JPH1097971A - Best focal point detecting method for photolithographic process and reticle used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and accurately detect the best focal point. SOLUTION: A resist is exposed by varying the set focus value of an aligner by a fixed width by using a reticle carrying a focus control pattern 1 in which one vertexes of two triangular patterns 1a and 1b are brought into point-contact with each other. When the resist is developed thereafter, a plurality of resist patterns to which the pattern 1 is transferred in different resolution states is formed. Then the appearance of the resist patterns are inspected with an optical microscope and the set focus value of the aligner when the vertexes of the two triangles are brought into point-contact with each other is compared with the best focal point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a best focus in a photolithography step of a semiconductor device manufacturing process, and more particularly to a method for easily detecting a best focus point and a focus shift amount.

[0002]

2. Description of the Related Art An exposure apparatus used in a photolithography step of a semiconductor device manufacturing process has a deep depth of focus.
Focus management is important in order to use the apparatus in the best condition where the limit resolution is high. Therefore, the following two typical methods have been conventionally used as a focus management method. The following description of the prior art is based on the premise that a positive resist is used.

In a first method, as shown in FIG. 7, a plurality of line patterns 11 and 12 are arranged in a vertical direction and a horizontal direction, respectively.
Is exposed using a reticle on which a resist coated on a silicon substrate is intentionally shaken at a constant width with a focus of an exposure apparatus.
1. The line widths x and y of each of the horizontal patterns 12 are measured. In this case, the line width x and y for each focus setting value when the focus is shaken at a fixed width is determined by an electron beam microscope (Scanning
The length is measured using an Electron Microscope (hereinafter, referred to as SEM). Then, as shown in FIG. 8, the focus setting value of the exposure apparatus is taken in the horizontal axis direction of the graph, the line width measured in the vertical axis direction is taken, and the measurement points are plotted. Find the best focus point from the points,
Is used. The curve (hereinafter, referred to as a CD-focus curve) shown in FIG. 8 is a graph in the case of a line pattern. A parabolic curve (CD-focus curve) is obtained.

In the second method, the same reticle as used in the first method is used, and exposure and development are performed while the focus of the exposure apparatus is shifted at a fixed width, similarly to the first method. Subsequently, the minimum separation resolution of the pattern for each focus set value of the line and space actually transferred is read using an optical microscope, and a CD-focus curve is obtained in the same manner as in the first method. Find the focus point. It is to be noted that as a result of applying the second method, a CD-focus curve is not obtained, and the adjacent line patterns 11 and 12 of the reticle shown in FIG. 7 are completely separated and resolved from the minimum separation resolution point. A simple method for finding the best focus point is also used.

[0005]

However, each of the conventional focus management methods has the following problems. In the first method, the line width must be measured by using the SEM after the exposure and the development, which is a method that requires much labor and time. In addition, in order to measure a resist image by scanning with an electron beam, a high-performance SEM with a low charge-up and a high resolution is required.
There was also a problem that costs were high.

On the other hand, the second method can be implemented relatively easily, but it is necessary for an operator to determine whether or not a resist remains in a space between line patterns. However, regarding this determination, there has been a problem of variation in accuracy such that variation between workers is extremely large. Further, in the case of the determination based on the line and space, there is also a trouble that two types of measurement of a vertical pattern and a horizontal pattern must be performed because astigmatism of the lens of the exposure apparatus exists.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a method capable of easily and accurately detecting a best focus point and a reticle used therefor. I do.

[0008]

According to a first aspect of the present invention, there is provided a method for detecting a best focus point in a photolithography process, comprising two or more polygonal patterns. Using a reticle having a focus management pattern in which any one of the vertices of each of the two polygonal patterns is in point contact with each other, the resist on the semiconductor substrate is exposed while the focus set value of the exposure apparatus is varied at a fixed width. An exposure step of performing a development process on the exposed resist to form a plurality of resist patterns in which focus management patterns are transferred as different shapes, and a visual inspection of the plurality of resist patterns using a microscope Is performed, the vertex of any one of two adjacent polygons is in point contact with each other. Inspection step of comparing the focus setting value of the exposure apparatus when exposing the strike pattern and the best focus point, is characterized in that it has a.

Further, in the method of detecting the best focus point in the photolithography step according to the present invention, the focus management pattern is composed of three or more polygonal patterns, and all of the contact points between adjacent polygonal patterns are formed. A reticle located on the same straight line is used.

According to a third aspect of the present invention, there is provided a method for detecting a best focus point in a photolithography step, wherein a dimension of one side of a polygonal pattern on the reticle is set to a dimension twice or more as large as a limit resolution of an exposure apparatus to be used. It is characterized by doing.

According to a fourth aspect of the present invention, there is provided a method of detecting a best focus point in a photolithography step, wherein the exposing step is performed using an exposure amount sufficient to obtain a resist pattern dimension identical to a design dimension. It is a feature.

A reticle according to a fifth aspect of the present invention is a reticle for detecting a best focus point in a photolithography process, and is composed of two or more polygon patterns, each of two adjacent polygon patterns. Wherein any one of the vertices has a focus management pattern in point contact with each other.

Further, in the reticle according to the present invention, it is preferable that the focus management pattern is composed of three or more polygonal patterns, and all contact points between adjacent polygonal patterns are located on the same straight line. It is a feature.

In a reticle according to a seventh aspect of the present invention, the dimension of one side of the polygonal pattern is twice or more as large as the limit resolution of an exposure apparatus to be used.

According to the present invention, the best focus point is detected according to the following procedure. A reticle on which a focus management pattern in which the vertices of any one of two adjacent polygonal patterns are in point contact with each other is prepared. As a preparatory operation before the exposure step, the exposure and development processes are performed by changing the exposure condition after setting the focus state of the exposure apparatus to the best focus point using the reticle. Then, also in the resist pattern formed after development, the exposure conditions in the case where the vertices of two adjacent polygons are in point contact with each other are determined in advance. As a regular focus management operation, exposure and development are performed by shaking the focus set value of the exposure apparatus at a fixed width using the reticle and the exposure conditions, thereby forming a plurality of resist patterns having different shapes. The appearance of the resist pattern is inspected using a microscope. At this time, it is checked which of the plurality of resist patterns is in a state where the vertices of two adjacent polygons are in point contact with each other. And
The focus set value of the exposure apparatus when exposing the resist pattern is compared with the best focus point.

If the focus state of the exposure apparatus deviates from the best focus point and is a so-called defocus state, or if defocus occurs locally in the semiconductor substrate, the above-described resist pattern The resolution decreases near the vertices of the polygon, and a visual inspection using a microscope confirms a resist pattern in which two vertices are separated or overlapped with the point contact state at the time of best focus. Therefore, by performing the above-described procedure, it is possible to easily and accurately perform the focus management of the current exposure apparatus, including the detection of the focus shift amount.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. The best focus point detection method in the photolithography process according to the present embodiment will be described using a case where a positive resist is used as an example.

FIG. 1 shows a first embodiment of a reticle used in the present method. This reticle has a focus management pattern 1 arranged such that one vertex of two triangular patterns 1a and 1b is in point contact with each other. In FIG. 1, two triangular patterns 1a, 1b
Although only one set is shown, a plurality of sets of this pattern may be provided in the reticle. The shape of each pattern is not limited to a triangle, but may be a polygonal pattern such as a quadrangle or a pentagon.

FIG. 2 shows a second embodiment of the reticle used in the present method. This reticle is composed of three rectangular patterns 101a, 101b, and 101c, and a focus management pattern arranged such that one vertex of each adjacent rectangular pattern makes point contact with each other and that these contact points are on the same straight line. 101. FIG. 2 is also similar to FIG.
Although only one set of the patterns 01a, 101b, and 101c is shown, a plurality of sets of this pattern may be provided in the reticle. Further, the shape of each pattern is not limited to a square, and may be another polygonal pattern.

