JPH10199793A - Focus monitoring method of aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus monitoring method of an aligner which can obtain an accurate defocus amount. SOLUTION: This method contains the following. A step (1); a pattern group constituted of many identical patterns 10 is formed on a photomask. The pattern 10 has two large pattern regions 12A, B, and a belt type region 18 which connects the large pattern regions and has a reduction part 16 whose width is locally reduced. The widths of the reduction parts are mutually different. A process (2); regarding each of the different defocus amounts, exposure is performed with its defocus amount, and the pattern group is transferred to a photosensitive material layer. A step (3); regarding the exposure with the set defocus amount, a transferred pattern wherein a reduction part of the transferred pattern corresponding to the reduction part of a pattern is physically isolated is specified. A step (4); a pattern corresponding to the transferred pattern which is specified is specified out of the pattern group. The maximum width out of the reduction parts of the belt type regions of the specified pattern is obtained. A calibration curve constituted of the corresponding relation of the defocus amount and the maximum width of the reduction part is formed. The allowable defocus amount is obtained from the calibration curve.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a focus monitoring method, and more particularly to a focus monitoring method for monitoring focusing of an exposure apparatus used in photolithography technology with high accuracy.

[0002]

2. Description of the Related Art In a pattern transfer process for manufacturing various semiconductor devices such as a memory device, a logical operation device, a CCD device, an LCD drive device, etc., a so-called photolithography process, a process for regulating an allowable defocus amount of an exposure apparatus. It is essential to monitor parameters accurately from the viewpoint of accurate pattern transfer. Hereinafter, unless otherwise specified, a resist formed on a substrate made of a wafer is simply referred to as a resist. Also, the transfer pattern means a pattern formed on or likely to be formed on a resist when a pattern formed on a photomask is transferred onto a resist formed on a substrate made of, for example, a wafer.

In recent years, with miniaturization of semiconductor devices, it has become difficult to transfer a fine pattern formed on a photomask to a resist with a desired process margin. In particular, in the pattern transfer process using an exposure device, the focus center set by the exposure device often does not always coincide with the focus center value at the time of transfer pattern formation, so that the defocus amount at the time of transfer pattern formation is accurately monitored. It is mandatory to do.

As a method for accurately monitoring the amount of defocus at the time of forming a transfer pattern,
TABrunner et al. Transferred a region provided on a photomask so as to have a phase difference of 0 degree and 90 degrees and a pattern having a width of K1 <0.5 relating to the region onto a resist, and the transferred pattern was defocused. Monitoring the shift amount in the horizontal direction with respect to the central axis on the long side of the pattern, thereby obtaining the defocus amount.
SPIE Proceedings Vol.2197 (1994) PP541-549. Here, K1 is defined as d = K, where NA is the lens numerical aperture of the exposure apparatus, λ is the wavelength, and d is the pattern width.
It is a constant given by 1 (λ / NA). Also, Kyoich
i Suwa et al. have proposed a method of obtaining the defocus amount by monitoring the decrease in the pattern width of the diamond-shaped pattern in the long-axis direction because the shape changes due to the defocus amount and the pattern width in the long axis direction decreases. Vol.2440 (19
95) Proposed on PP712-720.

[0005]

However, the conventional method described above has the following problems. First,
In a method using a photomask provided with regions having a phase difference of 0 degrees and 90 degrees, the smaller the pattern width is, the higher the measurement accuracy is. However, since a fine pattern of K1 <0.5 or less is used, However, there has been a problem that the transferred transfer pattern cannot be resolved, or even if the resolution can be achieved, the resist is peeled off. For example, NA
K1 = 0.0 when an i-line stepper with a value of 0.60 is used.
5 corresponds to 0.3 μm, and K1 = 0.
The pattern width of No. 4 corresponds to 0.24 μm. Also, NA
= 0.55 KrF stepper, K1 =
A pattern width of 0.5 corresponds to 0.23 μm, and K1
A pattern width of = 0.4 corresponds to 0.18 μm. Therefore, when a pattern having such a fine pattern width is formed as an isolated line with a length of about 10 μm, the pattern itself is not formed because the resist performance does not correspond to the pattern width. The adhesive strength of the pattern becomes small, and the pattern is peeled off. Further, the method using a diamond-shaped pattern has a drawback that it is difficult to obtain an accurate defocus amount when the amount of reduction in the pattern width is small compared to the length in the major axis direction of the diamond.

