JPH02117149A - Reflection type photosensor for detecting wafer - Google Patents

Abstract

PURPOSE:To obtain a highly reliable reflection type photosensor for detecting wafer no matter what the thickness of a film is on the rear of a wafer by installing a flood-lighting means which applies light having two kinds or more of wavelength to a wafer. CONSTITUTION:A V-shaped groove is provided in the center of a sensor-bracket 1 and two holes are made in both slanting faces of the groove so that respective holes are made to be perpendicular to respective slanting faces. Light emitting elements 2a and 2b are disposed in each hole of one side face of the groove and photodetectors 3a and 3b are disposed in each hole of the other side face of the groove. The light emitting elements 2a and 2b project light containing different wavelengths respectively. At least either of rays of reflecting light out of the rays of light projected by the light emitting elements 2a and 2b is detected by each photodetector 3a or 3b and detecting signals are outputted from each photodetector. Further, after being amplified, the signals are outputted onto a controller. As its sensor always performs stable operations no matter what the thickness of a film is on the rear of a wafer, improper matters such as detection failure, deviation of detecting positions of the wafer and the like are avoided and highly reliable detection of the wafer is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a reflective optical sensor for wafer detection that is used in semiconductor manufacturing equipment and detects the presence or absence and position of a wafer by utilizing reflection of light.

[Prior Art] FIG. 7 is a sectional view showing the structure of a conventional reflective optical sensor for wafer detection.

The sensor bracket 21 has a V-shaped groove in the center, and the upper side of the groove is chamfered. and,
A light projecting element 22 and a light receiving element 23 are disposed in holes provided perpendicularly to the two slopes of the central groove, respectively. The light emitting element 22 and the light receiving element 23 are arranged so that the center line of the light emitted from the light emitting element 22 and the center line of the light receiving field of the light receiving element 23 intersect on the vertical center line of the groove of the sensor bracket 21. It is located. Note that in FIG. 7, lines A, B, and C all indicate the position of the back surface of the wafer.

When a wafer is present above the sensor bracket 21, the light emitted from the light projecting element 22 is irradiated onto the back surface of the wafer. A portion of this irradiated light is reflected from the back surface of the wafer and enters the light receiving element 23, where it is detected and converted into an electrical signal.

FIG. 8 is a graph showing the sensitivity characteristics of the reflective optical sensor for wafer detection, with the horizontal axis representing the wafer detection position and the vertical axis representing the output of the light receiving element 23.

As is clear from FIG. 8, when the position of the wafer changes, the output of the light receiving element 23 changes. This is because the amount of light reflected from the back surface of the wafer and reaching the light receiving element 23 differs depending on the position of the wafer. That is, when the wafer is located at the point where the center line of the light emitted from the light projecting element 22 and the center line of the light receiving field of view of the light receiving element 23 intersect (B), the output of the light receiving element is greatest; ), the output of the light receiving element 23 becomes small when the back surface of the wafer is located at a higher position (A) or a lower position (C). When the wafer moves to a position higher than (A) or lower than (C), the output of the light receiving element 23 becomes even smaller in either case, and eventually becomes below the noise level.

In this way, since the output of the light receiving element 23 differs depending on the position of the wafer, the presence or absence of the wafer and its position are detected by determining whether the output of the light receiving element 23 is above a specific level.

[Problems to be Solved by the Invention] However, conventional reflective optical sensors for detecting wafers have the disadvantage that they are prone to inconveniences such as wafer detection errors and variations in detection accuracy.

FIG. 9 shows the reflection of light in a conventional reflective optical sensor using a light emitting element 22 with a peak wavelength of 700 nm, with the horizontal axis representing the film thickness on the back surface of the wafer and the vertical axis representing the reflectance from the wafer back surface. It is a graph diagram showing characteristics. As is clear from FIG. 9, when the film thickness on the back side of the wafer is K, almost no reflected light is obtained from the back side of the wafer. In this state, the level of reflected light is buried within the noise level. Therefore, even if the detection level of the amplifier connected to the light receiving element 23 is lowered, it is not possible to distinguish between noise and a signal due to reflected light.

