JPH0426205B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an exposure apparatus for forming fine patterns particularly in high-density semiconductor devices (hereinafter referred to as LSI).

Conventional configurations and their problems Recently, LSIs have become more and more densely packed, and the dimensions of the fine patterns of each element are now 1 micron or less. FIG. 1 shows a diagram of the principle of a conventional exposure apparatus. The photomask 1 is aligned with the Si wafer 2, and light is irradiated from the light source 3 for exposure. At this time, the positioning is performed by rotating (θ) and parallelly moving the stage 4 on which the Si wafer 2 is mounted in two axes (x, y) using the positioning marks provided on the Si wafer 2. This was done by overlapping the marks on the Si wafer 2, but the alignment accuracy was about ±0.3 microns, and when forming submicron elements,
The alignment accuracy is poor and it is not practical.

Further, FIG. 2 shows a principle diagram of a projection exposure apparatus, which is the mainstream of recent exposure apparatuses. Exposure is performed by forming a reduced image of the pattern on the mask 6 onto the Si wafer 7 through the reduction lens 5. At this time, the resolving power δ and the depth of focus Δ when the aberration-free optical system is completely focused on the Si wafer 7 are determined by diffraction and are given by the following equation.

δ=λ/1.28NA=λ/1.28(1+N)F 1/1.28√2...(1) Δλ/2(NA) ² =λ/2(1+N) ² F ² δ ² /λ...(2) NA=sinα=1/(1+N)F...(3) where NA is the numerical aperture, α is half of the angle from the focus of the objective lens to the lens, N is the magnification of the objective lens system, and F is the focal length of the lens. Given f and diameter D, it is given by F=f/D.

From equation (1), in projection exposure, by increasing the NA, it is possible to obtain resolution close to the wavelength of the light source. However, when the NA is increased, the field area becomes smaller, and the number of pixels per field itself also decreases. Exposure lenses require a field of 10 to 15 mm square due to chip size requirements, which limits the resolution to around 1 μm.
Therefore, there are practical problems in forming elements that require alignment of submicrons or less.

Purpose of the Invention In view of these conventional problems, the present invention provides an exposure apparatus that can perform highly accurate alignment in the atmosphere with a simple configuration and is suitable for forming fine patterns. The purpose is to

Structure of the Invention The present invention detects the return position of the returning light in the vicinity of the position where the light flux is narrowed down by the diffusion optical system through a diffusion optical system such as a lens for diffusing a coherent light flux, and A light-receiving element having a minute hole for passing the light is arranged, and the light beam passing through the minute hole is passed through a parallel optical system such as a collimator lens installed so that it becomes a parallel light beam, and then the parallel light beam is further divided into two light beams. The beam is passed through a two-beam splitting optical system such as a beam splitter or a parabolic mirror to split the amplitude into two beams, and then the two amplitude-split beams are superimposed and interfered by, for example, two reflecting mirrors.
By placing a sample having a diffraction grating arranged substantially parallel to the interference fringes obtained by the two beams interfered by the two reflecting mirrors in the optical path of the two beams, the two beams can be A plurality of diffracted lights are diffracted and return to the light receiving element through the two reflecting mirrors, the two-beam splitting optical system, and the parallel optical system, and the position information obtained from the light receiving element is transmitted. Basically, by rotating the two reflecting mirrors, the angle of incidence of the two beams on the diffraction grating is adjusted, and the pitch of the interference fringes of the two beams is made approximately equal to the pitch of the diffracted photons. The present invention realizes an exposure apparatus that can perform alignment for forming submicron patterns.

DESCRIPTION OF EMBODIMENTS FIG. 3 shows an overall configuration diagram of the positioning mechanism portion of an exposure apparatus in an embodiment of the present invention.

Coherent light R from the laser generator 10
is generated, and this light R is guided to a diffusion optical system 13 for diffusing the light R using reflecting mirrors 11 and 12,
Furthermore, it is guided to a pinhole 14 arranged near the focal position of the diffusing optical system 13, and further
The light R that has passed is converted into parallel light by a parallel optical system 15 such as a collimator lens so that it has a parallel light velocity, and is then incident on a two-beam splitting optical system 17 such as a beam splitter via a reflecting mirror 16, so that the light R has a parallel light velocity. The amplitude is divided into reflecting mirror R1 and transmitted light R2 having the same intensity. The amplitude-divided reflected light R1 and transmitted light R2 enter the reflecting mirror M1 and the reflecting mirror M2, respectively, and form an approximately equal angle φ with respect to the surface of the sample W such as a semiconductor wafer.
1, 2 beam splitting optical system 1 so that the beam enters at φ2
7. Place reflecting mirrors M1, M2 and sample W.

