JPS62226628A - Positioning method - Google Patents

Abstract

PURPOSE:To perform the positioning between a mask and a wafer with high accuracy of several mum order, by applying diffracted rays from moire fringe generated when holograms regenerating cylindrical waves of different focal length are overlapped thereon. CONSTITUTION:A laser beam 9 is reflected 10 and made an incidence to a reference hologram 5 on a mask 1, and the primary diffracted ray is converged into a photodetector 12 divided into four divisions by moving 3 a mask. The difference between the sum of signals of divided surfaces A, B and C, D is calcurated 16. According to the x-direction shift, a detected signal draws an S curve, and a beam passes the middle point between the surfaces A, B and C, D when the curve passes a point O. As to the y-direction, the difference between the sun of signals of surfaces A, D and B, C is used. A reference hologram 7 wherein the reference hologram 5 is rotated by 90 deg., a photo detector 15 and an operating circuit 19 are provided at the diagonal corner of a wafer. The mask is driven so as to process 2 the signals of (x) and (y) directions and obtain the point O of the S curve, and the poisition is fisced to an equipment. Then the laser beam 9 is applied on a moire fringe generated when the holograms 5 and 7 and the arranging holograms 6 and 8 of the wafer are overlapped thereon. The positioning between the mask and the wafer is performed by moving 4 the wafer and converging the primary diffracted rays from the moire fringe into photodetectors 13 and 14 divided into four divisions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for positioning a wafer and a mask in IC manufacturing with high precision.

[Prior art and its problems]

As the density of VLSI increases, the size of a single circuit pattern is becoming smaller. In the phosphorography technique for manufacturing this VLSI, it is necessary to determine the relative positions of the mask and the mask with high precision. Currently, such positioning is performed by a method of matching a large number of straight parallel stripes drawn on each of the wafer and mask. However, the placement accuracy of this easy method varies by about 0.2 μm, and the accuracy of the placement varies by about 0.2 μm. Do not use tM; it is not suitable for transferring even finer patterns. In these phosphorography,
Although a positioning angle of 0.01-0.05 .mu.m is required, there is currently no established method for positioning.

In order to achieve this highly precise placement, a positioning technology using moiré fringes has been developed.

This high-precision positioning method using moiré fringes has been published in the magazine ``Applied
ics, 1972, pp. 2455-2459, ``Photolithographic Mask Positioning Using Moiré Techniques''.
-Mask Algnment Uaing Mo
1r6 Technipues) J. In this method, equally spaced concentric circles with different pitches are drawn, and the shape of the moiré fringes produced as the difference frequency between them is observed using a microscope and the positions are aligned. An arrangement #1 degree of 0.2 μm is obtained.

However, since this method requires recognizing the shape of the stripes, it has not been applied to automatic measurements. By improving this method,
A method was devised to align equally spaced linear stripes with the same pitch by observing the diffracted light of moiré fringes that are generated.

This method can be used, for example, in magazines [Journal of Pakis 1-
Journal of Vh
ccutne 5science Technology
e, 1983, pp. 81-1276-1279.
t Techniue for X-ray Li
thography) J. This method involves overlapping the same equally spaced linear stripes drawn on the mask and irradiating laser light onto the moiré fringes, which change depending on the relative positional relationship. This is a method to align the positions by observing changes in the intensity of the folded light. With this method, a 10 nm dioptric aperture has been obtained, and automatic measurement of high n1 degrees is possible in order to measure the intensity of every 1 degree.

However, conversely, even with a fringe pitch of L, large displacements could not be measured.
For example, m-kai uses @ with a pitch of 1 μm.

This method is used to perform high-precision alignment after 1 μm alignment using another method, so 2
It requires multiple positioning steps, which complicates the process.

An object of the present invention is to solve these problems and provide a positioning method that allows highly accurate positioning.

[Elaborate means to solve problems]

The positioning method of the present invention has a first surface having a first hologram for reproducing cylindrical waves, and a second hologram for reproducing cylindrical waves having the same or different focal length as the first hologram. - the first hologram is positioned with respect to the observation surface, and the diffracted light generated by irradiating the moire fringes with coherent light is generated on the observation surface. The second surface is positioned so that it occurs at nine predetermined positions.

[Function/principle of the invention]

The shape of moiré fringes that occur when two holograms are stacked can be determined analytically. For example, the moiré fringes that occur when holograms that reproduce cylindrical waves with different focal lengths are brought together are produced as follows. The center line of the reference hologram is the X axis, and the hologram to be placed is relative to the reference hologram.

Assuming that they are shifted by ΔX in the X direction, the two holograms are each expressed by the following equations.

X”=ma”・・・・・・・・・・・・(
1) (X-Δx)”=nb” =・・・・・・・・・
... (2) Here, %a and b are the intervals between the innermost straight lines,
m.

n represents a positive integer. Moiré stripes are (]), (2)
Since it is expressed as the intersection of the equations, by setting L=mfn, the following equation is obtained.

In other words, moiré fringes that reproduce one cylindrical wave are generated.

Here, C is a function of a, b, and ΔX, but it is not an essential term because it only changes the distance between the straight lines relatively. This field 4&, if the holograms to be placed are different in the X direction @
a”/(b”The a is larger.

Sensitivity increases. For example, when b=L1a and n, the center of the moire fringe moves 4.8 times the amount of movement of the hologram to be placed. This method alone cannot align the positions in the X direction, but by placing a hologram parallel to the y axis in a different position,
It would be better if the positioning could be done in a similar way. Compared to the method of superimposing two zone plate holograms to generate concentric moiré fringes, this method makes it difficult to position the beam so that it does not focus on a point. It's a good idea to draw a pattern for it.

