JP2000058446A - Charged particle beam transfer exposure method, reticule by use thereof, and manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a transfer pattern to be less deformed, less deviated on a focal point, and reduced in fuzziness caused by astigmatism by a method wherein a fine pattern that is beyond a resolution limit of an optical system that projects a pattern beam is sparsely provided in a part of a reticule where a pattern is low in density. SOLUTION: A unit exposure region 1 is a square 1 mm2 in area on a reticle and transferred onto a photosensitive substrate by a lighting beam as being reduced in size. The unit exposure region 1 has a low-density pattern part 3 where small rectangular patterns 11 are comparatively sparsely dispersed and a high-density pattern part 5 where large strip patterns 15 are densely arranged. A large number of fine square patterns 13 whose side is, for instance, 0.08 μm long are dispersed separating from each other by a space of 0.12 μm in all the low-density pattern part 3. The resolution limit of a projection optical system is 0.08 μm or so on a wafer, so that the image of the fine pattern 13 gets fuzzy and is scarcely formed on the wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for transferring and exposing a semiconductor device circuit pattern or the like onto a sensitive substrate (wafer or the like) using a charged particle beam such as an electron beam or an ion beam, and a reticle used therefor. In particular, charged particle beam transfer that has been improved to reduce the difference in the focal position of the transfer pattern, distortion and astigmatism blur caused by the difference in Coulomb effect due to the uneven distribution of current density between the reticle and the sensitive substrate It relates to an exposure method and the like. Moreover,
The present invention relates to a method for manufacturing a highly accurate semiconductor device using such a charged particle beam transfer exposure method.

[0002]

2. Description of the Related Art The prior art will be described by taking transfer exposure using an electron beam as an example. The drawback of electron beam exposure is high accuracy but low throughput, and various techniques have been developed to overcome the drawback. At present, a figure portion batch exposure method called cell projection, character projection or block exposure has been put to practical use. In the figure part batch exposure method, a small circuit pattern with repeatability (about 5 μm square on the wafer)
Using a mask in which a plurality of similar small patterns are formed, transfer exposure is repeatedly performed using one small pattern as one unit. However, even in this method, the variable shaping method is used for pattern portions having no repeatability.

On the other hand, as an electron beam transfer exposure system aiming at a much higher throughput than the graphic partial batch exposure system,
An electron beam reduction transfer apparatus has been proposed in which a mask having a circuit pattern of an entire semiconductor chip is prepared, an electron beam is irradiated to a certain area of the mask, and an image of the pattern in the irradiation area is reduced and transferred by a projection lens. ing. In this type of apparatus, when the entire area of the mask is collectively irradiated with an electron beam to transfer the pattern at one time, the pattern cannot be transferred with high accuracy. Also, it is difficult to manufacture a mask serving as an original. Therefore, a system which has been studied vigorously recently does not expose one die (chips on a wafer) or a plurality of dies at once, but has a large optical field as an optical system, but the pattern is divided into small regions. And performing transfer exposure (hereinafter, referred to as a division transfer system). At this time, for each of the small areas, exposure is performed while correcting aberrations such as the focal point of the image of the small area formed on the surface to be exposed and the field distortion. This makes it possible to perform exposure with high resolution and accuracy over an optically wide area as compared with batch transfer of the entire die.

[0004]

In an exposure apparatus using a charged particle beam, it is known that a pattern to be exposed is blurred (including astigmatism blur) or distorted due to the Coulomb effect. In the variable molding method and the cell projection method which have been conventionally used, an area to be transferred at a time (unit exposure area) is as small as about 5 μm square. However, in the above-described split transfer system, the size is considerably large, about 100 μm square or more (this increases the throughput). When the unit exposure area is large as described above, when exposing a small area where the pattern in the area is unevenly distributed, the manner in which the Coulomb effect works depends on the location in the area.

A specific description will be given. FIG. 5 is a plan view schematically showing an example of a pattern having a partial difference in pattern density. Reference numeral 81 in the figure indicates a pattern in the unit exposure area. The area 81 includes a low pattern density portion 83 in which small patterns 87 are relatively sparsely distributed, and a large pattern 89.
There is a high pattern density portion 85 in which is relatively dense. Here, the patterns 87 and 89 are openings or highly transmissive parts on the reticle, and are parts to which a dose is given on the wafer. Such a pattern is called a positive pattern in this specification. The pattern formed by the opposite part, that is, the part that is not opened on the reticle or the part with low permeability, and the part that is not dosed on the wafer is called a negative pattern.

