JPS63142651A - Suction detector for substrate - Google Patents

Abstract

PURPOSE:To eliminate the erroneous detection due to a complicated pipe line and a change in the original pressure, to eliminate the erroneous detection due to a dust particle between a substrate and a substrate chuck and, at the same time, to remove the erroneous detection due to a change in the atmospheric pressure by a method wherein, before the substrate is sucked, a slice level to judge a suction state is set by a means to store a pressure value of the air pressure. CONSTITUTION:When a wafer does not exist, a vacuum ON/OFF signal g is set to an ON state 41 and the air pressure inside wafer chucks 2, 3 is lowered to the original pressure. At this stage, a value 42 of an output signal b of pressure sensors 4, 5 is taken into a sample- and-hold amplifier 9 and is stored there. Then, after the air pressure inside the wafer chucks 2, 3 has been restored to the atmospheric pressure and the wafer has been mounted, the air pressure is set again to the original pressure. During this process, the output signal b of the pressure sensors 4, 5 is stabilized at a fixed level 44. This output 44 from the sensor is compared with a slice level d by means of comparators 15, 16 so as to obtain a comparator output h. This comparator output h is read out by a wafer-suction-detecting signal j at the prescribed timing, and the suction rate is judged. For this process, a shift volume 46 is selected in such a way that its level does not cause a shift in the position of the wafer when the wafer is sucked by the wafer chucks 2, 3. By this method, it is possible to eliminate the erroneous detection due to the insufficient suction of the wafer.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a substrate suction detection device, for example, a device for transferring a wafer to a wafer in semiconductor manufacturing equipment, etc., particularly for detecting a wafer by using negative pressure of air. The present invention relates to a detection device that is applied to a device that transports a wafer using a wafer chuck or the like to determine whether or not a wafer is attracted to the wafer chuck.

[Prior art] Conventionally, in order to determine whether a substrate such as a wafer has been attracted to a wafer chuck, etc., the pressure difference between the source pressure of the exhaust system and the pressure at the measurement point (near the suction port of the wafer chuck) has been compared. One type of device (hereinafter referred to as device aA) determines the adsorption state by comparing the absolute pressure at a measuring point with a preset reference value (hereinafter referred to as device B). ).

[Problems to be Solved by the Invention] However, these devices have the following drawbacks.

First, device A requires piping to guide air pressure from two locations, the source pressure of the exhaust system and the measurement points, to the sensor, and has the drawback that the piping becomes complicated as the number of measurement points increases.

FIG. 3 shows a timing chart of various signals in a conventionally used device A, that is, a wafer suction detection device using a differential pressure sensor. In the figure, adsorption or detachment of the wafer is confirmed by comparing the slice level d' shifted by a predetermined value 51 from the source pressure e of the exhaust system with the pressure sensor b', and by the comparator output h' that is the result. . The pressure sensor is attached to a measurement point near the suction port of the wafer chuck.

In this case, a slice level d' for determining the adsorption state is set based on the source pressure e. Therefore, if the source pressure e fluctuates, it will directly affect the slice level d', so the comparator output h' may become a solid line as shown in the range 53 in Fig. In some cases, a signal indicating that the device is still attached may be output, resulting in false detection.

On the other hand, in device B, there is no complication due to piping, but as shown in FIG. 4, the slice level d' for determining the adsorption state is set by shifting by a constant value 54 with respect to atmospheric pressure a. Therefore, if the pressure sensor output b'' fluctuates due to fluctuations in the source pressure e, a signal indicating that the wafer is not suctioned even though it has been suctioned, such as in the range of 56, is output, resulting in false detection. It had the disadvantage of causing

Furthermore, as a common drawback of apparatus A and apparatus B, air leakage due to dust that has entered between the wafer and the wafer chuck causes the sensor output b' or b'' in Fig. 3 or 4 to become a one-point mirror line. In this case, an erroneous detection occurs that the wafer is not attracted to the wafer chuck even though the wafer is attracted to the wafer chuck in the interval indicated by 52 or 55.

The purpose of the present invention is to solve the problems in the conventional example described above.
In a substrate adsorption detection device that detects whether or not a substrate such as a wafer is adsorbed to a substrate chuck using air pressure, there are problems such as complicated piping, false detection due to fluctuations in source pressure, and problems between substrates and substrates. The objective is to eliminate false detections due to dust between the chucks, and at the same time eliminate false detections due to atmospheric pressure fluctuations.

[Means and effects for solving the problems] In order to achieve the above object, the present invention uses a means for storing the pressure value of air pressure such as an analog memory function, and uses a means for storing the pressure value of the air pressure, such as an analog memory function, to The feature is that a slice level is set to determine whether or not a state exists.

