JPH0141962B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detecting a position on the surface of an object, and particularly to a method and apparatus for detecting a position suitable when a directional pattern is formed on the surface of an object.

Conventionally, in printing equipment for printing IC, LSI patterns, etc. on the surface of semiconductor wafers, etc., in order to accurately align the wafer surface with a predetermined printing surface (predetermined plane), an optical focal position shift detection method is used. There are some that adopt One method for detecting this optical focal position shift is to irradiate a wafer, which is the surface to be inspected, with a beam of light having an elongated cross section in an oblique direction, and collect the reflected light through a vibrating slit. It has been considered to photoelectrically convert the optical signal and then detect the focal position based on the electrically processed output. This method detects how far the reflected light from the test surface is received relative to the center of vibration of the vibrating slit, thereby determining how far the test surface has shifted from a predetermined plane. It is something to know. However, in this method
It was found that the detection accuracy deteriorated due to the influence of the directionality of the IC pattern.

Here, the directionality of the IC pattern means that most of the linear patterns formed on the surface of the wafer, which is the surface to be inspected, extend in a specific direction (for example, two orthogonal directions) with respect to the wafer outline. do.

An object of the present invention is to provide an optical object surface position detection method and detection device that suppresses the influence of the directionality of an IC pattern or the like.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an object surface position detecting device applied to a focal point position detecting device for carrying out the method of the present invention, in which A is a side view thereof and B is a top view thereof. Light from a light source 1 (for example, an LED) is converted into a light beam by a condenser lens 2 and irradiated onto a slit 3 which is a long and narrow rectangle. Then, place the image 6 of slit 3 in the first position.
The image forming lens 4 is used to obliquely irradiate the wafer 5, which is the surface to be inspected. The reflected light of the slit image 6 from the wafer 5 passes through the second imaging lens 7, is reflected by the vibrating mirror 8, and is again imaged onto the elongated rectangular detection slit 9. The image 10 re-formed by the vibrating mirror 8 is swung left and right. When the wafer 5 is at the focal point, that is, at a predetermined plane which also serves as the printing surface, the center of vibration of the image 10 is arranged to exactly coincide with the position of the detection slit 9. The light of the vibrating image 10 that passes through the detection slit 9 is converted into an electrical signal by a photoelectric conversion element 11 and transmitted to a signal processing system.

A modulated output signal obtained by the photoelectric conversion element 11 is shown in FIG. A is a time when the wafer 5 is quite far from the focal position. Reimaged image 10
The center of vibration is located quite far from the detection slit 9, and therefore the amplitude of the vibration of the image 10 does not reach the detection slit 9, so no light passes through the detection slit 9, so no signal can be obtained. b is when the image 10 is located at a slightly distant position, and a part of the vibration amplitude of the image 10 passes through the detection slit 9. c is the time when the left end (or right end) of the vibration amplitude of the image 10 coincides with the left end of the detection slit 9. d is a time when the left end (or right end) of the vibration amplitude of the image 10 has passed the left end of the detection slit 9, and since the portion of light that has passed cannot pass through the detection slit 9, the modulated output signal decreases and becomes a valley. V is occurring. e
This is the case when the center of vibration of the image 10 coincides with the center of the detection slit 9, that is, when the surface of the wafer 5 coincides with the focal position (predetermined plane). f, g, h
and i correspond to d, c, b and a. Here, it should be noted that the modulated output signal e when the wafer 5 is at the focal position has a period that is 1/2 times the vibration period T of the vibrating mirror 8 (that is, the vibration period of the image 10), and This means that the period in the case of the output signal c is the same vibration period as the vibration period T.
Therefore, if the modulated output waveforms a to i are phase-detected using the reference wave of the vibration period T of the vibrating mirror 8, an output as shown in FIG. 3 can be obtained. That is, the signal e has no component of the vibration period T and the output is zero, and the signal c
The maximum value is . For focusing, the position of the wafer 5 may be adjusted so that the output becomes zero.

FIG. 4 is a circuit block diagram of the signal processing system.
After the modulated signal from the photoelectric conversion element 11 is amplified by an amplifier 41, a portion thereof is input to a peak hold circuit 42. The peak hold circuit 42 has a predetermined time attenuation coefficient and obtains a DC signal corresponding to the peak value of the modulated signal by maintaining the peak value of the modulated signal. This DC signal is input to the divider 43,
In the divider 43, the modulated signal from the amplifier 41 is divided by the DC signal from the peak hold circuit 42. As a result, the amplitude of the modulation signal from the divider 43 can be kept constant, and the AGC function can maintain a substantially constant value regardless of changes in the amount of light from the light source, the reflectance of the wafer, or the amount of passage through the detection slit. I am doing it.
Then, the modulated signal having a constant amplitude is phase-detected by the reference wave of the frequency generator T in the phase detector 44. The output of this phase detector 44 is as shown in FIG. 3, and the output becomes zero when the wafer 5 is at the focal position.