Here, it is assumed that the pattern density of the high pattern density portion 85 in the unit exposure region 81 is 50%, and the pattern density of the low pattern density portion 83 is 10%.
The Coulomb effect of the pattern beam that has passed through the reticle is
Since the current density of the beam is high when the beam density is high, the just focus point is set to the low pattern density portion 8 in the high pattern density portion 85.
Farther than three. Therefore, usually, transfer exposure is performed with each medium focus. In this case, the resolving power of the transfer pattern is lower than in the case where each is exposed by just focus. Also, the distortion of the entire unit exposure area 81 is different from the case where the pattern is uniformly distributed in the area.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and has a problem in transfer pattern distortion and a difference in focal position caused by a difference in Coulomb effect caused by uneven distribution of current density between a reticle and a sensitive substrate. It is an object of the present invention to provide a charged particle beam transfer exposure method and the like which are improved to reduce blur and astigmatism blur. Still another object of the present invention is to provide a method for manufacturing a highly accurate semiconductor device by using such a charged particle beam transfer exposure method.

[0008]

According to a first aspect of the present invention, there is provided a charged particle beam transfer exposure method comprising: forming a pattern to be transferred to a specific region on a sensitive substrate on a reticle; Irradiating a reticle with a charged particle beam, projecting a patterned charged particle beam (pattern beam) through the reticle onto a specific region on the sensitive substrate, and transferring the pattern;
A minute pattern smaller than the resolution limit of the optical system for projecting the pattern beam is dispersed and provided in a portion where the pattern density of the reticle is low.

By providing the fine pattern as described above in the low pattern density portion, the pattern density in the entire unit exposure region becomes uniform or approaches uniform. Since the extra fine pattern cannot be resolved by the exposure apparatus, the current density is reduced on the wafer and is projected on the wafer as a blurred pattern. Therefore, this pattern is not transferred. However, since the charged particle beam exists between the reticle and the wafer, it contributes to the Coulomb effect. Therefore, the distortion and blurring in the entire unit exposure area become uniform, and as a result, distortion correction is facilitated, and the pattern accuracy after correction is improved. Further, the blur becomes uniform, and the exposure resolution over the entire area is improved.

The present invention is not limited to a method of forming and transferring an entire pattern formed on a sensitive substrate on a reticle (divided transfer method and the like), and a method of partially exposing a figure portion collective exposure method such as cell projection. Can be applied to a method of forming the pattern by transfer and drawing the rest with a variable shaped beam or Gaussian beam.

[0011] The charged particle beam transfer exposure method according to the second aspect of the present invention includes the step of:
It is characterized in that a dummy pattern which does not hinder the pattern formation on the sensitive substrate is provided. In this case, since the dummy pattern is provided in a portion that does not hinder the formation of the device, the dummy pattern may be a pattern large enough to be resolved by the exposure apparatus.

According to a third aspect of the present invention, there is provided the charged particle beam transfer exposure method, wherein the reticle has a relatively low degree of absorption or scattering of the charged particle beam, and a transparent base film formed on the base film. A negative pattern film having a relatively high degree of absorption or scattering of a charged particle beam, and a minute hole smaller than the resolution limit of an optical system for projecting the pattern beam, on the negative pattern film in a portion where the negative pattern density is high. Are provided in a dispersed manner. The function of the holes is the same as the function of the fine pattern of the first embodiment.
In this embodiment, the holes may be provided on the entire surface regardless of the pattern density. Also in this case, the same effect as described above can be expected, and it is easier to manufacture a reticle by making holes on the entire surface. A semiconductor device manufacturing method according to the present invention is characterized in that exposure in a lithography step is performed using the above charged particle beam transfer exposure method.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. First, an electron beam exposure apparatus as an example of an apparatus for performing the method of the present invention will be described. FIG. 4 is a diagram showing an image forming relationship in the entire optical system of an electron beam exposure apparatus which is an example of an apparatus for performing the method of the present invention.

The electron gun 101 emits an electron beam downward. Below the electron gun 101, two stages of condenser lenses 103 and 105 are provided, and the electron beam passes through these condenser lenses 103 and 105 and forms a crossover image on a blanking aperture 107. Below the condenser lens 105, a rectangular opening 106 is provided. The rectangular opening 106 allows only the electron beam illumination light for an area corresponding to one exposure unit small area to pass. The image of the opening 106 is formed on the reticle 110 by the lens 109.

Below the opening 106, a blanking opening 107 is provided at a position where a crossover is formed. A deflector 108 is disposed below the deflector 108. The deflector sequentially scans the illumination light mainly in the X direction in FIG. 4 to illuminate a small area in the optical field including deflection on the reticle. Below the deflector 108, a condenser lens 109 is arranged. The condenser lens 109 is
The electron beam is converted into a parallel beam and hits the reticle 110,
The aperture 106 is imaged on the reticle 110.

The reticle 110 is shown in FIG.
Although only a small area is shown, it actually extends in a direction perpendicular to the optical axis (XY direction) and has many small areas.
When illuminating and exposing each small area within the visual field of the optical system, the electron beam is deflected by the deflector 108 as described above. The reticle 110 is placed on a reticle stage 111 that can move in the X and Y directions. The wafer 114, which is a material to be exposed, is also placed on a wafer stage 115 that can move in the X and Y directions. By scanning these reticle stage 111 and wafer stage 115 in the opposite Y directions, each small area in the die pattern is exposed. In addition, both stages 111 and 115 have
An accurate position measurement system using a laser interferometer is provided, and each small area is accurately joined on the wafer 114 by separate alignment means and adjustment of each deflector.

A projection lens 11 is provided below the reticle 110.
2 and 113 (objective lens) and a deflector 131 are provided. Then, one small area of the reticle 110 is irradiated with an electron beam, and the electron beam patterned by the reticle 110 is reduced and deflected by the projection lenses 112 and 113 to form an image at a predetermined position on the wafer 114. . An appropriate resist is applied on the wafer 114, and a dose of an electron beam is given to the resist, so that a reduced pattern of a reticle image is transferred onto the wafer 114. The wafer 114 is mounted on the wafer stage 115 movable in the direction perpendicular to the optical axis as described above.

Next, a charged particle beam transfer exposure method and a reticle according to one embodiment of the present invention will be described. FIG. 1 is a plan view schematically showing an example of a reticle used in the charged particle beam transfer exposure method according to the first embodiment of the present invention. The reticle of this example is a thin substrate made of Si or the like (a thickness of 1 μm, for example).
) Is a so-called stencil-type reticle in which patterns 11 and 15 having openings are opened. FIG. 2 shows a pattern in one unit exposure area 1. The unit exposure area 1 is, for example, a square of 1 mm square on a reticle,
At the same time, it is an area that is simultaneously reduced and transferred onto the sensitive substrate by receiving the illumination beam. If the reduction ratio is 1/4, an area of 250 μm square is exposed at a time on the wafer. To form a pattern of one semiconductor device, a reticle having thousands to tens of thousands of such unit exposure regions is used.

The unit exposure region 1 has a low pattern density portion 3 in which small rectangular patterns (positive patterns) 11 are relatively sparsely distributed and a high pattern portion in which large band-shaped patterns 15 are relatively densely arranged. It has a pattern density portion 5. The pattern area density of the small pattern 11 in the low pattern density part 3 is 10%
And the pattern density of the high pattern area density portion 5 is 50
%.

In this embodiment, in the low pattern density portion 3, small square micro patterns 13 each having a small side of 0.08 μm on a reticle are formed on one surface and dispersed at intervals of 0.12 μm. As a result, the total pattern density of the low pattern density portions 3 is about 50%. This value is 40% larger than the case where only the original small pattern 11 exists, and the uniformity of the pattern density with the high pattern density portion 5 is improved. Note that the shape of the individual minute pattern 13 may be a circle or a band.

The fine pattern 13 is 0.02 μm on the wafer if the resolution is sufficient if the reduction rate is 4.
It becomes the size of the corner. However, the resolution of the projection optical system is about 0.08 μm on the wafer, and
Is not blurred and resolved on the wafer.

FIG. 2 is a graph schematically illustrating the difference in beam intensity on a wafer between a normal device pattern and a minute pattern for Coulomb effect correction for explaining the above situation. The horizontal axis represents the position on the wafer, and the vertical axis represents the beam intensity. The beam intensity that has passed through the normal pattern is line 2
As shown by 1, it rises sharply. However, the intensity of the beam that has passed through the micropattern is a line like a low mountain that is gently continuous as shown by a line 23, and can hardly be considered as background noise with almost no contrast. Therefore, this pattern is not transferred. However, a charged particle beam that has passed through the fine pattern exists between the reticle and the wafer, and thus contributes to the Coulomb effect. Therefore, the distortion and blurring in the entire unit exposure area become uniform, and as a result, distortion correction is facilitated, and the pattern accuracy after correction is improved. Further, the blur becomes uniform, and the exposure resolution over the entire area is improved.

