Pressure sensor module having non-contaminating body and isolation member

A non-contaminating pressure sensor module having an isolation member is disclosed. The isolation member isolates a pressure sensor within the transducer module from exposure to fluids flowing through a conduit in the module. The transducer module may be positioned in-line within a fluid flow circuit carrying corrosive materials, wherein the pressure transducer module produces a control signal proportional to either a gauge pressure or an absolute pressure of the fluid flow circuit. The pressure transducer module of the present invention also avoids the introduction of particulate, unwanted ions, or vapors into the flow circuit.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
This invention relates generally to pressure transducers. More 
particularly, this invention relates to a pressure transducer modules 
which may be connected in-line in a chemically corrosive fluid flow 
circuit, wherein the pressure sensor used therein is isolated from the 
fluid flow circuit within a non-contaminating transducer body. 
II. Discussion of the Related Art 
During the production of semiconductors, the sensitivity to contamination 
of materials used to produce them is a significant problem faced by 
semiconductor manufacturers. Various processing systems have been designed 
to reduce the amount of foreign particles and vapors generated during the 
processing of these sensitive materials. It is critical that the 
semiconductor wafers be isolated from damaging particulate and chemicals. 
In an attempt to eliminate all sources of damaging contaminants, the 
equipment used to process the semiconductor wafers has necessarily been 
designed with this goal in mind. First, the various components of the 
processing equipment are commonly designed to reduce the amount of 
particulate generated and to isolate the processing chemicals from 
contaminating influences. The processing equipment commonly has monitoring 
and sensing devices connected in a closed loop feedback which are used in 
monitoring and controlling the equipment. These monitoring and sensing 
devices must also be designed to eliminate any contamination which might 
be introduced. 
During the processing of semiconductor wafers, highly corrosive hazardous 
chemicals are commonly used. When these chemicals are used, extremely 
severe conditions within or near the processing environment may be 
encountered. Such corrosive atmospheric environments are extremely hard on 
the monitoring and sensing equipment. Further, the monitoring and sensing 
equipment may transmit wafer damaging particulate, ions, or vapors as a 
result of exposure to the corrosive atmospheric environment. Metals, which 
are conventionally used in such monitoring devices, cannot reliably stand 
up to the corrosive environment for long periods of time. Hence, the 
monitoring and sensing devices must incorporate substitute materials. 
The highly corrosive environment may be created when hazardous chemicals 
are delivered to the processing equipment. Liquid transporting systems 
carry these chemicals from supply tanks through pumping and regulating 
stations and through the processing equipment itself. The liquid chemical 
transport systems, which includes pipes, tubing, valves, and fittings and 
related devices, are frequently made of plastics resistant to the 
deteriorating effects of the toxic chemicals. Of course, anything 
mechanical is subject to potential leakage and such leakage can create 
extremely hazardous conditions both to the processing of semiconductor 
wafers or other products and also to personnel who may have to tend and 
maintain the processing equipment. Hence, the chemical transport system 
must be designed such that leakage is avoided. The monitoring and sensing 
devices may incorporate sensors which also must be designed to avoid the 
introduction of particulate, unwanted ions, or vapors into the processing 
steps. 
An in-line mechanical fluid pressure responsive gauge separated from the 
fluid flow by a protective membrane is known in the art. The gauge is 
contained within a housing having a cavity filled with a sensor fluid. The 
cavity is formed adjacent the fluid flow and separated by the protective 
membrane. The sensor fluid contained within the cavity is typically a 
silicone oil. A change in pressure within the fluid flow affects the oil 
pressure within the cavity. The oil pressure is detected by the mechanical 
pressure responsive gauge. 
The fluid within the cavity typically has large thermo-expansions which 
cause large deflection changes in the protective membrane. The large 
deflection changes in the protective membrane increases the likelihood 
that the fluid within the cavity will leak into the fluid flow, 
contaminating the flow circuit. Also, the accuracy of the pressure gauge 
is negatively affected by the large thermo- expansions of the sensor 
fluid. Hence, a need exists for an in-line pressure gauge that does not 
leak contaminating fluids into the fluid flow circuit. Also, a need exists 
for a pressure gauge, wherein the accuracy is not affected by thermo- 
changes within the fluid flow circuit. 
