Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Groove formation
Reexamination Certificate
1998-01-29
2001-03-20
Wilczewski, Mary (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Groove formation
C438S045000, C438S057000
Reexamination Certificate
active
06204083
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an infrared-emitting element manufacturing method and an infrared-emitting element manufactured thereby and, more particularly, to a method of manufacturing an infrared-emitting element for emitting infrared rays by causing a bridge (heat-generating) portion made up of a silicon micromachining to generate heat, and an infrared-emitting element manufactured thereby.
BACKGROUND ART
As an infrared-emitting element used for a gas analysis sensor or the like, an infrared-emitting element for emitting infrared rays from a filament by energizing the filament to make it generate heat has conventionally been used.
Reference numeral
101
in
FIG. 22
denotes a conventional gas analysis system using an infrared-emitting element
102
with a filament.
More specifically, in this gas analysis system, infrared rays
141
emitted by the filament of the infrared-emitting element
102
are intermittently shielded by a chopper
142
, and become modulated infrared rays
144
, which enter a gas
143
via a filter
146
.
The modulated infrared rays
144
transmitting through the gas
143
are received by a light-receiving element
145
.
This gas analysis system
101
calculates the concentration of the gas
143
from the ratio of the maximum value to minimum value of the light-receiving power level upon receiving the modulated infrared rays
144
.
Accordingly, the gas analysis system
101
requires the modulated infrared rays
144
, and must comprise the chopper
142
because the infrared-emitting element
102
can emit only constant infrared rays.
In recent years, it is required that small-sized, low-cost gas analysis systems.
Development of infrared-emitting elements capable of modulated emitting infrared rays without using any chopper
142
is required.
Many infrared-emitting elements using a ceramic bulk material as a heat-generating element, a silicon micromachining, and the like have been developed.
In an infrared-emitting element using a ceramic bulk material as a heat-generating element, however, infrared rays cannot be modulated at a high frequency because the thermal conductivity of a high-temperature portion is small, and the heat capacity of the bulk material is large.
For example, when this infrared-emitting element emits infrared rays at 48 Hz, the difference between the lowest and highest temperatures at the heat-generating portion is only 150° C. and hence the difference between the minimum and maximum emission quantities of infrared rays is small.
In an infrared-emitting element using a silicon micromachining, as described in the following reference, boron is thermally diffused as a p
+
-type impurity into a silicon bridge structure to selectively etch and remove a sacrificial n-type layer. The p
+
-type layer of the silicon structure is formed into a bridge-building structure, and the bridge-building portion is made to generate heat, thereby emitting infrared rays (reference: Technical Digest of the 11th Sensor Symposium, 1992, pp. 169-172, Kimura et al.).
In the infrared-emitting element using the silicon micromachining, since the p
+
-type layer is formed by thermally diffusing boron, the bridge portion of the bridge-building structure is too thick, resulting in poor thermal response characteristics for the driving power.
If the bridge portion can be made thin, the thermal response characteristics for the applied electric power can be improved drastically.
However, when the bridge portion obtained by thermally diffusing boron is decreased in thickness to about the reciprocal of the absorption coefficient at a necessary infrared wavelength, the emissivity of infrared rays rapidly decreases to weaken the infrared emission intensity. At present, only an infrared-emitting element using a silicon micromachining with a bridge portion having a thickness of about 5 &mgr;m is realized.
In the conventional infrared-emitting element using the silicon micromachining obtained by thermally diffusing boron as a p
+
-type impurity, the thermal response characteristics are poor because of the thick bridge portion. If infrared rays are emitted under constant-voltage driving, an excessively large current may flow to fuse the bridge portion because a long time is needed to increase the resistance value by temperature rise upon applying the voltage.
To avoid this situation, a protective circuit must be arranged as a driving circuit for the infrared-emitting element, or a constant-current driving method must be employed. This complicates the arrangement of the driving circuit.
The conventional infrared-emitting element using the silicon micromachining obtained by thermally diffused boron as a p
+
-type impurity poses the above problems because the concentration of boron and the diffusion profile cannot be independently controlled with high precision in thermally diffusion method.
For an infrared-emitting element of this type, the concentration of boron and activation of boron to serve for an impurity layer are important factors to promote the emissivity of infrared rays.
However, thermal diffusion leads to a low concentration of boron and weak activation of boron to serve for an impurity layer, so the bridge portion cannot be made thin. Heretofore, even if a thin bridge portion can be formed, the emissivity of infrared rays decreases.
In thermal diffusion method, a thickness of the bridge portion is limited by a mechanical safety after etching.
DISCLOSURE OF INVENTION
The present invention has been made to solve the problems in the prior art, and has as its object to provide an infrared-emitting element manufacturing method capable of efficiently manufacturing, with high mass productivity at low cost, a high-performance infrared-emitting element which has high-speed thermal response characteristics and a high infrared emissivity, can be driven by a simple driving circuit, and enables stable constant-voltage driving, and an infrared-emitting element manufactured by the above method.
To achieve the above object, according to the present invention, there is provided an infrared-emitting element manufacturing method comprising steps of preparing a single-crystal silicon substrate the serving as an element substrate, forming an impurity layer as a heavily doped region by doping boron from an upper surface side of the element substrate by ion implantation at a peak concentration of not less than 1.5×10
19
atoms/cm
3
in order to form a heat-generating portion having a predetermined shape on the element substrate, performing annealing for the element substrate having the impurity layer under a predetermined condition for activating the impurity layer, forming a pair of electrodes to ohmic-contact two ends of the impurity layer in order to form an applying portion of a driving voltage for the heat-generating portion on the element substrate, and removing a lower portion of the impurity layer including a middle portion by anisotropic etching and forming a separation space in order to form the heat-generating portion on the element substrate into a bridge shape, wherein, when the driving voltage is applied to the heat-generating portion via the pair of electrodes, the heat-generating portion having the bridge shape can emit infrared rays in accordance with the driving voltage.
To achieve the above object, according to the present invention, there is provided an infrared-emitting element manufacturing method characterized in that the ion implantation is performed by doping boron at a dose of at least not less than 3.0×10
−14
ions/cm
2
.
To achieve the above object, according to the present invention, there is provided an infrared-emitting element manufacturing method characterized in that the heat-generating portion is formed to have a thickness of not less than 0.2 &mgr;m and not more than 5 &mgr;m.
To achieve the above object, according to the present invention, there is provided an infrared-emitting element manufacturing method characterized in that the heat-generating portion is formed to emit infrared rays at an
Akimoto Kenji
Karasawa Shiro
Kodato Setsuo
Ohya Seishiro
Yuasa Hiroyasu
Anritsu Corporation
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Wilczewski Mary
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