JPS63243803A - Gap setting device - Google Patents

Abstract

PURPOSE:To set an accurate gap by removing the ripple component of diffracted light and performing gap control based on a set target value. CONSTITUTION:The double diffraction grating consisting of a diffraction gratings 26a and 26b, and 27a and 27b provided to a mask 25, a wafer 24 respectively adjusts the gap between the mask 25 and wafer 26. At this time, a CPU 34 as a gap setting means drives a Z-axial table 22 continuously through a servo device 37 and a Z-axial driving mechanism 21 to sweep the gap. This CPU 34 samples the output of a gap sensor 35 simultaneously and takes a regressive analysis by employing an estimating method to remove the contained ripple component. Thus, the CPU 34 finds the gap desired value from the relation between a diffraction intensity signal from a photodetector 31 after the ripple component is removed and the output signal of the sensor 35 and controls the servo device 37 and Z-axial driving mechanism 21 so that the gap between the mask 25 and wafer 24 approximates the desired value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a gap setting device suitable for setting a gap between a mask and a wafer in an exposure apparatus for manufacturing VLSI, for example.

(Prior Art) For example, an exposure apparatus is known as a means for manufacturing a circuit pattern of a VLSI. When pattern transfer is performed using such an apparatus, it is necessary to set the gap between the mask and the wafer with high precision prior to exposure.

A method using a diffraction grating is known as a method for setting the gap between the mask and the wafer. As shown in FIG. 6, this setting method involves providing a striped diffraction grating 2 on a mask 1, providing a reflective surface 4 on a wafer 3, and irradiating a laser beam from the top surface of the mask 1 to create a striped diffraction grating 2. The first-order diffracted light intensity 1 (+1) or -1st-order diffracted light intensity 1 (-
This method sets the gap between the mask 1 and the wafer 3 by measuring 1>.

However, in this gap setting method, mask 1 also acts as a reflection type diffraction grating, so mask 1 → wafer 3 →
The first-order light or -first-order light that returned via the mask 1,
The light reflected on the mask 1 interferes, and as shown in FIG. 7, an interference wave with a period of λ/2 (λ is the wavelength of the laser beam) appears. For this reason, mask 1 and wafer 3
There was a problem in that it was difficult to detect the gap between the mask 1 and the wafer 3 with high precision due to the influence of the parallelism between the mask 1 and the wafer 3.

Therefore, we also proposed a gap setting device that eliminates the influence of the interference waves by providing a first striped diffraction grating on the mask side and a second two-dimensional grating on the wafer side opposite to this. (Japanese Patent Application No. Sho 61-135172: However, this is not publicly known).

An example is shown in FIG.

Wafer table 12 placed on Z-axis table 11
A wafer 13 is placed on top, and the wafer 1
A mask 14 is placed on the mask 3 with a predetermined gap (2) in between. At a predetermined position of this mask 14, a transmission type first diffraction grating 15a is provided.

15b is arranged. Also, a diffraction grating 15a.

Reflective second diffraction gratings 16a and 16b are arranged on the wafer 13 side facing -15b.

The pattern of the first diffraction gratings 15a, 15b is a stripe-like pattern, and the pattern of the second diffraction gratings 16a, 16b is a two-dimensional grating pattern, as shown in FIG. 9, for example. . And M2 diffraction grating 16b
The y-direction pitch P bwy of the second diffraction grating 16a is
The pitch is set to be different from the direction pitch Pawy.

Further, the distance mb between the second diffraction gratings 16a and 16b is
b=a+Pwx/2 (a: distance between first diffraction gratings 158.15b, Pwx:
The pitch of the second diffraction gratings 16a, 16b in the X direction) is set as follows.

These diffraction gratings 158 to 16b are irradiated with laser light C from a laser light source (not shown).

Among the lights diffracted by these diffraction gratings 15a to 16b, light in a specific direction, for example f(
0, 1) direction to the mirror 17a.

It is configured to lead to a light receiving optical system and a signal processing system (not shown) via 17b. Then, the two-axis table 11 is driven in the Z-axis direction using a signal obtained by the signal processing system to adjust the gap between the wafer 13 and the mask 14.

In the above configuration, from the laser light source to the first diffraction grating 1
The laser beam C irradiated onto 5a and 15b is transmitted through the diffraction grating 15.
a (15b) - Diffraction grating 16a (16b) - 4 While passing through diffraction gratings 1 and 5a (15b), it is diffracted by the action of the double diffraction grating.

Therefore, as shown in FIG. 10, zero-order and first-order diffracted lights in nine directions are obtained. For example, when looking at a pair of diffraction gratings 15a and 16a, the intensity of diffracted light 1 (0, 1) of 0th order in the X direction and 1st order in the y direction and the gap 2 have a relationship as shown in FIG. Become.

This device detects 0th order diffracted light in the X direction and ±1st order diffracted light in the y direction, so the diffraction grating 15a (1
The light reflected by step 5b) and the diffracted light do not interfere with each other. Therefore, based on the obtained diffracted light, the gap WA
By performing the adjustment, it is possible to set the gap with high precision without being affected by interference waves.

