JPH03270213A - Exposure process and applicable aligner and mask - Google Patents

Abstract

PURPOSE:To make the contrast between projected images sharper by a method wherein the phases of two lights immediately after passing through different positions on a mask are brought into inverse phases to each other and then said two lights are synthesized to irradiate an objective specimen. CONSTITUTION:The light L emitted from a light source 2 is divided into two lights L1, L2 and then the optical path length of these two lights L1, L2 reaching a mask 14 is changed so that the phases of the two lights immediately after passing through the different positions in the mask 14 may be brought into inverse phases to each other. When an objective specimen 3 is irradiated with the two synthesized lights L1, L2 with one light L1 passing through one specific transmission region while the other light L2 passing through the other transmission region on the mask 14 approach each other on the arranged position of the irradiated specimen 3, said two lights L1, L2 interfere with each other to be turned lower in the boundary region thereof. Through these procedures, the contrast between the projected images can be made sharper.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to exposure technology, and relates to a technology that is effective when applied to, for example, the IJ Sogerafie of semiconductor integrated circuit devices.

[Conventional technology]

As semiconductor integrated circuits become more highly integrated and the design rules for circuit elements and wiring become submicron order, G-line, 1
In a photolithography process in which a circuit pattern on a mask is transferred onto a semiconductor wafer using light such as a line, a decrease in the accuracy of the circuit pattern transferred onto the wafer becomes a serious problem. For example, when transferring a circuit pattern consisting of a transparent area P3, P2 and a light shielding area N formed on a mask 20 as shown in FIG. The phases of the lights immediately after passing through each of P and P are in the same phase as shown in Cb in the same figure, so the 20 lights interfere and strengthen each other in a place on the wafer that is originally a light-blocking area (Cb) in the same figure. Figure (C))
As a result, as shown in the same figure (ω), the contrast of the projected image on the wafer decreases and the depth of focus becomes shallow, resulting in a significant decrease in pattern transfer accuracy.

As a means to improve this problem, a phase shift technique has been proposed that prevents a decrease in the contrast of a projected image by changing the phase of light passing through a mask.

For example, in Japanese Patent Publication No. 62-59296, a transparent film is provided on one side of a pair of transmission areas sandwiching a light-shielding area, and a phase difference is created between the light transmitted through the two transmission areas during exposure. A phase shift technique has been disclosed in which the interference light is made to weaken each other at a location on the Ueno which is originally a light-blocking area. That is, when transferring the circuit pattern formed on the mask 21 as shown in FIG. A transparent film 22 having a transparent film ratio is provided. By appropriately adjusting the film thickness of the transparent film 52, the light immediately after passing through each of the transmission areas Pl and Pi has a phase difference of 180 degrees as shown in the figure, so that the wafer In the upper light shielding area N, these lights interfere and weaken each other ((C) in the same figure). As a result, the contrast of the projected image on the wafer is improved, the resolution and depth of focus are improved, and the mask 21
The transfer accuracy of the circuit pattern formed on the wafer is improved.

Furthermore, in Japanese Patent Application Laid-Open No. 62-67514, after removing a part of the light shielding area of the mask to form a fine open pattern, either the open pattern or the transparent area existing in the vicinity is made transparent. Phase shift technology that prevents the amplitude distribution of light that has passed through the transmission area from spreading laterally by providing a film and creating a phase difference between the light that has passed through the transmission area and the light that has passed through the open pattern. is disclosed.

[Problem to be solved by the invention]

According to the studies of the present inventors, the above-mentioned conventional phase shift method in which a transparent film is provided in a part of the transmission area of the mask and a phase difference is created between the light passing through the transparent film and the light passing through the transmission area in the vicinity thereof. The problem with the shift technique is that it takes a lot of time and effort to manufacture the mask.

That is, the actual mask on which the integrated circuit pattern is formed has various patterns I! ! Because it is roughly arranged,
This makes it extremely difficult to select a location for placing the transparent film, which places significant restrictions on pattern design.

