Chucks or sockets – With fluid-pressure actuator – Socket type
Reexamination Certificate
1999-03-11
2001-04-10
Bishop, Steven C. (Department: 3722)
Chucks or sockets
With fluid-pressure actuator
Socket type
C118S500000, C118S503000, C118S730000, C279S051000, C409S233000, C464S162000
Reexamination Certificate
active
06213478
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to reactors for processing semiconductor substrates, and more particularly, to a mechanism for holding and releasing a susceptor shaft in such reactors.
BACKGROUND OF THE INVENTION
A variety of reactors has been used to process semiconductor substrates. Typically, each reactor
100
included a reaction chamber
105
within which a susceptor
107
was mounted. Susceptor
107
supported one of more substrates
190
.
To improve process uniformity, typically, susceptor
107
was rotated by a rotation assembly that included pulleys
127
,
128
, and motor
123
. Those of skill in the art will appreciate that reactor
100
includes several other components. However, herein, only the components necessary to understand the limitations of prior art reactor
100
are considered.
For reactor
100
, a shaft
110
was part of susceptor
107
. To mount susceptor
107
in reaction chamber
105
, dome top
109
was removed from base
125
. Shaft
110
of susceptor
107
was placed in a slip-fit bore
115
of a spindle
113
.
Spindle
113
extended through reaction chamber
105
and was connected to a pulley
128
outside of reaction chamber
105
. Pulley
128
was driven by another pulley
127
, which in turn was driven by stepper motor
123
.
Normally, susceptor
107
assumed two positions, a lower wafer load position and an elevated wafer processing position. In
FIG. 1
, the dashed lines within reaction chamber
105
show the substrate processing position of susceptor
107
while the solid lines show the substrate load position.
One problem with reactor
100
was the coupling between spindle
113
and shaft
110
. To permit shaft
110
to fit inside bore
115
, bore
115
had a slightly larger diameter than a diameter of shaft
110
. The resulting small clearance between shaft
110
and bore
115
allowed susceptor
107
to move about within bore
115
as susceptor
107
was rotated during processing.
The movement within bore
115
resulted in a wobble of susceptor
107
. The wobble was most accentuated at the periphery of susceptor
107
and resulted in poor epitaxial characteristics.
The wobble of susceptor
107
also resulted in wearing of susceptor shaft
110
which in turn increased the clearance and resulted in a more severe wobble. Reactor
100
was stopped for maintenance when the movement of the susceptor associated with the wobble exceeded a predetermined limit.
To improve the quality of the epitaxial deposition and to reduce maintenance, there is a need to effectively eliminate susceptor wobble while keeping the installation and removal of susceptor
107
reasonably easy.
SUMMARY OF THE INVENTION
According to the principles of this invention, a novel collet assembly allows a susceptor shaft to be quickly installed and removed. Moreover, the novel collet assembly eliminates any movement of the susceptor shaft within the collet as the susceptor shaft is rotated. Therefore, the collet assembly eliminates wobble associated with the susceptor shaft moving about within the mechanism holding the susceptor shaft. Consequently, the collet assembly of this invention results in more uniform processing than in the prior art configuration described above.
The collet assembly is coupled to a rotary-linear drive unit. The collet assembly allows easy placement of a susceptor shaft within a collet of the collet assembly when the collet assembly is in a first position.
After the susceptor shaft is placed into the collet, the collet assembly is retracted to a second position by a spring force acting on a collet draw bar that is coupled to the collet. As the collet assembly is retracted by the spring force, the collet is closed about the susceptor shaft by the interaction between the collet and a collet spindle in which the collet is moveably mounted.
As the collet closes, the collet assembly exerts a pressure about a circumferential surface of a susceptor shaft that in turn holds the susceptor shaft firmly in place within the collet, i.e., holds the susceptor shaft stationary within the collet. Consequently, when the susceptor shaft is rotated by the rotary-linear drive unit, there is no wobble associated with movement of the susceptor shaft within the collet.
To disengage the collet, the rotary-linear drive unit provides a force that moves the collet upwards which in turn causes the collet to release the pressure on the susceptor shaft. Thus, a linear motion is used to engage and disengage the collet, while a rotary motion is used to turn the susceptor shaft.
In one embodiment, the collet is connected to a draw bar, which is spring loaded by a clamp spring. During normal operation, the clamp spring provides sufficient force to cause the collet to firmly grasp the susceptor. To release the susceptor shaft, another force, opposite in direction to the force of the clamp spring, is applied to the collet by a linear motion drive unit.
In one embodiment, the linear motion drive unit is a pneumatic unit that includes a piston assembly mounted within a cylinder. The linear motion drive unit is coupled to the collet draw bar by a motion coupler unit. The motion coupler unit allows the linear motion drive unit to transfer linear motion to the collet draw bar without requiring a corresponding linear movement of a rotary motion drive unit. Similarly, the rotary motion drive unit provides rotary motion to the collet draw bar independent of the state of the linear motion drive unit. In one embodiment, the motion coupler unit includes a sleeve having a top surface and a bottom surface bounding a wall of the sleeve with a first set of slots in the wall extending from the top surface, and a second set slots extending from the bottom surface. A first shaft is movably mounted in the first set of slots. A second shaft is movably mounted in the second set of slots.
When the sleeve is moved up by a linear motive force, the first set of slots engage the first shaft and move the first shaft up, while the second set of slots are orientated so that the vertical position of the second shaft remains in the original position. When the second shaft is rotated, the sleeve transfers the rotary motion to the first shaft independent of the position of the first shaft relative to the first set of slots. Thus, a rotary motion drive unit drives the second shaft, while a linear motion drive unit drives the sleeve in the motion coupler unit of this invention.
Thus, with the collet and the drive units of this invention, a susceptor shaft in a substrate processing reactor is grasped, engaged, and rotated by:
placing a susceptor shaft in a collet;
moving the collet in a first direction using a linear drive unit to release the susceptor shaft; and
moving the collet in a second direction opposite to the first direction to grasp the susceptor shaft wherein the first and second directions are about a longitudinal axis of the collet; and
rotating the collet using a rotary drive unit independent of a location of the collet along the longitudinal axis of the collet.
The combination of the collet assembly and the rotary-linear drive unit does not hinder the capability normally needed for a susceptor in a substrate processing reactor, and does eliminate a source of wobble. Therefore, reactors that utilize this invention have better process uniformity than the prior art reactors that had susceptor wobble associated with the mechanism used to grasp the susceptor shaft.
REFERENCES:
patent: 3625530 (1971-12-01), Parsons
patent: 4682920 (1987-07-01), Rodgers
patent: 4791841 (1988-12-01), Pruvot et al.
patent: 5096213 (1992-03-01), Terwilliger et al.
patent: 5198034 (1993-03-01), DeBoer et al.
patent: 5571324 (1996-11-01), Sago et al.
Bishop Steven C.
Gunnison Forrest
Gunnison, McKay & Hodgson LLP
Moore Epitaxial Inc.
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