JPH10312899A - Plasma processing method and plasma processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma processing method and a plasma processing device superior in fine machinability at a low pressure and excellent in reproducibility. SOLUTION: Reactive gas is introduced into a chamber 1 being a vacuum room, and plasma is generated in the chamber 1 by pulse high frequency power so as to conduct dry etching of a sample to be etched 6 placed in the chamber 1. A period wherein the plasma is generated by continuously supplying the high frequency power is provided, and impedance matching is conducted in this period. Desirably, effective input power in the case of plasma generation by the pulse high frequency power and the input power in the case of the plasma generation by the continuous high frequency power supply are set to be nearly equal mutually.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse plasma processing method using high frequency discharge and an apparatus therefor.

[0002]

2. Description of the Related Art A plasma is generated using a high-frequency discharge, and various processes such as dry etching for fine processing, sputtering, plasma CVD, and ion implantation for forming a thin film are performed using the plasma. I have. In addition, plasma generation in a high vacuum is required for miniaturization of processing dimensions and high-precision control of film quality.

[0003] In the following, as one application example of a plasma processing method using plasma, a case where plasma processing is used for dry etching, which is a kind of fine processing, will be described.

[0004] The progress of modern high-density semiconductor integrated circuits is bringing about a change that can be compared with the industrial revolution. Higher densities and higher integration of semiconductor integrated circuits are accompanied by miniaturization of element dimensions, improvement of devices, and chips. This has been realized by increasing the size of the area. At present, the element dimensions have been advanced to about the wavelength of light used for fine processing, and the use of excimer lasers and X-rays for lithography is promising. Here, it can be said that dry etching plays an important role along with lithography in realizing the formation of a fine pattern.

[0005] Dry etching utilizes a chemical or physical reaction on a solid phase surface of a substrate to be processed with a gas phase caused by radicals, ions, or the like present in a plasma to remove unnecessary portions of a thin film or a substrate. This is a processing technique for removing. Reactive ion etching (RIE), which is the most widely used dry etching technique, removes unnecessary portions of the sample surface by exposing the sample to a high-frequency discharge plasma of an appropriate gas to cause an etching reaction. is there. Necessary portions, that is, portions that are not removed by dry etching, are protected by a photoresist pattern usually used as a mask.

In order to further refine the processing in the future, it is necessary to make the directionality of the ions during dry etching uniform. To achieve this, it is necessary to reduce the scattering of ions in the plasma. It is essential. It is effective to lower the pressure in the plasma generator and increase the mean free path of the ions in order to make the directionality of the ions uniform.However, if the pressure in the plasma chamber is lowered, the radical density lowers and the etch density decreases. The problem that the speed becomes low occurs.

As a countermeasure, a high-density plasma device such as an inductively coupled plasma device or a helicon plasma device is being introduced. The high-density plasma device can generate one to two digits of high-density plasma compared to the above-described conventional parallel plate RIE device. Therefore, a dry etching rate equal to or higher than that of the RIE apparatus can be achieved even under a low pressure of about several Pa, which is lower by one to two digits.

[0008]

However, it has been found that the following problems occur in dry etching using a high-density plasma apparatus such as the above-described inductively coupled plasma apparatus or helicon plasma apparatus.

First, abnormalities in the etched shape due to charge-up, second, microloading effects, and third, deterioration and destruction of the gate insulating film.

A typical example of the occurrence of abnormalities in the etching shape due to charge-up is a notch in polycrystalline silicon etching. This phenomenon is that when polycrystalline silicon is etched by high-density plasma, a wedge-shaped notch is formed on the inner bottom surface of the outermost line pattern of the line-and-space pattern. Is believed to be due to different patterns of supply (e.g.,
K, K, Chi et al., 1995 DRY PROCES
S Symposium Proceedings, p. 75, The Institute of Electrical Engineers of Japan).

