JPH0917720A - Focusing check method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect focusing by linking focus adjustment to the manufacturing lot of wafers by extracting a library pattern which is most approximated to the pattern of a product and judging the focusing value of the product wafer by referring to a focusing value which is associated with the extracted pattern. SOLUTION: The pattern of a specific portion of a manufacturing line is read by a check camera 2, a computer system 3 stores the image data of the critical pattern of a product supplied from the check camera 2 in an image buffer memory, and contour extraction processing is made to the image data, thus extracting an actual processing pattern. To reduce the amount of processing data, a window is set to the actual processing pattern and the area of the actual processing pattern is calculated within the window. The area is compared with that of the image data of the same critical pattern registered in a library 5, a library pattern where an area difference is minimized is extracted, and focusing value attached to it is outputted to a display 7.

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 process of a semiconductor manufacturing process, and more particularly to a mask pattern performed in the patterning process. The present invention relates to a focus inspection method for determining whether or not focus adjustment is properly performed in an exposure process of projecting on a wafer.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, a lithographic 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 a wafer, an exposing step of exposing a pattern on the photoresist film, and developing the exposed photoresist to form a resist film. Parts,
It is divided into a developing step of exposing the film to be etched and an etching step of etching the exposed film using the developed resist film as a mask.

In the above-mentioned lithography process, in order to accurately pattern the deposited film, it is essential to project a mask pattern having no blur on the resist film in the exposure process. Therefore, the exposure apparatus has various focusing mechanisms. The exposure apparatus includes various types such as a scanning type projection exposure apparatus, a step type projection apparatus, an electron beam exposure apparatus and the like that require focus adjustment.

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 the state of good focus in exposure. The degree of goodness of focus is determined by, for example, displacing the focus position in a direction perpendicular to the photoresist film (moving the focus position in the direction into and away from the resist film) and at each of the plurality of focus positions. It is possible to develop and etch a plurality of exposed wafers under the same conditions, compare the formed patterns with each other, perform numerical assignment with the optimum pattern as a reference, and quantify this as a focus value. When the focus value is bad, there are problems such as the pattern being distorted, the corners being rounded, and the width being wider than the design value.

By the way, the focus value in the lithography process is the optimum focus value determined by the mechanical structural conditions of the exposure apparatus, and the deviation amount due to variations in thickness of individual semiconductor products (wafers), variations in coating resist film, and the like. It is generally calculated by adding. For example, the optimum focus value of the exposure system is that the bare wafer (test wafer) coated with photoresist is exposed and developed by shaking the focus in the direction perpendicular to the wafer surface, and the visual judgment is made. Is determined based on the resist shape and the like. Next, the amount of focus shift on the product wafer is based on the optimum focus value of the exposure device that was previously determined on the bare wafer, and the product wafer is exposed and developed by focusing before and after that, and the resist pattern Is prepared, and the state of the resist pattern is visually judged and determined.

Recently, when determining the optimum focus value of the exposure apparatus, a method of automatically measuring on the exposure apparatus side has been studied and is in the stage of practical use, but most of the determination still depends on human sensitivity. . From the aspect of managing quality control parameters in the semiconductor manufacturing process, the management of the optimum focus value has been regularly investigated as a QC control item for the optimum focus value of the exposure apparatus. The amount of deviation from the product wafer is generally operated as being unchanged after the focus position setting is once determined.

[0007]

However, although the conventional focus management method is partially mechanized, there is a lot of reliance on visual judgment for determining the optimum focus value.
Since subjective factors are included, it is difficult to make uniform judgments.

Further, focus control for bringing the exposure apparatus into the optimum focus state is not always performed, and it is not checked from one QC check determined by the quality control interval to the next QC check. But,
The state of the product wafer is not the same, and the focus value actually varies. Therefore, there arises a problem that the optimum focus value for the manufactured wafer is not stable.

Therefore, an object of the present invention is to make it possible to detect focus adjustment of an exposure apparatus in a form linked to a wafer manufacturing lot by automatically determining a focus state at a product wafer level. To do.

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

[0011]

In order to achieve the above object, the focus inspection apparatus of the present invention performs pattern exposure on a resist film coated on a wafer in an appropriate focus state in a patterning process of a semiconductor manufacturing process. In the focus inspection apparatus for determining whether or not, the image reading means for reading the pattern formed on the specific portion of the wafer, and the pattern to be formed on the specific portion of the wafer is exposed and patterned at a specific focus value, The read image obtained by reading the pattern formed on the wafer is read by the pattern storing means for holding the read image group of the patterns collected in advance for a large number of focus values together with the focus value of each image, and the image reading means. , The specific portion of the wafer during 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.

