JPH0554995A - Plasma processing device and operating method thereof - Google Patents

Abstract

PURPOSE:To provide a plasma processing device, which is equipped with a plasma generating microwave power supply to make pulse oscillation of the plasma on the time basis within a plasma chamber wherein a plasma producing gas in introduced and with which a high density plasma can be produced without increasing the microwave power to be input into the plasma chamber, and to provide an operating method for this device according to the described constitution which enables plasma production with the maximum density under the same microwave power condition. CONSTITUTION:A plasma processing device concerned is equipped with an exciting means 8 for molecules of plasma producing gas capable of adjusting the exciting energy and operating synchronous with pulses emitted by a microwave power supply 2. In case an electron beam generating device is used as a gas molecule exciting means, an electron beam is generated during pause of microwave pulse emission to irradiate the plasma producing gas, and the energy of the electron beam is adjusted to the region where excited section area of gas molecules is maximized, and thereupon the operation is conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a plasma processing apparatus for surface-treating a substrate by using plasma generated in a pulsed manner with time, and a method of operating the plasma processing apparatus having this structure.

[0002]

2. Description of the Related Art In the film forming and etching processes in semiconductor manufacturing, a microwave plasma processing apparatus capable of generating and maintaining stable plasma even at a low pressure has come to be used with the miniaturization of semiconductor devices. Most of them are ECR
This utilizes the (Electoron Cyclotron Resonance) phenomenon, and FIG. 5 shows an outline of the conventional configuration. In order to generate plasma using this apparatus, a plasma generation gas is introduced into the vacuum chamber 1 constituting the plasma chamber through the gas introduction pipe 14, and the microwave is transmitted from the microwave power source 2 while maintaining a desired pressure. Microwave power is introduced into the vacuum container 1 through the portion 22, and a magnetic field is formed in the vacuum container 1 by the solenoid 3 so that the strength of the magnetic flux density generated by the solenoid 3 satisfies the ECR condition with the microwave frequency. If so, the gas molecules are efficiently ionized and plasma is generated. At this time, plasma treatment is performed using microwaves that are pulse-oscillated to increase the peak power of the microwaves.

[0003]

In the conventional apparatus, a method of increasing the microwave power to be input is often used in order to increase the plasma density.
This method aims at the effect of increasing the energy of the electrons that ionize the gas molecules for plasma generation by increasing the microwave energy. Therefore, an increase in plasma density is accompanied by an increase in electron temperature in plasma. At this time, the microwave electric field that accelerates electrons for gas molecule ionization greatly differs depending on the site in the plasma chamber, and the magnetic field strength also varies depending on the site, so that the electron group in the plasma has a single energy level. Since they do not align and have a distribution of energy as a whole,
When the electron temperature rises, the number of high energy electrons (tens to hundreds eV) inevitably increases.

Therefore, this method has a problem in that the film quality is deteriorated by the incidence of high-energy electrons on the substrate. An object of the present invention is to configure a plasma processing apparatus capable of generating high-density plasma without increasing microwave power input to the plasma chamber, thereby suppressing deterioration of film quality due to incidence of high-energy electrons. Another object of the present invention is to provide an operating method that enables plasma generation with the highest density under the same microwave power when operating the plasma processing apparatus of this configuration.

[0005]

In order to solve the above problems, according to the present invention, a plasma is provided with a gas molecule excitation means that operates in synchronization with a pulse of a microwave that is repeatedly oscillated and stopped in a pulse shape. The processing device. In this case, an electron beam or the like that can generate electrons with uniform energy is suitable as the gas molecule excitation means. Further, it is preferable that the electron extraction electrode for the electron beam is made of the same metal material as the vacuum container in which plasma is generated.
Further, it is more preferable that the electron beam outlet and the plasma generating gas outlet into the plasma chamber are formed close to each other.

When the plasma generating gas excitation means is an electron beam generator, the method of operating the device is to generate an electron beam during the pause period of the microwave pulse and irradiate the plasma generating gas. The operating method is such that the energy of the electron beam extracted from the electron beam generator is adjusted to a region where the excitation cross-sectional area of the gas molecules for plasma generation is maximum.

[0007]

When the plasma processing apparatus is provided with the gas molecule exciting means that operates in synchronization with the microwave pulse, the exciting means metastables the gas molecules for plasma generation within the pause time of the microwave oscillated in a pulse shape. It can be excited to a level. Excited gas molecules can be ionized even at low electron energy, thus improving ionization efficiency and increasing plasma density without increasing microwave power, and thus the number of high energy electrons. It is possible to suppress the deterioration of the film quality due to the incidence of.

When the gas molecule excitation means is an electron beam generator, the electron beam is extracted by the DC potential difference between the cathode and the extraction electrode, so that the electrons in the extracted electron beam have uniform energy and deteriorate the film quality. The gas molecules can be excited to the metastable level without generating electrons having the energy of. In addition, by using an electron beam extraction electrode made of the same metal as the plasma chamber in consideration of contamination of the film, etc., in addition to the concern of contamination by attaching an electron beam generator,
Unknown adverse effects can be eliminated.

Furthermore, by bringing the electron beam outlet of the electron beam generator close to the gas outlet for plasma generation into the plasma chamber, a metastable level is established in the plasma generation gas introduced into the plasma chamber. The ratio of the number of gas molecules that are excited up to this point is high, and it is possible to generate a higher density plasma with smaller microwave power, and at the same time, it is possible to effectively suppress the deterioration of the film quality due to the incidence of high energy electrons. ..

