JP3313542B2 - Focus inspection method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a patterning (lithography) process for forming a film deposited on a wafer into a specific pattern, which is one of the steps of a semiconductor manufacturing process. The present invention relates to a focus inspection method for determining whether or not focus adjustment has been appropriately performed in an exposure step of projecting onto a wafer.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, a lithography process is indispensable for laminating a patterned film on a wafer. The lithography process is roughly divided into
A photoresist film forming step of applying a photosensitive film to a film to be patterned deposited on the wafer, an exposing step of exposing a pattern on the photoresist film, and developing the exposed photoresist to form a resist film Remove the part,
The process is divided into a developing process of exposing a film to be etched and an etching process of etching the exposed film using the developed resist film as a mask.

In order to accurately pattern the deposited film in the lithography process, it is essential to project a mask pattern without blur on the resist film in the exposure step. Therefore, the exposure apparatus has various focusing mechanisms. The exposure apparatus includes various types that require focus adjustment, such as a scanning projection exposure apparatus, a step projection apparatus, and an electron beam exposure apparatus.

Focus adjustment in an exposure apparatus is a quality control item in a semiconductor manufacturing process, and a focus value is used as a parameter indicating a state of good focus in exposure. The degree of good focus is determined, for example, by shifting the focus position in a direction perpendicular to the photoresist film (the focus position moves in a direction into the resist film and in a direction away from the resist film). A plurality of exposed wafers are developed and etched under the same conditions, the formed patterns are compared with each other, numerical values are assigned based on the optimal patterns, and these can be quantified as focus values. If the focus value is poor, problems such as distortion of the pattern, rounded corners, and a wider width than the designed value occur.

Incidentally, the focus value in the lithography process is set to an optimum focus value determined by the mechanical structure conditions of the exposure apparatus, and the amount of deviation due to variations in the thickness of individual semiconductor products (wafers), variations in the coating resist film, and the like. Is generally calculated. For example, the optimum focus value of the exposure apparatus is determined by visualizing a bare wafer (test wafer) coated with photoresist by exposing and developing a plurality of resist patterns by shifting the focus in the direction perpendicular to the wafer surface. Is determined based on the shape of the resist. Next, the amount of focus shift on the product wafer is based on the optimum focus value of the exposure apparatus determined earlier on the bare wafer, and the focus is shaken before and after that to expose and develop the product wafer, And the state of the resist pattern is visually determined to be determined.

Recently, in determining the optimum focus value of the exposure apparatus, a method of automatically measuring the focus value on the exposure apparatus side has been studied, and it is in the stage of practical use, but most of the determination still depends on human sensitivity. . In addition, from the aspect of quality control parameter management in the semiconductor manufacturing process, the optimal focus value management is regularly investigated as an QC control item for the optimal focus value of the exposure apparatus. Generally, the operation is performed on the assumption that the deviation amount from the product wafer does not fluctuate once the focus position setting is determined.

[0007]

However, in the conventional focus management method, although a part is being mechanized, the determination of the optimum focus value often depends on visual observation.
Since subjective factors are involved, it is difficult to make a uniform judgment.

Further, focus management for bringing the exposure apparatus into an optimum focus state is not always performed, and is not checked between one QC check defined by a quality control interval and the next QC check. But,
The state of the product wafer is not the same, and the focus value actually fluctuates. For this reason, there arises a problem that the optimum focus value for the manufactured wafer is not stable.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to enable focus adjustment of an exposure apparatus to be detected in a form linked to a production lot of wafers by automatically determining a focus state at a product wafer level. I do.

Another object of the present invention is to eliminate individual differences among staff members in determining an optimum focus value.

[0011]

In order to achieve the above object, a focus inspection apparatus according to the present invention performs a pattern exposure on a resist film applied on a wafer in an appropriate focus state in a patterning process of a semiconductor manufacturing process. In the focus inspection device to determine whether or not, the image reading means for reading the pattern formed on the specific portion of the wafer, and patterning by exposing the pattern to be formed on the specific portion of the wafer with a specific focus value, A read image obtained by reading a pattern formed on a wafer is read by a pattern storage means for holding a group of read images of patterns collected in advance with respect to a large number of focus values together with the focus value of each image, and the image reading means. The specific part of the wafer in the patterning process Of comparing the pattern and the read image group, characterized in that it comprises means for extracting an image most approximate, and output means for outputting a focus value was attached corresponding to the extracted image.