In view of the above situation, an object of the present invention is to provide a focus of an exposure apparatus which can obtain an accurate defocus amount without depending on the performance of a resist and without causing pattern peeling. It is to provide a monitoring method.

[0007]

In order to achieve the above object, a focus monitoring method (hereinafter, referred to as a first invention method) of an exposure apparatus according to the present invention is used for forming a transfer pattern by photolithography. A method for monitoring focusing of an exposure apparatus to be used, comprising: (1) a plurality of large pattern regions and a band-like region having a reduced portion for connecting the large pattern regions and locally reducing the width. Forming a pattern group consisting of a plurality of patterns of the same size on the photomask except that the widths of the reduced portions are different from each other; and (2) for each defocus amount set to be different from each other. Transferring the pattern group of the photomask to the photosensitive material layer on the substrate by exposing under the condition of the set defocus amount; Specifying, for each exposure, a transfer pattern physically separated by a transfer pattern reduction portion corresponding to a photomask pattern reduction portion from a transfer pattern group; and (4) using a set defocus amount. For each exposure, the photomask pattern corresponding to the specified transfer pattern is specified from the pattern group, the maximum width of the reduced portion of the specified pattern is obtained, and the correspondence between the defocus amount and the maximum width of the reduced portion is determined. Producing a calibration curve composed of the relations, and calculating an allowable defocus amount from the calibration curve.

Another focus monitoring method according to the present invention for an exposure apparatus (hereinafter referred to as a second invention method) is a method of monitoring focusing of an exposure apparatus used when forming a transfer pattern by photolithography. (1) Except for having a plurality of large pattern regions and a band-shaped region connecting the large pattern regions with each other and having a reduced portion having a locally reduced width, except that the widths of the reduced portions are different from each other. Forming a pattern group consisting of a plurality of patterns having the same size and shape on a photomask,
(2) for each defocus amount set differently from each other, exposing under a condition of the set defocus amount to transfer a pattern group of a photomask to a photosensitive material layer on a substrate; (3) Using the photosensitive material layer pattern as a mask, forming a group of etched layer patterns by etching the layer to be etched under the photosensitive material layer,
(4) For each exposure with the set defocus amount, the etching target layer physically separated by the reduced part of the etching target layer pattern corresponding to the reduced part of the pattern of the photomask in the group of the etching target layer pattern. A step of specifying a pattern; and (5) for each exposure with a set defocus amount, a pattern of a photomask corresponding to the specified layer pattern to be etched is specified from a pattern group, and a reduced portion of the specified pattern is selected. Obtaining a maximum width, and preparing a calibration curve based on the correspondence between the defocus amount and the maximum width of the reduction unit, and calculating an allowable defocus amount from the calibration curve.

In the first and second invention methods described above, the shapes and dimensions of the large pattern area and the strip area are arbitrary,
The width of the reduced portion is determined from the allowable defocus amount. The width of the reduced portion is, for example, 0.09 μm to 0.30 μm.
The width is set every 1 μm. The set defocus amount is, for example, 0.1 μm from −1.0 μm to 1.0 μm.
The defocus amount is different every step. The reduced part of the transfer pattern corresponding to the reduced part of the pattern of the photomask is separated by a smaller defocus amount as the width a of the reduced part of the pattern of the photomask is smaller, and the width is smaller under the condition of the defocus amount. The transfer pattern corresponding to the pattern having the reduced portion having a width smaller than a is all separated. Whether the transfer pattern is separated or not is determined by visual inspection.
For example, the transfer pattern is enlarged by using an SEM and visually checked. The type of the layer to be etched is not limited, and is, for example, a dielectric film such as a silicon oxide film or a metal film such as an aluminum film.