Further, such localization and non-uniformity of the electric charge also affect the etching rate itself. For example, if the photoresist mask is positively charged during etching by positive ions, the smaller the mask opening, the stronger the function of blocking the entrance of positive ions into the opening. Is slow, a so-called microloading effect may occur.

In addition, such an unbalanced charge supply causes deterioration and destruction of the gate insulating film of the MOS transistor. For example, it is known that when the gate insulating film becomes extremely thin, about 10 nm or less, the mutual conductance of a MOS transistor exposed to plasma deteriorates, and in extreme cases, dielectric breakdown occurs (for example, ERI).
GUCHI et al., IEICE TRANS. ELECT
RON. , VOL. E78-C, p. 261, The Institute of Electronics, Information and Communication Engineers). When the transistor size is reduced to 1 micron or less due to miniaturization, the LSI includes a transistor having a so-called antenna structure that is three to five digits or more of the wiring area or the transistor area. Since the antenna structure functions to increase the non-uniformity of the electric charge, deterioration and destruction of the gate insulating film due to plasma with miniaturization are considered to be an increasingly important issue.

As a method for solving the above-mentioned problem of the high-density plasma process, a pulse plasma process has been proposed (for example, Ohtake et al., DRY PROCESS SYMPOSIUM 1995,
p. 45, The Institute of Electrical Engineers of Japan). What is a pulsed plasma process?
An object of the present invention is to solve these problems by supplying high-frequency power for plasma generation in a pulse shape and providing an off time to alleviate local accumulation of electric charge. Actually, there is a decrease in electrons and generation of negative ions during the off-time, and it has been found that this effect improves the uniformity of the charge distribution.

However, considering practical use, the controllability and reproducibility of the conventional pulsed plasma process were not sufficient. It has been found that this is one of the main reasons that the impedance matching cannot be achieved in a reproducible constant state because pulse power is applied to the plasma. An impedance matching device is usually provided between a high-frequency power supply that supplies normal continuous high-frequency power and a plasma processing chamber to perform impedance matching with a high-frequency power supply having a characteristic impedance of 50Ω. In general,
The impedance matching device automatically monitors the reflected power from the load via the built-in directional coupler, and automatically changes the variable capacitance and variable inductance so that the value becomes the minimum value. To achieve. When such an impedance matching device is applied to pulsed plasma, the reflected power level is reduced when the pulse is off, so that matching cannot be performed accurately, sensitivity is effectively reduced, and a plurality of matching points appear. As a result, since the same matching conditions are not always obtained, the process results are different from time to time, and the reproducibility is deteriorated.

For this reason, conventionally, in order to improve reproducibility, an automatic control function of the impedance matching device is not used, and the impedance matching device is often used in a manual state. However, in the state of the manual, the impedance matching is not always the best, and as described above, the reproducibility is insufficient and the industrial use is not satisfactory.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a plasma generation method which is excellent in fine workability under low pressure and has good reproducibility.

[0017]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is to introduce a reactive gas into a vacuum chamber, generate a plasma in the vacuum chamber by pulsed high frequency power, and install the plasma in the vacuum chamber. A plasma processing method for performing plasma processing of a sample that has been provided, wherein a period for continuously supplying high-frequency power to generate plasma is provided, and impedance matching is performed within the period. .

At this time, it is desirable to provide a period in which plasma is generated by continuously supplying high frequency power at the beginning of the plasma processing. Further, it is desirable that the effective input power when generating plasma by pulsed high-frequency power and the input power when generating plasma by continuously supplying high-frequency power are substantially equal.

The present invention further provides a plasma processing apparatus for introducing a reactive gas into a vacuum chamber, generating plasma by pulsed high-frequency power in the vacuum chamber, and performing plasma processing on a sample placed in the vacuum chamber. A high-frequency power supply for supplying pulsed and continuous high-frequency power, and an impedance matching device are provided, and impedance matching is performed while the high-frequency power is supplying continuous high-frequency power.

It should be noted that such a high-frequency power supply capable of supplying pulsed and continuous high-frequency power may be used for plasma generation, or may be connected to a sample stage for bias application. Further, the high-frequency power supply capable of supplying pulse and continuous high-frequency power according to the present invention has a function of generating a gate signal when continuous high-frequency power is generated.

With the above configuration, the reproducibility of impedance matching is improved, so that the reproducibility of the process is greatly improved.
In addition, problems due to impedance mismatch at the power supply and matcher are also greatly reduced. According to our experimental results, when the high-frequency input power of continuous plasma is equal to the time-average input power of pulsed plasma, the plasma density generated by continuous plasma is approximately equal to that during pulsed plasma. I know. Therefore, the state of impedance matching during the period of the pulse plasma is further improved.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A plasma generating method and a plasma generating apparatus according to an embodiment of the present invention will be described below with reference to the drawings. Note that, in this embodiment, a description is given of an example in which dry etching, which is a kind of microfabrication, is performed as processing using plasma.

FIG. 1 is a schematic view showing a structure of a dry etching apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a chamber which is grounded and has an inner wall covered with an insulator such as ceramic, Teflon or quartz, and 2 denotes a spiral electrode to which pulsed high frequency power is applied. It is connected to a high-frequency pulse power supply 4 for plasma generation capable of supplying high-frequency power. The spiral electrode 2 is a dielectric plate 5 made of ceramic or the like.
A plasma is generated in the chamber 1 by the induced electromagnetic field through the. Note that the chamber 1 may have a double structure having an inner chamber made of quartz or the like.

Reference numeral 7 denotes a metal sample stage, the surface of which is coated with an insulating material. On the sample stage 7, a sample 6 to be etched is placed. The sample stage 7 is connected to a bias RF power supply 9 via a coupling capacitor 8.

A probe 10 is inserted into the chamber 1 from the side. Real-time plasma data is collected and transferred to the plasma controller 11. The probe 10 may be a mechanism that is inserted into the plasma only at the time of measurement in order to prevent corrosion due to plasma and deterioration of characteristics due to film deposition. Further, if an interferometer using a microwave is used in place of the probe 10, there is no concern about the above-described deterioration, and plasma data can be acquired for an arbitrary time. A gate signal is sent from a terminal 12 for generating a gate signal during continuous high-frequency generation to the impedance matching device 3 from the high frequency pulse power supply 4 for plasma generation, and the automatic impedance matching function is operated only when the gate signal is on. I have.

Next, a dry etching method using the dry etching apparatus configured as described above will be described with reference to FIG.

FIG. 2 shows a time change of various parameters in the dry etching apparatus according to the embodiment of the present invention. First, time t from the plasma generating high-frequency power supply 4
From = 0 to Tcw, continuous high-frequency power is supplied. Tcw is usually longer than the time required for the impedance matching device 3 to achieve impedance matching, and is usually several seconds. In the present embodiment, Tcw is set to 5 to 10 seconds. During that time, a gate signal was sent from the gate signal terminal 12 of the plasma generating high-frequency power supply 4 to the impedance matching device 3, and an instruction was made to automatically perform impedance matching.

Next, after t = Tcw, a high frequency pulse for plasma generation was supplied to the spiral electrode 3 from the high frequency power supply 4 for plasma generation (pulse high frequency power was supplied). Basic high frequency power frequency is 13.56MHz, 27MHz,
The frequency was set to 54 MHz. In addition, the high frequency input power of the continuous plasma at the time of performing the impedance matching was set to 200 W, the pulse frequency of the pulsed plasma was set to 100 kHz, the duty ratio was set to 50%, and the input power was set to 400 W.
This means that high-frequency input power for continuous plasma generation is
The purpose is to make it approximately equal to the time average input power in the pulsed plasma.

Thereafter, chlorine gas was added as a reactive gas to 50.
sccm, HBr gas was introduced into the 25 sccm chamber 1, and the pressure was adjusted to 1 to 3 Pa. The electron density was almost half or less in 20 μsec after turning off the plasma generating high-frequency power supply 4, and a rapid decrease in the electron density in the afterglow plasma was observed. When this was applied to the etching of phosphorus-doped polycrystalline silicon, the etching rate was 300 to 800 nm / sec, the oxide film selectivity was as good as 20 to 100, and the etching shape was anisotropic. No notch or shape abnormality due to charge-up was observed.

It is considered that the charge-up is reduced by the method of the present invention, in addition to the low electron density, the contribution of the nature of the negative ions is large. When high-energy positive and negative ions are incident on the sample to be etched, not only the charge of the incident ions is accumulated on the surface, but also the effect of secondary electrons emitted from the surface with the incident ions cannot be ignored. At the incidence of positive ions, secondary electron emission proceeds to increase the accumulation of positive charges, but at the incidence of negative ions, secondary electron emission acts to cancel the accumulation of negative charges. For this reason, the charge-up phenomenon is suppressed.

The present invention has been described with the embodiment. In the embodiment, the case where continuous plasma generation is performed at the time of plasma ignition is shown. However, continuous plasma generation is inserted in the middle of the process, and good impedance matching is achieved. It may be realized. In the embodiment of the present invention, the case of an etching apparatus has been described. However, it is needless to say that the present invention can be applied to an apparatus for performing processing using high vacuum plasma, such as plasma CVD, sputtering, and an ion source of an ion implantation apparatus. No.

[0032]

As described above, in the method of the present invention, a continuous plasma is generated, impedance matching is performed during the period, and the impedance matching state is fixed during the pulse plasma generation period. Further, the high-frequency input power for continuous plasma generation is made approximately equal to the time-average input power for pulsed plasma. The high-frequency input power of the continuous plasma is made equal to the time-average input power of the pulsed plasma, and the density of the plasma generated in the continuous plasma is approximately equal to that during the pulsed plasma, thereby improving the impedance matching state. Since the reproducibility of the impedance matching is improved in this way, the reproducibility of the process is also greatly improved, and the trouble due to the impedance mismatch at the power supply and the matcher is also greatly reduced.

The present invention is directed to high-precision plasma etching and CV
Applicable to D. According to the apparatus of the present invention, it is possible to realize etching and film deposition which are excellent in fine workability, have high mass productivity, have good uniformity, and have very little damage to devices such as gate oxide film destruction.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a dry etching apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing changes over time of various parameters in a dry etching method according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Chamber 2 Spiral electrode 3 High frequency pulse power supply for plasma generation 4 Dielectric plate 5 Sample to be etched 6 Metal sample base 7 DC pulse power supply for bias 8 Probe 9 Plasma controller 10 Capacitive circuit 11 Electron density detector 12 Bias Bipolar pulse power supply 13 Pulse μ-wave power supply 14 Mode converter 15 Coil

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H01L 21/3065 H01L 21/302 A

Claims (4)

[Claims] 1. A plasma processing method for introducing a reactive gas into a vacuum chamber and generating plasma by pulsed high-frequency power in the vacuum chamber to perform plasma processing on a sample installed in the vacuum chamber. A plasma processing method, comprising: providing a period in which high-frequency power is continuously supplied to generate plasma; and performing impedance matching within the period. 2. The plasma processing method according to claim 1, wherein a period in which high-frequency power is continuously supplied to generate plasma at the beginning of the plasma processing is provided. 3. The method according to claim 1, wherein the effective input power when generating plasma by pulsed high-frequency power is substantially equal to the input power when generating plasma by continuously supplying high-frequency power. The plasma processing method as described above. 4. A plasma processing apparatus for introducing a reactive gas into a vacuum chamber, generating plasma by pulsed high-frequency power in the vacuum chamber, and performing plasma processing on a sample installed in the vacuum chamber. A plasma processing apparatus, comprising: a high-frequency power supply that supplies pulsed and continuous high-frequency power; and an impedance matching device, wherein impedance matching is performed during a period in which the high-frequency power supply supplies continuous high-frequency power.