For example, in semiconductor manufacturing equipment that utilizes air pressure to adsorb wafers onto wafer chucks and transport them, pneumatic pressure is applied to a circuit that determines whether or not a wafer is mounted and adsorbed on the surface of the wafer chuck. This analog memory function is used to set the slice level to determine whether or not the wafer is in a suction state before suctioning the wafer to the wafer chuck. .

[Description of Examples] Hereinafter, the present invention will be described based on Examples using the drawings.

FIG. 1 is a block diagram of an apparatus for detecting adsorption to sea urchins according to an embodiment of the present invention.

In the figure, 1 is a control unit for controlling the source pressure of the exhaust system to be within a certain range, 2.3 is a wafer chuck for mounting and adsorbing a wafer, and 4 and 5 are wafer chucks for wafers. 2.3 is a pressure sensor for determining whether it is adsorbed or detached. Reference numeral 6 indicates piping to the wafer chuck 2.3, and the piping portion is drawn thinly to show that the source pressure is attenuated in the wafer chuck 3 disposed far from the source pressure portion.

7.8 is a buffer amplifier for sending the output signal from the pressure sensor 4.5 to the comparator 15.16, and 9.10 is a reference for determining whether or not the wafer is attracted to the wafer chuck 2.3. Naru Sly.

This is a sample/hold amplifier for creating sound levels. 11.12 is sample/hold amplifier 9
, 10 is a constant voltage element that subtracts a constant voltage from the hold output signal generated by the urchin, and creates a slice level for determining whether the sea urchin is attracted to the sea urchin or not.
13 and 14 are bias resistors for this purpose. 15.1
6 compares the slice level created by the sample/hold amplifier 9.10 and constant voltage element 11.12 with the outputs of the pressure sensors 4 and 5 outputted via the buffer amplifier 7.8. This is a comparator for determining the adsorption state or detachment state of.

17 and 18 are sample/hold pulse signals, 19°2
0 is a detection pulse signal for checking whether the wafer is attracted or detached. 21.22 is comparator 15
．． 16, which indicates the adsorption or detachment state compared to the slice level.

FIG. 2 shows a timing chart of various signals in the apparatus of this embodiment. Note that the signals a-=11 in the figure are signals at the positions indicated by the same symbols in FIG. 1, respectively.

In FIG. 2, a indicates atmospheric pressure, which is indicated by a thick line. b is the sensor output signal from the pressure sensor 4.5 via the buffer amplifier 7.8 in FIG.
This is the hold output signal stored at zero. d is a constant voltage 4 from the hold output signal C by constant voltage elements 11 and 12.
The signal obtained by subtracting 6 is the slice level for comparison with the sensor output. e is a signal indicating the source pressure supplied from the control section 1. In the case of this device, the source pressure is for adsorbing the wafer, so it is a negative pressure. Also,
The range indicated by 31 indicates the controllable range of the source pressure.

f is a signal indicating whether or not the wafer is mounted on the wafer chuck 2.3; a high level of 32 indicates a mounted state, and a low level of 33 indicates a detached state. g is a signal to switch the air pressure inside the wafer chuck 2.3 to the atmospheric pressure side or the original pressure side in order to attract the wafer to the wafer chuck 2.3, and the high level on the 34 side turns on the vacuum. The low level on the 35 side is the signal that turns off the vacuum and returns the pressure to atmospheric pressure. h is an output signal obtained by comparing the sensor outputs at the slice level d; 36 indicates the wafer adsorption state, and 37 indicates the detachment state. 38 is wafer chuck 2.3
This is a range that indicates that the pressure has reached such a level that even if the person leaves the quest, it will not have a negative impact on the quest, such as causing damage. Also, the signal f
The moment when the wafer changes from the attachment state 32 to the detachment state 33 is the moment when the wafer actually leaves the wafer chuck 2.3.

i is a sample for sampling the output from the pressure sensors 4 and 5 in 39 sampling periods in order to set the slice level d, and storing the value 42 of the output signal of the pressure sensor 4.5 at that time. /Hold signal.

During the hold period 40 of the sample/hold signal i,
A sampled value 42 is output as a hold output signal C. The pressure sensor output value 42 at this time is an output signal when the wafer chuck 2.3 is not attached to the wafer chuck, and differs depending on each wafer chuck. For example, regarding the wafer chucks 2 and 3 in FIG. 1, the sensor output value 43 on the wafer chuck 3 is higher than the sensor output value 42 on the wafer chuck 2, such as 43 on the wafer chuck 3 side and 42 on the wafer chuck 2 side. will be smaller.

j is a wafer adsorption detection signal for determining whether the wafer is adsorbed to the wafer chuck 2.3, and k is a signal for confirming whether the wafer is in a state where it can be removed from the wafer chuck. , l are signals for detecting whether or not the wafer has been released from the wafer chuck 2.3.