In particular, in the method of the second invention, when the layer to be etched is formed of a conductor, a prober is used in step (4) to determine separation or non-separation based on conduction and non-conduction of current. A large amount of data can be easily processed by using a prober to determine the separation or non-separation based on the conduction and non-conduction of the current.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings by way of examples. The following examples are illustrative for facilitating the understanding of the present invention, and the present invention is not limited to these examples. Embodiment 1 This embodiment is an embodiment of the focus monitoring method of the exposure apparatus according to the present invention, and is a method of monitoring the defocus amount of the exposure apparatus by visually confirming physical separation of a transfer pattern. . The defocus amount is an amount that deviates from true focus when the exposure apparatus is focused, and is represented by a distance in this specification. As shown in FIG. 1A, a pattern 10 used in this embodiment is a square pattern 12 having a side length L of 100 μm.
A and B at both ends, and both square patterns 12
This is a pattern in which A and B are connected by a band-shaped body pattern 18. The band-shaped pattern 18 has a maximum width W of 1.0 μm at the connection edge 14 with the square 12, and extends from the connection edge 14 to a reduced portion 16 having the shortest width a at the center separated by a length S of 3.5 μm. This is a band-shaped pattern whose width is uniformly reduced.

In the pattern forming step of this embodiment, the width a of the reduced portion 16 is set to 0.09 μm
From 0.01 to 0.30 μm in increments of 0.01 μm 22
The individual patterns 10 were formed on a photomask as a pattern group. Next, in the transfer step, the defocus amount of the exposure device is set to 0.1 μm from −1.0 μm to 1.0 μm.
The pattern group consisting of 22 patterns 10 on the photomask was transferred onto the resist film of the substrate for each different defocus amount by sequentially changing the steps. At the time of exposure, a KrF excimer laser beam having an exposure wavelength of 248 nm was used, and the conditions were such that the numerical aperture NA was NA = 0.60 and the resolution σ was σ = 0.60. Next, the exposed resist film was developed to form a group of transfer patterns. Reduction section 16 of pattern 10
The smaller the width a of the reduced portion 16 of the pattern 10, the smaller the reduced portion of the transfer pattern, the smaller the defocus amount, and the smaller the reduced portion of the width a under the condition of the defocus amount. All the transfer patterns corresponding to the pattern 10 are separated. Therefore, the separation of the transfer pattern is confirmed by SEM observation, and every time the exposure is performed at the set defocus amount, the transfer pattern in the transfer pattern reduction section corresponding to the reduction section 16 of the photomask pattern 10 in the transfer pattern group is physically determined. The transfer pattern that was separated in the above was identified. Next, for each exposure at the set defocus amount, the photomask pattern 10 corresponding to the transfer pattern specified to be separated is specified from the pattern group, and the maximum width a of the specified pattern 10 in the reduced portion 16 is determined. And the defocus amount of the exposure apparatus at that time, and a calibration curve as shown in FIG. 1B was obtained.

In actual exposure at the time of forming a resist,
The allowable defocus amount of the exposure apparatus with respect to the line width pattern having the line width a can be obtained from the calibration curve shown in FIG. For example, when a is 0.15 μm, the allowable defocus amount of the exposure apparatus is 0.58 to 0.59 μm. In the present embodiment, since the defocus amount of the exposure apparatus can be determined only by visually confirming whether the transfer pattern is separated or not, a line width measuring device or a device such as an overlay measuring device is not required and is simple. . By observing the transfer pattern corresponding to the pattern of FIG. 1A with different image height dependency, the image height dependency of the defocus amount can be obtained. Further, by observing the transfer pattern corresponding to the pattern of FIG. 1A in a different direction, it is possible to evaluate the direction dependency of the defocus amount.

