JPH0227621B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a multilayer film that is capable of simultaneously measuring the concentration of multiple ions using one chip of electrodes by providing a plurality of ion-sensitive membranes selectively sensitive to different ions on a semiconductor substrate. It relates to ion electrodes.

Multi-ion electrodes that respond to multiple ions are
Conventionally known as FET composite sensor or FET multi-sensor using FET. For example, Tokukai Akira
As shown in publications such as No. 56-72339 and Japanese Unexamined Patent Publication No. 54-24317, a plurality of FET gate sections are provided,
These are coated with a sensitive membrane that selectively responds to specific ions, and when these gates are placed in a test liquid, the conductivity of the gate changes depending on the concentration of specific ions in this liquid. This was used to measure the concentration of specific ions. FIG. 1 shows a FET composite sensor described in Japanese Patent Application Laid-Open No. 56-72339, in which FIG. 1a is a plan view and FIG. 2b is a sectional view taken along line A-A'. This is a FET
For example, prepare multiple pieces of
It measures PH and PNa simultaneously by attaching a PH-sensitive membrane and a PNa-sensitive membrane. That is, on a P-type semiconductor substrate 1, source regions 2-1 and 2-2 of the first and second FETs, a channel stopper 3,
Each gate part 4-1 of the first and second FET,
4-2 and a common drain part 5 are formed, and an insulating film 6 and a polysilicon 7- are formed on these regions.
1, 7-2, and further the first and second
Source electrodes S-1 and S-2 of each FET and a common drain electrode D are provided.

Another example where two FETs are formed on one chip.
A FET composite sensor is described in Japanese Patent Publication No. 56-38902, and a plan view thereof is shown in FIG. 2a. 1st
In contrast to the example shown in the figure, this is made by arranging two FETs horizontally. That is, a common substrate terminal 8, source parts 9 and 10 of each of FET1 and FET2, and a common drain part 11 are provided at the base of an elongated semiconductor substrate.
At the same time, source diffusion layers 12, 13, drain diffusion layers 14, and channel stopper 1 of each of FET1 and FET2 are formed from the base to the tip. The gate portion of each of FET1 and FET2 is located at the tip of the semiconductor substrate, and the equivalent circuit thereof is as shown in FIG. 2b.

Conventionally, a calomel electrode was used as a reference electrode, but a reference electrode formed by coating a hydrophobic organic polymer film on the gate part of an FET was developed in Japanese Patent Application Laid-Open No. 1983-
No. 81897 and Japanese Unexamined Patent Publication No. 100350/1983. Further, an FET composite sensor using such a reference electrode is disclosed in Japanese Patent Application Laid-open No. 81897/1983.
This composite ion sensor is shown in FIG. Figure 3a
is a plan view of the whole, and FIG. 3b is a sectional view at B'. A common drain part 16, a reference electrode and sensor source parts 17 and 18 are formed in the semiconductor substrate, the drain part 16 is provided with a drain electrode 20, the source part is provided with source terminals 21 and 22, and further connected to the substrate. A common electrode 24 is provided. Reference electrode and sensor gate parts 25, 26
is provided at the tip. As shown in FIG. 3b, insulating films 28 and 29 are provided to firmly adhere the hydrophobic organic polymer film 30 of the gate portion 25 of the reference electrode to the substrate and to prevent electrical leakage. It is provided. In this example, a pseudo electrode 19 is provided to keep the potential of the measurement liquid constant, and is connected to the terminal 23.

Composite sensors using these FETs are convenient to use, but they require equipment to keep the atmosphere clean during manufacturing, and the process is complicated, making them time-consuming and costly. Ta.

