JP4481477B2 - Resist pattern formation method and gate electrode formation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a resist pattern forming method good results are obtained by applying to create a gate electrode, relates to a gate electrode forming how using the resist pattern forming method.
[0002]
[Prior art]
At present, the information communication field is rapidly expanding, and therefore, a huge amount of information must be communicated. For this purpose, a communication system capable of high-speed and high-speed operation is required.
[0003]
Field-effect transistors are often used in high-frequency devices in the communication systems as described above, but in order to improve the high-frequency characteristics, it is necessary to shorten the gate length and the gate resistance. The means for making the cross-sectional shape of the gate electrode T-shaped is employed.
[0004]
As a means for forming a T-type gate electrode, a two-layer resist process or a three-layer resist process is known (for example, “Wakita et al., J. Vac. Sci. Technol. B13, 2725 (1995)”). The method of performing the lift-off process by combining resists having different patterning characteristics has become the mainstream.
[0005]
By the way, in the provided T-type gate electrode for the purpose of shortening the gate length and reducing the gate resistance, parasitic capacitance is generated between the umbrella portion constituting the T-type and the operation layer. There is a problem that the parasitic capacitance is greatly increased by miniaturization and enlargement of the umbrella portion.
[0006]
4A and 4B are side sectional views showing a principal part of a semiconductor substrate and a resist layer for explaining the prior art. FIG. 4A is a diagram for explaining a two-layer resist process, and FIG. It is a figure explaining a process.
[0007]
In the figure, 1 is a substrate, 2 is a first resist layer, 2G is an opening of a substantial gate electrode pattern, 3 is a second resist layer, 3G is an opening of an umbrella pattern, and 4 is a third layer. The eye resist layers and 4G respectively indicate openings for opening the opening of the umbrella pattern. In the present specification, a portion corresponding to a T-shaped vertical bar in a T-type gate electrode is referred to as a substantial gate electrode.
[0008]
In the configuration shown in the figure, an electron beam resist is used as the material of the first layer resist layer 2, and the material of the second layer resist layer 3 is an electron beam resist, photo resist, novolak, polydimethylglutar. An imide (PMGI), an alkali-soluble material, or the like is used, and an electron beam resist, a photo resist, or the like is used as the material of the third layer resist layer 4.
[0009]
When the T-type gate electrode is formed using the illustrated resist pattern, a parasitic capacitance is generated between the umbrella portion formed using the opening 3G of the umbrella portion pattern and the substrate 1.
[0010]
As a countermeasure, a structure in which the width gradually increases from the substantial gate electrode forming a strip on the contact surface with the substrate 1 toward the umbrella portion has been considered. The side walls defining the opening 2G at 2 must be forward tapered.
[0011]
However, when the opening of the substantial gate electrode pattern is formed in the resist layer, the opening side wall is almost vertical as shown in FIG. 4, or the opening 3G of the umbrella pattern shown in FIG. It is known that it becomes difficult to form a forward taper due to the influence of forward scattering and back scattering especially in electron beam lithography.
[0012]
[Problems to be solved by the invention]
In the present invention, a resist pattern which gradually widens from a substantially gate electrode pattern forming a strip toward an umbrella pattern can be easily formed by a very simple means. An attempt is made to contribute to the realization of a field effect semiconductor device capable of reducing the parasitic capacitance generated between the umbrella portion and the operation layer and capable of high-speed high-speed operation.
[0013]
[Means for Solving the Problems]
In the present invention, when creating a resist pattern for forming a T-type gate electrode, a substantial opening for the gate electrode pattern is formed in the first resist layer, and then the entire surface is irradiated with radiation. Thus, the resist layer side wall defining the opening is basically tapered, and the principle will be described below with reference to FIG.
[0014]
The first resist layer 2 is preferably an electron beam resist capable of reducing the gate length. Specifically, a ZEP series (general formula (1) made by Nippon Zeon Co., Ltd.) can be used. And PMMA (polymethylmethacrylate) are used.
[0015]
The second resist layer 3 which is a lift-off resist layer formed on the first resist layer 2 includes novolak, PMGI, a negative resist capable of forming a reverse taper shape, an alkali-soluble material, and the like. Used.
[0016]
Now, when forming the opening 2G for forming a substantial gate electrode in the first resist layer 2, the first resist layer which defines the opening 2G by irradiating the entire surface with radiation. It has been found that the side walls of 2 are forward tapered.
[0017]
This method utilizes the fact that the resist absorbs radiation, and the surface near the edge of the opening 2G is rounded by exposing only the vicinity of the surface of the first resist layer 2 to light. Forward taper.
