JPH0933481A - Optical scanning potentiometric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sensor excellent in resolution and strength by employing a silicon insulator (SOI) substrate as a semiconductor substrate. SOLUTION: An oxide 2 is deposited by about 100nm on the entire surface of a silicon substrate 1 of about 500μm thick and another silicon substrate 3 of 500nm thick is applied tightly thereto before being heated at 1000 deg.C, for example, to form a substrate 4. The substrate 4 is then polished to produce a substrate 1 of 1-2μm thick and an active layer 1A is formed thereon to obtain an SOI substrate 4A. Subsequently, the active layer 1A is etched to leave a part thereof. An oxide is then deposited by about 50nm on the entire surface of active layer 1A and a sensing part of Si3 N4 is formed by CVD. A metal electrode is deposited at the etched part before individual sensors are produced by dicing. A photocurrent generated in the active layer 1A by a light incident on the substrate 3 side can be taken out in the form of a signal from the electrode. This structure provides high mechanical strength even if the active layer 1A is made thin and the positional resolution can be enhanced through reduction in thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical scanning in which a sensing portion responsive to a substance is formed on one surface of a semiconductor substrate, and the other surface of the semiconductor substrate is irradiated with probe light to extract photocurrent as a signal. Type potentiometric sensor.

[0002]

2. Description of the Related Art Chemical substances that change due to, for example, the activity of microorganisms are measured by using an optical scanning potentiometric sensor. This optical scanning potentiometric sensor
In recent years, it has been developed for two-dimensionally measuring the pH of a substance dissolved in a liquid or a liquid soaked in the substance. Such a sensor is disclosed, for example, in Jpn.
J. Appl. Phys. Vol. 33 (1994) p
As described in p L394-L397 (hereinafter referred to as literature), a sensing unit that responds to a substance is formed on one surface of a semiconductor substrate, and the other surface of the semiconductor substrate is irradiated with probe light, At this time, the measurement can be performed by taking out the photocurrent induced in the semiconductor substrate as a signal.

The concentration distribution of the dissolved substance is measured by inserting or contacting the sensing portion of the optical scanning type potentiometric sensor with the target substance to be directly measured. The obtained data is output as a two-dimensional or three-dimensional density distribution image by computer processing. Not only the concentration distribution at a certain time but also the state of the change can be tracked in real time. The image obtained in real time can be easily compared with the electromagnetic wave image obtained by visual inspection, CCD camera or the like.

The applicant of the present application has filed a patent application on February 4, 1995 as an "optical scanning device" for the apparatus used for measuring the two-dimensional distribution of potentiometric such as pH. Ori (Japanese Patent Application No. 7-39114),
In addition, a patent application for a method for measuring the concentration distribution of a dissolved substance as a “method for measuring the concentration distribution of a dissolved substance” was issued on March 22, 1995 (Japanese Patent Application No. 7-90310).

By the way, in order to improve the position resolution of the above optical scanning potentiometric sensor, it is necessary to reduce the thickness of the semiconductor substrate on which the photocurrent is generated, that is, to reduce the thickness, as described in the above-mentioned document. However, in the conventional optical scanning potentiometric sensor, a silicon substrate is generally used by etching as the semiconductor substrate.

[0006]

However, the thickness of the silicon substrate as the semiconductor substrate is made small (thin).
Then, the mechanical strength thereof becomes smaller, and it becomes difficult to keep the mechanical strength stable.

The present invention has been made in consideration of the above matters, and an object thereof is to provide an optical scanning type potentiometric sensor having excellent positional resolution and a predetermined mechanical strength.

[0008]

In order to achieve the above object, the present invention forms a sensing portion responsive to a substance on one surface of a semiconductor substrate and irradiates the other surface of the semiconductor substrate with probe light. An optical scanning type potentiometric sensor for extracting a photocurrent as a signal by using an SOI substrate is used as the semiconductor substrate. Here, SOI is Silicon on In
It is a sulator.

