JPH027330A - Ecr plasma generating device - Google Patents

Abstract

PURPOSE:To make a reflected wave reducible in constant stability despite the variation of a coil current, etc., even using a continuous microwave by interposing a dielectric plate between a discharge chamber and a taper type waveguide and making the product of the thickness d (mm) and the dielectric constant epsilonof a dielectrics 70<dXepsilon<160. CONSTITUTION:In an ECR plasma generating device, a dielectric plate 9 is interposed between a discharge chamber 6 and a taper type waveguide 5, and the product of the thickness d (mm) and the dielectric constant epsilon of a dielectrics is made to 70<dXepsilon<160. In this case, as for the plate 9 interposed, a dielectrics which is an insulator and permeates a microwave can be used, e.g., a quartz plate or ceramics, etc., available. By the way when the sealing member composed of a dielectrics for sustaining the vacuum in the discharge chamber is interposed between the discharge chamber and the waveguide, it is needed that the coalescent substance of the sealing member and the dielectric plate meets the said condition. This enables a reflected wave to be reduced despite a microwave is a continuous pulse wave and over the wide range of a coil current and a microwave power.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to semiconductor manufacturing equipment using electron cyclotron resonance (ECR) plasma, such as an ECR etcher,
The present invention relates to an ECR plasma generator applied to ECRCVD, etc.

[Prior Art] In recent years, a process using electron cyclotron resonance (ECR) plasma has been developed in the semiconductor manufacturing process, and has been put into practical use as a chemical vapor deposition (CVD) device or an etching device.

Such an ECR plasma generator efficiently absorbs electric field energy into charged particles using microwaves transmitted from a microwave source and a magnetic field generated orthogonally to the electric field in a discharge chamber into which a gas serving as a plasma source is introduced. This method generates highly active plasma, extracts this highly active plasma using a divergent magnetic field, and causes it to collide with the sample surface, and an important issue is to minimize reflected microwave waves. If there are many reflected microwave waves,
Plasma cannot be generated efficiently, and if the reflected waves return to the microwave source, the magnetron, there are problems such as overheating.

It has been reported that it is effective to convert the microwave into a quasi-TM wave mode and introduce it into the discharge chamber in order to eliminate the reflected waves of the microwave.

For example, in the ECR plasma generator shown in FIG. 12, among the waveguides 20 to 60 connected to the microwave source 1, the waveguide 60 connected to the discharge chamber 70 is configured to perform mode conversion. That is, in the ECR plasma generator shown in FIG. 12, by inserting a dielectric plate inside the tapered waveguide 60, the microwave is converted into a quasi-TM wave having an electric field component also in the direction of propagation. There is.

[Problem to be solved by the invention] However, in order to keep the reflected waves as low as, for example, 3% or less through such microwave mode conversion, it is necessary to use pulsed waves as the microwave. When pulsed, plasma is generated intermittently and all at once, so reaction products adhering to the walls of the discharge chamber or reaction chamber peel off as particles and adhere to the sample. This caused element failure.

Furthermore, when the microwave is pulsed, the peak of the self-bias (Vpc) generated on the sample stage increases when a high frequency bias is applied to the sample stage, which may cause damage to the sample. Figures 13(a) and (b) show the self-bias (V
DC). As shown in the figure, when the microwave is continuous, the self-bias (VDC) is constant,
When the high frequency bias is 200W, it is -80V, but in the case of pulse, the value of -VDc is large when the microwave is stopped, and -2
It reaches as high as 00■.

On the other hand, when continuous microwaves are used, the reflected waves decrease only under specific conditions, and it is not possible to increase the speed of CVD or other processes by increasing the microwave power.

The present invention solves the above conventional problems and provides an ECR plasma generator that can always stably reduce reflected waves even when using continuous microwaves and regardless of changes in coil current, etc. purpose.

[Means for Solving the Problems] In order to achieve such an object, the present inventors investigated the thickness of the dielectric material inserted between the discharge chamber and the waveguide and the micro As a result of extensive research into the relationship between microwave reflectance and dielectric material, it was discovered that when a dielectric material satisfies specific conditions, microwave reflectance is minimized, leading to the present invention.

That is, the ECR plasma generator of the present invention includes a microwave source that generates microwaves, a rectangular waveguide for transmitting the microwaves, a tapered waveguide connected to the rectangular waveguide, and a microwave source for transmitting the microwaves. In an ECR plasma generation device consisting of a discharge chamber for generating plasma, a dielectric plate is inserted between the discharge chamber and the tapered waveguide, and the thickness of the dielectric is d (n+n+). It is characterized in that the product of ε and dielectric constant ε is 70<dXf<160.

Here, as the dielectric plate to be inserted, any dielectric material can be used as long as it is an insulator and transmits microwaves.
For example, a quartz plate, ceramics, etc. can be used.

When using a quartz plate as a dielectric plate, the dielectric constant of the quartz plate is 3.72 to 3.94 (10' to 108 cycles), so in order for 70×εXd<160, its thickness d ( mm) is about 20-40 mm, preferably 27-40 mm
37 questions.

In addition, when a sealing member made of a dielectric material for maintaining a vacuum in the discharge chamber is interposed between the discharge chamber and the waveguide, the combination of this sealing member and the dielectric plate must satisfy the above conditions. is necessary. For example, if the sealing member has a dielectric constant of El and a thickness of d, and the dielectric plate has a dielectric constant of E2 and a thickness of d2, then 70<ε.

Let Xd1+ε2xd<160.

The dielectric plate may be integrated with a sealing member. In this case, a dielectric plate having a dielectric constant and thickness that satisfies the above conditions may be used as a sealing member and provided at the entrance of the discharge chamber by sealing with an O-ring or the like.

If the dielectric plate is provided separately from the sealing member, it must be of a specified shape (
(usually disc-shaped) may be placed on the sealing member.

[Example] Hereinafter, an example of the ECR plasma generator of the present invention will be described with reference to the drawings.

The ECRCVD apparatus shown in Fig. 1 includes a microwave source 1 for generating microwaves, waveguides 2 to 5 for transmitting microwaves, a discharge chamber 6 for generating plasma, and a system for depositing the generated plasma onto a sample. A small coil 8 is provided around the discharge chamber 6 to generate a magnetic field. Microwave source 1 is a microwave generator such as a magnetron, which generates microwaves at an industrial frequency (2.45 GHz), for example. Waveguide 2
5 is a metal tube made of stainless steel or the like, and a power monitor section 3a is installed in the waveguide 3 to measure the incident power and reflected power of the generated microwave and monitor the reflected waves. The waveguide 4 is an E corner that changes the microwave transmission path to a right angle, and the waveguide 5
is a tapered waveguide and is connected to the discharge chamber 6.

A seal member 10 for sealing the discharge chamber 6 and the reaction chamber 7 from vacuum is attached between the waveguide 5 and the discharge chamber 6 via an O-ring.

The sealing member 10 is made of a quartz plate having a thickness of 17 mm, and a dielectric plate 9 made of a quartz plate having a thickness of 15 mm is placed thereon. That is, the thickness of both quartz plates is 32 mm.

Further, the discharge chamber 6 is designed as a microwave resonance chamber, and has a length corresponding to, for example, one wavelength of the microwave in vacuum in the electric field direction, and a microwave reflecting plate 12 is provided at one end thereof.

Due to the microwave resonance and magnetic field of the discharge chamber 6, highly active plasma of the gas introduced into the discharge chamber 6 can be generated.

The discharge chamber 6 is filled with gas for generating plasma, such as N2, o
2. It has a gas inlet 13 for introducing Ar, etc. A three-stub 11 is provided in the waveguide 5 because the impedance of the discharge chamber 6 changes due to the generation of plasma. The three stub 11 may be provided in another waveguide instead of the waveguide 5, but in order to achieve responsive matching, it is optimal to provide it in the waveguide immediately before the discharge chamber.
This makes it possible to further reduce reflected waves.

The reaction chamber 7 is a reaction chamber for performing CVD on a sample W such as a wafer substrate using plasma generated in the discharge chamber 6, and is equipped with a sample stage 14. The sample W is placed on this sample stage 14 by a transport mechanism (not shown). It is brought in and placed. When the reaction chamber 7 performs deposition, SiH4 and the like are introduced from the gas inlet 15. In this case, if the plasma generated is N2 plasma, it interacts with SiH4 and Si and N4 are deposited on the sample, and if it is 0□ plasma, SiO□ is deposited.

The discharge chamber 6 and the reaction chamber 7 are connected to a vacuum system (not shown),
Deposition is performed at a desired pressure (reduced pressure) depending on the purpose.