However, in such an object surface position detection method and apparatus, it is important to consider the following points. In other words, one is the directionality of the pattern on the surface of the wafer 5 and the direction in which the slit image 6 extends (the direction of the band-like distribution due to the irradiation light flux on the wafer).
The other important thing is the relationship between the direction in which the slit image 6 extends and the direction in which the displacement of the reflected image of the slit image is detected, that is, the relationship between the directionality of the pattern and the directionality of detection. . The light beam irradiated onto the wafer is a slit image, that is, its cross section is an elongated rectangle (or line). Therefore, if the pattern on the wafer is a linear pattern that matches the elongated direction of this slit image, the shape of the re-imaged image 10 will change depending on the position of the irradiation light beam on the wafer. come. That is, if the left half (or right half) in the width direction of the re-imaged slit-shaped image 10 reflected from the wafer 5 is a line of the pattern (the part that absorbs light). The slit-shaped image 10 and the detection slit 9 are parallel to each other, and the displacement detection direction of the image 10 with respect to the detection slit 9 coincides with the width direction of the image 10. Therefore, from the photoelectric conversion element 11, it is substantially rightward. produces a modulated output signal that is shifted in the direction (or left). FIG. 5 shows the output when the wafer at the focal position is moved laterally (horizontally). Originally, this output should be zero. However, the output changes depending on the irradiation position of the light beam on the wafer. This is due to the directional pattern on the wafer as described above. Generally, an IC pattern or the like includes many linear patterns in two orthogonal directions. Therefore, the direction of this striated pattern (two directions)
Assuming that φ is as shown in FIG. 1A, when the direction φ coincides with the elongated direction of the cross section of the irradiated light beam, the influence is greatest and the detection accuracy deteriorates. In addition, in this method of making the irradiation light beam obliquely incident on the surface of the wafer 5 and receiving the reflected light, the light amount distribution changes within the irradiation area of the wafer surface due to the difference in reflectance. If such a directional pattern (such as a group of linear patterns) exists, this will also cause deterioration in detection accuracy. In the apparatus of the embodiment of the present invention, the slit 3, the imaging lenses 4 and 7, and the detection slit 9 are generally arranged so that the traveling directions of the irradiated light beam and the reflected light beam are aligned in a direction different from the direction of the directional pattern. , the first
As shown in Figure A, it is turned in a direction different from the direction φ by, for example, 45 degrees. Furthermore, in the case of a linear pattern having such directional properties, the directional linear pattern can be obtained by irradiating the elongated direction of the cross section of the irradiated light beam at an angle of 45°, for example, so that it is different from the direction φ of the linear pattern. This is to suppress the negative influence of the detection accuracy on detection accuracy. That is, if an image of a long and narrow cross section intersecting the direction φ of the linear pattern is formed on the pattern (on the wafer), the reflected light is generally averaged and the influence of the irradiation position is reduced. In addition, at this time, the detection slit 9 is connected to the slit-shaped image 6 (or re-imaged image 1) on the wafer 5.
0), the displacement detection direction by the detection slit 9 also forms an angle of approximately 45° with respect to the pattern direction φ. The output obtained by irradiation according to the method of the invention is shown in FIG. As is clear from the figure, the output is maintained at approximately zero by horizontal movement of the wafer, and the extent to which the detection accuracy is degraded is improved.

The problem of detecting the focus of a surface to be inspected with a directional pattern also occurs with other optical methods. For example, in FIG. 7A, the reflected light is re-imaged on the detection slit 9' without being vibrated. When the re-imaged image 10' is placed on the detection slit 9' when the surface to be examined is in the focal position,
Since the amount of light passing through the detection slit 9' is at its maximum when the surface to be inspected is at the focal position, the maximum value is taken as the focal position. If the reflection characteristics change depending on the pattern on the surface to be inspected, an error will occur. In addition, in FIG. 7A, the photoelectric conversion element 11'' has two segments 1
It is divided into 1″a and 11″b, and the element 11″
The outputs of the segments 11''a and 11''b above and below the center are differentially extracted. If the test surface is at the focal position, the re-imaged image 10'' will be at the center of the element 11" and the differential output signal will be zero; however, if the test surface deviates from the focal position, the re-imaged image 10'' is offset from the center of element 11'', resulting in a differential output signal. In this case, too, it is similarly influenced by the pattern of the surface to be inspected. Therefore, the scope of application of the present invention is a method in which a focused light beam (imaging light beam) created by an imaging lens or the like is irradiated obliquely onto a surface to be inspected, and the focal position is detected using the reflected light. It can be generally applied to As described above, in the position detection method and apparatus of the present invention, which obliquely irradiates an imaging light beam onto the surface of an object on which a directional pattern is formed and receives the reflected light, By irradiating the beam with a band-shaped beam or detecting the displacement of the reflected beam in a direction different from the direction of the pattern, it is less susceptible to changes in reflection characteristics on the surface of a complex and fine pattern structure. Extremely accurate position detection is possible.

