CN110456609B

CN110456609B - A Proximity Correction Method for Maskless Digital Lithography

Info

Publication number: CN110456609B
Application number: CN201910733292.2A
Authority: CN
Inventors: 刘江辉; 刘俊伯; 赵立新; 唐燕; 胡松
Original assignee: Institute of Optics and Electronics of CAS
Current assignee: Institute of Optics and Electronics of CAS
Priority date: 2019-08-09
Filing date: 2019-08-09
Publication date: 2021-04-09
Anticipated expiration: 2039-08-09
Also published as: CN110456609A

Abstract

The invention discloses a proximity effect correction method suitable for maskless digital lithography, which utilizes the modulation mechanism of the digital micromirror to the phase amplitude of the light field, and analyzes the distribution of the peak value and the half-peak height and width of the light field caused by different gray levels. And finally the influence of line width and line spacing on the photosensitive medium, on the basis of empirical proximity effect correction, a look-up table suitable for maskless digital lithography technology is established, and grayscale information is added to the pixels of traditional digital masks. , so as to complete the design of the special proximity effect post-mask. This method can effectively make up for the defect that mask patterns cannot be added or modified due to the fixed size of a single pixel in maskless digital lithography, and optimizes proximity effects at small scales such as rounded corners, line width changes, and line ends shortened, etc. Phenomenon.

Description

Proximity effect correction method suitable for maskless digital lithography

Technical Field

The invention belongs to the application field of an optical principle technology in a photoetching technology, and particularly relates to a proximity effect correction method suitable for maskless digital photoetching.

Background

The micro-nano scale processing technology represented by the photoetching technology is a key development direction in the scientific and technological era, and downstream application products such as integrated circuit chips, micro sensors, metamaterials and the like are representative embodiments of national modernization and are closely related to the comprehensive strength of a country, national defense safety and the like. In the traditional optical lithography, the structure of the photosensitive medium layer comes from the pattern of the mask, which also means that the mask must be replaced in the replacement process, and the plate making cost and the processing period of the physical mask are additionally increased.

The micro-stereo lithography represented by maskless digital lithography adopts a Digital Micromirror Device (DMD) to replace the traditional physical mask, effectively reduces the lithography period and cost, avoids overlay error caused by mask replacement, and is one of the mainstream micro-nano scale processing technical means at present. The DMD is composed of arrayed digital microprisms, and the rotation angle of any microprism can be independently controlled by a computer terminal. Thus, by loading a specific digital mask pattern, the light-on state of any microprism on the DMD is controlled by "0" (pure black) and "1" (pure white), thereby combining the desired light field pattern. However, as the photolithography technology is developed to smaller scale, Optical Proximity Effect (OPE) caused by Optical diffraction phenomenon is unavoidable, such as corner rounding, line end shortening, line width variation, etc., which seriously affects the quality of the final pattern on the photosensitive medium layer.

Domestic patent 200810023485.0 discloses a proximity effect correction method for maskless digital lithography that optimizes the final exposure pattern by adding or deleting pixels in the digital mask pattern. However, since the pattern generated by the DMD is composed of the microprism array, adding or deleting any pixel causes significant pattern distortion when the number of pixels constituting the digital mask pattern is small. Therefore, the method for optimizing the proximity effect in the preparation of the small-scale structure composed of a small number of pixel points is explored, and the method has great significance for promoting the continuous development of the technical node of the maskless digital photoetching technology.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, optimize the proximity effect in the maskless digital lithography technology under a small scale and improve the lithography quality.

In order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows: a proximity effect correction method suitable for maskless digital lithography is provided, including: the DMD device recognizes gray scale information in a digital mask pattern based on a pulse width modulation principle and adjusts the amplitude intensity of a light field passing through a microprism in real time. For a single microprism, a light field model of the microprism on an image side is approximately in Gaussian distribution, gray information of pixel points on a digital mask pattern is changed, and the amplitude peak value and half-peak height and width of the light field on the image side can be effectively adjusted, so that the characteristic dimension, edge line width and the like of a photoetching line are influenced, and finally, special digital gray mask design is completed and the microprism is applied to the optimization of the proximity effect under a small scale.

Wherein the first step corrects for non-linear effects in maskless lithography. The nonlinear relationship between the identification of the gray scale information by the DMD device and the amplitude modulation of the light field and the nonlinear response curve of the photosensitive medium are included.

And secondly, establishing a lookup table according to an experience-Based Optical Proximity Correction (RB-OPC). Through actual process tests, photoetching feature size and edge line width size variation under the conditions of different gray levels, different density, different feature sizes, different angle lines and the like are established, and finally a lookup table under different process conditions is perfected.

And thirdly, modifying the original mask pattern according to the content of the lookup table. And drawing a specific proximity effect correction mask by adding and modifying the gray scale information of the pixel points in the original mask pattern, thereby realizing the proximity effect optimization of maskless digital lithography under small scale.

According to the method, the proximity effect correction lookup table based on experience is established, and the specific gray information is added into the original digital mask pattern, so that the defect that the mask pattern cannot be added or modified due to the fixed size of a single pixel point in the maskless digital photoetching technology is effectively overcome, and the proximity effects under small scale, such as corner rounding, line width variation, line end shortening and the like, are optimized.

