Lift pin impact management

Details Lift pin impact management Lift pin impact management

2001-03-30

2002-11-19

Blau, Stephen (Department: 3722)

Chucks or sockets

With magnetic or electrostatic means

C279S155000, C269S071000, C269S318000, C269S903000

Reexamination Certificate

active

06481723

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the preparation of substrates such as those used in semiconductor fabrication as well as in the manufacture of hard disk drives, and more particularly to a stop for pin lifter devices configured to raise and lower substrates.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform a variety of substrate preparation and fabrication operations in which substrates such as silicon wafers are manipulated within a process environment such as a process chamber. A common method of substrate manipulation is the use of lift pins that are configured to contact a wafer, typically on a back side or non-active surface of the substrate, and with a minimum of surface area contact. In the plurality of fabrication processes that may be performed in a process chamber, the substrate may be raised or lowered as required for both manipulation within the process chamber as well as in preparation for insertion into and removal from the process chamber.
In the prior art, lift pins are configured to raise and lower a substrate between constant, fixed positions in a processing environment such as a process chamber.
FIG. 1A
shows a typical lift pin assembly
10
within a process chamber. Lift pins
16
are attached to a yoke
20
, and travel through a support chuck
14
to a back side of a wafer
12
. When a wafer is to be lifted, the lift pins
16
are configured to contact the back side of the wafer
12
in at least three points to raise the wafer
12
off the support chuck
14
. The lift pins
16
then withdraw through the support chuck
14
and lower the wafer
12
on to the support chuck
14
. As is known, when a wafer
12
is disposed on the support chuck
14
, there is no contact between the lift pins
16
and the wafer
12
. Bellows
18
are configured around each of the lift pins
16
between the support chuck
14
and the yoke
20
enclosing the lift pins
16
and preventing any contamination of the portion of the lift pin that travels through the support chuck
14
.
The yoke
20
is attached to a shaft
22
which is raised and lowered by an actuator
24
. The actuator is typically pneumatic, and can also be electrical. The raising and lowering of shaft
22
raises and lowers the yoke
20
which raises and lowers the lift pins
16
in contact with the wafer
12
. The actuator
24
receives pneumatic supply, or electrical power and control through cable
26
.
The lower portion of the lift pin assembly
10
includes the lift pin stops
30
,
32
. An upper pin stop
30
is inserted through an upper pin stop housing plate
28
. The upper pin stop housing plate is connected to shaft
22
. Contact between the upper pin stop
30
and an upper pin stop plate
35
halts upward travel of the shaft
22
and raising of the lift pins
16
.
A lower pin stop
32
is inserted through a lower pin stop housing plate
34
. Contact between the upper pin stop housing plate
28
and the lower pin stop
32
halts downward travel of the shaft
22
and lowering of the lift pins
16
.
FIG. 1B
shows a closer view of upper pin stop
30
shown in FIG.
1
A. As described in reference to
FIG. 1A
, the upper pin stop housing plate
28
is attached to shaft
22
(not shown in FIG.
1
B). As the lift pin assembly
10
lifts the wafer
12
, upper pin stop housing
28
travels upward closing a gap
38
between upper pin stop housing plate
28
and upper pin stop plate
35
. Upward travel of upper pin stop housing plate
28
is halted by contact between a tip
36
of upper pin stop
30
and upper pin stop plate
35
. Upper pin stop
30
thus stops the raising of lift pins
16
and the wafer
12
.
FIG. 1B
shows that upper pin stop
30
is configured through upper pin stop housing plate
28
. Typically, pin stops
30
and
32
are threaded to provide for adjustment of the pin stop
30
,
32
position in housing plates
28
,
34
. The position of the upper pin stop
30
is therefore adjustable by raising or lowering the upper pin stop
30
in upper pin stop housing plate
28
. Adjustment of upper pin stop
30
sets the upper extent of the lift pin assembly
10
by establishing the point at which upper travel of upper pin stop housing plate
28
is halted. In a similar manner, the lower pin stop
32
(See
FIG. 1A
) sets the lower extent of the lift pin assembly
10
.
As can be seen in
FIG. 1B
, the contact between the tip
36
of upper pin stop
30
and the upper pin stop plate
35
that halts upward travel is a direct, surface to surface contact. In some prior art applications, the material from which the upper pin stop plate
35
is constructed is metal, and the material from which the upper pin stop
30
is constructed is metal, and so the resulting contact is metal to metal contact. In some prior art applications, the upper pin stop
30
has been constructed of a hard plastic, and so the resulting contact is hard plastic to metal. Additionally, some prior art applications incorporate hard plastic layers over the contact areas, also known as stopping surfaces, of upper pin stop housing plate
28
(See
FIG. 1A
) and upper pin stop plate
35
.
Each of the above described types of contact used in a pin stop assembly
10
result in problems with prior art pin stops. In the configuration where a metal pin stop
30
, contacts a metal upper pin stop plate
35
, the result is an abrupt, hard stop. An abrupt, hard stop is a rapid deceleration caused by hard surface to surface contact typically causing lift pin
16
vibration, bounce, or noise. The metal to metal hard stop can be so abrupt and hard that wafer
12
shifting on the lift pins
16
can result, and in some cases, wafer
12
fracture. Wafer
12
shifting, however slight, can be detrimental to process operations. By way of example, in plasma etching operations, wafer shifting introduces intolerable variance into the process.
The use of hard plastic pin stops or the use of hard plastic layers over the stopping surfaces and resulting hard plastic to metal contact can dampen an abrupt hard stop, but introduces inaccuracies in wafer
12
positioning. Over time, hard plastic exhibits deformation. The deformation results in a change in wafer
12
positioning, and a known requirement in wafer processing is constant, predictable wafer
12
positioning. Hard plastic deformation can result from repeated impact and contact in accordance with pin stop function and design, and can be exacerbated by heat. The deformation of hard plastic used in a hard plastic to metal contact configuration introduces an unacceptable variance.
One approach, as described above, to mitigating the problems associated with hard stops is to re-configure the metal to metal contact by, for example, introducing a hard plastic alternative. It has been found that hard plastic is generally unacceptable, as already described. Another approach to the hard stop problems is to mechanically dampen the movement of the shaft
22
(See
FIG. 1A
) at the actuator
24
(See FIG.
1
A). Unfortunately, known mechanical dampening techniques require more space than is available within a process chamber, and tend to contribute unacceptable cost to design and manufacture.
In view of the foregoing, there is a need to develop and implement a pin stop that can be easily and inexpensively utilized in all manner of substrate lift pin assemblies. The pin stop design should be able to be implemented in existing lift pin assemblies such as those within semiconductor wafer process chambers with a minimum of available space. The pin stop should reduce or eliminate the prior art problems caused by hard stops resulting in wafer shifting or breakage.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing a simple pin stop that is easily integrated into existing systems and assemblies, and produces a consistent, repeatable, and reliable pin stop while minimizing and eliminating unacceptable wafer shifting or breakage. The present invention can be implemented i

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