[0018]
The entire irradiation of the radiation may be performed before or after performing, for example, electron beam exposure for forming the opening 2G, or after the application of the first resist layer 2 or the first resist layer 2. It is effective even after any of a plurality of resist layers are stacked and patterned.
[0019]
The radiation used for the entire surface irradiation is preferably visible light, ultraviolet light, vacuum ultraviolet light, and the like. When the wavelength becomes longer than visible light, the energy of the radiation cannot cause the resist to be satisfactorily exposed, and it is shorter than vacuum ultraviolet light. When the wavelength is reached, the resist causes a side reaction and pattern formation becomes impossible.
[0020]
As a degree of radiation absorption in the resist, an absorption coefficient of about 0.01 to 6 is desirable with respect to a thickness of 0.1 [mm] of the resist layer. In the resist having the structure of the general formula (1), absorption is performed. If the coefficient is lower than 0.01, the light is exposed to the deepest part, and if it is higher than 6, only the extremely shallow part of the surface is exposed, and in any case, shape control becomes difficult.
[0021]
The exposure light source for forming the opening 2G for the substantial gate electrode in the first resist layer 2 is capable of ultra-fine processing of about 0.1 [μm] and absorbs ultraviolet rays and vacuum ultraviolet rays. It is effective to use an electron beam that is not involved in the process.
[0022]
It is desirable that the resist used for the first layer resist layer 2 contains an aromatic ring because the resist has a strong absorption in the ultraviolet region when the aromatic ring is present and depends on the use of this absorption. The shape control of the pattern, that is, the forward tapered shape in which the edge of the opening 2G is rounded becomes easy.
[0023]
In particular, a resist including a base resin having a structure represented by the general formula (1) is widely used in electron beam lithography, and such a resist can enjoy the effects of the present invention to the maximum. it can. Even in the case of other electron beam resists such as PMMA, a practically sufficient effect can be obtained.
[0024]
The wavelength of the radiation applied to the first-layer resist layer 2 is preferably 150 nm to 300 nm, and if the wavelength is less than 150 nm, the resist layer is reduced in film thickness (ozone ashing) during irradiation. When the wavelength exceeds 300 [nm], the energy is too low and the electron beam resist does not react.
[0025]
Accordingly, excimer light having a wavelength of 172 [nm] that can be appropriately absorbed by the resist in the above-mentioned wavelength range is preferable as the radiation irradiated on the entire surface of the first resist layer 2.
[0026]
From where it said, resist pattern forming method according to the present invention, it is at the gate electrode formation how,
(1)
Forming a first resist layer (for example, an electron beam resist layer 12 using ZEP520A) that absorbs radiation having a wavelength of 100 [nm] to 500 [nm] on a substrate (eg, Si wafer 11); Development is performed after the formation of the first resist layer in each of the steps of laminating and forming at least one resist layer on the resist layer, and exposing and developing the resist layer to form a pattern. Or a step of irradiating the entire surface of the first resist layer with the radiation at any stage before performing, or
[0027]
(2)
In (1), the material constituting the first resist layer comprises an aromatic ring, or
(3)
[0028]
In the above (1), the material constituting the first resist layer contains a substance represented by the general formula (1), or
[0029]
(4)
The gate electrode is formed using the resist pattern formed by the method according to any one of (1) to (3), or
[0031]
When the T-type gate electrode is formed using the resist pattern obtained by adopting the above means, the substantial gate electrode in the T-type gate electrode is an umbrella constituting the T-type from the surface in contact with the base. Since the shape gradually widens toward the portion, the parasitic capacitance generated between the umbrella portion and the operation layer (substrate) is reduced, and therefore the high frequency characteristics in the field effect semiconductor device are improved.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
For example, ZEP520A (trade name, manufactured by Nippon Zeon Co., Ltd.), which is an electron beam resist having the structure of the general formula (1) with respect to the wavelength of the radiation and the exposure of the resist, contains an aromatic ring, so Since it has a characteristic to absorb, the shape control in the resist pattern for forming the T-type gate electrode can be appropriately performed by using radiation in an appropriate wavelength range including the wavelength.
[0033]
Therefore, ZEP520A was applied to a Si wafer, and radiation from an excimer lamp having wavelengths of 172 [nm], 222 [nm], and 308 [nm] was irradiated to investigate the reactivity of the resist.
[0034]
With irradiation at 172 [nm] and 222 [nm], the resist layer thickness after development decreased as the irradiation time increased, but with irradiation at 308 [nm], there was almost no absorption near this wavelength. Nevertheless, there was no reduction in resist layer thickness.
[0035]
The reason for this is that when the radiation light source has a long wavelength, it is derived from the fact that it cannot supply photoreaction, that is, mainly energy sufficient to cause polymer breakage. By irradiation, selective exposure and layer thickness control of ZEP520A, that is, the electron beam resist surface layer having the structure of the general formula (1) are possible.
[0036]
FIG. 1 and FIG. 2 are explanatory views of the main surface slopes of the pattern formed on the electron beam resist layer, all copied from a micrograph.
[0037]
1A, 1B, 2A, and 2B, the basic process for creating the resist pattern shown in FIG. 1A is to apply an electron beam resist to the Si wafer 11 with a layer thickness of 3000 [Å]. The electron beam resist layer 12 is formed so as to be applied, and except for the case of (A), the entire surface is irradiated with radiation having a wavelength of 172 [nm], and then exposed using an electron beam of 30 [kV]. And performing development and rinsing to form a stripe 12A having a width of 0.2 [μm]. FIG. 1A is a comparative example.
[0038]
In the case of FIG. 1A, resist: ZEP520A
172 [nm] excimer light irradiation: 0 [seconds]
Exposure amount for forming the stripe 12A: 133 [μC / cm ² ]
Remaining layer thickness of resist layer 12: 0.287 [μm]
[0039]
In the case of FIG. 1B, resist: ZEP520A
172 [nm] excimer light irradiation: 1 [second]
Exposure amount for forming the stripe 12A: 110 [μC / cm ² ]
Remaining layer thickness of resist layer 12: 0.210 [μm]
[0040]
In the case of FIG. 2A, resist: ZEP520A
172 [nm] excimer light irradiation: 5 [seconds]
Exposure amount for forming the stripe 12A: 81 [μC / cm ² ]
Remaining layer thickness of resist layer 12: 0.134 [μm]
[0041]
In the case of FIG. 2B, resist: ZEP520A
172 [nm] excimer light irradiation: 25 [seconds]
Exposure amount for forming the stripe 12A: 60 [μC / cm ² ]
Remaining layer thickness of resist layer 12: 0.056 [μm]
[0042]
As is apparent from each figure, the edge of the stripe 12A in the resist layer 12 is rounded and the side wall is changed from substantially vertical to forward taper by irradiation with 172 [nm] excimer light.
[0043]
FIG. 3 is a diagram for explaining the relationship between excimer light irradiation time and forward taper (pattern formation angle). The horizontal axis represents excimer light irradiation time [seconds], and the vertical axis represents pattern angle. Each [°] is taken.
[0044]
The data in FIG. 3 is obtained by irradiating PMMA with excimer light having a wavelength of 222 [nm], drawing a stripe pattern with an electron beam of 50 [kV], and developing the excimer light. It can be seen that the pattern is inclined and becomes forward-tapered with irradiation.
[0045]
A process of manufacturing a field effect semiconductor device having a T-type gate electrode formed by applying the pattern forming method described above will be described.
[0046]
(1) By applying a metalorganic chemical vapor deposition (MOCVD) method, a 300 [nm] -thick resistance resistor GaAs layer on a semi-insulating GaAs substrate and a 20 [nm] -thickness An InGaAs channel layer, an impurity (Si) containing AlGaAs electron supply layer having a thickness of 25 [nm], and an impurity (Si) containing GaAs contact layer having a thickness of 50 [nm] are grown.
[0047]
(2) By applying the ion implantation method, oxygen ions are implanted into a part where the inter-element isolation region is to be formed to be inactivated, thereby forming the inter-element isolation region.
[0048]
(3) By applying a resist process in lithography technology, a resist layer having an opening corresponding to a portion where the source and drain ohmic electrodes of the active layer region inside the element isolation region are to be formed is formed. Form.
[0049]
(4) By applying the sputtering method, an AuGe layer having a thickness of 50 nm and an Au layer having a thickness of 300 nm are stacked on the entire surface including the inside of the opening.
[0050]
(5) By applying the lift-off method, the resist layer is removed together with the AuGe layer and Au layer thereon to form source and drain ohmic electrodes.
[0051]
(6) Impurity-containing GaAs contacts exposed between ohmic electrodes by applying a resist process in lithography technology and a wet etching method using an etchant as an H ₂ SO ₄ etching solution The layer is etched to form a gate recess, and an impurity-containing AlGaAs electron supply layer is exposed at the bottom.
[0052]
(7) A resist layer made of ZEP520A having a thickness of 0.2 [μm], a resist layer made of PMGI having a thickness of 0.5 [μm], and a resist layer made of ZEP520A having a thickness of 0.3 [μm] are sequentially applied. Thus, a three-layer resist layer is formed.
[0053]
(8) By applying the electron beam drawing method, 0.8 [μm] width electron beam drawing corresponding to the size of the opening formed in the resist layer made of ZEP520A which is the uppermost layer of the three-layer resist layer is performed. Then, ZEP-SD (trade name, manufactured by Nippon Zeon Co., Ltd., a mixed solution of methyl isobutyl ketone and methyl ethyl ketone) is used to develop the uppermost layer, and then NMD-W (trade name, manufactured by Tokyo Ohka Kogyo Co., Ltd., The resist layer made of PMGI as an intermediate layer is developed using a tetramethylammonium hydroxide) developer.
[0054]
(9) By applying the electron beam drawing method again, an electron beam drawing having a width of 0.1 [μm] corresponding to the size of the opening formed in the resist layer made of ZEP520A which is the lowermost layer of the three-layer resist layer is performed. Do.
[0055]
(10) Radiation from an excimer lamp having a wavelength of 172 [nm] is irradiated on the entire surface for 1.0 [second], and then ZMD-B (trade name, manufactured by Nippon Zeon Co., Ltd., a mixture of methyl isobutyl ketone and isopropyl alcohol) Solution) A resist layer made of ZEP520A in the lowermost layer is developed using a developer.
[0056]
Through the above resist pattern forming process, a structure for forming a target T-type gate electrode is obtained.
[0057]
(11) An Al layer having a thickness of 300 [nm] is formed on the entire surface by applying a vacuum deposition method.
[0058]
(12) By applying the lift-off method, the three-layer resist layer is removed together with the Al layer thereon to realize a T-type gate electrode.
[0059]
In the field effect type semiconductor device manufactured through the above steps, the umbrella portion of the T type gate electrode and the operation below the field effect type semiconductor device are compared with the field effect type semiconductor device manufactured without irradiating with an excimer lamp. It was confirmed that the parasitic capacitance generated between the two parts was reduced by 30%.
[0060]
【The invention's effect】
Resist pattern forming method according to the present invention, the gate electrode formation how to form the first layer of the resist layer which absorbs radiation of wavelength 100 on the substrate [nm] to 500 [nm], the first layer At least one resist layer is formed on the first resist layer, and the resist layer is exposed and developed to form a pattern, after the formation of the first resist layer in each step before the development. It is fundamental to irradiate the entire surface of the first resist layer at any stage in between.
[0061]
When the T-type gate electrode is formed using the resist pattern obtained by adopting the above-described configuration, the substantial gate electrode in the T-type gate electrode is an umbrella that forms the T-type from the surface in contact with the base. Since the shape gradually widens toward the portion, the parasitic capacitance generated between the umbrella portion and the operation layer (substrate) is reduced, and therefore the high frequency characteristics in the field effect semiconductor device are improved.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory view of a slope of an essential part of a pattern formed on an electron beam resist layer.
FIG. 2 is an explanatory view showing a slope of a main part of a pattern formed on an electron beam resist layer.
FIG. 3 is a diagram for explaining the relationship between excimer light irradiation time and forward taper (pattern formation angle);
FIG. 4 is a cutaway side view of a main part showing a semiconductor substrate and a resist layer for explaining a conventional technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 2 First layer resist layer 2G Substrate gate electrode pattern opening 3 Second layer resist layer 3G Umbrella pattern opening 4 Third layer resist layer 4G Umbrella pattern opening forming opening 11 Si wafer 12 Electron beam resist layer 12A stripe

Claims (4)

A step of forming a first resist layer that absorbs radiation having a wavelength of 100 [nm] to 500 [nm] on the substrate, a step of laminating and forming at least one resist layer on the first resist layer, The first resist layer at any stage between the formation of the first resist layer in each step of the resist layer exposure and development to form a pattern before the development. And a step of irradiating the entire surface with the radiation. 2. The resist pattern forming method according to claim 1, wherein the material constituting the first resist layer includes an aromatic ring. 2. The method of forming a resist pattern according to claim 1, wherein the material constituting the first resist layer comprises a substance represented by the following general formula (1).

4. A method for forming a gate electrode, comprising: forming a gate electrode using the resist pattern formed by the method according to any one of claims 1 to 3.

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