JP2794116B2 - Electron beam exposure method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam exposure method for forming a fine pattern using a variable-shaped electron beam exposure apparatus, and more particularly to a predetermined statistical deviation. And a method of forming a fine pattern having a pattern size smaller than the minimum pattern size that can be formed within the range of (1).

[Prior Art] FIG. 5 is a block diagram showing an example of the configuration of a conventionally used variable-shaped electron beam writing system. By irradiating the focused electron beam onto a substrate on which a pattern is to be formed, a chemical reaction is selectively induced on the substrate. Thereby, a desired pattern is drawn. The electron beam is formed into a rectangular shape having a required size in accordance with a pattern to be formed by using two apertures including a first shaping aperture and a second shaping aperture arranged above and below. The rectangular shaping electrode is placed between the two apertures. Thereby, the electron beam is deflected and shaped into a rectangular pattern of a required size by changing the overlap between the image and the aperture. The obtained shaped beam is reduced and projected to a desired position by a deflection electrode located further below. This allows
A desired pattern exposure is performed on the substrate.

The deflection area of the electron beam is usually as small as several mm square.
Therefore, in order to perform exposure processing on the entire surface of a mask or wafer as a substrate, it is necessary to move the XY stage to perform exposure processing. The movement of the stage is read into the processor by the laser interferometer. The read movement amount is compared with the position of the drawing pattern, and the correction amount is fed back to the beam deflection system. Thereby,
The drawing areas are connected with high accuracy. This method enables pattern drawing with a large exposure area.

The pattern data is input to the processor of the drawing system as an output from the CAD. The input pattern data is subjected to data processing such as pattern reduction, enlargement, division, etc., then converted into a format unique to the drawing system, and stored on a magnetic disk or the like. When an exposure process is performed, the processed data is transferred to an electron beam irradiation system, and an electron beam controlled based on the data is irradiated on the substrate to perform pattern drawing.

FIG. 6 is a schematic diagram showing an example of the configuration of an electron beam exposure apparatus of the electron beam writing system in FIG.
Referring to FIG. 6, electron beam emitted from electron gun 11
100 passes through the illumination lens 12 and is formed by the first forming aperture 13. Thereafter, the electron beam 100 passes through the shaping lens 14 and is shaped again by the second shaping aperture 15. The electron beam 100 thus shaped is
After being reduced by the reduction lens 16, the light passes through the projection lens 17. Electron beam 10 focused by projection lens 17
0 is moved to a predetermined position on the substrate 10 by the deflector 18. Thus, the electron beam 100 is irradiated on the substrate 10 on which a pattern is to be formed.

[Problems to be Solved by the Invention] Direct pattern writing with an electron beam is performed by direct exposure using an electron beam having a high resolution, so that a pattern to be formed has an extremely high resolution. In principle, a pattern with a resolution equal to the electron beam diameter can be exposed.

However, even if an electron beam is formed faithfully based on pattern data having a desired pattern size and irradiated onto a substrate, a pattern having a resolution equal to the electron beam diameter may not be obtained. For example, when the size of a desired pattern is 0.1 μm, the electron beam is shaped into a size of 0.1 μm according to the pattern size. 0.1μ
The pattern size of m is a very fine pattern size exceeding the limit performance of a normal variable-shaped electron beam exposure apparatus. As described above, a fine pattern having a pattern size smaller than the minimum pattern size that can be formed within a range of a predetermined statistical deviation (variation) is formed by using a predetermined variable-shaped electron beam exposure apparatus. In such a case, the following problem occurs. Since the electron beam is shaped beyond the limit performance of the electron beam exposure apparatus, the electron beam is very susceptible to the instability and disturbance of the apparatus. Therefore, it is very difficult to always stably obtain an electron beam formed into a minute size in accordance with a desired pattern size, for example, a fine pattern size such as 0.1 μm. Therefore, due to the inherent problem (stability, accuracy) of the electron beam exposure apparatus, even if an electron beam having a size smaller than a predetermined limit value is irradiated, a pattern having a pattern size equal to or smaller than the limit value is formed. There has been a problem that it cannot be formed within a predetermined statistical deviation range. That is, there is a problem that a pattern having a size smaller than a certain limit value cannot be formed with good reproducibility even if an electron beam having a size smaller than the certain limit value is used.

Therefore, the present invention has been made in order to solve the above problems, using a predetermined electron beam exposure apparatus, when the minimum value of a pattern that can be formed with good reproducibility is Wmin, Wmin or less It is an object of the present invention to provide an electron beam exposure method capable of forming a pattern having a size within a predetermined statistical deviation range.

[Means for Solving the Problems] An electron beam exposure method according to the present invention uses a predetermined variable shaping type electron beam exposure apparatus to obtain a minimum first shape that can be formed within a predetermined statistical deviation range. An exposure method performed when forming a fine pattern having a second pattern dimension smaller than the pattern dimension, comprising the following steps.