Furthermore, if a transparent film is provided on the mask, a process for inspecting the transparent film for defects is required in addition to a process for inspecting the integrated circuit pattern for defects, making the mask inspection process extremely complicated. . Furthermore, when a transparent film is provided on a mask, more foreign matter adheres to the mask, making it difficult to create a clean mask.

An object of the present invention is to provide a phase shift technique that eliminates the above-mentioned problems.

The above and other objects and novel features of the present invention will become apparent from the description of the specification and the accompanying drawings.

[Means to solve the problem]

A brief overview of typical inventions disclosed in this application is as follows.

One invention of the present application irradiates light onto a mask in which a predetermined pattern consisting of a light shielding area and an f1 pass area is formed, and irradiates the irradiated sample with the light that has passed through the transparent area of the mask. When transferring a predetermined pattern formed in , is an exposure method in which the phases of two lights immediately after passing through different parts of the mask are set to be opposite to each other, and then the two lights are combined and irradiated onto the sample to be irradiated.

[Effect]

According to the above-mentioned means, the phases of the two lights immediately after passing through different parts of the mask are set to be opposite to each other, and then the two lights are combined and irradiated onto the irradiated sample.
Where one light that has passed through a predetermined transmission area on the mask and the other light that has passed through another transmission area on the mask are placed close to each other on the irradiated sample, the boundary area between them is As a result of the two lights interfering and weakening each other, the contrast of the projected image is greatly improved.

[Embodiment 1] FIG. 1 shows a phase shift mechanism 1 of an exposure apparatus which is an embodiment of the present invention.

A phase shift mechanism 1 includes a light source 2 of an exposure device and a sample to be irradiated 3.
beam expander 4, mirror 5,
6, 9, half mirror 7, 8, corner mirror 1O1 optical path length variable mechanism 1 that minutely drives this corner mirror 10
1. It is constituted by an optical system consisting of a pair of lenses 12a and 12b, a reduction lens 13, and the like. A mask 14 on which an original image of a pattern to be transferred to the irradiated sample 3 is formed is positioned in an alignment system (not shown) of this optical system. The mask 14 is, for example, a mask (reticle) used in the manufacturing process of a semiconductor integrated circuit device, and the sample 3 to be irradiated is, for example, a semiconductor wafer made of silicon single crystal.

1 line emitted from light source 2 (wavelength 365 nm), etc.
L is the light that is expanded by the beam expander 4, then refracted by the mirror 5 in a direction perpendicular to the main surface of the mask 14, and then travels straight through the half mirror 7 provided in the middle of the optical path. Light L2 traveling in a direction perpendicular to
It is divided into two parts.

Light L2 is refracted through mirror 9 and corner mirror 10, and passes through a different path from light L1 to mask 1.
4 different locations are irradiated. The two lights Lr and Ls transmitted through different parts of the mask 14 are transmitted through the lenses 12a and 12.
b, is combined into one light L' through the mirror 6 and the half mirror 8, is reduced by the reduction lens 13, and is irradiated onto the irradiated sample 3 positioned on the XY table 15. .

In the phase shift mechanism 1, two lights from passing through the half mirror 7 to reaching the mask 14 are: L,
Since the optical path lengths of the two lights are different, by changing the height from the main surface of the mask 14 to the corner mirror 10 (the optical path length of the light L2), the two lights Lll immediately after passing through the mask 14 can be
A desired phase difference can be created between L2. For example, two lights L++L immediately after passing through the mask 14
* Corner mirror 1 when the phases of are in phase with each other
0 position is the origin, and by moving the corner mirror 10 in the vertical direction from this origin by a distance (d) defined by the following formula, the two lights Ll, immediately after passing through the mask 14, The phases of L2 are opposite to each other (phase difference 1
80 degrees). Above corner mirror 10
The vertical movement is performed using a variable optical path length mechanism 11 using, for example, a piezoelectric control element.

FIG. 2 is an enlarged cross-sectional view of the mask 14. As shown in FIG.

