Coating apparatus – Gas or vapor deposition
Reexamination Certificate
1998-08-12
2001-05-01
Lund, Jeffrie R. (Department: 1763)
Coating apparatus
Gas or vapor deposition
C118S725000, C118S724000
Reexamination Certificate
active
06224678
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to integrated circuit fabrication and, more particularly, to a chemical vapor deposition system employing a thermocouple mounting system designed to inhibit contact between the thermocouple and a quartz liner within the chemical vapor deposition system.
2. Description of the Related Art
Chemical vapor deposition (“CVD”) is a well-known process employed during the fabrication of an integrated circuit to deposit a thin film upon a substrate. A CVD process typically involves forming a non-volatile solid film (e.g., silicon dioxide, silicon nitride, polycrystalline silicon) on a substrate by reacting vapor phase chemicals that contain the required constituents. For example, silicon dioxide may be formed upon a semiconductor substrate by reacting silane and oxygen or by thermally decomposing tetraethylorthosilicate (TEOS). The thin film is formed by introducing the reactant gases into a reaction chamber and then decomposing the reactants and reacting them at a heated surface. Various inert carrier gases (e.g., H
2
, N
2
, Ar) may be used to carry the reactive gases into the chamber. The gaseous by-products of the reaction are desorbed and removed from the reaction chamber, along with the unconsumed reactant gases and the inert carrier gases.
The CVD process can take place in either pressurized or non-pressurized reaction chambers. Due to the stringent requirements of film uniformity, low-pressure chemical vapor deposition (“LPCVD”) reactors have gained in popularity. LPCVD reactors generally operate in the pressure range of 0.1 to 10 torr and the temperature range of 500 to 600° C. As such, the rate at which a solid film is formed at the surface of a semiconductor substrate is typically limited by the rate at which the reactant gases react rather than by the rate at which the reactant gases are supplied to the substrate by mass transport. By eliminating mass-transfer constraints on reactor design, the reactor may be optimized for high wafer capacity. In addition, low-pressure operation decreases gas-phase reactions, making LPCVD films less subject to particulate contamination.
Surface reaction rate is very sensitive to temperature, as shown by the following equation:
R=R
0
e
(−Ea/kT)
in which R is the rate of reaction, R
0
is the frequency factor, E
a
is the activation energy in eV, k is Boltzmann's constant, and T is the temperature in Kelvin. As such, precise temperature control is essential in an LPCVD reactor. Typically, the temperature control system receives data from thermocouples and adjusts power to furnace heating elements to maintain the temperature at a predetermined set point. Modem systems are capable of controlling temperatures over the range of about 300-1200° C. to an accuracy of about ±0.5° C. over a length of up to 40 inches (the “flat zone”).
Horizontal tube reactors are commonly used as LPCVD reactors because of their superior economy, throughput, uniformity, and ability to accommodate large-diameter (e.g., 150 mm) wafers. Horizontal reactors are, however, susceptible to particulate contamination of wafers placed in them. Wafers are aligned vertically and stacked in quartz racks or “boats” that support the wafers. A fused silica paddle supports the boats and is used to position the boats within the reactor. Considerable particle generation can occur when boat-laden paddles are dragged along the furnace tube during loading and unloading. The particles can land on the wafers and result in defects if particles become embedded in the growing film. The use of wheeled carriers can serve to somewhat reduce the generation of particles, but friction at the wheel bearings and movement of the wheels over the tube surface can still generate particles.
Greater reduction in the number of generated particles can be achieved by using suspended loading systems. In fully suspended loading systems, the boats and paddles are suspended at the end of a motor-driven rod and pushed into the furnace without touching the process tube walls. During processing the wafers remain suspended, and upon completion of processing the wafers are removed from the reactor, again without touching the walls of the tube. Soft-landing systems carry the boats into the process tube, lower the boats until the tube supports them, and then withdraw, leaving behind the boats and wafers. The paddles may remain within the tube or be withdrawn. Upon completion of processing, the boats and wafers are removed from the tube without touching the tube walls.
A recent innovation in furnace technology is the vertical furnace. In a vertical furnace, the wafers are also stacked side-by-side but are oriented horizontally rather than vertically (as in horizontal furnaces). The wafers are placed in boats or in perforated-quartz cages. The vertical orientation inhibits contact between the boats and the tube walls, and thus the formation of particles, without the use of suspended loading systems. Use of a vertical furnace may not completely eliminate particle formation, however. Vertical furnaces may include a quartz liner placed between the wall of the reactor and the quartz boat holding the wafers. The quartz liner may be used to confine the process gases in close proximity to the wafers during film formation. The thermocouple used to measure temperature within the furnace often includes an elongated housing placed between the wall of the furnace and the quartz liner with very close tolerance. If the thermocouple is misaligned, contact between the thermocouple and the quartz liner may cause formation of quartz particles that can contaminate the wafers. Further, such misalignment can result in incorrect temperature profiles because the temperature is being measured farther from the heating elements than called for by the furnace design criteria.
As an example, the Model Alpha 585S LPCVD reactor manufactured by Tokyo Electron Limited (Tokyo, Japan) includes a thermocouple housing inserted through an opening in the sidewall of the reactor and secured in place by an O-ring.
FIG. 1
depicts a cross-sectional view of the reactor. Thermocouple
14
is inserted through manifold
16
and resides between sidewall
12
of reactor
10
and quartz liner
20
.
FIG. 2
is an enlarged view of the circled portion of FIG.
1
. Thermocouple
14
is secured to manifold
16
by thermocouple mounting system
11
as follows: O-ring
22
is placed over the end of thermocouple
14
and secured in place with O-ring compression ring
24
and thermocouple mounting hub
26
to form a seal to preserve vacuum when reactor
10
is evacuated. Manifold
16
and thermocouple mounting hub
26
include threaded portions
18
and
28
, respectively, that are complementarily threaded to form an engagement when thermocouple mounting hub
26
is screwed onto manifold
16
. Clip ring
32
is then placed over notch
34
in the end of thermocouple
14
, and thermocouple mounting bushing
36
is coupled to the mounting hub. Thermocouple mounting hub
26
and thermocouple mounting bushing
36
include threaded surfaces
32
and
40
, respectively, that are complementarily threaded to form an engagement when thermocouple mounting bushing
36
is screwed onto thermocouple mounting hub
26
.
As currently configured, thermocouple
14
is held in place essentially only by the engagement formed between manifold
16
, O-ring
22
, compression ring
24
, and mounting hub
26
. The design of thermocouple mounting bushing
36
allows only a weak, if any, engagement between the bushing and clip ring
32
. Consequently, thermocouple
14
may wobble or move within manifold
16
, and thermocouple
14
may shift as much as 2 or 3 inches at the end opposite manifold
16
. As a result, contact between thermocouple
14
and quartz liner
20
may dislodge quartz particles from the boat and contaminate wafers contained within reactor
10
.
In addition, when reactor
10
is used as part of a solvent-based TEOS system, the solvent may lubricate O-ring
22
and render thermocouple
14
Foster Blake A.
Nelson Allan T.
Ramos Jesse C.
Advanced Micro Devices , Inc.
Conley & Rose & Tayon P.C.
Daffer Kevin L.
Lund Jeffrie R.
MacArthur Sylvia R.
LandOfFree
Modified thermocouple mounting bushing and system including... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Modified thermocouple mounting bushing and system including..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Modified thermocouple mounting bushing and system including... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2436709