JPH02280323A - Plasma etching method - Google Patents

Abstract

PURPOSE:To easily abter an inclining angle of the sidewall of a recess or an opening generated by etching by regulating total flow rate in reaction gas when the recess or the opening is formed. CONSTITUTION:A silicon substrate 4 provided with a mask is placed on an electrode 3, vacuum evacuated, and reaction gas 10 mixed with O2 gas and SF6 gas is introduced from a gas inlet tube 8. Then, high frequency power is supplied by a high frequency power source 7 between electrodes 2 and 3 to generate plasma. In this case, total flow rate is altered while O2 gas mixture ratio of the gas 10 is maintained constant, thereby varying O2 gas amount. When etching reaction is affected by the radical amount of O2 in the reaction gas, and total flow rate is increased/decreased, the inclining angle of a recess or a sidewall is decreased/increased. Thus, the inclining angle of the sidewall can be easily altered.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a plasma etching method for forming inclined surfaces on the side walls of recesses or openings in a material to be etched.

[Conventional technology]

The semiconductor pressure sensor has a depth of 100 mm from one surface of the semiconductor substrate.
- A semiconductor diaphragm is formed by digging the above-mentioned recesses, and when the diaphragm is deformed due to a pressure difference applied to both sides, the resistance value of the gauge resistor formed on the diaphragm changes. For this purpose,
Conventionally, a wet etching method using stop etching, for example, has been used to form a recess which requires digging a recess to a depth of 100 mm or more from one surface of a semiconductor substrate. For this reason, plasma etching is being considered to form recesses with appropriate slopes on the side walls. The plasma etching method is
For example, as described in Japanese Patent Publication No. 63-45469, it is also used when forming a pattern having inclined sidewalls in a polycrystalline silicon layer laminated on a single-crystal silicon plate.

It is necessary to perform an anisotropic etch to form the sloped sidewalls. No. tvgJ shows a plasma etching apparatus used for anisotropic etching, in which an upper electrode 2 and a lower electrode 3 are disposed facing each other in a reaction tank 1, and a material to be etched is placed on the lower electrode 3. The upper electrode is drawn out of the reaction tank 1 via an insulator 5 and connected to a high frequency electric wire via a blocking capacitor 6.The reaction tank 1 is connected to a reaction gas introduction pipe 8 equipped with a flow rate regulator 4. While evacuating the reaction tank 1, which has an open exhaust pipe 9, through the exhaust pipe 9, a reaction gas 1o is introduced from the introduction pipe 8, and the picture electrode 2.3 is
During this period, high frequency power from the high frequency power source 7 is applied to turn the reaction gas 10 into plasma. In order to perform anisotropic etching, the composition of the reaction gas and the pressure inside the power tank are adjusted, or a gradient is created in the impurity concentration of the material to be etched. By anisotropically etching the portion of the material to be etched that is not coated with the mask material for preventing etching, an inclined surface is formed on the side wall of the recess or opening formed by etching.

[Problem to be solved by the invention]

When etching a material to be etched with a masking material to prevent etching on its surface so that the side walls of recesses or openings formed by etching become sloped surfaces, it is necessary to re-react when trying to change the inclination angle of the sloped surfaces. It is necessary to readjust the gas mixture ratio and pressure, and to set new etching conditions. The angle of inclination of the sidewall of the recess or opening that occurs in the workpiece/sitching material depends on the mechanical properties of the material to be etched after etching, the adhesion of 'aBtJ covering the surface of the material to be etched, or the semiconductor embedded in the recess. It would be desirable to have an arbitrary value depending on the electrical characteristics of the layer, etc. However, it has not been easy to change the inclination angle of the sidewall as described above.

SUMMARY OF THE INVENTION An object of the present invention is to provide a plasma etching method that solves the above problems and allows the angle of inclination of the side walls of the recesses or openings formed in the material to be etched to be easily changed.

[Means to solve the problem]

In order to achieve the above object, the present invention applies a voltage between opposing electrodes, generates plasma in a reduced pressure reaction gas containing oxygen present between the electrodes, and generates a plasma in the vicinity of one of the electrodes. When forming four parts or openings by etching the parts of the material to be etched that are not covered by the mask, the total flow rate of the reaction gas is kept constant while keeping the oxygen gas mixture ratio in the reaction gas constant. By smoothing the etching, the slope shape of the side wall of the recess or opening caused by etching is changed.