In this way, conventional optical sensors for wafer detection cannot obtain reflected light with sufficient intensity from the back surface of the wafer when the film thickness on the back surface of the wafer is a certain thickness. Mistakes may occur or variations in detection accuracy may occur.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a reflective optical sensor for wafer detection that always operates stably and has high reliability regardless of the film thickness on the back surface of the wafer.

[Means for Solving the Problems] A reflective optical sensor for wafer detection according to the present invention includes a light projecting means for irradiating light of two or more wavelengths toward a wafer, and a light reflected from the wafer. The present invention is characterized by comprising a light receiving means for receiving light and converting its intensity into an electric signal, and a detecting means for detecting a wafer based on the intensity of light of at least one of the wavelengths received by the light receiving means.

[Function] In the present invention, light of two or more wavelengths is irradiated toward the wafer from the light projecting means. As mentioned above, for example, 700
In the case of irradiation light having a peak wavelength of nm, when the film thickness on the back surface of the wafer is K, almost no reflected light can be obtained.

However, the reflectance becomes extremely low in this way when the film thickness on the back surface of the wafer is a specific film thickness that corresponds to the peak wavelength of the irradiated light, and this specific film thickness varies depending on the wavelength of the light that irradiates the wafer. . Therefore, when the irradiation light emitted from the light projecting means has two or more wavelengths as in the reflective optical sensor for wafer detection according to the present invention, a portion of one of the wavelengths is reflected by the back surface of the wafer. Even if there is no light, the remaining wavelength portion is reflected from the back surface of the wafer and detected by the light receiving means.
converted into an electrical signal.

In this way, by irradiating the backside of the wafer with light of two or more wavelengths, even if the amount of reflected light decreases significantly at a certain film thickness, they can compensate for each other, and the wafer can be constantly and stably illuminated. can be detected.

Note that the light having two or more wavelengths includes light that does not have a peak wavelength and has a broad wavelength band.

[Example] Next, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a plan view showing the light emitting element and light receiving element portion (sensor section) of a reflective optical sensor according to the first embodiment of the present invention, and FIG. 2 is a cross section taken along the line ■-■ in FIG. 3 are block diagrams showing the outline of this embodiment.

The sensor bracket 1 has a 7-shaped groove in the center, and the upper side of the groove is chamfered. Two holes are provided perpendicularly to each slope on both slopes of the central groove. Light projecting elements 2a and 2b are arranged in the holes on one side, and light receiving elements 3a and 3b are arranged in the holes on the other side. As shown in Figure 2,
The light emitted from the light projecting element 2a or 2b illuminates the wafer 4 at a distance X from the sensor bracket 1 at an inclination angle θ with respect to the vertical direction, and is reflected from the wafer 4 at an inclination angle θ to the light receiving element 3a or 3b, respectively. arranged to reach. The light emitting element 2a and the light receiving element 3a and the light emitting element 2b and the light receiving element 3b form a pair, respectively.The light emitting element 2a has a wavelength of 700 nm (red), and the light emitting element 2b has a wavelength of 565 nm.
It emits light with a wavelength peaking at nm (green). On the other hand, the light-receiving element 3a has high light-receiving sensitivity for light with a wavelength of 700 nm, and the light-receiving element 3b has high light-receiving sensitivity for light with a wavelength of 565 nm.

The sensor section 9 of the reflective optical sensor for wafer detection according to this embodiment has the structure described above. Note that 5 is a cord connected to the light projecting elements 2a and 2b, and 6 is a cord connected to the light receiving elements 3a and 3b. These cords 5 and 6 are connected to two amplifiers 7, as shown in FIG. The output of each amplifier 7 is input to a pair of input terminals of an OR gate 8, and the output terminal of the OR gate 8 is connected to a controller (not shown).

