JP3911997B2 - Plasma doping equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technical field of introducing a substance in the vicinity of a solid surface, particularly to a doping technique using plasma.
[0002]
[Prior art]
As a plasma source for plasma doping, various sources are used in principle. For example, a DC plasma source and a high-frequency plasma source can be cited as typical examples. In order to generate a high plasma density at a particularly high degree of vacuum, an ECR plasma source or helicon wave plasma source equipped with a magnet is used.
[0003]
Hereinafter, a conventional example will be described with reference to a document in which the inventors have used an ECR apparatus in the past.
[0004]
Reference: Bunji Mizuno et al., “Plasma Doping Method for Trench Side Walls of 0.5 Micron or Less”, pages 319-322, 19th International Solid Device Material Conference, Extended, Abstract, 1987 (Bunji MIZUNO et al., Plasma Doping into the side-wall of a sub-0.5 um width trench, pp319-322, Extended Abstract of the 19 th Conference on Slid State Devices and Materials, is a Tokyo, 1987, the Japan Society of Applied Physics).
[0005]
According to this cited document, in order to achieve a sufficient plasma density at a vacuum degree of 5 × 10 ^-4 Torr in the reaction vacuum chamber, in addition to the 2.45 GHz microwave, a magnetic field of 825 Gauss is applied, and Electron Cyclotron Resonance ECR The state is realized.
[0006]
The reason for plasma doping at a high degree of vacuum is that the reaction with the surface of the sample to be processed is performed. Doping is dominant without lowering the density of atoms and molecules in the vacuum chamber and so-called CVD (Chemical Vapor Deposition). This is a necessary condition.
[0007]
In order to exhibit higher doping efficiency under such conditions, it is effective to realize a higher plasma density. For this purpose, the plasma density is improved by applying the above-mentioned ECR conditions or using a helicon antenna together with a divergent magnetic field forming magnet. The value of the magnetic field used in combination with the helicon wave is typically about 50 Gauss.
[0008]
[Problems to be solved by the invention]
In the conventional example, a magnet is used to generate a high-density plasma with a higher vacuum, but this alone cannot produce the required plasma homogeneity. In particular, non-uniformity becomes a problem when uniformly doping a planar semiconductor substrate or a liquid crystal substrate having a large area.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention controls the plasma in the vicinity of the sample surface by applying a potential to the processing table on which the sample to be processed is placed and generating a bias between the plasma and the sample surface. Since the magnetic field generated by the magnet used in combination with the coil of the helicon wave plasma source is not necessary, this is excluded so as not to increase the size, weight, and cost of the apparatus.
[0010]
Of course, a slight decrease in density occurs, but there is almost no influence at a dose of 10 × 10 ¹⁶ cm ⁻² used in semiconductors and liquid crystals, which is the main application.
[0011]
The present invention also includes a configuration in which optimum plasma can be obtained even when the coil and magnet of the helicon wave plasma source are used in combination.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
A plasma doping apparatus and method using a helicon wave plasma source that does not use a magnet will be described below with reference to FIG. FIG. 1 shows the structure of the apparatus.
[0013]
The structure of the main body is composed of a vacuum chamber 1 and a helicon wave plasma source 2 excluding structural parts. One or more vacuum pumps 3 are installed in order to make the vacuum chamber 1 high vacuum. A sample stage 4 is installed in the vacuum chamber 1 and a sample 5 is placed thereon. In this drawing, a flat sample 5 is shown, but it may be of any form. Of course, it is naturally necessary to provide a suitable sample stage 4. On the other hand, a conductive line 6 for supplying electric power to the helicon wave plasma source 2 is provided and a power source 7 is connected.
[0014]
A gas introduction port 8 installed in the vacuum chamber 1 is connected to a gas source necessary for generating plasma, and a desired gas is introduced into the vacuum chamber 1.
[0015]
A high frequency is supplied from the power source 7 to the conductive wire 6, and a desired gas is introduced from the gas inlet 8 before and after the plasma 9 is generated. Another power source 10 is connected to the sample stage 4. The power supply 10 may be either high frequency, low frequency alternating current or direct current. Further, an arbitrary form of pulse power source or a set of pulses may be superimposed on the AC or DC power.
