Refrigeration – Using electrical or magnetic effect – Thermoelectric; e.g. – peltier effect
Reexamination Certificate
2002-02-15
2003-10-21
Doerrler, William C. (Department: 3744)
Refrigeration
Using electrical or magnetic effect
Thermoelectric; e.g., peltier effect
C062S259200, C062S161000
Reexamination Certificate
active
06634177
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus for the monitoring and control of a wafer temperature in a semiconductor process chamber and more particularly, relates to an apparatus for the real-time monitoring and control of a wafer temperature positioned on an electrostatic chuck by using a plurality of thermoelectric cooling module and/or an optical sensor for sensing a temperature of the wafer.
BACKGROUND OF THE INVENTION
In the fabrication of modern integrated circuit devices, one of the key requirements is the ability to construct plugs or interconnects in reduced dimensions such that they may be used in a multi-level metalization structure. The numerous processing steps involved require the formation of via holes for the plug or interconnect in a dimension of 0.5 &mgr;m or less for use in high-density logic devices. For instance, in forming tungsten plugs by a chemical vapor deposition method, via holes in such small dimensions must be formed by etching through layers of oxide and spin-on-glass materials at a high etch rate. A high-density plasma etching process utilizing a fluorine chemistry is frequently used in the via formation process.
In a modern etch chamber, an electrostatic wafer holding device, i.e., an electrostatic chuck or commonly known as an E-chuck, is frequently used where the chuck electrostatically attracts and holds a wafer that is positioned on top. The E-chuck holding method is highly desirable in the vacuum handling and processing of wafers. In contrast to a conventional method of holding wafers by mechanical clamping means where only slow movement is allowed during wafer handling, an E-chuck device can hold and move wafers with a force equivalent to several tens of torr pressure.
Electrostatic chucking is a technique used to secure a wafer onto a susceptor in a wafer processing chamber. In more recently developed wafer processing technology, the electrostatic wafer holding technique is frequently employed in which a chuck electrostatically attracts and holds the wafer. It is a highly desirable technique used in the vacuum handling and processing of silicon wafers. In contrast to a conventional method of holding wafers by either gravity or mechanical clamping means where only slow motion of the susceptor is allowed during wafer handling, an electrostatic wafer holding device can hold wafers with a force that is significantly higher. Since there are no moving parts acting on the wafer, there are no particle generation or contamination problems in the processing chamber.
Electrostatic chucks have been used to overcome the nonuniform clamping associated with mechanical clamping devices. The electrostatic chuck utilizes the attractive coulomb force between oppositely charged surfaces to clamp together an article and a chuck. It is generally recognized that in an electrostatic chuck, the force between the wafer and the chuck is uniform for a flat wafer and a flat chuck. This is in contrast to a mechanical clamping system where the clamping is effected around the peripheral of a wafer. Special provisions must be made to compensate for the bowing at the center of the wafer caused by the pressure of cooling gas which is pumped in between the wafer and the pedestal that is supporting and cooling the wafer. For instance, in order to compensate for the bowing of the wafer, one solution is to make the pedestal in a domed or bowed shape. This is eliminated in an electrostatic chuck where the wafer is held on a substantially planar chuck surface with an even electrostatic force distributed according to the electrode layout. The electrostatic force is generally sufficient to prevent bowing of the wafer and to promote uniform heat transfer over the entire wafer surface.
In the normal operation of an electrostatic chuck, one or more electrodes formed in the chuck body induce an electrostatic charge on the surface of a dielectric material that is coated over the chuck surface facing the wafer, i.e., between the bottom surface of the wafer and the top surface of the chuck. A typical dielectric material that can be used for such purpose is, for instance, a polyimide material. The electrostatic force between the wafer and the chuck is proportional to the square of the voltage between them and to the dielectric constant of the dielectric layer, and inversely proportional to the square of the distance between the wafer and the chuck, i.e.,
Electrostatic Chucking Force=
k
(
V/d
)
2
wherein k is the dielectric constant of the dielectric layer. V is the voltage drop across the dielectric film, and d is the thickness of the dielectric layer. The charging/discharging time constant is RC. When R is very large for a thick oxide backing layer (i.e., d is very large), the electrostatic chucking force can be greatly reduced causing the electrostatic chucking of the wafer to fail.
Since the principal of electrostatic chucking is that there must exist an attractive force between two parallel plates, i.e., between the silicon wafer and the susceptor that have opposite electrical charges, the chucking efficiency is not only determined by the bias voltage, the electric constant of the system, the effective distance between the two parallel plates, but also determined by the wafer grounding efficiency. To utilize electrostatic chucking efficiently in a wafer processing chamber, the surface of the wafer should be electrically conductive so that it can be properly grounded.
A typical inductively coupled plasma etch chamber
10
is shown in FIG.
1
. In the etch chamber
10
, which is similar to a Lam TCP® etcher made by the Lam Research Corp., the plasma source is a transformer-coupled plasma source which generates high-density, low-pressure plasma
12
decoupled from the wafer
14
. The plasma source allows independent control of ion flux and ion energy. Plasma
12
is generated by a flat spiral coil
16
, i.e., an inductive coil, which is separated from the plasma by a dielectric plate
18
, or a dielectric window on top of the reactor chamber
20
. The wafer
14
is positioned away from the coil
16
so that it is not affected by the electromagnetic field generated by the coil
16
. There is very little plasma density loss because plasma
12
is generated only a few mean free paths away from the wafer surface. The Lam TCP® plasma etcher therefore enables a high-density plasma and high-etch rates to be achieved. In the plasma etcher
10
, an inductive supply
22
and a bias supply
24
are used to generate the necessary plasma field. Multi-pole magnets
26
are used surrounding the plasma
12
generated. A wafer chuck
28
is used to hold the wafer
14
during the etching process. A ground
30
is provided to one end of the inductive coil
16
.
In a typical inductively coupled RF plasma etcher
10
shown in
FIG. 1
, a source frequency of 13.56 MHZ and a substrate bias frequency of 13.56 MHZ are utilized. An ion density of approximately 0.5~2×10
12
cm
3
at wafer, an electron temperature of 3.5~6 eV and a chamber pressure of 1~25 m Torr are achieved or used.
In the typical plasma etch chamber
10
, a cooling means for the wafer backside is provided in an E-chuck for controlling the wafer temperature during the plasma processing. This is shown in
FIG. 2
for the plasma etcher
40
. In the conventional plasma etcher
40
, E-chuck
42
is provided for supporting a wafer
44
thereon. E-chuck
42
can be constructed of either a metallic material or of a polymeric material. A plurality of ventilation apertures (not shown) are provided in the E-chuck surface such that a cooling gas can be supplied to the backside
46
of the wafer
44
during plasma processing. The plurality of ventilation apertures in the E-chuck
42
is connected in fluid communication with a cooling gas inlet conduit
38
for feeding a cooling gas into the apertures. The cooling gas inlet conduit
38
is in turn connected to a gas supply line
36
, a flow control valve
34
and a cooling gas supply
32
. The pressure in the cooling gas supply line
36
is monitored by a pre
Huang Yu-Chih
Lin Kun-Tzu
Peng Jung-Huang
Shih Chu-Song
Doerrler William C.
Taiwan Semiconductor Manufacturing Co. Ltd.
Tung & Associates
Zec Filip
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