KR19980067515A - Focus measuring method of exposure apparatus and mask used therein - Google Patents

Abstract

The present invention discloses a focus measuring method of an exposure apparatus and a mask used therein.

In the focus measuring method of the exposure apparatus according to the present invention, the light transmission window is formed asymmetrically with respect to the optical axis of the condenser lens and thus diffracts the aperture for injecting light asymmetrically and the light incident from the aperture. The optimal focus of the exposure apparatus is measured using a mask having two pattern groups having different pitches.

The optimal focus of the exposure apparatus can be measured by measuring the relative movement on the pattern, which is the center of the two pattern groups engraved on the mask. This method does not require any special equipment and does not require a separate mask, which is complicated by a manufacturing process such as PSM, thus providing an easy measurement method at a lower cost.

Description

Focus measurement method of exposure apparatus and mask used therein

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a focus measuring method of an exposure apparatus and a mask used therein, and in particular, to a method for measuring an optimal focus of an exposure apparatus using a mask having a pattern group having a non-symmetrical aperture and a different pitch, and It is about mask to use.

Due to the high integration of semiconductor devices, the density of semiconductor devices to be formed in a unit area of a wafer is rapidly increasing. Therefore, the gap between semiconductor elements is getting narrower than before.

In order to form the semiconductor devices required on the wafer, there must be an exposure apparatus having a high resolution that can comply with a predetermined design rule. Once there is such an exposure apparatus, light can be irradiated to pattern a photoresist film in a desired shape to form a material layer pattern of a desired shape on a wafer, thereby making it possible to manufacture a semiconductor device capable of achieving high integration. have.

However, the problem lies in the focus margin of the exposure apparatus. Higher integration of semiconductor devices requires higher resolution, which means a reduced margin of focus of the exposure apparatus in use. Of course, if the focus margin is reduced, the photographic process must be more precise. Therefore, not only can it be guaranteed to proceed quickly, but also the process becomes complicated. One way to solve this problem is to find the optimal focus in the exposure apparatus currently in use. This is how to find the smallest focal cross section. Various methods have been proposed for this purpose. One example is the method proposed by IBM, which has devised a Phase Shift Mask (hereinafter referred to as PSM) that can measure focus using the principle of phase shift.

However, in the method of measuring the focus using the PSM, not only the manufacturing process of the mask is complicated, but also the phase error of the mask may cause an error in the focus measurement. In addition, due to the problem of bonding caused by the PSM production, it is difficult to apply to the mask for the actual device. In particular, since the size of the pattern formed on the PSM should be small and the thickness of the photoresist film should be thin during exposure, the problem of using a photoresist film of higher resolution than the currently used photoresist film is difficult to overcome. Becomes

Therefore, the technical problem to be achieved by the present invention is to provide a focus measuring method of an exposure apparatus that can use a conventional chromium mask to solve the above problems, but can increase the measurement accuracy.

Another object of the present invention is to provide a mask for use in the focus measuring method of the exposure apparatus.

1 is a view showing an example of an exposure apparatus having a typical aperture.

FIG. 2 is a schematic cross-sectional view of an exposure apparatus for explaining a focus measurement method of a semiconductor device according to an embodiment of the present invention.

3 is a plan view of an aperture used in the focus measurement method of a semiconductor device according to an embodiment of the present invention.

FIG. 4 is a diagram showing a result of simulating a relationship between a pitch change of a pattern engraved in a mask and a change in focal position of the exposure apparatus of FIG. 2 using the aperture of FIG. 3 and a displacement error of a pattern formed on a wafer accordingly. .

5 is a view showing a mask used in the focus measurement method of the exposure apparatus according to an embodiment of the present invention.

