JPH0666301B2 - Plasma etching method - Google Patents

Description

Detailed Description of the Invention TECHNICAL FIELD OF THE INVENTION

The present invention relates to a plasma etching method for etching silicon by generating plasma in sulfur hexafluoride (SF ₆ ) gas.

[Prior art and its problems]

When plasma etching is performed using SF ₆ gas, parameters such as the degree of vacuum in the reaction tank, the electrode interval, and the discharge power are adjusted in order to obtain a uniform etching amount on the surface of the member to be etched. However, there is a limit only by adjusting these parameters, and it is not possible to expect satisfactory homogeneity. Especially for the manufacture of semiconductor pressure sensors, plasma etching is used to form a large number of sensor chips having a diaphragm portion of about 25 μm in the center from a silicon wafer of about 450 μm with a diameter of 4 inches that fits the IC line. If the variation in etching amount becomes variation in the thickness of the diaphragm portion which determines the sensitivity, SF ₆
This has been a hindrance to the practical application of plasma etching.

[Object of the Invention]

An object of the present invention is to provide a plasma etching method using SF ₆ gas that eliminates the above-mentioned drawbacks and enables etching with a uniform etching amount over the entire surface of a member to be etched made of silicon having a large area. And

[Points of the Invention]

In the present invention, a member to be etched is mounted on a cathode plate out of an anode plate and a cathode plate which are arranged to face each other in a reaction tank, and SF ₆ gas and O
When performing the plasma etching by generating plasma in a mixed gas of ₂ gas, based on the recognition of the relationship of etching rates between the center portion and the peripheral portion of the surface of the etched member changes depending on the content of O ₂ gas In this case, two points, that is, when the O ₂ gas content is low and when the O ₂ gas content is high, at which the etching rates of the central part and the peripheral part are equal, are found in advance, and a mixed gas having one of the O ₂ gas contents is used. By performing etching by using the above method, a uniform etching amount can be obtained within the surface of the material to be etched, and the above-mentioned object is achieved.

Examples of the invention

FIG. 1 shows a plasma etching apparatus used in one embodiment of the present invention, in which a positive electrode plate 2 and a negative electrode plate 3 are arranged opposite to each other in a reaction tank 1. A silicon wafer 4 coated with a mask made of Al is placed on the cathode plate 3 which is connected to the ground, the chamber is evacuated through an exhaust pipe 5, and the gas introduction pipe 6 introduces SF ₆ gas from the introduction port 7. , O ₂ gas from the inlet 8 is mixed and introduced, and high frequency power of 13.56 MHz is applied between the bipolar plates 2 and 3 by the power source 9 to generate plasma in the space 10 between the polar plates, and the wafer 4 mask Etch the uncovered surface. now,
As shown in FIG. 2, a recess 41 having a depth d of 430 μm and a diameter D of 2 mm is formed on a 4-inch silicon wafer 4 having a thickness t of 455 μm.
When forming a large number of 3.5 mm pitch, the addition of O ₂ gas is SF ₆
The oxidation rate is increased because S generated by the decomposition of S is oxidized to SO ₂ and the action of S is blocked, but if the O ₂ content is gradually increased, the variation in the in-plane etching amount, that is, the outer peripheral portion The difference between the etching amount of 1 and the etching amount of the central portion changes as shown in FIG. The + indicates that the outer peripheral portion has a higher etching rate than the central portion, and the − indicates that the central portion has a higher etching rate than the outer peripheral portion. While the O ₂ content is low, the etching rate in the vicinity of the center is fast, and the variation in the etching amount decreases as the O ₂ content increases, and the content A becomes 0. After that, the outer peripheral portion has a higher etching rate, and the variation in the content B becomes maximum. After that, the O ₂ content decreases with an increase, and the variation in the content C becomes 0 again. Further, beyond this point, the etching rate becomes a region where the central portion is high again, and the variation in the etching amount increases as the O ₂ content increases. As a result of performing the plasma etching of the silicon wafer by controlling the O ₂ amount so that the in-plane variation of the etching amount obtained is 0 or around A or C, the etching amount is within the range of 430 ± 5 μm. The area to be entered is the area 11 shown by hatching in FIG. 4, and has an area of 115% of the area of the effective use area in the wafer surface shown by the dotted line 12. This is because the result shown in FIG. 5 when plasma etching is performed using only SF ₆ gas, that is, the area 11 where the etching amount falls within the range of 430 ± 5 μm is 26% of the in-plane effective area 12. It can be seen from the comparison that the improvement is remarkable.

【The invention's effect】

According to the present invention, and 0 in two places less time and more time points O ₂ gas when the variation in the plane of the etching amount of silicon by plasma etching was added O ₂ gas content in the SF ₆ gas By utilizing the above, it becomes possible to obtain a large number of chips etched at the same depth from a large-diameter silicon wafer by controlling the O ₂ gas content. In particular, it is extremely effective for manufacturing a semiconductor pressure sensor chip that requires that the diaphragm that determines the sensitivity has a uniform thickness.

[Brief description of drawings]

FIG. 1 is a sectional view of an apparatus used in an embodiment of the present invention, and FIG.
FIG. 3 is a cross-sectional view of a recess formed in a silicon wafer by this apparatus. FIG. 3 is a relationship curve diagram between variations in etching amount in the silicon wafer surface and O ₂ gas content in SF ₆ gas.
FIG. 5 is a plan view showing a region where the etching amount of a silicon wafer is within a predetermined range according to one embodiment of the present invention, and FIG. 5 is a plan view showing a similar region in the case of a conventional method. 1: Reactor, 2: Anode plate, 3: Cathode plate, 4: Si wafer, 7: SF ₆ gas inlet, 8: O ₂ gas inlet, 9: High frequency power supply.

Claims (1)

[Claims] 1. Two reaction electrodes, each consisting of an anode plate and a cathode plate, are opposed to each other in a reaction tank, the reaction tank is evacuated, and then sulfur hexafluoride (SF ₆ ) gas is introduced to produce SF ₆ gas. In the method of etching plasma by generating plasma inside, the member to be etched is mounted on the cathode plate connected to the ground, and the surface of the member to be etched is mixed by mixing oxygen (O ₂ ) gas with SF ₆ gas. The two locations, the time when the O ₂ gas content is low and the time when the etching rate is the same in the central part and the peripheral part, are found in advance, and a mixed gas having one of the O ₂ gas contents is supplied from the anode plate side. A plasma etching method characterized in that etching is performed by means of etching.