JPH0439601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention is directed to a device that exposes a semiconductor integrated circuit, particularly a device that exposes a semiconductor integrated circuit using X-rays. This relates to a distance control device in a proximity exposure apparatus that controls the value of .

[Background of the invention]

Normal integrated circuit IC or large-scale integrated circuit LSI etc.
A resist film is formed on a thin silicon plate (wafer), and the desired pattern formed on the mask is
By transferring the pattern onto this resist film and repeatedly performing processes such as etching and ion implantation according to the transferred pattern, a desired circuit is manufactured.

In the above-mentioned LSI and the like, in order to improve the degree of integration, it is required to form fine patterns in which the width of the lines constituting the circuit is 1 μm or less. In order to meet these requirements, soft X-rays (hereinafter simply referred to as X-rays) are used to transfer the pattern, which has a shorter wavelength than light and has better transfer accuracy.
It is proposed to use .

Several X-ray exposure devices that use such X-rays have been proposed, but because the X-ray generating part is small,
To transfer the size of the mask, X-rays are used in a radial direction. Further, the mask must be thin in order to transmit X-rays, and the pattern portion must be made of a material with high X-ray absorption, such as gold. Furthermore, as in a general optical exposure apparatus, in order to protect the mask and pattern portion, it is necessary to perform exposure while maintaining a gap between the mask and the wafer.

FIG. 1 schematically shows the relative positions of an X-ray source, a mask, and a wafer in an X-ray exposure apparatus. In FIG. 1, 1 is an X-ray source, 2 is a mask, and 3 is a wafer. When the pattern of the mask 2 is transferred to the wafer 3 due to the distance D from the X-ray source 1 to the mask 2, the gap S between the mask 2 and the wafer 3, and the distance X from the irradiation center, the pattern is shifted by Δ, and the shift It is well known that the amount Δ=S/D·X.

Therefore, in order to reduce the shift amount Δ, it is necessary to reduce the gap S, and in order to reduce the error in the shift amount Δ, it is necessary to reduce the error in the interval S.
For example, if D=100 cm, S=10 μm, and X=10 mm, Δ=1 μm. Here, the error of S is ±1μ
If m, the error in the shift amount Δ is ±0.1 μm.
On the other hand, when the pattern line width is 0.5 μm, the error in the shift Δ is preferably about ±0.05 μm, so the accuracy of the gap S must be set to ±0.5 μm.

An example of a method for measuring the gap between a mask and a wafer in a conventional X-ray exposure apparatus will be described with reference to FIG. First, with the wafer 3 not under the mask 2, the mask flatness measuring device 11 is positioned under the mask 2, and the absolute height and flatness of the mask 2 are measured and set as M(x, y). . Next, the absolute height and flatness of the wafer 3 are measured using the wafer flatness measuring device 12, and are set as W(x, y). The target gap is S(x,
y), the absolute height that the wafer 3 should be, the flatness Ws (x, y), and the amount that the wafer 3 should be deformed.
Wf (x, y) is as shown in equations (1) and (2).

Ws (x, y) = M (x, y) - S (x, y) (1) Wf (x, y) = W (x, y) - Ws (x, y) (2) Equation (1) , if we calculate the gap S(x, y) conversely from (2), we get
It will look like (3).

S (x, y) = M (x, y) - W (x, y) + Wf (x, y) (3) Even if the amount of deformation Wf (x, y) of the wafer 3 is ideal, The gap accuracy depends on the measurement accuracy of the wafer 3 and the mask. Furthermore, since there is a time difference during measurement, gap adjustment, and exposure, the accuracy of the gap S is limited to ±1 μm, which is insufficient to achieve ±0.5 μm.

As described above, the gap measurement accuracy in the conventional method is insufficient. Furthermore, since the flatness measurement is performed twice, it takes time and reliability deteriorates. Furthermore, since there are two flatness measuring instruments, the configuration must be complicated and large.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems of the prior art by providing a proximity exposure apparatus that can adjust the gap between a mask and a substrate such as a wafer to a desired value with a simple configuration, in a short time, and even during exposure. An object of the present invention is to provide a gap control device for a proximity exposure apparatus that can control the gap with high precision.