As the SOI substrate, a bonded SOI substrate in which two silicon substrates are directly bonded and one silicon substrate is polished to have a size of several micrometers (μm) or less, or a silicon substrate and a glass substrate. And anodic bonding, and a bonded SOI in which the silicon substrate is polished to a size of several μm or less, an SOS substrate in which a silicon layer is deposited on a sapphire substrate, or oxygen ions are implanted into the silicon substrate. SIM with oxide layer formed by
An OX substrate or the like can be used. Here, SOS is Silicon on Saphire, and SIMOX is Separation by I.
It is nplanted Oxyzen.

[0010]

In the optical scanning type potentiometric sensor of the present invention, since the semiconductor layer in which photocurrent is generated is formed by the SOI substrate, even if the semiconductor layer is made thin, the mechanical strength is large, and the semiconductor layer is conventional. Since it can be made thinner, the position resolution is improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings.

First, a first embodiment will be described with reference to FIGS. In the first embodiment, as the SOI substrate,
A bonded SOI substrate is used.

As a bond wafer, for example, a thickness of 500 μ
A silicon substrate 1 having a large mechanical strength of m is prepared [see FIG. 2 (A)].

The silicon substrate 1 is, for example, 1000 ° C.
Thermal oxidation is performed at 100 nm (n
m) oxide film (SiO ₂ layer) 2 is formed [FIG.
(B)].

As a base wafer, another thickness of, for example, 50
Prepare a silicon substrate 3 having a large mechanical strength of 0 μm,
The bond wafer 1 having the oxide film 2 formed thereon is brought into close contact therewith (see FIG. 2C).

By heating the closely contacted wafers 1 and 3 in that state at an appropriate temperature (for example, 1000 ° C.), the substrate 4 directly bonded through the oxide film 2 is formed [FIG. D)].

Of the substrate 4, the surface of the bond wafer 1 is ground and polished so that the thickness of the bond wafer 1 is 1-2.
By setting the thickness to about μm, the active layer 1A is formed [see FIG. 2 (E)].

As described above, the active layer 1A has a thickness of 1
A bonded SOI substrate 4A having a thickness of about 2 μm is formed [see FIG. 3 (A)]. Note that this FIG. 3 (A) is substantially the same as FIG. 2 (E).

The active layer 1A of the bonded substrate 4A is etched by applying an appropriate mask to leave a part of the active layer 1A [see FIG. 3 (B)]. The reference numeral 5 indicates an etched portion.

The entire surface of the etched active layer 1A of the bonded substrate 4A is thermally oxidized at, for example, 1000 ° C., and an oxide film (SiO 2) having a thickness of about 50 nm is formed on the entire surface.
₂ layers) 2'is formed (see FIG. 3C).

Oxide films 2, 2'of the bonded substrate 4A
The whole surface is covered with a Si ₃ N ₄ (silicon nitride) film 6 having an appropriate thickness (for example, 80 nm) by a known low pressure CVD method,
The sensing part responds to hydrogen ions [Fig. 3 (D)]
reference〕.

The sensing portion 6 formed on the bonded substrate 4A is etched by applying an appropriate mask,
A part of the active layer 1A is exposed [see FIG. 3 (E)]. Reference numeral 5'denotes an etched portion.

An appropriate mask is applied to the sensing portion 6 formed on the bonded substrate 4A, and Au (gold) is deposited on the etching surface 5'to form an ohmic contact 7 [see FIG. 3 (F)]. ].

Dicing is performed to obtain a chip state, and individual sensors are formed [see FIG. 3 (G)]. In this way, the optical scanning potentiometric sensor (pH sensor) S responsive to hydrogen ions as shown in FIG. 1 is formed.

As shown in FIG. 1, the optical scanning potentiometric sensor S manufactured as described above irradiates a light beam L such as visible light or infrared light from the substrate 3 side as probe light in the X and Y directions. By taking out the photocurrent induced in the active layer 1A as a signal from the ohmic contact 7, the two-dimensional or three-dimensional distribution of pH of the substance in contact with the sensing 6 can be measured.