Further, the focus inspection method of the present invention is a focus inspection method for determining whether or not pattern exposure on a resist film applied on a wafer was performed in an appropriate focus state in a patterning process of a semiconductor manufacturing process. An image reading step of reading a pattern formed on a specific portion of the wafer, and a pattern to be formed on the specific portion of the wafer is exposed and patterned with a specific focus value, and the pattern formed on the wafer is obtained by reading. A read image, a pattern storing step of holding a read image group of patterns collected in advance with respect to a large number of focus values together with the focus value of each image; and a reading section of the specific portion of the wafer in the patterning process read by the image reading means. Pattern and the read image group And compare, characterized in that it comprises a step of extracting an image most similar, and an output step of outputting a focus value was attached corresponding to the extracted image.

In the present invention, a large number of patterns of a specific portion of a product wafer prepared by shaking the focus in advance are registered as a pattern library together with the focus value of the pattern. Then, the pattern of the product read in the manufacturing process is compared with the library pattern to extract the most similar library pattern. The focus value of the product wafer is determined with reference to the focus value associated with the extracted pattern.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

First, the points of interest of the present invention will be described.
As shown in FIG. 3, when the pattern of the product wafer is observed, there is a portion where the pattern is likely to be short-circuited with the adjacent pattern due to the influence of the shape of the pattern and the undulation of the base. In such a portion where the pattern dimensional accuracy is severe, the pattern tends to change very sensitively to a focus change. Such a pattern is called a critical pattern.

The pattern of the product wafer exposed and developed at each focus stage when the focus is swung in the forward and reverse directions for the portion including the critical pattern is read as image data of an electron microscope image or a laser microscope image. Many are stored together with the focus value.
At this time, the number of samples to be registered is an appropriate number necessary for eliminating the variation between the samples of the product wafer.

In determining a focus value for a wafer actually processed in the manufacturing process, a critical pattern of an actually processed wafer is captured as an electron microscope image or a laser microscope image, and compared with a library pattern on a computer system.

As shown in FIG. 4, the difference between the overlapping area of the pattern indicated by the solid line and the pattern of the product wafer indicated by the dotted line registered in the library is calculated.
The determination of the optimal focus is determined as the focus value assigned to the library pattern when the difference between the areas is minimized. At this time, there may be a case where the dimensions are different due to a difference in the exposure time, etc., and they do not overlap well. However, it is possible to solve the problem by enlarging or reducing the pattern registered in the library and judging in a state where the difference is minimized. .

Further, in the developed pattern of the resist, there are cases where it is difficult to determine the pattern because the base of the resist is visible.
In such a case, it is effective to compare the pattern of the product wafer after patterning with the library pattern of the pattern after etching.

Further, the present determination method can be applied to the determination of the optimum focus of the apparatus if there is a pattern having a large change amount with respect to the focus. However, since a change in focus value can be quantitatively monitored by linking to a manufacturing lot number, focus management in a two-stage configuration as in the related art is not required.

FIG. 1 schematically shows an example of the configuration of a focus detection device embodying the present invention. In FIG. Are read by the inspection camera 2 combined with Conventional alignment techniques can be used to set the pattern reading position. The image data of the read pattern is supplied to the computer system 3. The computer system 3 determines the focus value of the product wafer being inspected by performing processing according to an algorithm described below. The computer system 3 is connected to a pattern library server 5 and a QC database server 6 via a local area network 4.
As described above, the pattern library server 5 holds a group of pattern image data obtained when the critical value of each part of the wafer is changed using the focus value as a parameter. Each image data is given a focus value. The pattern image holds a resist pattern, an etching pattern, or both patterns. The QC database server 6 holds quality control data in the semiconductor manufacturing process, and holds, for example, a manufacturing lot number of a wafer and various quality control parameters in the manufacturing process for this lot. The operation state of the system and the determination result of the focus value are shown to the attendant via the CRT display device 7.