As shown in Fig. 4, there is a pitch P on the surface of the sample W.
(for example, 1 μm), the two light beams R1
and non-pattern-formed areas (scribe lines, etc.) so that they are approximately parallel to the interference fringes formed by interference of R2.
It is formed. Diffracted lights R3 and R4 diffracted by the diffraction grating G are incident on photodetectors D1 and D2.

Further, the reflected light R1 is diffracted by the diffraction grating G of the sample W, and a plurality of diffracted lights are generated. Now, if we consider the counterclockwise direction as the positive direction with respect to the traveling direction of the diffracted light, among the multiple diffracted lights, as shown in Figure 5,
The 0th-order diffracted light R10 and the -1st-order diffracted light R11 pass through reflecting mirrors M2 and M1, respectively, and enter the two-beam splitting optical system 1.
7, the light passes through the reflecting mirror 16 and the parallel optical system 15 and returns toward the laser source. Similarly, the transmitted light R2 is also diffracted by the diffraction grating G of the sample W, producing a plurality of diffracted lights. Among the plural diffracted lights, as shown in Fig. 6, the 0th-order diffracted light R20 and the +1st-order diffracted light R21 pass through the reflecting mirrors M1 and M2, respectively, the two-beam splitting optical system 17, the reflecting mirror 16, and the parallel optical system 15 to generate a laser. Return to the source direction.

18 is each diffracted light R10, R11, R20, R2
1 is a light receiving element for detecting the position of each returning light, and is installed near the pinhole 14. As shown in FIG.
The c section, d section and the light receiving section are divided into four parts, and each lead wire a', b', c',
It can be extracted from d′. Further, in the center of the light receiving element 18, a hole e is provided through which the light R that has passed through the pinhole 14 passes. Hole e is on the optical axis.

The reflecting mirrors M1 and M2 have variable angles φ1 and φ2, as shown in FIGS. 8 and 9, respectively. When the optical axis direction is the z-axis, the rotation around the x-axis is α rotation, and the rotation around the y-axis is If the rotation around is β, it has means for rotating in the α and β directions. 19 is a movable frame for fixing the reflecting mirror; 20 is a support plate having a protrusion 20-a; and 21, 22 are micrometer heads fixed to the movable frame 19, and the micrometer heads 21, 22 can be operated. Therefore, the tips 21-a and 22-a of the micrometer head are connected to the support plate 20.
, the supporting plate 20 rotates in the α and β directions about the projection 20-a of the support plate 20 as a rotation center against the tensile force of the tension springs 23 and 24.

The wavelength of the laser is λ, and the diffraction grating G on the wafer W is
When the pitch of the reflected light R1 is diffracted by the diffraction grating G, the diffraction angle φ _d1 is expressed as P(sinφ _d1 − sinφ ₁ )=mλ ……(4) from the Bragg diffraction condition. It will be done. (However, m=0, 1, 2, 3...
positive integer) m = 0, that is, the diffraction angle φ _d10 of the 0th-order diffracted light R10 is P (sinφ _d10 − sinφ ₁ ) = 0 ... (5), and φ _d10 = φ ₁ , and the 0th-order diffracted light R10 is reflected light. equal to the incident angle φ1 of R1, reflecting mirror M2,2
Light beam splitting optical system 17, reflecting mirror 16, parallel optical system 1
5 and returns toward the laser source. m=
1, that is, the diffraction angle φ _d11 of the first-order diffracted light R11 is P(sinφ _d11 −sinφ ₁ )=λ (6). Now, when φ ₁ = −φ _d11, P=λ/2sinφ _d11 ...(7).