The operation of the apparatus of the embodiment shown in FIG. 1 will be described below with reference to the timing chart of FIG. 2.

First, with no wafer on the wafer chucks 2 and 3, the vacuum on/off signal g is turned on 41, thereby lowering the air pressure inside the wafer chuck 2.3 to the original pressure side. Then, the value 42 of the output signal of the pressure sensor 4.5 at this time is taken in and stored in the sample/hold amplifier 9 as the sample/hold signal i. After that, once the pressure inside the wafer chuck 2.3 is returned to atmospheric pressure and the wafer is mounted on the wafer chuck 2.3 (the signal f is set to the mounting state 32), the inside of the wafer chucks 2 and 3 is changed to the source pressure side again. Make it atmospheric pressure. At this time, the output signals of the pressure sensors 4 and 5 exhibit transient characteristics as shown in the figure, and settle down to a constant level 44. At this time, the level 44 may have dust attached to the wafer chucks 2 and 3, causing air leakage, resulting in an error such as 45.

Comparator 15.
16, and a comparator output is obtained as a result. This comparator output is read at a certain timing as the wafer suction detection signal j, and the suction state is determined. The level changed by the constant voltage element 11.12 to create the slice level d, that is, the shift amount 46, is the level that changes when the wafer is attracted to the wafer chuck 2.3.
．． The level is selected so that the wafer does not shift (fixed) even if 3 moves. This is the key point of the present invention, and by doing this, it is possible to falsely detect insufficient wafer suction due to attenuation caused by the piping system (the magnitude of the output value 42 in Figure 2) and air leakage due to dust, etc. is removed.

Further, as can be seen from FIG. 2, since the slice level is set based on the sensor output of 42, the influence of fluctuations in atmospheric pressure a can also be removed.

When removing the wafer from the wafer chucks 2 and 3,
First, turn on the vacuum on/off signal g to wafer chuck 2.
．． Return the pressure inside 3 to atmospheric pressure.

When detaching the wafer, the wafer detachment confirmation signal k is used to check whether the pressure inside the wafer chuck 2.3 has reached a level that will not damage the wafer even if the wafer is detached, and the pressure has reached such a level that the wafer can be detached. If the wafer is attached, the wafer is detached using the wafer attachment signal f. After the detachment operation is completed, the atmospheric pressure inside the wafer chucks 2 and 3 is set to the original pressure side again using the signal g, and a wafer detachment detection signal l is sent to determine whether the wafer has detached from the wafer chuck 2.3.
Judgment will be made.

In the above embodiment, the slice level d for the sensor output is set by the sample/hold amplifier 9. It was created using hardware using lO and constant voltage elements 11 and 12, but the sensor output value 42 was changed to A by software.
/D converter, then read the preset value for the measurement point (46 in Figure 2) from the software memory, perform calculations in the software, and calculate the slice level d. Another possible method is to perform the calculation.

Regarding wafer detachment, when checking whether or not wafer detachment is possible using the wafer detachment possible confirmation signal k, the value of the sensor output at this time is stored again in the same sample/hold amplifier. When determining whether or not the wafer has been detached based on the wafer detachment detection signal being raised, it is possible to detect the wafer detachment more reliably by using a method in which the wafer is occasionally adsorbed. Also, this can be done by software as described above.

[Effects of the Invention] As explained above, according to the present invention, by adding a simple function of storing the output value from the pressure sensor using hardware or software, it is possible to achieve this without complicating the piping.
It is now possible to accurately detect wafers even when there are fluctuations in source pressure, atmospheric pressure, and air leaks.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the present invention; Fig. 2 is a timing chart; Fig. 3 is a timing chart of a conventionally used differential pressure sensor; Fig. 4 is a timing chart of an absolute pressure sensor. . 2.3: Wafer chuck, 4.5: Pressure sensor, 9.1
0: Sample/hold amplifier, 15.18: Comparator, b, b', b'': Pressure sensor output, d, d', d
″ slice level, h, h', h': comparator output, i: sample/hold signal,

Claims (1)

[Claims] 1. Means for attracting the substrate to the substrate chuck using air pressure, means for detecting the pressure value of the air pressure, and memory for detecting and storing the pressure value before adsorbing the substrate to the substrate chuck. a means for calculating a slice level for determining whether or not the adsorption state is present based on the stored pressure value; and a means for comparing the pressure value of the air pressure detected by the detection means with the slice level. A substrate adsorption detection device comprising means for determining whether or not a substrate is adsorbed to the substrate chuck. 2. The substrate adsorption detection device according to claim 1, wherein the memory means is an analog memory. 3. The substrate suction detection device according to claim 1 or 2, wherein the slice level calculation means obtains the slice level by shifting the stored pressure value by a predetermined amount.