JPH05335223A - Method for forming resist pattern - Google Patents

Abstract

PURPOSE:To eliminate an irregularity in the size of a periodic pattern when a photomask used to form an opening pattern for a CCD image sensing device is manufactured by an electron-beam exposure operation. CONSTITUTION:In a vector-scanning electron-beam exposure device, its current density is always definite and its exposure time is proportional to an exposure amount. The exposure amount is in a linear relationship with the size of a pattern. The permissible range of a change in the exposure amount is decided according to the permissible range of the change in the size of the pattern, the value of the exposure amount is set in a multistage manner within the range, and the value is input, on the basis of random numbers, at random as the parameter of the exposure time in exposure data on individual graphics. In conventional cases, the size of a pattern is increased periodically along the joint of fields and this causes an irregularity in the sensitivity of a can. In this invention, an irregularity in the size of the pattern is made random inside each field, and an irregularity in the sensitivity is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a resist pattern which is applied in the field of manufacturing semiconductor devices, and more particularly to a method of forming a light receiving portion of a CCD (charge coupled device) image pickup device using an electron beam exposure device. The present invention relates to a method for eliminating a periodical variation in the dimension of each figure without decreasing the throughput when forming a photomask (reticle) having many identical figures.

[0002]

2. Description of the Related Art In the field of semiconductor device manufacturing, a photolithography technique for transferring a circuit pattern on a photomask onto a wafer while reducing the circuit pattern is used for miniaturization of semiconductor devices.
This is one of the technologies that has made the greatest contribution to high integration. This photomask is a transparent substrate, such as glass, with C
A metal thin film such as r (chrome) is formed as a light-shielding film according to a predetermined circuit pattern. The circuit pattern was created by photographing a pattern formed by artwork with a reduction camera in the early days, but in recent years, most of it is created by electron beam lithography. The outline of this preparation process is to first form a Cr layer as a light-shielding film on a transparent substrate such as a glass plate, and then coat an electron beam resist material on the surface to form a resist film. A circuit pattern is directly drawn on a resist film by using a computer-controlled electron beam exposure apparatus, unnecessary portions of the resist film are dissolved and removed by a development process, and the exposed portion of the Cr layer is exposed using the remaining resist film pattern as a mask. It is to be removed by etching.

The types of electron beam exposure apparatus are roughly classified into a raster scan system and a vector scan system. In the raster scan method, the electron beam constantly scans in a strip-shaped elongated field in one direction, and the XY table on which the photomask substrate is mounted moves in a direction perpendicular to the scanning direction of the electron beam. When you reach the desired shape in a certain field,
Only then is the electron beam turned on and drawing is performed.

On the other hand, in the vector scan method, the XY table on which the photomask substrate is placed is stationary while a certain field is selected, and the electron beam is generated based on the digital data indicating the type and coordinates of the figure. Move to a specific figure in the field and fill the figure by raster scanning. After drawing one figure, the beam is turned off, the beam is moved to the next figure in the same field, and turned on again to paint the figure.
When all the figures in one field have been drawn, X
Operate the Y table to select the next field.

This method is currently the mainstream of electron beam exposure apparatuses, and is particularly suitable for the purpose of drawing an isolated pattern of a substantially fixed size such as a hole pattern. The size of one field in the vector scan method is usually about 1 to 2 mm square due to various restrictions such as the aberration of the lens included in the electron optical system, the movable range of the aperture, and the variable range of the electron beam trajectory by the deflection coil. Is limited to. Therefore, a large number of these fields are joined together to form one device pattern.

Further, in recent years, a vector scan type apparatus using a variable shaped beam has been widely used. It illuminates a first shaping aperture with an electron beam and images this transmitted beam onto a second shaping aperture. The image of the first aperture is deflected with respect to the second aperture to form a variable shaped beam, which is used to draw the desired figure. This technique has significantly improved the throughput in the vector scan method.

[0007]

By the way, while moving from field to field as described above,
In the drawing method in which the AND / repeat type exposure is performed, variations in the pattern size are likely to occur periodically due to distortion of the deflection system, movement accuracy of the XY stage, and the like. As an example, FIG. 4 shows an example of forming an opening pattern corresponding to the light receiving portion of the CCD image pickup device. In the figure, hatched squares indicate patterns formed larger than the design size, white squares indicate patterns formed smaller than the design size, and arrow F indicates
Indicates a field boundary (seam). From this figure, it can be seen that patterns larger than the design size are concentrated along the field boundaries. Such periodical variation in dimensions causes sensitivity unevenness in the CCD image pickup device and is not practical for a photomask.

The accuracy of field splicing is about 0.1 μm in terms of 3σ (σ = standard deviation) even in a high-performance model in the current electron beam exposure apparatus. However, in the future CCD image pickup device, 16 Mbit DRAM, etc., the required accuracy for the dimensional uniformity of each figure forming the device pattern greatly exceeds the above value. For example, for the device pattern of the CCD image pickup device as described above, the design value L and the dimension L ′ realized on the photomask are used.
It is also required to suppress the variation of the difference ΔL from the difference of 0.03 μm or less in 3σ.

As a method of satisfying this required accuracy, a multiple drawing method has been proposed conventionally. For example, the 36th
Proceedings of the Second Joint Lecture on Applied Physics (Spring Annual Meeting 1989), p. 601, lecture number 3p-K-7, X
1/2 step movement of Y stage
Then, a technique has been reported in which each pattern is exposed four times in different fields. This allows
Field splicing errors caused by movement of the XY stage are averaged, and a pattern with high positional accuracy is obtained.

Further, the inventor of the present invention previously disclosed in Japanese Patent Laid-Open No. 62-213
In the Japanese Patent No. 272 publication, when a large pattern that does not fit in one field is divided into a plurality of times and drawn,
A technique is proposed in which the dividing position of this pattern is changed for each exposure and the exposure is performed with the amount of energy distributed for each exposure.

Although the multiple drawing method is certainly effective in satisfying the dimensional accuracy, it naturally causes a significant decrease in throughput as compared with the normal drawing method. Therefore, an object of the present invention is to provide a method for forming a resist pattern capable of suppressing the periodical size variation of a large number of identical figures without lowering the throughput.

[0012]

The method of forming a resist pattern of the present invention is proposed to achieve the above-mentioned object, and a plurality of identical resist patterns are formed on a resist film by irradiating an energy beam. In the method of sequentially drawing figures, the size of each figure is changed within an allowable range by randomly changing the irradiation amount of the energy beam corresponding to each of the plurality of same figures. To do.

According to the present invention, the random variation of the irradiation amount is varied based on a random number in the computer data corresponding to each of the plurality of identical figures, the parameter describing the irradiation time of the energy beam. It is characterized by carrying out by doing.

The invention is further characterized in that the energy beam is an electron beam.

[0015]

The inventor of the present invention cannot avoid dimensional fluctuation within a certain allowable range in the technique of drawing a large number of identical patterns by energy beam irradiation, so that this fluctuation is periodically generated along the seam of the field. It was found that the practical performance of the target device can be improved by not dispersing it but by distributing it evenly in the field. The size of each figure is large if the irradiation amount of the energy beam is large,
The smaller the amount is, the smaller the irradiation amount is. Therefore, the irradiation amount may be randomly changed for each figure.

In order to change the irradiation amount of the energy beam for each figure, it is necessary that computer data for controlling the irradiation be described in units of one figure.
Therefore, for example, when the electron beam is used as the energy beam, the present invention is naturally applied to the vector scan type electron beam exposure apparatus.

In the vector scan type electron beam exposure apparatus, since the current density is always constant, the irradiation time is proportional to the exposure amount. Further, in a region where the exposure amount required for resolution of the resist film is equal to or larger than the threshold value, as shown in FIG. 1, the dimension measurement value of the obtained pattern and the electron beam exposure amount are substantially proportional to each other. Therefore, the relationship between the dimension measurement value and the electron beam exposure amount as shown in FIG. 1 is obtained in advance according to the device used or the type of resist pattern to be formed, and the design dimension is indicated by the arrow A as the center. The allowable range of dimensional change is set, and the allowable range of exposure amount change as indicated by arrow B is determined accordingly.

The parameters describing the irradiation time in the computer data corresponding to each figure are changed based on the random numbers so that the exposure amount falls within the allowable range thus determined.

According to this method, the electron beam exposure amount for each figure in a certain field changes automatically and completely at random within a permissible range. Therefore, the dimension measurement value of the obtained figure is also random within the permissible range. Changes to.
Therefore, according to the present invention, it is possible to prevent the increase of the periodic pattern size in the vicinity of the seam of the field as in the conventional case. If the present invention is applied to, for example, the manufacture of a photomask for a CCD image pickup device, the yield can be significantly improved, and the uneven sensitivity of the manufactured CCD image pickup device can be eliminated. Moreover, in the present invention, since it is not necessary to perform multiple drawing, there is no fear that the throughput will be reduced.

[0020]

EXAMPLES Specific examples of the present invention will be described below. This embodiment is an example of manufacturing a stepper photomask for forming a pattern of a CCD image pickup device by electron beam exposure. First, on a commercially available mask blank having a Cr light-shielding film formed on a glass substrate, poly (2,2,2-trifluoroethyl-α-chloroacrylate) (manufactured by Toray Industries, Inc .; trade name EBR-9) Was applied to form a resist film.

Next, the permissible range of changes in the electron beam exposure amount was set. The pattern on the photomask used in the stepper with the reduction ratio of 1/5 is formed to be 5 times as large as the pattern on the wafer. For example, to resolve a 0.5 μm pattern on a wafer, 2.5 μm on the mask
Pattern is required, and the allowable variation at this time is about 0.05 μm in 3σ. That is, in FIG.
In such a characteristic diagram, the allowable range of dimensional change centering on the design size of 2.5 μm is 2.45 to 2.55 μm, and the range indicated by arrow A is 0.1 μm. Based on the actual measurement, the allowable range of exposure amount change corresponding to this allowable range of dimensional change was calculated to be 4.60 to
A 4.97μC / cm ^2, the range indicated by the arrow B was found to be 0.37μC / cm ^2.

Then, the above range 0.37 μm is set to 6
An exposure amount level of 64 steps was set by dividing it into three equal parts, and 64 kinds of irradiation times were set accordingly. This irradiation time is
In computer data, it is described by a parameter called shot rank. FIG. 2 shows a data format for controlling the variable shaped electron beam exposure apparatus by the vector scan method. This data format is used to CAD the circuit design drawing drawn on graph paper.
It is created when the image is read by the system and the image data at this time is converted into digital data for driving the electron beam exposure apparatus. The exposure data of the nth figure is roughly divided into exposure parameters and figure parameters. The exposure parameters include shot rank commands and shot ranks, and the figure parameters include figure codes, coordinate information, and other data. included. When the exposure data of the nth figure is completed, the (n + 1) th exposure data is similarly repeated.

In this embodiment, random numbers are generated when digital data conversion is performed in the CAD system, and 64 types of shot ranks are set based on preset correspondences between the random numbers and shot ranks. I randomly entered each figure.

FIG. 3 shows the result of actually performing electron beam exposure based on the exposure data created in this way, developing the resist film, and forming an opening pattern corresponding to the light receiving portion of the CCD image pickup device. .. This opening pattern is
Specifically, it is an opening pattern of the Al light shielding film. In the figure, hatched squares indicate patterns formed larger than the design size, white squares indicate patterns formed smaller than the design size, and arrow F indicates a field boundary (seam). As can be seen from this figure, the dimensions of the opening pattern vary randomly, and the periodic variation as in the conventional example shown in FIG. 4 has been eliminated. In the electron beam exposure process, no decrease in throughput occurred.

Furthermore, the CCD image pickup device manufactured by using such a photomask did not have any uneven sensitivity.

The specific embodiment of the present invention has been described above, but the present invention is not limited to this embodiment. For example, although the electron beam is used as the energy beam in the above-described embodiment, a focused ion beam, X-ray, etc. may be used. Further, as an example of a device in which a large number of the same figures are arranged to form an array, there are a memory device, a matrix drive circuit of various display devices, and the like in addition to the above-mentioned CCD image pickup device.

Further, in the above-described embodiment, the shot rank is set by the random number at the same time as the digital data conversion, but it may be set by performing an appropriate signal processing after the digital data conversion.

[0028]

As is apparent from the above description, by applying the present invention, in a device pattern in which a large number of identical figures are arranged, it is possible to eliminate the periodic variation in the dimension of each figure. .. This is extremely effective particularly in eliminating sensitivity unevenness in the CCD image pickup device. Moreover, since the present invention does not require multiple drawing, there is no fear of causing a decrease in throughput.

[Brief description of drawings]

FIG. 1 is a conceptual diagram illustrating a method of setting an allowable range of an electron beam exposure amount change based on an allowable range of a pattern dimension change in the present invention.

FIG. 2 is a format diagram of exposure data used to control a variable shaped electron beam exposure apparatus by a vector scan method.

FIG. 3 is a schematic view showing a random variation of pattern dimensions in a photomask for forming an aperture pattern of a CCD image pickup device produced by applying the present invention.

FIG. 4 is a schematic view showing a periodic variation of pattern dimensions in a photomask for forming an aperture pattern of a CCD image pickup device, which is created by a conventional method.

Claims (3)

[Claims] 1. A method of forming a resist pattern in which a plurality of identical figures are sequentially written on a resist film by irradiating an energy beam, wherein the energy pattern corresponding to each of the plurality of identical figures is formed.
A method of forming a resist pattern, characterized in that the dimension of each of the figures is varied within an allowable range by randomly varying the irradiation amount of the beam. 2. The random variation of the irradiation dose is performed by varying a parameter describing the irradiation time of the energy beam in the computer data corresponding to each of the plurality of identical figures based on a random number. The method for forming a resist pattern according to claim 1, wherein: 3. The method of forming a resist pattern according to claim 1, wherein the energy beam is an electron beam.