JP2003142371A - Method of electron-beam exposure and stencil reticle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stencil reticle, on which any pattern can be formed without applying complementary split. SOLUTION: A set of reticles 10 consists of two reticles 51, 53, on each of which same line-shaped patterns 55 are formed. In each of the line-shaped patterns 55 on the reticles 51, 53, a plurality of bridges 57 that connect the long sides of the pattern 55 are located in the longitudinal direction, where the locations of the bridges 57 are different between the reticle 51 and the reticle 53. At exposure, exposure for pattern transfer is made once for each of the reticles 51, 53 on a wafer. Thereby, positions, at which constrictions may possibly be generated when exposure is made using only one of the reticles, are fully exposed by the exposure using the other reticle, and as a consequence, generation of constrictions in the patterns is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam exposure method for forming a semiconductor device pattern or the like and a stencil reticle used in this electron beam exposure method.

[0002]

2. Description of the Related Art With the recent miniaturization and high integration of device patterns, development of an exposure technique using an electron beam (EB) has become active. Especially in the 100 nm rule or later, as a finer pattern forming technique, an electron beam reduction projection exposure method (EPL Electron Projection Lith
(ography) is drawing attention. This EPL is aimed at a high throughput and can be mass-produced in a memory, so that it is particularly attracting attention. Further, the EPL is capable of being reduced and transferred while scanning a circuit pattern on a reticle and printing it on a wafer (sensitive substrate), and is considered to be a promising mass production technology corresponding to device fabrication of a 70 nm node or later. In this EPL, PREVAIL or S
An electron optical system or system technology called CALPEL has been reported.

Such an EB exposure technique is different from the extension of the conventional direct writing technique such as cell projection in which the patterns of simple basic figure apertures are superposed to form a desired pattern, and an enlarged pattern of the desired pattern is reticulated. As a pattern (original pattern), the reticle pattern is directly subjected to reduction projection exposure to form a device pattern. This technique employs a reduction transfer method using a reticle and an EB optical system capable of irradiating a large-diameter beam. Through these techniques, the throughput can be significantly improved.

As one type of reticle used in this EB exposure technique, there is a stencil reticle in which a large number of holes through which electron beams pass is formed in a self-supporting thin film (membrane). The shape of the hole corresponds to the shape of the individual element figure of the pattern to be transferred. The scattering stencil reticle that is currently being specifically examined is one in which a perforated pattern is formed in a Si membrane having a thickness of about 2 μm. In such a scattering stencil reticle, the electron beam passing through the perforated pattern is not scattered, but the electron beam passing through the membrane part is scattered. Then, a contrast aperture is provided at or near the electron beam converging surface of the projection lens in the optical system of the exposure apparatus, and the electron beam scattered by this contrast aperture is trapped to prevent passage in the wafer direction. Then, the unscattered electron beam is imaged on the wafer to obtain the contrast of the pattern.

[0005]

In this scattering stencil reticle, the island-shaped non-perforated portion cannot be provided at the center of the perforated portion. This is because the part of the membrane forming the island-shaped non-perforated part cannot support gravity. This inconvenience is called the donut pattern problem. To address this issue, the perforations surrounding the island-shaped non-perforations are divided into two separate pattern areas that are projected separately onto the wafer. Expose. Then, connect the two holes on the wafer,
An exposed portion for one round and an island-shaped non-exposed portion in the center thereof are formed. Such a method is called complementary division.

Further, when the stencil reticle is used, there is a problem depending on the pattern length, in addition to the above-mentioned donut pattern problem. That is, when the length of the pattern is longer than the reference length (for example, several tens of μm), bending of the pattern due to the stress of the membrane, distortion due to its own weight, etc. are expected. Therefore, such a long linear pattern also requires complementary division. In particular, in the case of a high-density line-and-space pattern such as a memory gate layer, if the design value of the device is met, the pattern portion becomes long, and this problem becomes serious.

If the pattern has a leaf shape or a tongue shape (a leaf-shaped or tongue-shaped non-perforated portion has a cantilever structure), the pattern portion can be held, but the holding force is high. This is not sufficient, and the pattern portion bends in the direction of gravity and is easily deformed. Such patterns also require complementary division.

In the complementary division necessary in such a case, it takes time to divide the pattern and the reticle cost also increases.

The present invention has been made in view of the above problems, and it is possible to perform complementary division without performing
An object is to provide a stencil reticle capable of forming any pattern.

[0010]

In order to solve the above-mentioned problems, the electron beam exposure method of the present invention is to form a desired pattern on a stencil reticle in which a large number of holes corresponding to the shapes of element figures of a pattern are formed in a membrane. An electron beam exposure method of illuminating the reticle with an electron beam and projecting an image of the electron beam passing through the reticle onto a sensitive substrate to transfer the pattern onto the sensitive substrate,
Forming substantially the same pattern on the reticle of a sheet, and at the desired position of the hole of the pattern element figure of the reticle, provided with a thin membrane beam (bridge) connecting both edges of the hole, Here, in the two-sheet set reticle, the bridges are provided at different positions of the pattern, and the patterns of the two-set reticle are superposed on the same sensitive substrate for exposure.

A narrow beam connecting both edges of the reticle is provided in the hole of the reticle so that the pattern can be held in the direction of gravity. Therefore, even in the case of a donut pattern or a long line pattern, the complementary pattern is obtained. Patterning can be done on the stencil reticle without splitting. Since the width of the beam is sufficiently thin and the exposure dose enters from the periphery due to blurring or proximity effect, it is not transferred onto the wafer. Further, even if the beam is narrow, in the image transferred to the resist, the amount of accumulated electrons due to electron scattering may be reduced in the part where the beam is connected, and a constriction may be formed. Therefore, the same pattern is formed on at least two reticles, and beams are provided at different positions in these reticles. By exposing using these two reticles so that the patterns are overlapped with each other, there is a possibility that a constriction may occur when the exposure is performed using only one of the reticles. Since the exposure is completed, it is possible to prevent the constriction of the pattern from occurring.

In the present invention, if the width of the bridge is narrower than R × M (R: resolution limit of resist on wafer, M: magnification of projection lens), the beam is transferred to the sensitive substrate. Since it does not occur, a fine pattern can be accurately transferred.

In the present invention, it is preferable that the bridge is arranged obliquely with respect to the edge of the hole of the pattern element figure. When the bridge is provided perpendicularly to the longitudinal direction of the pattern, the portion corresponding to the bridge may become thin in the pattern transferred onto the wafer. On the other hand, by arranging the bridges obliquely with respect to the sides in the longitudinal direction of the pattern, it is possible to prevent the pattern transferred on the wafer from becoming thin. Alternatively, the width of the bridge can be increased within a range that does not cause a problem.

The stencil reticle of the present invention is a stencil reticle in which a large number of holes corresponding to the shapes of the element figures of the pattern are formed in the membrane, and the substantially same pattern is formed on the two reticles. At the desired position of the hole of the pattern element pattern of the reticle, a narrow beam (bridge) of the membrane connecting both edges of the hole is provided as described above.
The reticle is provided at different positions of the pattern.

[0015]

DETAILED DESCRIPTION OF THE INVENTION A description will be given below with reference to the drawings. First, the configuration of the electron beam exposure apparatus will be described with reference to FIG. FIG. 2 is a perspective view schematically showing the configuration of the entire optical system of the charged particle beam exposure apparatus using the reticle of FIG.
This figure shows a division transfer type electron beam projection exposure apparatus.
The electron gun 1 arranged in the uppermost stream of the optical system emits an electron beam downward. Below the electron gun 1, two stages of condenser lenses 2 and 3 are provided, and the electron beam is converged by these condenser lenses 2 and 3 and crosses over the blanking aperture 7. O. Image.

A rectangular aperture 4 is provided below the second-stage condenser lens. The rectangular aperture (illumination beam shaping aperture) 4 allows only an illumination beam that illuminates one subfield (a pattern small region that is one unit of exposure) of the reticle 10. The image of this aperture 4 is the lens 9
An image is formed on the reticle 10 by.

