JP2966943B2 - Probe for measuring plasma parameters - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monitoring technique for monitoring and controlling plasma generated by electric discharge, and more particularly to a probe used for monitoring reactive plasma used in a thin film forming process.

[0002]

2. Description of the Related Art Conventionally, a plasma process has been applied to film formation, sputtering, etching, cleaning and other surface modification. In these processes, reaction conditions have been controlled by controlling the pressure, flow rate, discharge current, voltage, power, and the like of the raw material gas and diluent gas.

[0003] However, these control factors are only external control factors of the discharge and cannot be controlled by detecting the internal state of the discharge. In a plasma process, when the size and shape of a reactor used and the shape and arrangement of discharge electrodes for generating plasma are different, it is known that external control factors greatly change so that comparison is difficult. Therefore, it has not been possible to accumulate a unified and general technology for controlling the plasma process, and it has been difficult to make the technology universal.

[0004] On the other hand, there has been proposed a method for measuring an internal factor of plasma, which is a unified and generally used scale for describing the state of plasma. Specifically, a probe is inserted into a discharge atmosphere, current-voltage characteristics flowing from the plasma to the probe are measured, and electron density, electron temperature, and the like in the plasma (hereinafter, such as electron density and electron temperature, etc.) Plasma internal parameters are abbreviated as plasma parameters). It has been known that plasma parameters of non-deposited plasma have been successfully grasped so far, and the simulation technology is also effective. However, in a reactive plasma in which a deposition material is used, since the reactant deposits on the measurement probe, it is difficult to measure the current-voltage characteristics itself using the probe, and the plasma parameters are accurately grasped. I couldn't. For example, Japanese Patent Application Laid-Open
Japanese Patent No. 31422 discloses a method for measuring a plasma density by removing a thin film deposited on a probe by heating the probe. Specifically, the publication discloses an example of CVD of a silane gas diluted to about 1%, and discloses a method of turning off heating at the time of measuring probe characteristics and a method of continuously heating the probe. However, stable performance was not obtained under ordinary plasma CVD film forming conditions, for example, under practical film forming conditions such as a film forming speed of 3.0 nm / min or more. That is, the performance was still insufficient for use in a plasma process such as forming an amorphous silicon solar cell with a silane gas concentration of 10 to 100%.

[0005]

SUMMARY OF THE INVENTION The present invention overcomes the above-mentioned problems and provides a probe which can be used stably for a long time regardless of the silane gas concentration.

[0006] A thin film of silicon or the like evaporates when heated to a high temperature, but at a high temperature, a chemical reaction simultaneously proceeds, and the electrical characteristics of the probe itself change. Therefore, it is required to suppress the influence of this chemical reaction and measure the plasma parameters stably.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a probe used for measuring a plasma parameter by providing a probe in a plasma process, wherein the length of the probe exposed to the plasma is 3 mm or less. This is a probe for measuring parameters.

FIG. 1 shows an example of a probe according to the present invention.
1 is a schematic sectional view. The probe of the present invention is characterized by the length of the probe tip 1 for detecting a plasma current. The tip detects the plasma current by being exposed to the plasma. In a reactive plasma, a reactive substance is deposited and the current value changes with time. Therefore, the temperature at the tip of the probe is raised to about 800 ° C or higher, and this reactant is removed to stabilize the current value. At this time, if the tip is longer than 3 mm,
Since the effect of high-temperature heating to 800 ° C. or higher is not exhibited, and the stability rapidly decreases in current measurement over time, the thickness is set to 3 mm or less in the present invention. It is practical to have a length of 0.1 mm or more from the viewpoint of the manufacture of the probe.

For heating the tip portion, a temperature of 800 ° C. or higher can be easily achieved by applying a current to the probe. For effective heating, it is preferable that the diameter of the probe is small, but if the diameter is too small, the mechanical strength and the thermal durability decrease. In addition, the effect when a chemical reaction occurs is extremely large. A preferred probe diameter is 0.05 mm to 0.2 mm.

[0010] The tip portion is preferably joined to the lead wire in an insulating sheath as shown in FIG. In addition, the shorter the tip is, the less power required for heating the probe is practical.

[0011] The role of the probe is to conduct a minute current from the plasma to the circuit for measuring the plasma parameter, and as a material for the probe to exhibit the effect of the present invention effectively, it is chemically stable. A high refractory metal is preferred. For example, tungsten, molybdenum, tantalum, platinum, palladium and the like can be effectively used.

The shape of the probe is not particularly limited, and FIG. 2 is an example of the probe of the present invention. Fig. 2
This is an example in which a single-hole insulating sheath is used, but there is no particular limitation except that the length of the tip portion 4 exposed to plasma is 3 mm or less. Preferably, the insulating sheath is further housed in a protective tube. The probe is inserted into the reactor for the plasma process using the protective tube. Further, it is preferable to provide a means for changing the position of the probe in this protective cylinder. That is, by moving the protective tube in and out of the reactor, its position can be changed without damaging the probe.

Next, a specific example of a method for measuring a plasma parameter using a probe will be described. First, apply current to the probe and heat it to about 800 ° C or higher. Then, a few seconds after the current is cut off, a voltage sufficiently higher than the plasma potential is applied to the probe to obtain a constant electron current (electron saturation current). Further, a constant ion current (ion saturation current) is obtained by applying a voltage lower than the plasma potential. As described above, the plasma parameter is obtained from the gradient of the current-voltage characteristic curve of the probe obtained by sweeping the voltage applied to the probe from the electron saturation current region to the ion saturation current region. Measurement circuits for measuring plasma parameters include a probe, a current detector,
The probe is constituted by a bias power supply and the like, and the probe is provided with electric wiring for introducing a current for heating.

