JP2005032853A - Method for measuring focusing characteristics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focusing characteristics measuring method performing focus measurement conveniently using an overlay measurement device used commonly in a semiconductor production process. <P>SOLUTION: A resist film is formed on a substrate and transferred with a first pattern by exposure. A second pattern is then transferred to overlay the latent image of the first pattern transferred onto the resist film. Subsequently, the resist film transferred with the first pattern and the second pattern is developed to form a resist pattern for measurement. Focusing variations are measured by measuring the amount of retraction caused by the focusing variations in the vertical angle of a resist pattern for measurement which is an isosceles triangle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging characteristic measuring method for measuring an imaging characteristic of a projection optical system of an exposure apparatus.
[0002]
[Prior art]
A fine pattern of a semiconductor integrated circuit is formed by projecting an original drawing on a mask onto a substrate using a projection optical system. A reduction projection exposure apparatus (stepper) widely used in LSI manufacturing will be described. The mask is illuminated with ultraviolet rays from a mercury lamp, and the light shielding film pattern on the mask is transferred onto the substrate. Usually, several hundreds of LSI chips are formed on a substrate. However, when a reduction projection apparatus is used, a pattern on a mask is baked on a wafer, the substrate is shifted, and baked again (step). & Repeat method) to form a pattern on the entire surface of the substrate. An LSI is manufactured by repeating a process of forming a pattern on a substrate using a lithography technique and processing the substrate based on the pattern. In an exposure apparatus that transfers the original drawing on the mask onto the substrate, the accuracy of the transferred image changes greatly due to focus fluctuations during exposure, and thus a technique for accurately measuring the best focus position of the projection optical system is required.
[0003]
As a method for measuring the best focus position of the projection optical system, there is Patent Document 1. As shown therein, there is a method of measuring various imaging characteristics of the projection optical system by forming rhombus marks on a substrate and measuring a predetermined length of the image. FIG. 7 shows a measurement example. The resist pattern 704 formed on the substrate has a rhombus shape elongated in the X direction and is arranged at regular intervals in the Y direction. By scanning such a resist pattern with the beam 702, scattered light is generated from an edge extending in the X direction. A profile 706 shows the relationship with the beam scanning position when the scattered light is converted into an optical signal level. The optical signal level is the highest at the center of the resist pattern in the X direction, and the optical signal level decreases as it goes to the tip on both sides. By detecting the length L of the signal waveform thus obtained, the length of the resist pattern is detected. FIG. 8A shows the resist pattern shape when the focus changes. Since the resist pattern formed on the substrate has a high image contrast in the vicinity of the best focus, the resist pattern is transferred to the vicinity of the tip. On the contrary, the pattern disappears from the tip because the contrast of the image decreases as the focus is deviated from near the best focus. From the above, the best focus position is calculated by plotting the relationship diagram between the resist pattern length and the focus variation as shown in FIG.
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-169266
[Problems to be solved by the invention]
Hereinafter, the problems of the conventional example will be described.
[0006]
In an exposure apparatus that transfers the original drawing on the mask onto the substrate, the accuracy of the transferred image changes greatly due to focus fluctuations during exposure, and therefore it is necessary to accurately measure the best focus position of the projection optical system. In the conventional measurement method, a dedicated apparatus mounted on the exposure apparatus is required to measure the diamond-shaped mark as a length. There are also many factors that affect the measurement accuracy due to the rotation of the substrate or beam and the beam profile.
[0007]
[Means for Solving the Problems]
In order to solve the conventional problems, the imaging characteristic measurement method of the present invention performs focus measurement easily using an overlay measurement apparatus widely used in a semiconductor manufacturing process, not an exposure apparatus.
[0008]
In this configuration, it is possible to easily measure the focus with high accuracy by constructing a measurable mark using the overlay measurement apparatus and using the mark. In addition, since the overlay measurement apparatus captures an image with a CCD camera and performs measurement by image processing, deterioration in measurement accuracy due to the beam profile and beam rotation can be removed, and measurement can be performed with high accuracy.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0010]
An embodiment of the present invention will be described with reference to FIGS.
[0011]
FIG. 1 is a diagram showing a process flow in the embodiment of the present invention. FIG. 2 is a diagram showing a pattern for forming the imaging characteristic measurement pattern of the present invention. FIG. 3 is a diagram showing a resist pattern for measuring imaging characteristics according to the present invention. FIG. 4 is a diagram in which a resist pattern for measuring imaging characteristics according to the present invention is formed on a substrate. FIG. 5 is a diagram showing an unexposed pattern when forming a resist pattern for measuring imaging characteristics according to the present invention. FIG. 6 is a schematic diagram of edge detection of the overlay measurement apparatus used in the embodiment of the present invention.
[0012]
A description will be given according to the process flow diagram in the embodiment of the present invention shown in FIG.
[0013]
First, in step (1), a positive resist is applied on a semiconductor substrate in order to form a resist pattern.
[0014]
Next, in a process (2), it transfers by exposure using the 1st pattern 231 shown to Fig.2 (a) to the resist on a semiconductor substrate.
[0015]
In the step (3), the resist is transferred onto the resist on the semiconductor substrate by exposure using the second pattern 232 shown in FIG. The second pattern 232 is obtained by rotating the first pattern 231 right or left by 90 degrees. The second pattern 232 is aligned with the latent image of the first pattern 231 transferred to the resist in step (2) and transferred under the same exposure conditions as in step (2).
[0016]
In step (4), a resist pattern 300 as shown in FIG. 3 is formed by developing the resist to which the first pattern 231 and the second pattern 232 are transferred. The resist pattern 300 is formed of a resist pattern 302 having isosceles triangles with apex angles facing each other and a resist pattern 304 having bases facing each other. A set of the pattern 302 and the pattern 304 is formed in the X direction and the Y direction. For example, a total of 63 resist patterns 300 are formed in a 7 × 9 matrix as shown in FIG. The 63 resist patterns are obtained by forming the first pattern 231 and the second pattern 232 by a step-and-repeat method under an exposure condition combining 7 types of exposure amount offsets and 9 types of focus offsets.
[0017]
Here, the first pattern 231, the second pattern 232, and the resist pattern 300 will be described.
[0018]
The mark 202 in FIG. 2A is a parallelogram. The mark 203 is obtained by inverting (turning over) the mark 202. A mark group 204 in which a plurality of mark 202 and mark 203 sets are arranged, a mark group 207 that is rotated 90 degrees clockwise, a mark group 211 that is further rotated 90 degrees, and a mark group that is further rotated 90 degrees A first pattern 231 is formed so that 215 is arranged on each side of the square 220.
[0019]
A second pattern 232 shown in FIG. 2B is obtained by rotating the first pattern 231 by 90 degrees clockwise.
[0020]
Further, the resist pattern shown in FIG. 3 is a portion where an unexposed portion that overlaps when the first pattern 231 and the second pattern 232 are superimposed is an isosceles triangle as shown in FIG.
[0021]
In step (5), the focus fluctuation amount is measured using the resist pattern formed up to step (4).
[0022]
The resist pattern 300 shown in FIG. 3 is measured by an overlay measuring apparatus, and the amount of positional deviation of each resist pattern is measured. The best focus is calculated from this positional deviation amount.
[0023]
This measurement will be described using a pattern in the X direction.
[0024]
6 shows a part of the resist pattern 302 and the resist pattern 304 of the resist pattern 300 shown in FIG. The measurement principle of superposition is that an image is captured by a CCD camera and measured by image processing. In the image captured from the CCD camera, black is defined as 0 and white is defined as 255, and the brightness is digitized within the area to detect each pattern position.
[0025]
FIG. 6 shows the shapes of the resist pattern 310 formed at the best focus and the resist pattern 320 formed at the defocus. When the pattern position of the resist pattern 310 formed at the best focus is used as a reference, the pattern corresponding to the apex angle of the isosceles triangle of each resist pattern is retreated in defocusing, causing a positional shift. This positional deviation amount is obtained by measuring the distance X1 between the first pattern 330 and the second pattern 332 and the distance X2 between the third pattern 334 and the fourth pattern 336 with an overlay device. Obtainable. In the best focus, the apex angle of the isosceles triangles of the resist pattern 304 and the resist pattern 302 is formed as an acute angle, so that the distance becomes large at the distance X1, and the distance becomes small at the distance X2. In defocusing, contrary to the best focus, the distance becomes smaller at the distance X1, and the distance becomes larger at the distance X2. And the difference of relative distance is calculated | required from the following formula.
[0026]
Δ = (X1−X2) / 2
By plotting the relationship between the relative distance difference and the focus value as shown in FIG. 6B, the best focus position of the projection optical system can be calculated.
[0027]
The same thing occurs with a resist pattern in the Y direction, which makes it possible to measure in the X and Y directions simultaneously.
[0028]
【The invention's effect】
As described above, according to the imaging characteristic measuring method of the present invention, it is possible to easily and accurately measure the focus by using an overlay measurement device instead of a special device. In addition, since the overlay measurement device captures an image with a CCD camera and measures it by image processing, it is possible to eliminate deterioration in measurement accuracy due to beam rotation, and to measure with high accuracy by averaging the beam profile. It is possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing a process flow in an embodiment of the present invention. FIG. 2 is a diagram showing a pattern for forming an imaging characteristic measurement pattern according to the present invention. FIG. 4 is a diagram showing a resist pattern for measuring imaging characteristics according to the present invention formed on a substrate. FIG. 5 is a diagram showing an unexposed pattern when forming a resist pattern for measuring imaging characteristics according to the present invention. 6 is a schematic diagram of edge detection of the overlay measurement apparatus used in the embodiment of the present invention. FIG. 7 is a schematic diagram of a measurement example in a conventional example. FIG. 8 is a schematic diagram of a measurement example in a conventional example. ]
202, 203 Mark 204, 207, 211, 215 Mark group 220 Square 231, 330 First pattern 232, 332 Second pattern 233, 334 Third pattern 300, 302, 304, 310, 320 Resist pattern 336 Fourth Pattern 702 beam 704 resist pattern 706 profile

