JPH01157524A - Control of gap by means of diffraction grating - Google Patents

Abstract

PURPOSE:To set a gap safely and surely by a method wherein a first object and a second object are faced in advance by keeping a comparatively large gap, its value is measured and a final gap which is smaller than the gap is set. CONSTITUTION:A height value and an inclination value of a mask 2 and a wafer 3 are measured by using other means; a levelling stage 12 is shifted upward in such a way that height values of three diffraction gratings G1, G2, G3 are all situated near the middle of positions Z1 and Z2; a position in a Z direction during this operation is stored as Hb. Then, while control circuits 10, 11 moves the stage 12 upward from the position Hb, the control circuits 10, 11 store its height position as Hsu when a monotonous change of an envelope wave EW is continued by H in the Z direction. In addition, while the stage is moved from a position Ht downward, a height position obtained in the same manner is stored as Hsd. When one forward and backward scanning operation has been completed, a height value HP' of a wafer 3 where an intensity value I of the envelope wave EW becomes a maximum is obtained by a mean value after these two positions have been added. By this setup, a coarse gap-detecting operation is completed; then, a precise gap-setting operation is started.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention aims to reduce the distance (gap) between a mask and a transferred substrate (wafer, etc.) in a close proximity (broxomity) exposure apparatus for manufacturing integrated circuits. Concerning how to control.

[Conventional technology]

Conventionally, in this type of exposure apparatus, it has been necessary to accurately set the distance (gap) between the mask and the wafer, and various gap detection and setting methods have been used. Among these proposals, an extremely precise and simple method is to provide a diffraction grating on the mask and use the corresponding area on the wafer as a reflective surface.
A known technique is to irradiate the diffraction grating with coherent light such as a laser or quasi-monochromatic light, and to set the gear knob to a predetermined value based on the intensity signal of the diffracted light that is diffracted and reflected by the diffraction grating and the reflecting surface. ing. This technology, for example,
This is as disclosed in detail in Japanese Patent No. 0-173835.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, since the mask and the wafer were set to have a final minute gap from the beginning, there was a problem that the mask and the wafer came into contact and were damaged. Particularly when the mask is for X-ray exposure, the member that carries the pattern of the mask is a thin film of about 1 to 2 μm thick, such as silicon thioside (SiN) or boron nitride (BN). Therefore, there was a high risk that the expensive mask would be damaged when it came into contact with the wafer.

Furthermore, if the parallelism between the mask and the wafer is poor, there is a problem in that the gap cannot be further reduced after the frame portion of the mask that holds the thin film comes into contact with the wafer.

The present invention was made in view of these problems, and an object of the present invention is to provide a control method for safely and reliably setting a gap.

[Means for solving problems]

The present invention is based on a conventional gap control method using a diffraction grating, and the envelope waveform of the intensity signal obtained by this method changes depending on the change in the amount of gap between the mask (first object) and the wafer (second object). The mask and wafer are positioned at a gap larger than the gap that should be originally set (set gap), and the maximum value on the envelope waveform is obtained near that gap. The gap between the mask and the wafer was adjusted so that the gap amount could be adjusted, and then the mask and wafer were moved closer together so that the maximum value on the envelope waveform corresponding to the set gap amount was obtained.

(Function) In the present invention, it is only necessary to have a gap detection system that detects the maximum value on the envelope waveform, and this gap detection system can detect and set the final gap amount between the mask and the wafer, and perform rough correction before that. Both the detection and setting of the gap amount are possible.

Therefore, there is no need to prepare another detection system for coarse gap detection and setting, or to provide a special mark pattern for coarse gap setting on a mask or wafer.

Thus, using conventional techniques, reliable gap setting is achieved without contact between the mask and the wafer.

〔Example〕

FIG. 1 schematically shows a method according to an embodiment of the invention, and FIG. 2 shows the variation of the intensity signal obtained by a conventional arrangement.

As shown in FIG. 1, a mask 2 on which a minus-dimensional diffraction grating 1 is formed and a wafer 3 on which a reflective surface is formed on the opposite side of the diffraction grating 1 are placed close to each other with a gap Z between them. When coherent parallel light B is irradiated perpendicularly from above the diffraction grating 1, the diffracted light DICDI') is directly reflected by the diffraction grating 1 and travels upward, propagates to the back side of the diffraction grating 1, and is reflected on the reflective surface of the wafer 3. The diffracted light D2 (D2') is reflected and then diffracted again by the diffraction grating 1, and the diffracted light D+ travels toward the back side of the diffraction grating 1, is reflected by the reflective surface of the wafer 3, and travels upward.
(D, +') is generated. Diffraction photons D+, Dz, D3
becomes the spatially interfered light DT, and the diffracted light DI', D2
', D3' become spatially interfered light DT', which are each photoelectrically detected. The magnitude of the detected photoelectric signal (intensity signal) changes depending on the amount of gap between the mask 2 and the wafer 3.