Upon excitation, the gas has an excitation cross section, that is, a probability of being excited, and this probability changes depending on the excitation energy. Therefore, in the case of an electron beam generator,
The electron beam is generated during the pause period of the microwave pulse to irradiate the gas for plasma generation, and the extraction voltage (potential difference between the cathode and extraction electrode) that is the excitation energy.
By adjusting, and operating the device as the extraction voltage that maximizes the excitation cross section, plasma generation efficiency is improved,
Higher density plasma can be generated with smaller microwave power, and at the same time, deterioration of film quality due to incidence of high-energy electrons can be effectively suppressed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the structure of a plasma processing apparatus according to the present invention. The difference from the conventional example (FIG. 5) is that a plasma generating gas excitation means 8 is installed, and the excitation means can take in the pulse signal of the microwave power source 2 as a synchronization signal by the signal cable 7. It is a point. In this figure, an electron beam generator 8 is used as the excitation means. As shown in FIG. 2, the electron beam generator 8 forms the electron beam by extracting the thermoelectrons generated by energizing the hot cathode 82 having a negative potential with respect to the ground from the DC power supply 86 with the extraction electrode 81 having the positive potential with respect to the ground. Is what
In the present invention, the output voltage can be adjusted to the extraction electrode 81 via the switching element 84, for example, a thyristor or the like, which is on / off controlled by the synchronizing signal sent from the microwave power source 2 of FIG. 1 via the signal cable 7. A DC voltage is applied from the power supply 85. Reference numeral 83 in the drawing is a blocking electrode for blocking the thermal electrons from advancing to the side opposite to the extraction electrode 81 and effectively utilizing the generated thermal electrons for forming an electron beam.

FIG. 3 is an operation timing chart of this apparatus. Based on this figure, the operation method of this apparatus will be described below with reference to the case where nitrogen (N ₂ ) is used as the plasma generating gas. The inside of the vacuum container 1 is once brought to a high vacuum state, and then a gas for plasma generation is introduced through the gas introduction pipe 14 to maintain a desired degree of vacuum. When a direct current is applied to the solenoid 3 in this state and a microwave having a repetition period of the order of ms is applied in a pulsed manner, plasma is repeatedly generated and extinguished according to on / off of the microwave. Here, the oscillation signal from the microwave power source is taken in, and in the pulse-off state, an electron beam with uniform electron energy is irradiated toward the vicinity of the plasma-producing gas introduction portion in the vacuum container 1. The energy of the electron beam at this time is set to a region where the excitation cross section of the gas molecules for plasma generation becomes maximum.

FIG. 4 shows the excitation cross section of nitrogen due to electron collision. When an electron having an energy of about 10 to 15 eV collides, a molecule energetically in the ground level is excited to the metastable level. It indicates that the probability of being That is, when nitrogen is used as the plasma generating gas, the electron beam energy is set to about 10 to 15 eV. It is known that nitrogen molecules excited to a metastable level with high internal energy by collision with an electron beam remain at that level for several seconds, and even if the electron beam irradiation is interrupted before the pulse-on state, The nitrogen molecule excited to the metastable level is maintained in a high energy state. The energetically high molecule has an electron temperature of several eV
Even when colliding with low-energy electrons in the plasma, it is ionized more easily than the ground-state electrons, and as a result, an increase in the plasma density can be achieved without increasing the electron temperature of the plasma.

[0014]

As described above, the plasma processing apparatus according to the present invention is provided with the gas molecule exciting means, and the gas molecules for plasma generation are excited to the metastable level while the microwave is off. Ionization in the microwave on state is promoted, the peak power of microwave power is suppressed, the deterioration of the film quality due to the incidence of high energy electrons is suppressed, the plasma density is increased, and highly efficient plasma processing becomes possible.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the configuration of a plasma processing apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a configuration of an electron beam generator in FIG.

FIG. 3 is a diagram showing a timing chart of microwave oscillation and electron beam generation when an electron beam generator is used as the gas molecule excitation means in the device of the present invention.

FIG. 4 is a diagram showing the excitation energy dependence of the excitation cross section of nitrogen gas.

FIG. 5 is a longitudinal sectional view showing a conventional configuration example of a plasma processing apparatus targeted by the present invention.

[Explanation of symbols]

1 vacuum container (plasma chamber) 1a gas outlet 1b electron beam outlet 2 microwave power supply 6 wafer 8 electron beam generator (gas molecule excitation means for plasma generation)

Claims (5)

[Claims] 1. A plasma processing apparatus provided with a microwave power source for plasma generation that temporally pulse-oscillates plasma for processing an object to be processed in a plasma chamber in which a gas for plasma generation is introduced. A plasma processing apparatus comprising a gas molecule excitation means for plasma generation, which operates in synchronization with a pulse of a microwave power source and can adjust excitation energy. 2. The plasma processing apparatus according to claim 1, wherein the gas molecule exciting means for plasma generation is an electron beam generator. 3. The plasma processing apparatus according to claim 2, wherein the electron beam extraction electrode of the electron beam generator is made of the same metal as that of the plasma chamber. 4. The plasma processing apparatus according to claim 2, wherein the electron beam outlet of the electron beam generator is close to the gas outlet for plasma generation into the plasma chamber. Plasma processing equipment. 5. The method for operating a plasma processing apparatus according to claim 2, wherein an electron beam is generated during a pause period of the microwave pulse to irradiate the plasma generating gas, and the electron beam generating apparatus is used. A method for operating a plasma processing apparatus, comprising: operating by adjusting the energy of an electron beam extracted from the device to a region where the excitation cross-sectional area of gas molecules for plasma generation is maximum.