Embodiment 2 In this embodiment, a predetermined transfer pattern is formed, and then a dielectric film such as a silicon oxide film or a conductive film such as aluminum formed on a substrate is formed using the transfer pattern as a mask. Etching was performed to remove the resist film. Then
The amount of defocus of the exposure apparatus is monitored by visually recognizing the physical separation of the formed dielectric film pattern or conductive film pattern. Pattern 2 used in this embodiment
0, as shown in FIG. 2A, the length L ₁ of one side between the square 12 and the strip 18 of the pattern of FIG.
A small square 22 of 0 μm is interposed, the length S of the band from the maximum width W of 1.0 μm to the shortest width a is 2.5 mm, and the pattern is vertically symmetric with respect to the line having the shortest width a.

In the pattern forming step of this embodiment, the width a of the reduced portion 16 of the pattern 20 is changed from 0.09 μm to 0.1 μm.
Twenty-two different patterns 20 were formed on the photomask as pattern groups up to 30 μm in increments of 0.01 μm. Next, in the transfer step, the defocus amount of the exposure apparatus is sequentially changed in steps of 0.1 μm from −1.0 μm to 1.0 μm under the same exposure conditions as in the first embodiment, and the defocus amount on the photomask is changed for each different set defocus amount A pattern group consisting of 22 patterns 20 was transferred onto a resist film on a substrate. Next, the exposed resist film is developed to form a group of transfer patterns, the silicon oxide film or the aluminum film formed on the substrate is etched using the group of transfer patterns as a mask, and then the resist film is peeled off. Thus, a group of silicon oxide films or aluminum film patterns was formed. The reduced portion of the silicon oxide film or the aluminum film pattern corresponding to the reduced portion 16 of the pattern 20 is separated by a smaller defocus amount as the width a of the reduced portion 16 of the pattern 20 is smaller, and the condition of the defocus amount is smaller. In the silicon oxide film or the aluminum film pattern corresponding to the pattern 20 having the reduced portion having a width smaller than the width a,
Separate all. Therefore, it is confirmed by SEM observation whether or not the formed silicon oxide film or aluminum film pattern is separated at the reduced portion. For each set defocus amount, the photomask of the group of the silicon oxide film or aluminum film pattern is used. A silicon oxide film or aluminum film pattern physically separated at the reduced portion of the silicon oxide film or aluminum film pattern corresponding to the reduced portion 16 of the pattern 20 was specified. Next, for each exposure at the set defocus amount, a photomask pattern 20 corresponding to the silicon oxide film or aluminum film pattern specified as being physically separated is specified from the pattern group, and the specified pattern 20 is reduced. A maximum width a of the part 16;
A calibration curve as shown in FIG. 2B was obtained by associating the amount of defocus with the exposure apparatus.

In exposure at the time of actual resist formation,
The allowable defocus amount of the exposure apparatus with respect to the line width pattern having the line width a can be obtained from the calibration curve shown in FIG. For example, when a is 0.15 μm, the allowable defocus amount of the exposure apparatus is 0.47 to 0.48 μm. In the present embodiment, in addition to the effect of the first embodiment, the defocus amount of the exposure apparatus is obtained from the separation of the pattern of the film to be etched actually formed by etching. Accuracy increases.

Embodiment 3 In this embodiment, a transfer pattern was formed, a conductive film such as aluminum formed on a substrate was etched using the formed transfer pattern as a mask, and then the resist film was peeled off. Then, whether or not the conductive film pattern is physically separated is determined based on the conduction of the current, and the defocus amount of the exposure apparatus is monitored. Pattern 30 of the present embodiment
As shown in FIG. 3 (a), the maximum width W of the strip pattern is 0.5 μm instead of the pattern 10 having the maximum width W of 1.0 μm shown in FIG. Except for the pattern 30, the dimensions of L and S are the same.

