An efficient multi-step lithography method using an improved Golomb equal-length coding algorithm

Abstract

The present invention discloses an efficient multi-step lithography method using an improved Golomb equal-length coding algorithm, comprising the following steps: Step 1: obtaining a lithography experimental condition m value based on the minimum exposure intensity and the outputtable maximum exposure intensity of the lithography experimental condition; Step 2: performing Golomb division transcoding on the grayscale value of a grayscale image representing the step depth according to the m value to obtain a first segment of equal-length coding; Step 3: calculating the m value and the grayscale value of the grayscale image using the Golomb compression coding rule to obtain a second segment of equal-length coding; Step 4: concatenating the first segment of coding and the second segment of coding to obtain a Golomb code; Step 5: performing a binary horizontal slice of the Golomb code to obtain a bit plane binary image; Step 6: sequentially exposing the binary image containing the first segment of coding at m times the exposure intensity, and exposing the binary image containing the second segment of coding at an exposure intensity twice as high as the adjacent segment of coding. The present invention can reduce the number of exposures to obtain a greater number of steps, thereby improving work efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of photolithography, and in particular to a high-efficiency multi-step photolithography method for improving the Golomb equal-length coding algorithm. Background Art

[0002] At present, the mainstream direct write lithography and mask lithography generally use multiple stacked exposure methods in multi-step lithography. The main method is to make a mask or expose and etch layer by layer based on the position and height of each step to achieve the purpose of multiple steps, or to use grayscale lithography to achieve n-2 exposures by n times according to different light intensities and exposure times. n However, they have the disadvantages of low efficiency and high requirements on lithography light intensity.

[0003] Existing direct write and mask multi-step lithography methods:

[0004] Direct-write lithography machines utilize digital micromirrors (DMDs) to project the designed pattern directly onto the photoresist for exposure and development. If a multi-step structure is required, varying the light intensity can be stacked to control the thickness of each exposure and development step. However, there are challenges with controlling the light intensity and insufficient experimental conditions for light intensity.

[0005] Mask: Masked lithography utilizes specially designed light-transmitting locations on a mask to achieve exposure. Depending on the mask and sample, it can be categorized as either contact or non-contact. For multi-step lithography, stacking multiple binary masks or grayscale lithography can be used. Multiple alignments significantly reduce lithography accuracy, leading to high costs and long processing cycles. Summary of the Invention

[0006] The purpose of the present invention is to provide an efficient multi-step lithography method using an improved Golomb equal-length coding algorithm. The present invention can reduce the number of exposures while obtaining more steps, thereby improving work efficiency and solving the problem of pure 2 n The limitations of the light intensity conditions of the photolithography method, the shortcomings of insufficient utilization of the maximum light intensity, and the limitations of mask lithography.

[0007] The technical solution of the present invention is a high-efficiency multi-step lithography method using an improved Golomb equal-length coding algorithm, comprising the following steps:

[0008] Step 1: According to the minimum exposure intensity required for the shallowest step under the lithography experiment conditions and the maximum exposure intensity that can be output by the lithography machine, a multiple of the effective maximum exposure intensity that can be output under the current lithography experiment conditions is obtained, and the multiple is represented by an m value;

[0009] Step 2: Perform Golomb division transcoding on the grayscale values of each pixel in the grayscale image representing the step depth according to the value of m to obtain the first segment of equal-length code;

[0010] Step 3: The m value and the grayscale value of the grayscale image are calculated using the improved Golomb compression coding rule to obtain the second segment of equal-length code;

[0011] Step 4: Concatenate the first segment code and the second segment code at the corresponding position according to the grayscale value of the grayscale image to obtain a set of Golomb codes corresponding to the grayscale value of the grayscale image;

[0012] Step 5: Perform a binary horizontal bit plane slice on the Golomb code obtained in step 4 to obtain a binary image corresponding to the binary bit order;

[0013] Step 6: Expose the bit plane binary image containing the first segment code in sequence with an equal m-fold exposure intensity, and expose the bit plane binary image containing the second segment code with an exposure intensity that increases stepwise with a geometric series multiple adjacent to 2.

[0014] In the above-mentioned efficient multi-step lithography method using the improved Golomb equal-length coding algorithm, the calculation formula of the m value is as follows:

[0015]

[0016] Where: I max Indicates the maximum exposure intensity that the lithography machine can output, I min Indicates the minimum exposure intensity required for the shallowest step under lithography experimental conditions.

[0017] In the aforementioned efficient multi-step lithography method using the improved Golomb equal-length coding algorithm, the first segment of code is obtained by first performing a division transcoding operation:

[0018]

[0019] Search for the maximum grayscale value f(x,y) in the grayscale image max , the first segment encoding length is:

[0020]

[0021] Where: f(x,y) is the grayscale value at position x,y of the grayscale image representing the step depth, ranging from 0 to 255; q is the number of 1s in the first segment of the Golomb code cut corresponding to the grayscale value of the image; Indicates the largest integer less than or equal to the calculated value;

[0022] The first equal-length code is preceded by q max -q 0s followed by q 1s.

[0023] The aforementioned efficient multi-step lithography method using the improved Golomb equal-length coding algorithm, the formula of the improved Golomb compression coding rule is as follows:

[0024]

[0025] c=m-2 k ;

[0026] r=f(x,y)modm;

[0027] Where: Indicates the maximum integer less than or equal to the calculated value; k is the interception parameter of the second segment code; c is the interception adjustment parameter; f(x,y)modm represents the remainder when f(x,y) is divided by m, f(x,y) is the grayscale value at position x,y in the grayscale image, and r is the binary value of the second segment code;

[0028] r' = converted to k+1-bit binary r;

[0029] The r' in the formula is the second segment of equal-length code.

[0030] The aforementioned efficient multi-step lithography method using the improved Golomb equal-length coding algorithm is characterized in that: in step 5, the bit plane transverse cut image is calculated as follows:

[0031]

[0032] Where: A a Represents a binary image of Golomb code a position, its number of pixels and original grayscale Figure 1 a is the Golomb code position, that is, the number of slice layers; b a,x,y is the Golomb code corresponding to the grayscale value of the grayscale image; x, y represent the position of the grayscale image; the total number of cut images is q max +k+1.

[0033] In the aforementioned efficient multi-step lithography method using the improved Golomb equal-length coding algorithm, in step 6:

[0034] For layers a greater than k+1, use mI min Expose in sequence with equal exposure intensity;

[0035] For layers a less than or equal to k+1, use I in turn min , 2 1 I min , 2 2 I min , 2 3 I min Until 2 k Imin Exposure intensity is processed exposure.

[0036] Compared with the prior art, the present invention uses Golomb coding to transcode and cut the image, achieving q of 255 grayscale values. max +k+1 slices, and then using the corresponding exposure intensity to achieve a one-to-one correspondence with the exposure depth, the present invention can achieve accurate etching of multiple steps with a limited number of exposures, greatly reducing the number of exposures, and can reduce the alignment error of multiple exposures, making the effect more accurate. The present invention can be applied to masks and direct-write lithography, which can save materials and process flows and reduce costs. At the same time, the method of the present invention can also be based on other horizontal slice algorithms of other digital image processing functions (such as log N), and can use adjacent 2 times the light intensity to achieve equal height step exposure, and can also use equal light intensity stacking to achieve multi-step exposure with related layers of light intensity and related depth. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic diagram of a grayscale image in an embodiment;

[0038] Figure 2 This is a schematic diagram of the grayscale image after Golomb transcoding and cutting;

[0039] Figure 3 It is a schematic diagram of the result after photolithography using the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the examples, but they are not intended to limit the present invention.

[0041] Example: An efficient multi-step lithography method using an improved Golomb equal-length coding algorithm,

[0042] Step 1: Obtain a multiple of the effective minimum exposure intensity that can be output by the lithography experiment conditions according to the minimum exposure intensity and the maximum exposure intensity that can be output by the lithography experiment conditions, where the multiple is represented by an m value. The calculation formula of the m value is as follows:

[0043]

[0044] Where: I max Indicates the maximum exposure light intensity that can be output, I min Indicates the minimum exposure intensity.

