JP2880262B2 - Wafer holding device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer holding apparatus for performing ultra-fine processing of a wafer and using synchrotron radiation as a light source.

[Conventional technology]

In a semiconductor manufacturing apparatus, as a wafer holding device for transferring a mask pattern onto a wafer, a vacuum suction type wafer holding device (for example, Japanese Patent Publication No. 1-14703) that vacuum-suctions and holds the back surface of the wafer is often used. Used.

5 (A) and 5 (B) are diagrams each showing an example of a vacuum suction type wafer holding device.

This vacuum suction type wafer holding device is configured to hold a wafer (not shown) by suctioning a back surface of the wafer by vacuum suction.
1 and an exhaust pump 406 for vacuum-sucking the wafer
A pipe 404 connecting the exhaust pump 406 and a suction pipe 408 described later; a valve 407 provided between the exhaust pump 406 of the pipe 404 and the holding base 401; a valve 407 of the pipe 404 and the holding base 401 Between the pressure in the pipe 404 and the pressure of the outside air introduced from the introduction pipe 411 (hereinafter referred to as “outside pressure”).
Called. A pressure sensor 405 for detecting the pressure difference between
When the output signal of the pressure sensor 405 confirms that the differential pressure indicated by the output signal has become larger than a predetermined value,
And a control circuit 410 for outputting an instruction signal for proceeding to the next step (for example, an instruction signal for proceeding the vacuum suction type wafer holding device to a wafer exposure position).

Here, the holding table 401 has a suction surface 402 which is flat-finished to maintain the flatness of the vacuum-sucked wafer.
If provided one by one and two each of four in the grooves 409 _1, 409 ₂ concentric engraved on the suction surface 402 in the center of the suction surface 402 (FIG. 4 (A) shown vertically and horizontally) Suction port
403, and a suction pipe 408 connecting each suction port 403 and the pipe 404. The valve 407 communicates the inside of the pipe 404 with the external space when closed, and the pipe 4 when opened.
04 and the exhaust pump 406 are communicated.

In this vacuum suction type wafer holding device, the wafer to be vacuum-sucked is transferred to a position where it comes into contact with the suction surface 402 of the holding table 401 by a known transfer hand (not shown). Thereafter, the valve 407 is opened, two concentric grooves 409 ₁ engraved on the suction surface 402 and suction surface 402 and the wafer that has been the transfer, 409 ₂ and a space formed by (hereinafter, "closed Space "). The gas inside is exhausted by the exhaust pump 406 through the respective suction ports 403, the suction pipe 408, and the pipe 404, so that the back surface of the wafer is vacuum-adsorbed. At this time, the pressure sensor 405 detects a pressure difference between the pressure in the pipe 404 and the outside air pressure, and outputs a signal indicating the pressure difference to the control circuit 410.
Output to The control circuit 410 outputs the instruction signal when confirming that the differential pressure indicated by the output signal of the pressure sensor 405 has become larger than a predetermined value.

On the other hand, when releasing the vacuum suction of the wafer, the valve 407 is closed, and outside air is sent into the pipe 404.

[Problems to be solved by the invention]

However, in the above-mentioned vacuum suction type wafer holding apparatus, since the mounting position of the pressure sensor 405 is between the valve 407 of the pipe 404 and the holding table 401, the exposure using a currently used deep ultraviolet light or the like as a light source. X-ray exposure apparatus using synchrotron radiation as a light source (for example, Japanese Patent Application No. 63-252991), although there is no problem with the fine processing performed by the apparatus.
In the case of performing ultra-fine processing on the wafer using
For the following reasons, a new problem has arisen in that the yield and the productivity are reduced.

(1) The pressure in the pipe 404 detected by the pressure sensor 405 differs from the pressure in the closed space because the structures of the pipe 404 and the suction pipe 408 are actually complicated.

(2) Since the differential pressure differs depending on the atmosphere in the space where the vacuum suction type wafer holding device is placed and the state of the back surface of the wafer, it is very difficult to obtain the differential pressure with high accuracy. It is not easy to accurately estimate the pressure in the closed space from the differential pressure detected by the pressure sensor 405.

