Method for controlling substrate temperature in a high temperature sputtering process

This high temperature heating sputtering process comprises the steps of: PA0 providing a semiconductor substrate (10) and a target (5) of a wiring material positioned opposite to the semiconductor substrate (10) in a vacuum chamber (1); PA0 sputtering a heated gas through a first gas supply unit to heat the semiconductor substrate (10) and to cause an electric discharge of the heated gas ions by using an electric discharge, PA0 to cause said heated gas ions to collide with a surface of the target (5); and PA0 depositing the target material from the surface of the target (5) onto the surface of the semiconductor substrate (10) by a sputtering process, wherein, the amount of heated gas supplied to the vacuum chamber (1) is decreased in accordance with an increase of a temperature of the semiconductor substrate (10), and simultaneously, supplying the same gas from a second gas supply means (4b) into the vacuum chamber (1) in the same amount as the decrease of gas from the first gas supply means so that the temperature of the semiconductor substrate is maintained at a constant value and the inner pressure of the vacuum chamber (1) is also maintained at a constant value.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a high temperature heating sputtering 
process, more particularly, it relates to a high temperature heating 
sputtering process which provides a sputter-deposited metal film having 
improved properties. 
2. Description of the Related Art 
In general, the metal wiring material of a semiconductor device, is made 
of, for example, an aluminum and an aluminum alloy, e.g., an aluminum 
alloy containing about 1 to 2% silicon. 
Recent development in the degree of integration and high density of 
semiconductor device elements have resulted in an even greater 
miniaturization of such elements, and thus the aspect ratio, i.e., the 
ratio of depth to width of a contact hole formed in the substrate, has 
become greater. The contact hole forms a step in a metal wiring region of 
a semiconductor device, and due to this increase of the aspect ratio, the 
step coverage of a contact hole has become difficult. 
In general, a sputtering process is used to deposit an aluminum and an 
aluminum alloy, sputtered from a target thereof, onto a substrate as a 
metal wiring material, and to improve the step coverage, a high 
temperature heating sputtering process has been developed wherein 
sputtering is carried out while a substrate, e.g., a silicon wafer is kept 
at a high temperature of, for example, 500.degree. to 600.degree. C. In 
this high temperature heating sputtering process, the substrate is heated 
to a temperature close to a melting point of the deposited metal, for 
example, 400.degree. to 500.degree. C. in a case of an aluminum, the 
aluminum is sputtered and deposited on the substrate, and the deposited 
aluminum is moved on the wafer so that a greater amount of metal is 
deposited in a contact hole, to thus improve the step coverage. 
In the high temperature heating sputtering process, the temperature of the 
substrate, for example, a silicon wafer, must be efficiently carried out, 
and therefore, a gas-assisted type sputtering device has been developed. 
FIG. 1 is a schematic view of a conventional gas-assisted type sputtering 
device. 
In a conventional high temperature heating sputtering process using the 
gas-assisted type sputtering device shown in FIG. 1, a substrate 10, for 
example, a silicon wafer, is arranged on a substrate holder 9 having a 
substrate supporter 17, in a vacuum chamber 1 having an exhaust gas 
control valve 8. Argon (Ar) gas for heating the substrate 10 is supplied 
through a gas supply means 4 having gas flow rate controller 7a and a 
needle valve 7b, while controlling the temperature of the substrate 10 by 
a heater controller 11 connected to a cartridge heater 3, and the argon 
gas is ionized by an electric discharge means 6 connected to a D.C. power 
source 14, so that the ions collide with a target 5 and the target 
material, for example, aluminum, is sputtered and deposited on the 
substrate 10. In FIG. 1, the numbers 12, 13, 15, and 16, denote a target 
fixing holder, a target supporting cooling plate, a permanent magnet, and 
a rotating part, respectively. 
The gas-assisted type heating method in a sputtering shown in FIG. 1 is 
superior to the well known infrared-ray heating method in a sputtering. 
Namely, in this infrared process, the heating effects, i.e., the infrared 
ray absorption ratios, are different due to, for example, a specific 
resistance of the wafer and kinds of deposits thereon, and thus a control 
of the temperature is difficult. Such problems do not arise in the 
gas-assisted type sputtering process. 
Nevertheless, in the high temperature sputtering process using the 
gas-assisted type sputtering device, the temperature of the wafer may be 
often varied by the kinetic energy of a sputtered target material which is 
deposited on a wafer, and by the kinetic energy of a secondary electron 
emitted from the surface of the target. Namely, the results of an 
experiment showed that the temperature of a wafer is increased by 
100.degree. to 150.degree. C. during the sputtering process, compared with 
the temperature at the start of the sputtering process, as shown in FIG. 