In the pattern forming step of this embodiment, a
Width from 0.09 μm to 0.30 μm, 0.01 μm
Twenty-two patterns 30 differing in m increments were formed on a photomask as a pattern group. Next, in the transfer step, the defocus amount of the exposure apparatus is set to 0.1 μm from −1.0 μm to 1.0 μm under the same exposure conditions as in the first embodiment.
The pattern group consisting of 22 patterns 30 on the photomask was transferred onto the resist film of the substrate for each different defocus amount, sequentially changing in steps. Next, the exposed resist film is developed, a transfer pattern is formed, the aluminum film formed on the substrate is etched using the transfer pattern as a mask, and then the resist film is peeled to form a group of aluminum film patterns. Formed. The reduced portion of the aluminum film pattern corresponding to the reduced portion 16 of the pattern 30 is:
As the width a of the reduced portion 16 of the pattern 30 is smaller, the pattern is separated by a smaller defocus amount, and under the condition of the defocus amount, the aluminum film pattern corresponding to the pattern 30 having the reduced portion having a width smaller than the width a is , All separated. Therefore, it was confirmed whether the aluminum film pattern was separated by conducting current using a prober,
For each set defocus amount, an aluminum film pattern physically separated by a reduced portion of the aluminum film pattern corresponding to the reduced portion 16 of the photomask pattern 30 was specified from the group of aluminum film patterns. Then
For each exposure with the set defocus amount, a photomask pattern 30 corresponding to the aluminum film pattern specified to be physically separated is specified from the pattern group, and the last of the reduced portions 16 of the specified pattern 30 is specified. The calibration curve as shown in FIG. 3B was obtained by associating the large a with the defocus amount of the exposure apparatus.

In the actual exposure at the time of forming the resist,
The allowable defocus amount of the exposure apparatus with respect to the line width pattern having the line width a can be obtained from the calibration curve shown in FIG. For example, when a is 0.15 μm, the allowable defocus amount of the exposure apparatus is about 0.4 μm. Example 3
In, in order to confirm the pattern separation by checking whether or not a current flows, the time required to confirm the separation can be greatly reduced, and data such as image height dependence of defocus and in-plane dependence of defocus can be obtained. Can be obtained in a short time and in a large amount.

Embodiment 4 In Embodiment 4, similarly to Embodiment 3, a transfer pattern is formed, and a conductive film such as an aluminum film formed in advance on a substrate is etched using the transfer pattern as a mask. Then, the resist was stripped. Then, whether or not the conductive film pattern is physically separated is determined based on the conduction of the current, and the defocus amount of the exposure apparatus is monitored. As shown in FIG. 4A, the pattern 40 used in this embodiment is a square pattern 12 having a side length L of 100 μm.
A and B at both ends, two square patterns 1
This is a pattern having a shape as if 2A and 2B were connected by a band-shaped pattern 18. The strip pattern 18 has a maximum width W of 0.5 μm at the connection edge 14 with the square pattern 12,
The width is uniformly reduced from the connection edge 14 to the reduced portion 16 having the minimum width a, and the distance from the maximum width W to the minimum width a is 6.0 μm.
This is the pattern of m.

In the pattern forming step of this embodiment, a
Width from 0.09 μm to 0.30 μm, 0.01 μm
Twenty-two patterns 40 differing in m increments were formed on a photomask as a pattern group. Next, in the transfer step, the defocus amount of the exposure apparatus is set to 0.1 μm from −1.0 μm to 1.0 μm under the same exposure conditions as in the first embodiment.
The pattern was sequentially changed, and 22 patterns 40 on the photomask were transferred as a pattern group onto the resist film of the substrate for each different defocus amount. Next, the exposed resist film is developed, a transfer pattern is formed, the aluminum film formed on the substrate is etched using the transfer pattern as a mask, and then the resist film is peeled to form a group of aluminum film patterns. Formed. Next, in the same manner as in Example 3, the calibration curve as shown in FIG. 4B was obtained by associating the width a of the reduction unit 16 with the defocus amount of the exposure device.