[Summary of the invention]

That is, in order to achieve the above object, the present invention has the following features:
Proximity exposure equipment uses a coarse transparent/opaque pattern that is repeated multiple times at a coarse period for distance measurement, and a fine pattern that consists of a plurality of parallel patterns that are arranged in parallel with a period narrower than the coarse period and with different periods from each other. means for holding a mask on which a transparent/opaque pattern is formed; and a means for illuminating a parallel light beam from an oblique direction onto a coarse transparent/opaque pattern formed on the mask and a plurality of fine transparent/opaque patterns formed on the substrate. an illumination means for projecting the coarse opaque pattern and a plurality of fine opaque patterns; and detecting the amount of light obtained through the coarse transparent pattern with respect to specularly reflected light from the substrate surface caused by the coarse opaque pattern projected by the illumination means. a first detection means having a photoelectric conversion means and detecting a direction of deviation between the substrate and the mask based on a signal according to the amount of light obtained from the photoelectric conversion means; Accordingly, a plurality of photoelectric conversion means are provided for detecting the amount of light obtained through the plurality of thin transparent patterns with respect to specularly reflected light from the surface of the substrate by the plurality of thin opaque patterns projected, and each of the photoelectric conversion means a second detection means for searching for a mutual peak relationship of each signal according to the amount of light obtained from the means; and moving the substrate up and down in accordance with the direction of deviation obtained from the first detection means;
Thereafter, by matching the peak relationships of the respective signals obtained from the second detection means, the distance between the substrate and the mask is controlled to a desired value determined by a plurality of thin transparent/opaque patterns. This is a control device for a proximity exposure apparatus, characterized in that it is equipped with a control means.

[Embodiments of the invention]

First, the principle of a distance control device in an X-ray exposure apparatus, which is an example of a proximity exposure apparatus according to the present invention, will be explained based on FIGS. 3 and 4. FIG. 3 is a side view of the X-ray exposure apparatus for explaining the principle of the interpolation control apparatus according to the present invention.

A circuit pattern (not shown) on a mask 2 is transferred to a resist film 22 on a wafer 3 by X-rays 21 from an X-ray source 1 located above. mask 2
is vacuum-adsorbed by a mask chuck (not shown), and a gap measurement pattern 24 is provided on the mask 2. The wafer 3 is vacuum-adsorbed by a chuck 23 (not shown), and the chuck 23 is moved up and down as shown by the arrow by a vertical movement mechanism 25 made of, for example, a piezo element. Further, the vertical movement mechanism 25 is placed on an XY table 26, and the XY table 26 moves in the XY direction as shown by the arrow.

In the X-ray exposure apparatus shown in FIG. 3, as described above, the transparent mask 2 is provided with the opaque pattern 25 for gap measurement, and the light 28 from the mercury lamp 27 as an example of the light source is collimated by the lens 29. An irradiation mechanism 15 is provided that irradiates the mask 2 with a beam of light and projects an opaque pattern 24 for gap measurement onto the wafer 3. Furthermore, a mechanism 16 for detecting the projected image on the wafer 3 is provided, and the detecting mechanism 16 detects the projected image on the wafer 3 by detecting the projected image on the solid-state image sensor 33.
It consists of a lens 37 and a solid-state image pickup device 33. This gap measuring device further includes a gap measuring computer 34 that includes a mechanism for measuring the brightness of the projected image and a mechanism for calculating the gap between the mask and the wafer from the measured value of the brightness according to a predetermined formula. ing. That is, the image of the solid-state image sensor 33 is taken into the gap measurement computer 34. on the other hand,
A part of the light from the mercury lamp 27 is transmitted to the half mirror 3
0 and enters an intensity sensor 32 such as a photodiode through a lens 31. The gap measurement computer 34 corrects the light amount (brightness) of the image based on the signal from the intensity sensor 32 and performs measurement calculations. Furthermore, the gap measurement computer 34 further calculates the gap 4 between the mask 2 and the wafer 3 from the calculated light amount (brightness) of the image according to a predetermined formula.

The X-ray exposure apparatus shown in FIG. 3 further includes a main controller 35 and a vertical motion controller 3.
6 is provided. The gap measurement computer 34 is connected to the main controller 35 and exchanges gap measurement values and measurement sequence commands. Also,
The main controller 35 controls the vertical motion controller 36 in response to the signal from the gap measurement controller 34.
The chuck 23 is moved up and down.

Next, an overview of the entire sequence of mask-to-wafer gap measurement and gap adjustment will be described. The wafer 3 is loaded onto the chuck 23 at another station (not shown), and is placed under the mask 2 on the XY table 26 with a sufficient gap S (for example, S=75±15 μm) so as not to contact the mask 2. It is then positioned. Next, the opaque pattern 24 for gap measurement is irradiated with light 28 to measure the gap. Adjust the gap S to a desired value, for example 10 μm±0.5 μm. At this time,
When the gap S is non-uniform as shown in FIG. 3, if the chuck 23 is a chuck that deforms the wafer 3, the gap 4 is made to a desired value while deforming the wafer 3.

When the gap S reaches a desired value, the mask 2 and the wafer 3 are aligned by an alignment mechanism 13 (not shown) (see FIG. 2), and then exposed to X-rays 21. Gap measurement is performed as needed; that is, if the gap needs to be adjusted even during exposure, the gap measurement and adjustment continues until the exposure is finished. After the exposure is completed, stop the gap measurement, lower the wafer 3, and place the wafer 3 on the XY table 26.
Move the part and bring another part to the exposure location, or
The wafer 3 is carried out to a wafer unload station (not shown).

Next, the principle of the control device according to the present invention will be explained based on FIGS. 4a, b, and c. Figure a is a schematic partial side view of the gap measuring device corresponding to Figure 3, figure b is a diagram showing the relationship between the output of the detected brightness signal and the gap, and figure c is a wafer imaged on a solid-state image sensor. Figure d is an example of a projected image of the mask gap measurement pattern.

Light 28 from the illumination source 27 is irradiated onto the striped gap measurement pattern 24 of the mask 2 as shown in FIG.
For example, when wafer 3 is imaged at position 3 indicated by the dotted line,
b, the shadow 42 of the pattern 24 as shown in c.
is slightly visible, and the output L of the brightness signal of the projected image measured by the gap measurement computer 34 becomes Lb' as shown in figure b.If Lb' is corrected by the signal from the intensity monitor 32, it becomes Lb. When the wafer 3 is at the position 3a indicated by the dashed-dotted line, the shadow 42 is not visible at all, and when the output of the brightness signal of the projected image is corrected, it becomes La. Also,
When the wafer 3 is at the position 3c indicated by the two-dot chain line, it is entirely covered by the shadow 42, so the output of the brightness signal is the lowest Lc. The relationship between the gap S between the wafer 3 and the mask 2 and the output L of the brightness signal eventually becomes a line graph as shown in figure b, and the gap S can be measured from the output L.

The relationship between this output L and the gap S is determined by using the parameter as the pattern part (opaque part) of the gap measurement pattern 24.
The width Pd, the inter-pattern (transparent part) width Pl, the irradiation incident angle Θ ₁ , and the observation direction angle Θ ₀ can be easily determined by ordinary geometric calculations. By manipulating this parameter, the relationship between the output L and the gap S can be varied in various ways.

In the following description, for ease of explanation, Pd is assumed to be Pd = Pl, Θ ₁ = Θ ₀ , and Pd is varied.

Further, when the wafer 3 is at the position 3c indicated by the two-dot chain line, if both the wafer 3 and the pattern 24 are mirror-finished,
The output L of the brightness signal should originally be low as Lc, but due to the reflected light 52 whose path is shown in Figure a, the output L becomes large and becomes L ₂ '. For this reason, as shown in figure b, the brightness output L
is as shown by the two-dot chain line _L2 , and the S/N decreases compared to the case without reflection, so mask 2 or wafer 3
It is desirable that an anti-reflection coating or anti-reflection measures be applied to the surface.

Next, an embodiment of a gap control device in a proximity exposure apparatus according to the present invention, which is based on the principle of the gap control device described above, will be described with reference to FIGS. 5 to 9. FIG. 5a is a diagram showing an example of a gap measurement pattern formed on the mask 2. FIG. In the present invention, patterns P ₁ and P ₂ shown in FIG. 5a are used simultaneously. In pattern P ₁ , P _l1 = P _d1 = 1 μm, in pattern P ₂ , P _l2 =
P _d2 =1.25 μm. FIG. 5b is a diagram showing the relationship between the output L of the brightness signal of the projected image and the gap S when the gap measurement pattern shown in FIG. 5a is used.

When patterns P ₁ and P ₂ with different pattern widths Pd and Pl are used simultaneously, the period of the brightness output L with respect to the gap S is larger for the pattern P ₂ with larger Pd and Pl, and the period of the brightness output L with respect to the gap S is larger. When increasing, the peaks of the output L of both patterns P ₁ and P ₂ coincide. The gap S when the peaks of the outputs L coincide is shown as P ₁₂ in figure b.

The value P ₁₂ of the gap S at which the peaks of the outputs L from the patterns P ₁ and P ₂ coincide is calculated by the following equation.

P ₁₂ = Pl ₁ ×Pl ₂ /Pl ₂ −Pl ₁ ×2 (4) Here, if Pl ₁ =1 μm and Pl ₂ =1.25 μm, then P ₁₂ =10 μm.

As a result, if the resolution of the brightness signal output L is the same, when using two patterns, P ₂ and P ₁ (Pl ₁ < Pl ₂ ), compared to using only the P ₂ pattern, The gap measurement accuracy is improved by the ratio N N = P ₁₂ /Pl ₂ (5) of P ₁₂ and Pl ₂ . In the example of FIG. 5, the improvement is eight times.

Next, a method for arranging the gap measurement pattern on the mask will be explained based on FIG. 6th
Figure a is a partial plan view of the mask, and Figure 6b is an enlarged view of section A in Figure a. Assuming that the opaque patterns P ₁ and P ₂ for distance measurement are placed on street 71,
As shown in Figure 6a, even with a 10mm□ chip 73,
Arrangement with a pitch of 5 mm or more is possible. Street 71 is sufficient because the measurement pitch is around 5mm.
The above is sufficient.

Also, when 20mm□ (4 chips) is imaged on an imaging surface of 10mm□, the resolution of the imaging surface is 250×250,
One pixel length = 10 mm/250 = 40 μm. Therefore, the size of the patterns P ₁ and P ₂ only needs to be 40 μm or more, and this size is equal to the width of the street 71 of 60 to 100 μm.
Since it is within m, there is no problem. Further, it is preferable that the respective patterns P ₁ and P ₂ for gap measurement be separated from the circuit pattern 72 and between the respective patterns by a distance of at least a pixel.

Next, operations for measuring the gap between the mask and the wafer and adjusting it to a desired set value will be described based on an example. FIG. 7 is a diagram showing the operation of moving the wafer for gap measurement and adjustment. That is, the wafer is positioned under the mask, and the gap S is 75 ± 15 μm.
This is a diagram showing the relationship between the gap S and the gap measurement time path from 10±1 μm. The vertical axis is the gap S, the horizontal axis is the time t, and the gap measurement is performed at a pitch of 50 μm (marked with ◎).
10μm pitch (○) and 0.1μm pitch (・mark)
Let's do it. Gap measurement with a pitch of 10 μm (marked with ◯) is carried out using the example shown in FIG. In addition, the gap measurement with a pitch of 0.1 μm (marked with *) is shown in Fig. 5, in which the signal output from _P1 is detected with a resolution of 1/10.
Also, 50 μm (◎ mark) is 5 μm, which is 5 times _{Pl 1 =} Pd ₁ and Pl ₂ = Pd 2 of P ₁ and P ₂ patterns in Fig. 5, respectively.
It suffices to set it to 6.25μm, and in FIG. 6, P ₁ ,
Just follow the pattern of P ₂ and place it in the street.

The overall flow is shown below. Wafer 3, which is initially at 75 μm, is moved up and down by the vertical mechanism, and the gap is 70 μm.
m, 10 μm (○ mark) is detected at 60 μm. then 50μ
It is detected together with m pitch (◎ mark) and 10 μm pitch (○ mark), and the absolute value of the gap can be seen for the first time here. this
The 50 μm pitch (marked with ◎) is used to judge the absolute value in this way, and generally the accuracy of the initial gap is considered and the pitch is determined so that it exists on both sides of the gap.

After determining the absolute value of 50 μm, a 10 μm pitch (marked with a circle) is detected, and the wafer 3 is raised to a gap with an absolute value of 10 μm. When the absolute value of the gap S exceeds 10 μm, the signal output L according to the P1 pattern shown in FIG. ₅ is detected, and the brightest peak L _p is searched for.
There are various search methods, but here we go one step too far and store the brightness data of each point in the gap measurement computer to search for peak 85.

Another embodiment of the gap measuring method will be described based on FIG. FIG. 8 is a diagram of the output L and the gap S of the brightness signal of the projected image shown in FIG. 5b, with a diagram of the output L and the gap S according to another pattern added.

In the embodiment shown in FIG. 7, if the gap is adjusted during alignment and exposure, the gap S must be corrected even if there is a slight deviation. In this case, if the direction of the deviation is not known, it may be necessary to move in the opposite direction to the correction. A pattern _P3 with another pitch is used for this direction detection. Since the output L due to pattern P ₃ does not have a peak at the required gap of 10 μm, the change in output L due to P ₃ when the gap S shifts 9
If 2 is detected, the direction of the shift can be determined.

