JPH0556014B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a reduction projection exposure apparatus that performs reduction exposure of a reticle image onto a semiconductor wafer in the process of manufacturing a semiconductor device.

(Prior Art) In this type of conventional reduction projection exposure apparatus, the inclinations of the reticle surface and the stage for mounting the wafer with respect to the main axis of the optical system are fixed during the period when at least one semiconductor wafer is exposed. was.

By the way, the wafer surface is locally uneven;
Currently, we must be prepared for a height difference of 3 μm within a 10 mm square area. Moreover, in consideration of field curvature and unevenness of the element surface when the wafer is in the middle of the process, the focus margin of the optical system is required to be 4 μm or more. However, if the resolution is further increased in the future, the focus margin will decrease and it will no longer be possible to obtain a sufficient focus margin. For example, NA (numerical aperture)
If you try to resolve 0.8 μm with a 0.4 lens, the focus margin will be less than 3 μm. In this case, there is a problem in that the current flatness of the wafer surface significantly reduces the accuracy of pattern transfer. Therefore, conventionally it has been difficult to increase the resolution.

In order to solve this problem, Japanese Patent Application No. 61-315367 discloses that a laser beam is irradiated onto the scribe line of the wafer, and the local tilt of the wafer surface is detected from the angle of the reflected light. Techniques are described for controlling the tilt of a wafer stage or reticle based on the results. In this way, even if an optical system with a narrow focus lens is used, highly accurate pattern transfer can be performed, and resolution can be improved.

However, in the tilt detection described in the above specification, in order to accurately detect the local tilt of the wafer surface, it is necessary to accurately irradiate a narrow aperture scribe line with laser light. This is because if the laser beam is projected onto the wafer surface without focusing, and if the wafer chip surface is uneven during the manufacturing process, a large amount of scattered light will be generated in addition to the reflected light. This is because the accuracy of detecting the inclination decreases. Therefore, in order to accurately detect the local inclination of the wafer surface, a very high-precision optical system is required, leading to a problem of increased costs.

(Problems to be solved by the invention) This invention was made in view of the above-mentioned circumstances.
It is now possible to accurately detect the local tilt of the wafer surface without being affected by scattered light due to unevenness on the wafer chip surface, without having to accurately project the laser beam only within the scribe line as in the past. It is an object of the present invention to provide a reduction projection exposure apparatus that is inexpensive and has high precision in pattern transfer.

[Structure of the Invention] (Means for Solving the Problems) In the reduction projection exposure apparatus according to the present invention,
A wafer surface local tilt detection unit that irradiates a diffraction pattern formed in an exposure area on a semiconductor wafer surface with laser light and detects the tilt of the exposure area with respect to the main axis of the optical system from the angle of the diffracted light; , and a fine movement section that tilts at least one of the wafer stage or the reticle with respect to the main axis of the optical system so as to correct the detected tilt.

(Function) In the reduction projection exposure apparatus having the above configuration, since the inclination of the exposure area is detected based on the angle of the diffracted light generated from the diffraction pattern, even if the chip body is irradiated with laser light, the chip surface The tilt can be detected without being affected by scattered light caused by the unevenness of the surface. Therefore, there is no need to focus the laser beam narrowly, the configuration of the optical system for detecting the tilt can be simplified, and an inexpensive reduction projection exposure apparatus with high precision in pattern transfer can be obtained.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an apparatus for performing reduction projection of, for example, 5:1, in which 1 is a light source system, 2 is a projection lens system,
3 is the main axis of the optical system, 4 is a reticle, 5 is a reticle fine movement unit for supporting the reticle and finely adjusting the inclination with respect to the main axis 3, 6 is a semiconductor wafer, and 7 is the wafer stage on which the wafer 6 is placed. A stage fine movement unit 8 is used to finely adjust the inclination with respect to the main axis 3, and a wafer surface local inclination detection unit 8 is used to detect a local inclination of the wafer surface (with respect to the main axis 3).

The wafer surface local tilt detection unit 8 is configured to irradiate a laser beam onto a diffraction pattern formed by unevenness formed in advance on an exposure area of the wafer surface, and to detect the local tilt of the wafer surface from the angle of the diffracted light. ing.

Next, with reference to FIG. 2, the principle of detection of the tilt detecting section 8 using diffracted light will be explained.

First, a laser beam 10 is irradiated onto a diffraction pattern 11 on the wafer from directly above the wafer 6 placed on the stage fine movement section 7 to generate diffracted beams 12 and 13.
Then, the local tilt of the wafer surface is detected from the diffraction angle θ.

When the local tilt angle of the wafer surface is α, the following relationship holds between the tilt angle α and the diffraction angle θ: −Sin(α)+Sin(θ−α)=nλ/d.

Here, the tilt angle α and the diffraction angle θ are each in radian units, λ is the wavelength of the laser beam, d is the pitch of the diffraction pattern, and n is the order of diffraction.

Considering that the tilt angle α is small, the above equation can be approximated as −α+{Sin(θ)−α・Cos(θ)}=nλ/d, and the tilt angle α is α=Sin(θ) −(nλ/d)/Cos(θ)+1.

FIG. 3 shows an example of a diffraction pattern due to unevenness formed on the scribe line 11 of the wafer 6. Figure 3 A is 2μm pitch, 1μm wide, 1μm apart.
In this case, for example, if a laser beam with a wavelength λ=1 μm is used, the diffraction angle θ will be about 30°. Since this diffraction pattern has a very narrow pitch, a similar pattern is rarely formed within the chip body, so accurate tilt detection can be performed without narrowing down the laser beam as in the conventional case. However, in some cases, similar patterns may be formed within the chip body, so in order to further improve the reliability of tilt detection, it is necessary to create an area around the chip that prohibits the formation of similar patterns. Alternatively, it is better to narrow down the laser beam to approximately the width of the scribe line so that diffracted light is not generated from similar patterns formed within the main body.

Figure 3B shows a band-shaped diffraction pattern tilted by an angle β with respect to the length direction of the scribe line 11. If the angle is set to a certain angle (for example, 25° or 75°), there is no need to narrow down the laser beam, and tilt detection can be performed more easily. If it is difficult to form a diffraction pattern at such an angle on the scribe line, the angle may be approximated by a step-like pattern as shown in FIG. 3C.

Figure 3D shows a diffraction pattern formed in the form of a dot matrix.Diffraction light is generated in both the X and Y directions of the wafer surface, so the diffraction pattern is formed in a dot matrix shape. and Y
Directional inclinations can be detected at the same time.

To detect the diffracted light generated from such a diffraction pattern, for example, a CCD arranged two-dimensionally is used.
An optical sensor consisting of: Furthermore, when using the diffraction pattern shown in FIG. 3D, detection can be performed by providing one-dimensional sensors in the X direction and Y direction, without using such a two-dimensional optical sensor. be able to.

Note that the diffraction pattern shown in Figure 3 does not necessarily have to be formed on the scribe line, but may be formed on a part of the chip body, but in this case, the area for the regular circuit formed inside the chip is limited. You need to be careful about limiting it.

As described above, since the tilt detection section 8 in the reduction projection exposure apparatus of the present invention detects the tilt using the diffracted light generated from the diffraction pattern caused by the unevenness, it is not affected by the scattered light due to the unevenness on the surface of the chip body. This eliminates the need for accurate tilt detection without narrowing down the laser beam.

Further, the reticle fine movement section 5 is configured to support a support base that supports the reticle 4 by a piezoelectric element, and to apply a control voltage given by the wafer surface local tilt detection section 8 to this piezoelectric element. . Similarly, the stage fine movement section 7 is configured to support the stage support base with a voltage element and apply a control voltage given by the detection section 8 to this voltage element.

Next, the usage and operation of the reduction projection exposure apparatus configured as described above will be explained. First, the wafer 6 is moved to a predetermined position by a normal alignment mechanism (not shown), and then the tilt detector 8 detects the tilt of the wafer surface for an exposure area, for example, one chip. Next, at least one of the reticle 4 and the wafer stage is tilted so as to correct the tilt detected in this manner. That is, when only the wafer stage is to be tilted, the wafer stage is tilted by the stage fine movement section 7 by the same magnitude as the above-mentioned detected tilt. On the other hand, when only the reticle 4 is tilted, this example performs a 1/5 reduction projection, so 5 of the detected wafer surface tilt is used.
It is necessary to tilt the reticle 4 by a factor of 10 times (10 times in the case of 1/10 reduction projection) using the reticle fine movement section 5. Note that the inclination may be corrected by a combination of fine movement of the reticle 4 and fine movement of the wafer stage.

