JPH0443409B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an exposure apparatus for devices having fine patterns, particularly semiconductor devices and the like having a submicron rule of 1 micron or less.

Conventional Structures and Problems Semiconductor devices have become increasingly dense in recent years, and the dimensions of semiconductor elements are on the verge of reaching submicron dimensions.
Conventional exposure using ultraviolet rays is already considered to have reached its limit in forming such fine patterns, and recently, exposure apparatuses using deep ultraviolet rays, X-rays, electron beams, ion beams, etc. have been in the spotlight. but,
The above-mentioned exposure equipment is not only expensive, but also
Exposure apparatuses using rays, electron beams, and ion beams have low beam intensity and long exposure times, so it has been difficult to apply them to the manufacture of mass-produced semiconductor devices.

Conventionally, photolithography using ultraviolet light has been used, but its resolution is around 1 μm due to light diffraction and interference, making it impossible to achieve submicron line widths. The theoretical line width is L=0.6×λ/NA (1+1/m), where λ: light waveform, NA: numeric aperture, and m: reduction projection ratio.

In the case of close exposure, m=1, N.A0.28, λ
= 435.6 nm, it means that only a line width of about 1.8 μm can be resolved.

In the case of reduction projection exposure, the numeric aperture NA can be increased, NA = 0.32, m = 10,
When λ=435.6 nm, the limit is to resolve a line width of approximately 0.9 μm.

Purpose of the Invention The present invention has been made in view of the problems of the conventional examples,
The object of the present invention is to provide a pattern forming apparatus for forming semiconductor integrated circuit devices having submicron fine element dimensions by light exposure.

Structure of the Invention In order to achieve a linewidth that is less than half of the limit resolution obtained by conventional exposure, the first lens uses a light beam that has been wavefront-divided by a grating formed on the reticle surface. In the spectral plane of the system, only the two diffracted lights are passed through a spatial filter,
This provides an exposure apparatus configuration in which these two light beams are crossed again by a second lens system, and interference fringes generated by one light beam are projected onto a substrate and miniaturized.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows the configuration of a reduction projection exposure apparatus a according to a conventional example and an exposure apparatus b according to the present invention. A comparison will be made below between the configuration of a conventional exposure apparatus and the configuration of the present invention. In the conventional exposure apparatus, a light beam emitted from a light source 1 is incident on the entrance pupil of a reduction projection lens 4 through a condenser lens 2. A reticle 3 is placed between the condenser lens 2 and the reduction projection lens 4, and the image emitted from the reticle 3 as a secondary light source is formed on the wafer 5 by the reduction projection lens 4, and the pattern on the reticle 3 is is formed on the wafer 5 in a reduced size.

On the other hand, as shown in FIG. 1b, the optical system according to the present invention has a configuration assuming that the light emitted from the light source 11 (in this figure, in order to obtain higher coherence, laser light is assumed, but the overall The optical system is a white optical system, and a white light source such as a mercury lamp may also be used. Light source optical system 13
Therefore, the light enters the entrance pupil of the first Fourier transform lens 15. A reticle 14 is disposed between the light source optical system 13 and the first Fourier transform lens 15, and the image emitted from the pattern of the reticle 14 as a secondary light source is once focused by the first Fourier transform lens, and then The image of the pattern on the reticle is projected onto the wafer 18 through the second Fourier transform lens 17. When the focal lengths of the first Fourier transform lens and the second Fourier transform lens are made equal, the pattern on the reticle is projected at the same magnification. By changing the focal lengths of the first and second Fourier transform lenses, reduced projection becomes possible. On the back focal plane of the first Fourier transform lens, the higher-order diffracted light of the pattern on the reticle is spatially distributed, and in the configuration of the present invention, a spatial filter 16 is arranged on this Fourier transform surface, By image processing the pattern formed on the reticle 14, a finer pattern is projected onto the surface of the semiconductor wafer 18 when the pattern on the reticle 14 is reduced and projected. Wafer 18 is held on a stage.

FIG. 2 shows a reticle used in the exposure apparatus of the present invention. FIG. 2a is a plan view of the reticle 14, and FIG. 2b is a sectional view thereof. Reticle 14
It consists of a window 42 that transmits light and a cross section 43 that blocks light.A phase grating 41 is formed in the window 42 that transmits light, and the pattern 42 is fine in the direction in which the phase grating is formed. be converted into Reticle 1
The incident light 44 is incident on the pattern 42, and as shown in FIG. It is diffracted. A sheath section 43 surrounding the pattern 42 is formed of a film of chromium, chromium oxide, or the like, and allows incident light 44 to pass only through the inside of the pattern.

In the example shown in FIG. 2, a phase grating 41 is used to obtain the diffracted light, but the grating may be an amplitude grating, or an Ethieret grating if the incident light is incident diagonally.

FIG. 3 is a diagram further explaining the principle of the exposure apparatus of the present invention. Light with a wavelength λ emitted from the light source 11 is expanded by a beam expander 20 and further made into parallel light by a collimator lens 21 . The phase grating 41 on the reticle is placed at the position x ₁ of the focal point ₁ of the first Fourier transform lens 15 . The pitch P ₁ of the phase grating 41 and the diffraction angle θ ₁ of the diffracted light have a relationship of P ₁ sin θ ₁ =λ. The light thus diffracted into a plurality of diffracted lights enters the Fourier transform lens 15, and further forms a Fourier spectrum image corresponding to each diffracted light on the back focal plane ξ. The coordinate ξ ₆₁ connecting the Fourier spectra of the first-order diffracted light is expressed as ξ ₆₁ = ₁ sinθ ₁ , and is completely separated from the Fourier spectrum of the 〇-order diffracted light ξ ₆₀ ξ _{60 1} sinθ ₀ = 0. Forms a Fourier spectrum image on the transformation plane. As shown in FIG. 1b, a spatial filter 16 is arranged on this Fourier transform surface, and as shown in FIG. 3, only the ±1st-order diffracted light passes through. This diffracted light passes through the second Fourier transform lens 17 and further passes through the wafer 18.
projected on top. The image projected onto the wafer 18 forms an image on the reticle, and the formed image in which the two light beams interfere is further refined into the pitch of interference fringes. The pitch P ₂ of the interference fringe is given by P ₂ =λ/2sinθ ₂ . At this time, the first Fourier transform lens 1 is placed at the front focal point of the second Fourier transform lens 12.
Since the Fourier transform surface of 5 is set, there is a relationship of ₁ sin θ ₁ = ₂ sin θ ₂ = ξ ₆₁ , and the relationship between the images through the first and second Fourier transform lenses is P ₂ = λ/2 sin θ ₂ = ₂ λ /2 ₁ sinθ ₁ = ₂ / ₁ P ₁ /2 ...(1) There is a relationship. Therefore, when ₁ = ₂ , the pitch _P2 of the interference fringes generated on the wafer 18 is half the pitch of the grating on the reticle, and an effect equivalent to doubling the resolution of the lens can be obtained. It will be done.

FIG. 4 shows a second embodiment of the present invention. The difference from the first embodiment is that the diffraction grating 4 of the reticle
The incident light source 11 that is incident on the reticle is obliquely incident on the reticle. At this time, the beam expander 20 and collimator lens 21 are also arranged diagonally. The light incident on the grating on the reticle is diffracted by the diffraction grating into 〇th order and ±1st order, and is then diffracted by the first Fourier transform lens 15 into 61, 62, 63, respectively, at the Fourier transform plane ξ.
A spectral image is formed. In this optical system, only the light focused on the 〇th order 61 and the -1st order 62 is the second
It is designed to pass through a Fourier transform lens 17. The light focused on the ±1st order 63 is filtered by the lens, but some of it remains as stray light on the wafer 1.
8, a spatial filter is placed near the Fourier transform surface to cut off the ±1st-order diffracted light.