On the other hand, ion electrodes of a type different from the above-mentioned FET sensor are also known, and the structure of one example is shown in FIG. FIG. 4a is a cross-sectional view showing the entire ion electrode, and FIGS. 4b and 4c are enlarged views of the ion-sensing portion. The example shown in FIG. 4b is the semiconductor substrate 3.
In the example shown in FIG. 4C, an insulating film 40 is inserted between the semiconductor substrate 34 and the ion-sensitive film 33. The ion electrode 32 assembled using the ion sensing section having one of the structures shown in FIGS. 4b and 4c is
Shown in Figure a. The sensitive part shown in FIG. 4c, which is formed on the semiconductor substrate 34 by sequentially forming an insulating film 40 and a sensitive film 33, is fixed to the lower end surface of the outer cylinder 38 by pasting or fusion, and is attached to the upper end of the outer cylinder 38. The cap 39 is tightly fitted to form the main body. Inside the main body, there is an outer cylinder 3.
A lead wire 37 is provided hanging inside the semiconductor substrate 8 , and a core wire 36 of the lead wire is connected to the semiconductor substrate 34 via an electrode 35 . The lead wire 37 is fixed to the cap 39 and led out. The electrode 35 is made of, for example, a conductive adhesive and connects the semiconductor substrate 34 and the core wire 36 electrically. Although such an ion electrode 32 has a simple structure and does not require complicated manufacturing steps, only one type of ion concentration can be measured with one chip. Furthermore, a separate reference electrode was required. Therefore, when measuring the concentration of different types of ions, multiple ion electrodes and reference electrodes must be immersed in the test liquid.
It was very troublesome.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology, to be able to measure the concentrations of different types of ions with one chip, and to be able to easily and inexpensively measure the concentrations of different types of ions without requiring any special manufacturing equipment or manufacturing process. The present invention aims to provide a multi-ion electrode that can be manufactured in a variety of ways.

The multi-ion electrode of the present invention includes a semiconductor substrate,
an isolation region that electrically isolates the semiconductor substrate into a plurality of regions, an insulating film formed on at least the plurality of regions on one surface of the semiconductor substrate, and an insulating film formed on the plurality of electrically isolated regions. ion-sensitive films of different types selectively formed on the insulating films of , and a plurality of ion-sensitive films formed respectively in the plurality of regions on the surface of the semiconductor substrate opposite to the side on which these ion-sensitive films are formed. It is characterized by comprising an electrode section.

The contents of the present invention will be explained below with reference to the drawings.

FIGS. 5a to 5e show the sequential manufacturing steps of an embodiment of the multi-ion electrode of the present invention. In this embodiment, four types of electrodes are formed on one chip. As shown in FIGS. 5a and 5b, one conductivity type semiconductor substrate 41
Next, isolation-diffusion regions 42 of opposite conductivity type are formed by diffusion from the front and back of the substrate, and the semiconductor substrate 41 is separated into a plurality of, here four "islands". here,
The semiconductor substrate 41 is desirably of n-type when the detected ions are positive ions, and of p-type when the detected ions are negative ions. Regarding the type of the semiconductor substrate 41, various diffusion layers such as Si, Ge, GaAs, etc. can be used, but here, to simplify the explanation, we will use n-type Si.
This will be explained using a (silicon) substrate as an example. Therefore, the isolation diffusion region 42 is formed by diffusing P-type impurities. FIG. 5a shows a sectional view taken along line AA' in FIG. 5b. During this separation and diffusion, an oxide film (SiO ₂ ) is formed on the surface of the semiconductor substrate 41. After forming the isolation diffusion region 42, only the oxide film 43 on the isolation diffusion region 42 on one surface of the semiconductor substrate is left, and the rest is removed by etching (FIG. 5c). Oxide film 43 remaining after etching process
It is desirable that the film thickness is several thousand Å or more. Next, as shown in FIG.
Form to a film thickness of around 1000 Å. The type of insulating film 44 is one that has excellent water resistance and is chemically stable.
A Si ₃ N ₄ film, an oxide film or nitride film of Al or Ta, or a mixed composition film of the above oxide film and nitride film can be used. The insulating film 44 can be formed by a method such as vapor deposition, sputtering, or CVD (Chemical Vapor Deposition). After that, Figure 5 e
As shown in FIG. 3, ion sensitive films 44 and 46 that selectively take in target ions are formed on the insulating film 44 of each "island" formed on the semiconductor substrate 41, and an electrode portion is formed on the back surface of the "island". 47 and 48 are formed to complete the chip of the multi-ion electrode 40.

Next, a specific example of the aforementioned ion-sensitive membranes 45 and 46 will be explained. Silicon nitride (Si ₃ N ₄ ), alumina (Al ₂ O ₃ ), and tantalum pentoxide (Ta ₂ O ₅ ) films can be used as ion-sensitive films when used as hydrogen (H ⁺ ) ion electrodes. Actual 1000Å
silicon nitride film or alumina (Al ₂ O ₃ )
When the membrane is used as an ion-sensitive membrane, the pH range is 53 to 13, which is almost the same as a conventional glass electrode.
An interfacial potential of 56 mV/PH is obtained. Furthermore Ta ₂ O ₅
When composed of a membrane, it exhibits excellent characteristics of 56 to 58 mV/PH at room temperature. Therefore, if the insulating film 44
When the insulating film 44 is formed with a composition of any one of Si ₃ N ₄ , Al ₂ O ₃ and Ta ₂ O ₅ , the insulating film 44 can also serve as a sensitive film of the hydrogen ion electrode, so new ions It is not necessary to form a sensitive film on the insulating film 44. In addition, hydrogen ion sensitive membranes include 6% CaO, 72% SiO ₂ , and 22% Na ₂ O (% is molar ratio), which are known as conventional glasses for glass electrodes.
Soda lime silicate glass with a composition of 68%
SiO ₂ , 25% Li ₂ O, 7% CaO or 67% SiO ₂ ,
Lithium glass having a composition of 25% Li ₂ O and 8% BaO can also be used as a material constituting the sensitive film. These inorganic films can be formed by a CVD method, a sputtering method, an electron beam evaporation method, an alkoxide solution coating method, or the like. Also sodium (Na ⁺ )
As an electrode, aluminosilicate glass ( _SiO2 - _{Al2O3 - Na2O} ), especially 60-80% _SiO2 , 10
Those with a composition of ~20% Al ₂ O ₃ , 10-20% Na ₂ O and borosilicate glass (SiO ₂ -B ₂ O ₃ ) can be used. Furthermore, as a potassium (K ⁺ ) electrode, aluminosilicate glass, especially 69% SiO ₂ , 4%
Those having a composition of Al ₂ O ₃ , 27% Na ₂ O and porosilicate glass can be effectively used. These glass films can also be formed by a CVD method, a sputtering method, an electron beam evaporation method, or an alkoxide solution coating method. The above PH, PNa and
The thickness of the ion-sensitive membrane for the PK electrode is preferably in the range of 500 to 2000 Å.

Instead of inorganic materials as mentioned above, the sensitive membranes of some ion electrodes are composed of ion exchange materials, antibiotics, etc. maintained in polyvinyl chloride, polyurethane, silicone rubber or other neutral hydrophobic matrices. You can also. For example, antibiotics such as valinomycin and crown ether are suitable for potassium ions (K ⁺ ), Nigishin and other antibiotics are suitable for sodium ions (Na ⁺ ), and calcium didodecyl phosphate and other antibiotics are suitable for calcium ions (Ca ²⁺ ). Ion exchange materials can be used.
Although the structure of a membrane sensitive to typical cations has been described above, the ion electrode of the present invention also functions satisfactorily with respect to anions. For example, if the sensitive film is made of a silver sulfide/silver iodide mixture,
Can be used as an electrode for ^CN- .
If it is composed of an AgCl film, it can be used as a chloride ion (Cl ^- ) electrode. However, when forming the above-mentioned anion-sensitive film, it is more desirable to use a p-type semiconductor substrate 41 as described above, and to form the isolation diffusion region 42 by diffusing n-type impurities.