<Code Description of Main Parts of Drawing>

10: condenser lens 18: wafer

34: 0 shading 36, 36a: ± 1 shading

40: First mask 42: First aperture

42a: Third light transmitting window 44: Focusing path when the pitch is large

46, 46a: ± 1st shading 48: focusing movement when the pitch is small

In order to achieve the above technical problem, the focus measuring method of the exposure apparatus according to the present invention comprises a condenser lens; An exposure having a mask at the front of the condenser lens on the same line as the condenser lens and an aperture controlling the amount of light incident on the mask at the front of the mask and on the same line as the mask In the method for measuring the focus of the apparatus, using an asymmetric aperture in which the light transmission window is formed asymmetrically as the aperture, and using a mask having a group of patterns having different pitches as the mask. It is characterized by.

The asymmetric aperture is formed by changing the light transmittance of the light transmission window formed in the symmetric aperture or changing the size of the light transmission window.

According to an embodiment of the present invention, the pattern group is formed of the first and second pattern groups, and is formed to be spaced apart from each other by a predetermined interval.

The first and second pattern groups are each formed of a plurality of first patterns having a first pitch and a plurality of second patterns having a second pitch.

The first and second patterns are formed in the same shape.

In the first and second pattern group, the first and second patterns are arranged in the same form.

The said 1st pattern and a 2nd pattern are formed in the width which belongs to the range of 0.1 micrometer-0.4 micrometer.

In order to arrange the first and second patterns, the first and second pitches having different sizes are arranged so as to have values belonging to 0.15 μm to 0.8 μm to form the first and second pattern groups.

The mask uses a chrome mask.

At least one light transmitting window is asymmetrically formed in the first aperture.

The light transmission window is formed in a rectangular shape having a horizontal and vertical length different from each other.

In order to achieve the above another technical problem, the mask used in the focus measuring method of the exposure apparatus according to the embodiment of the present invention comprises a glass substrate; And first and second pattern groups having different pitches spaced apart from each other by a predetermined interval on the glass substrate.

The first pattern group includes a plurality of first patterns having a first pitch and parallel to each other and arranged in the same direction.

The second pattern group includes a plurality of second patterns that have a second pitch and are parallel to each other and arranged in the same direction.

The first and second patterns are the same form.

The first and second pattern groups are the same arrangement form.

According to an embodiment of the present invention, the width of the first pattern or the second pattern is 0.1 μm to 0.4 μm.

According to an embodiment of the present invention, the first and second pitches are respectively 0.15 μm to 0.8 μm.

The second pitch is greater than the first pitch.

The first and second patterns are chromium patterns.

The present invention can easily measure the optimal focus of the exposure apparatus by using a conventional chrome mask having a pattern having a different pitch and asymmetric aperture, and easy to manufacture the mask, while low defect occurrence rate and low cost. In addition, the chromium mask is an ordinary mask that is still used in the industrial field, and does not require a special photosensitive film.

Hereinafter, a focus measuring method of an exposure apparatus and a mask used therein will be described in detail with reference to the accompanying drawings.

1 is a view showing an example of an exposure apparatus having a conventional aperture (aperture).

FIG. 2 is a schematic cross-sectional view of an exposure apparatus for explaining a focus measurement method of a semiconductor device according to an embodiment of the present invention.

3 is a plan view of an aperture used in the focus measurement method of a semiconductor device according to an embodiment of the present invention.

FIG. 4 is a diagram showing a result of simulating a relationship between a pitch change of a pattern engraved in a mask and a change in focal position of the exposure apparatus of FIG. 2 using the aperture of FIG. 3 and a displacement error of a pattern formed on a wafer accordingly. .

5 is a view showing a mask used in the focus measurement method of the exposure apparatus according to an embodiment of the present invention.

First, referring to FIG. 1, a conventional exposure apparatus is composed of a large number of components, but for convenience, FIG. 1 shows only three components necessary for expressing the basic principle described in the present invention. In FIG. 1, reference numeral 10 denotes a condenser lens, and reference numerals 12 and 14 are positioned in front of the condenser lens 10, respectively, and are masks and apertures that are colinear with the condenser lens 10. FIG. Although the mask 12 is a chrome mask and only one chromium layer pattern 12a is shown as a diffraction point in FIG. 1, a plurality of chromium layer patterns are formed on the mask 12.