The focus inspection method of the present invention is the focus inspection method for determining whether or not pattern exposure of a resist film coated on a wafer is 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 at a specific focus value and patterned, and the pattern formed on the wafer is obtained by reading. A pattern storing step of holding a read image group of read images of patterns, which have been collected in advance for a large number of focus values together with the focus value of each image, and a specific portion of the wafer of the patterning process read by the image reading means. The 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 created by focusing beforehand are registered as a pattern library together with focus values of the patterns. Then, the product pattern read in the manufacturing process is compared with the library pattern to extract the closest library pattern. The focus value of the product wafer is determined by referring 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 easily short-circuits 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 dimension accuracy is severe, the pattern tends to change very sensitively to the focus fluctuation. Such a pattern will be 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 direction and the reverse direction with respect to the portion including the critical pattern is used as read image data of an electron microscope image or a laser microscope image, and the image Many are stored together with the focus value.
At this time, the number of samples to be registered is an appropriate number necessary to eliminate the variation between the samples of the product wafer.

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

As shown in FIG. 4, the pattern of the solid line registered in the library and the pattern of the product wafer shown by the dotted line are overlapped to calculate the difference in area.
The determination of the optimum focus is made as the focus value attached to the library pattern when the difference in area is the minimum. At this time, it is conceivable that the dimensions are different due to the difference in exposure time or the like and they do not overlap well, but this can be solved by enlarging / reducing the pattern registered in the library and making a determination in the state where the difference is minimized. .

In the resist development pattern, it may be difficult to judge the pattern because the underlayer 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 it becomes possible to quantitatively monitor the change of the focus value by linking to the manufacturing lot number, it is not necessary to perform the focus management with the two-stage preparation as in the conventional case.

FIG. 1 schematically shows an example of the structure of a focus detection device for carrying out the present invention. In FIG. 1, the pattern of a specific portion of a wafer 1 on a manufacturing line is analyzed by an electron microscope, a laser microscope and an image converter. It is read by the inspection camera 2 combined with. Conventional alignment techniques can be used to set the pattern read 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 under inspection by performing processing according to an algorithm described later. The computer system 3 is connected to the pattern library server 5 and the QC database server 6 via the local area network 4.
As described above, the pattern library server 5 holds the data group of the pattern image obtained when the focus value is changed using the focus value as a parameter for the critical pattern of each part of the wafer. A focus value is attached to each image data. 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, for example, a wafer manufacturing lot number and various quality control parameter states in the manufacturing process for this lot. The operating 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). The contour extraction processing is performed on the image data of this product, and the actual processing pattern as shown by the dotted line in FIG. 4 is extracted. In order to reduce the amount of processed data, a window (comparison area) is set in the actual processing pattern, and the area of the actual processing pattern is calculated within the window. The area of the image data of the same critical pattern registered in the library 5 is compared. The library pattern with the smallest area difference is extracted. In addition, with respect to the line segment forming the contour of the pattern, the difference between the superimposed patterns may be accumulated, and the pattern having the minimum value may be extracted (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 to display the focus value of the product wafer to be inspected to the staff. This focus value is also sent to the QC database server 6 and recorded as management data linked to the wafer manufacturing lot number (S18). If a focus value outside the reference value is detected, the computer system 3
Or the QC database server 6 can alert the attendant. Therefore, it becomes possible to deal with the problem when the focus value becomes defective.

[0024]

As described above, according to the focus detecting apparatus and method of the present invention, the focus value is determined by comparing the pattern of the product wafer and the library pattern, and therefore, the individual difference in the determination of the focus value is performed. Is eliminated and the determination accuracy is improved. In addition, it becomes possible to constantly monitor focus fluctuations by linking to the manufacturing lot, and it is possible to deal with problems at the time of occurrence of defects, so that it is possible to perform management with higher accuracy than conventional regular quality management.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating an operation algorithm of a 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]

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

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/30 516Z

Claims (4)

[Claims] 1. A focus inspection apparatus for determining whether or not pattern exposure of a resist film coated on a wafer is performed in an appropriate focus state in a patterning step of a semiconductor manufacturing process, the focus inspection apparatus being formed on a specific portion of the wafer. A plurality of read images obtained by reading the pattern formed on the wafer by patterning by exposing the pattern to be formed on the specific portion of the wafer with a specific focus value. Pattern storage means for holding a read image group of patterns collected for each focus value together with the focus value of each image, a pattern of the specific portion of the wafer in the patterning process read by the image reading means, and the read image group And to 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 wafer manufacturing lot number in the patterning process. 3. The focus inspection apparatus according to claim 1, further comprising means for alerting an attendant when the output focus value exceeds a reference range. 4. A focus inspection method for determining whether or not pattern exposure of a resist film coated on a wafer is performed in an appropriate focus state in a patterning process of a semiconductor manufacturing process, the focus inspection method being formed on a specific portion of the wafer. The image reading step of reading the formed pattern, the pattern to be formed on the 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 prepared in advance. A pattern storing step of holding a read image group of patterns collected for the focus value together with the focus value of each image; 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 to 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.