Therefore, when the relationship between the amplitude intensity I of the intensity signal, that is, the optical DT (DT'), and the gap amount Z is determined, the relationship is as shown in FIG. 2. In FIG. 2, the horizontal axis represents the gap amount Z, and the vertical axis represents the intensity I. In FIG. 2, the waveform of the intensity signal is obtained as a beat waveform in which an interference wave whose amplitude changes finely shows a maximum value at every fixed gap amount. Specifically, as shown enlarged in Figure 3, the period λ/
It is a collection of approximately sinusoidal interference waves rw of 2 (λ is the wavelength of the coherent parallel light B), and the envelope wave EW of this interference wave IW is the gap amount Z+, Zz, Z3 as shown in FIG.
, Z4... take a local maximum value every certain amount.

The condition that the envelope wave EW becomes maximum is that the gap amount Z is Z=
(P2/λ)×M (where P is the pitch of diffraction grating 1, M
is any positive integer).

For example, P = 3.6 p m, λ - 0.6328 μm
Then, the gap amount that takes the maximum value is Z+=20.5
μm, Zz = 41.0 μm, Z3 = 61.4 μm
Takes the value of 1.=. Therefore, the pitch P and wavelength λ are determined appropriately, and the envelope wave EW is determined by setting the gap amount, for example, Zl.
is maximized.

Therefore, in this embodiment, as shown in FIG.
The gap is set based on the third maximum value of the envelope wave EW of the intensity signal so that 3 is obtained. Thereafter, the distance between the mask 2 and the wafer 3 is narrowed until the desired gap amount Z (20.5 μm) is obtained, and the gap is set so that the first maximum value of the envelope wave EW is obtained.

Now, FIG. 4 is a perspective view showing the arrangement of diffraction gratings suitable for setting the actual gap. Actually, the diffraction gratings G, , G2, and G3 are provided at three locations around the device pattern region of the thin film of the mask 2. Each grid Gl, G2,
In this embodiment, the lattice arrangement direction of G3 is determined to face the center of the mask 2. Of course, they may be arranged in any direction as long as two-dimensional alignment is achieved. A gap detection system is arranged above each of the diffraction gratings Gl, G2, and G3, and each of these detection systems irradiates the mask 2 with a coherent light beam B from a laser or the like, and also irradiates the mask 2 with the interfering light DT (D ) are equipped with condensing lenses L1, L2, and L3 for condensing light, and the condensed light DT (DT') is converted into a photoelectric signal according to the intensity (light amount) by the respective light receiving elements 8.9.13. be done. .

FIG. 5 shows a specific configuration in which a control system for gap setting is added to the configuration shown in FIG. 12" is fixed by suction. In this embodiment, in order to tilt the surface of the wafer 3 and move it up and down in the Z direction (direction to change the gap with the mask 2), the leveling stage 12 is positioned at three equal locations below the stage 12. It is movable by means of a drive 5.6.7 provided. Each of these drive parts 5.6.7
It is equipped with an encoder and the like for determining the amount of movement of the wafer 3 in the vertical direction.

Now, the intensity signal detected by the light receiving element 8 is transmitted to the control circuit 1.
0, and the drive unit 5 moves the leveling stage 12 up and down at the corresponding position based on the command from the control circuit 10. Similarly, the intensity signal detected by the light receiving element 9 is processed by the control circuit 11, and the drive unit 6 is processed by the control circuit 1.
The position of the leveling stage 12 is moved up and down based on the command from 1. Note that illustration of a circuit that controls the drive section 7 based on the intensity signal from the light receiving element 13 is omitted.

The control circuits 10 and 11 basically use the process shown in FIG. 6 to find the position where the envelope wave EW of the intensity signal is at its maximum. That is, in FIG. 6, the gap amount is at the position Ha (
The leveling stage 12 is gradually brought closer to the mask 2 from a position where the gap is wider than the maximum position of the envelope wave EW, and when the monotonous decrease of the envelope wave EW continues by ΔI'' in the Z direction, the wafer 3 at that time (leveling The height of the stage 12) is read from the encoder of the drive unit 5.6.7 and stored as the height Hs. And its position (height Hs)
By returning the height of the leveling stage 12 by ΔH (moves by ΔH in the direction away from the mask 2), the wafer 3 is moved to the position Hp corresponding to the maximum value of the envelope wave EW.
Set.

