JPS58103653A - Gas sensor and its production - Google Patents

Abstract

PURPOSE:To obtain a small sized and durable sensor which consumes less electric power and has high accuracy by holding a semiconductor thin film differing in conductivity from a semiconductor substrate in space on said substrate, providing a gas sensitive film through an insulating material on the semiconductor thin film, and heating only the semiconductor thin film. CONSTITUTION:A hole 9' is provided to a support 9 of ceramics and an SiO2 film is beforehand formed on the interfaces 12', 12'' of a silicon substrate 1'- 1'' and the support 9 in such a way that there is a silicon thin film 2 doped with B at >=7X10<19>cm<-3> on the hole 9''; thereafter, a p type silicon layer (much smaller in conductivity than the layer 2) is formed thereon. An insulating film (SiO2) 7 is formed on the film 2, and a gas sensitive film 5 of metallic oxide such as SnO2 of ultrafine particles is formed on the film 7. Electrodes 3', 3'' for heating only the film 5 to high temp. are provided in the openings 8', 8'' of the film 7, and electrodes 6', 6'' for the purpose of measuring the electrical characteristics of the film 5 are provided. Thus, only the thin film 2 is heated by which the film 5 is heated to the necessary high temp. and the small sized sensor having high accuracy and good durability is obtained without deterioration by chemical combination of the electrodes and Si.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved gas sensor and SOA manufacturing method, which has particularly low power consumption, fast response speed, uniform characteristics, and realizes high precision and high reliability. The aim is to provide a lightweight, ultra-small gas sensor.

Currently, various types of gas sensors are being proposed, including sintered bodies, thick film types, thin film types, and ultrafine particle film types.

Among these, one of the present inventors, for example, patent application No. 63-1030
The ultrafine particle film type proposed in No. 26 is similar to other types 7
It has the highest gas sensitivity compared to

Generally, these semiconductor gas sensors are said to have a problem with accuracy. The inventor of the present invention conducted a detailed study on the cause and found that one of the major factors is variation in the operating temperature of the gas sensitive body or gas sensitive membrane.

Therefore, the present inventor has proposed, for example, Utility Model Application No. 55-182434.
No. 66-182435, we proposed a method for controlling the operating temperature of an ultrafine particle gas-sensitive membrane with high precision. With this proposal, it is possible to manufacture a gas sensor with an ultrafine particle gas-sensitive film using the same microfabrication technology currently used in VLSI manufacturing, so it is smaller and smaller than other types of sensors. The accuracy and uniformity are also very good.

And because we can now control the operating temperature, we not only end up with higher precision.

The reduction in heat capacity due to the reduction in one dimension of the feature not only shortened the heating response time of the gas-sensitive membrane, but also reduced power consumption.

However, even in the conventional proposal made by the present inventor, unresolved problems remained. The problem will be explained using FIG. 1.

Note that Figure (IL) is a top view, and Figure (b) is a sectional view at Moom' in Figure (&).

As shown in the figure, a p-type silicon substrate 1 is bonded to a support 9 such as alumina through an 8i0z film 7.

An ultrafine particle gas sensitive membrane 6 is provided. 3′.

3' is an electrode for applying power to the substrate 1; 4', 4;
'.

Reference numeral 4'' is an electrode for measuring electrical characteristics such as electrical resistance or capacitance of the sensitive membrane 6. Now, only the part of the gas-sensitive membrane 6 needs to be heated; In the case of the conventional example shown in FIG.
The problems were that the entire structure was heated and that the heat generated in the substrate 1 was transmitted through the ceramic support made of alumina or the like and escaped. Further reduces power consumption, and only the gas-sensitive membrane 6 can be heated to several hundred degrees Celsius.
There was an urgent need to solve the contradictory problem of heating to such high temperatures.

Furthermore, in the conventional example shown in FIG.
If you try to heat it to several hundred degrees Celsius, electrode 3'.

Interface between 3# and silicon substrate 1 (a', a' part)
Because the metal is heated to several hundred degrees Celsius, over a long period of time, the alloy layer (Pt-
Another problem that remained unsolved was that the performance of electrodes S/ and S# deteriorated due to changes in the performance of electrodes S/ and S# (such as Mo-8i, Mo-8i, and Mu-8i systems).