Next, the operation of the reflective optical sensor for wafer detection of this embodiment configured as described above will be explained.

When light with peak wavelengths of 700 nm and 565 nm is emitted from the light projecting elements 2a and 2b, the light is reflected by the back surface of the wafer 4 and has peak sensitivity wavelengths of 700 nm and 565 nm, respectively.
The light is incident on the 65 nm light receiving elements 3a and 3b.

In FIG. 4, the horizontal axis shows the film thickness on the back surface of the wafer 4, and the vertical axis shows the reflectance of the wafer back surface, and the 700 nm and 565 nm light emitted from the light projecting elements 2a and 2b used in this example are shown.
FIG. 3 is a graph diagram showing the reflection characteristics of light having a peak wavelength of m. The solid line indicates the reflectance of light having a peak wavelength of 565 nm, and the broken line indicates the reflectance of light having a peak wavelength of 700 nm. As is clear from FIG. 4, in the case of light with a peak wavelength of 565 nm, it is hardly reflected when the film thickness on the back surface of the wafer 4 is around 1, and when the film thickness is outside the vicinity of K1, the reflectance is is large. Also, the peak wavelength is 70
In the case of 0 nm light, it is hardly reflected when the film thickness on the back surface of the wafer 4 is around 2, and the reflectance is large when the film thickness is outside the vicinity of K2.

For this reason, for example, when the film thickness on the back surface of the wafer 4 is 1,
As described above, the light emitted from the light emitting element 2b is hardly reflected by the back surface of the wafer 4, and the light receiving element 3b, which is set to the normal detection level, cannot detect this light.
Even if the detection level is lowered, only noise will be detected in the end.

However, a sufficient amount of light emitted from one of the light projecting elements 2a is reflected by the film thickness of 1/2 on the back surface of the wafer. Because of this, the light receiving element 3a can detect this light at the normal detection level.

In this way, when the film thickness on the back surface of the wafer 4 is approximately 1 or 2, the reflected light of either one of the lights emitted from the light projecting elements 2a and 2b is detected by the light receiving element 3a or 3b. . A detection signal is output from the light receiving element 3a or 3b that has detected this reflected light, and after this signal is amplified by the amplifier 7, it is input to the OR gate 8. When a signal from either the light receiving element 3a or 3b is input, the OR gate 8 transmits this signal to a controller 8 (not shown).
Output to.

Next, if the film thickness on the back surface of the wafer 4 is not close to 1 or 2, the light emitted from the light projecting elements 2a and 2b is both reflected on the back surface of the wafer 4, and the light receiving elements 3a and 3 are reflected, respectively.
b. The detection signals output from each of the light receiving elements 3a and 3b are amplified by the amplifier 7 and input to the OR gate 8. The OR gate 8 calculates these detection signals and outputs them to a controller (not shown).

The sensor section 9 of this reflective optical sensor for wafer detection
If there is no wafer 4 above, none of the light emitted from the light projecting elements 2a and 2b is detected by the light receiving elements 3a and 3b, so no detection signal is input to the OR gate 8.
No detection signal is output from the OR gate 8 to the controller.

In this way, since the detection signal is always input to the controller when the wafer 4 is at the predetermined position, it is possible to reliably detect whether or not the wafer is present at the predetermined position.

As mentioned above, the reflective optical sensor for wafer detection of this embodiment always operates stably regardless of the film thickness on the back surface of the wafer, so inconveniences such as wafer detection errors and detection position deviations are avoided, and reliability is improved. It is possible to detect wafers with high accuracy.

Next, a second embodiment of the present invention will be described.

FIG. 5 is a plan view showing a second embodiment of the present invention, and FIG. 6 is a schematic configuration diagram thereof.

