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Claims  |
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What is claimed is:
1. A semiconductor wafer for sensing and recording processing conditions to
which the wafer is exposed, comprising:
a semiconductor substrate having a plurality of regions spaced upon one
surface of said substrate;
at least one sensor lithography formed within each of said regions for
producing during use an analog signal responsive to a processing
condition;
a signal acquisition/conditioning circuit coupled to an output of said
sensor and lithography formed upon said substrate for converting said
analog signals to digital signals;
a microprocessor system lithography formed upon said substrate having a
stored instruction set, said system comprises:
an input port coupled to an output of said acquisition/conditioning circuit
for receiving said digital signals; and
a random access memory having an addressable data bus connected to said
input port for recording said digital signal during times in which a
select said stored instruction set is executed.
2. The semiconductor wafer as recited in claim 1, wherein said plurality of
regions are spaced substantially equi-distant from each other across said
substrate with said acquisition/conditioning circuit and said
microprocessor system arranged between select said regions.
3. The semiconductor wafer as recited in claim 1, further comprising a
power source formed within said substrate.
4. The semiconductor wafer as recited in claim 1, wherein said signal
acquisition/conditioning circuit comprises an amplifier circuit, a sample
and hold circuit, and an analog-to-digital converter.
5. The semiconductor wafer as recited in claim 1, wherein said signal
acquisition/conditioning circuit comprises a multiplex circuit coupled to
receive the analog signal from a plurality of sensors and further adapted
for producing a serial time-division multiplex output corresponding to the
analog signal from each said sensor.
6. The semiconductor wafer as recited in claim 1, wherein said signal
acquisition/conditioning circuit and said microprocessor system are
synchronously controlled from an external control circuit, and said
external control circuit is coupled to, and can be accessed through, an
input probe pad arranged upon said semiconductor substrate, wherein said
input probe pad is operably connected to an external input device during
times in which said external control circuit is accessed through said
input probe pad.
7. The semiconductor wafer as recited in claim 6, wherein said external
input device comprises a keyboard.
8. The semiconductor wafer as recited in claim 1, further comprising an
output port coupled to said data bus for receiving said digital signals
upon said data bus during times in which a select said stored instruction
set is executed.
9. The semiconductor wafer as recited in claim 8, wherein said output port
comprises an output probe pad operable connected during use to an external
output device.
10. The semiconductor wafer as recited in claim 9, wherein said external
output device comprises an electronic display.
11. The semiconductor wafer as recited in claim 1, wherein said sensor
comprises a light emitting diode and a photodiode formed within said
substrate and spaced apart from each other a select distance, said light
emitting diode produces during use a light beam capable of reflection from
a remote target and said photodiode receives during use said reflected
light beam during times in which said remote target is a calibrated
distance from said semiconductor substrate.
12. A semiconductor wafer for sensing, recording and retrieving processing
conditions to which the wafer is exposed, comprising:
a semiconductor substrate having a plurality of regions spaced upon one
surface of said substrate;
a plurality of sensors lithography formed within each of said regions for
producing during use a plurality of analog signals responsive to a
plurality of processing conditions existing across substantially the
entire said substrate;
a multiplex circuit coupled to receive said plurality of analog signals
from said plurality of sensors;
a sample and hold circuit coupled to serially receive multiplex output from
said multiplex circuit and temporarily store said multiplex output;
an analog-to-digital converter coupled to the output of said sample and
hold circuit for producing a plurality of digital signals corresponding to
respective said plurality of analog signal;
a microprocessor system lithography formed upon said substrate having a
programmable read only memory for storing an instruction set, said system
comprises:
an input port coupled to an output of said analog-to-digital converter for
receiving said digital signals;
a random access memory having an addressable data bus connected to said
input port for recording said digital signals within said random access
memory during times in which a select said stored instruction set is
executed; and
an output probe pad arranged upon said semiconductor substrate capable of
electrical connection to an external output device for retrieving said
digital signals from said random access memory during times in which a
select said stored instruction set is executed.
13. The semiconductor wafer as recited in claim 12, wherein said multiplex
circuit, said sample and hold circuit, said analog-to-digital converter
and said microprocessor system are synchronously controlled from an
external control circuit, and said external control circuit is coupled to,
and can be accessed through an input probe pad arranged upon said
semiconductor substrate, wherein said input probe pad is operably
connected to an external input device during times in which said external
control circuit is accessed through said input probe pad.
14. The semiconductor wafer as recited in claim 12, wherein said external
output device comprises an electronic display.
15. The semiconductor wafer as recited in claim 13, wherein said external
input device comprises a keyboard.
16. The semiconductor wafer as recited in claim 12, further comprising a
rechargeable power supply, said battery is formed within said substrate
and is connected to said sensors, said multiplex circuit, said sample and
hold circuit, said analog-to-digital circuit and said microprocessor
system.
17. The semiconductor wafer as recited in claim 12, wherein a pair of said
plurality of said sensors comprises a light emitting diode and a
photodiode formed within said substrate and spaced apart from each other a
select distance, said light emitting diode produces during use a light
beam capable of reflection from a remote target and said photodiode
receives during use said reflected light beam during times in which said
remote target is a calibrated distance from said semiconductor substrate.
18. A method for sensing, recording and retrieving processing conditions
into and from a semiconductor wafer, comprising the steps of:
providing a semiconductor substrate having a plurality of sensors spaced
upon said substrate;
sensing a plurality of processing conditions placed upon said semiconductor
substrate;
assigning an analog signal to each of said plurality of processing
conditions;
multiplexing each analog signal into a stream of analog signals;
converting said stream of analog signals into a plurality of digital
signals; and
encoding each of said plurality of digital signals and placing said encoded
digital signals upon a data bus connected to an array of memory cells.
19. The method as recited in claim 17, further comprising:
providing a signal acquisition/conditioning circuit and a microprocessor
system upon said substrate;
providing a conductive input probe pad upon said substrate, said input
probe pad is connected to an input of said acquisition/conditioning
circuit and said microprocessor system; and
sending an instruction set, and programmable control signals to said
acquisition/conditioning circuit and said microprocessor system from an
input device connectable to said input probe pad.
20. The method as recited in claim 17, further comprising:
providing a decoder circuit and an output probe pad connected to said data
bus;
addressing select said array of memory cells and sending a digital
information signal representative of information stored within said cells
upon said data bus; and
decoding said digital information signal and forwarding said decoded
digital information signal to an output device connectable to said output
probe pad. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to semiconductor wafer processing and more
particularly to a wafer which can sense and record processing conditions
to which the wafer is exposed, and can also write the recorded processing
conditions to an external output device brought in electrical contact with
the wafer.
2. Background of the Relevant Art
The fabrication of an integrated circuit generally employs numerous
processing steps. Once a starting material or bulk substrate is provided,
many masking layers and processing steps are presented to the substrate to
form an overall semiconductor topography. The topography includes
diffusion regions, dielectrics, contacts, metallization and passivation
necessary to form an integrated circuit.
An exemplary sequence of steps involves growing thin film material upon the
wafer substrate. Thereafter, photoresist is coated upon the thin film and
a lithography mask is imaged upon the photoresist in order to allow
radiation to polymerize certain photoresist areas. The non-polymerized
photoresist can be removed and previously deposited, underlying thin film
material (e.g., polycrystalline silicon, metallization, silicon oxide,
silicon nitride or spin-on glass) can be etched away to form a desired
geometric structure. Individual masks requiring many processing steps are
needed in order to form active areas into which, for example, field effect
transistors (FETs) are lithographically placed. Capacitor plates and/or
dielectrics as well as resistive elements can also be formed upon the
substrate topography in order to assist FET operation.
Each process step must be carefully monitored in order to provide an
operational integrated circuit. Throughout the imaging process, deposition
and growth process, etching and masking process, etc., it is critical, for
example, that temperature, gas flow, vacuum pressure, chemical gas
composition and exposure distance be carefully controlled during each
step. Careful attention to the various processing conditions involved in
each step is a requirement of optimal semiconductor processing. Any
deviation from optimal processing conditions may cause the ensuing
integrated circuit to perform at a substandard level or, worse yet, fail
completely.
Conventional techniques used for monitoring processing conditions generally
involve various transducers placed within the processing chamber or upon
the chamber wall. The transducers attempt to read the processing
conditions to which the wafer is exposed. However, in many chambers, there
is a significant distance between the wafer and the transducer location.
If, for example, the transducer is placed on the deposition or anneal
chamber inner wall, the transducer will read a different temperature than
the temperature to which the actual wafer is exposed. It is well known
that, for example, temperature, gas flow rate and/or gas composition is
dissimilar at the chamber wall as opposed to the middle of the chamber,
where the wafer generally resides. The thermal conductivity of a wafer is
not equal to the thermal conductivity of the ambient chamber area or
chamber wall. Still further, areas of laminar and non-laminar flow exist
throughout the chamber. While transducers on the chamber wall may indicate
laminar flow within a specified flow rate, the wafer placed near the
center of the chamber may instead be subject to deleterious non-laminar
flow outside acceptable flow specification limits. There exists many
further examples of processing condition readings taken from the chamber
wall or ambient within the chamber which do not correspond to readings at
the wafer surface. In order to precisely determine processing conditions
at the wafer, it is critical that measurements be taken upon the wafer and
the readings be recorded in situ.
As defined herein, "processing conditions" refer to various processing
parameters used in manufacturing an integrated circuit. Processing
conditions include any parameter used to control semiconductor manufacture
and/or semiconductor operation such as temperature, processing chamber
pressure, gas flow rate within the chamber, and gaseous chemical
composition within the chamber. Processing conditions still further
include parameters used to measure vibration and acceleration (or
movement) of the wafer through the chamber, and to control the accurate
placement of an image and etchant upon the wafer. Specifically, it is
important to monitor the relevant position of a mask with respect to the
wafer surface. Many types of exposure techniques are used such as contact
printing, proximity printing, projection printing and step-and-repeat
printing. Each of these exposure techniques many require an accurate
determination of the distance between the wafer and the mask as well as
the distance between the wafer and the radiation source. Conventional
exposure techniques may use monitors placed on the printing equipment
which mechanically measure the distance between a wafer chuck or holder
and the mask or source. In order to determine a true distance between the
wafer's upper surface and the mask or source, approximation may be needed
as to the wafer's thickness. Generally, a standardized thickness is used.
Unfortunately, wafers usually have varying thickness depending upon the
number of processing steps used or upon the initial substrate thickness.
Dissimilar wafer thickness can lead to inaccurate or imprecise knowledge
as to the relative distance between the wafer's upper surface and the mask
or source.
Wafer thickness not only determines proper mask or source placement, but it
also determines wafer etch effectiveness. A standard dry etch chamber
utilizes a chamber filled with a gas (generally reactive gaseous material)
and a pair of electrodes, wherein one electrode is sized to accommodate a
wafer. Many conventional dry etch chambers having spaced electrodes cannot
achieve optimal etch of the wafer unless the spacing between one electrode
and a wafer placed on the other electrode is calibrated prior to and
monitored throughout each wafer etch operation. Slight changes in the gap
or distance between the wafer and the opposing electrode may substantially
change the plasma etch rate. It is well known that etch rate varies
depending upon the spacing between the wafer and the opposing electrode as
well as the operating pressure, temperature and gas flow rate exerted upon
the wafer. Etch rate often increases as the voltage across the electrodes
(sheath voltage) increases. Furthermore, sheath voltage will increase as
the spacing or gap decreases, or if the rf voltage upon a powered
electrode increases. Conventional methods used to calibrate and monitor
spacing generally use mechanical means such as clay balls to measure and
calibrate the electrode gap. Clay balls deform when opposing electrodes
contact the balls, a resulting measurement can then be achieved from the
deformed balls. Measurements taken from the balls do not accurately and
consistently correspond with the gap which causes the deformation. Thus,
indirect, mechanical measurement generally lacks accuracy needed for true
calibration.
In order to overcome the problems with mechanical calibration, a more
precise measurement/calibration technique using non-mechanical (i.e.,
optical) measurement principles has been recently devised, and is
described in co-pending, commonly owned, U.S. patent application Ser. No.
08/033,025 (herein incorporated by reference). Patent application Ser. No.
08/033,025, illustrates optical linear encoders mounted to the chamber
housing instead of directly upon the wafer itself. Although linear
encoders provide suitable calibration between the electrodes, they are not
directly coupled to the wafers, nor can they directly read the actual
distance between one electrode and a wafer surface of a wafer arranged on
the other electrode. Again, approximations are needed to extrapolate the
actual distance based upon the measured distance taken at the
housing-mounted linear encoder.
It is important not only to measure processing conditions upon the wafer,
but it is equally important to measure processing conditions across the
entire wafer surface. Oftentimes, processing parameters vary across the
wafer surface. Gas flow chambers generally place a greater flow rate near
the center of the chamber than at the wafer edges (i.e., near the chamber
walls). As such, large area wafers placed in such a chamber may receive
greater gas nucleation and/or deposition near the wafer center than at the
edges. Further, due to the radiant heat of the chamber walls, a greater
temperature exists at the edge of the wafer than at the center. These are
but a few examples of processing condition gradients which occur across a
standard wafer. Modern wafers of eight inch diameter or larger are even
more susceptible to processing condition gradients. In order to reduce the
deleterious effects of such gradients, it is important to first ascertain
that gradients occur, and then to closely monitor their occurrence during
actual wafer processing. Unless the gradients can be sensed at various
points across the entire wafer surface, the gradients cannot be
ascertained and certainly cannot be monitored in situ.
SUMMARY OF THE INVENTION
The problems outlined above are in large part solved by the programmable
semiconductor wafer of the present invention. That is, the semiconductor
wafer hereof can be placed into standard semiconductor
processing/fabricating equipment. The semiconductor wafer can be placed
into a processing chamber where in situ readings are taken and stored
within the semiconductor wafer. The readings can be retrieved by an
external output device in order for an operator to determine whether
processing conditions are correct before standard wafers are introduced
into the fabricating unit. Thus, the semiconductor wafer operates as a
"smart wafer" which can be easily placed at a wafer location within a
standard wafer fabrication unit and within the standard processing flow.
The semiconductor wafer not only senses processing conditions taken at the
wafer processing site, but also stores those conditions within a memory
array arranged upon the wafer itself. Still further, the wafer can sense
one or more processing conditions at select regions across the wafer
surface in order to accurately determine processing condition gradients to
which the wafer is exposed. Even still further, the stored processing
conditions can be easily retrieved from the memory array via an output
probe pad arranged upon the wafer. Yet further, the wafer can be easily
programmed through an input probe pad also arranged upon the wafer.
By placing sensors directly upon the wafer and by arranging a plurality of
sensors across the wafer surface, an accurate gradient reading of various
processing conditions can be obtained and recorded for future use.
Importantly, the processing conditions can be fed into an output device
which can then alter the process parameters before standard wafers are
introduced. An on-board processor formed upon the wafer can be programmed
to compute and wave shape average signals sent from the sensor in order to
enhance signal-to-noise ratio, and provide gain. Most notably, the
processor can output (i.e., download) stored digital data to an external
processor, wherein the external processor can calculate projected wafer
yields based upon the processing conditions exerted across the wafer.
Based upon those yields, the operator can then adjust or modify the
process equipment in order to improve those yields prior to the chamber
receiving a wafer to be processed. By placing the programmable wafer
inside an actual processing chamber and within the standard processing
flow, the programmable wafer hereof can act as an in situ, smart wafer to
obtain more accurate, actual readings of what subsequently placed standard
wafers would experience while in the same process chamber and while
undergoing the same processing conditions.
The programmable semiconductor wafer is well suited for measuring the
distance between the upper surface of the wafer and the mask, the
radiation source, and/or the etch electrode. The semiconductor wafer
overcomes inaccuracies of conventional measuring techniques and can more
precisely measure actual spacing or distance at or from the wafer's upper
surface.
Broadly speaking, the present invention contemplates a programmable
semiconductor wafer for sensing and recording processing conditions to
which the wafer is exposed. The semiconductor wafer comprises a
semiconductor substrate having a plurality of regions spaced upon one
surface of the substrate, and at least one sensor lithographically formed
within each of the regions capable of producing an analog signal
responsive to a processing condition. A signal acquisition/conditioning
circuit is coupled to an output of the sensor and is lithographically
formed upon the substrate for converting the analog signals to digital
signals. A microprocessor system is also lithographically formed upon the
substrate, wherein the microprocessor system includes a stored instruction
set and comprises an input port coupled to an output of the
acquisition/conditioning circuit for receiving the digital signals. The
microprocessor system further comprises a random access memory and a data
bus connected between the random access memory and the input port for
recording the digital signals during times in which a select stored
instruction set is executed.
The plurality of regions are preferably placed substantially equi-distant
from each other across the substrate with the acquisition/conditioning
circuit and the microprocessor system arranged between select regions. It
is preferred that the signal acquisition/conditioning circuit includes an
amplifier circuit, a sample and hold (S/H) circuit, and an
analog-to-digital (A/D) converter. The acquisition/conditioning circuit
further includes a multiplex circuit adapted for receiving an analog
signal from each of a plurality of sensors and further adapted for
producing a multiplexed serial output responsive to each sensor output.
The signal acquisition/conditioning circuit and the microprocessor system
are synchronously controlled from an external control circuit. The
external control circuit is coupled to, and can be accessed through, an
input probe pad arranged upon the semiconductor substrate, wherein the
input probe pad is capable of electrical connection or contact by an
external input device. The input probe pad includes other connection means
and can be configured to receive optically transmitted, acoustically
transmitted, and/or inductively transmitted information. Thus, the input
probe pad herein is not limited solely to a mechanical receptor, such as a
bonding pad, but also may include a photosensor, a microphone, or any
other type of well known transducer, etc.
The present invention further contemplates a semiconductor wafer for
sensing, recording and retrieving processing conditions to which the wafer
is exposed. The semiconductor wafer comprises a semiconductor substrate, a
plurality of sensors, a multiplex circuit, a sample and hold (S/H)
circuit, an analog-to-digital (A/D) converter, and a microprocessor, each
of which is lithography formed upon the substrate. The multiplex circuit
is coupled to receive a plurality of analog signals from the sensors, and
the S/H circuit is coupled to serially receive multiplex output from the
multiplex circuit and temporarily store that output. The A/D converter is
coupled to the output of the S/H circuit for producing a plurality of
digital signals corresponding to the plurality of analog signals. The
microprocessor system includes a programmable read only memory for storing
a set of instructions which are written into the semiconductor wafer via
an input probe pad and an external input device/driver connectable to the
input probe pad. The microprocessor system also includes a memory array
(or random access memory) and an output probe pad capable of electrical
connection to an external output device. The output probe pad provides a
conductive channel through which digital signals can be read or retrieved
from the random access memory.
The present invention still further contemplates a method for sensing,
recording and retrieving processing conditions into and from a
semiconductor wafer. The method comprises the steps of providing a
semiconductor substrate having a plurality of sensors spaced upon the
substrate. A plurality of processing conditions exerted upon the substrate
are then sensed by the sensors, and an analog signal is then assigned to
each of the plurality of processing conditions and each analog signal is
multiplexed into a stream of analog signals. The stream of analog signals
can then be converted into a plurality of digital signals, wherein the
digital signals can be encoded and placed upon a data bus addressably
connected to an array of read/write memory cells. A decoder circuit may
also be provided having an output probe pad connected to the data bus. A
select array of memory cells can be addressed and digital information
signals, stored within the cells, can be sent to the data bus where the
digital information signals can be decoded and forwarded to an output
device connectable to the output probe pad.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the invention will become apparent upon
reading the following detailed description of the invention and upon
reference to the accompanying drawings in which:
FIG. 1 is a plan view of a programmable semiconductor wafer according to
the present invention;
FIG. 2 is a block diagram and associated signal flow of a programmable
semiconductor wafer according to the present invention;
FIG. 3 is a block diagram and associated signal flow of a signal
acquisition and conditioning circuit according to the present invention;
FIG. 4 is a block diagram and associated signal flow of a CPU, memory, and
input/output arrangement of a processor according to the present
invention; and
FIG. 5 is a cross-section view of a dry etch chamber showing opto-electric
electrode position detection and calibration technique utilizing a
programmable semiconductor wafer according to the present invention.
While the invention is susceptible to various modifications and alternative
forms, specific embodiments thereof are shown by way of example in the
drawings and will herein be described in detail. It should be understood,
however, that the drawings and description thereto are not intended to
limit the invention to the particular forms disclosed, but on the
contrary, the intention is to cover all modification, equivalents and
alternatives falling within the spirit and scope of the present invention
as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
Turning now to the drawings, FIG. 1 illustrates a plan view of a
programmable semiconductor wafer 10. Wafer 10 includes numerous circuits
formed upon its surface topography according to standard fabrication
techniques. The circuits contained within wafer 10 are necessary to sense,
store and retrieve processing conditions exerted upon the wafer. Circuits
include sensors 12 placed within select regions 14 configured across the
surface of wafer 10. Each region 14 includes at least one sensor 12 and
preferably many sensors capable of reading one or numerous processing
conditions. A sensor within each region is configured to detect a single
processing condition. If more than one sensor is formed within each
region, then numerous processing conditions can be detected based upon the
number of sensors so formed. Sensors 12 can read, store and retrieve one
or many processing conditions registered within each region 14 and across
the semiconductor wafer. Regions 14 are preferably placed substantially
equi-distant from one another across the entire wafer surface in order to
obtain an accurate gradient reading thereon. FIG. 1 illustrates only four
sensors 12 placed within each of seven regions 14. However, it is
understood that, provided there is more than one sensor in each region,
less than or more than four sensors can be formed within each region
depending upon the number of processing conditions requiring detection.
Furthermore, there can be as few as two regions or much more than seven
regions arranged in wafer 10.
Placed between select regions 14 is a semiconductor power device 16 capable
of photoelectronic conversion or of direct electrical storage using
conventional capacitor arrays or a thin film lithium battery. Power device
16 can store power upon an electrode structure formed within wafer 10 as
illustrated in U.S. Pat. No. 5,142,331 (incorporated herein by reference).
Power device 16, utilizing a photoelectric battery, is capable of
converting photon energy to electrical energy and storing that energy upon
an electrode for subsequent use by various circuits contained with wafer
10. Although U.S. Pat. No. 5,142,331 illustrates GaAs substrate upon which
the photoelectric storage electrode is formed, it is understood that a
similar electrode structure with similar storage capability can also be
formed upon other types of bulk substrate material, including silicon, in
accordance with conventional techniques known in the art.
Placed between select regions 14 and spaced from power supply 16 is a
signal acquisition/conditioning circuit 18 and a processor 20 containing
read only as well as read/write memory. Acquisition/conditioning circuit
18 is connected between processor 20 and each sensor 12 contained within
each region 14. Circuit 18 provides a data-conversion function, while
processor 20 contains digital components which perform computer and/or
peripheral interfacing tasks. Acquisition/conditioning circuit 18 includes
circuitry necessary to accommodate the input or sensor voltage of each
sensor 12 into a digital signal acceptable for processor 20. To transform
the analog signal from each sensor 12 to a digital data stream acceptable
by processor 20, a multiplex circuit as well as an A/D converter and
amplifier is needed as part of circuit 18. Furthermore, to increase the
speed at which the information can be accurately converted, a S/H circuit
may also be used as part of circuit 18 to compress analog signal
information. The parts or components of circuit 18 is illustrated in FIG.
3 and will be described further hereinbelow.
Coupled to acquisition/conditioning circuit 18, as well as processor 20, is
an external control circuit 22 which can be arranged in one or more
locations between regions 14 as would be necessary to maximize the use of
semiconductor real estate. External control circuit 22 is capable of
receiving programmable input from an external device and, based upon that
input, provide timing pulses, enables, etc., to circuit 18 as well as
processor 20. Input indicia into external control circuit 22 is provided
via an input probe pad 24. Pad 24 is a conductive, substantially planar
structure connected to the input of circuit 22 similar to a bonding pad
arrangement normally associated with the periphery of an integrated
circuit die. Pad 24 is of sufficient size to allow repeated mechanical
alignment and contact with an external probe source. Probe pad 24 allows
data to be input into circuit 22 necessary for programming and
reprogramming of processor 20.
Wafer 10 further includes an output probe pad 26. Probe pad 26, may be
configurated similar to input probe pad 24 for allowing mechanical access
from an external output device necessary for receiving digital information
stored within the read/write memory of processor 20. Probe pad 26 can also
be a non-contact receptor for allowing optical or acoustic access from an
external communication device. Thus, in whatever form desired, output
probe pad 26 is connected to an output port of processor 20 as shown in
FIGS. 2 and 4.
Referring now to FIG. 2, a block diagram and signal flow of integrated
circuits placed upon a single monolithic wafer 10 is shown. Specifically,
sensors 12 can sense processing conditions such as temperature, gas flow,
gas composition, pressure, force, light waves, sonic waves, magnetic
disturbance, static charge, vibration, acceleration, etc., necessary to
stimulate the sensor, or transducer, and produce an analog signal 30
proportional to the stimulus. There is preferably numerous analog signals
sent to acquisition/conditioning circuit 18 from various regions across
wafer 10. For example, a gas flow magnitude which passes across wafer 10
may register at select sensors 12 arranged at each region 14. The sensors
will present simultaneous analog signals to circuit 18. In order to
accommodate the simultaneous signals, a multiplex circuit associated with
the acquisition/conditioning circuit 18 is needed.
Acquisition/conditioning circuit 18 multiplexes the simultaneous signals
and converts the analog signals to digital signals 32 and presents signals
32 to an input port 34 of processor 20. As input port 34 receives signals
32, it buffers those signals and presents buffered signals 35 to a
read/write memory array within processor 20. When enabled, output port 36,
associated with processor 20, presents stored signals 37 within the memory
array to output probe pad 26.
Power supply 16 is capable of providing analog voltage levels with
sufficient current drive to sensors 12 as well as acquisition/conditioning
circuit 18. Moreover, supply 16 can present necessary digital power levels
with sufficient current drive to processor 20. External control circuit 22
is connected to acquisition/conditioning circuit 18 and processor 20, as
shown, in order to present any and all timing signals and/or enable
signals necessary to time stamp analog signals, and present those signals
as digital signals to processor 20. The enable signals activate input and
output ports in order to store and retrieve digital information into and
from processor 20. Control circuitry and associated logic is well known in
the microprocessor arts and will be described further hereinbelow. Timing
and enable output signals can be programmed within external control logic
circuit 22 and can be changed or modified by input from an external input
device (not shown) via input probe pad 24. An external input device, e.g.,
keyboard, modem, etc., can be connected to input probe pad 24 to modify or
update the programmed external control output. Universal asynchronous
receiver-transmitter (UART) of common design can be formed upon the wafer
to provide serial communication to an external controller. An external
probe affixed to the input device may be configured to electrically
contact the input probe pad 24 using conventional probe means in order to
input, for example, encoded keyboard entry. An output probe pad is also
adapted to receive digital information across the data bus of processor 20
during times in which output port 36 is enabled. Input probe pad 24 and
output probe pad 26 can be made slightly larger than conventional bonding
pads in order to allow ease of mechanical connection by an external probe
without requiring substantial visual aid. A clocking circuit of common
design using counter/sequencer techniques can be connected to circuit 18,
port 34 to provide time-stampled data entry to processor 20, similar to
well-known computer timing principles. An initial bit can be used to
signal reception of data by processor 20 and the type of data to be
received. Subsequent data is then transmitted in one or more bytes in
accordance with the time-stamped initiator.
Sensors 12 described herein are necessary for detecting various processing
conditions, and are fabricated upon wafer 10 according to well known
semiconductor transducer design. For measuring temperature, a popular
transducer is a thermistor. A thermistor includes a thin-film resistor
material having a high temperature coefficient. A magneto-resistive
material may also be used to measure the amount of magnetic flux exerted
upon the wafer. A resistance-to-voltage converter is often formed within
the wafer between distal ends of the resistive-sensitive material (either
thermistor or magneto-resistive material). The resistance-to-voltage
converter includes an inverting amplifier arrangement, wherein the
thermistor is connected between the inverting input and output of the
amplifier. Other suitable resistance-to-voltage converters include a
bridge amplifier. Bridge amplifiers are well suited for producing an
output voltage proportional to a resistance value of the sensor (i.e.,
thermistor or magneto-resistive material). Bridge amplifiers are generally
a combination of an inverting amplifier and a Wheatstone bridge of common
design. Another exemplary temperature sensor includes a thermocouple made
of two dissimilar conductors lithography formed upon the wafer. When the
junction between the conductors is heated, a small thermoelectric voltage
is produced which increases approximately linearly with junction
temperature. A further exemplary temperature sensor includes a silicon
diode thermosensor which can produce, with increasing temperature, a
corresponding linear increase in diode voltage. By connecting the diode
between a positive supply and a load resistor, current-to-voltage
conversion can be obtained from the load resistor.
Sensors 12 may also be used to measure pressure, force or strain placed at
select regions across wafer 10. There are may types of pressure
transducers capable of measuring the atmospheric pressure exerted upon the
wafer. A suitable pressure transducer includes a diaphragm-type
transducer, wherein a diaphragm or elastic element senses pressure and
produces a corresponding strain or deflection which can then be read by a
bridge circuit connected to the diaphragm or cavity behind the diaphragm.
Another suitable pressure transducer may include a piezoresistive material
placed within the semiconductor substrate of wafer 10. The piezoresistive
material is formed by diffusing doping compounds into the substrate. The
resulting piezoresistive material produces output current proportional to
the amount of pressure or strain exerted thereupon.
Sensors 12 may also be used to measure fluidic flow rate across wafer 10.
In addition, humidity and moisture sensors can also be formed upon wafer
10. A suitable method for measuring fluid velocity is based upon the
frequency of vortex production as a streamlined fluidic flow strikes a
non-streamlined obstacle formed upon wafer 10. A method for measuring
fluid flow generally involves the formation of vortices produced at a
periodic rate on either side of the obstacle. Thus, an alternating
pressure difference occurs between the two sides. Above a threshold (below
which no vortex production occurs), the frequency is proportional to fluid
velocity. Of many methods of detecting the alternating pressure
difference, a hot thermistor is preferably placed in a small channel
between the two sides of the obstacle. The alternating directions of flow
through the channel periodically cool the self-heated thermistor thereby
producing an ac signal and corresponding electric pulses at twice the
vortex frequency. Accordingly, a semiconductor surface embodying a
thermistor and an obstacle protruding from the substrate in front of the
thermistor can provide solid-state flow rate measurement.
Sensors 12 can also | | |