[Brief explanation of drawings]

1A and 1B show the configuration of a position detection device suitable for implementing the method according to the embodiment of the present invention; FIG. 2 is a diagram showing the waveform of a modulated signal obtained from the device in FIG. 1; Figure 3 is a diagram showing the output obtained by phase detection of the modulated signal, Figure 4 is a block diagram of a circuit that processes the modulated signal obtained from the device in Figure 1, and Figures 5 and 6 are The surface to be inspected is the focal position (predetermined plane)
FIG. 7A and FIG. 7B are diagrams showing the configuration of a light receiving system of a position detection method according to another embodiment. [Explanation of symbols of main parts], 1...Light source, 5...
...Test surface (wafer), 6...Light beam of elongated cross section,
7...Imaging lens, 8...Vibrating mirror, 9...Slit.

Claims (1)

[Claims] 1. A method of obliquely irradiating a focused light beam onto the surface of an object on which a pattern having a predetermined directionality is formed, receiving the reflected light from the object surface, and changing the light receiving position according to the change in the light receiving position. A method of generating a changing electric signal and detecting the position of the object surface with respect to a predetermined plane based on the electric signal, the method comprising: changing the shape of the light beam irradiating the object surface on the object surface according to a predetermined plane of the pattern. A method for detecting the surface position of an object characterized by forming a long and thin strip in a direction different from the direction of the object. 2 The patterns on the object surface are orthogonal to each other 2
Claim 1, characterized in that when the object includes many linear patterns extending in the direction, the belt-like direction of the irradiation light beam on the object surface is set in a direction different from either of the two directions of the linear patterns. The method described in section. 3. Claims characterized in that when the reflected light from the surface of the object is received and the change in the light receiving position is detected, the direction in which the change in the light receiving position is detected is different from the predetermined direction of the pattern. The method according to item 1 or 2. 4 A focused beam of light is irradiated obliquely onto the surface of an object on which a pattern with predetermined directionality is formed, and the reflected beam of light from the surface of the object is received to generate an electrical signal that changes according to changes in the receiving position. A method for detecting the position of the object surface with respect to a predetermined plane based on the electric signal, wherein the direction in which a change in the receiving position of the reflected light beam is detected is the direction of the pattern when viewed on the object surface. A method for detecting the surface position of an object, characterized in that: 5 The patterns on the object surface are orthogonal to each other 2
Claim 4, characterized in that when a linear pattern includes a large number of linear patterns extending in a direction, the direction in which the change in the light receiving position is detected is set to a direction different from either of the two directions of the linear pattern. Method described. 6. A device for detecting the position of a surface of an object on which a pattern having a predetermined directionality is formed with respect to a predetermined plane, comprising: converting light from a light source into an imaging light beam obliquely incident on the surface of the object; a first imaging optical system having an optical axis arranged in a direction different from the predetermined direction of the pattern when viewed from above; a second imaging optical system having an optical axis arranged in substantially the same direction as the optical axis of the first imaging optical system when viewed on the object surface; a photoelectric detection means for outputting an electric signal corresponding to a change in the light receiving position of the light beam on the predetermined detection surface; What is claimed is: 1. A surface position detection device for an object, comprising: a beam shaping member that shapes a beam into a band shape extending in a direction, and detects a position of the object surface with respect to a predetermined plane based on the electric signal. 7 The patterns on the object surface are orthogonal to each other 2
When the first imaging optical system includes many filament patterns extending in the direction, the optical axis direction of the first imaging optical system on the object surface is set in a direction different from either of the two directions of the filament pattern, and the light beam 7. The device according to claim 6, wherein the band-like direction of the imaging light beam shaped by the shaping member on the object surface is set in a direction different from either of the two directions of the linear pattern. .