The sensor bracket 11 of one sensor part has almost the same shape as the first embodiment, but two light projecting elements 12a and 12b are arranged on one slope, and one light projecting element is arranged on the other slope. The difference is that only one light receiving element 13 is provided. The light projecting elements 12a and 12b are arranged at the same distance from the light receiving element 13, and the angle at which each of the light projecting elements 12a and 12b views the light receiving element 13 is λ.

The light emitting element 12a is 700 nm (red), the light emitting element 12
b emits light with a peak wavelength of 565 nm (green), and the light receiving element 13 emits light with a peak wavelength of at least 565 nm and 70 nm.
It has broad detection characteristics that can detect light in a wide range of wavelengths including 0r++++ light. And the light projecting element 12
a and 12b and the light receiving element 13 are coded 15 and 16.
is connected to one amplifier 17 by. The output of this amplifier 17 is given to a controller (not shown).

Next, the operation of this embodiment will be explained.

When the wafer 4 is on the sensor section 19 of the reflective optical sensor for wafer detection configured as described above, the light emitting element 12
The light emitted from a and 12b is reflected by the back surface of the wafer 4 and detected by the light receiving element 13, as shown by the broken line in FIG. The detection signal output from the light receiving element 13 is amplified by the amplifier 17 and output to the controller.

When the film thickness on the back surface of the wafer 4 is 1 or 2 as shown in FIG. 4, the light emitting element 12a or 12b is
The light emitted from one side is not detected because it is hardly reflected on the back surface of the wafer 4, but the light from the other side is emitted from the wafer 4.
A sufficient amount of light is reflected from the back surface and reaches the light receiving element 13.

In this way, the reflective optical sensor for wafer detection of this embodiment also has the same function as the first embodiment, regardless of the film thickness on the back surface of the wafer 4.
It always operates stably, avoids wafer detection errors and detection position deviations, and enables highly reliable wafer detection. Furthermore,
One sensor unit of this embodiment has only one light receiving element 13 with a wide detection wavelength range, so compared to the first embodiment, it is less complicated to provide an external calculation unit such as an OR gate. This has the effect of avoiding the

[Effects of the Invention] As explained above, the reflective optical sensor for wafer detection according to the present invention emits light of a plurality of different wavelengths from the light projecting means, receives these reflected lights by the light receiving means, and detects the reflected light. Since the presence or absence and position of the wafer are detected based on the intensity of light, reflected light can be stably obtained from the back surface of the wafer, the device always operates stably, and the reliability of wafer detection is extremely high.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the first embodiment of the present invention, FIG. 2 is a sectional view taken along the line ■-■ in FIG. 1, and FIG.
FIG. 4 is a graph showing the reflection characteristics of the light emitted from the light projecting element used in the first embodiment with respect to the film thickness on the back surface of the wafer, and FIG. 5 is a diagram showing the structure of the present invention. FIG. 6 is a plan view showing the second embodiment, FIG. 6 is a schematic configuration diagram thereof, FIG. 7 is a cross-sectional view showing the structure of a conventional reflective optical sensor for detecting a wafer, and FIG. FIG. 9 is a graph showing the sensitivity characteristics of the light receiving element with respect to the detection position, and FIG. 9 is a graph showing the reflection characteristics of the light emitted from the light projecting element with respect to the film thickness on the back surface of the wafer. 1.11.21; Sensor bracket, 2a, 2b, 12
a, 12b, 22; light emitting element, 3a, 3b, 13, 23
; Light receiving element, 4; Wafer, 5.6°15.16. Code, 7, 17; Amplifier, 8; Or Gate

Claims (1)

[Claims] (1) A light projecting means for irradiating light of two or more wavelengths toward a wafer, a light receiving means for receiving reflected light of the light from the wafer and converting its intensity into an electrical signal, and the light receiving means 1. A reflective optical sensor for detecting a wafer, comprising: a detection means for detecting a wafer based on the intensity of light of at least one wavelength received by the sensor.