[0016]
The potential difference generated between the generated plasma 9 and the sample 5 is controlled mainly by the power of the power source 10 connected to the sample stage 4. Atomic and molecular ions contained in the plasma 9 are injected into the surface of the sample 5 by this potential difference. At the same time, the process of adsorbing atoms and molecules of electric neutral radicals contained in the plasma 9 to the surface of the sample 5 and the so-called knock-on process in which the adsorbed atoms and molecules are struck from the surface of the sample 5 by the ions are mixed. Occur.
[0017]
In this embodiment without a diverging magnetic field, the diameter of the plasma 9 is small immediately after leaving the helicon wave plasma source, and the uniformity is not sufficient. However, sufficient uniformity can be realized when the plasma 9 is controlled by the electric power or magnetic field superimposed on the sample stage 4 and reaches the sample 5.
[0018]
When plasma doping is performed, a process is performed by introducing a certain amount of gas. At that time, it is important to exhaust the vacuum chamber 1 to a sufficient level or more. In this embodiment, the exhaust speed is set to 1400 L / sec and sufficient exhaust is performed to generate a high vacuum and high density plasma condition that contributes to improving the controllability of the doping process.
[0019]
Next, a plasma doping apparatus in the second embodiment will be described. Here, an embodiment in which the internal volume of the vacuum vessel is made variable in order to generate an appropriate plasma potential will be described with reference to FIG. In the figure, parts corresponding to those in FIG. In FIG. 2, two variable systems are described together. One is a mechanism for making the internal volume of the vacuum chamber 1 variable by providing a bellows 11 at an intermediate portion of the vacuum chamber 1. The other is a vacuum chamber 1 provided with a sliding mechanism 13 using a driving device 12 while being kept electrically insulated from the vacuum chamber 1 while keeping a vacuum on the sample table 4 and the inner wall of the vacuum chamber 1. The effective internal volume is made variable.
[0020]
Although both may be used together, it is often sufficient to employ either one. The purpose of this embodiment is to change the relationship between the volume of the vacuum chamber 1 and the surface area of the sample 5 to be processed according to the desired potential difference in order to appropriately generate a potential difference generated between the plasma and the sample to be processed. is there. When the area of the inner wall of the vacuum chamber 1 is increased relative to the area of the sample 5, a relatively high potential difference can be easily obtained. Conversely, when the area of the inner wall of the vacuum chamber 1 is decreased, a low potential difference can be easily obtained. Become. These quantitative relationships use the shape of the sample 5 to be processed, the form of the vacuum chamber 1, the gas to be used, and here, as an example, an example in which electric power is applied to the helicon wave plasma and the sample stage 4, but the form of the plasma source However, the optimum state can be created by making the internal volume of the vacuum chamber 1 variable.
[0021]
【The invention's effect】
As described above, according to the present invention, by controlling the plasma by controlling the electric field in the vicinity of the substrate to be processed, it is possible to effectively perform the plasma doping without using the magnet electromagnet for the divergent magnetic field as ancillary equipment. It can be implemented and contributes to cost reduction.
[0022]
In addition, when plasma doping is performed using a helicon wave plasma source, an effective potential difference between the plasma and the sample to be processed can be generated by a mechanism that can be adjusted by changing the effective inner wall area of the vacuum chamber. High doping is possible.
[Brief description of the drawings]
FIG. 1 is a block diagram of a plasma doping apparatus in a first embodiment of the present invention. FIG. 2 is a block diagram of a plasma doping apparatus in a second embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Helicon wave plasma source 3 Vacuum pump 4 Sample stand 5 Sample 6 Conductive wire 7 Power source 8 Gas inlet 9 Plasma 10 Power source B
11 Bellows 12 Drive 13 Slide mechanism

Claims (1)

  A plasma doping apparatus using a helicon wave plasma source, comprising a variable volume means for changing the volume of a reaction vacuum chamber in accordance with a plasma potential between a generated plasma and an object to be processed. .

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