JPH04360526A - Fine pattern forming method - Google Patents

Abstract

PURPOSE:To form more precisely a fine pattern at the time of pattern transferring and direct writing by electron beam excitation dry etching. CONSTITUTION:In electron beam excitation dry etching 106 wherein a reaction gas adsorption layer formed on the substrate surface is irradiated with an electron beam, working is performed under a condition that gas etching is restrained by cooling an object 104 to be worked.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming fine patterns, and more particularly to a method for forming fine patterns by electron beam excitation dry etching.

0002

2. Description of the Related Art The problems of reactive ion etching, which is a typical conventional semiconductor processing technique, and the electron beam excitation dry etching technique used to overcome these problems will be described.

In the current microfabrication process of LSI manufacturing, as shown in FIG. 5, a resist pattern 503 on a workpiece 504 is etched by reactive ion etching (RIE) using plasma of a reactive gas (active species 502). By transferring, a fine structure on the order of half a micron is formed. However, this method exposes the semiconductor substrate to plasma or charged particles (ions) 501 generated within the plasma, causing damage 505 due to ion bombardment.

On the other hand, as shown in FIG. 4, in electron beam excitation dry etching, an electron beam 404 is irradiated onto a reactive gas adsorption layer 401 formed on the surface of a workpiece 403 to promote a chemical reaction. This is a processing method in which surface atoms 402 are removed as volatile reaction products 405 with a reactive gas. This processing method uses a chemical reaction on the surface of the workpiece due to irradiation with an electron beam, which has a much smaller mass than the ions used in conventional reactive ion etching, resulting in less damage. Processing can be achieved. Furthermore, by applying an electric field to impart directionality to the electron beam, it is possible to perform anisotropic etching similar to conventional ion etching.

[0005]

[Problems to be Solved by the Invention] As described above, electron beam excitation dry etching is an excellent processing method for forming microstructures with low damage, but the reaction between the reaction gas and the workpiece does not occur even at room temperature. For combinations of materials and gases where gas etching progresses easily and gas etching cannot be ignored, it becomes difficult to transfer fine patterns with high precision. In other words, Figure 1
As shown in (a), the workpiece 104 is subjected to gas etching 1 of the processed side wall in parallel with the electron beam excited dry etching and gas etching 105 that proceed in the vertical direction.
02 occurs, side etching 103 occurs, and the initial resist pattern 101 cannot be faithfully transferred. Furthermore, in the case of a material in which the gas etching rate is significantly dependent on surface orientation, it is difficult to obtain an arbitrary processed shape.

An object of the present invention is to form a finer pattern by electron beam excitation dry etching.
It is an object of the present invention to provide a fine pattern forming method that suppresses the effects of the gas etching described above and realizes etching only in the electron beam irradiation area.

Another object of the present invention is to realize even higher precision pattern transfer in a fine pattern forming method using electron beam excitation dry etching.

[0008]

[Means for Solving the Problems] In general, the rate of gas etching using a reactive gas increases as the temperature of the substrate increases, and a thermal activation process is performed in which a barrier in a chemical reaction is overcome by thermal energy. On the other hand, in electron beam excitation dry etching, the reaction excitation effect due to electron beam irradiation is different from this thermal effect, so by cooling the substrate during etching, processing can be performed while suppressing gas etching. As shown in FIG. 1B, only the electron beam excited dry etching 106 progresses in the vertical direction on the workpiece 104.

The present invention performs dry etching at a low temperature by adding a sample stage equipped with a substrate cooling mechanism to a conventional electron beam excitation dry etching apparatus, thereby realizing fine pattern transfer with higher precision.

0010

[Operation] When the adsorption layer formed on the surface of the substrate is irradiated with an electron beam, it is possible to realize an excited state.
As a result, the chemical reaction between the reactive gas molecules and the substrate material can be promoted. When using a gas that reacts with the constituent atoms of the substrate to produce volatile reaction products as the adsorption gas,
Etching can be performed by simultaneously irradiating an electron beam and supplying a reactive gas (electron beam excitation dry etching).

Mask pattern transfer by electron beam excitation dry etching can be performed as follows. The workpiece, on which a resist pattern has been formed by light exposure or electron beam exposure, is cleaned, placed in a vacuum chamber, and evacuated.
After obtaining a sufficiently high vacuum, the oxide film on the substrate surface is removed using an ion shower or the like to obtain a clean substrate surface. Thereafter, after cooling the substrate to a predetermined temperature, electron beam excitation dry etching is performed by simultaneously performing electron beam irradiation and supplying a reactive gas.

The effect of suppressing gas etching as described above is also effective in direct writing technology in which a focused electron beam promotes a surface excitation reaction in a minute area. This is because when the reaction gas 202 is supplied to the surface of the workpiece 206 through the gas nozzle 205 as shown in FIG.
Since gas etching 203 corresponding to the concentration distribution of the reaction gas occurs, the etching pattern when performing electron beam excitation dry etching 204 using the focused beam 201 is as shown in FIG. It becomes possible to suppress the effect of etching, and a desired etching pattern as shown in FIG. 2(b) can be obtained.

[0013]

EXAMPLE An example of etching GaAs using chlorine Cl2 as a reactive gas will be shown below.

In carrying out the present invention, the apparatus shown in FIG. 3 was used. The experimental apparatus consists of a vacuum chamber 309, a reaction excitation electron gun 302, a gas introduction system, and a substrate heating/cooling system. A turbo molecular pump and a rotary pump are used in the vacuum evacuation system 305, and a high vacuum on the order of 10-7 Torr can be obtained. The reaction excitation electron gun 302 is capable of stably irradiating the sample with an electron beam even when the reaction gas 312 is introduced by using a differential pumping system. The gas introduction system includes a gas storage chamber 311 and an introduction valve 310, and supplies gas to the vacuum chamber 309 through a variable leak valve. Further, the sample stage 307 on which the workpiece 304 is placed is equipped with a substrate heating and cooling mechanism. When heating the substrate, the temperature of the workpiece can be raised by an infrared heater 308 provided at the bottom of the vacuum chamber. Furthermore, since liquid nitrogen 306 can be introduced into this sample stage from outside the vacuum chamber, by using it in conjunction with an infrared heating mechanism, it is possible to set the substrate temperature over a wide range from around the liquid nitrogen temperature to several hundred degrees Celsius. It is. In addition, in Figure 3, 30
1 indicates an electron gun power supply, and 303 indicates a lens system.

SAL601-ER by electron beam exposure
After removing the oxide film on the surface of the GaAs wafer with the U7 resist pattern using hydrochloric acid, the wafer was placed in a vacuum chamber 309 and evacuated. After obtaining a sufficiently high vacuum, the substrate temperature was increased to 75°C to remove trace amounts of contamination and oxide film formed on the wafer surface during sample transportation.
A chlorine gas of 1.5 x 10-4 Torr was introduced into the vacuum chamber, and a few nanometers of the surface was removed by gas etching to obtain a clean surface of GaAs. Thereafter, the substrate was cooled to −50° C., and a fine pattern was transferred by electron beam excitation dry etching by simultaneously supplying chlorine gas and irradiating an electron beam. The chlorine gas pressure during etching was 1.5 x 10-4 Torr, and the acceleration voltage and current density of the electron beam were 10 kV and 1.4 μA/cm, respectively.
2. Regarding the sample formed as above,
As a result of comparing the fine pattern with a sample etched with the substrate temperature at room temperature, it was found that good pattern transfer was achieved with very little side etching due to gas etching.

[0016]

Effects of the Invention The present invention uses liquid nitrogen or the like to process the workpiece substrate in electron beam excitation dry etching, which promotes surface excitation reactions and performs etching with low damage by irradiating the reactive gas adsorption layer with an electron beam. By cooling the substrate, gas etching with the reactive gas is suppressed, and only etching based on the electron beam irradiation effect is performed. According to the method of the present invention, since the effect of gas etching can be ignored during pattern formation, it is possible to transfer a fine pattern according to a set value by electron beam excitation dry etching. In other words, it is possible to perform electron beam-excited dry etching under conditions that suppress the effects of side etching caused by gas etching, making it possible to form fine patterns with higher precision during resist pattern transfer and direct writing using a focused electron beam. .

The microstructure created as described above is based on a processing method that utilizes a chemical reaction caused by electron beam irradiation, and is characterized by low damage, and can be applied to next-generation semiconductor manufacturing processes and devices with new functions. can be expected.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the substrate cooling effect in electron beam excitation dry etching.

FIG. 2 is a diagram illustrating a direct writing technique method using electron beam excitation dry etching.

FIG. 3 is a diagram showing an experimental apparatus for carrying out the present invention.

FIG. 4 is a diagram illustrating an etching mechanism of electron beam excitation dry etching.

FIG. 5 is a diagram illustrating a reactive ion etching mechanism.

[Explanation of symbols]

101 Resist pattern 102 Gas etching 103 Processing side wall (side etching) 104 Workpiece 105 Electron beam excitation dry etching + gas etching 106 Electron beam excitation dry etching 201
Focused electron beam 202 Reactive gas 203 Gas etching 204 Electron beam excitation dry etching 205
Gas nozzle 206 Workpiece 301 Electron gun power supply 302 Electron gun 303 Lens system 304 Workpiece 305 Exhaust system 306 Liquid nitrogen 307 Sample stage 308 Infrared heater 309 Vacuum chamber 310 Gas introduction valve 311 Gas storage chamber 312 Reaction gas 401 Reaction gas adsorption Layer 402 Surface atoms 403 Workpiece 404 Electron beam 405 Volatile reaction products 501 Ions 502 Active species 503 Resist pattern 504 Workpiece 505 Processing damage

Claims (1)

[Claims] Claim 1: In electron beam-excited dry etching by irradiating an electron beam after adsorbing a reactive gas, the workpiece is cooled to suppress gas etching with the reactive gas, and anisotropy is achieved only in the electron beam irradiated region. A fine pattern forming method characterized by performing fine pattern transfer with low damage by chemical etching.