The illumination source is preferably white light so as not to cause interference with the pattern. However, the pattern pitch
If it is 3μm or more, the interference is 0.2μ even if a laser is used.
The gap S can be measured precisely by adjusting the pattern pitches Pd and Pl.

If the optical system for gap measurement is designed so as not to block the X-rays, as shown in FIG. 3, gap measurement can be made even during exposure. Further, if it is configured directly above the mask, the entire structure can be made compact. The solid-state imaging device may be a TV, a photodiode, a photomultiplier, or any other device that can detect changes in brightness. Further, both illumination and detection may be of a scanning type.

〔Effect of the invention〕

As explained above, according to the present invention, coarse transparent/opaque patterns are repeated multiple times on a mask at coarse intervals, and rough transparent/opaque patterns are arranged side by side at intervals narrower than the coarse intervals and with different intervals from each other. Since a thin transparent/opaque pattern consisting of multiple layers was formed,
With a simple configuration, the gap between the mask and the substrate such as a wafer can be adjusted to the desired value with a high precision of 0.2 μm or less in a short time, and even during exposure, without image distortion of the rotating pattern. The effect is that exposure can be performed with high resolution.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of an X-ray exposure device, FIG. 2 is a perspective view of an X-ray exposure device and a conventional gap measuring device,
FIG. 3 is a side view of an X-ray exposure apparatus for explaining the principle of a control device according to the present invention, and FIG. 4 is a diagram for explaining the principle of a control device according to the present invention. a is a side view showing the gap measurement part in Fig. 3, b is the output of the detected brightness signal and the gap
c is a diagram showing an example of a projected image on a wafer formed on a solid-state image sensor, d is a diagram showing a gap measurement pattern formed on a mask,
FIG. 5 is a diagram showing an embodiment of the distance control device in the proximity exposure apparatus according to the present invention.
a is a diagram showing an example of the gap measurement pattern formed on the mask, and b is a diagram showing the relationship between the output of the brightness signal of the projected image and the gap when the gap measurement pattern shown in a is used. FIG. 6 is a diagram showing a method of arranging a measurement pattern on a mask, in which a is a partial plan view of the mask, and b is a diagram showing A in a.
7 is a diagram showing the operation of moving the wafer for distance measurement and distance adjustment. FIG. 8 is a diagram showing the output of the brightness signal of the projected image and the distance in another embodiment of the present invention. FIG. 2... Mask, 3... Wafer, 24... Opaque pattern for gap measurement, 15... Illumination mechanism (27...
... illumination source, 29 ... lens), 16 ... projection image detection mechanism (37 ... lens, 33 ... solid-state image sensor), brightness measurement mechanism and gap measurement mechanism (gap measurement computer), S ... mask) and the gap between the wafer and the wafer, L...output of a signal indicating the brightness of the projected image.

Claims (1)

[Scope of Claims] 1. In a proximity exposure device, a coarse transparent/opaque pattern is repeated in plural times at a coarse period for distance measurement, and a rough transparent/opaque pattern is arranged at a narrower period than the coarse period and with different periods from each other. means for holding a mask formed with a plurality of thin transparent/opaque patterns formed on the mask; illumination means for projecting the coarse opaque pattern and a plurality of fine opaque patterns on the substrate by illuminating the coarse opaque pattern; a first detection device having a photoelectric conversion means for detecting the amount of light obtained through the photoelectric conversion means, and detecting a direction of deviation between the substrate and the mask based on a signal corresponding to the amount of light obtained from the photoelectric conversion means; and a plurality of photoelectric conversion means for detecting the amount of light obtained through the plurality of thin transparent patterns with respect to specularly reflected light from the surface of the substrate caused by the plurality of thin opaque patterns projected by the illumination means. and a second detection means that searches for the mutual peak relationship of each signal according to the amount of light obtained from each of the photoelectric conversion means, and a second detection means that moves the substrate up and down according to the direction of deviation obtained from the first detection means. Then, by matching the mutual peak relationships of the respective signals obtained from the second detection means, the distance between the substrate and the mask is controlled to a desired value determined by a plurality of thin transparent/opaque patterns. 1. A distance control device in a proximity exposure apparatus, characterized in that the distance control device is provided with a distance control means. 2. An interval control device in a proximity exposure apparatus according to claim 1, characterized in that an antireflection film is formed on the back surface of the opaque pattern of the mask.