JPH0395452A - Gas sensitive element - Google Patents

Abstract

PURPOSE:To measure the concentration of oxygen as well as ozone at ordinary temperatures, and to manufacture and solidify an element on a semiconductor substrate during processing thereof by forming a layer of lanthanum fluoride having the atomic composition ratio of La:F=1:2-1:3 on said semiconductor substrate. CONSTITUTION:An n-type silicon substrate n-Si is heated in dried O2, on which SiO2 is formed. Lanthanum fluoride LaF3 is laminated thereover through high frequency sputtering. The lanthanum fluoride has the atomic composition ratio of La:F=1:2-1:3. Further, an electrode 1 as a film having the intermediate characteristic of platinum and platinum black is laminated which can secure an electric conduction with a Pt leading wire with a large surface area and high activation, and the Pt wire is bonded. When the obtained element is left in the atmosphere containing O2 or O3, O2 or O3 is adsorbed by the electrode 1. The adsorbing effect is high and considerably active enough to allow LaF3 to trap O2 or O3 as an oxygen ion O<2->. The composition ratio of LaF3 makes it possible to maintain and form a crystal as the trap center.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a gas-sensitive element sensitive to oxygen 0 and ozone 0.

``Prior Art'' Oxygen sensors currently in practical use can be roughly divided into those for room temperature operation and those for high temperature operation. Representative ones for room temperature operation are the Clark type oxygen sensor and the Garhani cell type. Oxygen sensors are known, and stabilized zirconia oxygen sensors have been proposed for high temperature operation. The Clark-type oxygen sensor has two electrodes: a cathode made of platinum (PT) that acts as a working electrode, and an anode made of silver (Ag) that acts as a counter electrode to the cathode. ), and the oxygen to be measured is taken into the electrolytic solution through a diaphragm exhibiting oxygen permeability such as Teflon or polyethylene. Then, the potential of the cathode electrode was set to −0.2
When the voltage is set to about V, the next electrode reaction begins.

Cathode: Ox + 2 HzO + 4 e- →
4 (OH) anode: 4Ag+ 4 C2- →4
8gcl+4e power supply voltage is usually -0.6V to -0. 8■
is set to measure the magnitude of the limiting current, and the oxygen concentration is detected from the magnitude of this limiting current. In other words, in general, the electrolytic reaction has a decomposition voltage EA (-0.2■
) occurs when the voltage exceeds a certain limit voltage EB (
In the above -〇. 6V to -0. Even if 8 V) is applied, the limiting current 1. The current cannot exceed a certain value (this is called the limiting current). The decomposition voltage EA, limit voltage EB, and limit current (2) vary depending on the type and concentration of ions present in the electrolytic solution, and each ion has a unique value, and these values EA. If EB and IB are measured, the type of ion can be determined from the decomposition voltage EA, and the limiting current I
The concentration of ions can be detected from B, and therefore, the oxygen concentration can be detected by measuring the limiting current in the Coolak type oxygen sensor.

Also, unlike the Clark type oxygen sensor, which requires an external voltage circuit, the Galhani cell type oxygen sensor has an internal electromotive force in the electrolytic cell itself, and uses a potassium hydroxide (KOH) aqueous solution as the electrolytic solution. Platinum (PT) is used as the cathode that acts as the electrode, and lead (Pb) is used as the counter anode.
, Teflon is used for the diaphragm, and oxygen is taken into the electrolytic solution by passing through the Teflon membrane. Then, an electromotive force is generated by the next electrode reaction.

Cathode: 02+2H20 +4e1→4(011)?
Node: 2 Pb-+ 2 Pb”+ 4 e2 P
b''+4 (OH)-→2 Pb (OH) 2 This reaction rate is proportional to the oxygen concentration, so if the two electrodes are connected with a resistor, the oxygen concentration can be detected from the magnitude of the current. On the other hand, a stabilized zirconium oxygen sensor uses calcium oxide (CaO) on zirconium oxide (ZrO).
) and another type that similarly solidifies 11helium oxide (Y203) in ZrOz. Either type is shaped into a cylinder and placed in the air.
The atmosphere of the object to be measured heated to 300°C or higher is injected into the hole. Stabilized zirconia allows only ○- ions to pass through, so a potential difference is created between the outer and inner surfaces of the cylinder according to the partial pressure ratio of 0, resulting in an equilibrium state.If this potential difference is measured, the oxygen concentration in the atmosphere can be determined. can be detected.

"Problems to be Solved by the Invention" However, since the Clark type oxygen sensor and the Galhany cell type oxygen sensor require an electrolytic solution, their lifespan is extremely short due to deterioration of the electrodes, diaphragm, etc. On the other hand, zirconia oxygen sensors do not require an electrolytic solution, but their operating temperature is as high as 300°C or higher, and they require additional equipment to control the temperature at high temperatures. It does not satisfy the condition of being easily measurable, and it also does not match the semiconductor manufacturing process, making it difficult to miniaturize through integration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a gas sensing element that can measure the concentration of not only ozone but also oxygen at room temperature, and that can be manufactured using a semiconductor process and solidified. With the goal.

"Means and operations for solving the problem" In order to achieve the above object, the present invention in claim (1) includes layering lanthanum fluoride on a semiconductor substrate, and in which fluorine:lanthanum in the lanthanum fluoride is layered. An electrode having an atomic composition ratio of 1:2 to 1:3 and having an intermediate property between platinum and platinum black is laminated on the lanthanum fluoride layer, and an electrode having an intermediate property between platinum and platinum black. Activates adsorbed oxygen molecules and ozone molecules,
? At high temperatures, oxygen ions are captured at the capture center of the lanthanum fluoride. In claim (2), an insulating layer is interposed between the semiconductor substrate and the lanthanum fluoride.

"Example" Below, an example of the gas sensing element according to the present invention will be described based on the drawings. FIG. 1 shows the structure of the first embodiment, and n-Si in the figure is an n-type silicon substrate. The substrate n
-Si wafer thickness is about 450 μm, and the n-Si substrate is heated in dry 02.
A silicon oxide layer (111sio) is formed on the n-Si substrate. Lanthanum fluoride LaF3 is laminated on the silicon oxide film Si02 by high frequency sputtering. When a film of lanthanum fluoride LaF3 was formed under different sputtering conditions, experimental data as shown in Table 1 below was obtained.

Table 1 Regarding setting of LaF3 sputtering film, that is, sputtering parameters, 8r
(Anoreco) Gas pressure 80mtorr, 20m
torr5 mtorr, and in each case, the sputtering power (anode voltage/power) was set to 1.
5KV・120W, 1.25KV・80W, 1.
OK V・50W, 0.8KV・30W, 0. 6
The test was carried out in 5 stages of KV and 20W, and therefore, the film conditions were set in 15 types (3 types x 5 stages). As a result, as shown in Table 1 above, 0. 6K V・2
At a sputtering power of 0 W, discharge occurred, but the length of the lanthanum fluoride LaF3 film could not be observed. On the other hand, as the sputtering power becomes higher, the sputtering rate increases, but the area covered by the film becomes narrower, which deteriorates the uniformity. The smaller the spanner power is, the better the uniformity will be, but if the spanner power is smaller, the uniformity will be higher. 8K
If the voltage is less than 30W, the discharge becomes unstable and no film is formed.
The uniformity decreases as the mark is reached. The data described below in this example is as follows: Ar gas pressure 80 mtorr, spatter power]. ．． The film thickness is 100 at 5KV/120W.
0 people is used, but the film thickness is 500 people to 3
Approximately 1,000 people is thought to be appropriate, and may be selected at an appropriate time depending on usage conditions, etc. The above lanthanum fluoride LaF. On the film, platinum PT is laminated by sputtering and separated from one electrode 1. Electrode 1 is intended to operate as a working electrode for activating oxygen, and is made of lanthanum fluoride LaF*.
It is also possible to laminate the laminate over the entire surface of the film, or only in a predetermined range depending on the usage conditions. Since the electrode 1 is for adsorbing oxygen and activating it, it is preferable to have a large surface area and high activation, and if this condition is not met, platinum black is ideal. however,
If it is completely platinum black, it will not be possible to ensure sufficient electrical continuity with the platinum PT wire to be bonded as a lead wire. Therefore, it is laminated as a film exhibiting properties intermediate between platinum and platinum black. The data to be described later in this example uses data obtained by forming an electrode 1 having intermediate properties between platinum and platinum black to a thickness of 100 people. A platinum PT wire is bonded to the layer exhibiting intermediate properties between platinum and platinum black.