[0045] Step 2: Perform Golomb division transcoding (dividing and taking the quotient) on the grayscale value (0-255) of the grayscale image representing the step depth according to the m value to obtain the first segment of code; the first segment of code is obtained by first performing division transcoding:

[0046]

[0047] Search for the maximum grayscale value f(x,y) in the grayscale image max , the first segment encoding length is:

[0048]

[0049] Where: f(x,y) is the grayscale value at position x,y of the grayscale image representing the step depth, ranging from 0 to 255; q is the number of 1s in the first segment of the Golomb code cut corresponding to the grayscale value of the image; Indicates the largest integer less than or equal to the calculated value;

[0050] The first equal-length code is preceded by q max -q 0s followed by q 1s.

[0051] Step 3: Calculate the m value and the grayscale value of the grayscale image using the Golomb compression coding rule to obtain the second segment code; the formula of the improved Golomb compression coding rule is as follows:

[0052]

[0053] c=m-2 k ;

[0054] r=f(x,y)modm;

[0055] Where: Indicates the maximum integer less than or equal to the calculated value; k is the interception parameter of the second segment code; c is the interception adjustment parameter; f(x,y)modm represents the remainder when f(x,y) is divided by m, f(x,y) is the grayscale value at position x,y in the grayscale image, and r is the binary value of the second segment code;

[0056] r' = converted to k+1-bit binary r;

[0057] The r' in the formula is the second segment of equal-length code.

[0058] Step 4: Concatenate the first segment code and the second segment code at the corresponding position (i.e., i, j) according to the grayscale value of the grayscale image to obtain a set of Golomb codes corresponding to the grayscale value of the grayscale image;

[0059] Step 5: Perform binary horizontal slicing on the Golomb code obtained in step 4 to obtain a binary image corresponding to the binary bit order. The calculation formula for the horizontal slicing is as follows:

[0060]

[0061] Where: A a Represents a binary image of Golomb code a position, its number of pixels and original grayscale Figure 1 a is the Golomb code position, that is, the number of slice layers; b a,x,y is the Golomb code corresponding to the grayscale value of the grayscale image; x, y represent the position of the grayscale image.

[0062] Step 6: sequentially expose the first segment of the coded image in the binary image using m times the exposure intensity, and expose the second segment of the coded image in the binary image using adjacent doubled exposure intensities.

[0063] The high k layer (a is greater than k) uses mI min The exposure intensity is sequentially exposed, which is equivalent to exposing the first segment of the coded image with m times the exposure intensity in sequence;

[0064] The first k layers (a is less than or equal to k) use I in turn min , 2 1 I min , 2 2 I min , 2 3 I min Until 2 k I min The exposure intensity is processed and exposed, which is equivalent to exposing the image of the second segment of the binary image with an exposure intensity that is twice as large as that of the adjacent image.

[0065] The applicant carried out an example operation according to the above steps, and first determined the maximum light intensity multiplier value to be used: m, based on the grayscale image characteristics and the photolithography machine characteristics.

[0066] In this embodiment, m=32 grayscale images are as follows Figure 1 As shown, the decimal grayscale values of a, b, c, and d are 4, 45, 64, and 176 respectively.

[0067] Perform Golomb transcoding on the grayscale value and fill the image with zeros, such as Figure 2 As shown, we get:

[0068] a:00000,000100; b:00001,001101;

[0069] c:00011,000000; d:11111,010000.

[0070] Finally, the first photo was exposed with one times the intensity, the second photo was exposed with two times the intensity, the third photo was exposed with four times the intensity, and the sixth and subsequent photos were exposed with m = 32 times the intensity due to experimental conditions. The results are as follows: Figure 3 As shown, from Figure 3 It can be seen from the figure that the present invention can also obtain good experimental results with a limited number of exposures.

[0071] In summary, the present invention utilizes the Golomb encoding method to transcode and cut images, realizes a few-bit plane cutting of 255 grayscale values, and then utilizes the corresponding exposure intensity to achieve a one-to-one correspondence with the exposure depth. The present invention can realize accurate etching of multiple steps with a limited number of exposures, greatly reducing the number of exposures, and can reduce the alignment error of multiple exposures, making the effect more accurate. The present invention can be applied to masks and direct-write lithography, can save materials and process flow, and reduce costs. At the same time, the method of the present invention can also be based on other horizontal cutting algorithms of other digital image processing functions (such as log N), and can use adjacent 2 times the light intensity to realize equal height step exposure, and can also use equal light intensity stacking to realize multi-step exposure of related layers of light intensity and related depth.

Claims

1. An efficient multi-step lithography method using an improved Golomb equal-length coding algorithm, characterized by: The following steps are involved: Step 1: According to the minimum exposure intensity required for the shallowest step under the lithography experiment conditions and the maximum exposure intensity that can be output by the lithography machine, a multiple of the effective maximum exposure intensity that can be output under the current lithography experiment conditions is obtained, and the multiple is represented by an m value; Step 2: Perform Golomb division transcoding on the grayscale values of each pixel in the grayscale image representing the step depth according to the value of m to obtain the first segment of equal-length code; Step 3: The m value and the grayscale value of the grayscale image are calculated using the improved Golomb compression coding rule to obtain the second segment of equal-length code; Step 4: Concatenate the first segment code and the second segment code at the corresponding position according to the grayscale value of the grayscale image to obtain a set of Golomb codes corresponding to the grayscale value of the grayscale image; Step 5: Perform a binary horizontal bit plane slice on the Golomb code obtained in step 4 to obtain a binary image corresponding to the binary bit order; Step 6: sequentially expose the bit plane binary image containing the first segment code using an equal m-fold exposure intensity, and expose the bit plane binary image containing the second segment code using an exposure intensity that increases stepwise by a geometric series of multiples adjacent to 2; The formula of the improved Golomb compression coding rule is as follows: c=m-2 k ; r = f(x, y) mod m; Where: represents the maximum integer less than or equal to the calculated value; k is the second-segment encoding interception parameter; c represents the interception adjustment parameter; f(x, y) mod m represents the remainder when f(x, y) is divided by m, f(x, y) represents the grayscale value at the x, y position of the step depth grayscale image, and r is the second-segment encoding binary value; r′=converted to k+1-bit binary r; The r′ in the formula is the second segment of equal-length code.

2. The efficient multi-step lithography method using the improved Golomb equal-length coding algorithm according to claim 1, characterized in that: The calculation formula of the m value is as follows: Where: I max Indicates the maximum exposure intensity that the lithography machine can output, I min Indicates the minimum exposure intensity required for the shallowest step under lithography experimental conditions.

3. The efficient multi-step lithography method using the improved Golomb equal-length coding algorithm according to claim 1, characterized in that: The first segment of the code is obtained by first dividing and transcoding: Search for the maximum grayscale value f(x, y) in the grayscale image max , the first segment encoding length is: Where: f(x, y) is the grayscale value at position x,y of the grayscale image representing the step depth, ranging from 0 to 255; q is the number of 1s in the first segment of the Golomb code cut corresponding to the grayscale value of the image; Indicates the largest integer less than or equal to the calculated value; The first equal-length code is preceded by q max -q 0s followed by q 1s.

4. The efficient multi-step lithography method using the improved Golomb equal-length coding algorithm according to claim 1, characterized in that: In step 5, the bit plane transverse cut graph is calculated as follows: Where: A a The binary image of Golomb coding position a has the same number of pixels as the original grayscale image; a is the Golomb coding position, that is, the number of slice layers; b a，x，y is the Golomb code corresponding to the grayscale value of the grayscale image; x, y represent the position of the grayscale image; the total number of cut images is q max +k+1.

5. The efficient multi-step lithography method using the improved Golomb equal-length coding algorithm according to claim 4, characterized in that: In step 6: For layers a greater than k+1, use mI min Expose in sequence with equal exposure intensity; For layers a less than or equal to k+1, use I in turn min , 2 1 I min , 2 2 I min , 2 3 I min Until 2 k I min Exposure intensity is processed exposure.

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