In the optical scanning potentiometric sensor S, since the semiconductor layer for generating photocurrent is formed by the active layer 1A of the bonded SOI substrate 4A, even if it is thinned, the mechanical strength is large. Moreover, since the semiconductor layer can be made thinner than before, the position resolution is improved.

In the above embodiment, FIG.
Before performing the dicing shown in FIG.
A silicon substrate 3 side of A is etched by applying an appropriate mask to thin the bonded SOI substrate 4A [FIG.
After that, the individual sensors S may be formed by dicing to obtain a chip state (see FIG. 4B).

In the embodiment described above, the bond wafer 1
Although both the base wafer 3 and the base wafer 3 are made of silicon substrates, the base wafer 3 may be made of a glass substrate instead. In this case, it is preferable to bond the base wafer 3 made of a glass substrate and the bond wafer 1 made of a silicon substrate by anodic bonding.

In this way, when the base wafer 3 is made of a glass substrate, the probe light L on the base wafer 3
Is less absorbed, the generated photocurrent increases.

Next, a second embodiment will be described with reference to FIG. This embodiment is similar to the first embodiment shown in FIG.
Bonded SOI substrate 4A formed in the first half step shown in
This is a method in which the chip is first made into a chip state and the sensor is formed in that state.

That is, the bonded SOI substrate 4A formed by the procedure shown in FIGS. 2A to 2E is diced into an appropriate size to form a chip 8 [FIG.
(See (A)].

The entire chip 8 is thermally oxidized at an appropriate temperature (for example, 1000 ° C.) to form an oxide film 2'on the entire surface [see FIG. 5 (B)].

Low pressure CVD is performed on the upper surface of the oxide film 2'formed on the upper surface of the substrate 1 in the bonded SOI substrate 4A.
A Si ₃ N ₄ film 6 having an appropriate thickness (for example, 80 nm) is deposited by using the method (see FIG. 5C). This Si ₃ N ₄ film 6 becomes a sensing part.

The sensing part 6 formed on the bonded SOI substrate 4A is etched by applying an appropriate mask to expose a part of the active layer 1A [see FIG. 5 (D)]. Reference numeral 5'denotes an etched portion.

An appropriate mask is applied to the sensing portion 6 formed on the bonded SOI substrate 4A, and Au (gold) is deposited on the etching surface 5'to form an ohmic contact 7 [FIG. 5 (E)]. reference〕.

By doing so, an optical scanning potentiometric sensor S responsive to hydrogen ions can be obtained. In this case, needless to say, the silicon substrate 3 on the side irradiated with the probe light may be etched as in the first embodiment.

The operation and effect of this second embodiment is the same as that of the above-mentioned first embodiment, and therefore its explanation is omitted.

Further, a third embodiment will be described with reference to FIG. In the third embodiment, an SOS substrate in which a silicon layer is deposited on a sapphire substrate is used.

That is, an appropriate thickness (for example, 500 μm)
On the upper surface of the sapphire (α · Al ₂ O ₃ ) substrate 9, a silicon layer 10 having an appropriate thickness (for example, 1 μm) is epitaxially grown to form an SOS substrate 11 (see FIG. 6A).

The silicon layer 10 of the SOS substrate 11 is thermally oxidized at an appropriate temperature (for example, 1000 ° C.) to form an oxide film (SiO ₂ layer) 12 on the upper surface thereof (see FIG. 6B).

Silicon layer 1 on the SOS substrate 11
On the upper surface of the oxide film 2'formed on the upper surface of 0, an appropriate thickness (for example, 8
A Si ₃ N ₄ film 6 of 0 nm) is deposited [see FIG. 6 (C)].

The Si ₃ N ₄ film 6 serving as the sensing portion formed on the SOS substrate 11 is etched by applying an appropriate mask to expose a part of the silicon layer 10, and then the sensing portion 6 is appropriately exposed. A mask is applied, and Au is deposited on the etched portion to form an ohmic contact 7 (see FIG. 6D).

