JPH10149897A - Plasma processing method - Google Patents

Abstract

(57) [Problem] To provide a plasma processing method capable of stably igniting plasma without damage by ions of a sample and thereby performing a stable process on the sample over a long period of time. A plasma process for introducing a gas into a reaction vessel (plasma generation chamber 21 and sample chamber 23), applying a microwave and a magnetic field, generating plasma by electron cyclotron resonance excitation, and processing the sample S. A method of igniting a plasma by applying microwaves,
A plasma processing method, wherein a magnetic field is applied so that a magnetic flux density on a sample S is in a range from +10 Gauss to -200 Gauss.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for generating plasma by excitation of electron cyclotron resonance (ECR) and etching or CV etching a sample.
The present invention relates to a plasma processing method for performing processing such as D.

[0002]

2. Description of the Related Art Plasma is generated using ECR.
The apparatus that irradiates the sample with this plasma can generate highly active plasma in a low pressure region as compared with normal high-frequency plasma and the like, and is excellent in directivity and uniformity of ion flow. Therefore, it is widely used in the manufacture of highly integrated semiconductor elements and the like.

[0003] However, a plasma processing apparatus utilizing this ECR may not generate plasma even if microwaves are introduced during the repetition of etching processing of an aluminum alloy film (Al alloy film) or a polysilicon film. ,
That is, there is a problem that ignition of plasma may be difficult. If the plasma cannot be ignited stably,
Since processing such as etching cannot be performed and microwaves are not used for generation of plasma, direct incidence on a sample may burn the resist or destroy a device formed on the sample.

The reason why the ignition of the plasma becomes difficult is considered as follows, for example, in the etching of an Al alloy film by the plasma of a mixed gas of Cl ₂ and BCl ₃ . When etching the Al alloy film,
The resist masking the Al alloy film is also physically sputtered by the plasma irradiation, reacts with ions or radicals such as Cl, BCl or Al, and adheres to the reaction vessel as a reaction product. Then, the reaction product accumulates in the reaction vessel while repeating the etching process, and inhibits plasma ignition. For example, when deposited on the microwave introduction window, the incidence of the microwave into the reaction vessel is hindered, and it becomes difficult to match the microwave.

It is also considered that the etching of polysilicon is caused by the adhesion of a resist.

In such a case, the method of igniting the plasma is to increase the power of the microwave introduced into the reaction vessel or to increase the magnetic field generated by the magnetic field generating coil to increase the magnetic flux density on the sample to 200 gauss or more. And so on.

However, when the power of the microwave is increased, the plasma (ion) density in the plasma increases, and as a result a large amount of ions enter the sample, so that damage (charge-up damage) due to ions of the sample increases. . In the manufacture of a semiconductor device, the damage caused by the ions lowers the yield of the semiconductor device.

When the magnetic flux density on the sample is increased,
Since the ECR excitation point, which is a plasma generation point, usually approaches the sample, the amount of plasma (ions) reaching the sample increases. Therefore, if the magnetic flux density on the sample is increased,
As in the case where the microwave power is increased, the damage of the sample due to ions increases.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and has been made for a long term by enabling stable plasma ignition without ion damage of a sample. It is an object of the present invention to provide a plasma processing method capable of performing stable processing on a sample.

[0010]

According to the plasma processing method of the present invention, a sample is processed by introducing a gas into a reaction vessel, applying a microwave and a magnetic field, and generating plasma by electron cyclotron resonance excitation. A plasma processing method, characterized in that when igniting plasma by applying a microwave, a magnetic field is applied so that a magnetic flux density on a sample is in a range of +10 gauss to -200 gauss.

The range of the magnetic flux density on the sample is determined with respect to the magnetic flux density at the center position on the sample, with the center on the sample as the evaluation position of the magnetic flux density. Also,
As for the magnetic flux density, the polarity of the magnetic field generated in the reaction vessel to cause electron cyclotron resonance excitation is + (positive).