In the actual exposure at the time of forming the resist,
The allowable defocus amount of the exposure apparatus with respect to the line width pattern having the line width a can be obtained from the calibration curve shown in FIG. For example, when a is 0.15 μm, the allowable defocus amount of the exposure apparatus is 0.47 to 0.48 μm. Since the pattern used in this example has a shape in which a large pattern is joined to a small line width pattern,
In addition to the same effects as in the third embodiment, the optical proximity effect appears remarkably, and as shown in FIG. 4B, the degree of change in the defocus amount at which the pattern separates with respect to the change in the width a is slow. Yes, the defocus value can be obtained with higher accuracy.

[0023]

According to the method of the present invention, since the defocus amount of the exposure apparatus is determined by separating the transfer pattern or the pattern of the layer to be etched, the method is simple and highly accurate. Also, since the pattern to be etched is formed of a conductor and the pattern separation is determined based on whether or not a current flows through the prober, a large amount of data on the amount of defocus can be acquired in a short time. To improve.

[Brief description of the drawings]

FIG. 1A is a pattern diagram of a pattern used in Example 1, and FIG. 1B is a calibration curve obtained in Example 1.

FIG. 2A is a pattern diagram of a pattern used in Example 2, and FIG. 2B is a calibration curve obtained in Example 2.

3 (a) is a pattern diagram of a pattern used in Example 3, and FIG. 3 (b) is a calibration curve obtained in Example 3.

FIG. 4A is a pattern diagram of a pattern used in Example 4, and FIG. 4B is a calibration curve obtained in Example 4.

[Explanation of symbols]

10 ... pattern used in Example 1, 12 ... square pattern, 14 ... connection edge, 16 ... reduced part, 18 ...
Band pattern, 20: pattern used in Example 2, 22: small square, 30: pattern used in Example 3, 40: pattern used in Example 4.

Claims (3)

[Claims] 1. A method for monitoring focusing of an exposure apparatus used when forming a transfer pattern by photolithography, comprising: (1) connecting a plurality of large pattern areas to each other and having a width Having a band-shaped region having a reduced portion locally reduced, the step of forming a pattern group consisting of a plurality of patterns of the same dimensions on the photomask except that the width of the reduced portion is different from each other, (2) for each defocus amount set differently from each other, exposing under a condition of the set defocus amount to transfer a pattern group of a photomask to a photosensitive material layer on a substrate; (3) For each exposure at the set defocus amount, the transfer pattern group is physically separated at the transfer pattern reduction section corresponding to the photomask pattern reduction section. (4) for each exposure at the set defocus amount, a photomask pattern corresponding to the specified transfer pattern is specified from a group of patterns, and the last of the reduced portions of the specified pattern is specified. Producing a calibration curve based on the correspondence between the defocus amount and the maximum width of the reduction section, and calculating an allowable defocus amount from the calibration curve. 2. A method for monitoring focusing of an exposure apparatus used when forming a transfer pattern by photolithography, comprising: (1) connecting a plurality of large pattern regions to each other, and Having a band-shaped region having a reduced portion locally reduced, the step of forming a pattern group consisting of a plurality of patterns of the same dimensions on the photomask except that the width of the reduced portion is different from each other, (2) for each defocus amount set differently from each other, exposing under a condition of the set defocus amount to transfer a pattern group of a photomask to a photosensitive material layer on a substrate; (3) (4) etching the layer to be etched under the photosensitive material layer using the photosensitive material layer pattern as a mask to form a group of etched layer patterns; For each exposure with a constant defocus amount, specify an etched layer pattern that is physically separated by a reduced portion of the etched layer pattern corresponding to the reduced portion of the photomask pattern from the group of etched layer patterns. (5) For each exposure with the set defocus amount, a photomask pattern corresponding to the specified layer pattern to be etched is specified from the pattern group, and the maximum width of the reduced portion of the specified pattern is determined. Determining a permissible defocus amount from the calibration curve, comprising: obtaining a calibration curve comprising a correspondence between the defocus amount and the maximum width of the reduction unit. 3. The focus monitoring method for an exposure apparatus according to claim 2, wherein the layer to be etched in step (3) is formed of a conductor.
3. The focus monitoring method for an exposure apparatus according to claim 2, wherein in step (4), separation and non-separation are determined based on conduction and non-conduction of current.