Collins et al., in U.S. Pat. No. 5,316,035 (the '035 patent) describes the 
use of a capacitance proximity monitoring device in corrosive atmosphere 
environments. In one embodiment of the '035 patent, the capacitance 
proximity device is described as being incorporated into a functional 
apparatus, such as a valve or coupling for tubing. The capacitance 
proximity device serves as a functional portion of the apparatus and 
creates a sensing field within a predetermined area. It is then used to 
determine the change of electrical characteristics within the 
predetermined area as various fluids flow past the predetermined area. The 
current related to the sensing field changes when the liquid target media 
is present, versus air or gas in the tubing when the liquid target media 
is absent, thereby producing an indication of the presence or absence of 
the target media. The complex valving often includes a fluid which may 
leak into and contaminate the processing fluid flow. 
The '035 patent does not disclose or even consider a device capable of 
determining various pressures within the chemical transport system of the 
processing equipment. Monitoring the pressure within the chemical 
transport system is useful for several reasons. First, a change in 
pressure within the system may be indicate leakage within the system. 
Second, the pressure within the transport system is regulated to avoid 
exceeding predetermined safety limits. Third, the pressure within a fluid 
flow circuit may be controlled to actuate various processing tools 
connected to the processing equipment. 
Therefore, a need exists for a non-contaminating pressure transducer which 
may be positioned in-line within a fluid flow circuit carrying corrosive 
materials, wherein the pressure transducer determines either a gauge 
pressure or absolute pressure of the fluid flow circuit. A need also 
exists for a pressure transducer that avoids the introduction of 
particulate, unwanted ions, or vapors into the flow circuit. The present 
invention overcomes these and other disadvantages of the related art. 
SUMMARY OF THE INVENTION 
The purpose of the present invention is to provide a pressure transducer 
module that may be coupled in-line to a flow circuit of corrosive fluid, 
wherein either the gauge pressure or absolute pressure within the flow 
circuit may be determined. The pressure transducer module includes a 
pressure sensor within an non-contaminating body. In the preferred 
embodiment, the components of the pressure transducer module includes a 
housing, a cap, an electrical connector, pressure fittings, an isolation 
membrane, a pressure sensor, electronic circuitry, a spacer ring and a 
hold down ring. 
The cap of the housing is removably attached to the housing by mating 
threads formed on an internal surface of the cap and on the external 
surface of the housing. An electrical connecter is mounted into the cover, 
allowing electrical leads within the housing to mate with external 
conductors when the cover is attached. 
The housing has a bore extending therethrough, which forms a passage or 
conduit through which fluids flow, when the transducer is connected 
in-line within a fluid flow circuit. Aligned and sealably connected to 
each open end of the bore are pressure fittings. The pressure fittings are 
constructed from a chemically inert material and are readily available and 
known to those skilled in the art. The housing also has a cavity extending 
from an external surface thereof in communication with the bore. A lip is 
preferably formed in the housing at the intersection of the cavity and 
bore. The lip has an inner dimension that is less than the inner dimension 
of the housing. The isolation membrane, pressure sensor, electronic 
circuit, spacer ring and hold down ring are all contained within the 
cavity of the housing. 
The isolation membrane is sealed against the lip of the housing within the 
cavity. In this manner, the cavity of the housing is isolated from the 
fluid flow. The isolation membrane is preferably constructed of an 
anti-corrosive, chemically inert material with polytetrafluoroethylene 
being preferred. The pressure sensor is bonded, pressed, heat welded or 
otherwise attached to the isolation membrane. The pressure sensor may be 
of a capacitance or piezoelectric type. A hybrid or fully integrated 
electronic circuit disposed in the housing is operatively coupled to the 
pressure sensor and to the aforementioned connector. 
The electronic circuit develops a signal which is a measure of the pressure 
within the flow circuit from information sensed by the pressure sensor. 
This electronic circuit may also be used in combination with temperature 
sensitive components to adjust the pressure measurement based upon 
temperature changes within the flow circuit. As mentioned, the electronic 
sensor is coupled by electrical leads to the electrical connector and 
power may be transmitted to the electronic circuit through the electrical 
leads mating at the connector with an external power supply. Further, an 
analog output such as a standard 4-20 milliamps signal proportional to the 
calculated pressure may be transmitted through additional electrical 
leads. 
The isolation membrane and pressure sensor are contained within the cavity 
by a combination of the spacer ring and hold down ring. The hold down ring 
has threading formed on its surface that mates with threading formed on 
the internal surface of the valve body defining the cavity. 
Without limitation, the housing, isolation membrane, spacer ring, and hold 
down ring are constructed of the same polymer to avoid leakage when the 
transducer is subject to thermal expansion. In the preferred embodiment 
tetrafluoroethylene fluorocarbon polymers are used. These polymers reduce 
the amount of abraded particulate, are chemically inert, and provide a 
non-contaminating pressure transducer module. 
OBJECTS 
It is accordingly a principal object of the present invention to provide a 
non-contaminating pressure transducer adapted to be connected in-line in a 
fluid flow circuit. 
Another object of the present invention is to provide a pressure transducer 
module wherein its pressure sensor component is isolated from the fluid 
flow circuit by a non-contaminating barrier. 
Yet another object of the present invention is to provide a pressure 
transducer module having an isolation member that is in direct contact 
with a pressure sensor, the isolation member acting to isolate the sensor 
and associated electronic circuitry from potentially corrosive processing 
chemicals and precluding introduction of contaminating substances into the 
processing fluids being transported. 
Still another object of the present invention is to provide a pressure 
transducer wherein a gauge pressure or absolute pressure of the flow 
circuit is measured non-intrusively. 
These and other objects, as well as these and other features and advantages 
of the present invention will become readily apparent to those skilled in 
the art from a review of the following detailed description of the 
preferred embodiment in conjunction with the accompanying drawings and 
claims and in which like numerals in the several views refer to 
corresponding parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring first to FIGS. 1 and 2, the pressure transducer module is 
generally identified by numeral 10. The pressure transducer is shown as 
having a base 12 which is used in mounting the pressure transducer module 
10 to processing equipment (not shown). The module generally includes a 
housing or body 14, pressure fittings 16 and 18 and a cover or cap 20. An 
electrical connector 22 of known construction may be removably attached to 
the cover 20. The pressure fittings 16 and 18 serve as a inlet and a 
outlet to the transducer body 14 and are of known construction. 
Those skilled in the art will recognize that the pressure transducer 
housing may take on various shapes, however a generally cylindrical shape 
as shown is preferred. A cylindrical pressure transducer body is easily 
manufactured and fluids flow more readily through a cylindrical bore or 
cavity within the transducer. The housing 14 and cover 20 are preferably 
manufactured from a chemically-inert, non-contaminating polymer such as 
polytetrafluoroethylene. 
The cover may have threading formed on an internal surface that mates with 
threading as at 24 in FIG. 3 formed on an external surface of the housing. 
The cover may thus be screwed to the housing and may further have a 
suitable o-ring seal (not shown) positioned therebetween to allow the 
cover to be hermetically sealed to the housing. A vent 26, shown in FIG. 
2, may be formed through the housing wall, thereby venting an interior of 
the housing. The vent 26 allows a pressure sensor contained within the 
housing to determine a gauge pressure. Without such a vent absolute 
pressure within the fluid flow circuit is measured. The particular 
features of the various components of pressure transducer will now be 
discussed. 
Referring to FIGS. 3 and 4, the internal construction of the pressure 
transducer is shown. A bore 28 extends through the housing forming a 
conduit, whereby when the pressure transducer module 10 is connected 
in-line, with a fluid flow circuit, via pressure fittings 16 and 18, the 
bore 28 serves as a passage within the fluid flow circuit. One end of the 
bore opening forms the inlet and the other end of the bore forms an outlet 
to the fluid flow circuit. The orientation of the pressure transducer 
module within the fluid flow circuit may be reversed without affecting the 
effectiveness of the pressure transducer. 
A cavity 30 extends all the way from an outer surface of the housing 20 to 
the bore 28. Near the region within the housing where the cavity 30 and 
bore 28 intersect, an annular lip 32 is formed. The lip 32 further defines 
an opening to the cavity from the bore. As further discussed below, the 
lip may have various shapes. 
A thin flexible polymer disk membrane 34 is positioned on the lip 32 of the 
cavity. In the preferred embodiment both the housing 14 and the flexible 
membrane 34 are manufactured from tetrafluoroethylene fluorocarbon 
polymers. One such tetrafluoroethylene fluorocarbon polymer is sold under 
the TEFLON.RTM. trademark by E. I. dupont Nemours. In the preferred 
embodiment, the disk membrane is preferably molded rather than sprayed or 
manufactured by some other process that may leave pinhole paths therein. 
When the pressure transducer module is fully assembled, the annular 
surface contact between the flexible membrane and the housing lip 32 is 
such that a hermetic seal is formed therebetween. 
Referring next to FIG. 5, the thin, flexible, Teflon membrane 34 is shown 
in greater detail. Without limitation, the membrane is preferably 
constructed to have a thickness in a range between 0.001 and 0.040 inches. 
The upper surface 36 is abraded so as to create a pattern of grooves or 
channels. Now, when the upper surface 36 of the membrane is pressed 
against the base 38 of the pressure sensor 40, any air pockets that might 
otherwise have formed between the sensor base 38 and the membrane are 
relieved, allowing more intimate contact between the membrane and the 
pressure sensor 40. The flange 52 of the spacer 50 and the o-ring 54 are 
dimensioned to allow a slight gap between the sensor 40, o-ring 54, and 
spacer 50. The inner surface of the spacer 50 may also have a pattern of 
grooves or channels formed thereon, thereby creating a passage for the 
relieved air to escape into a central region of the cavity. 
Referring again to FIGS. 3 and 4, the pressure sensor 40 is positioned on 
top of the flexible membrane 34. The pressure sensor may be of a 
capacitance type or piezoelectric type known to those skilled in the art. 
The base 38 of the pressure sensor is in direct contact with the membrane 
and may be either in pressure contact with or bonded to the membrane by an 
adhesive, thermal welding or by other known means. 
In one embodiment generally shown in FIG. 6, an alumina ceramic pressure 
sensor is comprised of a thin, generally compliant ceramic sheet 42 having 
an insulating spacer ring 44 sandwiched between a thicker, non-compliant 
ceramic sheet 46. The first thin ceramic sheet or diaphragm is 
approximately 0.005 to 0.050 inches in thickness with a typical thickness 
of 0.020 inches. The thicker ceramic sheet has a thickness range between 
0.100 to 0.200 inches. The spacer may be constructed of a suitable 
polymer. The apposed faces of ceramic disks 42 and 46 are metalized by 
metals such as gold, nickel or chrome to create plates of a capacitor. A 
similar capacitive pressure transducer is described by Bell et al. in U.S. 
Pat. No. 4,177,496 (the '496 patent). Other capacitive pressure 
transducers similar to that described in the '496 patent are available and 
known in the art. 
Referring again to FIG. 4, an electronic circuit module 48 is positioned 
above the ceramic pressure sensor 40 and is electrically coupled to the 
conductive surfaces of the ceramic pressure sensor. The electronic circuit 
module 48 is also connected by suitable leads, not shown to interval 
contacts of the connector 22 (FIG. 1). In the preferred embodiment the 
electrical connector 22 is made of a chemically inert material and 
preferably may be of a type available from Pneumatico, part number 
po3rsd-00004-24. 
The electronic circuit module 48 develops a control signal proportional to 
the pressure within the flow circuit using analog information received 
from the pressure sensor 40 related to changes in its capacitance due to 
deformation of member 42 by the fluid pressure acting on it. The 
electronic circuit may also adjust the pressure as the temperature within 
the flow circuit changes by including a thermistor or like component 
therein. 
In FIGS. 3 and 4, a cup shaped spacer member 50 is disposed above the 
pressure sensor 40 so as to exert a force on the upper surface of the 
pressure sensor 40, holding the sensor flat against the membrane 34. The 
spacer 50 further has a circumferential flange 52 (FIG. 4) which transfer 
a force against the membrane 34 and lip 32 of the cavity. An o-ring 54 may 
be positioned between the flange 52 of the spacer and the membrane, 
wherein through its elastomeric properties, the force may be transferred 
from the spacer member 50 against the membrane to clamp it against the 
annular cavity lip 32. A threaded hold down ring 56 is rotated in mating 
relation with the inner threads of the cavity of the housing or body 14, 
thereby engaging the spacer member 50 and forcing it against the pressure 
sensor 40 and membrane 34. 
In order to reduce dead space, the distance "d" (FIG. 4) that the flexible 
membrane is displaced from the lumen of the bore 28 should be kept to a 
minimum. The decrease in dead space reduces the chance of accumulation of 
debris and contamination. The decrease in dead space also reduces or 
eliminates the chance of air bubbles being trapped in the dead space and 
then suddenly released back into the flow circuit. The release of these 
air bubbles from the dead space has a negative impact on the semiconductor 
processing. The inner diameter of the lumen "D" should be equal to or 
exceed 2*(d). Ideally, the dimension, d, will be far less than the 
dimension, D, in measurement. 
FIG. 7 shows an alternative embodiment wherein the spacer member 50 has 
rounded edges as at 58. The rounded edges help focus the force of the 
spacer 50 against the flexible membrane 34 and the lip 32 of the cavity. 
This arrangement also eliminates the need for the o-ring 54. However, 
o-ring 54 may be positioned between the membrane and the lip 32 (see FIG. 
13). The flange 52 of the spacer 50 and the o-ring 54 are dimensioned to 
allow a slight gap between the sensor 40, o-ring 54, and spacer 50. The 
inner surface of the spacer 50 may also have a pattern of grooves or 
channels formed thereon, thereby creating a passage for the relieved air 
to escape. Further, the spacer 50' may have a bore extending through a 
center section, thereby extending the passage into the cavity of the 
housing. 
FIG. 8 illustrates another preferred embodiment wherein the lip 32' of the 
cavity is stepped. The o-ring 54, when compressed by the spacer member 50, 
is made to conform to the shape of the step and pushes or forces the 
flexible membrane 34, causing it to bend and mold to the shape of the 
stepped lip 32 to provide a seal against ingress of fluid. In yet another 
embodiment, the o-ring 54 may be positioned between the membrane and the 
lip 32' (see FIG. 15). 
FIG. 9 illustrates another preferred embodiment having the end of the 
spacer member flange 52 rounded, wherein the flange is forced against the 
o-ring 54 which, in turn, forces the o-ring against the flexible membrane 
34. 
FIG. 10 illustrates yet another preferred embodiment wherein the o-ring 
seal 54' is contained within an annular groove or recess 60 formed within 
the lip 32'. The flexible membrane 32 is forced against the o-ring 54', 
sealing the edges of the lip 32' thereby preventing the fluid of the flow 
circuit from leaking into the cavity of the housing. This shield 
arrangement is preferred in circumstances where the fluid flow pressure is 
less than the atmospheric pressure. In such a circumstance, the shield 
arrangement eliminates the possibility of the o-ring being drawn into the 
fluid flow circuit. 
FIG. 11 illustrates yet another embodiment wherein an annular ridge 62 is 
formed along the surface of the lip 32. When the membrane is compressed 
against the lip, the membrane conforms to the shape of the ridge. In this 
manner, an effective seal is formed between the membrane sheet and the 
housing lip. 
FIG. 12 shows yet another embodiment wherein the lip has a multiple step 
wherein the o-ring 54 is positioned on the lower step below the membrane 
32. An additional annular sealing ring 64 having an external groove 66 for 
receiving an o-ring 68 and an internal groove 70 for receiving an o-ring 
72 provides an additional seal between the housing 14 and the pressure 
sensor 40. The additional annular sealing ring 64 is shown as being 
positioned between a top step 74, and the first spacer ring 76. The spacer 
member 50 is in direct contact with both the first spacer ring 76 and the 
pressure sensor 40. In this manner, the interior of the housing is sealed 
from the fluid circuit independently of the seal created between the 
membrane 32 and the pressure sensor 40. A drain channel 78 extends through 
the housing 14 to an external surface. The drain channel 78 is positioned 
between the top step 74 and the lower step to which the seal 54 is in 
contact. If fluid from the flow circuit leaks past o-ring 54, the drain 
channel 78 allows this fluid to drain out of the housing without 
contaminating or affecting the sensor 40. 
When the o-ring 54 is positioned on the fluid flow circuit side (see FIGS. 
10 and 12-15), the o-ring must be manufactured from a chemically inert 
material. A perfluoroelastomer, such as KALREZ available from dupont 
Nemours, Inc., is suitable for this purpose. Other materials such as 
CHEMRAZ, an elastomeric PTFE available from Greene, Tweed & Co., Inc. is 
equally suitable. 
Having described the constructional features of the present invention the 
mode of use will now be discussed. The user couples the pressure 
transducer module 10 into a fluid flow circuit through pressure fittings 
16 and 18. As fluid flows through the flow circuit, the pressure distorts 
the thin ceramic plate 38 of the pressure sensor 40 as a function thereof, 
and thus changes the capacitance of the ceramic pressure sensor. The 
change in capacitance is related to the pressure within the flow circuit. 
This change in capacitance is detected by the electric circuit 48 which, 
in turn, produces an analog signal proportional to the pressure. The gauge 
pressure or absolute pressure may equally be determined. 
Those skilled in the art will recognize that the transducer output may be 
calibrated so that minimum output values are associated with minimum 
pressure and maximum output pressures are associated with maximum 
pressure. For example, a transducer intended to measure 0 to 100 psig 
(pounds per square inch gauge) can be calibrated to read 4 mA (milliamps) 
at 0 psig and 20 mA at 100 psig. 
By providing the inert Teflon membrane which is in intimate contact with 
the ceramic diaphragm 38 of the pressure sensor, the working fluid does 
not contact the surfaces of the sensor which could lead to contamination. 
The sealing arrangements disclosed insure that the working fluid does not 
enter the cavity of the housing 14 and adversely affect the electronic 
circuity. 
This invention has been described herein in considerable detail in order to 
comply with the patent statutes and to provide those skilled in the art 
with the information needed to apply the novel principles and to construct 
and use such specialized components as are required. However, it is to be 
understood that the invention can be carried out by specifically different 
devices, and that various modifications, both as to the equipment details 
and operating procedures, can be accomplished without departing from the 
scope of the invention itself.