First and second light transmitting windows 14a and 14b are formed in the aperture 14 and are symmetrically formed with respect to the optical axis passing through the center of the condenser lens 10.

When the pattern is formed on the wafer 18 by the exposure apparatus having such a configuration, the light reaching the aperture 14 is masked through the first and second light transmitting windows 14a and 14b. Incident on (12) and diffracted by the chrome pattern 12a engraved in the mask (12). The diffracted light by the chromium pattern 12a is composed of diffracted light by the light passing through the first light transmitting window 14a and the first light transmitting window 14b, and the first and second light transmitting windows ( Since 14a and 14b are symmetrically formed in the aperture 14, diffracted light incident on the condenser lens 10 is also incident symmetrically about the optical axis.

The diffracted light by the chromium pattern 12a is clocked around the zero-order light 20 and the zero-order light 20 passing through the mask 12 in the same direction as the direction incident on the mask 12 without being diffracted. ± 1, ± 2, .. diffracted light diffracted at a predetermined angle in a direction or counterclockwise, although multi-order diffracted light is included, higher order light of more than 0th order light 20 and ± 1st order light 22 may be Outside the condensing range. Therefore, in FIG. 1, only the 0th order light 20 used for pattern formation and the ± 1st order light 22 shown by the dotted line (---) are shown.

On the other hand, light incident on the condenser lens 10 symmetrically with respect to the optical axis is condensed at a predetermined focus of the condenser lens 10 to expose the photosensitive film on the wafer 18.

The exposure apparatus determines the resolution or focus of the apparatus by determining the wavelength of the light used with the setting and the numerical aperture of the apparatus, namely NA (Numerical Aperture). However, no matter how well the exposure apparatus is aligned, there are factors that change the focus. For example, aberrations such as field curvature and astigmatism of the lens system used in the exposure apparatus, defects in planarization of wafers and chucks, automatic focusing and automatic leveling errors, lens heating, and pressure differentials. There may be environmental changes, and in the process of directly offsetting the optimal focus, an erratic light may be a factor that causes the focus change.

Even if the focus of the exposure apparatus changes due to such a change in focus, the diffraction light incident on the condenser lens 10 is incident symmetrically with respect to the optical axis in the exposure apparatus as shown in FIG. 1. 10) on the optical axis. Therefore, the movement of the focus according to the defocus is moved along the optical axis. In other words, the focus moves in the direction of the arrow 24 perpendicular to the wafer 18 in FIG. 1 and no movement of the focus appears to the left or the right. Therefore, optimal focusing is difficult.

FIG. 2 is an exposure according to an embodiment of the present invention having a first mask 40 and a first aperture 42 different from the mask 12 and aperture 14 used in the exposure apparatus shown in FIG. 1. Although the device is schematically illustrated, there is no difference in the configuration of the exposure apparatus illustrated in FIG. 1, but the first mask 40 has a chrome pattern having a uniform pitch as in the mask 12 illustrated in FIG. 1. The chrome pattern group which does not form this but has a different pitch is formed (it mentioned later about the said 1st mask 40). In addition, unlike the aperture 14 of FIG. 1, the first aperture 42 is an asymmetric aperture with respect to the optical axis of the condenser lens 10. Reference will be made to FIG. 3 to describe the first aperture 42 in more detail. Referring to FIG. 3, a third light transmitting window 42a is formed asymmetrically with respect to the optical axis of the condenser lens 10 in the first aperture 42. The third light transmitting window 42a is positioned in a region outside the center region through which the optical axis of the first aperture 42 passes. In FIG. 3, the third light transmitting window 42a has a rectangular shape having a horizontal length and a vertical length 42c and 42d that are different from each other. However, the third light transmitting window 42a restricts the shape of the third light transmitting window 42a. It is not. Accordingly, the third light transmitting window 42a may be a general quadrangle including a square and a rectangle, or a geometric shape of a circular or polygonal shape. In addition, although only one third light transmission window 42a is shown in the first aperture 42 shown in FIG. 3, the first aperture 42 includes one or more light transmission windows if the asymmetry is maintained. You may.

For example, the actual numerical value of the first aperture 42, for example, the horizontal and vertical lengths 43a and 43b of the first aperture 42 are equal to 2 μm, and the third light transmitting window 42a is the same. The rectangular and horizontal lengths 42c and 42d may be 0.5 μm and 0.4 μm, respectively.

Reference numeral 42b not mentioned in the description of FIG. 3 denotes an opaque portion of the first aperture 42.

An asymmetric aperture, such as the first aperture 42, changes the light transmittance of either light transmission window in an aperture having a light transmission window symmetrical with respect to the optical axis (e.g., 14 in FIG. 1) or It can also form by changing the area of a light transmission window.

Therefore, the asymmetric aperture does not only mean that the light transmission window is formed on either side of the optical axis, and even if the light transmission window is symmetrically formed on the aperture, the ratio is different if the area or the light transmittance of each light transmission window is different. You can see that it is symmetrical.

Next, a case in which light is incident on an exposure apparatus having such a configuration will be described. The light incident on the first aperture 42 passes through the third light transmitting window 42a engraved on the right side of the first aperture 42 to enter the first mask 40. . Light passing through the third light transmitting window 42a is incident on a diffraction point, that is, the chrome pattern 40a at a predetermined incident angle with respect to the first mask 40. The light incident on the first mask 40 is diffracted by the chrome pattern 40a of the first mask 40, and the diffracted light includes 0th order light, ± 1st order light, ± 2nd order light, .. However, the high-order light of more than ± 2 light shielding is out of the range of the condenser lens 10, so the illustration is omitted, and only the 0-order light 34 and the ± 1-order light 36, 36a are shown in FIG.

Referring to the light diffracted in FIG. 2, the light diffracted by the first mask 40 does not exhibit diffraction symmetry since the first aperture 42 is asymmetrically unfolded. This can be easily seen by examining the paths of the diffracted zero-order light 34 and the ± first-order light 36, 36a. Since the center of the diffracted light becomes zero-order light, looking at the path of the zero-order light 34 to see the path of the light diffracted by the first mask 40, the zero-order light 34 is symmetrical to the condenser lens 10. It is not incidentally, but enters asymmetrically to either side. As such, when light is incident on a specific portion of the lens without being incident on the front surface of the lens, the focus of the light is changed in its position on the focal plane of the lens. In addition, when defocus occurs, the movement of the focal point moves along the zero-order light 34 of light passing asymmetrically through the condenser lens 10. As a result, when defocusing, the focal point does not follow the optical axis as shown in FIG. Without being moved in the direction of the solid line arrow 44 having a predetermined angle with respect to the optical axis. The direction of the arrow corresponds to the movement of the photoresist pattern formed on the wafer. Although the description so far has not been mentioned, the pitch between the chrome patterns 40a engraved in the first mask 40 is greater than the pitch between the general patterns.

Next, a case in which the pitch between the chrome patterns 40a engraved in the first mask 40 is narrower than the general case will be described with reference to FIG. 2.