Furthermore, in this device, the (0.1) diffracted light obtained by the diffraction gratings 15a and 16a and the diffraction grating 15b.

Since the grating pitch in the y direction of the second diffraction gratings 15a and 15b is different from the (0.1) diffracted light obtained by the diffraction grating 16b, the diffracted light is detected in different directions as shown in FIG. Ru. Therefore, the intensity of both these diffracted lights is 11
From (0,1), [2 (0°1), if we perform the paralysis of Δl-11(0,1)-I2 (0,1), we can obtain a curve as shown in Figure 12. . Therefore, the optimum gap can be set by detecting the zero-crossing point of this curve.

However, with this device, as shown in FIG.
Because the multiple reflected light interferes between the mask 14 and the wafer 13, the curve shown in FIG.
As shown in the figure, a ripple whose amplitude changes every time the gap changes by λ/2 occurs, and as a result, a plurality of zero-crossing points are detected, making it impossible to perform accurate gap positioning.

(Problems to be Solved by the Invention) As described above, the above-mentioned gap setting device using a double diffraction grating has a problem in that the accuracy of the FJ1 adjustment is reduced due to the influence of ripples due to multiple reflections.

The present invention was made to solve these problems, and an object of the present invention is to provide a gap setting device that eliminates the influence of ripples included in the detection signal and allows accurate gap adjustment.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a striped first structure provided on a first object.
and a second diffraction grating in the form of a two-dimensional grating provided on a second object facing the first object. A gap setting device for adjusting a gap between bodies, comprising: a drive mechanism for changing the gap between the two objects; a gap detection means for outputting a signal corresponding to the gap between the two objects; and a relationship between an output signal of the gap detection means and the intensity of the diffracted light received by the light receiving means while controlling the drive mechanism to continuously change the gap. The target Wij! is calculated, and the ripple is removed from this relationship to set the gap target value. and drive control means for controlling the drive mechanism to bring the gap closer to the gap target value set by the target Wi setting means.

(Function) When the target value setting means controls the drive mechanism to continuously change the gap between the first and second objects, the light receiving means receives a continuous intensity signal of the diffracted light including ripples. is detected. This ripple is removed by the target value setting means. Ripple removal methods include, for example, simultaneously sampling the output of the light receiving means and the output from the gap detecting means and obtaining an estimated curve by regression analysis, or filtering the output of the light receiving means with a low-pass filter. is possible. The target value setting means calculates a gap target value (target value of the gap detection means) from the relationship between the thus obtained diffraction intensity signal of the light receiving means from which the ripple component has been removed and the output signal of the gap detection means. Melt. The drive control means then controls the drive/vJ mechanism so that the gap between the mountain handles approaches the obtained gap target value.

Therefore, according to the present invention, the optimum target value is set after removing the ripple of the diffracted light obtained by the double diffraction grating, and the gap control is performed based on this target value. You can set the gap accordingly.

(Example) FIG. 1 shows an embodiment of the present invention.

A wafer table 23 is placed on a two-axis table 22 that is driven in the Z-axis direction (it may be driven in a tilt direction) by a two-axis drive mechanism 21 . A wafer 24 is placed on the wafer table 23, and a mask 25 is placed on the wafer 24 with a predetermined gap 2 between the wafer 24 and the wafer 24. This mask 2
At predetermined positions of 5, there are two transmission type first diffraction lenses 26.
a, 26b are arranged. Furthermore, two reflective second diffraction gratings 27a and 27b are arranged on the wafer 24 side facing the first diffraction gratings 26a and 26b.

These diffraction gratings 26a to 27b are, for example, the ninth gratings mentioned above.
It consists of a pattern as shown in the figure.

These diffraction gratings 26a to 27b are irradiated with laser light C from a laser light source 28 via a mirror 29.

Among the lights diffracted by these diffraction gratings 26a to 27b, light in a specific direction, for example, I(
0, 1) direction is guided to a photodetector 31 via mirrors 30a and 30b. The light reception signal of this photodetector 31 is differentially amplified by a photoamplifier 32 and output as a difference signal ΔI. This difference signal Δ
After being A/D converted at a predetermined sampling time in the A/Dlj converter 33, the signal (2) is taken into the CPU 34.

On the other hand, a plurality of gap sensors 35 are installed at a plurality of positions on the lower surface of the two-axis table 22 to serve as gap detection means for measuring the displacement of the seven-wheel table 22 in the Z-axis direction. The gap sensor 35 is composed of a displacement sensor such as a micro sense, and its output signal is A/D converted by an A/D converter 36 at the same sampling time as the A/D converter 33. The A/D converted data is taken into the CPLJ34.

The CPLI 34 serves as target value setting means for setting a gap target value, which will be described later, based on these input data. The servo device 37 adjusts the gap so that the gap target value set by the CPU 34 is equal to the output of the gap sensor 35.
It controls the shaft drive mechanism 21.

In the above configuration, before setting the gap, the CPU 34 first sets 20 as the initial value of the gap target and provides it to the servo device 37 (step 81 in FIG. 2). The servo device 37 drives the two-axis drive mechanism 21 to adjust Z so that the output of the gap sensor 35 becomes equal to the initial target value 20.
Move the axis table 22 to the initial position.

Next, the CPU 34 continuously drives the two-axis table 22 via the two-axis drive mechanism 21 by giving a signal to the servo device 37 to sweep at a predetermined speed with respect to the target value, thereby reducing the gap 2. Make it sweep. Then, the CPU 34 simultaneously samples the difference signal Δ■ and the output of the gap sensor 35 while performing the sweep (step S2
). As a result, data of a difference signal Δ■ with respect to the sensor output as shown by black dots in FIG. 3, for example, is obtained, but this data includes a ripple component.

Therefore, the CPU 34 performs regression analysis on the obtained data using an estimation method such as the least squares method to obtain a curve R from which ripple components have been removed as shown in FIG. 4 (step 83). Then, a point (zero cross point) at which the difference signal Δ■ becomes 0 is found on the obtained curve R, and the output value of the gap sensor 35 at that point is set as the gap target value (step 84).

The gap target value obtained in this way is
7 is given. Therefore, the servo device 37 thereafter controls the Z-axis drive mechanism 21 so that the gap 2 matches the target gap value.

As described above, according to this embodiment, the curve R from which ripples have been removed is obtained by regression analysis of the sampled data, and the gap target value is determined based on this curve R. Accurate target values can be given without the influence of ripples.

In the above embodiment, the ripple component was removed by regression analysis, but for example, as shown in FIG. The removed difference signal Δ
A similar effect can be obtained by sampling (2).

Furthermore, in the above embodiment, a gap sensor is used as a gap detection means, but if the Z-axis table is driven by a piezoelectric element, for example, the voltage applied to the piezoelectric element may be used as a signal corresponding to the gap. This eliminates the need to provide a special sensor.

Note that a single set of double diffraction gratings may be used, and in this case, the point where the curve shown in FIG. 11 crosses a predetermined threshold value may be set as the target setting point.

When using two sets of diffraction gratings, the difference signal Δ■ is ΔI=It (0,-1)-12(0,-1)Δl-
11(0,1)-12(0,-1)Δl-1t (0
, -1)-12(0,1), etc.

Note that the present invention is not particularly limited in its application to setting the gap between a mask and a wafer, but can also be applied to other uses in which the gap is set with high precision.

[Effects of the Invention] As described above, according to the present invention, it is possible to eliminate the influence of the ripple component of the detection signal, and it is possible to improve the gap setting accuracy.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a gap setting device according to an embodiment of the present invention, FIG. 2 is a flowchart showing the operation of the device, FIG. 3 is a diagram showing points sampled by the device, and FIG. The figure shows a curve obtained by regression analysis using the same device, FIG. 5 shows the configuration of a gap setting device according to another embodiment of the present invention, and FIGS. 6 to 14 show a conventional gap setting device. FIG. 2 is a diagram for explaining the device. 1.14.25...Mask, 2...Diffraction grating, 3.
13.24... Wafer, 4... Reflective surface, 11...
Z-axis table, 12...Wafer table, 15a. 15b, 26a, 26b...first diffraction grating, 16a
, 16b, 27a, 27'o--second diffraction grating, 1
7a, 17b, 29.30a, 30b--Mirror, 3
5...Gap sensor. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 10 Figure 11 Figure 12

Claims (4)

[Claims] (1) A drive mechanism that changes the gap between a first object and a second object that are arranged facing each other; a gap detection means that outputs a signal corresponding to the gap between the two objects; a first diffraction grating in the form of a stripe provided on the object; a second diffraction grating in the form of a two-dimensional grating placed on the second object to face the first diffraction grating; a laser light source that irradiates a laser beam onto the first diffraction grating; and among the diffracted light that passes through the first diffraction grating, is reflected by the second diffraction grating, and then passes through the first diffraction grating again, the a light receiving means for receiving diffracted light of zeroth order in a direction orthogonal to the stripe direction of the first diffraction grating and ±1st order diffracted light in the stripe direction; target value setting means for determining a relationship between the output signal of the gap detection means and the intensity of the diffracted light received by the light receiving means and removing ripples from this relationship to set a gap target value; and drive control means for controlling the drive mechanism to bring the gap closer to the gap target value set by the gap setting device. (2) The target value setting means includes means for simultaneously sampling the output signal of the gap detection means and the intensity of the diffracted light received by the light receiving means, and a regression analysis of the data sampled by this means. The gap setting device according to claim 1, further comprising means for obtaining a gap target value. (3) The target value setting means includes a low-pass filter that removes high-frequency components of the continuously obtained intensity signal of the diffracted light, and an output of the low-pass filter and an output of the gap detection signal. 2. A gap setting device according to claim 1, further comprising means for obtaining said gap target value from. (4) Two sets each of the first diffraction grating and the second diffraction grating are provided, and the target value setting means corresponds to the zero crossing point of the difference signal of the diffraction light intensity obtained by each set of diffraction gratings. 2. The gap setting device according to claim 1, wherein the output signal value of said gap detection means is set as said gap target value.