Heating – Processes of heating or heater operation – Including preparing or arranging work for heating
Reexamination Certificate
2000-04-21
2001-06-26
Wilson, Gregory (Department: 3749)
Heating
Processes of heating or heater operation
Including preparing or arranging work for heating
C432S249000, C118S725000, C118S666000, C219S444100
Reexamination Certificate
active
06250914
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-116338, filed Apr. 23, 1999, filed the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a wafer heating device used in a semiconductor fabrication equipment, and a method of controlling the same.
FIG. 1
shows an outline of a conventional epitaxial growth system. This system is used when a thin layer of silicon is deposited on a surface of a wafer.
An susceptor
12
of annular shape is disposed inside a reaction chamber
11
. A wafer
10
is supported at the edge thereof on the susceptor
12
. The susceptor
12
is supported at the edge thereof by a cylindrical drum
13
, and mounted on a rotary drive mechanism (not shown) via the drum
13
. With rotation of the susceptor
12
, the wafer
10
held thereon is rotated.
Within the drum
13
, a first heater
21
is disposed in a position facing a lower surface of the wafer
10
. As shown in
FIG. 2
, the first heater
21
is formed by arranging a heater in a spiral shape (or in a zigzag shape, or in a multiple-stripe shape), and has a disc shape as a whole. Further, a second heater
22
of annular shape is arranged so as to surround the first heater
21
. The first heater
21
is used for heating the wafer
10
. The second heater
22
is mainly used for heating the susceptor
12
. The first heater
21
and the second heater
22
are not rotated.
A reaction gas supply nozzle
15
is provided at a ceiling portion of the reaction chamber
11
. A silicon layer is deposited on the heated wafer
10
by supplying a reaction gas including silicon compound from this nozzle
15
. Rotation of the wafer
10
promotes growth of the silicon layer, and improves uniformity of a thickness of the formed silicon layer.
Radiation thermometers
31
and
33
are mounted on the ceiling portion of the reaction chamber
11
. A feedback control of powers of the first heater
21
and second heater
22
is performed by measuring surface temperatures of the wafer
10
and the susceptor
12
with these radiation thermometers
31
and
33
.
FIG. 2
shows a plan view of the part of the first heater
21
and the second heater
22
. In
FIG. 2
, reference numeral
21
denotes the first heater for heating the wafer, and
22
denotes the second heater mainly for heating the susceptor
12
. A broken line
23
denotes an outer periphery of the wafer.
In a control method as described above, a temperature of the wafer can be accurately controlled in the vicinity of a measuring point of the temperature on the surface of the wafer
10
. However, the temperature of the wafer cannot be accurately controlled in the other positions. Therefore, non-uniform temperature distribution occurs within the surface area of the wafer
10
. In order to obtain an uniform thickness of a silicon layer to be formed, it is necessary to heat the wafer
10
not so as to generate a temperature difference within the surface area of the wafer
10
. Large non-uniformity of the thickness of the formed silicon layer causes deterioration of quality and yield of semiconductor devices to be fabricated by using the wafer.
Recently, in order to improve chip multiprobe yield (an yield of devices per unit area of a wafer), the diameter of wafer is gradually increasing, such as 200 mm, 300 mm. In a wafer of a large diameter, it has become more difficult to heat the wafer uniformly within the surface area of the wafer.
Among factors which prevent uniform heating of the wafer, there is a phenomenon that heat flow is taken away from wafer via the susceptor supporting the edge of the wafer and that the temperature of the peripheral area of the wafer decreases. Since the susceptor has a larger thickness and a relatively larger heat capacity than those of the wafer, a large quantity of heat is taken from the wafer to the susceptor, and the temperature of the peripheral area of the wafer decreases. In order to prevent such decrease of the temperature in the peripheral area of the wafer, the second heater
22
for heating susceptor is provided.
FIG. 3
is an example of a control block diagram relating to powers of the first heater
21
and the second heater
22
in the above conventional semiconductor fabrication equipment. As shown in
FIG. 3
, the powers of the first heater
21
and the second heater
22
are independently controlled by separate PID-method closed loops. The power of the first heater
21
is controlled by using the temperature of the wafer
10
as a feedback signal, and the power of the second heater
22
is controlled by using the temperature of the susceptor
12
as a feedback signal. Further, when wafer
10
is not set on the susceptor, the power of the first heater
21
is fixed at a predetermined value.
A method of operating the semiconductor fabrication equipment shown in
FIGS. 1-3
will be described.
The epitaxial growth system shown in
FIG. 1
is a type of single wafer processing. The wafer
10
is treated one by one as follows. The wafer
10
is transferred into the reaction chamber
11
by a transfer robot (not shown). Then, a silicon layer is deposited on the surface of the wafer
10
in the reaction chamber
11
. After deposition of the silicon layer has been completed, the wafer
10
is transferred from the reaction chamber
11
by the transfer robot. Thereafter, a new wafer is transferred into the reaction chamber
11
, and a silicon layer is deposited again on the new wafer.
In a process of treating one wafer, a setting temperature of the wafer is program-controlled in accordance with a pattern as shown in
FIG. 4
, for example. In this example, the setting temperature of the wafer is set to 800° C. at first, and the temperature is maintained for 1 minute. However, since no temperature of the surface of the wafer is obtained while exchanging wafers, the power of the heater
31
is fixed at a predetermined value (for example, a value at which the temperature of a wafer is expected to be stabilized at about 800° C.). During this time, the wafer
10
is transferred into the reaction chamber
11
by the transfer robot (not shown) through a gate (not shown) located at the peripheral wall of the reaction chamber
11
.
FIG. 5
shows an operation of the system when the wafer
10
is transferred onto the susceptor
12
. As shown in
FIG. 5
, pins
17
ascend from under the wafer
10
, and receive the wafer
10
from the transfer robot. Thereafter, the transfer robot moves back to the outside of the reaction chamber
11
, and the gate is closed. The wafer
10
is heated to a temperature close to 800° C. in a state of being set on the pins
17
.
When the temperature of the wafer
10
has rised to nearly 800° C., pins
17
descend and the wafer
10
is transferred onto the susceptor
12
. Next, rotation of the susceptor
12
is started. The temperature of the wafer
10
is maintained at 800° C. for 1 minute by a feedback control, as shown in FIG.
4
. Then, the setting temperature value is linearly raised to 1000° C. for 3 minutes. If the wafer
10
is rapidly heated, the thermal stress increases, which causes deterioration of the quality of a silicon layer to be deposited. Therefore, the wafer is gradually heated as described above.
After the setting temperature value has reached 1000° C., the temperature is maintained for 4 minutes, during which a reaction gas including silicon compound is supplied onto the surface of the wafer
10
. Thereby, a silicon layer is deposited on the wafer
10
.
Then, supply of the reaction gas is stopped, and the setting temperature value is linearly lowered to 800° C. for 1 minute. After the setting temperature has been lowered to 800° C., the gate of the reaction chamber
11
is opened, pins
17
are raised, and the transfer robot is advanced, and the wafer
10
is transferred to the transfer robot.
(Problems of the conventional heater controlling method)
In the conventional heating device shown in
FIGS. 1-4
and the temperature con
Ito Hideki
Iwata Katsuyuki
Katsumata Hirofumi
Ohashi Tadashi
Takahashi Hidenori
Pillsbury & Winthrop LLP
Toshiba Machine Co. Ltd
Wilson Gregory
LandOfFree
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