descent optimization procedure based on sensitivity analysis, and steps S1-S4 are repeated until the optimization reaches the required accuracy or a stop condition is reached;

[0033] Step S6: Repeat steps S1-S5 to find the minimum error at different focus positions, thereby obtaining the best parameter combination of exposure dose, focus position and development time.

[0034] As an implementation of the present invention, the step S1 needs to fix the target microlens at the focus position, and calculate the exposure dose distribution inside the photoresist through exposure simulation based on grayscale lithography technology of digital micromirror device (DMD).

[0035] As an embodiment of the present invention, the measurement of the dissolution rate in step S2 needs to determine the local dissolution rate from the local exposure dose according to an empirical dissolution rate model.

[0036] As an embodiment of the present invention, during the development in step S3, the developer is an alkaline developer.

[0037] As an implementation manner of the present invention, there are two ways to evaluate the error in step S4: one is to evaluate the local height difference between the measured value and the target value; the other is the mean square error from a global perspective.

[0038] As an embodiment of the present invention, if the optimization in step S5 reaches the stop condition, it indicates that the exposure dose and the development time have reached the optimal state.

[0039] An example is given below. Figure 1-4 As shown:

[0040] This embodiment includes: when the error requirement is less than 10 -4 μm 4 Under the conditions of optimization, the optimal combination of three process parameters is obtained, such as Figure 3 As shown. A 20 μm thick positive photoresist is exposed to produce a microlens structure. Error analysis is performed on the microlens structure, and the simulated error analysis results are compared. The microlens structure produced in this embodiment is as shown Figure 4 shown.

[0041] This embodiment is produced by the following steps:

[0042] Step 1: Spin-coat a layer of photoresist on the silicon wafer.

[0043] The silicon wafer 12 is cleaned and dried, and a 20 μm thick positive photoresist 11 is spin-coated. The photoresist is PMER P-LA900PM photoresist.

[0044] Step 2: Pre-bake the photoresist.

[0045] The silicon wafer coated with the photoresist was placed on a hot plate for pre-baking at 115° C. for 6 minutes.

[0046] Step 3: Expose on the DMD exposure system.

[0047] according to Figure 3 The optimization results are based on Figure 2 The exposure is performed on a DMD maskless grayscale lithography system. The exposure light source is 405nm ultraviolet light 1. After being processed by the homogenizing element 2 and the collimating element 3, the light beam is reflected by the reflector 4 to the surface of the DMD 5. The computer 6 transmits the digital mask information to the DMD and controls the switch of the micromirror in the DMD. After being reflected by the DMD, the ultraviolet light passes through the imaging lens 7 and the projection microscope lens 8 and finally exposes the sample 9 on the platform 10.

[0048] Step 3: Development.

[0049] The exposed structure was developed by immersion method, the developer was P-7G alkaline developer, and the development time was 510s.

[0050] Step 4: Evaluate the error.

[0051] The prepared microlens structure was observed by scanning electron microscopy (SEM), and the height information of the prepared three-dimensional microstructure was obtained by a three-dimensional laser scanner. The microlens array structure is as follows Figure 4 The local height difference between the measured value and the target value is calculated to evaluate the manufacturing performance. The local error distribution of the simulated structure at the best focal length shows good consistency with the local error distribution of the target structure.

[0052] In summary, the present invention is based on the optimization mechanism of nonlinear errors of coupled parameters of photolithography process, and proposes a method for dynamic control and optimization of microlens surface shape based on "target input-parameter output". This numerical optimization based on exposure simulation, development simulation and the steepest descent method based on sensitivity analysis can automatically obtain the best parameter combination of exposure dose, focus position and development time, which can realize the precise control of the three-dimensional surface shape of microlenses and greatly improve the manufacturing accuracy of 3D microstructures.

[0053] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0054] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for dynamically adjusting and optimizing the microlens surface shape, characterized in that: The method comprises the following steps: Step S1: input the target microlens structure profile equation and the exposure dose determined by the initial experiment to calculate the exposure dose distribution inside the photoresist; Step S2: performing exposure simulation using initial parameters and combining with an empirical dissolution rate model to determine the dissolution rate distribution; Step S3: using the fast marching algorithm to simulate the development process and determine the optimal development time under the current exposure dose; Step S4: evaluating the error between the simulated microlens structure and the target profile, determining whether the accuracy requirement is met, and checking whether the stop condition is met; Step S5: If the accuracy requirement is not met, the exposure dose is adjusted using a steepest descent optimization procedure based on sensitivity analysis, and steps S1-S4 are repeated until the optimization reaches the required accuracy or a stop condition is reached; Step S6: Repeat steps S1-S5 to find the minimum error at different focus positions, thereby obtaining the best parameter combination of exposure dose, focus position and development time.

2. A method for dynamically adjusting and optimizing the microlens surface shape according to claim 1, characterized in that: The step S1 requires fixing the target microlens at a focal position, and calculating the exposure dose distribution inside the photoresist through exposure simulation using grayscale lithography technology based on a digital micromirror device (DMD).

3. The method for dynamically adjusting and optimizing the microlens surface shape according to claim 2, characterized in that: The measurement of the dissolution rate in step S2 needs to determine the local dissolution rate from the local exposure dose according to an empirical dissolution rate model.

4. The method for dynamically adjusting and optimizing the microlens surface shape according to claim 3, characterized in that: During the development in step S3, the developer is an alkaline developer.

5. The method for dynamically adjusting and optimizing the microlens surface shape according to claim 4, characterized in that: There are two ways to evaluate the error in step S4: one is to evaluate the local height difference between the measured value and the target value; the other is the mean square error from a global perspective.

6. A method for dynamically adjusting and optimizing the microlens surface shape according to claim 5, characterized in that: If the optimization reaches the stop condition in step S5, it means that the exposure dose and the developing time have reached the optimal state.

7. The method for dynamically adjusting and optimizing the microlens surface shape according to claim 1, characterized in that: The stop condition in step S4 includes the maximum program running time or the minimum exposure dose step length.

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