Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-11-30
2001-03-20
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192170, C204S192220, C216S002000, C216S016000, C216S051000, C438S050000, C438S054000
Reexamination Certificate
active
06203673
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a thin-film microstructure sensor in which a thin-film platinum temperature-sensitive resistor is formed on an insulation layer of a substrate. The thin-film microstructure sensor is suitably applied to a flow sensor, a humidity sensor, a gas sensor or a temperature sensor. The present invention further relates to a method of producing a thin-film platinum temperature-sensitive resistor on an insulation layer of a substrate through a sputtering process.
(2) Description of the Related Art
A thin-film microstructure sensor in which a thin-film platinum layer is provided on an isolated substrate for the purpose of measurement is known. The thin-film microstructure sensor of this type utilizes temperature-resistance characteristics of the thin-film platinum layer for measuring a flow rate of fluid, for measuring a humidity of an ambient atmosphere, for detecting presence of a gas in an ambient atmosphere, or for measuring a temperature of an ambient atmosphere. The thin-film microstructure sensor is capable of converting a change in resistance of the platinum layer into a change in temperature of the fluid or the ambient atmosphere. In the thin-film microstructure sensor, the measurement or the detection is performed based on the resistance-to-temperature conversion. The thin-film microstructure sensor is suitably applied to a flow sensor, a humidity sensor, a gas sensor or a temperature sensor.
For example, a conventional thin-film microstructure sensor uses a silicon substrate having an insulation layer, and a size of the substrate is on the order of a millimeter square. In the conventional thin-film microstructure sensor, a recessed portion is provided in the silicon substrate, and a bridge portion, including a heating element of platinum and two temperature-sensing elements of platinum, is provided over the recessed portion of the substrate. Some proposals for the arrangement of the bridge portion in the conventional thin-film microstructure sensor have been made in order for the heating element to efficiently generate heat and reduce heat loss to the substrate or to a supporting base which supports the substrate thereon.
A method of measuring a flow rate of a fluid used by the thin-film microstructure flow sensor will now be explained. That is, the thin-film microstructure flow sensor is placed into a flow of a fluid such that the temperature-sensing elements of the bridge portion extend in a direction perpendicular to the direction of the fluid flow. The temperature-sensing elements of the flow sensor are an upstream temperature-sensing element and a downstream temperature-sensing element with respect to the fluid flow. A control circuit of the flow sensor supplies voltage to the heating element and the upstream and downstream temperature-sensing elements of the bridge portion such that electric current flows through the bridge portion to increase a temperature of the bridge portion. The voltage supplied to the bridge portion is controlled by the control circuit such that both the bridge portion and the fluid are held at a constant temperature. The flow sensor under this condition measures a flow rate of the fluid based on a change in the voltage supplied to the bridge portion.
Japanese Laid-Open Patent Application No. 61-235726 discloses a flow measuring apparatus including a conventional thin-film microstructure flow sensor of the above-mentioned type. The flow measuring apparatus measures a flow rate of a specific gas used in a fabrication process of a semiconductor device. The flow measuring apparatus of the above-mentioned publication includes several thin-film microstructure sensors, such as a thin-film microstructure flow sensor provided in an internal passage of the semiconductor device, a stagnant gas flow sensor provided in a stagnant gas passage of the semiconductor device, and a temperature sensor provided at an inlet of the internal passage directed to the thin-film microstructure flow sensor. The temperature sensor is used to retain a temperature of the gas at the inlet of the internal passage.
Generally, accuracy of measurement of the thin-film microstructure sensors greatly depends on a temperature coefficient of resistance (TCR) of the platinum layer on the substrate. However, there is a problem in that the TCR of the platinum layer of the thin-film micro-structure sensors which are produced by manufacturing processes may vary greatly. The resistance-temperature characteristics of the sensor in operation are very sensitive to variations of the TCR of the platinum layer. The yield of the thin-film microstructure sensors providing a desired level of accuracy of measurement will be lowered due to the variations of the TCR, which will increase the cost of manufacture.
In addition, in the conventional thin-film microstructure sensors, such as flow sensors, humidity sensors and gas sensors, the heating element of the platinum layer is heated to an increased temperature above a room temperature. Repeated use of the conventional thin-film microstructure sensors over a prolonged time may cause migration in the platinum layer, and a value of resistance of the platinum layer tends to vary significantly. Therefore, there is a problem in that the accuracy of measurement of the conventional thin-film microstructure sensors is not reliable if the variations of the resistance value of the platinum layer exceed the order of several percents.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved thin-film microstructure sensor in which the above-described problems are eliminated.
Another object of the present invention is to provide a thin-film microstructure sensor having a thin-film platinum temperature-sensitive resistor which provides a large TCR with little variation for measurement of a fluid flow rate or another quantity while providing a stability of resistance for repeated use over a prolonged time.
Still another object of the present invention is to provide a method of producing a thin-film platinum temperature-sensitive resistor through a sputtering process wherein the resistor provides a large TCR with little variation for measurement of a fluid flow rate or another quantity while providing a stability of resistance for repeated use over a prolonged time.
The above-mentioned objects of the present invention are achieved by a thin-film microstructure sensor comprising: a substrate which has an insulation layer; and a thin-film platinum temperature-sensitive resistor which is provided on the insulation layer of the substrate, the thin-film platinum temperature-sensitive resistor comprising at least one platinum layer which has a maximum crystal grain size above a reference grain size.
The above-mentioned objects of the present invention are achieved by a method of producing a thin-film platinum temperature-sensitive resistor, the method comprising the steps of: forming a first insulation layer on a substrate; forming a platinum layer on the first insulation layer of the substrate by performing a sputtering process; forming a second insulation layer on the platinum layer; and performing a patterning of the platinum layer through etching by using the second insulation layer as a mask, so that a thin-film platinum temperature-sensitive resistor is produced on the first insulation layer of the substrate, wherein the sputtering process is performed under sputtering conditions in which a radio-frequency power is set in a range of 0.54 W/cm
2
to 2.74 W/cm
2
and a temperature of the substrate is set in a range of 100° C. to 500° C. in such a manner that a maximum crystal grain size of the platinum layer is above a reference grain size.
The above-mentioned objects of the present invention are achieved by a method of producing a thin-film platinum temperature-sensitive resistor, the method comprising the steps of: forming a first insulation layer on a substrate; forming a platinum layer on the first insulation layer of the substrate by performing a sputte
Azumi Junichi
Kaminishi Morimasa
Sato Yukito
Shoji Hiroyoshi
Yamaguchi Takayuki
Chacko-Davis Daborah
Nguyen Nam
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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