JPH0194618A - Reduction stepper - Google Patents

Abstract

PURPOSE:To obtain a device capable of assuring high resolution with respect to a general fine pattern on a flat surface as well as assuring both high resolution and sufficient depth of focus with respect to a pattern of contact holes and the like by disposing a means for making the dependency of light intensity on its wavelength in light relating to exposure variable. CONSTITUTION:An exposure device for projecting a mask pattern on a substrate is provided with a means for making the dependency of light intensity on its wavelength in light relating to exposure variable. For example, a reflector 1, a wavelength band setting device 2, an excimer laser resonator 3, a mirror 5, an illumination optical system 6, a reticle 7, a projection lens 8, a substrate stage 9, a control computer 10, etc., are provided. The wavelength band setting device 2 has a plurality of etalons each of which is different in a quality factor. The exposure wavelength band can be arbitrarily set by selecting an etalon having a quality factor corresponding to the desired wavelength band and inserting it into a light path of laser. The wavelength band of exposure is designated by means of input to the control computer 10. Selection and insertion of etalons can be automatically performed by the device 2 on the basis of its data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reduction projection exposure apparatus used for microfabrication of solid-state devices such as semiconductor devices, magnetic bubble devices, and superconducting devices.

[Conventional technology]

Conventionally, fine patterns in solid-state devices such as LSIs have been mainly formed using a fine projection exposure method.

The above method uses a projection lens to project a mask pattern.
Transfer is performed by forming an image on a substrate coated with resist. The critical resolution in the reduction projection exposure method is proportional to the exposure wavelength and inversely proportional to the numerical aperture of the projection lens, so improvements in resolution have been promoted by shortening the wavelength of n-point light and increasing the numerical aperture of the projection lens. Ta. On the other hand, the depth of focus of the projection lens is proportional to the exposure wavelength and inversely proportional to the numerical aperture of the projection lens. For this reason, the depth of focus is rapidly decreasing as the resolution is improved. That is, with the above-mentioned conventional method, it is difficult to make the pattern finer and to ensure a sufficient depth of focus at the same time, and especially when aiming at high resolution, the depth of focus becomes very shallow. Incidentally, the projection exposure method is discussed, for example, in Semiconductor Lithography Technology, Hoko Part, Sangyo Tosho, Chapter 4, pages 87 to 93.

[Problem that the invention seeks to solve]

As the integration of LSIs increases, the miniaturization and three-dimensionalization of elements simultaneously progress, and the need to form fine patterns on a substrate having a large uneven step structure on its surface has become stronger.

However, as mentioned above, in the current reduction projection exposure method, when the resolution limit is raised, the depth of focus becomes shallow. For this reason,
The entire exposed area of the substrate surface is kept within the above depth of focus,
It has become difficult to resolve fine patterns. In particular, when contact holes are formed, in addition to the fact that the depth of focus is originally small, the formation of contact holes is generally performed after a considerable surface step has been formed on the element, so the lack of depth of focus is serious.

An object of the present invention is to use an optical system having a short exposure wavelength and a large numerical aperture to ensure high resolution for general fine patterns on a flat surface, while also It is an object of the present invention to provide a projection exposure apparatus that can ensure both high resolution and sufficient depth of focus for images.

[Means for solving problems]

The above object is to provide a means for making the wavelength dependence of the light intensity of the light involved in exposure, in particular, the wavelength band width, variable in a reduction projection exposure apparatus, and to provide a means for making the wavelength dependence of the light intensity of light involved in exposure variable, and within a certain distance in the optical axis direction according to the wavelength band width. This is achieved by providing a projection exposure means that can continuously image the mask pattern.

[Effect]

According to studies by the present inventors, the depth of focus of an isolated pattern such as a hole pattern with a small proportion of transparent parts can be effectively increased by continuously imaging the pattern in the optical axis direction. On the other hand, when exposure is performed using light of different wavelengths,
Due to the chromatic aberration of the projection lens, the mask pattern is imaged at different positions depending on the wavelength. Therefore, by performing exposure using light having a relatively wide wavelength band, the mask pattern can be continuously imaged in the optical axis direction. Therefore,
By widening the wavelength band of each exposure, it is possible to effectively increase the depth of focus of an isolated pattern with a small proportion of transparent parts, such as a hole pattern.

However, as is well known, when the wavelength band is widened in a pattern such as a line-and-space pattern that has a relatively large proportion of transparent parts, the light intensity contrast decreases due to chromatic aberration. For this reason, it is necessary to narrow the wavelength band width for these patterns having a large proportion of transparent parts to sufficiently reduce chromatic aberration.

The exposure apparatus according to the present invention can change the wavelength band width of each exposure by means of varying the wavelength dependence of the light intensity of the light involved in the exposure. For patterns with a relatively large proportion of transparent parts, such as line-and-space patterns, exposure is performed using a relatively wide wavelength band width. Exposure can be performed. This makes it possible to form fine patterns on flat surfaces using a large numerical aperture and short wavelength exposure light, while also making it possible to form hole patterns with sufficient depth of focus even on substrates with large steps on the surface. becomes.

Next, it will be shown that the depth of focus of the hole pattern is increased by continuously imaging the pattern in the optical axis direction.

In an orthogonal coordinate system with the Z-axis as the optical axis, the light intensity distribution numerical value of the hole pattern imaged at 2=0 is i, (x.

y+z). In Figure 3(a), i(x+yt z)
An example of calculation is shown below. However, the calculation example is for a 0.3 μm square contact hole exposed to kvF excimer laser light using a projection lens with a numerical aperture of 0.4. Now, the above pattern is + from Z=-ω on the same optical axis.
Assuming that the image is formed in a −-like manner in (1), the light intensity distribution function (x, y, z) at this time is as follows, and does not depend on the position 2 in the optical axis direction. By the way, as can be seen from Fig. 3(a), it can be regarded as 1(xyz)20 for z(-3μm, 3μm<z. Therefore, it is discretized for numerical calculation.

r(xtytz)zΣ l (X v 'J p nΔ
2) ΔZn=-12 However, ΔZ=0.25 μm I (x v V v
z). However, the scale of the light intensity (vertical direction) is
This is a change from the one in Figure (a). Figure 3(a) and 3rd
As can be seen by comparing Figure (b), the image quality does not change even if the images are formed continuously, and in principle, the depth of focus can be made infinitely large.

〔Example〕

Example 1 Hereinafter, five embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a reduction projection exposure apparatus according to an embodiment of the present invention. This device consists of a reflector 1. Wavelength band setting device 2. Excimer laser resonator 3. Mirror 5. Illumination optical system 6
．． Reticle 7, projection lens 8, substrate stage 9. It is comprised of a control computer 10 and other various elements necessary for a reduction projection exposure apparatus.

The wavelength band setting device 2 has a plurality of etalons with different Q values, and any one of them can be inserted into the laser optical path. Therefore, by selecting an etalon having a Q value corresponding to a desired wavelength band within an allowable range and inserting it into the laser optical path, the exposure wavelength band can be arbitrarily set. The exposure wavelength band is specified by inputting it into the control computer 10 of the exposure apparatus, and based on this data, the wavelength band setting device 2 automatically selects and inserts the etalon.

In FIG. 1, the wavelength band setting device 2 is installed outside the laser resonator 3, but the method is not limited to this method in reality. That is, the wavelength band setting bag g12 may be inserted into the laser resonator 3, or the two may be integrated. Further, instead of etalons having different Q values, for example, a grating may be used. In this case, a relatively narrow bandwidth is preferably set by an etalon with a high Q value, and a relatively wide bandwidth is preferably set by a grating.

Next, using this apparatus, the pattern on the reticle 7 was projected and exposed onto a resist-coated substrate fixed on the substrate stern 9, and then developed to form a resist pattern.

KrF was used as the excitation gas for the excimer laser resonator 3. The wavelength band width of the laser when the band was not controlled by the wavelength band setting device 2 was about 0.5 nm.

First, the wavelength band setting device 2 sets the exposure wavelength band width to approximately 0.
．． The wavelength was set to 0.003 nm. For the projection lens used, the chromatic aberration due to this bandwidth is extremely small and is at a practically negligible level. Exposure was performed with the surface arrangement of the substrate set variously in the optical axis direction, and the range in the optical axis direction in which various fine patterns were resolved, that is, the depth of focus for the patterns was investigated. At the same time, the uniformity of pattern resolution over the entire exposed area was investigated using a substrate with a flat surface and a substrate with various unevenness and steps on the surface. As a result, hole patterns with diameters of 0.3 μm and 0.5 μm were resolved at focal depths of 1 μm and 2 μm, respectively.

Also, 0.3 μm and 0.5 μm line and space batons, or depths of focus of approximately 1.5 μm and 2.5 μm, respectively.
It was resolved with m. Furthermore, even if the substrate surface is extremely flat,
Due to the field distortion of the projection lens, it was difficult to resolve a hole pattern with a diameter of 0.3 μm over the entire exposed area.

Furthermore, as the unevenness of the substrate surface increased, it became difficult to resolve the other patterns on the entire surface.

Next, the wavelength band setting device 2 sets the exposure wavelength band width to approximately 0.
．． Similar batten formation was attempted by changing the thickness to 1 μm. According to the design data of the projection lens used, in the above band, the pattern is continuously imaged over about 10 μm in the optical axis direction due to the chromatic aberration of the lens. As a result, it became impossible to resolve the line and space button at all, but on the other hand, the line and space button had a diameter of 0.3 μm and a
．． The depth of focus of each 5 μm hole pattern increased to approximately 8 μm. This makes it possible to form the hole pattern all over the exposed region even when the substrate surface is highly uneven.

Example 2 FIG. 2 is a block diagram of another embodiment of the present invention.

In this apparatus, a wavelength scanning device 12 is provided in place of the wavelength band setting device in the first embodiment.

The wavelength scanning device 12 is composed of an etalon and a mechanism that controls its angle with respect to the laser beam, and narrows the wavelength band of the laser beam to about 0.003 nm, and by changing the angle, the center wavelength of the band is adjusted. change. Therefore, by changing the angle of the etalon during exposure and scanning the exposure wavelength, the imaging position of the mask pattern can be moved in the optical axis direction. In addition, the control computer can synchronize the timing of excimer laser pulse oscillation and etalon angle setting as specified in advance, so exposure can be performed using any exposure amount for each wavelength within the above scanning range. can be done.

In addition to changing the angle of the etalon with respect to the laser beam, methods for changing the center wavelength include changing the distance between the two plane plates that make up the etalon, or changing the pressure of the gas sealed between the two plane plates. Known means such as changing the type or type may be used.

A pattern was actually formed using this apparatus, and effects similar to those of the first example were confirmed.

Next, still another embodiment of the present invention will be described.

According to the inventor's study, the depth of focus of the fine pattern is
It is effectively increased by superimposing images whose imaging positions change continuously in the optical axis direction on the same optical axis.

The above method involves projecting and exposing a mask pattern onto a substrate using light in a relatively wide band, and continuously imaging the mask pattern in the optical axis direction within a range of chromatic aberration corresponding to the wavelength band. By.

Realized.

This method is undesirable in dense patterns with a large proportion of light-transmitting parts, as it causes a decrease in image contrast, but is extremely effective in isolated hole patterns, etc., with a small proportion of light-transmitting parts.

In order to demonstrate the effects of the present invention, we will first discuss the light intensity distribution of images when images whose imaging positions change continuously in the optical axis direction are superimposed.