As described above, various ion-sensitive films are formed on the "island" insulating film 44 separated by the isolation diffusion regions 42 of the semiconductor substrate 41, thereby configuring a plurality of ion electrodes on one chip. Although we have described a new multi-ion electrode, by forming the sensitive membrane of one of the multiple electrodes with a certain type of hydrophobic organic polymer membrane, we can eliminate the need for reference, which was previously required separately from the ion electrode. Electrodes can be realized on the same chip. As the organic polymer film in this case, for example, polyvaraxylylene (trade name: Parylene) is effective. Paraxylylene dimer, which is the raw material, is sublimed at a temperature of 80 to 200℃ to produce a 600 to 800
After being decomposed into monomers at a temperature of °C, they are deposited on the desired insulating film. The polymer formed at this time is extremely uniformly formed on a fixed surface of arbitrary shape,
At the same time, since the number of ion dissociative groups on the polymer surface is far smaller than that of metal oxide insulators, it functions as a reference electrode that is insensitive to ions. In addition, polyvinyl chloride and polyvinylidene chloride films are also effective. These can be applied by applying a polymer dissolved in a solvent to a given insulating film and then evaporating the solvent, or by applying the polymer in a molten state and cooling it, or by applying a monomer or prepolymer to the insulating film and then heating it. , whether to polymerize by adding an initiator or by irradiating with radiation or ultraviolet rays;
It can be formed by plasma polymerization.

In the above explanation, separation of electrode "islands" when forming multiple sensitive films on one chip was achieved by diffusing impurities of the opposite conductivity type to the silicon semiconductor substrate 41. There is a method of separation,
Examples thereof are shown in FIGS. 6 to 8.

FIG. 6 shows an example in which a material with a fast oxidation rate, such as polysilicon, is used as the semiconductor substrate 51. The front and back surfaces of the substrate other than the regions to be separated are covered with a mask 52 (FIG. 6a). As this mask
A Si ₃ N ₄ film is used. After that, the exposed polysilicon is oxidized in an oxidizing atmosphere, and the oxidized isolation region 5 is
3 (Figure 6b). Thereafter, as shown in FIG. 6c, an insulating film 54 is deposited on the chip surface.
As shown in FIG. 6d, ion sensitive membranes 55, 56 and electrode portions 57, 58 are formed to complete a multi-electrode chip.

FIG. 7 shows a case where the mask 62 is formed only on one surface (FIG. 7a). At this time, the substrate 61
Since the oxidation progresses uniformly from the back side, the oxidized isolation region 63 becomes as shown in FIG. 7b. The subsequent steps are similar to the examples shown in FIGS. 6c and 6d, but when forming the electrode parts 67 and 68, the insulating film 63 on the back surface is uniformly removed or as shown in FIG. 7d. It is necessary to remove the insulating film 63 only from the portions where the electrode portions 67 and 68 are to be formed.

In the example shown in FIG. 8, first, a semiconductor substrate (polysilicon) 72 is placed on an insulating substrate 71 shown in FIG. 8a.
After forming (FIG. 8b) and applying an oxide mask 73 (FIG. 8c), an oxidized isolation region 71' extending up to the insulating substrate 71 is formed (FIG. 7d). Thereafter, ion sensitive membranes 75, 76 and electrode parts 77, 78 are formed in the same manner as in FIG. 7d to complete the process.

Next, FIG. 9 shows an actual example of an ion electrode incorporating the multi-ion electrode chip described above.

As shown in FIG. 9, a tip 93 formed according to the embodiment described above is attached to the tip of an outer cylinder 94. In this case, an insulating adhesive 9 is used between the outer cylinder 94 and the chip 93 to prevent electrical leakage and liquid leakage.
Seal with 5. Furthermore, a lead wire 96 is inserted into the outer cylinder 94.
1,96-2 and its core wire 92-1,92
-2 is connected to the sensor chip 93 via electrodes 91-1 and 91-2. Lead wire 96-1, 96-
2 is fixed to the lid 97 and led out. electrode 91
-1 and 91-2 are made of conductive adhesive, for example,
Connect the sensor chip 93 and the core wires 92-1, 92-2. The sensitive part of the multi-ion electrode of the present invention having such a configuration has an extremely simple structure.
By interposing an insulating film between the sensitive film and the substrate, swelling of the sensitive film and the accompanying electrical leakage are eliminated, and good characteristics can be stably maintained over a long period of time.

As shown in the embodiments above, according to the present invention, 1
A multi-ion electrode that can simultaneously measure the concentration of various ions on a chip can be realized, and its manufacturing equipment and manufacturing process can be simplified.

Furthermore, by covering one of the electrodes with an organic polymer film that is insensitive to ions, a reference electrode for measuring ion concentration can also be formed on the same chip, making it possible to reduce the size of the electrode.

[Brief explanation of drawings]

Figures 1a and b are a plan view and a cross-sectional view showing the configuration of an example of a conventional FET composite sensor, and Figure 2a is a
3 and b are plan views and equivalent circuit diagrams showing the configuration of another example of a conventional FET composite sensor, and FIGS. FIGS. 4a, b and c are sectional views showing other examples of conventional ion electrodes using semiconductor wafers. FIGS. Cross-sectional views and plan views showing the configuration in an example of sequential manufacturing steps, FIGS. 6 a to d, and FIG. 7 a
-d and FIGS. 8a to 8e are cross-sectional views showing the configurations of three other examples of the multi-ion electrode of the present invention in the sequential manufacturing process, and FIG. 9 is a cross-sectional view of an ion electrode incorporating the multi-ion electrode of the present invention. FIG. 2 is a cross-sectional view showing an example configuration. 41, 51, 62, 72...semiconductor substrate, 4
2, 53, 63, 71, 71'...separation area, 4
3, 52, 62, 73...mask, 44, 54,
64, 74... Insulating film, 45, 46, 55, 5
6, 65, 66, 75, 76... ion sensitive membrane,
47, 48, 57, 58, 67, 68, 77, 7
8,91-1,91-2... Electrode part, 92-1,
92-2... Core wire, 93... Chip, 94... Outer cylinder, 95... Insulating adhesive.

Claims (1)

[Scope of Claims] 1. A semiconductor substrate, an isolation region that electrically isolates the semiconductor substrate into a plurality of regions, and an insulating film formed on at least the plurality of regions on one surface of the semiconductor substrate; Different types of ion-sensitive films selectively formed on the insulating films on the plurality of electrically isolated regions, and on the surface of the semiconductor substrate opposite to the side on which these ion-sensitive films are formed. , and a plurality of electrode parts respectively formed in the plurality of regions. 2. The multi-ion electrode according to claim 1, wherein the separation region that separates the semiconductor substrate into a plurality of regions includes an impurity diffusion region having a conductivity type opposite to that of the semiconductor substrate. 3. The multi-ion electrode according to claim 1, wherein the separation region that separates the semiconductor substrate into a plurality of regions is formed by an insulator region formed by oxidizing the semiconductor substrate. . 4. The insulating film formed on the surface of the semiconductor substrate is made of an oxide or nitride of silicon, aluminum, or tantalum, or a mixed composition of these oxides and nitrides. A multi-ion electrode according to scope 1. 5. The multifunction device according to claim 1, wherein a reference electrode is formed by providing an organic polymer film insensitive to ions on an insulating film formed on one of the plurality of regions. ion electrode. 6 Claims 1, 2, 3, and 3, characterized in that the semiconductor substrate is made of silicon.
The multi-ion electrode according to item 4 or 5.