The diffraction grating 41 on the reticle in this embodiment is preferably of an echelon type, and is preferably formed so that the intensity of the 0th-order diffracted light is equal to the intensity of the 1st-order diffracted light. If the intensities of the 0th-order and -1st-order diffracted lights are not equal, a filter is installed on the Fourier transform surface ξ to equalize the respective light intensities. The pitch P ₁₁ of the diffraction grating on the reticle and the diffraction angle 2θ ₁₁ of the diffracted light are P ₁₁ sin2θ ₁₁ = λ, and by the same argument shown in Figure 3, the pitch P ₁₂ of the interference fringe is P ₁₂ = λ/2sin2θ ₁₂ = ₂ 〓/2 ₁ sinθ ₁₁ = _2/1・P ₁₁ cosθ ₁₁ …(2) At this time, the light _emitted from the grating with the pitch of P ₁₁ is
Since the full field angle of the first Fourier transform lens can be used, a finer pitch of interference fringes can be realized compared to the first equation.

FIG. 5 shows a reticle image and a transferred image on a wafer according to the present invention. A pattern similar to that shown in FIG. 2a is formed on the reticle 14. The light diffracted from the phase grating on the reticle 14 is reflected by the orientation and pitch of the phase grating in the Fourier spectral plane of the first Fourier transform lens.
Furthermore, the position of the spectral image differs depending on the order of the diffracted light from the phase grating. The spectral image obtained by the vertical striped phase grating 41 on the reticle corresponds to 60 for the 0th order, 65 for the +1st order, and 66 for the -1st order.
The spectral image obtained by the horizontal striped phase grating on the reticle corresponds to 60 for the 0th order, 61 for the +1st order, and 62 for the -1st order. When there are phase gratings with different pitches, spectral images are obtained at different positions.
On this spectral plane, the 〇 order light is cut off, ±
When only the first-order light is passed through, the image obtained on the wafer by the second Fourier transform lens corresponds to the vertical phase grating, as described in 81, and the image obtained by the second Fourier transform lens is a finely divided vertical interference image, as described in 81. The image becomes a fringe image, and the image corresponding to the horizontal phase grating becomes a horizontal interference fringe image as shown at 80. Furthermore, the pitch of interference fringes corresponding to the pitch on the reticle is obtained on the wafer as given by Tables (1) and (2).

FIG. 6 shows a resist forming process using the present invention. FIG. 6a shows the reticle pattern transferred onto the wafer for the first time, and the minimum line width is the resolution W by the reduction projection lens.
It corresponds to The pattern is a positive resist and is formed on a chip 90 on a wafer 18. The chip 90 includes, for example, figures 91 and 92 with wide gate widths corresponding to peripheral circuits, a pattern 93 that requires a narrow pattern and forms a gate inside a memory cell, and a sense amplifier circuit for reading out cell signals. A gate pattern 94 such as the following is formed. The cell pattern 93 and the sense amplifier pattern 94 are designed to have a pattern shape that is an integral multiple of the pattern obtained by interference fringe exposure. FIG. 6b shows areas 95, 96, 97
Each of them consists of a peripheral portion 95 corresponding to figures 91 and 92 with wide gate widths, a cell portion 96 corresponding to the cell pattern 93, and an amplifier portion 97 corresponding to the sense amplifier pattern. There is no need to expose interference fringes in the peripheral portion 95, so the peripheral portion 95 is black. In the cell portion 96, since vertical interference fringes are exposed, a vertical phase grating is formed and light is transmitted, so the color is white.

In addition, in the amplifier section 97, since horizontal interference fringes are exposed, a horizontal phase grating is formed and the color is white. According to the principles of the present invention, the light transmitted through the reticle of FIG. 93 is exposed so that vertical interference fringes 98 overlap. Further, in the amplifier portion 97, horizontal interference fringes 99 are superimposed on the pattern 94 and exposed. Patterns 91 and 92 are not exposed. As a result, when the development is performed again, Fig. 6 d
As shown in FIG.
Then, a subdivided amplifier pattern 101 is formed.