(3) Because it is not easy to accurately estimate the pressure in the closed space for the above reason, the process must proceed to the next step after the differential pressure detected by the pressure sensor 405 becomes sufficiently small. The maximum suction force becomes excessive, causing a slight distortion on the wafer that is being vacuum-sucked. However, when ultra-fine processing is performed on the wafer, even a slight distortion generated on the wafer causes deterioration in pattern transfer accuracy. This leads to a decrease in yield. Further, there is a problem that extra time is required for the wafer suction operation, which causes a reduction in productivity.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wafer holding apparatus capable of improving yield and productivity at the time of ultrafine processing by sucking a wafer with a minimum suction time and an optimum suction force and then proceeding to the next step. Is to provide.

[Means for solving the problem]

A wafer holding device according to the present invention is a holding device provided with a holding table for holding a wafer on a suction surface by vacuum, wherein a suction tube formed on the holding table for supplying a vacuum to the suction surface; A pressure sensor provided in the holding table for detecting pressure information in the pipe or in the closed space of the suction surface.

In addition, it has an introduction pipe formed in the holding table for introducing outside air around the holding table, and the pressure sensor has a pressure of the suction pipe or the suction surface, and an external pressure around the holding table. Is to detect the differential pressure.

In addition, the apparatus has a timer for measuring a time during which vacuum is supplied to the absorption tube, and has means for detecting an abnormality based on each data of the time measured by the timer and the differential pressure output by the pressure sensor. It is.

Further, the wafer is exposed by X-rays.

[Operation] In the wafer holding apparatus of the present invention, since the pressure sensor detects the pressure in the suction pipe or in the closed space of the suction surface,
The pressure on the back surface of the wafer can be detected with high accuracy irrespective of the atmosphere in the space where the wafer holding device is installed and the state of the back surface of the wafer that is vacuum-adsorbed.

Further, the pressure sensor directly detects the pressure in the closed space of the suction tube or the suction surface by detecting a pressure difference between the pressure in the closed space of the suction tube or the suction surface and the external pressure around the holding table. Even if the outside air pressure near the holding table changes,
The difference between the pressure on the front surface and the pressure on the back surface of the wafer can be accurately detected.

In addition, the difference between the pressure on the front surface of the wafer and the pressure on the back surface can be set to an optimum value by means for detecting an abnormality based on the data measured by the timer and the differential pressure output by the pressure sensor. In addition, since the wafer is suctioned with the optimum suction force, the distortion of the wafer can be minimized, and the wafer can be vacuum-adsorbed in a minimum suction time.

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

FIGS. 1A and 1B are views showing a first embodiment of the wafer holding device of the present invention.

The wafer holding device of the present embodiment includes a holding table 1 for holding a wafer (not shown) by vacuum-sucking the back surface thereof;
An exhaust pump 6 for vacuum-sucking the wafer, a pipe 4 connecting the exhaust pump 6 and a suction pipe 8 described later, a valve 7 provided between the exhaust pump 6 of the pipe 4 and the holding table 1, The holding table 1 has a suction surface 2 which is flat-finished to maintain the flatness of the wafer after vacuum suction.
And four in each of _two concentric grooves 91 and 92 formed in the center of the suction surface 2 and two concentric grooves 9 ₁ and 92 formed in the suction surface 2 (FIG. 1 (A), top and bottom, left and right in FIG. 1A). This is the same as the vacuum suction type wafer holding device shown in FIG. 5 in that a suction port 3 and a suction pipe 8 connected to each suction port 3 and the pipe 4 are provided. However, the pressure sensor 5 is provided inside the holding table 1, and the pressure of the outside air (outside air pressure) introduced from the introduction pipe 11 connecting the pressure sensor 5 to the external space and the suction pipe 8 are provided.
A timer 12 is provided for detecting a pressure difference from the internal pressure and measuring the evacuation time, and further, the control circuit 10 determines that the pressure in the suction pipe 8 indicated by the output signal of the pressure sensor 5 exceeds a predetermined value. Determination means 10 for determining whether or not the exhaust time indicated by the timer 12 when
₁ is different from the vacuum suction type wafer holding device shown in FIG.

Here, the valve 7, like the valve 407 shown in FIG. 5, connects the inside of the pipe 4 with the external space when closed, and connects the inside of the pipe 4 with the exhaust pump 6 when opened. It is.