The present inventors have found that the density of plasma (ions) can be reduced by reducing the magnetic flux density on a sample, that is, by reducing the magnetic flux density on the sample or making the polarity opposite to that of the sample, thereby reducing the damage of the sample by ions. We paid attention to.

Then, using a device in which reaction products were deposited in the plasma generation chamber and the sample chamber, it was tested whether stable plasma ignition was easy by changing the magnetic flux density on the sample in a direction of decreasing the magnetic flux density.

As a result, when the magnetic flux density on the sample is from +10 gauss to -200 gauss, the plasma becomes extremely easy to ignite. He confirmed that he could do it.

The present invention has been made based on the above findings, and the magnetic flux density on a sample has been increased from +10 gauss to -2.
By applying a magnetic field so as to be in the range of 00 Gauss, it is possible to facilitate stable and stable plasma ignition without flickering, and it is possible to reduce damage caused by ions of the sample by lowering the magnetic flux density as compared with the prior art.

[0016]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view showing a plasma processing apparatus using ECR.

The reaction vessel is divided into a plasma generation chamber 21 for generating plasma and a sample chamber 23 for extracting the generated plasma and processing the sample.

A microwave introduction window 21a is provided at the center of the upper wall of the plasma generation chamber 21 to hermetically seal the plasma generation chamber and to introduce microwaves from this window. The microwave introduction window 21a is made of quartz, alumina (Al ₂ O ₃ ), or the like. In the center of the lower wall of the plasma generation chamber 21, a circular plasma outlet 21b is provided.
Is provided, and the plasma generated in the plasma generation chamber 21 is drawn out to the sample chamber 23 from here. The plasma is drawn by a magnetic field. This magnetic field is formed by a magnetic field generating coil 35 described later, and is a divergent magnetic field whose magnetic flux density decreases toward the sample chamber 23. In order to supply gas to the plasma generation chamber 21, a gas supply pipe 24 is provided.
Is provided.

One end of a waveguide 22 is connected to the microwave introduction window 21a, and the other end of the waveguide 22 is connected to a microwave oscillator (not shown). A magnetic field generating coil 35 for generating a magnetic field required for ECR excitation is provided concentrically with the plasma generating chamber 21. The magnetic field required for ECR excitation (ECR magnetic field) is about 875 Gauss when the microwave frequency is 2.45 GHz. A position where the magnetic field strength satisfies the ECR magnetic field (E
At the (CR excitation point), plasma is mainly generated.

A sample table 27 is provided in the sample chamber 23, on which a sample S is mounted by electrostatic attraction or the like. A gas supply pipe 25 is provided on a side wall of the sample chamber 23,
An exhaust port 23a is opened in the lower wall.

Further, in order to control the magnetic field intensity near the sample stage, an auxiliary coil 36 is provided below the sample stage 27. The central axis of the auxiliary coil 36 is concentric with the central axis of the magnetic field generating coil 35. In the auxiliary coil 36,
By passing a current in a direction opposite to that of the magnetic field generating coil 35, a magnetic field having a polarity opposite to that of the magnetic field generated by the magnetic field generating coil 35 can be generated. Here, the magnetic field generated by the magnetic field generating coil 35 is + (positive).

The plasma processing method of the present invention will be described with reference to an example in which an Al alloy film such as Al-Si-Cu is etched using this apparatus. The sample S is a silicon wafer on which, for example, an Al alloy film is formed and further masked with a resist in a predetermined pattern.

After evacuating the plasma generation chamber 21 and the sample chamber 23 to a required pressure, a mixed gas of, for example, Cl ₂ and BCl ₃ is supplied as an etching gas, and the plasma generation chamber 21 and the sample chamber 23 are set to a predetermined pressure. .

A current is passed through the magnetic field generating coil 35 to form a magnetic field required for ECR excitation in the plasma generating chamber. Further, by passing a predetermined amount of current through the auxiliary coil 36 in a direction opposite to that of the magnetic field generating coil 35, the magnetic flux density at the center position on the sample S is set to a range from +10 gauss to -200 gauss. .

