JPH053734B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] In a horizontal incidence type microwave plasma processing apparatus, a microwave transmission window is constituted by a plurality of small windows having an interval of λg/4.

[Industrial Field of Application] The present invention relates to a microwave plasma processing apparatus, and particularly to improvement of a plasma processing apparatus for higher performance.

As a process technology for semiconductor manufacturing, dry processing has become a very important technology for miniaturization and high integration of semiconductor devices. In such dry processes, plasma processing using microwaves has recently been used, such as the ashing process of resist films using oxygen (O ₂ ) plasma,
It is used in the process of plasma etching polycrystalline silicon films with carbon tetrafluoride (CF ₄ ) + oxygen gas. This microwave (2.4GHz) plasma treatment
Compared to conventional plasma processing using high frequency (13.56MHz), this method has the advantage of high excitation efficiency.

However, such a microwave plasma processing apparatus still has some points that have not been sufficiently studied, and these problems must be studied and improved.

[Prior Art] Generally, in a microwave plasma processing apparatus, a microwave generation section and a plasma processing section (chamber) are connected by a waveguide. There have been many methods in which a window is provided and microwave power is introduced into the plasma processing chamber through the microwave-transmitting window. Here, the microwave-transmitting window is a window that allows microwaves to pass through while vacuum-sealing the inside of the plasma processing chamber, and quartz or alumina is suitable material.

By the way, in this way, a microwave transmission window is provided perpendicular to the direction of microwave propagation (electric field direction).
In contrast to the so-called vertical incidence method of microwaves, the inventor has developed a microwave plasma processing apparatus which can be called the so-called horizontal incidence method of microwaves, in which a microwave transmission window is provided horizontally in the direction of microwave propagation ( (See patent application No. 59-252909).

FIG. 4 shows a side sectional view of the horizontal incidence type microwave plasma processing apparatus, and FIG. 5 is a cross section AA' of the same figure. 1 is a microwave transmission window, 2 is a wafer to be processed, 3 is a waveguide, and 4 is a plasma processing chamber.The 2.45GHz microwave generated by a magnetron (not shown) is passed through a rectangular microwave guide. The microwave is guided through the wave tube 3 onto a microwave transmission window 1 arranged horizontally in the direction of microwave propagation (electric field direction), transmitted through the transmission window 1, and introduced into the plasma processing chamber 4.

On the other hand, in the plasma processing chamber 4, the wafer 2 is placed parallel to the transmission window 1, and while vacuum is being sucked from the exhaust port 5, a reaction gas is flowed in from the other gas inlet 6 to reduce the pressure to 0.1 Torr. It should be around a few Torr. Then, the inflowing reaction gas is turned into plasma by the microwave, and the plasma-excited gas reacts with the wafer to perform plasma etching.

Compared to vertical incidence processing equipment, horizontal incidence processing equipment has far less microwave reflection, excellent matching, generates plasma efficiently, and processes wafers at high speed. . In microwave plasma processing equipment, microwaves are transmitted through atmospheres with different dielectric constants (ε).
There is a problem in that it must be introduced sequentially into a transmission window and a vacuum (depressurized), and in vertical incidence processing equipment, when matching is done in the vacuum state of the plasma processing chamber (no plasma is being generated), the plasma will not be generated. In this state, the reflection becomes strong and matching cannot be achieved, which is a paradoxical state, and the matching is not very good. On the other hand, in the horizontal incidence method, the electric field is applied perpendicularly to the transmission window, which improves this, allows for a smaller plasma processing chamber, and has the advantage of good microwave matching and extremely low microwave reflection. be. For details, please refer to the above mentioned patent application No. 59-252909.
Please refer to the issue.

[Problems to be Solved by the Invention] By the way, in such a horizontal incidence type microwave plasma processing apparatus, one of the important problems is the microwave transmission window 1, which is easily damaged. There is a drawback.

As mentioned above, quartz or alumina are suitable materials to maintain vacuum sealing and transmit microwaves, but quartz has good heat resistance, but it cannot be etched by fluorine-based gases such as _CF4 . It is easy to process, and is not suitable for processing semiconductor substrates.

Therefore, in the etching process of semiconductor substrates, an alumina plate is used as the transparent window 1, but alumina rapidly deteriorates in bending strength and becomes brittle at temperatures above 200°C, so the alumina plate is used as a vacuum-sealed window. Because of this, they cannot withstand atmospheric pressure and often break down. In microwave plasma processing equipment,
Normally, the transmission window area is 300 to 400 mm due to plasma heat.
heated to ℃.

Therefore, if the transmission window is made smaller, the strength against destruction can be maintained, but then a plasma region of the required size cannot be obtained.

The present invention proposes a microwave plasma processing apparatus that eliminates these drawbacks.

[Means for solving the problem] The purpose is that the microwave transmission window is λg/4 (λ
This can be achieved by a microwave plasma processing apparatus constructed of a plurality of windows spaced apart by a distance of g: wavelength within the tube.

[Function] The larger the opening area of the microwave transmission window in the microwave plasma processing apparatus, the larger the plasma area, which is desirable for increasing the processing capacity and making the processing uniform. However, large aperture area transmission windows are especially desirable for alumina plates for semiconductor processing.
It has the disadvantage of being easily destroyed.

Therefore, in the present invention, the plasma processing chamber is used as a sub-waveguide with respect to the waveguide, and the transmission window that couples the two is a directional coupler having a plurality of coupling holes with an interval of λ ₉ /4. Breakage is prevented by reducing the effective opening of the transmission window covered by the alumina plate.

In other words, the wave traveling in the waveguide that supplies microwaves is phase-strengthened at the coupling hole λ ₉ /4 away and radiated into the plasma processing chamber. Sufficient electric field is provided.

Thereby, a sufficient plasma area can be obtained even with a substantially small transmission window, and the above-mentioned problem can be solved.

[Example] Hereinafter, an example will be described in detail with reference to the drawings.

FIG. 1 is a side sectional view of a microwave plasma processing apparatus according to the present invention, in which the same members as in FIG. 4 are given the same symbols.

As shown in the figure, the microwave transmission window 1 has a support frame 12 interposed below the alumina plate 11, and as shown in FIG. , 1S'. and,
The distance between the centers of two square aperture transmission windows is λg/4
Make the interval .

In this way, the small slit-shaped windows are difficult to break, and the plasma processing chamber becomes a sub-waveguide for microwaves, so even if the opening area of each window is small, sufficient plasma can be generated. area is obtained. That is, like a microwave directional coupler, a hole is created in the coupling system so that one phase becomes the other phase, and the plasma region becomes similarly wide.

To explain with a specific numerical example, when oxygen plasma is excited in a reduced pressure of 1 Torr using microwaves (2.45 GHz) with a power of 1.5 KW, the conventional 110 mmφ
An alumina transmission window with a circular aperture of 200 mL failed within 2 minutes. However, each has a width of 110 in the direction of travel.
When two slit-shaped aperture transmission windows with a length of 27 mm and a center distance of λg/4 (approximately 37 mm) are provided,
The window remained intact even after 10 minutes of plasma exposure.

FIG. 3 shows a cross-sectional perspective view of the transmission window portion of the embodiment explained in FIGS. Very obvious.

Although the above example has been described with two square opening windows, the invention is not limited to two windows.

[Effect of the invention] As can be seen from the above explanation, according to the present invention,
This eliminates damage to the alumina transmission window and contributes to improving the performance of the microwave plasma processing apparatus.

[Brief explanation of the drawing]

FIG. 1 is a side cross-sectional view of a microwave plasma processing apparatus according to the present invention, FIG. 2 is a plan view of the microwave plasma processing apparatus according to the present invention as seen from the wafer side, and FIG. 3 is a cross-sectional view of the transmission window portion thereof. A perspective view, FIG. 4 is a side sectional view of a conventional microwave plasma processing apparatus, and FIG. 5 is a sectional view taken along line AA' in FIG. 4. In the figure, 1 is a transmission window, 2 is a wafer, 3 is a waveguide, 4 is a plasma processing chamber, 5 is an exhaust port, 6 is a reaction gas inlet, 11 is an alumina plate, 12 is a support frame, 1S, 1S' shows a square aperture transmission window.

Claims (1)

[Claims] 1 Microwave plasma that introduces microwaves into a plasma processing section through a microwave transmission window provided parallel to the direction of microwave propagation, converts gas in the plasma processing section into plasma, and plasma-processes a sample to be processed. 1. A microwave plasma processing apparatus, wherein the microwave transmission window is composed of a plurality of windows having an interval of λg/4 (λg: tube wavelength).