Next, the operation of the focus detection device will be described with reference to FIG.

First, the computer system 3 temporarily stores the image data of the critical pattern of the product supplied from the inspection camera 2 in a built-in image buffer memory (not shown) (S12). An outline extraction process is performed on the image data of this product to extract an actual processing pattern as shown by a dotted line in FIG. In order to reduce the amount of processing data, a window (comparison area) is set for the actual processing pattern, and the area of the actual processing pattern is calculated within the window. The area is compared with the area of the image data of the same critical pattern registered in the library 5. A library pattern with the smallest area difference is extracted. It is also possible to accumulate the difference between the superimposed patterns for the line segments constituting the contour of the pattern and extract the pattern having the minimum value (S1).
4). The focus value attached to (or associated with) the extracted library pattern is read (S1).
6). This focus value is output to the display device 7 and the attendant displays the focus value of the product wafer to be inspected. This focus value is also sent to the QC database server 6 and recorded as management data linked to the wafer lot number (S18). If a focus value outside the reference value is detected, the computer system 3
Or by the QC database server 6 to alert the attendant. Therefore, it is possible to deal with a problem when a problem occurs in the focus value.

[0024]

As described above, according to the focus detection apparatus and method of the present invention, the focus value is determined by comparing the pattern of the product wafer with the library pattern. Is eliminated, and the determination accuracy is improved. In addition, it is possible to constantly monitor the focus fluctuation by linking to the production lot, and to cope with the problem at the time of occurrence of a defect. Therefore, it is possible to perform management with higher accuracy than the conventional regular quality control.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a focus inspection device according to the present invention.

FIG. 2 is a flowchart illustrating an operation algorithm of the computer system.

FIG. 3 is an explanatory diagram illustrating a pattern change due to a focus change.

FIG. 4 is an explanatory diagram illustrating a comparison between a detection pattern and a library pattern.

[Explanation of symbols]

 Reference Signs List 1 wafer 2 inspection camera 3 computer system 4 local area network 5 server for storing pattern library 6 server for storing quality control data 7 CRT display device

Continuation of the front page (51) Int.Cl. ⁷ identification code FI H01L 21/30 516Z (58) Investigation field (Int.Cl. ⁷ , DB name) H01L 21/027 G03F 7/20 521 G03F 7/207 G03F 9/02

Claims (4)

(57) [Claims] 1. A focus inspection apparatus for determining whether or not pattern exposure on a resist film applied on a wafer is performed in an appropriate focus state in a patterning process of a semiconductor manufacturing process, wherein the focus inspection apparatus is formed on a specific portion of the wafer. Image reading means for reading a pattern formed on the wafer, a pattern to be formed on a specific portion of the wafer is exposed and patterned with a specific focus value, and a large number of read images obtained by reading the pattern formed on the wafer are obtained in advance. Pattern storage means for holding a group of read images of patterns collected for each focus value together with the focus value of each image; and a pattern and the read image group of the specific portion of the wafer in the patterning process read by the image reading means. And extract the closest image Focus inspection apparatus characterized by comprising: a stage, and an output means for outputting a focus value was attached corresponding to the extracted image. 2. The focus inspection apparatus according to claim 1, further comprising storage means for storing the output focus value together with a manufacturing lot number of the wafer in the patterning process. 3. The focus inspection apparatus according to claim 1, further comprising means for calling a clerk when the output focus value exceeds a reference range. 4. A focus inspection method for determining whether or not a pattern exposure on a resist film applied on a wafer has been performed in an appropriate focus state in a patterning process of a semiconductor manufacturing process, comprising: An image reading step of reading the formed pattern, exposing and patterning a pattern to be formed on a specific portion of the wafer with a specific focus value, and reading a large number of read images obtained by reading the pattern formed on the wafer in advance. A pattern storing step of holding a group of read images of the patterns collected for the focus values together with the focus values of each image; and a pattern of the specific portion of the wafer in the patterning process and the read image group read by the image reading means. And extract the closest image Degree and the extracted focused inspection method characterized by comprising an output step of outputting a focus value was attached corresponding to the image.