When the pitch between the chrome patterns 40a engraved in the first mask 40 is small, the first mask 40 passes through the third light transmitting window 42a of the asymmetric first aperture 42. The incident light is diffracted by the chromium pattern 40a which becomes the diffraction point of the mask, where the diffraction angle is larger as the obstacle size becomes smaller at the diffraction point, as is well known. Therefore, even in the case of diffracted light of the same order as the light diffracted by the first mask when the pitch between the patterns is larger among the light diffracted by the first mask 40 where the pitch between patterns is smaller than the general case, the diffraction angle is The diffracted light diffracted by the narrow pitch mask is larger. Therefore, in the case where a large pitch chromium pattern is formed in the first mask 40 in FIG. 2, the first and second diffraction beams 36 and 36a diffracted therefrom are incident on the condenser lens 10. In the case where a small pitch chromium pattern is formed in the mask, the ± 1st order beams 46 and 46a diffracted therefrom are not incident on the condenser lens 10, and only the + 1st order beam 46 is the condenser lens 10. It can be seen that the incident on. However, the + 1st order light 46 passes through the lens surface opposite to the lens surface through which the 0th order light 34 passes by the diffraction angle. As a result, when the pitch between the chromium patterns 40a engraved in the first mask 40 is small, the focus is determined by the 0th order light 34 and the + 1st order light 46. In addition, during defocus, there is a shift of focus, and there is a shift of focus in the direction indicated by the dashed-dotted arrow 48 in the opposite direction as when the pitch between the chrome patterns 40a is large. However, the angle formed by the optical axis and the dashed-dotted arrow 48 is smaller than when the pitch of the chrome pattern 40a is large. As the pitch between the chrome patterns 40a engraved on the first mask 40 is large and small, the left and right movements of the pattern formed on the wafer 18 become larger or smaller and the movement directions are opposite to each other. Able to know.

Based on the above contents, the simulation results are shown in FIG. 4. In FIG. 4, the horizontal axis represents a change in position of a focal point in μm, and the vertical axis represents a displacement error of a pattern according to a change in position of the focal point in nm. In Fig. 4, reference numerals ■, □, ●, ○, ◇ and ◆ are 0.3 μm, 0.34 μm, 0.38 μm, 0.42 μm, 0.46 μm between the pitches of the chrome patterns 40a engraved on the first mask 40, respectively. And graphs showing a displacement error of a pattern according to a change in position of the focal point at 0.50 μm. Referring to FIG. 4, when the pitch between the chrome patterns 40a engraved in the first mask 40 has a specific value, for example, when 0.3 μm, the focus position of the exposure apparatus is changed, the first mask is changed. The image of the chrome pattern 40a engraved on (40) was found to be changed to either left or right. When defocused to increase the position of the focus, it was found that the image of the chrome pattern 40a is displaced in the right direction. The opposite result was obtained when the defocused position was decelerated. In addition, when the defocus of the focus is fixed to a specific value (for example, −0.24 μm), the displacement error of the pattern formed on the wafer as the pitch between the chrome patterns 40a engraved in the first mask 40 increases. Was increased.

It can be seen that the simulation result is the result as described with reference to FIG. 2.

This result is obtained by using the asymmetric first aperture 42. In the focus measuring method of the exposure apparatus according to the present invention, exposure is performed using such a property of the asymmetric first aperture 42. Measure the optimum focus of the device. Specifically, in the above description, the first mask 40 is regarded as a mask having a large pitch between the chrome patterns 40a and a small mask. However, as shown in the simulation result of FIG. 3, one mask has a different pitch. The pattern should be formed. Therefore, it is obvious that the first mask 40 should be a mask having patterns having different pitches together.

An example of such a mask used for focus measurement of an exposure apparatus according to an embodiment of the present invention can be seen in FIG. 5. Referring to FIG. 5, a mask having patterns having different pitches formed at the same time includes first and second pattern groups 50 and 52 spaced apart from each other by a predetermined distance on a glass substrate. Looking at 50, the first pattern 50a having the first pitch P1 is arranged in parallel in the same direction.

Looking at the said 2nd pattern group 52, the 2nd pattern 52a which has the 2nd pitch P2 is arranged in parallel in the same direction. Although the shape and arrangement direction of the said 1st and 2nd patterns 50a and 52a may be different, it is assumed that it is the same in this example. The first and second patterns 50a and 52a are chromium patterns, the widths of which are the same but may be different. The first and second pitches P1 and P2 have different sizes. The second pitch P2 is greater than the first pitch P1. However, the first pitch P1 may have a large size of the first and second pitches P1 and P2. As an example of the first and second pitches P1 and P2, the first pitch P1 is preferably 0.3 μm and the second pitch P2 is 0.5 μm, but the available value is within 0.15 μm to 0.8 μm. Can be selected. In addition, in the embodiment of the first and second patterns 50a and 52a, the first and second patterns 50a and 52a are preferably 0.2 µm, but other available values are selected within 0.1 µm to 0.4 µm. You may. In FIG. 4, reference numerals C1 and C2 denote center patterns of the first and second pattern groups 50 and 52, respectively.