In a Cartesian coordinate system with the Z axis as the optical axis direction, plane Z = 0
The three-dimensional light intensity distribution function of the image whose imaging plane is 1
(xpytz). Position this image on the same optical axis Z=
The light intensity distribution function I(X + 3' t Z ) of the composite image when images are formed continuously from -L to Z=L is expressed as follows. However, here, w(Q) is the relative intensity ratio of the image formed at Z=Q to the image formed at Z=0.

Since it is N simple, assuming that all the relative intensity ratios are 1 and discretizing the integral, I(X+yyZ)"Σ x(xyytz nΔl1)
−ΔL −・・■n=−N However, 2N+1 is obtained. In FIG. 4, N=8. The calculation results for each term on the right side and the left side of Equation 0 when Δff=0.25 μm are shown.

However, the scale of the light intensity is appropriately: A scale. Note that the calculation is for a 0.3 μm square contact hole exposed to krF excimer laser light using a projection lens with a numerical aperture of 0.4.

From a comparison of I(Xsy+Z) and i(x+ypz), it can be seen that the range in the optical axis direction where a good light intensity distribution can be obtained, that is, the depth of focus, increases by about 70% due to the above superposition.

In general, the depth of focus further increases as the value of N increases, but there is a concern that image deterioration may occur as a result. Therefore, we will focus on the light intensity distribution at Z=0 when the value of N is increased. By the way, Zku-8・ΔQ, 8-ΔQ <
Since it can be regarded as l(X+5'tz)20 for z, the above light intensity distribution is.

■(Xsy+z)=Σ 1(Xryv nΔl2)−
Δ2n=-+v 2 Σ 1(xpyy-nΔQ)・ΔQ n=-6 ・・・■ In other words, even if a value of N of 8 or more is used, the obtained light intensity distribution is almost the same as that when N is 8. does not change. this is,
This is a phenomenon peculiar to isolated patterns with a small proportion of light transmitting parts, such as contact holes, where the light intensity distribution approaches 0 as the defocus increases. Therefore, for the above-mentioned pattern, by increasing N and enlarging the range in which images are continuously formed, it is possible in principle to increase only the depth of focus to any extent without deteriorating the image quality.

The same mask pattern can be imaged continuously in the optical axis direction by performing projection exposure using exposure having a finite wavelength band and a projection lens that is not achromatized for the above wavelength band. can be done. That is, because the imaging position for each wavelength within the above band differs due to chromatic aberration,
This allows the image plane to be continuously distributed in the optical axis direction.

At this time, when the imaging plane shifts in the optical axis direction due to a change in wavelength within the above band, fluctuations in imaging magnification, field curvature, and D distortion must be kept within a certain tolerance range.

Furthermore, since the light intensity generally varies depending on the wavelength within the band, the light intensity of the image differs depending on the imaging position.

By the way, considering a narrow wavelength range, the relationship between the wavelength and the imaging position can generally be expressed by a linear equation, so w(Q) in equation (2) can be expressed as the light intensity wavelength dependence (wavelength spectrum) of the light involved in exposure. can be considered equivalent to Needless to say, in order to obtain uniformity of the image in the optical axis direction, it is desirable that w(12) be regarded as 1. Therefore, the wavelength spectrum of the light involved in exposure is preferably rectangular or trapezoidal with constant light intensity only within the band.

Example 3 A mask pattern was transferred onto a resist film coated on a substrate using a krF excimer laser beam narrowed to a wavelength band width of 0.1 nm, and then developed to form a resist pattern. According to the design data of the projection lens, the fifth
As shown in the figure, the mask pattern is continuously imaged over a distance of about 10 μm in the optical axis direction corresponding to the above wavelength band.

Within the range including the above image formation position, the surface position of the resist-coated substrate was set variously in the optical axis direction, and exposure was performed to examine the range in which the pattern was resolved. The pattern used for evaluation was a 0.3 μm square hole pattern. As a result, it was found that the range in the optical axis direction of the substrate surface position where the above pattern is resolved, that is, the effective depth of focus, was about 8 μm.