Next, the operation of the ECRCVD apparatus with such a configuration will be explained.

First, continuous microwaves are generated from the plasma source 1. This microwave reaches the tapered waveguide 5 through the waveguides 2 to 4, and when it travels from there into the discharge chamber 6, it is efficiently mode converted by the presence of the dielectric plate 9 and the seal member 10. .

A gas serving as a plasma source is introduced into the discharge chamber 6 through a gas inlet 12, and a desired magnetic field is generated by a small coil 8, and the microwaves transmitted here resonate to efficiently generate electric field energy. is absorbed and a highly active plasma is generated.

At this time, the impedance of the discharge chamber 6 changes due to the introduction of the gas and disappears by the wavelength of the microwave, but this change is detected by the power monitor section 3a as an increase in reflected waves. Adjust the microwave wavelength and perform matching.

In addition, in this device, quartz plates were used as the dielectric plate 9 and the seal member 10, and the relationship between the total thickness of the dielectric plate 9 and the seal member 10 and the microwave reflectance at each N2 flow rate was actually measured. is shown in Figure 2. in this case,
The microwave uses a 100 Hz pulse wave, the microwave power is 600 W, and the coil current is 185 A.

Incidentally, the coil current is in the range of 165A to 21OA, and 8750auss is generated inside the cavity.

As is clear from Figure 2, the reflectance of the quartz plate becomes minimum within a certain thickness range, and even when the plasma gas flow rate is low (NZ flow rate = 58 CCM), the reflected waves can be suppressed to 3% or less. did it.

Further, using a 15 nua quartz plate as the 17 mm seal member 11 and the dielectric plate 9, reflected waves were measured when the coil current was changed. Other conditions are the same as in the case of FIG. The results are as shown in Figure 3, when the coil current 1
We were able to stably suppress reflected waves to 3% or less at 70A or higher.

Furthermore, using the same sealing member and dielectric plate, the reflected waves were measured when the plasma gas was changed using continuous microwaves (power: 600 W). In this case, the relationship between the coil current and the reflected wave and the relationship between the microwave power and the reflected wave are shown in FIGS. 4 to 7 and 8 to 11, respectively.

As shown in FIGS. 4 to 7, except for the case where the gas flow rate was 5 SCCM, the reflected waves could be stably suppressed to 3% or less.

In addition, as shown in Figures 8 to 11, except for the case of 58CCM and the case of 02 gas with a gas flow rate of 158CCM, it was possible to stably reduce the reflected wave to 3% or less over a wide range of microwave power. .

[Effects of the Invention] As is clear from the above embodiments, the ECR plasma generator of the present invention can be used regardless of whether the microwave is a continuous wave or a pulsed wave, and whether the coil current or microwave power is Reflected waves can be reduced over a wide range. This improves plasma generation efficiency and speeds up processing such as CVD and etching to which this apparatus is applied.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an embodiment of the ECR plasma generator of the present invention, Figure 2 is a diagram showing the relationship between dielectric thickness and microwave reflectance, and Figure 3 is a diagram showing an example of an ECR plasma generator using pulsed microwaves. Figures 4 to 7 are diagrams showing the relationship between coil current and reflected waves when continuous microwaves are used, and Figures 8 to 7 are diagrams showing the relationship between coil current and reflected waves when continuous microwaves are used. Figure 11 is a diagram showing the relationship between microwave power and reflected waves when continuous microwaves are used, Figure 12 is a diagram showing a conventional ECR plasma generator, and Figures 13 (a) and (b) are diagrams showing the relationship between microwave power and reflected waves when continuous microwaves are used. FIG. 3 is a diagram showing the relationship between self-bias and self-bias. Fig. 2 1...Microwave source 2...Rectangular waveguide 5...Tapered waveguide 6...Discharge chamber 7...・Reaction chamber 8... Coil 9... Dielectric plate 10... Seal member 11... Sleeve stub 14... Sample stage W... Sample

Claims (1)

[Claims] A microwave source that generates microwaves, a rectangular waveguide for transmitting the microwaves, a tapered waveguide connected to the rectangular waveguide, and a discharge chamber for generating plasma using the microwaves. A dielectric plate is inserted between the discharge chamber and the tapered waveguide, and the product of the thickness d (mm) of the dielectric and the dielectric constant ε is 70<d× An ECR plasma generator characterized in that ε<160.