Both the reticle of the first and second embodiments have the focus management patterns 1, 10 in the reticle.
The arrangement of 1 is such that the focus management pattern includes the center coordinates of the reticle, and the other arrangements may be arbitrarily arranged at desired coordinates. Further, it is preferable that the dimension of one side of the polygonal pattern is set to be at least twice the critical resolution of the exposure apparatus used. This is because if the dimensions of the pattern were set near the limit resolution, lack of sharpness in the formation of the resist pattern and narrowing of the depth of focus would occur. This is because the factor of the pattern resolving power is taken into account, and it becomes difficult to understand the influence of the important focus fluctuation.

First, prior to a regular focus management operation, initial data is obtained according to the following procedure. (1) The best focus point of the exposure apparatus is obtained, and the focus of the apparatus is adjusted to the best focus state. At this time, the best focus point of the exposure apparatus
At the time of exposure, a reticle provided with lines and spaces having several types of dimensions is used, and exposure and development are performed by fixing the exposure amount to an arbitrary value and shaking the focus to a fixed width. Subsequently, the line width at which the minimum separation and resolution is performed at each focus point is read using a metal microscope, and the focus point at which the minimum line width is separated and resolved is determined as the best focus point. (2) After fixing the focus set value of the exposure apparatus to the best focus point, using the conventional reticle for focus management (FIG. 7), only the exposure amount among the exposure conditions is shaken at an arbitrary pitch, and the exposure is performed on the semiconductor substrate. Exposure to resist,
Perform development processing. Then, the actual size of the formed resist pattern is measured using a length measuring SEM, and the same size as the design size of the resist pattern (however, if the reticle is compatible with a 1/5 reduction type exposure apparatus, the pattern on the reticle is Is 5 times the design size of the resist pattern). The exposure amount is referred to as Eopt. Thus, the preparatory work is completed.

When performing the regular focus management operation, the reticle of the first or second embodiment and the exposure amount obtained as the initial data are used, and only the focus set value of the exposure apparatus is set at a constant width. Shake to expose the resist coated on the semiconductor substrate (exposure step).

For example, specifically, the reticle of the second embodiment is used, and the exposure wavelength λ of the exposure apparatus is 436 n
m, numerical aperture NA = 0.55, resist film thickness = 1.2 .mu.m
m, Eth (minimum exposure amount at which resist can be removed by exposure)
= 85 mj, Eopt = 130 mj, critical resolution = 0.6
In the case of 5 μm, the rectangular patterns 101a and 101 in FIG.
Since one side of b and 101c is preferably at least twice as large as the critical resolution size, it is set to 1.30 μm or more, and actually 2.0 μm. The range of the focus setting value is -2.0 μm.
m to +0.2 μm, the pitch is 0.1 μm, and the exposure amount E
Exposure is performed at opt = 130 mj.

Next, the resist coat after the exposure is subjected to a developing process to form resist patterns having different resolution states (shapes) by changing the focus set value (developing step). Thereafter, the appearance of these resist patterns is inspected using an optical microscope (inspection step). At this time, it is checked which of the plurality of resist patterns is in a state where the vertices of two adjacent polygons are in point contact with each other. Then, the focus set value of the exposure apparatus when exposing the resist pattern is compared with the best focus point.

If defocusing occurs, the appearance of the focus shift in the light-collecting direction and the dispersion direction when the appearance inspection is performed using an optical microscope, and when the reticle of the first embodiment is used, As shown in FIGS. 3 and 4, when the reticle according to the second embodiment is used, as shown in FIGS. 3a, 3b, 103
a, 103b and 103c or overlapping resist patterns 2 and 102 are confirmed. Therefore, searching for a resist pattern in which the vertices of the polygon are in point contact with each other, and checking the focus set value at the time of forming the resist pattern, the focus state of the current exposure apparatus, including the detection of the focus shift amount, can be determined. You can figure out.

According to the best focus point detecting method of this embodiment, the reticle focus management pattern 1,
By devising the shape of 101, the focus shift is immediately reflected as a difference in the resist pattern shape, and the focus state of the exposure apparatus can be confirmed using an optical microscope. Therefore, the labor and time required for the operation can be reduced as compared with the conventional method that requires a high-performance measurement SEM, and the focus management can be performed at low cost. In addition, since the pattern shape is clearly different between the best focus and the defocus, there is relatively little variation in judgment among operators, and focus management can be performed accurately.