On the other hand, in the conventional method of exposure using light whose band is sufficiently narrowed so that monochromatic aberration can be ignored, the depth of focus of the pattern described above was only about 1 μm. In an actual LSI, there are uneven steps on the surface. In order to resolve the above-mentioned pattern over the entire exposed area regardless of uneven steps, a depth of focus of at least 2 μm is required. Therefore, with the conventional method, it was difficult to apply the above-mentioned pattern to an actual LSI, but it has become possible by using the one-line method.

Note that the projection lens of the projection exposure apparatus used in this example was 1
It was a monochromatic lens made of a single material, synthetic quartz. Therefore, there is a slight change in the imaging magnification depending on the n-light wavelength, that is, the imaging position, and if the substrate surface position differs in the optical axis direction,
A pattern misalignment occurred at the periphery of the exposure area. This is not an effect intended by the present invention, and must be suppressed as much as possible.Therefore, the projection lens has variations in magnification, field distortion, field curvature, etc. when the exposure wavelength is changed. It is necessary to use one designed so that the imaging plane can be shifted in the optical axis direction while keeping the value within a certain tolerance range. Further, the light source used for exposure and the wavelength band width of each exposure tip are not limited to those shown in this embodiment, and may be used. However, the above wavelength band width is set so that the distance on the optical axis at which the mask pattern is continuously imaged corresponding to the band width is greater than or equal to λ (central wavelength, NA is the numerical aperture of the projection lens used for exposure). It is desirable that This is because the effect of increasing the depth of focus λ can hardly be expected.

Example 4 Next, another embodiment of the present invention will be shown.

k r F By using an etalon to narrow the wavelength band width of the excimer laser beam to 0.0025 nm and changing the etalon angle, the center wavelength can be reduced to 24 nm.
0.0025n from 8.3nm to 248.35nm
It was shifted by m and exposed for 94 pulses. At this time, in order to set the wavelength dependence of the light intensity of the light contributing to exposure as shown in FIG. 6, the number of pulses for each of the shifted wavelengths was changed as shown in FIG. 7. The projection lens using X, the evaluated pattern, and the evaluation method are the same as in the first embodiment.

In this example, a hole pattern of 0.3 μm square can be formed with a hole pattern of approximately 4 μm.
It was possible to resolve the image with a depth of focus of . Therefore, the following pattern forming method is possible.

(1) The reduction projection exposure includes a step of performing reduction projection exposure onto a resist film through a mask pattern having a desired shape, and a step of developing the resist film, and the reduction projection exposure is performed using a projection lens having a numerical aperture NA. In a pattern forming method performed using light of wavelength λ, the imaging position on the optical axis of the mask pattern is centered at the imaging position with respect to the center wavelength λ.
A pattern forming method characterized by continuous distribution over λ.

(2) The wavelength band width of the light involved in the reduction projection exposure is
(1) characterized in that the imaging position on the optical axis of the mask pattern is determined to be continuously distributed within the range due to the chromatic aberration of the projection lens corresponding to the bandwidth.
) pattern forming method described.

(3) By scanning the wavelength of the light involved in the reduction projection exposure during the exposure, the imaging position on the optical axis of the mask pattern can be determined by the chromatic aberration of the projection lens.
At the same time as moving over the range, the moving speed of the imaging position is controlled as specified in advance by adjusting the scanning speed of the wavelength, or exposure is performed as specified in advance in synchronization with the scanning of the wavelength. A pattern forming method characterized by performing exposure while changing the amount of light.

(4) The pattern forming method according to (2) or (3) above, wherein the wavelength dependence of the light intensity of the light involved in the reduction projection exposure is trapezoidal or bimodal.

(5) The pattern forming method as described in (1) above, wherein the light used for the reduction projection exposure is excimer laser light.