Next, the operation of the wafer holding device of this embodiment will be described with reference to FIGS.

The wafer vacuum-sucked on the holding table 1 is transferred to a position where the wafer comes into contact with the suction surface 2 of the holding table 1 by a known transfer hand (not shown). Thereafter, the valve 7 is opened, and the space (sealed space) formed by the conveyed wafer and the suction surface 2 and the two concentric grooves 9 ₁ and 9 ₂ carved on the suction surface 2 is formed. Is exhausted by the exhaust pump 6 through each of the suction ports 3, the suction pipe 8 and the pipe 4, so that the back surface of the wafer is vacuum-adsorbed. Pressure sensor 5
Detects the differential pressure P between the pressure in the suction pipe 8 and the outside air pressure,
A signal indicating the differential pressure P is output to the control circuit 10.

At this time, the relationship between the evacuation time t from the start of vacuum suction and the differential pressure P indicated by the output signal of the pressure sensor 5 in the case where there is no leakage from the outside air in the closed space is, for example, the second
This is shown by a solid line in the figure.

That is, before the wafer is vacuum-sucked (exhaust time t).
(= 0), since the valve 7 is closed once to allow the inside of the pipe 4 to communicate with the external space, the pressure in the suction pipe 8 becomes equal to the external pressure, and the differential pressure P = 0 [Torr]. Thereafter, when the vacuum suction of the wafer is started, the suction pipe 8
, The pressure P decreases as the evacuation progresses, so that the differential pressure P increases. At the evacuation time t = t ₁ indicated by point A, the differential pressure P = P _X1 , and the evacuation time t indicated by point C = T ₂ , the differential pressure P = P _X2 and the exhaust pressure t = t ₃ indicated by the point E, the differential pressure P = P _X3 .

Here, the difference between the pressure on the front surface and the pressure on the back surface of the wafer required to hold the wafer by vacuum suction (hereinafter, referred to as the pressure).
This is referred to as “predetermined differential pressure”. Assuming that P ₀ is a differential pressure P _X1 indicated by a point A in FIG. 2, the differential pressure between the pressure in the suction pipe 8 detected by the pressure sensor 5 and the outside air pressure is Since the difference between the pressure and the pressure on the back surface accurately corresponds to the difference pressure P indicated by the output signal of the pressure sensor 5,
When it is confirmed that the pressure difference is larger than the predetermined differential pressure P ₀ (= P _X1 ) (that is, the pressure in the suction pipe 8 is smaller than a predetermined value), the control circuit 10 By outputting an instruction signal for proceeding to the next step (for example, an instruction signal for proceeding the wafer holding device to the wafer exposure position), the wafer can be output with a minimum necessary suction force and a minimum required evacuation time. Can be adsorbed in vacuum.

Further, in the above description, it is assumed that there is no leakage from the outside air in the closed space. However, in actuality, the wafer is distorted, the dust adhered to the back surface of the wafer and the wafer when the wafer is placed on the suction surface 2 are distorted. Leakage from outside air occurs in the closed space due to the positional relationship with the suction surface 2. In this case, the relationship between the evacuation time t from the start of vacuum suction and the differential pressure P indicated by the output signal of the pressure sensor 5 is represented by, for example, a broken line in FIG. 2, and the differential pressure P at the same evacuation time t is Therefore, the size is smaller than that in the case where there is no leakage from the outside air in the closed space. That is, at the evacuation time t = t ₁ indicated by the point B, the differential pressure P = P _Y1 (P _Y1 <P _X1 ) and the evacuation time t = t indicated by the point D
_{At 2} , the differential pressure P = P _Y2 (P _Y2 <P _X2 ).

However, in the wafer holding device of the present embodiment, the differential pressure P indicated by the output signal of the pressure sensor 5 accurately corresponds to the difference between the pressure on the front surface and the pressure on the back surface of the vacuum-sucked wafer. The differential pressure P is equal to the predetermined differential pressure P ₀ (= P
_X1 ), it was confirmed that it became larger than (exhaust time t = t2 in FIG. ₂ ). By causing the control circuit 10 to output the instruction signal, leakage from the outside air occurred in the closed space. Even in such a case, the wafer can be vacuum-sucked with a minimum required suction force and a minimum required evacuation time.

Further, the relationship between the evacuation time t and the differential pressure P when the maximum allowable leak from the outside air to the enclosed space occurs is measured in advance, and in this case, the differential pressure P is equal to the predetermined differential pressure. Exhaust time t when P ₀ (= P _X1 ) (in the case shown by the dashed line in FIG. 2, exhaust time t = point F =
t ₃ ) is determined, and the evacuation time t = t ₃ is set to a predetermined evacuation time.
By setting it as T ₀ , even if the evacuation time t from the start of vacuum suction of the wafer measured by the timer 12 becomes longer than a predetermined evacuation time T ₀ (= t ₂ ), the output signal of the pressure sensor 5 is obtained. Is the predetermined differential pressure P ₀ (= P _X1 ).
If it does not become larger, the control circuit 10 may output an instruction signal to stop the vacuum suction of the wafer or a signal to notify the abnormality.

Therefore, by operating according to the flowchart showing the control circuit 10 and the judging unit 10 ₁ in Figure 3,
The yield and the productivity can be improved.

That is, when the vacuum suction of the wafer is started, the control circuit 10 reads the output signal of the pressure sensor 5 and the output signal of the timer 12 (step 71). The determination means 10 _1,
The exhaust time t indicated by the output signal of the timer 12 is a predetermined exhaust time.
Determines greater or not than T ₀ (step 72), the when evacuation time t is larger than the predetermined evacuation time T ₀ is to output a signal indicating for example abnormal from the control circuit 10 (step 73). On the other hand, the when evacuation time t is less than the predetermined evacuation time T _0, the difference pressure P indicated by the output signal of the pressure sensor 5 determines whether greater than a predetermined differential pressure P ₀ (step 74) , when the difference pressure P is smaller than the predetermined differential pressure P ₀ is returned to the operation in step 71. Further, when the difference pressure P is greater than the predetermined differential pressure P ₀ is to output the instruction signal from the control circuit 10 (step 75).

When the vacuum suction of the wafer is released, the valve 7 is closed and the outside air is sent into the pipe 4.

In the wafer holding apparatus of the present embodiment, the pressure sensor 5 is provided below the holding table 1, and the gas in the suction pipe 8 is introduced from a position near the lower part of the holding table 1 of the suction pipe 8, thereby allowing the inside of the holding table 1 to be introduced. Even if a cooling water pipe for cooling a wafer being exposed is provided, a place for installing the pressure sensor 5 can be secured.

FIGS. 4A and 4B are views showing a second embodiment of the wafer holding device of the present invention.

As shown in FIG. 4B, the wafer holding device of the present embodiment is configured such that a pressure sensor 35 provided in the holding table 31
31 Figure 4 of the outer concentric grooves 39 ₂ provided on the suction surface 32 of the (A) introducing provided on the leftward oblique opening 46 than the second
In the closed space introduced through the introduction pipe 45 of the above, and the pressure of the outside air introduced through the first introduction pipe 41 (outside atmospheric pressure)
And the control circuit 40 does not have a timer for detecting the pressure difference between
It differs from that shown in FIG. _{1 in} that it does not have 10 ₁ .

Therefore, in the wafer holding device of the present embodiment, since the pressure sensor 35 detects the differential pressure using the pressure in the closed space, the pressure on the back surface of the vacuum-sucked wafer is set to the first pressure.
Detection can be performed with higher accuracy than that shown in the figure.

Further, the control circuit 40 has only a function of outputting an instruction signal for proceeding to the next step when confirming that the pressure in the closed space indicated by the output signal of the pressure sensor 35 has become smaller than a predetermined pressure.

Further, in the wafer holding apparatus of the present embodiment, the pressure sensor 35 is provided below the holding table 31 and gas is introduced into the holding space 31 through the second introduction pipe 45 to introduce gas in the closed space. Even in the case where a pipe for cooling water for cooling the wafer inside is provided, an installation place for the pressure sensor 35 can be secured.

Also in this embodiment, provided with a timer for measuring the exhaust time, the determination unit 10 ₁ shown in Figure 1 to the control circuit 40
By providing a pressure sensor within a predetermined evacuation time
When it is confirmed that the differential pressure indicated by the output signal of 35 has become larger than a predetermined differential pressure (that is, the pressure in the closed space has become smaller than a predetermined value), the control circuit 40 An instruction signal for proceeding to the next step (for example, an instruction signal for proceeding the wafer holding device to the wafer exposure position) may be output.