FIG. 3 is a diagram showing a sectional structure of a reticle used in the charged particle beam transfer exposure method according to the third embodiment of the present invention. The reticle 31 is composed of a thin Si-based film 33 (membrane, 0.1 μm in thickness) and scatterers 35 and 37 (0.5 μm in thickness) made of a heavy metal such as W or Ta.
Is formed as a negative pattern. The portion without the scatterer films 35 and 37 passes through the electron beam without much scattering, and the portion with the scatterer films 35 and 37 is considerably scattered when the electron beam passes. As a result, the current density of the beam passing through the portion without the scatterer film becomes relatively high. A stop (not shown) arranged between the projection lenses 112 and 113 in the projection optical system of the electron beam exposure apparatus shown in FIG. 4 blocks a highly scattered beam from reaching the wafer, and does not reach the wafer. In this case, a good contrast image is formed.

On the reticle 31, a high pattern density portion 41 where the negative pattern 35 is relatively sparse, and a negative pattern 35
However, there is a low pattern density part 43 where the density is relatively high. For this reason, the average (current density) on the optical path differs between the pattern beam that has passed through the high pattern density portion 41 and the pattern beam that has passed through the low pattern density portion 43, and the difference in the Coulomb effect between the reticle and the wafer. Get out. In the embodiment of FIG. 3A, a large number of fine holes 39 are formed in the scatterer film 37 to reduce the difference. In this example, only the scatterer film 37 in the low pattern density portion 43 is perforated by a technique such as etching.

On the other hand, in FIG. 3B, the high pattern density portion 41 'and the low pattern density portion 43' are distinguished over the entire surface of the reticle, and the base film 33 'and the scatterer films 35' and 37 '.
Are formed in the optical axis direction. Such a hole can be formed by a technique such as ion beam drilling without employing a masking step, so that the reticle manufacturing process is simplified.

Next, an example of the mode of use of the exposure apparatus of the present invention will be described. FIG. 6 is a flowchart showing an example of the semiconductor device manufacturing method of the present invention. The manufacturing process of this example includes the following main processes. Wafer manufacturing process for manufacturing a wafer (or wafer preparing process for preparing a wafer) Mask manufacturing process for manufacturing a mask to be used for exposure (or mask preparing process for preparing a mask) Wafer processing process for performing necessary processing on a wafer Wafer Chip assembling step of cutting out the chips formed on the chip one by one to make it operable Chip inspecting step of inspecting the resulting chips Each of the steps further includes several sub-steps.

Among these main processes, the main process that has a decisive effect on the performance of a semiconductor device is a wafer processing process. In this step, designed circuit patterns are sequentially stacked on a wafer, and a number of chips that operate as memories and MPUs are formed. This wafer processing step includes the following steps. A thin film forming step (using CVD, sputtering, etc.) for forming a dielectric thin film serving as an insulating layer, a wiring portion, or a metal thin film forming an electrode portion (using CVD or sputtering, etc.) A lithography process of forming a resist pattern using a mask (reticle) in order to selectively process etc. An etching process of processing a thin film layer or a substrate according to a resist pattern (for example, using a dry etching technique) An ion / impurity implantation diffusion process Resist stripping step Inspection step for inspecting the processed wafer Further, the wafer processing step is repeated by a necessary number of layers to manufacture a semiconductor device that operates as designed.

FIG. 7 is a flowchart showing a lithography step which is the core of the wafer processing step shown in FIG. This lithography step includes the following steps. A resist coating step of coating a resist on a wafer on which a circuit pattern has been formed in the preceding step An exposing step of exposing the resist A developing step of developing the exposed resist to obtain a resist pattern Stabilizing the developed resist pattern Annealing Step for Using the exposure apparatus of the present invention in the above-mentioned exposure step, the accuracy of pattern formation in the lithography step is greatly improved.
In particular, the process related to realizing the required minimum line width and the overlay accuracy corresponding thereto is a lithography process, in particular, an exposure process including alignment control, and it has been difficult until now by applying the present invention. Semiconductor devices can be manufactured.

[0029]

As is apparent from the above description, according to the present invention, when a semiconductor device circuit pattern or the like is transferred and exposed on a sensitive substrate using a charged particle beam such as an electron beam or an ion beam, Distortion and blurring of a transferred image in a small area to be transferred at a time can be made uniform, and as a result, a pattern with good accuracy and resolution can be exposed. Further, it is possible to provide a method for manufacturing a semiconductor device with high accuracy by using such a charged particle beam transfer exposure method.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing an example of a reticle used in a charged particle beam transfer exposure method according to a first embodiment of the present invention.