Claims (6)

Forming a resist film on the substrate;
Transferring the first pattern to the resist film by exposure;
Transferring the second pattern by exposure so as to be superimposed on the latent image of the first pattern transferred to the resist film;
Developing the resist film to which the first pattern and the second pattern have been transferred to form a measurement resist pattern;
An imaging characteristic measuring method, comprising: measuring a focus fluctuation amount by measuring a retraction amount of an edge of the measurement resist pattern. The imaging characteristic measuring method according to claim 1, wherein the first pattern is a parallelogram, and the second pattern is the first pattern turned upside down. 3. The imaging characteristic measuring method according to claim 2, wherein the measurement resist pattern is an isosceles triangle formed by overlapping the first pattern and the second pattern. The imaging characteristic measuring method according to claim 1, wherein the edge is an apex angle of an isosceles triangle. The measurement resist pattern includes a first resist pattern composed of the two isosceles triangles whose apex angles are opposed to each other, and a second resist pattern composed of the two isosceles triangles whose bases are opposed to each other. The imaging characteristic measuring method according to claim 4, wherein: 6. The imaging characteristic measurement according to claim 5, wherein, in measuring the receding amount of the edge of the measurement resist pattern, a difference in apex angle distance between the first resist pattern and the second resist pattern is taken. Method.

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