In the above text, only Fourier transform lenses have been discussed, but these first and second Fourier transform lenses do not necessarily have to satisfy the Fourier transform conditions, and can be used as lens systems with normal tanθ conditions. However, it is possible for those with image processing capabilities above.

In addition, with this exposure system, by directly projecting the image on the reticle without passing through a spatial filter, a reduced projection image similar to conventional ones can be obtained on the wafer, making it possible to use it as a reduced projection exposure material in the same way as conventional methods. can.

Effects of the Invention As described above, in the exposure apparatus of the present invention, by performing image processing on the Fourier transform plane of the Fourier transform lens, it is possible to realize a resolution that is more than twice that of a conventional lens. Furthermore, vertical and horizontal interference fringes can be formed simultaneously. Furthermore, interference fringes with different pitches can be formed simultaneously.

[Brief explanation of the drawing]

Fig. 1a is a schematic diagram of an exposure apparatus using a conventional reduction projection optical system, Fig. 1b is a schematic diagram of an exposure apparatus using a Fourier transform lens system according to an embodiment of the present invention, and Figs. 2a and b 3 is a schematic plan view and a sectional view of a reticle used in the present invention, and FIG.
FIG. 4 is a diagram illustrating the principle of the exposure apparatus according to the second embodiment of the present invention,
FIG. 5 is a diagram showing a subdivision method of pattern formation according to the present invention, and FIGS. 6 a to 6 d are a pattern formed by photolithography in a pattern forming process according to the present invention, a reticle according to the present invention, a reticle according to the present invention, and a reticle according to the present invention. FIG. 6 is a diagram showing an exposure state of interference fringes and a subdivided pattern. 11...Light source, 13...Light source optical system, 14...
Reticle, 15...first Fourier transform lens,
17... Second Fourier transform lens, 18... Wafer, 16... Spatial filter, 41... Grid,
60, 61, 62, 63...spectral image, 8
0, 81, 98, 99...interference fringes.

Claims (1)

[Scope of Claims] 1. A light source, a light source optical system, a reticle, a first lens system, a spatial filter, a second lens system, and a substrate, and a grating is formed on the reticle surface,
A light beam emitted from the light source is incident on the reticle surface through the light source optical system, the wavefront of the light beam is split by a grating on the reticle, and the light beam is incident on the first lens system. The spatial filter provided near the spectral plane blocks a portion of the light flux that has passed through the first lens system to obtain two appropriate light fluxes, and guides the two light fluxes to the second lens system; An exposure apparatus characterized in that interference fringes generated using the second light beam that has passed through the second lens system are projected onto the substrate. 2. The exposure apparatus according to claim 1, wherein the incident angle of the light beam incident on the reticle is in the normal direction of the reticle. 3. Among the light that has passed through the grating, only the ±1st-order diffracted light is passed through a spatial filter, and the ±1st-order diffracted light is simultaneously projected onto the substrate. The exposure apparatus described. 4 The incident angle of the light beam incident on the grating is at an angle to the grating, and the exit angle from the grating of either of the ±1st order diffracted light and the 0th order diffracted light is equal, and 2. The exposure apparatus according to claim 1, wherein the light intensity of the diffracted light and the light intensity of the first-order diffracted light are adjusted to be equal by a spatial filter. 5. The exposure apparatus according to claim 1, wherein the grating on the reticle is a phase grating. 6 has a light source, a light source optical system, a reticle, a first lens system, a spatial filter, a second lens system, and a substrate, and a grating is formed on the reticle surface,
A light beam emitted from the light source is incident on the reticle surface through the light source optical system, the wavefront of the light beam is split by a grating on the reticle, and the light beam is incident on the first lens system, and the spectrum of the first lens system is A spatial filter corresponding to the reticle provided near the surface blocks a part of the light flux that has passed through the first lens system to obtain two light fluxes, and these two light fluxes are transmitted to the second lens system. generating interference fringes on the substrate using the two light fluxes that have passed through the second lens system, and attaching and detaching the reticle and spatial filter in the optical system without passing through the spatial filter. An exposure apparatus characterized in that an image of the reticle is directly projected onto a substrate.