This mask 14 is made of, for example, transparent synthetic quartz glass with a refractive index of about 1.47, and has a main surface with a refractive index of about 500 to 3.
A metal layer 16 made of Cr or the like is formed to have a thickness of about 1,000 mm. Upon exposure, the metal layer 16 becomes a light-shielding region through which no light passes, and the other regions become transmissive regions B through which light passes. The integrated circuit pattern is composed of the light-shielding area and the transparent area B, and has, for example, five times the actual size.

3(a) and 3(b) are examples of integrated circuit patterns formed on the mask 14. FIG. The circuit pattern P1 shown in FIG. 2A is composed of a shaded area A indicated by diagonal lines and a transmissive area B, for example, L-shaped, surrounded by the shaded area. On the other hand, the circuit pattern P shown in FIG.
The transmission region B of the circuit pattern P has the same shape as the transmission region B of the circuit pattern P1, and inside the transmission region B whose dimensions are enlarged, there is a circuit pattern P, the same shape as the transmission region B of the circuit pattern P1,
This is a pattern in which light-shielding areas A of the same size are arranged. That is, the transparent region B of the circuit pattern P2 substantially matches the pattern of the peripheral portion of the transparent region B of the circuit pattern P. These two circuit patterns P1P2 are
These are a pair of patterns for transferring a circuit pattern P (shaded area) as shown in FIG. 3(C) onto a wafer with high precision, and both are arranged at a predetermined location on the mask 14 at a predetermined interval. .

Next, a method for creating the mask 14 will be briefly described.

First, after polishing and cleaning the surface of a synthetic quartz glass plate, a Cr film is deposited on the entire main surface by a sputtering method to form a film of, for example, 500 to 3,000 layers, and then the entire surface of this Cr film is deposited. Apply photoresist to the surface. Next, based on the integrated circuit pattern data encoded in advance on a magnetic tape or the like, an integrated circuit pattern is printed on the photoresist using an electron beam exposure method, and then the exposed portion of the photoresist is removed by development, and the exposed Cr film is removed. is removed by wet etching to create an integrated circuit pattern. The pair of circuit patterns P1. The pattern data of P2 is obtained by enlarging or reducing the data of the light shielding area A or the transmitting area B of one of the circuit patterns, or by performing the logical product of the inverted data of one circuit pattern and the data of the other circuit pattern. It can be created automatically by

For example, the pattern data for the circuit pattern P2 can be automatically created by performing the logical product of the data obtained by enlarging the pattern of the transparent area B of the circuit pattern P1 and the inverted data of the transparent area B of the circuit pattern P. can.

In order to transfer the integrated circuit pattern formed on the mask 14 onto the wafer 3, the wafer 3 whose surface is coated with photoresist is first positioned on the XY child table 5 of the exposure apparatus shown in FIG. The b-mask 4 for positioning the circuit pattern P in the alignment system is such that one of the beams divided by the half mirror 7 is connected to the pair of circuit patterns P.
This is done so that when the circuit pattern data of one of I and P2 is irradiated, the other light L2 is accurately irradiated to the other circuit pattern data. Next, the corner mirror 10 is vertically moved and the phase difference is adjusted so that the phases of the two lights immediately after passing through the mask 14, L, are opposite to each other. To accurately position the mask 14 and adjust the phase difference between the two lights, L,
For example, the fifth EiU (a), (b) formed on the mask 14
) a pair of alignment marks M,, M2 as shown in
Take advantage of. Mark M., M.

, each of which is connected to the shaded area A
For example, a square transmitting area B is surrounded by a transparent area B, and their dimensions and shapes are exactly the same. If the positioning of the mask 14 and the adjustment of the phase difference between the lights and the lights L2 are performed accurately, the light L1 that has passed through the mark M1 and the light L2 that has passed through the mark M2 will interfere with each other and disappear completely. Therefore, the projected image M of the marks M, , M, is not formed on the wafer 3. That is, by identifying the presence or absence of the projected image M on the wafer 3, it is possible to easily determine whether the positioning of the mask 14 and the adjustment of the phase difference between the lights, , L, and the like are performed accurately.

