Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-05-18
2001-12-25
Utech, Benjamin L. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S720000, C438S722000, C252S079100
Reexamination Certificate
active
06333270
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of carrying out plasma-enhanced etching of a vanadium oxide film, and more particularly to such a method in which an etching ratio of a vanadium oxide film to an underlying insulating layer is enhanced. The invention relates also to an etching gas to be used in such a method.
2. Description of the Related Art
Vanadium oxide is known as a material having a resistance which varies much in dependence on a temperature, and is widely used by virtue of such characteristic. For instance, a temperature detecting film and an infrared ray detecting film are composed of vanadium oxide.
For instance, Japanese Unexamined Patent Publication No. 58-42368 has suggested a solid-state image sensor including a photo-absorptive layer composed of vanadium oxide.
In fabrication of a temperature detecting film from vanadium oxide, a vanadium oxide film having a thickness of about 50 to about 200 nm is first deposited, and then, the thus deposited vanadium oxide film is treated for defining a region only in which a temperature is varied, in order to efficiently cause temperature fluctuation.
A vanadium oxide film has been conventionally treated by either ion milling in which a vanadium oxide film is physically etched by ion bombardment, or plasma-enhanced etching in which vanadium oxide is made to chemically react with highly volatile material to thereby evaporate vanadium oxide into a desired pattern. For instance, the ion milling is described Japanese Unexamined Patent Publication No. 64-64273, and also in Wada et al., Society of Photo-optical Instrumentation Engineers Proceeding, 1997, Vol. 3224, pp. 46, line 5, and the plasma-enhanced etching is described in Buhey et al., Journal of Vacuum Science and Technology, 1986, Vol. A4, pp. 440-442.
However, the ion milling is accompanied with a problem as follows.
FIG. 1
is a cross-sectional view of a semiconductor device including a semiconductor substrate
1
, wiring layers
2
formed in the semiconductor substrate
1
, a first insulating layer
3
formed on the semiconductor substrate
1
, a vanadium oxide film
4
formed on the first insulating layer
3
, and a second insulating layer
5
formed on the vanadium oxide film
4
.
When the vanadium oxide film
4
is to be etched by the ion milling, the first insulating film
3
cannot avoid to be etched together, because the underlying first insulating layer
3
has almost the same etching rate as an etching rate of the vanadium oxide film
4
. As a result, as illustrated in
FIG. 1
, the wiring layers
2
formed below the first insulating layer
3
are damaged.
In addition, in the ion milling, thermions are radiated from an ion, milling apparatus in order to neutralize ions. As a result, a circuit formed in the semiconductor substrate
1
below the patterned vanadium oxide film
4
may accumulate much electric charges therein, which often causes breakdown of the circuit.
In the plasma-enhanced etching, breakdown of a circuit caused by accumulation of electric charges does not occur. Though Buhey et al. have set forth that a mask to be formed on a vanadium oxide film when plasma-enhanced etching is to be carried out has to be composed of gold (Au), such a golden mask is accompanied with a problem as follows.
When the golden mask is removed, there has to be used an etchant containing iodine and potassium iodide. The use of such an etchant may vary characteristic of a vanadium oxide film after removal of the golden mask, or may cause a vanadium oxide film to be molten. In addition, it is impossible by existing technique to both increase an etching rate of a vanadium oxide film and enhance a ratio in an etching rate between a vanadium oxide film and an underlying insulating layer, that is, an etching selection ratio.
Hence, a portion of an underlying insulating layer located below an unmasked portion of a vanadium oxide film may be etched with the result that a thin portion of the insulating layer is formed with a hole, and resultingly, a wiring layer located below the hole is also etched.
SUMMARY OF THE INVENTION
In view of the above-mentioned treatments of a vanadium oxide film, there is a need in improvement in an etching rate of a vanadium oxide film, improvement in an etching selection ratio between a vanadium oxide film and an underlying insulating layer, and a mask used for keeping an underlying insulating layer unetched and composed of materials other than gold.
It is an object of the present invention to provide a method of carrying out plasma-enhanced etching of a vanadium oxide film which method is capable of enhancing an etching ratio of a vanadium oxide film to an underlying insulating layer.
In one aspect, there is provided a method of carrying out plasma-enhanced etching of a vanadium oxide film formed on an insulating layer, wherein there is used an etching gas containing a fluoride gas, which fluoride has fluorine (F) atoms by six or greater.
There is further provided a method of carrying out plasma-enhanced etching of a vanadium oxide film formed on an insulating layer, wherein there is used an etching gas containing a fluoride gas at a volume ratio of 10% or greater, which fluoride has fluorine (F) atoms by six or greater.
A fluoride gas may be selected from SF
6
gas, C
2
F
6
gas and C
3
F
8
gas, for instance.
The above-mentioned methods can enhance etching reactivity of a vanadium oxide film, and further enhance an etching ratio between a vanadium oxide film and an underlying insulating layer relative to the conventional methods. Accordingly, it is now possible to prevent the underlying insulating layer from being etched together, when the vanadium oxide film is etched.
For instance, the insulating layer may be composed of silicon nitride.
It is preferable that the etching gas is a mixture gas containing a fluoride gas and a carbon dioxide gas. This ensures that a vanadium oxide film has en etching rate equal to or greater than 200 nm/min.
There is still further provided a method of carrying out plasma-enhanced etching of a vanadium oxide film, including the steps of (a) depositing one of a resist film and an insulating film on a vanadium oxide film, (b) patterning the one of a resist film and an insulating film to thereby form a mask, and (c) carrying out plasma-enhanced etching of a vanadium oxide film through the use of an etching gas containing a fluoride gas, which fluoride has fluorine (F) atoms by six or greater.
There is still further provided a method of carrying out plasma-enhanced etching of a vanadium oxide film, including the steps of (a) depositing one of a resist film and an insulating film on a vanadium oxide film, (b) patterning the one of a resist film and an insulating film to thereby form a mask, and (c) carrying out plasma-enhanced etching of a vanadium oxide film through the use of an etching gas containing a fluoride gas at a volume ratio of 10% or greater, which fluoride has fluorine (F) atoms by six or greater.
The above-mentioned methods prevent the vanadium oxide film from being exposed to atmosphere, and hence, it would be possible to etch the vanadium oxide film without exerting a harmful influence on characteristic of the vanadium oxide film.
It is preferable that a flow rate of the etching gas in the step (c) is set equal to 100 sccm or greater.
An etching gas usually has a pressure in the range of 7 Pa to 12 Pa. By flowing the etching gas at 100 cc per minute or greater with an etching gas pressure being kept in the range of 7 Pa to 12 Pa, the etching gas stays in an etching chamber for a shorter period of time than before, resulting in facilitation in etching reaction.
It is preferable that the insulating film is deposited so as to have a thickness of 60 nm or smaller in the step (a).
For instance, the insulating film may be composed of silicon dioxide or silicon nitride.
It is preferable that the insulating film is patterned in the step (b) by plasma-enhanced etching through the use of a mixture gas containing a CHF
3
gas and an oxygen gas, in which case, the mi
NEC Corporation
Sughrue & Mion, PLLC
Umez-Eronini Lynette T.
Utech Benjamin L.
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