Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2002-09-13
2003-06-17
Meier, Stephen D. (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S200000
Reexamination Certificate
active
06579741
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to sensing devices. More particularly, the present invention relates to monolithically integrated, compound semiconductor sensing devices and methods of manufacturing such devices.
BACKGROUND OF THE INVENTION
Sensing devices are used in various applications, some of which subject these sensing devices to harsh operating conditions such as temperature extremes, dirty environments and electromagnetically active surroundings. For example, in the automobile industry sensing devices are used in crankshaft position detection, wheel speed sensors, brushless electric motors, and other environments subject to wide temperature variations. Automotive sensor specifications require sensors that continually operate with significant change in performance across temperatures ranging from −40° C. to over 200° C.
One conventional sensing device is a magnetic field sensing device. A magnetic field sensing device can be fabricated using a silicon semiconductor Hall sensor that is typically integrated into a silicon semiconductor signal conditioning circuit. A signal conditioning circuit is used to convert the output signal from the Hall sensor into a signal that is useful for its intended application.
Silicon Hall sensors possess the disadvantages of lower sensitivity and signal-to-noise ratio because of the low electron mobility of silicon. Accordingly, these silicon devices lack precision and require demanding signal conditioning circuitry. Additionally, traditional silicon circuitry is not suitable for use over a wide temperature range, particularly at temperatures greater than about 150° C. At higher temperatures, issues such as leakage current and parasitic conductance significantly impact the operation of silicon circuitry.
Sensing devices utilizing compound semiconductor technology are also available. Manufacture of these devices, however, involves separate fabrication of the integrated circuit components. In a standard manufacturing process, a magnetic field sensor, such as a Hall sensor, a magnetoresistor or a magnetotransistor, is fabricated by depositing at least one layer, usually multiple layers, of compound semiconductor material such as InSb on a substrate material. Typically, each of the layers used to form the magnetic field sensor has a different composition or contains a different dopant or dopant level than the adjacent layers. The materials used to form the layers in the manufacture of magnetic field sensors may be deposited as thin epitaxial films utilizing a process such as metal organic chemical vapor deposition (MOCVD), vapor phase epitaxy (VPE), liquid phase epitaxy (LPE) or molecular beam epitaxy (MBE). In a separate process, an application specific integrated circuit (ASIC) to provide signal conditioning is manufactured.
A prior art method for manufacturing a sensing device is shown in
FIGS. 1A-1D
. Referring to
FIG. 1A
, a substrate
10
having a top surface
12
may comprise a compound semiconductor material such as semi-insulating GaAs or other suitable III-V compound semiconductor material. Referring now to
FIG. 1B
, a sensor element
14
is shown on the surface
12
of the substrate
10
. The sensor element may be any conventional sensor element, including a magnetic sensor, such as a Hall effect or magnetoresistive type sensor. Such a structure can be formed by one or more epitaxial layers. As shown in
FIG. 1C
, a separate substrate
20
is provided for manufacture of a signal conditioning circuit, which may be fabricated using either silicon or compound semiconductor technology.
FIG. 1D
shows an example of signal conditioning circuit layers incorporating a heterojunction bipolar transistor (HBT) structure
22
deposited on substrate
20
. As is known in the art, an HBT structure may include active layers such as an emitter layer
24
, a base layer
26
and a collector layer
28
. These layers may be etched or otherwise treated in conventional ways to form the elements of the signal conditioning circuit. Additional layers, such as dielectric layers and metallization layers (not shown), may be formed to provide contacts for interconnection with another device, and to interconnect elements of the signal conditioning circuit with one another. After separate fabrication of the magnetic sensor element and the signal conditioning circuit, the two structures are interconnected by wirebonding the structures together to form a completed sensing device.
Separate fabrication of the sensor and the signal conditioning circuit has several drawbacks. Wirebonding uses valuable space on both the sensor and signal conditioning circuit. Wirebonded devices tend to exhibit lower reliability than integrated devices that do not require wirebonding of the separate elements. In addition, the wire-bonding process is labor-intensive, costly and increases the size of the finished assembly.
It would be useful to provide a sensing device capable of operating over a wider temperature range than devices fabricated using silicon semiconductor signal conditioning circuits. It would also be advantageous to provide a process for manufacturing a compound semiconductor sensing device having a sensor and signal conditioning circuit that is less labor intensive, more reliable and less expensive than methods that involve separate device fabrication and interconnection.
SUMMARY OF INVENTION
Accordingly, one aspect of the present invention provides a monolithically integrated, compound semiconductor sensing device including a signal conditioning circuit and a sensor element. In one embodiment, a sensor element including one or more compound semiconductors is epitaxially deposited over a first portion of the substrate surface. In another aspect of the invention, the semiconductor layers which will be used to form the signal conditioning circuit (the “signal conditioning epitaxy”) is formed by epitaxial deposition of one or more compound semiconductors on second portion of the substrate surface.
In a preferred embodiment, the signal conditioning epitaxy include one or more III-V compound semiconductor. Similarly, the sensor element includes at least one III-V compound semiconductor, which typically is different from the compound semiconductor used in the signal conditioning epitaxy. Preferably, the surface of the substrate is formed from GaAs.
In a preferred embodiment, the sensor is a magnetic sensor, such as a Hall effect or magnetoresistive sensor. In one aspect of the invention, the sensor is in direct contact with the substrate surface. In another aspect of the invention, a buffer layer may be disposed between the substrate surface and the sensor. Similarly, a buffer layer may be disposed between the signal conditioning epitaxy and the substrate surface.
Another aspect of the invention involves a method of manufacturing a monolithic compound semiconductor sensing device. The method includes forming signal conditioning epitaxy adapted to form a signal conditioning circuit on a substrate surface and providing a well in the signal conditioning epitaxy to expose the substrate surface. In another aspect of the invention, a sensor is formed in the well structure.
In one embodiment of the invention, formation of the well structure within the signal conditioning circuit involves etching the well within the signal conditioning epitaxy after deposition of the signal conditioning epitaxy. According to a further embodiment of the invention, formation of the well within the signal conditioning circuit involves masking the substrate surface, depositing the signal conditioning epitaxy over the mask and removing the mask to provide a well.
In still another embodiment of a the invention, a method of manufacturing a monolithic compound semiconductor sensing device is provided which includes forming a sensor on a substrate surface and providing a well in the sensor to expose the substrate surface. A signal conditioning epitaxy is formed within the well formed in the sensor.
According to one embodiment of the invention, the step of providing a well in the se
Douglas Edward W.
Palmer Christopher
Schwed Stephen
Emcore Corporation
Lerner David Littenberg Krumholz & Mentlik LLP
Meier Stephen D.
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