This operation is similarly performed for each of the diffraction gratings G+, Gz, and G3 of the mask 2, and the mask 2 and the wafer 3 are set parallel to each other with a predetermined gap amount.

Next, the overall operation of this embodiment will be explained.

First, the height and inclination of the mask 2 and wafer 3 are measured using other means (such as a capacitive gap sensor with low precision), and the heights (gaps) of the diffraction gratings G+, G2, and G3 at three locations are all measured. The leveling stage 12 is positioned on one side (
direction of mask 2). The position in the Z direction at this time is read from the encoder and stored as I-Ib.

Next, the control circuit 10.11 moves the wafer 3 back and forth once between the position Hb and a position Ht above this (on the mask side). The interval between the position Ht and the position Hb is set to approximately P2/λ, and corresponds to exactly one cycle of the envelope wave EW.

When the envelope wave EW monotonically decreases by ΔH in the Z direction as shown in FIG. 6 while moving the leveling stage 12 upward from the position Hb, the control circuit 10.11 adjusts the height position at that time. is stored as Hsu. Further position Ht
When the monotonous decrease of the envelope wave EW continues for ΔH in the Z direction while moving the leveling stage 12 downward from
The control circuit 10.11 stores the height position at that time as Hsd. When one reciprocating scan of the leveling stage 12 is completed, the control circuits 10 and 11 generate the envelope wave EW.
The height Hp' of the wafer 3 at which the intensity I is maximum is determined by Hp'-(Hsu+Hsd)/2. This completes the rough gap detection operation between the mask 2 and the wafer 3, and then moves on to the precise gap setting operation.

The control circuit 10.11 controls the height of the wafer 3 at all points of the diffraction gratings G2 and G3 at three locations (Hll)+2P.
The drive unit 5 is moved so that the position Ha is slightly lower than 2/λ.
．． The leveling stage 12 is driven by open control (driving not based on an intensity signal) based only on the output of the encoder 6.7.

When the three heights of the wafer 3 are set to the position Ha, the control circuit 10.11 determines the position Z1 where the first maximum value of the envelope wave EW is obtained, just as in FIG. Find Hs. Then, the wafer 3 is returned to the position Hp lowered by ΔH from the position iH3, and the gap amount Z1 between the mask 2 and the wafer 3 is set to be necessary for exposure. As a result, the gap amount is 2 at each point of the three diffraction gratings G, , G2, and G3.
1, mask 2 and wafer 3 are kept parallel.

〔Effect of the invention〕

As described above, according to the present invention, the first object and the second object are made to face each other with a relatively large gap in advance, and after measuring the value, a smaller final gap is set. This eliminates the inconvenience of causing damage to the object and the second object by causing them to come into contact with each other, or being unable to set the gap between the two objects correctly.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of implementing the method in the embodiment of the present invention, Fig. 2 is a diagram showing the waveform of the intensity signal in this embodiment, and Fig. 3 is a diagram showing the waveform of the intensity signal in the embodiment. A partially enlarged view of the intensity signal waveform, FIG. 4 is a diagram showing an example of the arrangement of the diffraction grating for gap detection and the detection optical system, FIG. 5 is a diagram showing the configuration of the gap control system, and FIG. FIG. [Explanation of symbols of main parts] ■... -dimensional diffraction grating, 2... Mask (first object), 3... Wafer (second object), 5.6.7... Drive section (Drive mechanism), 8.9.13・
... Light receiving element, 10.11... Control wholesale circuit, B... Coherent parallel light, D+ (D+'), D2 (D2'), D3 (D!')
, DT (D7')...diffraction light, G, , G2, G3...-dimensional diffraction grating, EW...
Envelope wave, Applicant: Nippon Telegraph and Telephone Corporation Nippon Kogaku Kogyo Co., Ltd.

Claims (1)

[Scope of Claims] A first object is provided with a diffraction grating, a second object facing the first object is provided with a reflective surface, the diffraction grating is irradiated with coherent light or quasi-monochromatic light, and the diffraction grating is detecting a signal corresponding to the intensity of the diffracted light diffracted and reflected by each of the reflecting surfaces, and detecting a signal corresponding to the intensity of the diffracted light that is diffracted and reflected by each of the reflecting surfaces, and detecting the 1st
In a method of controlling a gap amount between an object and a second object to a predetermined value, the first object and the second object are positioned so that the gap amount is larger than a set gap amount that should be originally set, and the gap is adjusted to a predetermined value. The gap position at which the envelope waveform of the intensity signal becomes maximum is determined by changing the relative distance between the first object and the second object in a range near the amount, and the set gap amount is determined based on the determined gap position. The first
A gap control method using a diffraction grating, characterized by setting a distance between an object and a second object.