FIG. 2 is a graph schematically showing a difference in beam intensity on a wafer between a normal device pattern and a minute pattern for Coulomb effect correction. The horizontal axis represents the position on the wafer, and the vertical axis represents the beam intensity.

FIG. 3 is a diagram showing a cross-sectional structure of a reticle used in a charged particle beam transfer exposure method according to a third embodiment of the present invention.

FIG. 4 is a diagram showing an image forming relationship in the entire optical system of an electron beam exposure apparatus which is an example of an apparatus for performing the method of the present invention.

FIG. 5 is a plan view schematically showing an example of a pattern having a partial difference in pattern density.

FIG. 6 is a flowchart illustrating an example of a semiconductor device manufacturing method according to the present invention.

FIG. 7 is a flowchart showing a lithography step which is the core of the wafer processing step of FIG. 6;

[Explanation of symbols]

Reference Signs List 1 unit exposure area 3 low pattern density part 5 high pattern density part 11 small pattern 13 minute pattern 15 large pattern 31 reticle 33 Si base film 35, 37 heavy metal film (negative pattern) 39 hole 41 high pattern density part 43 low pattern density part 45 holes

Claims (9)

[Claims] 1. A pattern to be transferred to a specific area on a sensitive substrate is formed on a reticle, the reticle is illuminated with a charged particle beam, and a patterned charged particle beam (pattern beam) passing through the reticle is patterned. A method of projecting and forming an image on a specific area on the sensitive substrate to transfer the pattern; a minute pattern smaller than the resolution limit of an optical system that projects the pattern beam on a portion where the pattern density of the reticle is low. A charged particle beam transfer exposure method, wherein 2. A pattern to be transferred to a specific region on a sensitive substrate is formed on a reticle, the reticle is illuminated with a charged particle beam, and a patterned charged particle beam (pattern beam) passing through the reticle is formed. A method of projecting and forming an image on a specific area on the sensitive substrate and transferring the pattern; providing a dummy pattern that does not interfere with the pattern formation on the sensitive substrate in a portion where the pattern density of the reticle is low. And a charged particle beam transfer exposure method. 3. A pattern to be transferred to a specific area on a sensitive substrate is formed on a reticle, the reticle is illuminated with a charged particle beam, and a patterned charged particle beam (pattern beam) passing through the reticle is formed. A method of projecting and imaging the specific area on the sensitive substrate to transfer the pattern; the reticle includes a transmission base film having a relatively low degree of absorbing or scattering the charged particle beam; A negative pattern film having a relatively high degree of absorbing or scattering the charged particle beam formed in the negative pattern film of the portion having a high negative pattern density,
A charged particle beam transfer exposure method, wherein minute holes smaller than the resolution limit of the optical system for projecting the pattern beam are provided in a dispersed manner. 4. The charged particle beam transfer exposure method according to claim 3, wherein said holes are provided on the entire surface regardless of the pattern density. 5. A Coulomb effect caused by uneven distribution of a current density distribution between a reticle and a sensitive substrate, wherein said minute pattern, dummy pattern or hole is provided in a direction in which a current density in a region transferred at a time becomes uniform. The charged particle beam transfer exposure method according to any one of claims 1 to 4, wherein a difference, a distortion, and an astigmatism blur of a focal position of a transfer pattern caused by the change are reduced. 6. A reticle having a pattern to be transferred to a specific region on a sensitive substrate, wherein fine patterns smaller than the resolution limit of an optical system for transferring the pattern are dispersed in a portion where the pattern density is low. A reticle characterized by being provided. 7. A reticle having a pattern to be transferred to a specific region on a sensitive substrate, wherein a dummy pattern which does not hinder the pattern formation on the sensitive substrate is provided in a portion where the pattern density is low. A reticle characterized by the following. 8. A reticle having a pattern to be transferred to a specific area on a sensitive substrate, wherein the reticle has a relatively low degree of absorption or scattering of a charged particle beam, and a reticle formed on the reticle. A negative pattern film having a relatively high degree of absorbing or scattering a beam;
A reticle, wherein minute holes smaller than the resolution limit of an optical system for projecting the pattern beam are dispersedly provided. 9. A method for manufacturing a semiconductor device, comprising performing exposure in a lithography step using the charged particle beam transfer exposure method according to claim 1. Description: