JPH01243359A - Plasma doping - Google Patents

Abstract

PURPOSE:To apply doping to groove side walls or the like by utilizing the electron cyclotron resonance absorption of microwaves to perform the discharge decomposition via the plasma decomposition and applying the pulse magnetic field to ion particles generated by decomposition to provide kinetic energy on a substrate to be doped or near it. CONSTITUTION:A vacuum chamber 11 is kept vacuum with an exhaust hole 12, microwaves from a microwave oscillator 14 are fed to a plasma generation chamber 15 through a wave guide 13, at the same time the magnetic field from an electromagnet 16 is applied. Under this condition, the source gas such as B2H6 is introduced through a gas guide port 17, the pulse electric field from a pulse power source 18 is applied to a substrate holder 19. Plasma is radiated to an Si substrate 100 supported by the holder 19 through a plasma window 21 to implant B ions, kinetic energy is applied to B ions by the pulse current, the doping controllability is improved, doping is effectively applied to finely machined portions.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates primarily to a plasma doping method for implanting impurities into semiconductors, insulators, metals, and thin films thereof.

BACKGROUND OF THE INVENTION Conventionally, so-called ion implantation, in which an impurity element to be implanted is ionized and accelerated by a high electric field of 100 keV and implanted into a substrate, has been widely used as a method for diffusing impurities into a solid. However, due to the recent increase in the density of integrated circuits, it has become necessary to form extremely shallow junctions, and the gas containing impurities must be plasma decomposed.
There are many attempts to achieve shallow junctions by accelerating with a low electric field below V. Among these, a plasma ion doping device that uses microwave electron cyclotron resonance absorption (ECR) to generate plasma has a configuration as shown in FIG. A vacuum chamber 31 is evacuated to a vacuum through an exhaust hole 32. Microwaves are introduced from a microwave oscillator 34 into a plasma generation chamber 35 through a waveguide 33 . Electromagnet 3
6 applies a magnetic field to the plasma generation chamber 35. 3
Reference numeral 7 denotes a gas introduction port through which impurity gases such as B2H6, PH3, and As H3 and carrier gases such as H2, He, and Ar are introduced. Plasma with a high degree of dissociation can be obtained by setting the strength of the magnetic field to satisfy the electron cyclotron resonance conditions. The ions in the generated plasma hit the substrate 3
The DC electric field applied by the DC power source 8 passes through the plasma extraction window 39, reaches the substrate holder 40, and is driven into the substrate 100 on the holder 40.

Problems to be Solved by the Invention However, in such conventional plasma doping technology, since ions are drawn into the substrate at low voltage, insulating deposits of dopant elements are formed on the substrate surface, preventing ions from reaching the substrate and causing impurities. There was a problem with doping controllability. In addition, in response to the demand for forming shallow junctions on the sidewalls of deep grooves formed on substrates in recent miniaturization technology, doping is applied only to the bottom of the grooves because the ion acceleration direction is only perpendicular to the substrate. There was also the problem that it could not be done. Furthermore, since the plasma distribution is large due to the electric field distribution caused by the microwave mode, there is a problem that it appears as a doping treatment distribution. In addition, in order to increase the processing area, the plasma chamber must be placed at a considerable distance, so the highly dissociated plasma is attenuated by collisions between particles, resulting in poor processing efficiency. This has hindered the practical application of plasma doping equipment and such doping methods.

The present invention aims to solve such problems.

Means for Solving the Problems In order to solve the above problems, the present invention uses a frequency capable of imparting kinetic energy to the ion particles contributing to the processing that are present in the substrate to be processed or in the plasma near the substrate. It has been found that the above problems can be solved by applying a pulsed electric field having a The present invention provides a high-performance plasma doping apparatus and doping method using the above-mentioned means.

Effects The effects of the present invention produced by using the above-mentioned means are as follows. In the conventional method, the ions were extracted only by the attenuation of the applied magnetic field and the DC electric field applied to the substrate, but in the present invention, kinetic energy is regenerated mainly for the ions near the substrate, and the generated ion species are extracted. It is used effectively, and the direction of movement is also given to the direction other than perpendicular to the substrate. This makes it possible to always give kinetic energy to the ions even if insulating deposits are formed on the substrate surface, and it is also possible to perform fine processing. This makes it possible to effectively dope the side walls of the grooves.

Embodiment As an embodiment, an example in which the plasma doping apparatus of the present invention is applied to boron doping into a crystalline silicon substrate 100 will be described.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Representative embodiments of the present invention will be shown below based on the drawings. FIG. 1 is a schematic diagram of a plasma ion doping apparatus of the present invention. 11 exits the vacuum chamber and is evacuated to vacuum through the exhaust hole 12. Microwaves are introduced from a microwave oscillator 14 into a plasma generation chamber 15 through a waveguide 13 . A magnetic field is applied to the plasma generation chamber 15 by the electromagnet 16 . 1
Reference numeral 7 denotes a gas inlet port through which a source gas such as B2H6 is introduced.

Reference numeral 18 denotes a power source for applying a pulsed electric field, which is added in the present invention, and the pulsed electric field is applied to the substrate holder 19. By setting the strength of the magnetic field in the plasma generation chamber to satisfy electron cyclotron resonance conditions, a plasma 20 with a high degree of dissociation and containing many ions is generated. The generated plasma passes through the plasma extraction window 21 and reaches the substrate holder 19. Furthermore, in the vicinity of the substrate holder, the AC power supply 18 again gives kinetic energy to mainly ions and electrons in the plasma and directs them to the crystalline silicon substrate 100. Ions containing boron are implanted to form an impurity doped layer. At this time, if the strength of the magnetic field near the substrate is set to 100 to 300 Gauss by setting the electromagnet, kinetic energy can be given to the ions more effectively. The frequency of the pulse is set at 50 Hz to 500 KHz in order to mainly give energy to ions containing boron and hydrogen ions. If the frequency is lower than these, if a highly resistive film is deposited on the substrate surface, no electric field will be applied to the plasma, and if the frequency is higher, ions will no longer be able to follow it. Furthermore, since the magnetic flux density near the substrate is several tens to hundreds of Gauss, the applied electric field causes high-frequency magnetron discharge, resulting in a state in which the plasma from the microwave electron cyclotron and the high-frequency plasma are superimposed. This is different from the original highly active plasma.

Further, a case will be described in which the pulse width ratio is changed in order to lengthen the time for drawing positive ions into the substrate.

The equipment is common, and by lengthening the time of the negative potential of the pulse, the time for accelerating the ions and implanting them into the substrate can be lengthened.

However, if this is made too long, a high resistance layer will be formed on the substrate, which will become charged and ions will not be accelerated.
Efficiency will actually deteriorate. Therefore, it is preferable to set the ratio of the pulse width in the negative potential state to the pulse width in the positive potential state to be between 1:10 and 10:1, and an optimum condition exists between this range.

Effect of the invention The effects of the present invention are as follows.

First of all, doping controllability is improved. In Fig. 2(a), the pulse voltage of, for example, 20 KHz applied to the substrate is kept constant, the doping time is varied, and B
2 shows the change in sheet resistance when crystalline silicon is doped with boron by plasma decomposition of 2 Hs. It can be seen that the sheet resistance decreases as the doping time increases. FIG. 2(b) shows the change in sheet resistance when the pulse width ratio is changed when silicon wafers are doped using the same B2H6 gas. Similarly, it can be seen that the sheet resistance decreases as the pulse width of the negative voltage increases. These results were also very uniform within a 5 inch silicon wafer. The second effect is that the side walls of deep grooves can be doped with good uniformity.

The third effect is that a junction can be formed by simultaneously implanting an impurity element exhibiting a pa type and an impurity element exhibiting an n type in a single implantation. Figure 3 shows an example of B
2 shows the depth distribution of impurities when a junction is formed by simultaneous plasma decomposition of 2 He and A S H3. The horizontal axis is depth and the vertical axis is concentration. The concentration of boron and arsenic is 0.17z
It can be seen that the reversal occurs at point m, indicating that shallow joints were implanted and formed at the same time.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the plasma ion doping apparatus of the present invention, and Figures 2 (a) and (b) show changes in sheet resistance when boron is implanted into crystalline silicon by varying the doping time and pulse width ratio, respectively. Figure 3 shows the depth distribution of impurity elements, showing that shallow junctions can be achieved by simultaneously implanting boron and arsenic according to the present invention, and Figure 4 is a schematic diagram of a conventional plasma ion doping device. . 11... Vacuum chamber, 12... Exhaust hole, 13.
...Waveguide, 14...Microwave oscillator, 15...
Plasma generation chamber, 16... Electromagnet, 17... Gas inlet, 18... Pulse power supply, 19... Substrate holder, 20... Plasma, 21... Plasma drawer window. Name of agent Patent attorney Toshio Nakao (1 person) Figure 2 Dohisono/jef- (seconds) Negative pulse plot/earth potential width ratio Figure 3 Depth (C)'m)

Claims (7)

[Claims] (1) In the ion doping method, in which gas containing impurity elements is discharge decomposed and ionized ions are implanted into the substrate using an electric field, the discharge decomposition is performed by plasma decomposition using microwaves and electron cyclotron resonance absorption, and the doping process is performed on or near the substrate. A plasma doping method characterized by applying a pulsed electric field at a frequency capable of imparting kinetic energy to ion particles generated by plasma decomposition, and implanting ions into a substrate by the electric field. (2) The plasma doping method according to claim 1, characterized in that the frequency of the pulsed electric field is 50 Hz to 500 KHz. (3) The plasma doping method according to claim 1, wherein the pulse waveform is a rectangular wave, a triangular wave, or a sawtooth wave. (4) The plasma doping method according to claim 1, characterized in that the ratio of the applied rectangular pulse widths is from 1:10 to 10:1. (5) The plasma doping method according to claim 1, characterized in that a magnetic field is further superimposed in the vicinity of applying the pulsed electric field. (6) The plasma doping method according to claim 1, characterized in that a DC electric field is further superimposed on the pulsed electric field. (7) The plasma doping method according to claim 1, wherein the gas containing the element to be doped is a mixed gas of at least two types.