Method of manufacturing semiconductor device by sputter doping

Details Method of manufacturing semiconductor device by sputter doping Method of manufacturing semiconductor device by sputter doping

2001-04-24

2004-08-31

Pert, Evan (Department: 2829)

Semiconductor device manufacturing: process

Introduction of conductivity modifying dopant into...

C438S513000

Reexamination Certificate

active

06784080

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to impurity introduction methods and apparatuses thereof to introduce, in a low temperature range (temperature range of, for example, 250° C. to very low temperature), impurity composed of atoms and molecules to a surface portion of a solid sample such as a semiconductor substrate, and also relates to manufacturing methods of a semiconductor device using such impurity introduction method.
As a technique to introduce impurity to the surface portion of the solid sample, plasma doping method in which impurity is ionized and introduced to a solid with low energy is known as disclosed in, for example, U.S. Pat. No. 4,912,065.
Now, a plasma doping method will be described below as a conventional impurity introduction method with reference to FIG.
8
.
FIG. 8
illustrates a schematic structure of an impurity introduction apparatus used for the conventional plasma doping.
FIG. 8
shows a vacuum chamber
10
, a sample holder
11
provided inside the vacuum chamber
10
for holding a solid sample
12
which is composed of a silicon substrate or the like and to which impurity is introduced, a pressure reducing pump
13
for reducing the pressure inside the vacuum chamber
10
, a source gas feed
14
for supplying doping gas including a desired element, such as B
2
H
6
, to the vacuum chamber
10
, a microwave guide
15
connected to the vacuum chamber
10
, a quartz plate
16
provided between the vacuum chamber
10
and the microwave guide
15
, and an electromagnet
17
arranged outside the vacuum chamber
10
. The microwave guide
15
, the quartz plate
16
and the electromagnet
17
constitute plasma generation means. In
FIG. 8
, a plasma region
18
and a high-frequency power supply
19
connected to the sample holder
11
through a capacitor
20
are also shown.
In the impurity introduction apparatus having the structure above, the doping gas such as B
2
H
6
introduced from the source gas feed
14
is made into plasma by the plasma generation means, and boron ions in the plasma are introduced to the surface portion of the solid sample
12
by the high-frequency power supply
19
.
After a metal interconnection layer is formed on the solid sample
12
having thus introduced impurity, a thin oxide film is formed on the metal interconnection layer in the prescribed oxidizing atmosphere. There-after, a gate electrode is formed on the solid sample
12
by a CVD device or the like to obtain, for example, a MOS transistor.
There is a problem that in general the gas including the impurity which becomes electrically active when introduced to the solid sample such as a silicon substrate, such as the doping gas composed of B
2
H
6
, is highly dangerous.
In addition, under the plasma doping method, all the substances included in the doping gas are introduced to the solid sample. Taking as an example the doping gas composing B
2
H
6
, although only boron is the effective impurity when introduced to the solid sample, hydrogen is also introduced to the solid sample at the same time. If hydrogen is introduced to the solid sample, a lattice defect is undesirably generated at the solid sample during the thermal treatment such as epitaxial growth performed thereafter.
Therefore, the inventors of the present invention have conceived that an impurity solid including the impurity which becomes electrically active when introduced to the solid sample is arranged in the vacuum chamber, and plasma of rare gas as inert or reactive gas is generated in the vacuum chamber and the impurity solid is sputtered by ions of the rare gas so that the impurity is separated from the impurity solid.
FIG.
9
. shows a schematic structure of an impurity introduction apparatus used for plasma doping which utilizes an impurity solid including impurity. The elements in
FIG. 9
identical to those in
FIG. 8
are denoted by the identical numerals and description thereof will not be repeated.
This impurity introduction apparatus is characterized in that the device is provided with a solid holder
22
for holding an impurity solid
21
including impurity such as boron and a rare gas feed
23
for introducing rare gas into the vacuum chamber
10
. When gas such as Ar gas is introduced into the vacuum chamber
10
from the rare gas feed
23
, the Ar gas is made into plasma by the plasma generation means and boron is sputtered from the impurity solid
21
by the Ar ions in the Ar plasma. Boron thus sputtered is mixed into the Ar plasma to become plasma doping gas and then introduced to the surface portion of the solid sample
12
.
However, although it is true that impurity is generated from the impurity solid
21
when the plasma doping is carried out as described above, problems still remain that throughput is not satisfactory because the amount of impurity generated is not sufficient and that the impurity cannot be introduced to the region extremely close to the surface at the surface portion of the solid sample.
SUMMARY OF THE INVENTION
In view of the above, a first object of the present invention is to improve throughput by increasing the amount of impurity generated when inert or reactive gas is introduced into a vacuum chamber to generate impurity from an impurity solid, and a second object thereof is to achieve introduction of the impurity to the region extremely close to the surface at the surface portion of a solid sample.
In order to achieve the first object, a first impurity introduction method according to the present invention comprises the steps of: holding, in a vacuum chamber, an impurity solid which includes impurity and a solid sample into which impurity is introduced; introducing inert or reactive gas into the vacuum chamber to generate plasma composed of the inert or reactive gas; applying to the impurity solid a voltage which allows the impurity solid to serve as a cathode for the plasma, and performing sputtering of the impurity solid by ions in the plasma, so that the impurity included in the impurity solid is mixed into the plasma; and applying to the solid sample a voltage allowing the solid sample to serve as a cathode for the plasma to introduce the impurity mixed into the plasma to the surface portion of the solid sample.
According to the first impurity introduction method, the ions in the plasma advance toward the impurity solid with great energy when the voltage allowing the impurity solid to serve as a cathode for the plasma is applied to the impurity solid, so that the impurity included in the impurity solid is sputtered efficiently and mixed with high concentration into the plasma composed of the inert or reactive gas. Furthermore, since the high-concentration impurity ions mixed into the plasma advance toward the solid sample with great energy when the voltage allowing the solid sample to serve as a cathode for the plasma is applied to the solid sample, the high-concentration impurity ions are introduced to the surface portion of the solid sample. Thus, a high-concentration impurity layer can be formed with high safety without causing a lattice defect at the surface portion of the solid sample.
In order to achieve the first and second objects above, a second impurity introduction method according to the present invention comprises the steps of: holding, in a vacuum chamber, an impurity solid which includes impurity and a solid sample into which impurity is introduced; introducing inert or reactive gas into the vacuum chamber to generate plasma composed of the inert or reactive gas; applying to the impurity solid a voltage allowing the impurity solid to serve as a cathode for the plasma, and performing sputtering of the impurity solid by ions in the plasma, so that the impurity included in the impurity solid is mixed into the plasma; and applying to the solid sample a voltage allowing the solid sample to serve as an anode for the plasma to introduce the impurity mixed into the plasma to the solid sample.
According to the second impurity introduction method, the ions in the plasma advance toward the impurity solid with great energy when the

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