CN112612190B - Method for improving alignment failure of photoetching process - Google Patents

Abstract

The invention discloses a method for improving the alignment failure of a photoetching process, which comprises the following steps: firstly, manufacturing a test photomask, and placing alignment marks on the test photomask; secondly, manufacturing corresponding structural sheets according to different process platforms; exposing by using a test photomask and finishing the subsequent film growth; thirdly, coating a photoresist on the structural sheet, and performing alignment test of different alignment marks to complete the collection of alignment signal data; fourthly, analyzing data, and selecting alignment marks with relatively good signal quality from all the comparison marks; and fifthly, placing the alignment mark with the alternative duty ratio into a light shield of the mass production product, further confirming the improvement effect of the product alignment state, and selecting the optimal alignment mark. The invention can improve the covering capability of the film layer step by optimizing the size of the standard alignment mark. The alignment marks with different sizes are flexibly designed according to the characteristics of different process platforms, so that alignment signals are effectively improved, and the occurrence of alignment failure is reduced.

Description

Method for improving alignment failure of photoetching process

Technical Field

The invention relates to the field of semiconductor integrated circuit manufacturing, in particular to a method for improving alignment failure of a photoetching process.

Background

As technology nodes of an integrated circuit manufacturing process are made smaller and smaller, devices in a unit area are made larger and smaller, line widths are made thinner and smaller, and requirements on process capacity are made higher and higher. Some non-critical layers, which are typically larger in design size, do not require special attention to their process capabilities. However, as technology nodes become smaller, the design size of these non-critical layers also becomes smaller, and the requirement for mass production cannot be met by the existing photolithography process.

Generally, to improve the lithographic process capability, a higher-order apparatus (having a higher numerical aperture NA and a narrower exposure wavelength) may be used, or an Optical Proximity Correction (OPC) method, a Phase Shift Mask (PSM) method, or a combination thereof may be used to obtain a higher lithographic process capability and meet the requirement of mass production. But these methods are not applicable to the implanted layer.

For lithography, there are two most important process control items, one is strip width control, and the other is alignment control. As the feature size of the product becomes smaller, the requirements for strip width and alignment control become higher. In the current 0.5um product, the requirement of the strip width is generally not more than 10 percent of the central value, namely the strip width is changed between 0.5 +/-0.05 um; the requirement for alignment is different according to different levels, generally speaking, the requirement for alignment is highest when the polycrystal and the Kong Guangke are used, particularly, when the hole is used for photoetching, the requirement for alignment is higher because the hole is divided into an active region and a hole on the polycrystal, and the alignment deviation of the hole on part of the polycrystal is even required to be less than 0.14um. In the present IC circuit fabrication process, a complete chip is usually subjected to tens to twenty photolithography steps, in which, except for the first step, the remaining steps are subjected to alignment before exposure of the pattern of the step with the pattern left in the previous step. The process of alignment exists in the process of exposure of the upper plate and the wafer, and the aim is to cover the pattern on the photoetching plate on the existing pattern on the wafer with maximum precision. It includes the following parts: a reticle alignment system, a wafer alignment system (including LSA, FIA, etc.). For the NIKON Step & Repeat machine, registration, i.e. positioning, it is not actually registered with the pattern on the wafer in direct alignment with the pattern on the reticle, but rather is independent of each other, i.e. determining the reticle position is an independent process, determining the wafer position is another independent process. The principle of its alignment is that there is a fiducial mark on the exposure table, which can be considered as the origin of the coordinate system for positioning, with respect to which all other positions are determined. The reticle and wafer are positioned by aligning them with the fiducial marks, respectively. After the position of the two is determined, the patterns on the mask are transferred to the wafer in alignment.

Due to the process particularity of the power device product, online alignment failure frequently occurs. Alignment strategy optimization based on standard size Alignment marks can reduce Alignment failure to a certain extent, but the failure rate is still large, and rework cost and production period are increased.

As shown in fig. 1, under the effect of different process steps, the standard size alignment mark may have problems of void defects, poor symmetry, poor shape retention, etc., resulting in poor alignment signal (MCC is low and does not conform to sine and cosine curves), and thus the alignment cannot be completed normally. One notable parameter characteristic of the alignment mark is the duty cycle, (Line/Pitch) × 100% in fig. 1, where Line is the effective Line width of the alignment mark and Pitch is the size of an alignment unit, which contains Line and space.

For wafers (wafers) with alignment failures, the alignment failure problem can be improved by optimizing the alignment light source, the alignment mark types, different alignment levels, and the like, but the overall improvement effect is limited.

Disclosure of Invention

The invention aims to solve the technical problem of providing a method for improving the alignment failure of the photoetching process, improving the alignment signal and improving the alignment precision.

In order to solve the above problems, the method for improving lithography process alignment failure according to the present invention comprises:

the first step is to make a test mask and place the alignment marks on the mask.

Secondly, manufacturing corresponding structural sheets according to the film layer structures of different process platforms; and exposing the structural sheet by using the test photomask, and finishing the subsequent film growth.

Thirdly, coating a photoresist on the structural sheet, and performing alignment test of different alignment marks to complete the collection of alignment signal data.

And fourthly, analyzing data, and selecting the alignment marks with relatively good signal quality from all the comparison marks.

And fifthly, placing the alignment mark with the alternative duty ratio into a light shield of the mass production product, further confirming the improvement effect of the product alignment state, and selecting the optimal alignment mark.