Drawings

Fig. 1 is a model diagram of maskless digital lithography, wherein 1 is a DMD device, 2 is a light source adjusting system, 3 is a plane mirror, 4 is a digital mask pattern, 5 is a projection objective, and 6 is a three-axis moving stage.

Fig. 2 shows the unit area optical power intensity of the gray scale value of the upper portion of the digital mask at the image side of the projection objective tested in the previous stage.

FIG. 3 is a diagram of one digital mask pattern according to the present invention, which includes an original mask pattern without proximity correction and a corrected mask pattern.

Fig. 4 is a graph showing one of patterns obtained under a metallographic microscope after actual arrayed exposure using the mask shown in fig. 3 and a comparison with a theoretical pattern, where fig. 4(a) is one of the patterns obtained under the metallographic microscope and fig. 4(b) is the theoretical pattern.

Detailed Description

The invention is further described below with reference to the drawings and preferred embodiments.

Preferred embodiment 1:

in this example, the main components include a light source adjusting system 2, a DMD device 1, a projection objective 5, a three-axis moving workpiece stage 6, a computer control end, a slit focus detecting system, and the like. The ultraviolet light source is modulated and filtered by the light source modulation system 2 to output uniform i-line ultraviolet light beams (365 +/-5 nm), the light beams pass through the ultraviolet reflecting mirror 3 (double-sided coating) and obliquely enter the DMD device 1 at a special angle, the DMD device 1(TI, 2048 multiplied by 1600, and the size of a single prism is 7.56 multiplied by 7.56 mu m) can automatically identify gray values of all pixel points in the digital mask pattern 4, and the micro-prism corresponding to the non-0 gray pixel point is rotated, and the part of the micro-prism can reflect the ultraviolet light beams to the projection objective 5(-7.56 x). The slit focus detection system and the three-axis motion workpiece table work together to ensure that the silicon wafer is in the best focus surface for light sensing. In this example, the recording medium used was AZ9260 positive photoresist, and the matching photolithography process was the same as the manual thereof.

Firstly, a specific gray matrix pattern is loaded into the DMD device 1, and an ultraviolet irradiation meter is used for measuring the amplitude peak value of an ultraviolet light field at the working distance behind a projection objective. The test quantity can be reduced by adopting a mode of 10 gray levels at intervals, and finally, an interpolation method is used for fitting data to obtain the light field amplitude peak value and the half peak height width corresponding to different gray levels on the digital mask.

Drawing a plurality of grating lines which carry different gray scales and have different fringe density degrees, and leading the grating lines into the DMD device 1. And (3) carrying out multiple actual exposure tests on the AZ9260 positive photoresist, and measuring the characteristic sizes of the photoetching patterns corresponding to different light field amplitude peak values and half peak heights and widths in multiple detection modes such as a step profiler and a metallographic microscope.

After multiple tests, a photoetching line characteristic dimension and edge line width dimension change lookup table under various factors such as gray level of pixel points of the digital mask, photoetching line density degree, process conditions and the like is established according to an experience-based proximity effect correction method.

Drawing a binary original digital mask pattern, and calculating whether proximity effect exists in a right angle part, a line end part and a line edge part. For example, in this example, a digital mask with a gray scale value of 160 is used and the exposure time is set to match the final pattern size on the silicon wafer with the design value. And then, according to the lookup table, modifying the gray scale information of part of the pixel points, and drawing the digital mask pattern carrying the gray scale information after the proximity effect correction, wherein in the example, the gray scale value at the line end is increased to 200 to optimize the line end shortening phenomenon, and the gray scale value at the inner corner is decreased to 120 to optimize the redundancy phenomenon.

And (3) introducing a drawn proximity effect correction mask into the DMD, carrying out actual exposure verification on the AZ9260 positive photoresist, and further modifying and perfecting the lookup table until an actual exposure pattern meets the design requirement (figure 4), wherein the pattern obtained by adopting the modified digital mask exposure is obviously superior to the pattern exposed by the unmodified digital mask at corners and line ends and is closer to the design pattern.

According to the method for correcting the proximity effect based on the gray information, under the condition that extra process cost and process period are not added, the defect that a mask pattern cannot be added or modified due to the fact that the size of a single pixel point is fixed in the maskless digital photoetching technology is effectively overcome, and the phenomena of proximity effects under small scales, such as corner rounding, line width change, line end shortening and the like, are remarkably optimized.

Claims

1. A proximity effect correction method suitable for maskless digital lithography is characterized by comprising the following steps: the method comprises the following steps:

the first step, correcting the nonlinear effect in maskless photoetching, including the nonlinear relation between the identification of the DMD device to the gray information and the light field amplitude modulation, and the nonlinear response curve of the photosensitive medium;

secondly, establishing a lookup table according to a Rule-Based Optical Proximity Correction (RB-OPC) method, establishing photoetching feature size and edge line width size variation under the conditions of different gray levels, different densities, different feature sizes and different angles of lines through actual process tests, and finally perfecting the lookup table under different process conditions;

and thirdly, modifying the original mask pattern according to the content of the lookup table, and drawing a specific proximity effect correction mask by adding and modifying the gray information of the pixel points in the original mask pattern, thereby realizing the proximity effect optimization of maskless digital lithography under small scale.