(6) In the projection lens, the wavelength band width;
or for each wavelength within the range of the wavelength scan,
Variations in the imaging magnification of the mask pattern, field curvature and field distortion of the imaging surface of the mask pattern are within predetermined tolerance ranges, and the imaging surfaces differ in the optical axis direction. The pattern forming method according to (2) or (3) above.

〔Effect of the invention〕

As described above, the reduction projection exposure apparatus according to the present invention is a reduction projection exposure apparatus that performs reduction projection exposure of a mask pattern onto a substrate, and is provided with means for varying the wavelength dependence of the light intensity of the light involved in the exposure. As a result, the image formation position of the pattern on the mask by the projection lens can be arbitrarily distributed using the chromatic aberration of the lens, so that the depth of focus can be increased according to the exposure pattern.

Therefore, shorter exposure wavelengths, higher numerical apertures of projection lenses,
Also, it is possible to cope with the lack of depth of focus caused by an increase in uneven steps on the surface of the substrate due to the three-dimensional element structure. Therefore, by using the reduction projection exposure apparatus according to the present invention, it is possible to remove a major obstacle when applying the reduction projection exposure method to fine pattern formation in solid-state devices such as LSI, and expand the scope of application of the reduction projection exposure method. It can be expanded to the production of even finer solid-state devices.

Furthermore, by using the pattern forming method according to the present invention, it is possible to increase the depth of focus of a pattern having an isolated transparent part, such as a contact hole in the reduction projection exposure method. It is possible to deal with the lack of depth of focus due to increased unevenness on the substrate surface, tilt of the substrate, and curvature of field of the projection lens due to the increase in the numerical aperture of the lens and the three-dimensional element structure. .

Therefore, by appropriately using the pattern forming method according to the present invention when manufacturing solid-state devices such as LSIs, it is possible to remove major obstacles when applying the reduction projection exposure method to the pattern, and expand the scope of application of the reduction projection exposure method. It can be extended to the manufacture of even finer solid-state devices.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a block diagram showing another embodiment of the present invention, Fig. 3 is a characteristic diagram showing the effects of the present invention, and Fig. 4 is a block diagram showing an embodiment of the present invention. , yX diagram showing the action of the present invention, Fig. 5 is a characteristic diagram showing the principle of an embodiment of the present invention, Fig. 6 is a characteristic diagram 2 showing the conditions of an embodiment of the present invention, Fig. 7 FIG. 2 is a diagram for setting conditions of an embodiment of the present invention. 1...Reflector, 2...Wavelength band setting device, 3...
Excimer laser resonator, 4... Output mirror, 5... Mirror, 6... Illumination optical system, 7... Reticle, 8...
Projection lens, 9...Substrate stage, 10...Control computer, 12 7I! 1 No. 2-3rd Ward of the Country (b. No. 4 l Figure 5)

Claims (1)

[Scope of Claims] 1. A reduction projection exposure apparatus for projecting and exposing a mask pattern onto a substrate, comprising means for varying the wavelength dependence of the light intensity of the light involved in the projection exposure. . 2. Reduction projection exposure according to claim 1, wherein the means for varying the wavelength dependence of the light intensity is a means for varying the wavelength band width of the light involved in the exposure. Device. 3. The reduction according to claim 1, wherein the means for making the wavelength dependence of the light intensity variable is a means for changing the wavelength of the light involved in the exposure during the exposure. Projection exposure equipment. 4. In the projection lens that performs the projection exposure, the imaging plane of the mask pattern differs in the optical axis direction for each wavelength of light involved in the projection exposure, and the imaging magnification of the mask pattern varies. 2. The reduction projection exposure apparatus according to claim 1, wherein curvature of field and distortion of field of said image forming surface are within predetermined tolerance ranges. 5. The reduction projection exposure apparatus according to claim 1, wherein the light used for the projection exposure is excimer laser light.