The present invention can solve the above-mentioned problems in the past. That is, by using the gas sensor of the present invention, power consumption can be further reduced, and the gas sensitive membrane 6 can be used.
The contradictory problems remaining in conventional gas sensors, such as heating the gas to high temperatures of several hundred degrees Celsius, can be solved all at once, and as is clear from FIG. 2, the gas sensor of the present invention Since the temperature of the electrodes 3', 3' can be made extremely low compared to the temperature of the sensitive membrane 60, the problem of electrode deterioration in conventional gas stations is solved at the same time, resulting in excellent long-term stability. It becomes possible to realize a highly reliable gas sensor.

The present invention will be explained in detail below.

FIG. 2 shows an embodiment of the gas sensor of the present invention. Figure (IL) is a top view; Figure (b) is a sectional view at Moum' in Figure (IL); Figure (0) is a bottom view. Portions having the same functions as those of the conventional example shown in FIG. 1 will be given the same reference numerals to avoid redundant explanation. In addition, Figure 2 (IL)
For the sake of simplicity, the part of the ultrafine particle gas-sensitive film 6 shown in FIG. 2(b) is not shown.

Now, the gas sensor of the present invention shown in FIG.
There are two major differences compared to the conventional gas sensor shown in the figure.

'The first is that the thin layer 2 is bridged between the substrates 1', 1'. As is clear from Fig. 2, the resistance value of the thin layer 2 portion is larger than the resistance value of the substrate 1' and 1'' portions, so the electric power applied between the terminals s1.a# causes the thin layer 2 to It is easy to generate heat locally. Also, since the contact area between the substrates 1', 1' and the support body 9 is narrow, the amount of heat radiated through the support body is reduced, and power consumption is reduced accordingly.

The second is 8' between the electrodes 3', 3' and the substrates 1', 1';
Since the temperature of the alloy layer formed in the 8' portion can be made lower than the temperature of the thin layer 2, deterioration of the electrode can be prevented.

As is clear from the above description, in the gas sensor of the present invention, only the gas-sensitive membrane 6 can be heated to several hundred degrees Celsius, and power consumption can be reduced. Further advantageously, the temperature of the portions 8' and 8' does not rise to several hundred degrees Celsius as in the conventional case, so deterioration of the electrodes can be prevented.

Note that the electrodes 3', 3' may be formed at the 12', 12' portions, and heating power may be applied via the substrates 1', 11'.

In order to further reduce power consumption, holes 9' are formed in the support 9.
has been established. These openings are formed in the substrates 1' and 1 as described later.
It is also effective when manufacturing a gas sensor having a structure in which the thin layer 2 is crosslinked by selectively leaving the ' portion.

FIG. 3 shows another embodiment of the gas station of the present invention. Figure (II) is a top view, and Figure (b) is a bottom view.

The thin layer 1o is selectively formed by etching the silicon substrate 1 from its back surface. That is, in the embodiment shown in FIG. 2, the thin layer 2 is bridged between the substrates 1', 1', whereas the thin layer 2 is formed on a part of the substrate.
This is reflected in the structure provided with. Compared to the embodiment shown in FIG. 2, since the silicon substrates 11' and 11' are left extra, this is disadvantageous in that the heat capacity increases accordingly, but on the other hand, it is easier to handle in the manufacturing process. This is an advantage. In the embodiment shown in FIG. 2, from the viewpoint of the mechanical strength of the thin layer 2, it is necessary to take care in handling the substrate if the thin layer 2 is formed and then the substrate (', 1') is bonded to the support 9. , in the embodiment of FIG. 3, the substrate 11'
. A major advantage in manufacturing is that there is no problem in handling even if this is done.

Incidentally, as in the embodiment shown in FIG. 2, the electrodes 3', 3'
may be formed on the silicon substrate side.

Although omitted in FIG. 3 (IL) for the sake of simplicity, the gas-sensitive membrane 6 shown in FIGS. 1 and 2 is omitted.

It is desirable to provide it on top of the thin layer 10.

Furthermore, a modification of the embodiment shown in FIG. 3 will be described.

If the support 9 is not provided with the openings 9', an air layer will be formed between the thin layer 10 and the support 9, so that less heat will be radiated from the heated thin layer. Therefore support 9
Whether or not to provide the hole 9' in the gas sensor can be decided based on comprehensive judgment from the installation location of the gas sensor of the present invention, the structure of the support, thermal conductivity, etc., and from the viewpoint of minimizing power consumption. .

Furthermore, as is clear from FIG. 3 (IL), the electrode 3'
.

When a voltage is applied across 3#, not only the thin layer 10 but also the substrate 1. Current also flows through the portions j' and '11'.

Considering the purpose of locally heating a portion of the thin layer 1o, it is preferable to reduce the current flowing through the portions 11' and 11'. Therefore, it is preferable that this portion has a high electrical resistance value. The first method of increasing the resistance value is to make the portions 11' and 11' as small as possible. To make it even smaller, 11', '1
1' is partially removed by etching it from the top, bottom or side.

The second method is electrically apparently 11', 11. This is a method of increasing the resistance value of the ' part. For example, 11' while the other parts are p-type silicon.

A part or the entire area of the portion 11' is configured to be n-type. Alternatively, an electrode may also be provided in the n-shaded region to apply a reverse bias between the p-type and n-shaded regions.

The third method is to adhere to the board and then remove the parts 11' and 11' by 1 per "1". This is the method.

A fourth method is to selectively control the impurity concentration in the thin layer 2 or 10 portion to selectively lower the resistance value of that portion compared to other portions.

The fifth method will be explained using FIG. 4.

A portion of the thin layer 1o (shown in dotted lines) is completely covered with the substrate 1'.

1', 11', and 11'. It is larger than the surface of the chip, and its thermal conductivity is also an order of magnitude lower.

Electrodes 3' are applied to the thin layer 1o through the holes 12', 12'.
If 3' is provided and a voltage is applied, it can be used as a local heater.

In the embodiments described above, except for the embodiment shown in FIG. 4, it is not necessarily necessary to provide the electrodes S/ and S# on the top surface. Electrodes provided on support 9 (not shown)
It is also possible to apply a voltage to the parts of the substrate 1', 1'. In this case electrode 3'.

Since there is no need to provide 3', it is desirable to increase the chip area by that amount.

In the embodiments described above, for example electrode 3'.

By flowing a constant current between electrodes 3' and measuring the voltage between the terminals, the resistance value between electrodes a/a and a# and the power applied to the resistor can be calculated. On the other hand, the resistance value of the thin layer 2 shows a certain temperature dependence.

By measuring the resistance value, the temperature of the thin layer portion can be determined. The temperature dependence of the resistance value of the thin layer 2 is stored in advance, and the temperature of the thin layer 2 can be determined by comparing the measured resistance value with the stored value. Similarly, the correlation between the heating power or heating temperature applied to the thin layer and the electrical properties of the sensitive film at various concentrations of the gas to be tested is once memorized, and then the electrical properties The test gas can be detected by comparing the actual measured value with the stored value. - As mentioned above, the sensor of the present invention not only can detect the operating temperature of the gas-sensitive membrane in the operating state with high precision, but also has the feature of great practical value in that it can control it with high precision. There is.

Furthermore, in the above embodiments, it has been mentioned that the heater also serves as a temperature sensor, but a temperature sensor for detecting the ambient temperature is provided at a separate location from the heater, and changes due to ambient temperature can be calculated and processed. It can also be corrected.

What is shown in FIG. 6 is another modification of the embodiment described using FIG. Curved pattern of thin layer 2 (dotted line)
It becomes. This kind of thing can also be implemented in the cases of FIGS. 2 and 4. In this case, a design advantage is that the resistance value of the thin layer portion can also be set by the pattern shape. It is also advantageous in that the resistance value of the portion where the gas-sensitive film 6 is provided can be locally increased, allowing for localized heating.

As is clear from the above description, it goes without saying that various modifications can be made without departing from the spirit of the invention. For example, it is also possible to vary the thickness of the thin layer 2 locally.

Next, the manufacturing process for obtaining the gas sensor of the present invention will be described.

An example in which silicon is used as the material constituting the thin layer 2 and the substrates 1/, 1# will be described.

For example, an aqueous solution of ethylenediamine/pyrocatechol (17ml ethylenediamine, sml water - 3g pyrocatechol) can be used to remove silicone containing boron.
The etching speed in the direction is s 2 x 1
o"aa-""-6x 1o"ax-" (Resistivity:
In the range of 10-1 to 1o2Ω-cIII), it is almost so
It is known that it shows a constant value of pm/br. <1
oO〉When observing the etching depth when a sample of silicon polished at a one-degree angle was etched for 10 minutes with the above etching solution, it was found that when the concentration of electrically active poron atoms in silicon exceeds 7×1019cIIr3, the etching depth increases. It is known that the etching speed becomes slower. If the concentration is below this limit, it is p-type.

It is also known that etching is performed at a nearly constant rate for both n-type etching.

The manufacturing method of the present invention can be effectively implemented by utilizing the phenomenon described above. This will be explained in detail using FIG. Part of thin layer 2 is selectively 7 x 10” 9
(It is necessary to have a boron concentration of 1'1Ir5 or more (not shown).

As shown in FIG. 2(0), a p-type silicon substrate on which an r-type thin layer 2 has been formed is adhered onto a support 9 having a hole 9'.

The support is made of a material that is resistant to corrosion by silicone etching solutions and has high resistivity.

For example, it is preferably made of alumina. Furthermore, as shown in FIG. 2(b), for example, at the boundary parts 12', 12' between the support body 9 and the substrate,
Before etching, a corrosion-resistant film such as 5102 film may be formed in advance. Since the SiO2 film is hardly etched, when the silicon substrate is etched from the hole 9' side, the boundary part 12' is etched by anisotropic etching.

The silicon substrate 1', 1'' on top of 12' is selectively left.

The portions 12' and 12' may be defined depending on the state of adhesion. .

Next, a manufacturing method and other embodiments will be described using FIG. 6. In the etching solution (75 ml of ethylene diamine, 24 ml of water, 12 g of pyrocatechol) at 105 to 116° C., an electrode 3' or 3
', and a negative voltage is applied to the platinum electrode in the etching solution, i.e. 0.6
By performing etching while applying a voltage of approximately V, it is possible to leave the n-type thin layer 2 and etch only the p-shaded region. For example, a thin layer with a thickness of 1 μm or less can be formed with high precision. It is known that the p-type etching rate at this time is 1.26-1.76 μl/min. It is also known that at this time, the n-shadow area is etched by less than 6 people/minute.

By the way, as shown in FIG. 2(0), the silicon thin layer 2
The zero width W' is narrower than the width W of the silicon substrates 1', . In order to realize such a structure, before performing the above-mentioned etching, the thin layer portions 13' and 13' in FIG. 2(0) of the n-type thin layer 2 in FIG. It is important to convert it to p-type. Alternatively, before performing the above etching, 13', 1
It is necessary to remove the 3" portion of the SiO2 film and the n-type thin layer below it in advance. In that case, the structure shown in FIG. 2(C) will be obtained.As is clear from the above explanation, The resistance value can be appropriately set not only by the impurity concentration but also by the pattern left by etching.

The electrodes s/, 31 may be formed before the etching is performed, or may be formed after the etching is completed. Alternatively, the electrode surface may be coated with a coating film when etching silicon, and the coating film may be removed after etching is completed.

Although not shown in FIG. 6, for example, the substrate 1
It goes without saying that a normal IC circuit or a memory element may be formed in the n-type island-like thin layer portion separated by the p-shaded region on the upper part of ' or 1'. It shows silicon, but G
Other semiconductor materials such as a45s can also be used to practice the invention.

Now, the gas-sensitive film 6 in Figure 2 is composed of an ultrafine particle film formed using an evaporation method in a gas. A method for manufacturing such a gas-sensitive ultrafine particle film has already been proposed, for example, in Japanese Patent Application No. 100620/1982, but in order to selectively form it at specific positions, it is possible to use, for example, a metal mask. I can do it. Figure 2 (I
L), electrodes 4', 4'I 4
By using a metal mask that covers the area other than the area where the ``'' is formed, it is possible to selectively form the Sn oxide ultrafine particle film 6, for example.

It goes without saying that the gist of the present invention will not be impaired even if various conventionally known gas-sensitive films can be used as the gas-sensitive film in addition to the ultrafine particle film formed by the evaporation method in gas. There is no combination of the various embodiments described above,
It goes without saying that deformation is also possible. By the way, as the present inventor proposed in Japanese Patent Application No. 64-68138, by changing the operating temperature of the ultrafine particle gas-sensitive membrane, the same sensitive membrane can be changed. can detect multiple gases. In the gas sensor of the present invention, the sensitive part and the heater part can be miniaturized, so it has become practical to provide, for example, a plurality of sensitive films in close proximity and to vary the operating temperature of each to operate steadily at a predetermined temperature. Therefore, not only can detection accuracy and precision be improved by operating multiple gas-sensitive membranes in the same state for gas detection, but also humidity can be detected by operating at least one of them near room temperature. I can do it.

In the gas sensor of the present invention, not only was it possible to reduce the heating power by using the thin layer 2, but also the heat capacity of the membrane inner body could be reduced by using the ultrafine particle membrane as the gas-sensitive membrane. The practical value is improved by an order of magnitude faster thermal response speed when the gas-sensitive membrane is operated not only in a steady state but also when the temperature is raised and lowered within a predetermined temperature range. did.

As mentioned above, the gas sensor of the present invention has excellent features such as low power consumption, high-speed response, high precision, and high reliability, and can be manufactured uniformly in a reduced size, so it has great industrial value. It's a beautiful thing.

[Brief explanation of the drawing]

Figure (&) is a top view, Figure (b) is a cross-sectional view at Moum' in Figure (IL), and
Figure (0) is a bottom view. FIG. 3(&), Cb) shows another embodiment of the gas sensor of the present invention, in which FIG. 3(IL) is a top view and FIG. 1(b) is a bottom view. Fourth
The figure is Figure 3 (&). FIG. 6 is a top view showing a modification of the embodiment shown in FIGS. 3(a) and 6(b), and FIG. FIG. 2 is a cross-sectional view for explaining the method of manufacturing a gas sensor of the present invention. (for sensitive membrane), 6... Gas sensitive membrane, e', e
'... Electrode (for wire bonding), 7...
...8i02 membrane. 9...Support, 9'...Opening (of the support), S/, S#...Opening (SiO2
of the membrane). :1 Figure C'109' Figure 4

Claims (1)

Scope of Claims: (1) A semiconductor layer has a semiconductor layer held in space by the substrate in at least a portion of the semiconductor substrate, and a gas-sensitive film is provided on the thin layer with an insulating film interposed therebetween; A gas sensor comprising means for applying electrical power to the thin layer and means for measuring electrical characteristics of the sensitive membrane. 1 (2)) The correlation between the heating power or heating temperature applied to the thin layer and the electrical characteristics of the sensitive film at various concentrations of the test gas is stored in the storage means, and then the electrical characteristics are stored. 2. The gas sensor according to claim 1, wherein the gas sensor is configured to detect a gas to be detected by comparing an actual measured value and a stored value. (3) The gas sensor according to claim 1, wherein the sensitive film is a film made of ultrafine particles. (4) The gas sensor according to claim 1, wherein the substrate and the thin layer are made of silicon. (@ Silicon constituting the thin layer is 7×10 as an impurity.
The gas sensor according to claim 4, characterized in that it contains a poron of 19cIr3 or more. (6) The gas sensor according to claim 1, wherein the thin layer and the electric plate have different conductivity types. ('7) The gas sensor according to claim 1, wherein the thin layer is a layer in which impurities are thermally diffused or ion-implanted into the substrate, or a layer epitaxially grown on the substrate. . (8) The gas sensor according to claim 11, wherein the thin layer is formed so that the area approximately at the center thereof is large. (9) The gas sensor according to claim 1, wherein the substrate is adhered to a support having a higher electrical resistance than the thin layer. (10) The gas sensor according to claim 9, wherein the support has an opening. (11) The gas sensor according to claim 1, 8, or 9, characterized in that a plurality of thin layers are provided. (12) The gas sensor according to claim 11, wherein at least one of the gas-sensitive films disposed on each of the plurality of thin layers (1') is configured to detect humidity. . (13) By selectively etching a part of the semiconductor substrate on which the insulating film has been formed, a semiconductor thin layer held in multiple spaces is formed on the substrate, and then evaporation in gas is performed. A method for manufacturing a gas sensor, comprising forming a gas-sensitive film made of ultrafine particles on the thin layer.