Also, the diffraction angle φ _d2 when the transmitted light R 2 is diffracted by the diffracted photon G is expressed as P(sin φ _d2 −sin φ ₂ )=mλ (8) based on the same Bragg diffraction condition. (However, m = 0, 1, 2...positive integer) m = 0, that is, the diffraction angle φ _d20 of the 0th order diffracted light R20 is P (sinφ _d20 − sinφ ₂ ) = 0 ... (9), and φ _d20 = φ ₁ , and the 0th-order diffracted light _R20 becomes light that is equal to the incident angle φ2 of the transmitted light R2 and has the opposite direction, and is reflected by the reflecting mirror M1 and the 2-beam splitting optical system 1.
7, passes through a reflecting mirror 16 and a parallel optical system 15, and returns to the direction of the laser source.

m=1, that is, the diffraction angle φ _d21 of the first-order diffracted light R21 is P(sinφ _d21 −sinφ ₂ )=λ (10). Now, when φ _d21 = −φ ₂ , P=λ/2sinφ _d21 ...(11).

Here, as shown in Fig. 10, φ ₁ ≠ (−φ ₂ ), φ ₁ ≠
(−φ _d1 ), φ ₂ ≠ (−φ _d21 ), each diffracted light R1
0, R11, R20, and R21 pass through the parallel optical system 15, but do not pass through the hole e of the receiving element 18, and the 10th
As shown by the dotted lines in the figure, the light receiving portion of the light receiving element 18, a,
Return to position b, c, or d. When the light intensity received by each light-receiving surface is converted into an electrical signal, extracted as position information, and the rotation mechanisms of reflectors M1 and M2 are operated, and no diffracted light enters each light-receiving part a, b, c, and d. In other words, as each diffracted light passes through the hole e (on the optical axis) of the light receiving element 17, φ ₁ ≒ (−φ ₂ ) ≒ (−φ _d1 ) ≒ (+φ _d21 )
...(12) It can be done as follows.

Further, if the pitch of interference fringes formed by interference between the reflecting mirror R1 and the transmitted light R2 is 〓, it is expressed as 〓=λ/sinφ ₂ −sinφ ₁ (13). In this case, from equation (12), equation (13) becomes 〓≒λ/2sinφ _d1 ……(14), and from equation (7), equation (14) becomes 〓≒λ／2sinφ _d11 =P ……(15 ) The pitch of the interference fringes formed by the interference of the two beams of reflected light R1 and transmitted light R2 can be made approximately equal to the pitch P of the diffraction grating G on the sample W.

In this way, by making the pitch P of the interference fringes of the two light beams almost equal to the pitch P of the diffraction grating G on the sample W, the interference fringes of the two light beams R1 and R2 are emitted from the diffraction grating G. Lights R3 and R4 diffracted by the wavefront splitting diffraction grating G are obtained,
The photodetectors D1 and D2 provide a light intensity that shows a positional relationship between the interference fringes of the two light beams and the grating G with very good resolution. Using the light intensity indicating this positional relationship, the positional relationship between the interference fringes of the two light beams and the sample W is detected, and the position of the sample W (direction perpendicular to the interference fringes and rotation around the optical axis) is corrected. Luminous flux R1, R2
The interference fringes and the sample W are aligned. In other words, by using a He-Cd laser with a wavelength of 4416㎜ as a laser beam, the interference fringe is 1 μm.
By using a diffraction grating G with a pitch of 1 .mu.m, it is possible to align a sample W such as a semiconductor wafer with a precision of several hundred degrees or less with respect to the interference fringes.

Thereafter, exposure may be performed by exposing the pattern forming portion (semiconductor element forming portion) of the sample W, that is, the semiconductor wafer. In addition, this pattern exposure, along with the alignment mechanism described above,
Accurate pattern exposure can be performed using an exposure apparatus having an exposure function capable of realizing the method proposed by the applicant using laser two-beam interference. Further, after performing the alignment method according to the present invention described above, it is also possible to perform fine pattern exposure using an exposure apparatus such as a projection exposure apparatus.

As a second embodiment, in the first embodiment, a light receiving element 18 having a light receiving part divided into four parts was used, but four light receiving elements are mounted on an easy-to-process substrate having a hole in the center for passing light. A similar effect can be obtained by using a light receiving element unit with fixed elements.

In addition, as a third example, each diffracted light R10,
A light-receiving element having a matrix of light-receiving surfaces for receiving the return light from R11, R20, and R21, and having a microhole in the center for allowing the light to pass through is attached to the pinhole 1.
4, the return position of each diffracted light beam can be obtained as two-dimensional position information, making it easier to match the pitch of the interference fringes to the pitch P of the diffraction grating G.

In addition, by arranging the light receiving element 18 near the focal point of the diffusing optical system 13, in other words, each diffracted light R
10, R11, R20, and R21 are most focused, the pitch of the interference fringes is adjusted to the diffraction grating G in order to return to the light-receiving surface of the light-receiving element 18 as light.
It is possible to adjust the pitch P more accurately. A pinhole 1 is located near the focal point of the diffusing optical system 13.
4. By arranging the light receiving element 18, excess diffracted light can be blocked and the pitch of the interference fringes can be more accurately matched to the pitch P of the diffraction grating G.

Effects of the Invention As described above, according to the present invention, the diffraction grating on the sample is arranged substantially parallel to the interference fringes obtained by the interference fringes of two light beams, and a plurality of The diffracted light is received as return light by a light receiving element and extracted as position information. For example, by rotating two reflecting mirrors, the angle of incidence of the two light beams on the diffraction grating is adjusted, and the pitch of the interference fringes of the two light beams is adjusted. By making the pitch of the diffraction grating almost equal, it becomes possible to detect the relative positional relationship between the interference fringes of the two light beams and the sample with a high precision of several 100 mm or less, with a simple configuration, large throughput, and , an exposure apparatus capable of forming submicron patterns can be realized.

[Brief explanation of drawings]

Figure 1 is a diagram of the principle of a conventional exposure device;
The figure is a principle diagram of a conventional projection exposure apparatus, and FIG. 3 is an overall configuration diagram of an exposure apparatus according to an embodiment of the present invention.
FIG. 4 is a plan view of a sample W having a diffraction grating G used in the same apparatus, FIG. 5 is a diagram showing the optical path of light when reflected light R1 of the apparatus is diffracted by the diffraction grating G, and FIG. is a diagram showing the optical path of light when transmitted light R2 of the same device is diffracted by the diffraction grating G, FIG. 7 is a plan view of the light receiving element 18 used in the same device, and FIG. 8 is a reflection mirror used in the same device. A front view of M1 and M2, FIG. 9 is a side view of reflecting mirrors M1 and M2 used in the same device, and FIG. 10 is a front view of each diffracted light beam R10 and R1 of the same device.
1, R20, and R21 are φ ₁ ≠ (−φ ₂ ), φ ₁ ≠ (−
φ _d1 ) and φ ₂ ≠ (−φ _d21 ). 10... Laser generator, 14... Pinhole, 15... Parallel optical system, 17... 2 beam splitting optical system, 18... Light receiving element, M1, M2... Reflecting mirror, R1... Reflected light, R2 ...Transmitted light, W...sample, G...diffraction grating, R10...0th order diffraction light, R
11...-1st order diffracted light, R20...0th order diffracted light,
R21...+1st order diffracted light.

Claims (1)

[Scope of Claims] 1 A light-receiving element is arranged near a coherent light beam, an optical system is provided that divides the amplitude of the light beam, overlaps it, and causes interference, and forms interference fringes in space by causing the two amplitude-divided beams to interfere with each other. A diffraction grating arranged substantially parallel to the interference fringes is arranged in the optical path of the two light beams, and the light diffracted by the diffraction grating is further returned through the optical system, and the intensity of the returned light is adjusted at the light receiving element. An exposure apparatus characterized in that the pitch of the interference fringes is adjusted to be approximately equal to the pitch of the diffraction grating by measuring the pitch of the interference fringes. 2. Exposure according to claim 1, characterized in that a light-receiving element is arranged near a position where the light flux is narrowed down by the diffusion optical system through a diffusion optical system for diffusing coherent light speed. Device. 3. A coherent light beam is passed through a diffusion optical system for diffusing, a pinhole is placed near a position where the light beam is focused by the diffusion optical system, and a light receiving element is placed near the light beam that has passed through the pinhole. Furthermore, it has an optical system that divides the amplitude of the light beam and overlaps it to interfere with each other, forms interference fringes in space by interfering with the two amplitude-divided light beams, and uses a diffraction grating arranged approximately parallel to the interference fringes. The pitch of the interference fringes can be adjusted to the pitch of the diffraction grating by placing the light in the optical path of the two beams, returning the light diffracted by the diffraction grating through the optical system, and measuring the intensity of the returned light at the light receiving element. An exposure device characterized by adjusting the exposure so that they are approximately equal. 4. An exposure apparatus according to claim 3, characterized in that the light receiving element comprises a light receiving element having a light receiving section divided into four parts and having a microhole for passing a light beam.