2. This increase of the temperature causes variations in the properties of 
the deposited material film, for example, the surface of the film is 
undulated or becomes white and cloudy, and the deposited film is not 
homogeneous in the direction of the film thickness. 
Accordingly, to control the temperature of the substrate on which a target 
material is deposited, the temperature of the heater block 2 must be 
controlled, but the control response time is slow, and therefore, in the 
gas-assisted type sputtering device shown in FIG. 1, the amount of gas 
supplied is varied to improve the control response time. Nevertheless, to 
make an abrupt change in the temperature, the amount of gas supplied must 
be extremely varied, with the result that the inner pressure of the vacuum 
chamber is varied and thus the sputtering condition is varied. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a high temperature heating 
sputtering process wherein a temperature of a wafer is maintained within a 
required range so that the properties of the deposited film are improved. 
According to the present invention, there is provided a high temperature 
heating sputtering process comprising the steps of: 
providing a semiconductor substrate (10) and a target (5) of a wiring 
material positioned opposite to the semiconductor substrate (10) in a 
vacuum chamber (1); 
supplying a heated gas through a first gas supply means (4a) to heat the 
semiconductor substrate (10) and to cause an electric discharge of heated 
gas ions by using an electric discharge, to cause said heated gas ions to 
collide with a surface of the target (5); 
depositing the target material from the surface of the target (5) onto the 
surface of the semiconductor substrate (10) by a sputtering process 
wherein, an amount of heated gas supplied to the vacuum chamber (1) is 
decreased in accordance with an increase of the temperature of the 
semiconductor substrate (10), and simultaneously, supplying the same gas 
from a second gas supply means (4b) into the vacuum chamber (1) in the 
same amount as the decrease of gas from the first gas supply means so that 
the temperature of the semiconductor substrate is maintained at a constant 
value and the inner pressure of the vacuum chamber (1) is also maintained 
at a constant value.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment of the present invention will now be described 
with reference to the drawings. 
FIG. 3 shows a gas-assisted type sputtering device by which high 
temperature sputtering process according to the present invention is 
carried out, as an example. 
As shown in FIG. 3, in the device according to the present invention, an 
infrared ray thermometer 20, a transparent window 21, a second gas supply 
means 4b having a mass flow controller 19a and a needle valve 19b, and an 
ionization vacuum indicator 18, are provided in addition to the elements 
provided in a conventional device. 
The second gas supply means 4b feeds the same gas, for example, Ar, into 
the vacuum chamber 1; the quantity of gas being controlled by the mass 
flow controller 19a. The ionization vacuum indicator 18 is a pressure 
detector which detects an inner pressure of the vacuum chamber 1. 
A substrate 10, e.g., a silicon wafer, is provided on a substrate holder 9 
and supported thereon by a substrate supporter 17. An argon (Ar) gas is 
fed by a first gas supply means 4a into a hole of a block heater 2 heated 
to a temperature of about 600.degree. C. by a cartridge heater 3, and thus 
the substrate 10 is heated to a temperature of about 465.degree. C. by the 
heated Ar gas. Note, when Ar gas is not supplied, the substrate is heated 
only to 380.degree. C. After heating the substrate to about 465.degree. 
C., the Ar gas is ionized by an electric discharge means 6, while 
controlling the temperature of the substrate 10. The ionized Ar ions 
collide with a target 5 of Al-Si (1 wt %) alloy so that the target 
material (Al-Si) is sputtered and deposited onto the substrate 10. 
When a deposited film having a thickness of 1.mu. has been deposited on the 
substrate for a time of 75 seconds, since sputtered particles of Al and Si 
having a kinetic energy collide with the surface of the substrate 10, the 
temperature of the substrate 10 is increased by about 70.degree. C., and 
this increase is detected by the infrared thermometer 20. Therefore, up to 
the point at which the deposition of the target material on the substrate 
is started, 17.5 SCCM Ar gas is fed into the vacuum chamber 1 through the 
heater block 2 and then the Ar gas flow rate is decreased at a rate of 
17.5/75 (SCCM/sec). Simultaneously, at the other gas supply system, for 
example, the second gas supply means 4b, the Ar gas flow rate is increased 
at a rate of 17.5/75 (SCCM/sec), so that the degree of vacuum is 
maintained at 5 mm Torr, which pressure is detected by the electric 
discharge vacuum indicator 18. Accordingly, the change of the temperature 
of the substrate, e.g., a silicon wafer, can be kept within .+-.10.degree. 
C. of the desired range, and thus an aluminum film having homogeneous 
properties in the direction of the film thickness can be obtained.