When using such a chromium mask, it is possible to measure the optimum focus of the exposure apparatus by measuring the relative movement of the center pattern (C1, C2) of the first and second pattern group (50, 52). The hatches of the center patterns C1 and C2 are inserted to indicate that the center pattern is a center pattern. There is no special difference from the other patterns 50a and 52a.

As described above, in the focus measuring method of the exposure apparatus according to the present invention, since the light transmitting window is formed asymmetrically with respect to the optical axis of the condenser lens, the aperture for injecting light asymmetrically and the light incident from the aperture are used. The optimal focus of the exposure apparatus is measured using a mask having two groups of patterns having different pitches for diffraction.

The optimal focus of the exposure apparatus can be measured by measuring the relative movement on the pattern, which is the center of the two pattern groups engraved on the mask. This method does not require any special equipment and does not require a separate mask, which is complicated by a manufacturing process such as PSM, thus providing an easy measurement method at a lower cost.

The present invention is not limited to the above embodiments, and it is apparent that many modifications can be made by those skilled in the art within the technical idea of the present invention.

Claims (20)

Condenser lens; A mask located on the same line as the condenser lens in front of the condenser lens; A method for measuring the focus of an exposure apparatus having an aperture in front of the mask and controlling an amount of light incident on the mask located on the same line as the mask, the method comprising: The aperture measuring method of the exposure apparatus is characterized by using an asymmetric aperture in which the light transmitting window is formed asymmetrically as the aperture, and a mask having a pattern group having different pitches as the mask. . The method of claim 1, wherein the asymmetric aperture is formed by varying the light transmittance of the light transmission window formed in the symmetric aperture. The method of claim 1, wherein the asymmetric aperture is formed by varying the size of a light transmission window formed in the symmetric aperture. The method of claim 1, wherein the pattern group is formed of a first group and a second pattern group, and the pattern group is formed to be spaced apart from each other by a predetermined interval. The method of claim 4, wherein the first and second pattern groups are each formed of a plurality of first patterns having a first pitch and a plurality of second patterns having a second pitch. . The method of claim 4, wherein the first and second patterns are formed in the same shape. The method of claim 5, wherein the first and second patterns in the first and second pattern groups are arranged in the same shape. The method of claim 6, wherein the first pattern and the second pattern are formed in a width in a range of 0.1 μm to 0.4 μm. The method of claim 7, wherein the first and second patterns having different sizes are arranged to arrange the first and second patterns so that the first and second patterns have a value ranging from 0.15 μm to 0.8 μm. A mask for use in the focus measurement method of the exposure apparatus, characterized in that forming a. 2. The method of claim 1, wherein the mask uses a chrome mask. The method of claim 1, wherein at least one light transmitting window is asymmetrically formed in the first aperture. 8. The method of claim 3 or 7, wherein the light transmitting window is formed in a rectangular shape having different horizontal and vertical lengths. Glass substrates; And And a first and a second pattern group having different pitches spaced apart from each other by a predetermined distance on the glass substrate. 14. The mask of claim 13, wherein the first pattern group comprises a plurality of first patterns having a first pitch and arranged in parallel with each other and in the same direction. 15. The mask of claim 14, wherein the second pattern group comprises a plurality of second patterns having a second pitch and parallel to each other and arranged in the same direction. 16. The mask of claim 15, wherein the first and second patterns have the same shape. 16. The mask of claim 15, wherein the first and second pattern groups have the same arrangement. The mask of claim 16, wherein the first pattern and the second pattern have a width in a range of 0.1 μm to 0.4 μm. 16. The mask of claim 15, wherein the first and second pitches have different pitches and have pitches in the range of 0.15 탆 to 0.8 탆. 19. The mask of claim 18, wherein the first and second patterns are chromium patterns.