On the other hand, the other pair is formed on the back side of the substrate n-Sj. An aluminum layer M with an overlapping contact is formed as a pole by vapor deposition, sputtering, etc., and a lead wire 2 such as a platinum PT wire is bonded to the aluminum layer M. Thereafter, electrodes 1 to lanthanum fluoride LaF. Cover the other layers with Caher wood. The cover material is PSG (Phospho Silicate Gl).
ass) is preferred.

Then, when the gas sensing element of the first embodiment described in Section 2 is exposed to an atmosphere containing zero oxygen or ozone, the electrode 1, which exhibits properties intermediate between platinum pt and platinum black, will have zero oxygen.

and ozone 03 are adsorbed. The electrode 1 exhibits an intermediate property between platinum PT and platinum black, and has a so-called honeycomb-like state with minute irregularities, and has a large surface area, so it has a high adsorption effect, and like platinum black, it has a high adsorption effect on the oxygen. 0 ■ and ozone 0
It exhibits sufficient activation to cause lanthanum fluoride LaF3 to capture 3 as oxygen ions 02''.Lanthanum fluoride LaF. oxygen ion 02
It is approximately the same as the ionic radius of -, which is 1.4 people. Therefore, it is thought that the above oxygen ion O2 is captured in the missing part of F1 in the crystal of lanthanum fluoride LaF3, and this missing part of F1 is thought to be the center of capture of 02-. . As mentioned above, lanthanum fluoride LaFz is F
It seems that the missing part of is the center of capture, so La:
If the atomic composition ratio of F is in the range of 1=2 to 1:3, it is possible to form a layer that can sufficiently maintain crystallinity and capture 02-. Further, this gas sensing element is an oxide film of silicon St (SiO). and lanthanum fluoride LaF* as a dielectric layer.
As shown in FIG. 2, the capacitance changes depending on the applied voltage and exhibits MIS diode characteristics. In an oxygen 02 atmosphere, the gas phase/Pt (electrode 1)/LaF. , at the three-phase interface 1/2・02 (gas) + 2 e- ;=! Q
The reaction of ``-'' generates an interfacial potential due to oxygen ions 02-, which lowers the applied voltage. Therefore, the threshold voltage that creates an inversion layer on the Si substrate changes to the positive potential side. 0 captured by lanthanum fluoride LaFz
The diode characteristics change depending on the amount of 2-, and the oxygen concentration can be detected based on this amount of change. If this amount of change was taken as data, something like the one shown in FIG. 3 was obtained.

The data in FIG. 3 is a characteristic diagram showing the response waveform when oxygen 02 of various concentrations at 300 cc per minute was injected into the test chamber. In addition, when detecting the oxygen concentration, as described above, when <02- is captured at the capture center of lanthanum fluoride LaF3, a potential difference is generated, so this potential difference is measured, or based on this potential difference, a The concentration of oxygen or ozone can also be detected by measuring the value of the current flowing through a single resistor connected to the outside.

4 and 5 show a second embodiment, in which a p-type silicon wafer with a film thickness of 450 μm is used as the semiconductor substrate, and on the semiconductor substrate p-Si, similar to the first embodiment, Lanthanum fluoride LaFz having a film thickness of 1000 nm is laminated by sputtering. Lanthanum fluoride LaF3
Similarly to the first embodiment, the atomic composition ratio La:F is set to 1:2 to 1:3. Lanthanum fluoride LaF
On the film No. 3, platinum PT is laminated by sputtering. In this example, 11 12 is also used as the electrode 1 exhibiting an intermediate property between platinum and platinum black under the same conditions as in the first example. Laminated to the thickness of a person. The electrode 1 is bonded with aluminum M as an extraction electrode 3. On the other hand, there is a film thickness of 500 mm on the back surface of the substrate pSi.
0 person's O5 The aluminum layer M of the ivy contact is laminated by sputtering or vapor deposition, and the lead wire 2 is attached to the Al5M layer.
Bonding. Further, the electrode 1 is covered with psc (used as a cover material) except for the part of the electrode 1 which becomes the sensing surface and has properties intermediate between platinum and platinum black.

In the second embodiment, as well as in the first embodiment, in an atmosphere containing oxygen 02 and ozone 03, oxygen 02
Odun 03 is activated in the layer with intermediate properties between platinum and platinum black of electrode 1, and as shown in FIGS.
- is captured by lanthanum fluoride LaF3, similarly to the zirconia oxygen sensor, [where const: constant, R: gas constant, T: absolute temperature, F: Faraday constant,
A potential φ such as Po2: oxygen partial pressure] is generated, and this potential φ
, a potential difference 7 occurs between the two electrodes. Moreover, if 02- exists in lanthanum fluoride LaF3, 02-
The surface electrons (minority carriers) of the p-Si substrate move toward the substrate due to the negative charge of the p-Si substrate, increasing the concentration of genuine tags on the surface of the p-Si substrate. As shown in FIG. 7, when a negative voltage is applied to the extraction electrode 3, that is, the electrode 1, which has properties intermediate between platinum and platinum black, 02- in the lanthanum fluoride LaF3 diffuses toward the M layer, which is the other electrode. do.

As shown in FIG. 8, the voltage applied to the extraction electrode 3 is
If it is increased in the direction (2), the movement of 02- will be reduced, the dielectric constant of lanthanum fluoride LaFs will increase, and the resistance and capacitance will increase accordingly. If the applied voltage is further increased in the positive direction, the resistance of the lanthanum fluoride LaF3 increases, which prevents the movement of electrons from the p-Si substrate to the lanthanum fluoride LaFz in the opposite direction, as shown in FIG.
Electrons accumulate on the surface of the p-Si substrate, forming a depletion layer, and the capacitance between the M electrode and the electrode 1 decreases. This capacitance change is
This can also be understood from the measurement data shown in FIG. 1O. At this time, 0 is captured by lanthanum fluoride LaF3.
2", that is, depending on the oxygen concentration, the substrate p-
Since the hole concentration in Si is changing, the threshold voltage that creates a depletion layer will also change.

Therefore, when measuring the ozone detection ability of the gas sensing element of this example heated at 80°C and at room temperature, the 11th
Data as shown in the figure and FIG. 12 were obtained. In both cases, the ozone concentration to be measured was 1%, and the flow rate was 10n/m.
The gas sensing element is placed in the test chamber in the atmosphere. A measuring device 5 is connected between both electrodes of the gas sensing element to measure the value of current flowing due to the potential difference generated depending on the oxygen concentration. Compared to the data obtained with the gas sensing element heated to 80°C as shown in Figure 12, although the values and response speed of the data measured at room temperature are lower, this shows that measurements can be made satisfactorily even at room temperature. There is.

In addition, in FIG. 12, the injection of ozone was stopped and nitrogen gas N2 was injected, and thereby the recovery characteristics were also tested. In this example as well, the above capacitance and current value? Of course, the concentration of oxygen and ozone can also be detected by the potential difference and resistance value between the two electrodes.

For example, if the ozone concentration generated by an ozone generator using an ultraviolet lamp and another ozone generator is determined by the current value and resistance value generated between the two electrodes using the measuring device 5, data as shown in FIG. 13 will be obtained. Ta.