A blanking deflector 5 is arranged below the beam shaping aperture 4. The deflector 5 deflects the illumination beam when necessary and strikes the non-aperture portion of the blanking aperture 7 so that the beam does not strike the reticle 10.
An illumination beam deflector 8 is arranged below the blanking aperture 7. The deflector 8 mainly sequentially scans the illumination beam in the lateral direction (X direction) in the drawing to illuminate each subfield of the reticle 10 within the field of view of the illumination optical system.
An illumination lens 9 is arranged below the deflector 8.
The illumination lens 9 forms an image that has passed through the beam shaping aperture 4 on the reticle 10.

The reticle 10 has many subfields and is mounted on a movable reticle stage 11. Move the reticle stage 11 in the direction perpendicular to the optical axis (XY direction).
By moving to, the subfields on the reticle that illuminate a wider area than the field of view of the illumination optical system are illuminated. A position detector 12 is attached to the reticle stage 11. The structure of the reticle 10 will be described later.

Below the reticle 10, a projection lens 15,
19 and a deflector 16 are provided. The electron beam passing through one subfield of the reticle 10 is projected onto the wafer (sensitive substrate) 2 by the projection lenses 15 and 19 and the deflector 16.
An image is formed at a predetermined position on 3. An appropriate resist is applied onto the wafer 23, and a dose of an electron beam is applied onto the resist to reduce the pattern on the reticle 10 (1/4 in one example) and transfer it onto the wafer 23.

At the point where the reticle 10 and the wafer 23 are internally divided by the reduction ratio, the crossover C.I. O. And a contrast opening 18 is provided at the crossover position. The opening 18 blocks the electron beam scattered by the non-patterned portion of the reticle 10 from reaching the wafer 23.

Directly above the wafer 23 is a backscattered electron detector 22.
Are arranged. The backscattered electron detector 22 detects the amount of electrons reflected by the exposed surface of the wafer 23 or the mark on the stage. From this detection information, the relative positional relationship between the reticle 10 and the wafer 23 allows the beam characteristics in the projection optical system to be known.

The wafer 23 is moved in the XY direction through the electrostatic chuck.
It is mounted on a wafer stage 24 that can move in any direction. A position detector 25 is attached to the wafer stage 24. By synchronously scanning the reticle stage 11 and the wafer stage 24 in mutually opposite directions based on the positions detected by the position detectors 12 and 25, respective parts in the chip pattern extending beyond the visual field of the projection optical system. Are sequentially exposed.

The respective lenses 2, 3, 9, 15, 19 and the deflectors 5, 8, 16 are provided with power source control units 2a, 3a, 9 respectively.
It is controlled by the controller 31 via a, 15a, 19a and 5a, 8a, 16a. The reticle stage 11 and wafer stage 24 are also controlled by the controller 31 via the control units 11a and 24a. Further, the stage position detectors 12 and 25 and the backscattered electron detector 22 also send signals to the controller 31 via the interfaces 12a, 25a and 22a. The controller 31 controls the stage position from the sent signal.

Next, a scatter stencil reticle according to an embodiment of the present invention will be described with reference to FIG. Figure 1
FIG. 1 is a diagram schematically showing a scattering stencil reticle according to a first embodiment of the present invention, FIG. 1 (A) is a plan view of a line and space pattern, and FIG. 1 (B) is a reticle structure. FIG. The reticle (group) 10 of this example is composed of two reticles 51 and 53 in which openings of the same line and space pattern are formed. At the time of exposure, each of the reticles 51 and 53 is transferred and exposed once onto one wafer. The line-and-space pattern is a long line-shaped pattern 55 extending in the Y direction arranged in a plurality of columns in the X direction with a space having the same width as the pattern 55. In this example, the long side of the linear pattern 55 has a length of 500 μm, and the width (short side length) thereof is 400 nm.

As shown in FIG. 1B, each reticle 5
The linear patterns 55 of 1 and 53 are provided with a plurality of bridges (beams) 57 connecting the long sides of the patterns in the longitudinal direction of the pattern 55. In this example, the width of the bridge 57 is 100 nm, and the interval between the bridges 57 is 20 μm. Here, the positions at which the bridge 57 is provided are different between the reticles 51 and 53. That is, when both reticles are overlapped with each other, the positions of the line-shaped patterns 55 match but the positions of the bridge 57 do not match.
In one example, the position of the bridge 57 is 10 μm for each reticle.
It is offset.

In this example, the width of the bridge 57 is 100n.
Although the width is m, the width is preferably narrower than R × M. Where R is the resolution limit of the resist on the wafer,
M is the magnification of the projection lens when the reticle side is viewed from the wafer side, and M = 4 in the case of this electron beam exposure apparatus whose reduction magnification is 1/4. The resolution limit of the resist on the wafer is, for example, about 50 nm in the 70 nm node. Therefore, in this case, the width of the bridge 57 is preferably 200 nm (= 50 nm × 4) or less. Further, the bridge width is more preferably 100 nm or less, though it depends on the beam blur amount of the exposure apparatus, the characteristics and thickness of the resist or reticle material, and the like.

However, when such a bridge 57 is provided, most of the bridge 57 is not transferred to the resist on the wafer, but the root of the bridge 57 may remain as a constriction in the resist.

FIG. 3 is a diagram schematically showing a state in which a pattern having a bridge is transferred to a resist on a wafer.
Reduction ratio of exposure equipment is 1/4, resist resolution limit is 5
0 nm. In this example, the bridge is provided at a right angle to the long side of the line pattern and has a width of 20.
It is 0 nm (= R × M). When this line pattern is exposed and transferred onto the wafer, the width of the bridge is 50 nm, which is almost the same as the resolution limit at the 70 nm node, and is not transferred onto the wafer. However, the neck 63 may remain at the root of the bridge as shown in the figure, and the line pattern 61 may become thin at this portion.

The constriction 63 becomes smaller when the width of the bridge on the reticle is narrowed. Also, by arranging the bridges obliquely with respect to the long sides of the line pattern (which will be described later with reference to FIG. 4), the constriction is reduced and the positions of the constrictions on both sides of the line pattern are in the direction of each long side. It shifts. Therefore, the width of the pattern does not become narrower than that in the case where the constrictions are on both sides facing each other (when the bridge is perpendicular to the long side of the line pattern).

In the case of the scattering stencil reticle 10 of this embodiment, since the position of the bridge 57 is different between the two reticles 51 and 53, the root of the bridge as described above in the pattern on the wafer onto which one of the reticles is transferred. The portion where the waist is formed corresponds to the portion having no bridge when the other reticle is transferred. Therefore, when these reticle patterns are overlaid and exposed, all the parts of the pattern are fully exposed by any one of the reticles, so that the amount of accumulated electrons on the resist due to electron scattering at the bridge part is reduced. Can be suppressed. Therefore, it is possible to obtain a resist pattern with less constriction and satisfying the required value of CD.

As described above, by providing the bridge in the apertured portion of the pattern longer than the pattern division reference length (for example, about 30 μm), even a long line-shaped pattern is prevented from being distorted by its own weight and the like. It can be formed into a stencil reticle. In the case of a donut pattern, a leaf-shaped pattern, or a tan-shaped pattern, the width and pitch of the bridge are appropriately selected according to the pattern shape. It should be noted that the places where the bridges are provided may take a long processing time in the method of judging and processing corresponding to the individual pattern shapes, and thus may be arranged randomly like a mesh on the reticle.

FIG. 4 is a diagram showing a stencil reticle according to a second embodiment of the present invention, and is an enlarged plan view of a line pattern on the reticle. The scattering stencil reticle of this example is substantially the same as the stencil reticle of FIG. 1, and is composed of two reticles 71 and 73, but a bridge 77 is formed obliquely to the long side of the linear pattern 75. . The positions of the bridge 77 of the two reticles 71 and 73 are different.

By forming the bridge 77 obliquely, the width of the bridge can be made thicker than 100 nm, but it is preferably 100 nm or less in consideration of CD controllability. The angle θ2 of the bridge 77 with respect to the long side of the linear pattern 75 is preferably 45 degrees.

Example A gate layer was exposed to produce a logic device of 100 nm node.
The gate length on the reticle was about 280 nm. The reticle has a structure similar to that of the scattering stencil reticle of FIG.
It has a bridge located at °. The width of the bridge of each reticle is 80 nm, and the distance between the bridges is 20 μm.

As the reticle blank, an SOI wafer in which an appropriate amount of boron was dosed for the purpose of stress control was used in which main strut and minor strut structures were formed. E on this blanks membrane
Apply B resist (ZEP520, thickness 0.5μm) and draw the target pattern using EB direct drawing machine.
A scattering stencil reticle was made.

The above-mentioned two scattering stencil reticles are set in an electron beam projection exposure apparatus, and an 8-inch silicon wafer (P type, low efficiency 4 to 6Ω is set on the wafer stage 24.
cm, crystal axis (100) plane was placed. On the wafer, a chemically amplified resist for EB exposure (NEB22 manufactured by Sumitomo Chemical Co., Ltd.) was applied to a thickness of 0.3 μm, and this resist was prebaked on a 110 ° hot plate for 120 seconds. did. Then, the reticle was aligned using the FIA mark for alignment which was previously arranged on the wafer.

At the time of exposure, the electron beam acceleration voltage is 100 kV, the reduction ratio is 1/4, and the collective exposure area on the wafer is 0.
It was 25 mm square. The optimum exposure dose at this time was about 30 μC / cm ² in total for each exposure (two exposures) using two reticles. The beam current on the reticle is 15 μA, and the reticle aperture ratio is about 1 for the entire layer.
Since it was 0%, the on-wafer beam current was 1.5 μA. After exposing one of the two reticles, the reticle stage was moved, and then the other reticle was exposed.

After completion of the exposure, the wafer was taken out and subjected to PEB treatment with a hot plate. Treatment condition is 100 ℃ 2
Minutes. The development was carried out for 1 minute using a 2.38 wt% TMAH aqueous solution as a developer, and then rinsed with pure water. The exposure pattern after development is a length measuring machine (CD-SEM
Machine). As a result, it was confirmed that the resist pattern image in the portion where the bridge was formed was not thin, and it was also confirmed that sufficient resolution was obtained.

[0039]

As is apparent from the above description, when the reticle according to the present invention is used, the time for complementary division processing can be significantly reduced and the reticle cost can be greatly suppressed.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a scattering stencil reticle according to a first embodiment of the present invention, FIG. 1 (A) is a plan view of a line and space pattern, and FIG. 1 (B) is a reticle structure. It is a partially expanded view explaining.

FIG. 2 is a perspective view schematically showing the configuration of the entire optical system of a charged particle beam exposure apparatus using the reticle shown in FIG.

FIG. 3 is a diagram schematically showing a state in which a pattern having a bridge is transferred to a resist on a wafer.

FIG. 4 is an enlarged plan view showing a stencil reticle according to a second embodiment of the present invention.

[Explanation of symbols]

10 reticle (group) 51, 53 reticle 55 line pattern 57 bridge (beam) 71, 73 reticle 75 line pattern 77 bridge

Claims (4)

[Claims] 1. A desired pattern is formed on a stencil reticle in which a large number of holes corresponding to the shape of element figures of a pattern are formed in a membrane, the reticle is illuminated with an electron beam, and the electron beam that has passed through the reticle is on a sensitive substrate. An electron beam exposure method for transferring the pattern onto the sensitive substrate by projecting and forming an image onto the sensitive substrate, wherein substantially the same pattern is formed on the two reticles, and the pattern element figure of the reticle is formed. A thin membrane beam (bridge) connecting both edges of the hole is provided at a desired position of the hole, and in the reticle of the two-sheet set, the bridge is provided at a different position of the pattern, An electron beam exposure method, characterized in that the patterns of two reticles are superimposed and exposed on the same sensitive substrate. 2. The electron beam exposure method according to claim 1, wherein the width of the bridge is narrower than R × M (R: resolution limit of resist on wafer, M: magnification of projection lens). 3. The electron beam exposure method according to claim 1, wherein the bridge is arranged obliquely with respect to the edge of the hole of the pattern element graphic. 4. A stencil reticle having a large number of holes corresponding to the shape of a pattern element figure formed in a membrane, wherein substantially the same pattern is formed on the two reticles, and the pattern element of the reticle. A stencil reticle characterized in that a thin membrane beam (bridge) that connects both edges of the hole is provided at a desired position of the figure hole in the two reticles at different positions of the pattern.