JPS6328995B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dry etching a semiconductor substrate, and more particularly to a method for dry etching a silicon oxide layer, which is a semiconductor substrate, selectively faster than a silicon layer.

In the manufacturing process of semiconductors, especially ICs and LSIs, there is a strong demand for consistent and continuous automatic processing. In dry etching, which is one of the steps, when etching a silicon oxide layer on a silicon substrate, it is necessary to selectively etch the silicon oxide layer faster than the silicon layer. If the etching speed of silicon is fast, as soon as even a little bit of the underlying silicon substrate is exposed, only that silicon will be suddenly etched away. The etching rate of silicon oxide is 10 compared to normal silicon.
More than double the selectivity is required.

Conventionally, CF ₄ gas has been used for dry etching, but when this gas is used, the etching rate of silicon is faster than that of silicon oxide.
By using a fluorinated hydrocarbon gas such as C ₂ F ₆ or C ₃ F ₈ , which has a larger molecular weight than CF ₄ , silicon oxide can be etched selectively to silicon to some extent, but sufficient selectivity is still not achieved. Because of this, it has not been used stably and practically. Furthermore, there is a method of selectively etching by mixing reducing hydrogen gas with these fluorinated hydrocarbon gases (for example, Japanese Patent Publication No. 7315/1983), but even if the purpose is almost achieved, the use of hydrogen gas poses an excessive risk. Since this method involves problems with workability and equipment, it is difficult to say that it is practical.

As a result of intensive research into a method for selectively and quickly etching a silicon oxide layer on a silicon wafer without the above-mentioned drawbacks, the inventors of the present invention have found that a method for selectively and quickly etching a silicon oxide layer on a silicon wafer has been developed using fluorinated hydrocarbon gases such as CF ₄ , C ₂ F ₆ , and C _{3 .} F ₈ , C ₄ F ₁₀ gas, etc. and an inert gas, such as helium gas or argon gas, are placed in a vacuum state at a flow rate ratio of 1:1 to 1:100, preferably 1:5 to 1:20. When a silicon oxide layer on a silicon wafer is etched by introducing a mixed gas into a parallel plate plasma etching system, reactive sputter etching system, or reactive ion etching system to form a plasma state, it is possible to etch the silicon oxide layer on a silicon wafer at high speed and with high selectivity. The inventors have discovered that silicon oxide layers can be etched by etching the silicon oxide layer, and have completed the present invention.

According to the present invention, the mixing ratio of the fluorinated hydrocarbon gas and the inert gas has a wide permissible range, so there is no variation in etching even if the ratio of the mixed gas changes slightly. In addition, the degree of vacuum during etching does not need to be the conventional high vacuum (0.1 Torr or less), so it is not affected by residual gas or generated gas, and has the advantage that strict control of the degree of vacuum is not required. . Moreover, even though conventionally, silicon oxide is a low molecular weight fluorinated hydrocarbon which selectively etches faster than silicon oxide when used alone, the method of the present invention etches silicon oxide more selectively than silicon oxide. The ability to selectively, quickly and stably etch is of great industrial value.

Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited by the following Examples.

Example 1 Parallel plate type etching device (manufactured by Tokyo Ohka Kogyo Co., Ltd.)
OAPM-AL-300) 1x with a vacuum pump
After exhausting to 10 ^-3 Torr, 5 c.c./C ₃ F ₈ gas
The pressure is temporarily set to 0.08 Torr while introducing it at a flow rate of 100 c.c./min, and then the pressure is set to 0.4 Torr by introducing helium gas at a flow rate of 100 c.c./min. Next, output 150W (150J/
s) High frequency power with a frequency of 13.56 MHz was applied to generate plasma, and silicon oxide and silicon were etched. As a result, it was found that the etching rate ratio of silicon oxide to silicon was 12:1, and that silicon oxide could be selectively etched. The etching rate of silicon oxide at this time was 1200 Å/min (20 nm/s).
On the other hand, when helium gas was not introduced, the etching rate ratio was 4:1, and the etching rate of silicon oxide was 800 Å/min (13.3 nm/s).
The effect of introducing helium gas was significant.

Figure 1 was obtained by plotting the etching rate while varying the pressure inside the etching chamber.
Figure 2 shows a plot obtained by removing helium gas in the same manner.

As can be seen from FIGS. 1 and 2, if an inert gas is introduced during dry etching, the silicon oxide layer can be selectively etched at a high speed. It was also found that the pressure inside the etching chamber could be controlled without much concern.

Example 2 C ₃ F ₈ gas was applied at 5 c.c./min to a parallel plate type etching device (OAPM-AL-300 manufactured by Tokyo Ohka Kogyo Co., Ltd.)
While introducing at a flow rate of , the pressure was temporarily set to 0.08Torr,
Next, introduce argon gas at a flow rate of 20c.c./min.
It was set to 0.15Torr. Next, output 150W (150J/s),
When etching was performed by applying high frequency power with a frequency of 13.56 MHz, the etching rate of the silicon oxide layer was 1000 Å/min (16.7 nm/s), and the etching rate of the silicon layer was 100 Å/min (1.67 nm/s).
s), and the ratio was 10:1.

[Brief explanation of the drawing]

Both Figures 1 and 2 are graphs showing the relationship between the pressure inside the vacuum chamber and the etching rate. Figure 1 shows the case when the helium gas of the present invention is added, and Figure 2 shows the case when the helium gas is removed. This is the case. A...Silicon oxide, B...Silicon.

Claims (1)

[Scope of Claims] 1. A method for dry etching a semiconductor substrate in which a silicon oxide layer is selectively etched faster than a silicon layer, characterized by etching with fluorinated hydrocarbon to which an inert gas is added. 2. The dry etching method according to claim 1, wherein the inert gas is helium gas or argon gas. 3 The amount of inert gas added is fluorinated hydrocarbon gas 1
1-100.