JPS6031909B2 - Etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of forming very fine features by ion etching.

In particular, the present invention relates to a method of ion irradiation etching of a substrate faithfully to a shape formed on the substrate by electron beam lithography or X-ray lithography. [Background of the Invention] Recently, ion irradiation etching has been used for microfabrication of magnetic materials and metals on semiconductors.

For example, when a part of the metal 2 on the semiconductor 1 is processed by ion irradiation etching as shown in FIG. 1, the photoresist 3 is processed by a photoetching process. The exposed metal 2 is exposed using the photoresist 3 as a mask with an ion beam (normally, the ions are neutralized because they are electrically neutralized after being accelerated)
Etching by irradiating. However, if the substrate has unevenness as shown in FIG. 1, the photoresist 3 deposited on the protrusions becomes thin. Since the ion beam also etches the photoresist, it has the drawback that the metal in the convex or stepped portions is partially etched, resulting in wire breakage. In addition, as a method to overcome this drawback, M. Cangel is “comparison”
of the properties of diffe
rentma reals usid as mask
s phantom rion-beam e hing”.(J,
VaC. Sci Technol. , Vol. 12,M
．． 6, 1975, p. 1340-1343) describes a method in which a resist pattern is formed, metal is formed on the entire surface, the resist and the metal on it are then removed, and the remaining metal pattern is used as a mask. The process of removing the cutter and the metal above it is a technically unstable process as it causes damage to the workpiece and the metal pattern.

In addition, electron beam resists or X-ray resists are etched at a faster rate by ion beams than regular photoresists, so they do not serve as a mask material, and this is due to the fact that they are not suitable for ion irradiation etching even in the case of flat substrates. Met.

That is, there has been a drawback in that electron beam or X-ray lithography techniques suitable for forming fine shapes cannot be fully utilized in ion irradiation etching techniques suitable for fine processing.
OBJECTS OF THE INVENTION It is an object of the present invention to provide a method that eliminates the drawbacks of the above-mentioned conventional techniques and allows microfabrication by ion irradiation etching.

SUMMARY OF THE INVENTION The method of the present invention for achieving the above objects is illustrated in FIG.

First, a molybdenum film (or tungsten film) 4 is deposited on the surface of the material to be etched on the a-substrate 1, and a photoresist (or electron beam resist, X-ray resist) 3 is processed.
Next, the molybdenum film (or tungsten film) 4 is etched in an atmosphere containing fluorine, such as by plasma etching using carbon tetrafluoride gas. Next, the material 2 to be etched is etched using, for example, argon ions, using the molybdenum film 4 as a mask. Finally, the processed material 2 is obtained by removing the molybdenum film d. The method of the present invention was developed as a result of extensive experiments by the inventor.

That is, as shown in FIG. 3, when a metal other than molybdenum and tungsten (for example, titanium, tantalum) is used as a mask material for processing the material 2 to be etched on the substrate 1, and the metal 5 is plasma-etched using the resist as a mask, the third The structure has a gentle cross section as shown in the figure. When the material 2 to be etched is etched by ion irradiation using such a metal 5 as a mask, the etched cross section also becomes a smooth cross section. Therefore, it is not preferable to obtain a fine shape. On the other hand, as shown in Figure 4, if molybdenum or tungsten 4 is used as the etching mask metal and the metal 4 is etched using the resist 3 as a mask, a steep cross-sectional structure is essential to obtain a fine shape by ion irradiation etching. It is something. EXAMPLES OF THE INVENTION Hereinafter, the present invention will be explained in detail with reference to examples.

Embodiment 1 FIG. 5 shows an example in which the present invention is applied to the manufacture of photomasks.

As shown in FIG.
．． Chromium 7 with a thickness of 1 micron and molybdenum 8 with a thickness of 0.2 microns were deposited by the vacuum hologram deposition method.

Next, a b-electron beam resist 9 was applied, drawn, and developed to obtain a shape with a minimum dimension of 0.5 microns. Only molybdenum was etched using carbon tetrafluoride gas plasma using the C resist 9 as a mask. Next, the chromium 7 was etched by ion irradiation etching using argon ions using molybdenum and the resist as a mask. At this time, the resist was completely etched, but the molybdenum 8 was approximately 0.1 micron thick. Finally, molybdenum was removed using a mixed solution of sodium hydroxide solution and hydrogen peroxide solution to obtain a fine shape of chromium 7. The minimum dimension of the finally obtained chromium shape was about 0.5 microns, and it was possible to very faithfully copy the dimension drawn by the electron beam. Embodiment 2 FIG. 6 shows an example in which the present invention is applied to a Schottky barrier gate of a field effect transistor using magnetized gallium.