Therefore, by correcting the inclination of the exposure area as described above before exposing the exposure area of the wafer surface, it is possible to transfer a highly accurate pattern onto the wafer surface with this correction made. become.

After adjusting the inclination in this way, the pattern is transferred from the light source system 1 to the corresponding chip via the reticle 4.

In the above embodiment, the fine movement parts 5 and 7 are provided for each of the reticle and the wafer stage, but as long as the fine movement part is provided for at least one, there is no need to provide a tilt correction mechanism for the other. There is no problem.

Also, here we have explained the case where detection and pattern transfer are repeated for each chip.
It is also possible to first detect the inclination of each chip over the entire wafer, and then adjust the inclination of each chip based on the detection results to transfer the pattern.

Furthermore, the diffraction pattern does not necessarily have to be formed by concavities and convexities; for example, after forming concavities and convexities, a material different from that of the wafer is filled in the concavities to form a diffraction pattern with a flat surface. It is also possible to obtain light.

[Effects of the Invention] As described above, according to the present invention, the local tilt of the wafer surface can be accurately detected without narrowing the laser beam to a narrower width than the width of the scribe line. can be easily done. Therefore, a reduction projection exposure apparatus capable of highly accurate pattern transfer can be manufactured at a relatively low cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the overall configuration of a reduction projection exposure apparatus according to an example of the present invention, and FIG. 2 is for explaining the principle of detecting a tilt of a wafer surface local tilt detecting section provided in the apparatus of FIG. and FIG. 3 are diagrams showing examples of diffraction patterns used for tilt detection. 3...Main axis of optical system, 4...Reticle, 5...
Reticle fine movement section, 6... Wafer, 7... Stage fine movement section, 8... Wafer surface local tilt detection section.

Claims (1)

[Claims] 1. Laser light is irradiated onto a diffraction pattern consisting of a plurality of strip patterns or dot patterns regularly arranged close to each other in an exposure area on a semiconductor wafer surface, and the diffraction light is A wafer surface local tilt detection section that detects the tilt of the exposure area with respect to the main axis of the optical system based on the angle; and a wafer surface local tilt detection section that detects the tilt of the exposure area with respect to the main axis of the optical system; 1. A reduction projection exposure apparatus, comprising: a fine movement section that tilts against the surface of the image. 2. The reduction projection exposure apparatus according to claim 1, wherein the diffraction pattern is arranged on a scribe line formed on the surface of the semiconductor wafer. 3. According to claim 1, each of the plurality of band-shaped patterns constituting the diffraction pattern is arranged obliquely with respect to a scribe line formed on the surface of the semiconductor wafer. reduction projection exposure equipment. 4. The reduction projection exposure apparatus according to claim 3, wherein each of the plurality of strip patterns has a stepped shape. 5. The reduction projection exposure apparatus according to claim 1, wherein the plurality of dot-like patterns constituting the diffraction pattern are arranged in a matrix. 6. Laser light is irradiated onto a diffraction pattern consisting of a plurality of band-like patterns or dot-like patterns regularly arranged close to each other in the exposure area of the semiconductor wafer surface, and the main axis of the optical system is determined from the angle of the diffracted light. Detecting the inclination of the exposure area with respect to the main axis of the optical system, and adjusting the inclination of the exposure area by tilting at least one of the wafer stage or the reticle with respect to the main axis of the optical system according to the detection result, so as to correct the detected inclination. , A reduction projection exposure method characterized in that exposure is performed on a semiconductor wafer surface whose inclination has been adjusted. 7. The reduction projection exposure method according to claim 6, wherein the diffraction pattern is arranged on a scribe line formed on the surface of the semiconductor wafer. 8. Claim 6, wherein each of the plurality of band-shaped patterns constituting the diffraction pattern is arranged obliquely with respect to a scribe line formed on the semiconductor wafer surface. reduction projection exposure method. 9. The reduction projection exposure method according to claim 8, wherein each of the plurality of strip patterns has a stepped shape. 10. The reduction projection exposure method according to claim 6, wherein the plurality of dot-like patterns constituting the diffraction pattern are arranged in a matrix.