In a further improvement, in the first step, the alignment marks are alignment marks of different types and different duty ratios.

In a further improvement, the second step requires that the grown film layer be consistent with the film layer structure of the actual product.

The further improvement is that the structure wafer in the second step is a sample wafer for verifying the test photomask and the alignment mark, and the manufacturing process characteristics are consistent with those of mass production products.

In a further improvement, in the third step, the alignment signal data includes signal strength, signal integrity and overlay accuracy residuals at different duty ratios.

A further improvement is that, in the fourth step, during data analysis, the duty ratio alignment mark with the largest signal intensity and signal integrity and the smallest alignment precision residual is selected as the alternative design size by comparing the alignment signal intensity, the signal integrity and the alignment precision residual under different duty ratio marks.

According to the method for improving the alignment failure of the photoetching process, the step coverage capability of the film layer is improved through the alignment marks under different duty ratios, different alignment marks are flexibly selected according to different process platforms, and the alignment effect is improved.

Drawings

Fig. 1 is a schematic diagram of the theoretical topography of the alignment mark.

FIG. 2 is a test reticle layout for alignment marks at different duty cycles.

Fig. 3 is a graph comparing signal integrity under different duty cycle marks.

Fig. 4 is a graph comparing signal strength at different duty cycle marks.

Fig. 5 is an overlay accuracy residual comparison graph.

FIG. 6 is a schematic flow chart of the method of the present invention.

Detailed Description

The method for improving the alignment failure of the photoetching process comprises the following steps in order to solve the problem of alignment failure in photoetching alignment:

firstly, a test photomask is manufactured, and alignment marks of different types and different duty ratios are all placed on the test photomask, as shown in fig. 2, fig. 2 shows a photomask including alignment marks of different types and different duty ratios, and the different alignment marks are used for aligning different film structures under different subsequent process platforms.

And secondly, manufacturing corresponding structural sheets according to the film layer structures of different process platforms. The structure wafer is a sample wafer for verifying the test photomask and the alignment mark, and the manufacturing process characteristics of the structure wafer are consistent with those of a mass production product. And exposing the structural sheet by using the test photomask, and finishing the subsequent film growth to make the film structure consistent with that of the actual mass production product.

And thirdly, coating photoresist on the structural sheet, and performing alignment test of different alignment marks to complete the collection of alignment signal data.

And fourthly, analyzing data, and selecting the alignment mark with better signal intensity, signal integrity and alignment precision residual error under different duty ratios. As shown in fig. 3-5, fig. 3 is a graph comparing signal integrity at different duty cycle marks. Fig. 4 is a graph of signal strength versus duty cycle for different duty cycle markers. Fig. 5 is an overlay accuracy residual comparison graph.

During data analysis, the duty ratio alignment mark with the largest signal intensity and signal integrity and the smallest alignment precision residual error is selected as the alternative design size by comparing the alignment signal intensity, the signal integrity and the alignment precision residual error under different duty ratio marks, namely the alignment mark with the best effect in fig. 3-5. Other alignment marks with poor actual effect are discarded.

And fifthly, placing the alignment mark with the alternative duty ratio into a photomask of an actual mass production product, further confirming the improvement effect of the alignment state of the product, and selecting the optimal alignment mark for mass production.

According to the method for improving the alignment failure of the photoetching process, the covering capability of the film layer step can be improved by optimizing the size of the standard alignment mark, namely changing the duty ratio of the alignment mark. According to the characteristics of different process platforms, the alignment marks with different sizes can be flexibly designed, the alignment signals can be effectively improved, and the occurrence of alignment failure can be greatly reduced.

The above are merely preferred embodiments of the present invention, and are not intended to limit the present invention. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (4)

1. A method for improving alignment failure in a photolithography process, comprising the steps of:

firstly, manufacturing a test photomask, and placing alignment marks on the test photomask; the alignment marks are different types and different duty ratios of alignment marks; the duty ratio is the percentage of the ratio of the effective line width of the alignment mark to the whole size of the contrast mark unit;

secondly, manufacturing corresponding structural sheets according to the film layer structures of different process platforms; exposing the structural sheet by using a test photomask, and finishing the subsequent film growth;

thirdly, coating a photoresist on the structural sheet, and performing alignment test of different alignment marks to complete the collection of alignment signal data; the alignment signal data comprises signal intensity, signal integrity and alignment precision residual errors under different duty ratios;

fourthly, analyzing data, and selecting the alignment mark with relatively good signal quality from all the comparison marks as an alternative alignment mark;

fifthly, placing the alternative alignment marks in the light shield of the mass production product, further confirming the improvement effect of the alignment state of the product, and selecting the optimal alignment mark.

2. The method for improving lithography process alignment failure as claimed in claim 1, wherein: in the second step, the grown film layer needs to be consistent with the film layer structure of the actual product.

3. The method for improving lithography process alignment failure as claimed in claim 1, wherein: the structure wafer in the second step is a sample wafer for verifying the test photomask and the alignment mark, and the manufacturing process is consistent with that of mass production products.

4. The method for improving lithography process alignment failure as claimed in claim 1, wherein: and in the fourth step, during data analysis, selecting the duty ratio alignment mark with the maximum signal intensity and signal integrity and the minimum alignment precision residual as the alternative design size by comparing the alignment signal intensity, the signal integrity and the alignment precision residual under different duty ratio marks.

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