FIG. 14 shows the third embodiment, in which a P-type silicon substrate is used as the silicon substrate of the first embodiment, and the structure is otherwise the same as that of the first embodiment, and the manufacturing method and conditions are also the same as those of the first embodiment. This is the same as the example and the second embodiment. Then, when 02- is captured from the atmosphere into lanthanum fluoride LaFz, the second
As in the example, it operates according to the concentration of 02, and the capacitance changes, and the potential difference, current, and resistance value of both electrodes change, making it possible to measure the concentration of oxygen 0 and ozone 0 in the atmosphere. . At this time, the oxide film SiO2 exhibits a polarization effect as shown in FIG. 15, and the other functions are the same as in the second embodiment.

FIG. 16 shows a fourth embodiment, in which an N-type source 6 and drain 7 are formed on the p-Si substrate of the third embodiment, and the source 6 and drain 7 have 15 16 ? The M electrode is attached by vapor deposition, and the other manufacturing conditions and structure are the same as in the second embodiment.

When lanthanum fluoride LaF 3 captures 02- from the atmosphere of oxygen 02 or ozone 03, lanthanum fluoride LaF. The 02− captured by l becomes a negative potential, and the N channel between the source 6 and drain 7 in the substrate p-St is controlled by a negative potential corresponding to the 02 concentration of the lanthanum fluoride LaF 3. Therefore, if the current flowing between the source 6 and drain 7 electrodes M due to the electric current tA8 is measured by the ammeter 9, oxygen is 0. The current value corresponding to the concentration of Odun 03 can be measured.

In the present invention, silicon is used as the semiconductor substrate in each of the above embodiments, but other materials may be used, and either P-type or N-type material may be used. In addition to oxygen 0■ and ozone 03 as sensitive gases,
It is also possible to measure the concentration of N08.

"Effects of the Invention" As described above, the gas sensing element according to the present invention can measure not only ozone but also oxygen concentration at room temperature, can be manufactured using a semiconductor process, can be solidified, and can be used. It can also be effective from above.

[Brief explanation of drawings]

The drawings show embodiments of the gas-sensitive element according to the invention, and
The figure is a structural diagram of the gas sensing element of the first embodiment, and the second figure is the structural diagram of the gas sensing element of the first embodiment.
Figure 3 is a capacitance-voltage characteristic diagram of the gas sensing element shown in Figure 1, response waveform diagram at room temperature for various oxygen concentrations of the gas sensing element shown in Figure 1, Figure 4 is a structural diagram of the gas sensing element of the second embodiment. , FIGS. 5 to 9 are explanatory views explaining the operation of the gas sensing element shown in FIG. 4, and FIG. 10 is a capacitance-voltage characteristic diagram of the gas sensing element shown in FIG. 4 in ozone and oxygen in nitrogen gas. 11th
The figure shows the response waveform of the gas-sensitive element shown in Fig. 4 in 1% ozone at room temperature, and Fig. 12 shows the response waveform of the gas-sensitive element shown in Fig. 4 at 1% ozone.
A diagram of the response waveform in ozone at 80°C, Figure 13 is a characteristic diagram showing the ozone concentration dependence at room temperature of the gas sensing element of Figure 4, and Figure 14 is a structural diagram of the gas sensing element of the third embodiment. , FIG. 15 is an explanatory diagram showing the operation of the gas sensing element of FIG. 14, and FIG. 16 is a structural diagram of the gas sensing element of the fourth embodiment. 19 tρ applied voltage (V)

Claims (2)

[Claims] (1) Lanthanum fluoride is layered on a semiconductor substrate, and the atomic composition ratio of La:F in the lanthanum fluoride is 1:2.
~1:3, and an electrode having an intermediate property between platinum and platinum black is laminated on the lanthanum fluoride layer. (2) The gas-sensitive element according to claim (1), characterized in that an insulating layer is interposed between the semiconductor substrate and the lanthanum fluoride.