Measuring and testing – Fluid pressure gauge – Combined
Reexamination Certificate
2000-07-06
2002-12-17
Patel, Harshad (Department: 2855)
Measuring and testing
Fluid pressure gauge
Combined
Reexamination Certificate
active
06494100
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a vacuum chamber and, more particularly, to a circuit and apparatus for verifying evacuation of the chamber after a substrate is loaded into the chamber for processing.
2. Description of the Related Art
A substrate is generally defined as a material upon which processing takes place. For example, a substrate can receive deposition, etch, implant, heat (anneal) and various clean cycles. A popular type of substrate is one which is silicon-based and generally known as a semiconductor wafer. Substrate, however, is a term henceforth used to encompass any object which receives processing and therefore is defined to extend beyond a semiconductor wafer.
In many instances, optimal substrate processing involves placing the substrate inside a chamber containing an ambient dissimilar from that which surrounds the chamber. Ambient within the chamber may be controlled to ensure processing is carried out according to a specific processing “recipe.” Using the semiconductor wafer example, certain types of deposition require wafers within a chamber be subjected to a vacuum and substantial temperatures. Low pressure, high temperature deposition upon the wafer is well recognized as, for example, low pressure chemical vapor deposition (“LPCVD”). Low pressure processing to produce a LPCVD film is but one example of many involving a chamber and pressurization within that chamber. Pressurization levels within a chamber to effectuate optimal processing of the substrate is critical not only to produce accurate film properties, but also to minimize contamination within the chamber during any or all of the various processing steps beyond deposition.
When film is being deposited, etchant delivered, dopants implanted or temperatures applied, it is important that extraneous material not be allowed to enter the chamber during those critical processing steps. For example, if gas or particulate matter enters the chamber during LPCVD processing, the ensuing film may suffer improper conformality and/or electrical properties. It is therefore desired that the chamber ambient receive proper pressurization levels before processing is applied to the substrate. This implies that all apertures and/or orifices into the chamber be sealed after the substrate is loaded and before the substrate is processed.
FIG. 1
illustrates one example of an application involving a chamber
10
which can be pressurized (i.e., a pressurized chamber). A mechanism
12
is used for loading one or more substrates
14
into chamber
10
prior to evacuating the chamber. In the example provided, chamber
10
may be configured as a horizontal tube LPCVD reactor which can be used to deposit doped or undoped dielectric films upon exposed surfaces of substrate
14
. Further to that example, substrate
14
may be a silicon-based semiconductor wafer fixed on edge within a carrier secured to a paddle or plunger
16
. Thus, the carrier which secures one or more wafers, defined as substrate
14
, may be secured to a door
18
to which plunger
16
is coupled. Within the semiconductor fabrication industry, chamber
10
can be referred to as a furnace or reactor, which can receive radiated heat via resistive heating coils surrounding the reactor. Chamber
10
interior walls may be made of quartz or metallic material which are somewhat inert to reactant gasses
20
metered into chamber
10
at one end of the chamber. The other end of chamber
10
is coupled to a vacuum pump which extracts reactant byproducts
22
in the direction shown.
Metering the reactant gasses
20
, and evacuating byproducts
22
occur only if it is known that the inside of chamber
10
is properly sealed. This requires knowing that door
18
is properly sealed against exterior ambient ingress. Door
18
may be designed to close in the direction of arrows
24
until a seal occurs between a flange
26
at one end of chamber
10
and a sealing membrane
28
arranged on a chamber-facing surface of door
18
. Membrane
28
may comprise an o-ring, and flange
26
may be stainless steel or quartz. Flange
26
comprises a relatively planar surface upon which membrane
28
can be compressed when door
18
closes. Once compressed, membrane
28
seals the interface between door
18
and chamber
10
.
Before processing can occur (i.e., before reactant gas is metered into the chamber and byproducts removed), it is important to ensure the chamber's integrity by verifying closure of door
18
. Many conventional mechanisms are available to provide door closure verification. A popular mechanism may involve a proximity switch
30
mounted to the exterior surface of chamber
10
. Proximity switch
30
is generally considered a “contact” switch which movably reciprocates when placed in contact with a protrusion
32
of door
18
. Merely as an example, door
18
may include a protrusion
32
and chamber
10
exterior housing may include a receptacle
33
. As protrusion
32
enters receptacle
33
toward which switch
30
extends, protrusion
32
surface will contact and thereafter move the switch lever from a normally open position to a closed position. Of course, there may be numerous other mechanisms on which switch
30
is mounted and from which switch
30
is activated. The receptacle/protrusion mechanism is shown only as an example.
Entry of protrusion
32
into the receptacle
33
of chamber
10
hopefully coincides with the compression (i.e., seal) of membrane
28
against flange
26
. When moved, protrusion
32
should manually brush against the lever of switch
30
, causing that lever to transition upon a contact as shown in further detail in FIG.
2
.
FIG. 2
illustrates closure of lever
34
between a pair of contacts
36
a
and
36
b.
Closure of lever
34
across contacts
36
produces a signal from switch
30
upon conductor
38
.
In many instances, there may be two switches. A second switch
40
may be present as shown in
FIGS. 1 and 2
. Switch
40
may suffice as a back up if switch
30
is rendered inoperable. Switch
40
may also serve as a fail stop to prevent protrusion
32
from unduly pressing against chamber
10
housing should switch
30
fail. Switch
40
, similar to switch
30
, comprises a pair of contacts
42
a
and
42
b,
and a lever
44
which reciprocates between contacts
42
. A conductor
46
extends from switch
40
to indicate status of the switch and, more importantly, whether door
18
is closed against flange
26
.
The nature of proximity switches in general and the mechanism by which they are mounted does not always allow accurate verification of door closure. Proximity switches rely upon movement of the levers
34
and
44
when contacted with protrusion
32
. If the protrusion and/or door should become misaligned, then actuation of levers may not occur indicating the door is open when in fact it is closed. Furthermore, integrity of the contacts may be lessened through extensive wear, also resulting in a switch that is open when the door is actually closed. Conversely, membrane
28
, and the integrity by which membrane
28
mates with flange
26
, may be reduced after repeated door closure so that the seal between those structures will eventually fail even though switches
30
and
40
indicate switch closure.
Conventional proximity switches and their use in verifying door closure is therefore not always absolute. In actuality, proximity switches mostly determine the status of the switches and not necessarily the status of door closure or, more importantly, status of pressure within the chamber. If the door is closed but the switches fail and do not indicate closure, then the processing tool will hold off its processing until the misreading problem has been solved. This can reduce processing throughput. Conversely, if the switches indicate the door is closed and yet the door is open, then gasses external to the chamber will be drawn into the chamber along with the evacuated byproducts. Ingress of, for example, oxygen or hydrogen into chamber
10
during LPCVD oxide or nitride f
Conley & Rose & Tayon P.C.
Cypress Semiconductor Corp.
Daffer Kevin L.
Patel Harshad
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