In particular, when the reticle of the second embodiment shown in FIG. 2 is used, uneven coating at the time of resist coating,
Even if the pattern shape abnormality due to the base foreign matter occurs,
There is an advantage that detection is easy because a plurality of contact points are continuous. In addition, in the best focus state, a plurality of points in point contact can be observed in a continuous state, so that it is possible to easily perform a determination at the time of inspection using an optical microscope, and to improve the inspection accuracy. .

The technical scope of the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention. For example, in this embodiment, an example in which a positive resist is used has been described. However, a method corresponding to a negative resist can be used by using a reticle in which the pattern is inverted between black and white in this embodiment. Further, specific numerical values such as the exposure apparatus conditions, the size of the focus management pattern, the range of the focus set value, and the pitch used in the present embodiment can be appropriately changed.

[0029]

As described above in detail, according to the best focus point detecting method in the photolithography process of the present invention, the high-performance length measurement S
The detection of the best focus point and the focus shift amount can be easily performed without using the EM.
In addition, since it is possible to reduce the variation in the judgment between the workers, it is possible to improve the accuracy of the focus management.

[Brief description of the drawings]

FIG. 1 is a diagram showing a reticle according to a first embodiment used in a best focus point detection method according to an embodiment of the present invention;

FIG. 2 is a diagram showing a reticle according to a second embodiment.

FIG. 3 is a diagram showing a resist pattern at the time of defocusing when the reticle of the first embodiment is used.

FIG. 4 is the same drawing.

FIG. 5 is a diagram showing a resist pattern at the time of defocusing when a reticle of the second embodiment is used.

FIG. 6 is the same drawing.

FIG. 7 is a diagram showing a reticle used in a conventional focus management method.

FIG. 8 is a graph showing the relationship between focus and pattern line width in the same method.

[Explanation of symbols]

1, 101 Focus management pattern 1a, 1b Triangular pattern (polygonal pattern) 101a, 101b, 101c Square pattern (polygonal pattern) 2, 3, a, 3b, 102, 103a, 103b, 103
c Resist pattern at defocus 11, 12 Line pattern

Claims (7)

[Claims] 1. A reticle having a focus management pattern, which is composed of two or more polygonal patterns and in which any one vertex of each of two adjacent polygonal patterns is in point contact with each other, is provided on a semiconductor substrate. An exposure step of exposing the resist by swinging a focus set value of an exposure device at a constant width, and a plurality of resist patterns in which the focus management pattern is transferred as a different shape by performing development processing on the exposed resist. A developing step of forming a resist pattern, and performing an appearance inspection of the plurality of resist patterns using a microscope to expose the resist pattern in a state where any one vertex of two adjacent polygons is in point contact with each other. An inspection step of comparing a focus set value of the exposure apparatus at the time of the exposure with a best focus point. Best focus point detection method in photolithography process. 2. The method for detecting a best focus point in a photolithography process according to claim 1, wherein the focus management pattern is formed of three or more polygonal patterns, and all contact points between adjacent polygonal patterns are formed. A method of detecting a best focus point in a photolithography process, wherein reticles located on the same straight line are used. 3. The method of detecting a best focus point in a photolithography process according to claim 1, wherein a dimension of one side of the polygonal pattern on the reticle is at least twice as large as a limit resolution of an exposure apparatus to be used. A best focus point detection method in a photolithography process, characterized in that: 4. A method for detecting a best focus point in a photolithography step according to claim 1, wherein the exposure step uses an exposure amount sufficient to obtain the same resist pattern dimension as a design dimension. A method for detecting a best focus point in a photolithography process, comprising performing exposure. 5. A reticle for detecting a best focus point in a photolithography process, wherein the reticle is composed of two or more polygon patterns, and any one vertex of each of two adjacent polygon patterns is a point. A reticle, wherein a focus management pattern in contact with the reticle is formed. 6. The reticle according to claim 5, wherein the focus management pattern is composed of three or more polygon patterns, and all contact points between adjacent polygon patterns are located on the same straight line. Reticle to feature. 7. The reticle according to claim 5, wherein a dimension of one side of the polygon pattern is at least twice as large as a limit resolution of an exposure apparatus to be used.