[Effect]

By changing the total flow rate while keeping the oxygen gas mixture ratio of the oxygen-containing reaction gas constant, the amount of oxygen gas changes. The etching reaction is influenced by the amount of oxygen radicals in the reaction gas, and if the total flow rate of the reaction gas is increased, the angle of inclination of the side walls of the recesses or openings that are formed due to an excess of oxygen radicals will become smaller. Become. Reducing the total flow rate reduces the amount of oxygen radicals and the sidewalls become erect and nearly vertical. If the total flow rate is further reduced to reduce the placement of oxygen radicals, the inclination angle will further increase, and the sidewalls of the recesses or openings will have a downwardly open shape. Even if the total flow rate is increased or decreased in this way, if the mixing ratio of the component gases of the reaction gas is the same, there is no need to change the plasma generation conditions each time, and the inclination angle can be easily controlled.

〔Example〕

Using the apparatus shown in FIG. 1, a silicon substrate 4 provided with a silicon oxide film mask is placed on the lower electrode 3, the interval between the upper electrode 2 and the lower electrode 3 is set to 50 mm, and a vacuum is drawn from the exhaust pipe 9. At the same time as exhausting the tank, a reaction gas 10 containing a mixture of 08 gas and SFh gas is introduced from the introduction pipe 8, and the pressure inside the tank is reduced to 0.
4 Torr, and 150 W of high frequency power was supplied between the upper and lower electrodes from the high frequency power source 7 to generate plasma. 0. Change the gas flow rate to IO5CCM, SP&
When the gas flow rate is 23.33CCM%, that is, the O□ gas mixing ratio is 30%, 0. Radical consumption efficiency is high, and a recess 11 with side walls standing perpendicular to the silicon substrate 4 is formed as shown in FIG. When the total flow rate was 203CCM and the total flow rate was 66.75CCM, there were too many zero-rich radicals, and the mixture of zero-reactant gases had a concave portion 12 with an upwardly open side wall as shown in Figure 2 (bl). When the ratio is unchanged and the 0. gas flow rate is 53 CCM and the total flow rate is 16.73 CCM, the 0. It was formed.t! There was no need to change the plasma generation conditions other than the flow rate.The pressure inside the tank was
By using a device that changes the degree of opening and closing of the exhaust system valve even when the total flow rate changes, the pressure was able to settle within a constant pressure range within a few seconds. A similar method can be applied to patterning a polycrystalline silicon layer stacked on a semiconductor substrate, and the inclination angle of the edge sidewall of the polycrystalline silicon layer pattern can be adjusted as desired.

〔Effect of the invention〕

According to the present invention, the amount of oxygen radicals in the plasma can be changed by changing the total flow rate of the reaction gas without changing the mixing ratio of oxygen gas, thereby maintaining the plasma generation conditions constant. It is now possible to adjust the inclination angle of the side wall of the recess or opening formed in the material to be etched by etching. Therefore, controlling the shape of the recesses or openings becomes an object, and is effective in various fields such as creating substrates with arbitrary mechanical properties, improving thin film adhesion in one process, and creating embedded devices with new shapes. It can be applied to

[Brief explanation of drawings]

FIG. 1 is a sectional view of an example of a plasma etching apparatus used for carrying out the present invention, and FIG.
+ is a sectional view showing the shape of a recess formed according to an embodiment of the present invention. l: reaction tank, 2: upper electrode, 3: lower electrode, 4: silicon substrate, 7: high frequency power supply, 8: gas introduction pipe, 9: exhaust pipe, lO: reaction gas, 11, 12.13: concave agent Attorney Gen Yamaguchi, ---□Figure 1 Figure 2

Claims (1)

[Claims] 1) A voltage is applied between opposing electrodes to generate plasma in a reduced pressure reaction gas containing oxygen present between the electrodes, and a material to be etched is placed near one of the electrodes and has a pattern of mask material on its surface. When forming recesses or openings by etching the areas not covered by the mask, by adjusting only the total flow rate of the reaction gas while keeping the mixing of oxygen gas in the reaction gas constant, the recesses created by etching can be Alternatively, a plasma etching method characterized by changing the slope shape of the side wall of the opening.