The measurement is performed by a single probe method using a single probe,
It is performed by a double probe method using a set of three probes, a three probe method using three probes, a heating probe method using a heated probe, a high frequency probe method applying a high frequency voltage, and the like. Will be

The probe of the present invention is installed in a processing plasma device such as plasma CVD, sputtering, etching, plasma cleaning, plasma polymerization, or surface modification by plasma, and can effectively measure plasma parameters.

[0016]

EXAMPLE 1 FIG. 3 shows a specific apparatus for carrying out the present invention. As the processing plasma device, a capacitively coupled high-frequency glow discharge device is used, and the reaction vessel 7 is made of stainless steel. As the probe for measuring the plasma parameters, a double probe 8 having a shape shown in Fig. 1 and using a tongue wire having a diameter of 0.1 mm and having a length of 1.5 mm exposed to plasma was used. . A bias voltage was applied between the probes 8, and a current value flowing into the probes 8 at this time was measured by an ammeter 9. From the voltage-current characteristics of the probe 8, the electron density,
Plasma internal parameters such as ion density and electron temperature were determined. Monosilane 1 sccm, hydrogen 10
Film formation was performed at a sccm pressure of 0.2 torr and a discharge power of 40 W. The deposition rate was 9.0 nm / min. Plasma parameters are
Measurements were taken every 10 minutes for 90 minutes. Even after 90 minutes, the current-voltage characteristics of the probe did not change, confirming that extremely stable measurement was performed. Electron density obtained by this method,
The reproducibility of the values of ion density and electron temperature was within 2%.

Example 2 In Example 1, the length of the portion of the probe exposed to the plasma was set to 3.0 mm, and the measurement was performed. The current-voltage characteristics gradually changed after 60 minutes. It was confirmed that the probe was practically no problem because it could be used for 60 minutes. 90
In the minutes after measurement, the plasma parameters were measured with good reproducibility within 20% reliability.

Example 3 An apparatus shown in FIG. 4 using a glass reactor was used as a processing plasma apparatus. The probe for measuring the plasma parameters has the shape shown in Fig. 2 and the diameter.
A double probe 8 using a 0.1 mm tungsten wire and having a length of 2.0 mm exposed to plasma was used. A bias voltage was applied between the plasma and the probe 8, and a current value flowing into the probe 8 at this time was measured by an ammeter 9. Probe 8
Plasma internal parameters such as electron density, ion density, and electron temperature were determined from the current-voltage characteristics of. Film formation was performed using 2 sccm of disilane, 10 sccm of hydrogen, a pressure of 0.1 torr, and a discharge power of 40 W as source gases. The deposition rate was 15 nm / min. Plasma parameters were measured every 10 minutes for 90 minutes. Even after 90 minutes, the current-voltage characteristics of the probe did not change, confirming that extremely stable measurement was performed.
The reproducibility of the electron density, ion density, and electron temperature values obtained by this method was within 3%.

Comparative Example 1 In Example 1, the length of the portion of the probe exposed to the plasma was 4.0 mm, and the measurement was performed. The current-voltage characteristics gradually changed after 5 minutes. In plasma CVD, the use for 5 minutes involves practical problems and falls outside the limited conditions of the present invention. In the measurement after 90 minutes,
Plasma parameters contained a 200% error.

[0020]

FIG. 5 shows the measurement errors of the plasma parameters obtained from the above Examples and Comparative Examples with respect to the length of the probe exposed to the plasma. As is clear from the figure, the reproducibility of the plasma parameters measured using the probe of the present invention was extremely high, and the controllability and stability of the plasma were significantly improved. As a result, the reproducibility of film formation, sputtering, etching, cleaning, surface modification, and the like to which the present invention was applied was significantly improved. In addition, by improving controllability,
The film formation process can also be precisely controlled, greatly contributing to quality improvement and structure control of the thin film. in this way,
The present invention is a very useful invention for a processing plasma.

[Brief description of the drawings]

FIGS. 1 and 2 are schematic cross-sectional views of an example of a probe according to the present invention.

FIG. 3 is a diagram showing an apparatus for measuring a plasma parameter in the first embodiment.

FIG. 3 is a diagram showing an apparatus for measuring a plasma parameter in a third embodiment.

FIG. 5 shows the effect of the present invention, in which the horizontal axis shows the length of the probe and the vertical axis shows the measurement error of the plasma parameters after 90 minutes have elapsed.

[Explanation of symbols]

 1: probe 2: lead wire 3: insulating sheath 4: probe 5: lead wire 6: insulating sheath 7: stainless steel reactor 8: double probe 9: current detector 10: high frequency power supply 11: Condenser 12: High-frequency electrode 13: Ground electrode 14: Capacitive probe for plasma potential measurement 15: Bias power supply 16: High-frequency potential detection circuit 17: High impedance circuit 18: Amplifier 19: Power supply for probe heating 20: Glass reactor 21: Metal plate electrode

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05H 1/00 H01L 21/3065 H01L 21/31 C23C 16/52

Claims (1)

(57) [Claims] 1. The length of a probe exposed to plasma is 3 mm.
A probe for measuring a plasma parameter, characterized in that: