Heater assembly for heating a wafer

Details Heater assembly for heating a wafer Heater assembly for heating a wafer

2002-08-13

2004-04-13

Fuqua, Shawntina (Department: 3742)

Electric heating

Heating devices

Combined with container, enclosure, or support for material...

C219S443100, C219S462100, C219S465100, C219S448140, C219S467100, C392S418000, C118S724000, C118S725000, C118S500000

Reexamination Certificate

active

06720533

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the manufacturing of semiconductor devices. More particularly, the present invention relates to a heater assembly for heating a wafer.
2. Description of the Related Art
Generally, a semiconductor device is manufactured by forming a minute electronic circuit pattern on a substrate. The circuit pattern comprises a great number of electronic elements and wiring connecting the electronic elements.
More specifically, a silicon wafer, namely, a small thin circular slice of pure silicon, is produced from an ingot of crystalline silicon. Then, an electronic circuit is formed on a surface of the wafer (wafer fabrication, FAB process), the wafer is cut into a plurality of individual chips, and each chip is combined with a lead frame. An operating test is then performed on the chip to ensure that the semiconductor device is fully functional.
In the FAB process, a thin film is formed on the surface of the wafer, and the thin film is patterned to form an electronic circuit for performing a specific function. Hence, if the thickness of the thin film is not uniform over the entire surface of the wafer, a residual stress occurs on the surface of the wafer. As a result, the integrated circuit may not be formed properly.
The rate at which the material constituting the thin film layer is deposited on the wafer is greatly dependent on the temperature of the wafer. Specifically, assuming all other deposition conditions to be the same, the thin film is formed more quickly and hence, more thickly, on a wafer surface at a high temperature than at a low temperature. The deposition process of forming the thin film is carried out while the wafer is repeatedly heated and cooled. Accordingly, the temperature varies across the wafer surface, especially between a peripheral portion and a central portion of the wafer. Thus, the thin film may be formed non-uniformly over the wafer surface. Stress will occur at the boundary where the thickness of the film changes. The stress deforms the thin film, which phenomenon is referred to as “a slip phenomenon”. Consequently, an IC patterned on the deformed thin film may lose its functional stability. That is, temperature uniformity is an essential factor for fabricating a semiconductor device having functional stability. In consideration of the recent trend in semiconductor technology for devices having higher degrees of integration acquired through reducing the critical dimension of the circuit patterns thereof, the temperature uniformity of the wafer surface is increasing in importance as a processing condition to be established during the semiconductor device manufacturing process.
Chemical vapor deposition (CVD) is the method usually used for forming the thin film in the semiconductor device manufacturing process. Thermal CVD is being used more frequently for forming such thin films. In thermal CVD, material is deposited by means of heat-induced chemical reactions of reactant gases supplied to a surface of a heated wafer. The thermal CVD process are classified into atmospheric pressure CVD (APCVD) and low pressure CVD (LPCVD) processes on the basis of the pressure in the CVD apparatus. LPCVD is especially suitable for depositing a metal silicide having a high melting point to form a polycide that is generally used as a wiring material of a highly integrated circuit device.
The LPCVD apparatus includes a susceptor for supporting and fixing a wafer on an upper surface thereof, and a heater disposed below the susceptor for providing heat to the susceptor. That is, the heat generated by the heater radiates to the susceptor and is conducted from the susceptor to the wafer. Therefore, the temperature of the wafer surface is dependent on the amount of heat conducted from the susceptor, and the conducted heat from the susceptor is mainly dependent on the amount of heat radiating from the heater. That is, the temperature of wafer surface is mainly dependent on the amount of heat radiating from the heater.
However, even though equal amounts of heat radiate to the peripheral portion and the central portion of the wafer from the heater, the surface temperature at the peripheral portion of the wafer is lower than that at the central portion of the wafer because a significant amount of heat is lost at a side surface of the peripheral portion of the wafer whereas most of the heat is conserved at the central portion of the wafer. Consequently, the surface temperature of the wafer is much lower at the peripheral portion than at the central portion of the wafer.
Various attempts have been made to structure the heater to decrease the temperature difference between the various surface portions of the wafer. For example, U.S. Pat. No. 6,031,211 entitled “ZONE HEATING SYSTEM WITH FEEDBACK CONTROL SYSTEM” discloses a heating system and method for producing temperature uniformity at the surface of the wafer. The disclosed heating system includes a plurality of heating sections that are controlled independently to generate different amounts of heat used for heating respective portions of the wafer. Furthermore, a heater assembly of a GENUS 7000 (trade name) CVD apparatus made by GENUS Co. Ltd. U.S.A, which is a widely used thermal CVD apparatus, includes an inner heater for heating a central portion of a susceptor and an outer heater for heating a peripheral portion of the susceptor. The inner heater and outer heater are discrete from each other and are respectively controlled to generate more heat at the peripheral portion than at the central portion. Accordingly, heat loss at the side surface of the peripheral portion of the wafer is compensated for by the outer heater, in an attempt to produce temperature uniformity on the surface of the wafer.
However, the dual heater system does not produce such temperature uniformity even when the outer heater is generating more heat than the inner heater.
FIG. 1
is a schematic cross-sectional view of the conventional dual heater assembly of the GENUS 7000 thermal CVD apparatus made by GENUS Co. U.S.A.
FIG. 2
is a schematic plan view of the dual heater assembly. Referring to
FIGS. 1 and 2
, the conventional dual heater assembly
90
includes a susceptor
40
for supporting a wafer
50
, a plurality of heaters
10
disposed below the susceptor
40
for providing heat to the susceptor
40
, an electrical power source for supplying electric current to the heaters
10
and a support
30
for supporting the heaters
10
.
The heaters
10
include an outer heater
12
for heating a peripheral portion of the susceptor and an inner heater
14
for heating an inner portion of the susceptor. The outer heater
12
and the inner heater
14
are separated from each other by a space
16
for preventing heat transfer between the outer heater
12
and the inner heater
14
. In addition, the outer heater
12
and the inner heater
14
are controlled to operate independently. Each of the heaters
10
is made of a thin plate of graphite. Heat is generated due to the internal resistance of the heaters
10
when the electric current is supplied to the heaters
10
. The electrical power source includes a first source (not shown) for providing current to the outer heater
12
and a second source
20
for providing current to the inner heater
14
.
The second source
20
comprises a connection member
24
for guiding electric current from an external power source to the inner heater
14
, a lead member
22
which is connected to an input terminal formed on the bottom surface of the inner heater
14
, and a controller (not shown) for controlling the electric current supplied through the connection member
24
and lead member
22
according to a surface temperature of the wafer
50
. The lead member
22
comprises a corrosion-resistant and heat-resistant material and is screwed onto the input terminal.
The support
30
is made of quartz, which is corrosion-resistant to acid or alkali materials except hydrogen fluoride and thus, is very chemically stable. Hence, the support
30
is not e

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