In the above description, the pressure sensor 5 shown in FIG. 1 and the pressure sensor 35 shown in FIG. 4 detect a differential pressure between the pressure in the suction pipe 8 or the closed space and the outside air pressure. However, the pressure may be directly detected in the suction pipe 8 or the closed space. In particular, when the outside pressure is controlled to be a constant value, there is no particular need to detect the differential pressure. In this case, since it is not necessary to introduce outside air into the two pressure sensors 5, 35, the introduction pipe 11 and the first introduction pipe 41 become unnecessary.

When the pressure in the suction pipe 8 or the closed space is directly detected, a pressure sensor including a load cell is provided.
It may be provided in the suction tube 8 or any place in the closed space.

Further, the shape of the suction surface of the holding table may be a pin chuck method in which a plurality of columnar projections are provided on the surface of the holding table facing the back surface of the wafer to be vacuum-sucked.

[Effects of the Invention] The present invention is configured as described above, and has the following effects.

By detecting the pressure in the suction tube or the closed space with a pressure sensor provided in the holding table, the wafer can be suctioned with an optimum suction force, and the distortion generated in the wafer can be minimized. Since the wafer can be vacuum-sucked in a minimum suction time, there is an effect that the yield and the productivity can be improved at the time of ultrafine processing.

[Brief description of the drawings]

FIG. 1 is a view showing a first embodiment of a wafer holding apparatus according to the present invention, wherein (A) is a top view of a holding table, (B) is a schematic configuration diagram of the apparatus, and FIG. FIG. 3 is a graph showing the relationship with the differential pressure, FIG. 3 is a flowchart for explaining the operation of the control circuit and the judgment means, and FIG. 4 is a diagram showing a second embodiment of the wafer holding device of the present invention; FIG. 5B is a top view of the holding table, FIG. 5B is a schematic configuration diagram of the apparatus, FIG. 5 is an example of a vacuum suction type wafer holding apparatus, FIG. 5A is a top view of the holding table, and FIG. It is a schematic structure figure of an apparatus. 1,31… Holder, 2, 32… Suction surface, 3, 33… Suction port, 4,
34 …… Piping, 5,35 …… Pressure sensor, 6,36 …… Exhaust pump, 7,37 …… Valve, 8,38 …… Suction pipe, 9 ₁ , 9 ₂ , 39 ₁ , 3
9 ₂ ... groove, 10, 40 ... control circuit, 10 ₁ ... judgment means, 11 ...
... Introduction pipe, 12 ... Timer, 41 ... First introduction pipe, 45 ...
Second inlet pipe, 46 …… Inlet, A, B, C, D, E, F …… Point, P, P
_X1 , P _X2 , P _X3 , P _Y1 , P _Y2 …… Differential pressure, P ₀ …… Predetermined differential pressure, t, t ₁ , t ₂ , t ₃ … Exhaust time, T ₀ … Predetermined exhaust time .

Continuation of the front page (72) Inventor Yuji Chiba 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Canon Inc. (56) References JP-A-4-71215 (JP, A) JP-A-2-67745 ( JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/027

Claims (4)

(57) [Claims] 1. A holding apparatus having a holding table for holding a wafer on a suction surface by means of a vacuum, a suction tube formed in the holding table for supplying a vacuum to the suction surface, and a suction tube in or inside the suction tube. A pressure sensor provided in the holding table for detecting pressure information in a closed space of the suction surface. 2. An apparatus according to claim 1, further comprising an introduction pipe formed in said holding table for introducing outside air around said holding table, wherein said pressure sensor detects a pressure of said suction pipe or said suction surface and a pressure around said holding table. 2. The method according to claim 1, wherein a pressure difference from an outside air pressure is detected.
The wafer holding device as described in the above. 3. A means for measuring a time during which vacuum is supplied to the absorption pipe, and means for detecting an abnormality based on each data of the time measured by the timer and the differential pressure output by the pressure sensor. 2. The wafer holding device according to claim 1, comprising: 4. The wafer holding apparatus according to claim 1, wherein said wafer is exposed by X-rays.