Etching a substrate: processes – Nongaseous phase etching of substrate – With measuring – testing – or inspecting
Reexamination Certificate
2001-10-31
2003-07-01
Powell, William A. (Department: 1765)
Etching a substrate: processes
Nongaseous phase etching of substrate
With measuring, testing, or inspecting
C216S016000, C216S052000, C216S065000, C216S061000, C438S707000
Reexamination Certificate
active
06585909
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention broadly relates to a method for manufacturing an oxide thin-film for use in a bolometer and to a non-cooling type infrared ray sensor using the oxide film.
A bolometer utilizes temperature variation of electrical resistance of a metal film or a semiconductor film which is thermally insulated from a substrate material. A temperature coefficient of electrical resistance (TCR) and electrical resistance value are exemplified as characteristics required for materials for the bolometer.
In general, as the electrical resistance value of the material for the bolometer becomes higher, Johnson noise also becomes higher. This phenomenon is not preferable.
On the other hand, when the electrical resistance becomes low, a difference between wiring resistance other than the bolometer and an electrical resistance value of the material for the bolometer becomes small. This phenomenon is not desirable also.
In consideration of the above, it is desirable that the electrical resistance value of the material for the bolometer falls within the range between 5 and 100 K&OHgr; at the room temperature.
In other words, if a resistive element thin-film for the bolometer has a thickness within the range between 50 and 1,000 nm, electrical resistivity required for the material for the bolometer desirably falls within the range between about 0.025 and 10 &OHgr;cm.
In addition, temperature resolution of an infrared ray sensor (NETD) is inversely proportional to a TCR absolute value of the material for the bolometer. Accordingly, the infrared sensor having lower NETD can be obtained by using the material for the bolometer with a higher TCR absolute value.
Generally, an alloy thin-film such as a nickel iron alloy has TCR of about 0.5%/K, and as a result, it is not preferable for the bolometer material of the infrared rays sensor with high sensitivity.
In contrast, a vanadium oxide thin-film has a relatively high TCR of about 2%/K as disclosed in Japanese Unexamined Patent Publication (JP-A) No. Hei. 11-271145. Consequently, it is generally used for the material of the bolometer.
Alternatively, a part of vanadium V is attempted to be replaced by the other element such as manganese Mn disclosed in Japanese Unexamined Patent Publication (JP-A) No. 2000-143243. In consequence, it has been reported that the TCR absolute value can be increased up to about 4%/K.
However, the material having higher TCR for the bolometer must be developed in order to achieve further higher sensitivity or multiple pixels of the infrared ray sensor.
To achieve such a purpose, suggestion has been made about use of a provskite type Mn oxide represented by La
1
−x Srx MnO
3
, La1−x Cax MnO
3
, Pr
1
−x Srx MnO
3
as the material for the bolometer.
This technique utilizes such phenomenon that the perovskite type Mn oxide has high TCR within a semiconductor region, thus obtaining a value of about 3%/K as the TCR absolute value.
However, this value is not particularly high compared to such a case that a part of vanadium oxide base is replaced by Mn. To this end, the infrared rays sensor utilizing the characteristic of the semiconductor region of the perovskite type Mn oxide does not has a specific advantage in comparison with the infrared ray sensor using the conventional vanadium oxide based material.
In contrast, another attempt has been made about use of the other characteristics of the above perovskite type Mn oxide for the infrared ray sensor, as disclosed Japanese Unexamined Patent Publication (JP-A) No. 2000-95522.
The above perovskite type Mn oxide has a unique characteristic indicative of phase transition between an insulator and a metal. In such phase transition, the provskite type Mn oxide transfers from an insulating state of high temperature into a metal state of low temperature in accordance with variation of magnetic property.
Under this circumstance, the temperature, at which the transition between the insulator and the metal occurs, can be set near the room temperature by adjusting Sr composition x in the above La
1
−x Srx MnO
3
.
In this case, the electrical resistance is largely varied in the transition between the insulator and the metal, thus obtaining higher TCR. By employing such characteristic, it is expected that the infrared ray sensor with higher sensitivity can be realized compared to the conventional sensor. In practical, it has been reported that the material has excessively high TCR of 5% K or more, particularly exceeding 10%/k.
Thus, the infrared ray sensor can have high sensitivity or multiple pixels by utilizing the perovskite type Mn oxide as the material for bolometer. However, a sol-gel method is used during producing the perovskite type Mn oxide thin-film in the aforementioned JP-A No. 2000-95522.
As described in the above Patent Publication, for example, each coating agent for octane based MOD method (organic metal deposition) of La, Sr, Mn is mixed with a desired ratio, is applied on an oxide substrate, is dried, and then is annealed for crystallization at a high temperature.
In this event, it is necessary to anneal at high temperature of approximately 1000° C. in order to realize an excellent transition between the insulator and metal in the perovskite type Mn oxide thin-film.
As the other methods, use is made of a deposition method such as a laser ablation method or a sputtering method. For example, as described in applied physics letters (Appl. Phys. Lett.) 74 volume. 290 page, 1999, high deposition temperature of 700° C. or more is required so as to obtain the excellent transition between the insulator and the metal even when these deposition methods will be used.
As discussed above, high TCR exceeding 5%/K can be obtained by utilizing the transition between the insulator and the metal inherent to the perovskite type oxide. Consequently, it is expected that the non-cooling type infrared ray sensor with higher sensitivity than the conventional case can be realized by using the perovskite type Mn oxide as the material for the bolometer.
Generally, a receiving portion of the non-cooling type infrared ray sensor is formed on a Si substrate. Further, a signal read-out circuit is arranged in the Si substrate under the receiving portion. On the other hand, the resistive element for the bolometer is formed on a bridge structure body placed on the Si substrate via a thermal insulating gap.
Specifically, the resistive element for the bolometer is formed on the Si substrate having the signal read-out circuit. To this end, the material for the bolometer must have consistency with a Si production process in addition to the high TCR.
From viewpoint of the consistency with the Si production process, it is required that deposition temperature is low at 400~500° C. or less and that a physical etching method such as ion-milling can not be utilized during forming the pattern of the resistive element for the bolometer. This is because the physical etching gives damage for the signal read-out circuit of Si formed on an under layer.
Considering such a problem with respect to the production process, the perovskite type Mn oxide thin-film has important disadvantages as the material for the bolometer.
First, as described above, the high deposition temperature is necessary in order to increase TCR with this material, namely, to obtain the excellent transition between the insulator and the metal. More specifically, the temperature of about 1000° C. is necessary in the case of the sol-gel method while the temperature of 700° C. or higher is required in the sputtering method.
As long as the high deposition temperature is required, it is difficult to apply the attractive material having high TCR to the Si production process.
Practically, the thin-film is merely formed on SrTiO
3
(100) resistant to high deposition temperature, namely, on an oxide single crystal substrate instead of the Si substrate according to an embodiment disclosed in the above-mentioned JP-A No. 2000-95522.
Second, a reactive ion etching method is not applicable to form the pattern of the res
Kubo Yoshimi
Kumagai Toshiya
Mizuta Susumu
Shimakawa Yuichi
Tsuchiya Tetsuo
National Institute of Advanced Industrial Science & Technology
Powell William A.
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