(A) forming an electron beam into a shape having a first pattern dimension;

(B) The pattern is formed at a second irradiation amount that is smaller than the first irradiation amount according to the second pattern size based on the first irradiation amount when forming a pattern having the first pattern size. Irradiating the substrate to be irradiated with an electron beam.

[Operation] In the present invention, the electron beam is formed into a shape having the first pattern dimension as a limit performance of the predetermined variable-shaped electron beam exposure apparatus. Therefore, the formed electron beam is hardly affected by instability or disturbance of the apparatus.
The electron beam formed with stability in this manner has a second irradiation amount smaller than the first irradiation amount corresponding to the first pattern size.
The substrate is irradiated with the irradiation amount. Thereby, a fine pattern having a second pattern dimension smaller than the first pattern dimension can be formed within a predetermined statistical deviation range.

FIG. 1 is a schematic diagram showing a distribution of energy stored in a resist when an electron beam is irradiated on the resist. At this time, the size of the electron beam to be irradiated is set to a size ranging from the position indicated by the one-dot chain line to ± σ (standard deviation) in the distribution of the stored energy. The dissolution rate of the resist depends on the stored energy. For example, in the case of a negative resist, the greater the stored energy, the more difficult it is to dissolve the resist during development. Therefore, as the amount of irradiation of the resist with the electron beam increases, the size of the pattern formed after development increases. In FIG. 1, Eth is, for example, in the case of a negative resist, a threshold energy for making the resist hardly soluble, and it is assumed that the irradiation amount A is larger than the irradiation amount B. At this time, as shown in the drawing, when the exposure processing is performed at the irradiation amount A, a pattern having a pattern size W _A is formed, and when the exposure processing is performed at the irradiation amount B, a pattern having a pattern size W _B smaller than W _A is formed. A pattern is formed. The present invention
By utilizing this, a pattern having a pattern size equal to or smaller than a limit pattern size of a predetermined variable-shaped electron beam exposure apparatus is formed.

The relationship between the irradiation amount of the electron beam and the size of the pattern to be formed can be obtained by a simulation using the Monte Carlo method. The Monte Carlo method is a numerical calculation technique using random numbers, and is applied to an area where mathematical analysis is difficult, such as multidimensional numerical integration and physical phenomena of many systems having complicated interactions. Now, using a variable-shaped electron beam exposure apparatus, a pattern dimension capable of keeping a range of ± 10% of the pattern dimension within a range of ± 3σ (three times the standard deviation value) is set to 0.3 μm. in this case,
The pattern data used in the variable-shaped electron beam writing system has a pattern width of 0.3 μm. That is,
The electron beam is shaped so that one side is 0.3 μm. FIG. 2 shows the relationship between the simulated pattern size and the dose (irradiation amount) under such conditions. Referring to FIG. 2, the dose amount reduced from the dose amount corresponding to the reference pattern size of 0.3 μm corresponds to the pattern size of 0.2 μm and 0.1 μm as indicated by arrows. Are plotted. In the graph of FIG. 2, pattern profiles (pattern shapes) corresponding to each of 0.3 μm, 0.2 μm, and 0.1 μm are schematically depicted.

By exposing the electron beam using the simulation data shown in FIG. 2, a fine pattern of 0.3 μm or less is formed. 3A, 3B and 3C are partial cross-sectional views showing a method of forming a fine pattern according to the present invention in the order of steps.

Referring to FIG. 3A, three silicon substrates (wafers) 1
A layered resist is formed. The resist having the three-layer structure is a resist 4 having a thickness of 0.45 μm formed on the uppermost layer.
And an SOG (spin-on-glass) 3 having a thickness of 0.16 μm formed as an intermediate layer, and a novolak polymer 2 having a thickness of 1.4 μm formed as a lowermost resist.
As the resist formed on the uppermost layer, SAL601-ER7 (trade name, manufactured by Shipley) is used. This resist is a chemically amplified high-sensitivity resist. This resist is a negative resist composed of three components. The three components are a novolak resin, an activated crosslinker, and a radiation-sensitive acid generator. The energy of the electron beam irradiated to the resist is used only for generating an acid as a catalyst. The cross-linking reaction of the resist is performed by post-exposure baking (PEB) after electron beam irradiation. By this mechanism, this type of resist exhibits high sensitivity and high solubility.

Referring to FIG. 3B, resist 4 is irradiated with electron beam 100 shaped so as to have a beam width of Web = 0.3 μm. The irradiation amount at this time is, as shown in FIG.
The amount depends on the pattern size of each of 1 μm and 0.2 μm.

Thereafter, a post-exposure bake treatment is performed at a temperature of 105 ° C. for 2 minutes. Referring to FIG.
The reaction is performed using an aqueous solution of AH (trimethyl ammonium hydroxide). Thereby, a pattern 4a having a pattern size Wp according to the irradiation amount is obtained. In FIG. 2, when an electron beam is irradiated with an irradiation amount corresponding to a pattern size of 0.1 μm, a pattern 4a having an average value of Wp = 0.12 μm is obtained. Also, in FIG.
When the electron beam is irradiated at an irradiation amount corresponding to the pattern size of 2 μm, a pattern 4a having an average value of Wp = 0.21 μm is obtained. In this case, the current density of the irradiated electron beam is 0.6 A / cm ² . Further, when an electron beam is irradiated with an irradiation amount corresponding to a pattern size of 0.2 μm, the average value of the resist pattern sizes actually formed on 16 wafers is 0.216 μm, and the standard deviation (σ ) Is 0.017 μm. From these results, it is understood that a pattern showing excellent reproducibility can be obtained only by reducing the irradiation dose by using the electron beam shot size of 0.3 μm as the limit performance of the variable-shaped electron beam exposure apparatus. You. In other words, beyond the limit performance of a given variable-shaped electron beam exposure apparatus, a finer pattern is formed within a certain statistical deviation within an electron beam beam.
It can be formed without changing the size of the shot.

FIG. 4 is a flowchart showing a pattern data processing flow performed by the processor shown in FIG. 5 in the above embodiment. W indicates the size (width or height) of a desired pattern to be formed;
Indicates the minimum size of a pattern that can be formed with good reproducibility using a predetermined electron beam exposure apparatus. Referring to FIG. 4, first, pattern data is read, and it is determined whether the pattern size W is smaller or larger than Wmin. W is
If it is smaller than Wmin, the pattern size is changed to Wmin. This means that the data of the pattern size used for beam control of the electron beam exposure apparatus is Wmin,
This means that the forming size of the electron beam is set based on Wmin. Next, as shown in FIG. 2, the simulator refers to a table showing the relationship between the irradiation amount of the electron beam and the size of the pattern to be formed, and determines the optimum irradiation so that the pattern size becomes W. The amount is set. Thereafter, the data set as described above is written to a file and used as pattern data.

In the above embodiment, only the uppermost resist is patterned as shown in FIG. 3C.
The intermediate layer and the lowermost layer are selectively removed by a normal etching process, so that a pattern finally used as a mask can be formed. Further, in the above-described embodiment, the case where a pattern is formed on the resist applied on the wafer has been described. However, the present invention can also be applied to a case where an exposure master mask such as an X-ray mask is formed. In such a case, a metal film or the like is used as the substrate.

[Effects of the Invention] As described above, according to the present invention, a fine pattern having a pattern size equal to or smaller than the minimum pattern size, which is the limit performance of a predetermined variable-shaped electron beam exposure apparatus, is unique to the electron beam exposure apparatus. Can be formed with good reproducibility without being affected by the problems (stability, accuracy).

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a distribution of energy stored in a resist when an electron beam having a predetermined size is irradiated on the resist. FIG. 2 is a graph showing a relationship between a pattern size simulated based on a pattern size of 0.3 μm and an electron beam irradiation amount applied to the embodiment of the present invention. 3A, 3B, and 3C are partial cross-sectional views illustrating a method of forming a fine pattern according to the present invention in the order of steps. FIG. 4 is a flowchart showing a pattern data processing method according to the present invention. FIG. 5 is a block diagram showing the configuration of a conventionally used variable-shaped electron beam writing system. FIG. 6 is a schematic diagram showing a configuration of a variable-shaped electron beam exposure apparatus used in the drawing system of FIG. In the figure, 1 is a silicon substrate, 4 is a resist, 4a is a pattern, 10 is a substrate, and 100 is an electron beam.

Continuation of the front page (56) References JP-A-54-89579 (JP, A) Vac. Sci. Techno l. B6 (6), NoV / Dec (1988) PP. 1828-1831 J.P. Vac. Sci. Techno l. B7 (6), NoV / Dec (1989) PP. 2044-2047 IEICE Technical Report, Vol. 89, No. 173 (1989-8-18) P.P. 1-6 (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/027 G03F 7/20 504 G03F 7/20 521

Claims (1)

(57) [Claims] 1. A fine pattern having a second pattern size smaller than a minimum first pattern size that can be formed within a predetermined statistical deviation range using a predetermined variable-shaped electron beam exposure apparatus. An electron beam exposure method for forming an electron beam into a shape having the first pattern dimension, and a first irradiation amount when forming a pattern having the first pattern dimension. Irradiating the electron beam onto a substrate on which the pattern is to be formed at a second dose that is smaller than the first dose according to the size of the second pattern.