As shown in FIG. 6a, an n-type epitaxial layer 11 (electron concentration 2.5×1 Isobada-3 thickness 0.15 μm) was grown on a semi-insulating gallium phosphide substrate 10.

Next, after etching the n-type layer in unnecessary portions to form a mesa shape, a source 12 and a drain 13, which are ohmic contacts, were formed using c gold and germanium alloy. Next, d molybdenum (thickness 0.2 micron) 14, gold (
15, tungsten (thickness 0.2 microns)
Micron) 16 was vacuum deposited, and a 0.5 micron shape 17 was formed using a negative electron beam resist. Using the e-electron beam resist 17 as a mask, the tungsten 16 was etched with carbon tetrafluoride gas plasma. The gold 15 was etched by ion irradiation etching using f argon ions using the electron beam resist and tungsten as a mask. Finally, the first layer metal, molybdenum 14, and the mask material, tungsten, were etched using carbon tetrafluoride gas plasma. At this time, 0.5 micron gold 1
From the shape of No. 5, an effective gate length of 0.3 microns was obtained. Embodiment 3 FIG. 7 shows an example in which the present invention is applied to the manufacture of a mask for X-ray phosphorography.

As shown in FIG. 7a, a silicon substrate 1 with a thickness of 500 r
8, boron nitride 19 was added.

Next, gold 20 (thickness 1r) and molybdenum 21 (thickness 0.2 French m), which are X-ray absorbers, are vacuum-deposited. Next, an electron beam resist pattern 22 is obtained by electron beam lithography. Next, as shown in FIG. 2B, the molybdenum 21 is processed using carbon tetracarbon gas plasma using the electron beam resist 22 as a mask. Next, the structure shown in FIG. 3c is obtained by etching the gold 20 with argon ions. Finally, as shown in Figure d, the center of the silicon substrate 18 is poured from the back side with a mixture of hydrofluoric acid, nitric acid, and acetic acid (
It is removed by etching using a volume ratio of 1:4:1. In this way, the X-ray mask was completed.
Although the molybdenum film 21 can be removed by the same method as in Example 1, it can also be left as part of the X-ray absorber. In this example, a combination of molybdenum and gold was used as the material to be processed, but a combination of tungsten and aluminum (or silicon or chromium) as the material to be processed can be processed by using ion irradiation etching with chlorine gas. It is possible.

As explained above, according to the present invention, ion irradiation etching can be performed faithfully to the shape realized in the photoresist (or electron beam resist, or X-ray resist).
In this example, application to a photomask, a field effect transistor, and an X-ray mask is shown, but the present invention can also be widely applied to electrodes for magnetic valve elements, surface acoustic wave elements, etc.

〔Effect of the invention〕

The present invention enables microfabrication by ion etching, thereby making it possible to increase the density, miniaturize, and lower the cost of various electronic devices, and the effects thereof are extremely large.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the conventional etching method, FIG. 2 is a cross-sectional view showing the etching method of the present invention, FIG. 3 is a cross-sectional view showing the state when metals other than molybdenum and tungsten are used, and FIG. The figure is a cross-sectional view showing the state of etching when molybdenum or tungsten of the present invention is used, FIG. 5 is a cross-sectional view showing an example in which the present invention is applied to the production of a photomask, and FIG. FIG. 7 is a cross-sectional view showing an example in which the present invention is applied to a type field effect transistor. In the figure, 1 is a substrate, 2 is a material to be etched, 3 is an etching resist material, 4 is molybdenum or tungsten, 5 is a metal other than molybdenum and tungsten, and 6 is a metal other than molybdenum or tungsten.
7 is a glass substrate for a photomask, 7 is chromium, 8 is molybdenum, 9 is an electron beam resist, 10 is a semi-insulating gallium oxide substrate, 11 is an n-type epitaxial layer, 12 is a source electrode, 13 is a drain electrode, 14 is molybdenum , 15 is gold,
16 is tungsten, 17 is negative electron beam resist, 1
8 is a silicon substrate, 19 is a boron nitride film, 20 is gold, 2
1 is molybdenum, and 22 is an electron beam resist. Figure 1 Figure 3 Figure 4 Figure 2 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1. In the process of processing materials by etching,
A step of depositing a molybdenum film or tungsten film on the surface of the material, a step of etching the molybdenum film or tungsten film in an atmosphere containing fluorine gas, and etching the material by ion irradiation using the molybdenum film or tungsten film as a mask. An etching processing method characterized by: