JPH01283919A - Plasma doping method - Google Patents

Abstract

PURPOSE:To prevent the occurrence of crystal defects such as breakdown of crystal lattices, by forming an oxide film having the thickness of 10nm or more on the surface of each semiconductor substrate which is placed in a vacuum container beforehand. CONSTITUTION:An oxide film having the thickness of 10nm or more is formed on the surface of each semiconductor substrate 3 which is placed in a vacuum container 1. A region wherein defects occur due to doping is an SiO2 layer whose depth is 30nm from the surface. Crystal defects such as dislocation seldom occur in an Si layer beneath the SiO2 layer. The very thin oxide film of 10nm or more is formed on the surface of each semiconductor substrate beforehand, and plasma doping characterized by the less occurrences of the crystal defects in the surface during the doping is performed through the oxide film. In this way, the occurrences of the crystal defects in the surface layer of the semiconductor can be suppressed to the Iow rate only by said doping.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plasma doping method in which plasma is generated in an atmosphere containing impurities and impurities are introduced into a semiconductor substrate maintained at 400° C. or lower.

[Conventional technology]

Thermal diffusion has long been used as a method for introducing impurities as donors or acceptors into a semiconductor substrate to form a semiconductor region with a predetermined conductivity type and impurity concentration, and recently ion implantation has also been used. It became so. However, the thermal diffusion method has drawbacks such as poor uniformity of impurity concentration and the complicated manufacturing process, which takes a long time, while the ion implantation method has expensive equipment and There are disadvantages such as the need for high temperature heat treatment. By eliminating these drawbacks, the temperature of 400°C in a vacuum container with an atmosphere containing specified impurities was improved.
The following plasma doping method, in which a semiconductor substrate maintained at a predetermined temperature is placed and a glow discharge is generated in a container to introduce impurities into the gas, is disclosed in Japanese Patent Application Laid-Open No. 59-218727, which was filed by the applicant and others. It is known from the publication no.

[Problem to be solved by the invention]

As described in the above publication, unlike the ion implantation method, according to the plasma doping method, the concentration of the introduced impurity is highest at the surface of the semiconductor substrate and shows a profile that decreases in the depth direction, and the depth is also 500 mm. ~150
Deep junctions, which are extremely shallow and therefore suitable for forming shallow junctions and shallow ohmic contact layers, also depend on appropriate heat treatment conditions. Furthermore, since this method requires low energy during doping, crystal defects such as crystal lattice destruction do not occur in the surface layer of the semiconductor substrate. However, crystal defects such as dislocations occur in the shallow il region within about 30n layers from the surface of the semiconductor substrate, and this causes distortion in the crystal, resulting in a drawback that a uniform semiconductor region cannot be formed.

An object of the present invention is to provide a plasma doping method that eliminates the above-mentioned drawbacks and eliminates the occurrence of such types of crystal defects in the surface layer of a semiconductor substrate, or minimizes the occurrence thereof.

[Means to solve the problem]

In order to solve the above problems, in the plasma doping method of the present invention, an oxide film with a thickness of 10 nm or more is formed in advance on the surface of a semiconductor substrate placed in a vacuum container.

[Effect]

An oxide film with a thickness of 10 nm or more absorbs a significant portion of the energy during doping, thereby suppressing the generation of crystal defects in the underlying semiconductor substrate.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. An n-type single-crystal silicon plate with a specific resistance of about 100 Ω was used as the semiconductor substrate, and an oxide film with a thickness of 30 ns was formed on its surface by dry oxygen oxidation at 100° C. Plasma doping of boron was performed on this silicon substrate using the apparatus shown in FIG. In FIG. 2, a lower electrode 21 and an upper electrode 22 are disposed in the vacuum chamber 1 at a distance of 508. The silicon substrate 3 on which the oxide film was formed as described above was placed on the lower electrode 21, the inside of the container 1 was evacuated using the evacuation system 4, and the degree of vacuum was measured with a vacuum gauge 5. In addition, the silicon substrate plate 3 is maintained at 200° C. by the heater 6 in the lower electrode 21, and the BJi gas from the cylinder 71 is transferred to the cylinder 72.
The mixture was diluted to 11,000 pp using He gas as a carrier gas from the reactor using a regulating circuit 81.82, and the pressure inside the container was adjusted to 4 Torr using a vacuum valve 83.

In this state, a DC voltage of 900 V was applied between the electrodes 21 and 22 by the power source 9 to generate a glow discharge with a power of 2-A/-, which continued for 60 seconds. The results showed that boron was doped and the concentration distribution was as shown in FIG. The region where defects occur is the 5IOt layer at a depth of 30n from the surface, and crystal defects such as dislocations hardly occur in the Si layer below this.As a result, when plasma doping is performed using the conventional method, the The lifetime of minority carriers, which was previously

When the thickness of the 5ift layer is made thinner than 30 nm, the surface impurities of the Si layer become high, but some crystal defects enter the Si layer. However, compared to the case where the thickness of 5iaxrH is less than Ion-, for example, 2 nm like a natural oxide film, the crystal defects in the Si layer are significantly reduced.

If Si is directly plasma-doped without forming a 510□ film and removed by etching about 3On- from the surface, the crystal defects generated in 5lli will be removed, but S
It is difficult to control the etching to remove such a precise thickness of irM. On the other hand, if the 5ift layer formed according to the present invention is to be removed, it can be easily done using hydrofluoric acid.

In the above embodiment, helium was used as the carrier gas, but similar effects can be obtained when using a gas such as hydrogen, or when using a gas other than BtHb gas as the doping impurity gas.

〔Effect of the invention〕

According to the present invention, plasma doping, which causes fewer surface crystal defects during doping, is applied to the surface of a semiconductor substrate using Ion-
By simply forming the extremely thin oxide film described above in advance and performing the process through the oxide film, it is possible to further suppress the occurrence of crystal defects in the semiconductor surface layer. Therefore, it is easy to improve the characteristics of various semiconductor devices manufactured by impurity doping.

[Brief explanation of the drawing]

FIG. 1 is a depthwise concentration distribution diagram of boron immediately after boron doping according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a plasma doping apparatus used for implementing the present invention. l: vacuum container, 21.22: electric bridge, 3: silicon substrate,
6: Heater, 71: BzHh gas cylinder, 72:
Hega (4chi/am3) Figure]

Claims (1)

[Claims] 1) A method in which a semiconductor substrate maintained at a temperature of 400°C or less is placed in a vacuum container having an atmosphere containing a predetermined impurity as a dopant, and a glow discharge is generated in the container to introduce the impurity into the semiconductor substrate. , a plasma doping method characterized in that an oxide film with a thickness of 10 mm or more is formed in advance on the surface of a semiconductor substrate placed in a vacuum container.