A microwave is introduced into the plasma generation chamber 21 to excite the etching gas by ECR to ignite the plasma.

The amount of current flowing through the auxiliary coil 36 is reduced as necessary, and the diverging magnetic field mainly formed by the magnetic field generating coil 35 is adjusted to guide the plasma onto the sample stage 27 in the sample chamber 23. Then, the Al alloy film on the sample S is etched.

According to this method, stable plasma ignition without flicker is possible, and the damage of the sample due to ions can be reduced by lowering the magnetic flux density at the time of plasma ignition as compared with the conventional method.

In this example, the same gas is used for both the plasma ignition and the plasma processing. However, when the plasma is ignited, a gas such as N ₂ or Cl _{2 which} is easy to ignite the plasma is used. May be used.

Although the description has been made by taking the etching of the Al alloy film as an example, it goes without saying that the plasma processing method of the present invention can also be applied to the etching of a polysilicon film or the etching of a silicon oxide film.

[0031]

Embodiments of the present invention will be described below.

Using the ECR plasma processing apparatus shown in FIG. 1, the ignition of the plasma was evaluated by changing the magnetic flux density on the sample table. The magnetic flux density on the sample stage was changed by fixing the amount of current flowing through the magnetic field generating coil 35 and changing the amount of current flowing through the auxiliary coil 36. Here, the polarity of the magnetic field generated by the magnetic field generating coil 35 is + (positive).

The conditions for plasma ignition are as follows. The gas used was N ₂ and the flow rate was 200 sccm. The pressure in the sample chamber 23 is 3, 4, 6, 8 mTor.
r. The microwave frequency was 2.45 GHz and the power was 600 W. The ECR excitation point was formed in the plasma generation chamber 21 at a position about 60 mm from the plasma outlet.

Table 1 shows the results of evaluating the ignition of this plasma.
Shown in Indicates that the ignition was good and the plasma did not flicker. ○ indicates that the ignition was good, but the plasma sometimes flickered once every several times. Δ indicates that the ignition is good but the plasma flickers. × indicates poor ignition, in which the plasma flickers even if ignited. That is,
◎ and ○ indicate good ignition, Δ indicates occasional poor ignition, and × indicates poor ignition.

[0035]

[Table 1]

From this result, the magnetic flux density on the sample stage is +1
It is understood that the ignition is good when it is between 0 Gauss and -200 Gauss. In particular, when the magnetic flux density on the sample stage was around -50 gauss to -120 gauss, the most favorable ignition was obtained without plasma flicker.

Although this result uses N ₂ gas, similar results can be obtained with various gases such as Cl ₂ , BCl ₃ , O ₂ , and Ar.

The Al alloy film was etched using the ECR plasma processing apparatus shown in FIG. 1, and the damage (charge-up damage) of the sample due to ions was evaluated by measuring the withstand voltage of the antenna MOS capacitor.

As a result, it was confirmed that the damage to the sample can be reduced by setting the magnetic flux density on the sample stage to +10 gauss or less. Conversely, the magnetic flux density on the sample stage is increased by +1.
When the value was 00 Gauss or more, damage to the sample increased.

[0040]

According to the plasma processing method of the present invention, it is possible to stably ignite a plasma without damaging the sample by ions. As a result, a stable treatment can be performed on the sample over a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view showing a plasma processing apparatus using ECR.

[Explanation of symbols]

 Reference Signs List 21 plasma generation chamber 21a microwave introduction window 21b plasma outlet 22 waveguide 23 sample chamber 23a exhaust port 24 gas introduction pipe 25 gas introduction pipe 27 sample table 35 magnetic field generating coil 36 auxiliary coil S sample

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/3065 H01L 21/302 B

Claims (1)

[Claims] 1. A plasma processing method for introducing a gas into a reaction vessel, applying a microwave and a magnetic field, and generating plasma by electron cyclotron resonance excitation to process the sample. When the plasma is ignited, the magnetic flux density on the sample increases from +10 gauss to -20.
A plasma processing method, wherein a magnetic field is applied so as to be in a range of 0 Gauss.