Binarized 0-pi phase multifocal element preparation method based on difference mapping

Abstract

The invention discloses a binary 0-pi phase multifocal element preparation method based on difference mapping, and the method comprises the steps: determining a phase difference calculation formula according to a Rayleigh-Sommerpheny formula, and calculating the phase difference of a multifocal element; mapping the phase difference to an independent variable of Fourier series according to a coordinate transformation formula, and obtaining a radial abrupt change point of the multi-focus element according to a Dammann grating design principle; obtaining a 0-pi structure according to the radial abrupt change point, and generating a GDS file for photoetching processing and a photoetching mask file; etching a photoresist pattern consistent with the 0-pi structure on the photoresist on the quartz substrate according to the photoetching mask plate file; and transferring the photoresist pattern to the quartz plate, and removing the residual photoresist. The application gets rid of a long-focus application scene in which a conventional multi-focus phase element is mostly located in a Fraunhofer diffraction region and a Fresnel diffraction region, is suitable for a short-focus application scene, and is simple in mapping and short in calculation time.

Description

Technical Field

[0001] The present application relates to the field of optical technology, and in particular to a method for preparing a binary 0-π phase multi-focus element based on difference mapping. Background Art

[0002] In the actual processing of semiconductors, how to separate a single chip or display unit from a large-sized wafer substrate has always been a technical challenge faced in mass production. The traditional blade cutting process has technical problems such as wide kerf, easy edge collapse, and debris splashing. With the maturity of laser hidden cutting technology, more and more research institutions have applied this technology to the processing of various brittle materials. For thicker wafer substrates, single-focus laser hidden cutting requires multiple scanning processes by successively changing the position of the focus inside the material, which not only affects the processing efficiency, but also increases additional processing errors and reduces the processing yield. Therefore, how to simultaneously focus multiple equally spaced focal points inside the substrate has become the only way to improve cutting efficiency and yield.

[0003] Existing multi-focal element design methods are mainly based on the theory of long focal length and small numerical aperture, including Fraunhofer diffraction and Fresnel diffraction methods, which are gradually applied from far to near focal lengths. However, as some application scenarios require smaller and smaller laser power windows and smaller and smaller focal spot sizes, the required focal length of the focusing system must also be shortened. In this case, the traditional Fraunhofer diffraction and Fresnel diffraction methods will no longer be applicable. Summary of the invention

[0004] To this end, the present application provides a method for preparing a binary 0-π phase multi-focal element based on difference mapping to solve the problem in the prior art that Fraunhofer diffraction and Fresnel diffraction are not suitable for short-focus application scenarios.

[0005] In order to achieve the above objectives, this application provides the following technical solutions:

[0006] In a first aspect, a method for preparing a binary 0-π phase multi-focus element based on difference mapping comprises:

[0007] Step 1: Determine a phase difference calculation formula according to the Rayleigh-Sommerfeld formula, and calculate the phase difference of the multi-focus element;

[0008] Step 2: Mapping the phase difference to the independent variable of the Fourier series according to the coordinate transformation formula, and obtaining the radial mutation point of the multi-focus element according to the Dammann grating design principle;

[0009] Step 3: obtaining a 0-π structure according to the radial mutation point of the multi-focus element;

[0010] Step 4: Generate a GDS file for photolithography processing according to the 0-π structure, and generate a photolithography mask file according to the GDS file;

[0011] Step 5: Carving a photoresist pattern consistent with the 0-π structure on the photoresist on the quartz substrate according to the photolithography mask file;

[0012] Step 6: Transfer the photoresist pattern to a quartz wafer and remove the remaining photoresist.

[0013] Preferably, in step 1, the phase difference calculation formula is:

[0014]

[0015] in, represents the phase difference, k represents the wave number, d represents the focal distance, r represents the radial coordinate, and f represents the focal length of the objective lens.

[0016] Preferably, in step 2, the coordinate transformation formula is:

[0017]

[0018] Here, x represents the independent variable.

[0019] Preferably, in step 5, etching a photoresist pattern consistent with the 0-π structure on the photoresist on the quartz substrate according to the photolithography mask file includes exposure, development and fixing operations.

[0020] Preferably, in step 5, the mask used when engraving a photoresist pattern consistent with the 0-π structure on the photoresist on the quartz substrate according to the photolithography mask file is metal chromium or metal nickel.

[0021] Preferably, in step 6, a dry etching process is used when transferring the photoresist pattern onto the quartz wafer.

[0022] Preferably, the dry etching process is reactive ion beam etching, ion beam etching or inductively coupled plasma reactive ion beam etching.

[0023] Preferably, in step 6, a stripping solution is used to remove the remaining photoresist.

[0024] Preferably, the degumming solution is acetone, inorganic acid or sulfuric acid and hydrogen peroxide.

[0025] In a second aspect, a short-focus multifocal element is prepared according to a method for preparing a binary 0-π phase multifocal element based on difference mapping.

[0026] Compared with the prior art, this application has at least the following beneficial effects:

[0027] The present application provides a method for preparing a binary 0-π phase multi-focus element based on difference mapping, including: determining a phase difference calculation formula according to the Rayleigh-Sommerfeld formula, and calculating the phase difference of the multi-focus element; mapping the phase difference to the independent variable of the Fourier series according to the coordinate transformation formula, and obtaining the radial mutation point of the multi-focus element according to the Dammann grating design principle; obtaining a 0-π structure according to the radial mutation point of the multi-focus element; generating a GDS file for lithography processing according to the 0-π structure, and generating a photolithography mask file according to the GDS file; engraving a photoresist pattern consistent with the 0-π structure on the photoresist on the quartz substrate according to the photolithography mask file; transferring the photoresist pattern to the quartz wafer, and removing the remaining photoresist. The present application gets rid of the long-focus application scenario in which the multi-focus phase element is mostly in the Fraunhofer diffraction region and the Fresnel diffraction region in the past, and is suitable for short-focus application scenarios, and the mapping is simple and the calculation time is short. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more intuitively illustrate the prior art and the present application, exemplary drawings are given below. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing the present application; for example, those skilled in the art are capable of easily making conventional adjustments or further optimizations to the addition / reduction / attribution division, specific shapes, positional relationships, connection methods, dimensional ratios, etc. of certain units (components) based on the technical concepts and exemplary drawings disclosed in the present application.

[0029] Figure 1 A flow chart of a method for preparing a binary 0-π phase multi-focus element based on difference mapping provided in this application;

[0030] Figure 2 A schematic diagram of the axial multi-focus principle structure provided for this application;

[0031] Figure 3 A schematic diagram of the phase structure of a multi-focus element provided in an embodiment of the present application;

[0032] Figure 4 A schematic diagram of the diffraction effect provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] The present application is further described below in detail through specific embodiments in conjunction with the accompanying drawings.

[0034] In the description of this application: unless otherwise specified, the meaning of "plurality" is two or more. The terms "first", "second", "third", etc. in this application are intended to distinguish the objects referred to, and do not have special meanings in terms of technical connotations (for example, they should not be understood as emphasizing the importance or order, etc.). Expressions such as "including", "comprising", "having", etc. also mean "not limited to" (certain units, components, materials, steps, etc.).

[0035] The terms such as "upper", "lower", "left", "right", "middle", etc. cited in this application are usually used to indicate the general relative position relationship for the purpose of intuitive understanding by referring to the drawings, and are not absolute limitations on the position relationship in the actual product.

[0036] See also Figure 1 The present application proposes a method for preparing a binary 0-π phase multi-focal element based on difference mapping for a short-focus focusing objective lens, and uses a semiconductor photolithography process to process it on a suitable optical element substrate based on the calculated phase structure. The method includes:

[0037] S1: Determine the phase difference calculation formula according to the Rayleigh-Sommerfeld formula, and calculate the phase difference of the multi-focus element;

[0038] Specifically, under the short-focus focusing condition, the principle of achieving axial multi-focality is as follows: Figure 2 As shown, Figure 2 In the example, the focal length of the objective lens is f, the number of focal points to be achieved is m, and the focal distance between these focal points is d. Then the focal lengths of these focal points are: m =f+md(m=0, ±1, ±2,...).

[0039] For the short-focus diffraction scene involved in this application, the original Rayleigh-Sommerfeld formula is used, and its expression is as follows:

[0040]

[0041] In formula (1), i represents an imaginary number, r represents the radial coordinate, λ represents the wavelength of the incident light, and u in represents the square distribution on the front surface of the focusing mirror, u out represents the output field distribution, k represents the wave number (k=2π / λ), represents the equivalent focusing phase of a focusing lens with a focal length of f, r' represents the distance from a point on the image plane to a point on the object plane, and α represents the angle between the focused light and the optical axis. According to the above regulations, we have:

[0042]

[0043] Therefore, in order to achieve focusing, the equivalent focusing phase It must satisfy the following form:

[0044]

[0045] In Equation (3), A represents a constant. Let A = kf. Therefore, for the focus with a focal length of f + d, its equivalent focusing phase is:

[0046]

[0047] The difference between its equivalent focusing phase and the focal length f of the objective lens is:

[0048]

[0049] Here, usually d << f, then the phase difference can be expressed as:

[0050]

[0051] It can be seen from Equation (6) that is a linear phase. Then it can be concluded that in the case of a short-focus focusing objective lens system, adding a linear phase at its entrance can make the focus shift by d.

[0052] Therefore, in this step, the phase difference calculation formula can be derived according to the Rayleigh-Sommerfeld formula, and the phase difference of the multi-focus element to be fabricated can be calculated according to the phase difference calculation formula.

[0053] S2: Map the phase difference to the independent variable of the Fourier series according to the coordinate transformation formula, and obtain the radial mutation points of the multi-focus element according to the design principle of the Dammann grating;

[0054] Specifically, based on Step S1, in order to achieve the distribution of a series of n foci, the focal lengths of the foci are: f m = f + md (n = 2m + 1, m = 0, ±1, ±2,...), and its equivalent overall phase should satisfy:

[0055]

[0056] It can be seen from Equation (7) that the first term represents the phase of the objective lens. Then the second term is the condition that the phase of the multi-focus element to be calculated should satisfy, that is:

[0057]

[0058] In Equation (8), satisfies the energy conservation.

[0059] For a periodic function t(x), x represents the independent variable, and its Fourier series expansion form is:

[0060]

[0061] By analogy between equation (8) and equation (9), it is obvious that when the following conditions are met:

[0062]

[0063] Equation (8) is the Fourier series expansion form of a radial function, which can obviously be compared to the structure of a Vidamer grating, that is, within one amplitude grating period, its Fourier spectrum is completely determined by the coordinates of those mutation points in the grating structure {(a l , b l )} (where l = 1, 2, 3, ... are positive integers), the Fourier series of the grating represented by the coordinates of the mutation point is the DC component when n = 1, and T(n) is expressed as:

[0064]

[0065] When n≠1, T(n) is expressed as:

[0066]

[0067] Now the amplitude grating is replaced by a phase distribution grating to improve the diffraction efficiency. Suppose that the phase values ​​provided by the grating in one period are and two different values, the complex radiation transmittance can be expressed as:

[0068]

[0069] Using Euler's formula, equation (13) is simplified to:

[0070] t p (x)=[2t(x)-1]sinθ+icosθ (14)

[0071] Its spectrum function, the spectrum at each level can still be expanded by Fourier series:

[0072]

[0073] Then when m=0, we have:

[0074] T p (0)=[2T(0)-1]sinθ+icosθ (16)

[0075] Then when m≠0, we have:

[0076] T p (m)=2T(m)sinθ (17)

[0077] Because BOE (diffractive optical element) generally adopts a 0-π structure, then θ = π / 2, and the spectrum order can be summarized as:

[0078]

[0079] Then its power spectrum function is:

[0080] P(m)=|T p (m)| 2 (19)

[0081] According to the above derivation, a clear optimization design direction is pointed out for the subsequent optimization algorithm. The optimization design idea is: under the coordinate transformation that satisfies formula (10), find a set of mutation points {(a l , b l )}, so that it satisfies the uniform distribution of light intensity in the required order diffraction spectrum.

[0082] S3: Obtaining the 0-π structure based on the radial mutation points of the multi-focus element;

[0083] Specifically, because the set of mutation points in the transformation of conventional Dammann gratings is very mature and very easy to obtain, this step can obtain the radial mutation points of the desired multi-focus element based on the found Dammann grating mutation points to obtain the 0-π structure.

[0084] S4: Generate a GDS file for photolithography processing according to the 0-π structure, and generate a photolithography mask file according to the GDS file;

[0085] Specifically, after the 0-π structure is obtained, it can be processed onto the element substrate according to the obtained phase structure. During the preparation, semiconductor photolithography technology is used on quartz (SiO 2 ) to process the required spot structure.

[0086] In this step, the normalized radius structure obtained in the above steps is a circular grating structure, a GDS file corresponding to the photolithography process is drawn, and a photolithography mask file is generated using the GDS file.

[0087] S5: Carving a photoresist pattern consistent with the 0-π structure on the photoresist on the quartz substrate according to the photolithography mask file;

[0088] Specifically, in this step, a photolithography mask is used to perform exposure, development, fixing and other operations on the photoresist on the quartz substrate, thereby leaving a photoresist pattern consistent with the design structure on the quartz substrate, wherein the mask uses metal chromium and metal nickel.

[0089] S6: The photoresist pattern is transferred to the quartz wafer and the remaining photoresist is removed.

[0090] Specifically, in this step, the photoresist pattern is transferred to the quartz wafer using a dry etching process, and the pattern on the quartz wafer is consistent with the design structure, wherein the etching depth h is related to the refractive index N of the component material, namely:

[0091]

[0092] In this step, the dry etching process adopts reactive ion beam etching, ion beam etching or inductively coupled plasma reactive ion beam etching.

[0093] In this step, a stripping solution is used to remove the remaining photoresist. The stripping solution used is acetone. Mineral acid and sulfuric acid hydrogen peroxide are used to remove the metal mask.

[0094] Example:

[0095] Design requirements: wavelength: 1137nm, focusing lens: 75mm, the number of focal points to be designed: 2, focal distance: 5mm, then according to the method provided in this application, the phase structure of the multi-focus element is obtained as follows Figure 3 As shown, the diffraction effect is as follows Figure 4 shown.

[0096] The present application is aimed at a short focal length focusing physical processing system. According to the focal length f of the objective lens, the number of focal points m required to be realized and the focal spacing d, a method for preparing a binary 0-π phase multi-focal element based on difference mapping is proposed. The method breaks away from the long-focus application scenario in which the multi-focal phase elements are mostly in the Fraunhofer diffraction region and the Fresnel diffraction region in the past, and can be applied to short-focus application scenarios. In addition, the difference iteration algorithm used is simpler to map and has a shorter calculation time than the conventional phase iteration optimization algorithm, and will not fall into the optimization trap brought by the iteration algorithm. The traditional iteration optimization algorithm not only has a long calculation time, but also the obtained phase is mostly a continuous phase, which increases the difficulty of subsequent component processing. The mapping process of the present application is a process of applying the existing mapping scheme of lateral beam splitting to axial multi-focal points according to the mapping of the existing beam splitting nodes. The phase structure obtained is a binary phase of 0-π, which has a simple structure, high uniformity between focal points, and the amount of calculation can be almost ignored. It is very beneficial to the processing of semiconductor processes used in subsequent component production.

[0097] The present application also provides a short-focus multifocal element, which is prepared according to a method for preparing a binary 0-π phase multifocal element based on difference mapping provided in the present application.

[0098] The technical features of the above embodiments may be arbitrarily combined (as long as there is no contradiction in the combination of these technical features). To make the description concise, not all possible combinations of the technical features in the above embodiments are described; these embodiments that are not explicitly written should also be considered to be within the scope of this specification.

Claims

1. A method for preparing a binary 0-π phase multi-focus element based on difference mapping, characterized in that: include: Step 1: Determine a phase difference calculation formula according to the Rayleigh-Sommerfeld formula, and calculate the phase difference of the multi-focus element; Step 2: Mapping the phase difference to the independent variable of the Fourier series according to the coordinate transformation formula, and obtaining the radial mutation point of the multi-focus element according to the Dammann grating design principle; Step 3: obtaining a 0-π structure according to the radial mutation point of the multi-focus element; Step 4: Generate a GDS file for photolithography processing according to the 0-π structure, and generate a photolithography mask file according to the GDS file; Step 5: Carving a photoresist pattern consistent with the 0-π structure on the photoresist on the quartz substrate according to the photolithography mask file; Step 6: Transfer the photoresist pattern to a quartz wafer and remove the remaining photoresist.

2. The method for preparing a binary 0-π phase multi-focus element based on difference mapping according to claim 1, characterized in that: In step 1, the phase difference calculation formula is: in, represents the phase difference, k represents the wave number, d represents the focal distance, r represents the radial coordinate, and f represents the focal length of the objective lens.

3. The method for preparing a binary 0-π phase multi-focus element based on difference mapping according to claim 1, characterized in that: In step 2, the coordinate transformation formula is: Here, x represents the independent variable.

4. The method for preparing a binary 0-π phase multi-focus element based on difference mapping according to claim 1, characterized in that: In step 5, etching a photoresist pattern consistent with the 0-π structure on the photoresist on the quartz substrate according to the photolithography mask file includes exposure, development and fixing operations.

5. The method for preparing a binary 0-π phase multi-focus element based on difference mapping according to claim 1, characterized in that: In step 5, the mask used when etching a photoresist pattern consistent with the 0-π structure on the photoresist on the quartz substrate according to the photolithography mask file is metal chromium or metal nickel.

6. The method for preparing a binary 0-π phase multi-focus element based on difference mapping according to claim 1, characterized in that: In step 6, a dry etching process is used to transfer the photoresist pattern to a quartz wafer.

7. The method for preparing a binary 0-π phase multi-focus element based on difference mapping according to claim 6, characterized in that: The dry etching process is reactive ion beam etching, ion beam etching or inductively coupled plasma reactive ion beam etching.

8. The method for preparing a binary 0-π phase multi-focus element based on difference mapping according to claim 1, characterized in that: In step 6, a stripping solution is used to remove the remaining photoresist.

9. The method for preparing a binary 0-π phase multi-focus element based on difference mapping according to claim 8, characterized in that: The degumming solution is acetone, inorganic acid or sulfuric acid and hydrogen peroxide.

10. A short-focus multi-focal element, characterized in that: The short-focus multifocal element is prepared according to the method for preparing a binary 0-π phase multifocal element based on difference mapping according to any one of claims 1 to 9.

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