In this way, the mask 14 is positioned and illuminated.

After adjusting the phase difference of L2, the original image of the integrated circuit pattern formed on the mask 14 is optically
The image is reduced in size and projected onto the wafer 3, and the above operations are repeated while sequentially moving the wafer 3 in a stepwise manner.

FIG. 4 (Al is a cross-sectional view of the mask 14 in the region where the circuit pattern P1 is formed, and FIG. 4) shows the mask 14 in the region where the circuit pattern P2 is formed.
4 is a sectional view of FIG.

Light immediately after passing through the transmission area B of the circuit pattern P,
The light L2 immediately after passing through the transmission area B of the circuit pattern P2 is the 46th J (a'), (b')
As shown, the phases are opposite to each other. Further, the transparent region B of the circuit pattern P2 is the same as that of the circuit pattern P1.
Since it matches the pattern of the peripheral part of the transparent iJ region B, the amplitude of the composite light L' of the two lights,
)become that way. Therefore, this combined light L°
When irradiated upward, as shown in the same figure (a), the original light L
They interfere and weaken each other at the boundary between L and L2. As a result, as shown in FIG. 3(e), the contrast of the image projected onto the wafer 3 is significantly improved, and the resolution and depth of focus are significantly improved.

In this way, the exposure apparatus of the first embodiment divides the light generated from the light source 2 into two lights L2, and each time the optical path length of these two lights LL and L2 is changed until they reach the mask 14, The two lights L1. immediately after passing through the mask 14. The phases of L2 are set to be opposite to each other, and then the two lights, L, are combined and irradiated onto the wafer 3. Further, the mask 14 of the first embodiment has one circuit pattern P2.
has a pair of circuit patterns P, , P2 such that the transmission region B of the circuit pattern P matches the peripheral pattern of the transmission region B of the other circuit pattern P. Therefore, by transferring the integrated circuit pattern formed on the mask 14 onto the wafer 3 using the exposure apparatus, the light transmitted through the transmission area B of the circuit pattern P1 and the transmission area B of the circuit pattern P are removed. The light L° obtained by combining with the light L2 transmitted through the wafer 3 interferes and weakens each other at the boundary between the original light , L, and the contrast of the image projected onto the wafer 3 is greatly improved. Therefore, the circuit pattern P can be transferred to the wafer with high precision.

Therefore, in the exposure method of Example 1, the following effects can be obtained.

(1) Unlike conventional phase shift technology, there is no need to provide a phase shift means such as a transparent film on the mask, so there are no restrictions on pattern design. In this Example 1,
When transferring one circuit pattern onto a wafer, it is necessary to form a pair of circuit patterns on a mask, and this pair of circuit patterns can enlarge or reduce the data in the light-blocking area or transparent area of one of the circuit patterns. It can be automatically created by performing a logical AND operation between the inverted data of one circuit pattern and the data of the other circuit pattern.

(2) There is no need for the step of inspecting the transparent film for defects, which was essential in conventional phase shift technology.

In the first embodiment, the pair of circuit patterns can be inspected for defects in the same way as for ordinary masks by comparing them with the original pattern data. In addition, dimension inspection can be performed in the same manner as for ordinary masks by laser length measurement or the like. Therefore, the mask inspection process does not become complicated.

(3) Since no phase shift means such as a transparent film is provided on the mask, it can be cleaned in the same manner as a normal mask. Therefore, it is possible to create a mask that is as free from foreign matter as a normal mask.

(4) According to (1) to (3) above, it is possible to improve the transfer accuracy of a circuit pattern without requiring a great deal of time and effort to manufacture a mask.

[Example 2] FIGS. 6(a) and 6(b) are other examples of a pair of circuit patterns formed on the mask of Example 1.

Each of the circuit pattern P shown in FIG. Consisting of

Pair of circuit patterns P1. P2 is a pair of patterns for transferring the circuit pattern P (shaded area) as shown in FIG.
are arranged at predetermined locations at predetermined intervals. The circuit pattern P consists of four patterns PA, Pi P c, and FD having the same size and shape. The transparent area BA of the circuit pattern P1 corresponds to the pattern PA and is 1
Transparent region B of one circuit pattern P1 corresponds to pattern PC. In addition, the transparent region B of the circuit pattern P2,
is the pattern P, and the transparent area B of the circuit pattern P2,
is pattern P.

corresponds to each. That is, the circuit pattern P is a pattern in which the transmission regions B of the pair of circuit patterns PI and P2 are alternately arranged.

FIG. 7(a) is a partial sectional view of the mask 14 in the area where the circuit pattern P1 is formed, and FIG. 7Cb) is a partial sectional view of the mask 14 in the area where the circuit pattern P2 is formed. It is.

The light immediately after passing through the transmission area B of the circuit pattern P1 and the light L2 immediately after passing through the transmission area B of the circuit pattern P2 are different from each other as shown in FIG. 7 (a'>, (b')). The phases of the two lights L1.
As shown in the same figure (C), the combined light L of L2 is combined with the original light L1. The boundaries of L2 become closer together. Therefore,
When this combined light L'' is irradiated onto the wafer 3, the same figure (
As shown in d), the original lights Ll and L2 interfere and weaken each other at the boundary. As a result, as shown in ffl (el), the contrast of the image projected onto the wafer 3 is significantly improved, and the resolution and depth of focus are significantly improved.

[Example 3] FIGS. 8(a) and 8(b) are still another example of a pair of circuit patterns formed on the mask of Example 1.

The circuit pattern P1 shown in FIG.
For example, it consists of a square transmission area B.

The transmission area B of the circuit pattern P2 shown in FIG.
They are arranged outside each side of the transparent region B of the circuit pattern P1. The pair of circuit patterns P1 and P2 are a pair of patterns for transferring the circuit pattern P (the shaded part) as shown in FIG.
Both are arranged at predetermined locations on the mask 14 at predetermined intervals.

FIG. 9(a) is a partial sectional view of the mask 14 in the region where the circuit pattern P is formed, and FIG. 9(b) is
3 is a partial cross-sectional view of the mask 14 in a region where the circuit pattern P2 is formed. FIG.

Light L immediately after passing through transmission area B of circuit pattern P1
1 and the light L2 immediately after passing through the transmitting region B of the circuit pattern P2 have opposite phases to each other, as shown in FIGS. 9(a') and (b'). In addition, in the composite light L' of the two lights, L, the boundaries of the original lights, L, approach each other, as shown in Figure (C). Therefore,
When this combined light L° is irradiated onto the wafer 3, the same figure (
As shown in d), the original lights, L, interfere and weaken each other at the boundary. As a result, as shown in FIG. 3(e), the contrast of the image projected onto the wafer 3 is significantly improved, and the resolution and depth of focus are significantly improved.

As above, the invention made by the present inventor has been specifically explained based on examples, but the present invention is not limited to the above-mentioned examples, and it is understood that various changes can be made without departing from the gist of the invention. Needless to say.

In the above description, the invention made by the present inventor was mainly applied to a mask used in the manufacturing process of a semiconductor integrated circuit device, which is the field of application in which the invention was made, but the present invention is not limited to this. Not a thing,
The present invention can be widely applied to all exposure techniques in which a predetermined pattern formed on the mask is transferred by irradiating light transmitted through a mask onto a sample to be irradiated.

〔Effect of the invention〕

Among the inventions disclosed in this application, the effects obtained by typical inventions are briefly described below.