It was. 6c [Hologram 9 to reference hologram
The following L is used to perform 0 rotations and superimposed rotations. Assuming that the center line of the reference hologram 101 shown in FIG. Become.

y-ma ・・・・・・・・・ (4)
(X-ΔX)=na' (5)
Here, a is the interval between the innermost straight lines, and m and n are positive integers.0 Moiré fringes are expressed as the intersection of equations (1) and (2), so if t=m10, the following equation This produces moiré fringes that reproduce spherical waves.

(X-ΔX y"=t, a" ・・・・・・・・・
(6) When observing these moire fringes, the moire fringes do not change as the placed hologram moves in the y direction, but move in the x direction in proportion to the hologram's movement value. Therefore, positioning in the X direction is possible by observing the diffracted light of moiré fringes. Furthermore, in order to perform positioning in the %yX direction, a hologram having a center line on the y-axis may be placed at another position and used as a reference hologram. in this way,
Although it is not possible to generate moiré fringes with high sensitivity, it is possible to generate spherical waves by using linear fringes that are easy to draw, and it is possible to create a focused beam that is easy to position.

〔Example〕

FIG. 1 is a block diagram illustrating an embodiment of the present invention. First, the light emitted from the laser 9 is applied to the reference hologram 5, which is drawn on a part of the mask 1, by the half mirror 10.
The manipulator 3 is moved so that the +1st-order diffracted light from the hologram 5 converges and enters the four-division source detector 12. This 4-split photodetector 12 is
It is the same as the one used to align the focus position of the laser head of the original disk, and has the structure shown in Figure 3. In Figure 3, the four-part planes are A, B, and C.

, D, and for example, to match the positions in the X direction,
The arithmetic circuit 16 is designed to calculate the sum of the photodetection signals of side A and side B, and 0.
Take the difference between the sums of No. 15 on side and D side. At this time.

As the manipulator moves in the X direction, the signal draws an S-shaped curve mf as shown in the characteristic diagram of FIG.

When passing through the 0 point here, the +1st-order diffraction source of the − and holograms has passed through an intermediate position between the A and B planes and the C and D planes. Similarly, alignment in the X direction is performed using a difference signal between the sum of the photodetection signals of the A side and the D side and the sum of the photodetection signals of the B side and the 0th side.

In this embodiment, a reference hologram 5 is placed diagonally on the wafer.
A reference hologram 7, a photodetector 15, and an arithmetic circuit 19 are arranged by rotating 9011.

These signals in the X direction and %y direction are input to a processor 2 such as a personal computer equipped with a GP-IB interface, and the 1m of both n1 and 0 of the S-shaped signal shown in FIG.
To illustrate the point, examples are the Kozue stage, Pulse Tanabata, and GP-IB! A signal is sent to the manipulator 3 equipped with a pulse motor drive device to move the mask.

When both Nos. 16 and 16 are placed at the 0 point position, this mask has been placed at position [8] with respect to the device. At this time, a positional deviation of 171008 degrees in beam diameter can be detected.

Therefore, if the beam can be narrowed down to several micrometers, a positional deviation n of about several tens of micrometers can be detected.

Next, the light emitted from the laser 9 is irradiated onto the moire fringes generated by overlapping the reference holograms 5 and 7 with the arrangement holograms 6 and 8 recorded on the wafer, and the +1
The manipulator 4 is moved so that the next diffraction source converges and enters the four-split source detector 13,14. These photodetectors 13 and 14 are the same as photodetectors 12 and 15,
.

Similar to the alignment procedure, the wafer can be aligned to the mask.

If this method is modified, in equation (3), the moire fringe is designed to move 10 times as much as the placed hologram, and if the beam can be narrowed to a few μm, the moire fringe can be It is possible to detect a movement of several micrometers, and it is also possible to detect a movement of several micrometers of the arranged hologram.

〔Effect of the invention〕

As described above in detail, the positioning method of the present invention makes it possible to align the mask and wafer with high precision with a variation of several μmm by utilizing the diffracted light of moiré fringes.

[Brief explanation of drawings]

FIG. 1 is a block diagram illustrating the configuration of an embodiment of the present invention, FIG. 2 is a plan view of an example of moiré fringes that occur when a reference hologram and a placement hologram collide, and FIG.
The configuration diagram of the four-division element detector shown in the figure,! Figure 4 is a characteristic diagram of the output signal from the four-split photodetector in Figure 1.0 1...Mask, 2...Wafer, 3.4
...Manipulator, 5, 7, 101...
...Reference hologram, 6.8.102... Placement hologram, 9... Laser. 10... Half mirror 111... Mira* 12 p13.14, 15... Photodetector, 16, 17, 18.

Claims (3)

[Claims] (1) A first hologram that reproduces a cylindrical wave.
and a second surface having a second hologram that reproduces a cylindrical wave having the same or different focal length as the first hologram to generate moiré fringes,
The hologram is positioned with respect to the observation surface, and the second surface is positioned so that diffracted light generated by irradiating the moire fringes with coherent light is generated at a predetermined position on the observation surface. positioning method. (2) The positioning method according to claim 1, wherein the surfaces of the first hologram and the second hologram are superimposed so that the stripes of each hologram overlap in parallel. (3) The positioning method according to claim 1, wherein the surfaces of the first hologram and the second hologram are superimposed so that the stripes of the holograms are perpendicular to each other.