A predetermined pattern formed on the mask by irradiating light onto a mask on which a predetermined pattern consisting of a light blocking area and a transmitting area is formed, and irradiating the irradiated sample with the light that has passed through the transmitting area of the mask. When transferring the image onto the irradiated sample, the light emitted from the light source is divided into two beams, and the optical path length of each of the two beams until it reaches the mask is changed, whereby different parts of the mask are transferred. The phases of the two lights immediately after passing through are set to be opposite to each other, and then the two lights are combined and the front l! c! According to the exposure method of the present application in which the irradiated sample is irradiated, one light that has passed through a predetermined transmission area on the mask and the other light that has passed through another transmission area on the mask are irradiated onto the irradiation sample. At locations that are placed close to each other, the two lights interfere and weaken each other in the boundary area, so the contrast of the projected image is greatly improved.

Thereby, pattern transfer accuracy can be improved without requiring a great deal of time and effort to manufacture the mask.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is an overall view of a phase shift mechanism provided in an exposure apparatus that is an embodiment of the present invention. FIG. 2 is an enlarged sectional view of a mask that is an embodiment of the present invention. , Figures 3(a) and 3(b) are plan views of a pair of circuit patterns formed on this mask, and Figures 1 and 3(C) are plan views of the circuit pattern obtained by combining the pair of circuit patterns. The plan view, gJ4 (a) to (e), shows the amplitude of the light transmitted through the transmitting region of the circuit pattern shown in FIGS. 3(a) and (b).
Figure 5 (a) is a plan view of a pair of alignment marks formed on this mask, and Figure 5 (C) is a composite diagram of the pair of alignment marks. A plan view of the circuit pattern obtained by
b) is a plan view showing another example of a pair of circuit patterns formed on the mask of the present invention; FIG. 6(C) is a plan view of a circuit pattern obtained by combining the pair of circuit patterns; FIGS. 7(a) to (e) are explanatory diagrams showing the amplitude and intensity of light transmitted through the transmission area of the circuit batten shown in FIGS. 6(a) and (b), respectively, and FIG. a) and (b) are plan views showing other examples of a pair of circuit patterns formed on the mask of the present invention, and FIG.
C) is a plan view of a circuit pattern obtained by combining this pair of circuit patterns, and FIGS. 9(a) to (e) are transparent areas of the circuit pattern shown in FIGS. 8(a) and (b). 10(a) to (d) are explanatory diagrams showing the amplitude and intensity of light transmitted through the transmission area of a conventional mask, respectively.
Figures (a) to (a) are explanatory diagrams showing the amplitude and intensity of light transmitted through the transmission area of a conventional mask provided with a transparent film, respectively. 1... Phase shift mechanism, 2... Light source, 3... Irradiated sample (semiconductor wafer), 4... Beam expander, 5.6.9... Mirror 7° 8... Half mirror −
□10... Corner mirror 11... Optical path length variable mechanism,
12a, 12b...lens, 13...reduction lens,
14.20.21...Mask, 15...XY table, Process 6...Metal layer, 22...Transparent film.

Claims (1)

[Claims] 1. By irradiating light onto a mask in which a predetermined pattern consisting of a light blocking area and a transmitting area is formed, and irradiating the irradiated sample with the light that has passed through the transparent area of the mask,
An exposure method in which a predetermined pattern formed on the mask is transferred onto the irradiated sample, the light emitted from a light source being split into two lights, and each of the two lights reaching the mask. By changing the optical path length, the phases of the two lights immediately after passing through different parts of the mask are set to be opposite to each other, and then the two lights are combined and irradiated onto the sample to be irradiated. Exposure method. 2. A light splitting means that splits the light generated from the light source into two, and by changing the optical path length of each of the lights split by the light splitting means until they reach the mask, immediately after passing through different parts of the mask. The method is characterized by having a phase shift mechanism including an optical path length variable means for making the phases of the lights opposite to each other, and a light combining means for combining the two lights passing through the mask and irradiating the irradiated sample onto the irradiated sample. An exposure apparatus used in the exposure method according to claim 1. 3. It has a pair of circuit patterns such that the light transmitted through the transmission area of the first circuit pattern and the light transmitted through the transmission area of the second circuit pattern are placed close to each other on the irradiated sample. 2. A mask used in the exposure method according to claim 1.