In the optical scanning type potentiometric sensor S constructed as in the third embodiment, the absorption of the probe light L in the sapphire substrate 9 is reduced,
The photocurrent generated increases.

The present invention is not limited to the above embodiment, but a SIMOX substrate may be used as an SOI substrate, for example. That is, as shown in FIG. 7, by irradiating the silicon substrate 12 having an appropriate thickness (for example, 500 μm) with the oxygen ion beam I3, the oxide layer (SiO ₂ layer) 14 is formed at a predetermined depth t in the silicon substrate 12. With S
The IMOX substrate 15 may be used, and the sensing unit 6 may be formed on the upper surface of the SIMOX substrate 15 by the method described above. In this case, since the oxide layer 14 having a desired thickness can be formed at the position of the predetermined depth t, the active layer 1
The thickness of A can be reliably controlled, and a sensor with a better position resolution can be obtained.

Also in the embodiment shown in FIGS. 5 to 7, the substrate 3, 9 or 14 side on which the probe light is irradiated may be etched by applying an appropriate mask.

Further, in each of the above-mentioned embodiments, the sensing portion 6 is made of a Si ₃ N ₄ film and is an optical scanning type potentiometric sensor which responds to hydrogen ions. Using valinomycin, quaternary ammonium salts, tin compounds, porphyrin compounds, etc., sodium ions other than hydrogen ions,
An optical scanning potentiometric sensor that responds to potassium ions, chloride ions, etc. can also be obtained.

[0047]

As described above, according to the present invention, since the semiconductor layer in which photocurrent is generated is formed of the SOI substrate, the mechanical strength is large even if the semiconductor layer is thin, and the semiconductor layer is also thin. Since it can be made thinner than before, the position resolution is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an optical scanning type potentiometric sensor according to a first embodiment.

FIG. 2 is a diagram showing a first half of a manufacturing process of the sensor.

FIG. 3 is a diagram showing the latter half of the manufacturing process of the sensor.

FIG. 4 is a diagram showing a modification of the first embodiment.

FIG. 5 is a diagram showing a main part of a manufacturing process of an optical scanning potentiometric sensor of a second embodiment.

FIG. 6 is a diagram showing a main part of a manufacturing process of an optical scanning potentiometric sensor of a third embodiment.

FIG. 7 is a diagram for explaining another manufacturing method of the SOI substrate.

[Explanation of symbols]

1, 3, 12 ... Silicon substrate, 1A ... Active layer, 4A ... Bonded SOI substrate, 6 ... Sensing part, 9 ... Sapphire substrate, 10 ... Silicon layer, 11 ... SOS substrate, 13 ...
Oxygen ion beam, 14 ... Oxide layer, 15 ... SIMOX
Substrate, L ... Probe light.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuki Tanabe 2 Higashimachi, Kichijoin Miya, Minami-ku, Kyoto-shi, Kyoto

Claims (5)

[Claims] 1. An optical scanning potentiometric sensor, wherein a sensing portion responsive to a substance is formed on one surface of a semiconductor substrate, and the other surface of the semiconductor substrate is irradiated with probe light to extract photocurrent as a signal. An optical scanning potentiometric sensor characterized in that an SOI substrate is used as the semiconductor substrate. 2. The optical scanning type SOI substrate according to claim 1, wherein the SOI substrate is a bonded SOI substrate in which two silicon substrates are directly bonded and one silicon substrate is polished to a size of several micrometers or less. Potentiometric sensor. 3. The optical scanning potentiometer according to claim 1, wherein the SOI substrate is a bonded SOI substrate in which a silicon substrate and a glass substrate are anodically bonded and the silicon substrate is polished to a size of several micrometers or less. Metric sensor. 4. The optical scanning potentiometric sensor according to claim 1, wherein the SOI substrate is an SOS substrate having a silicon layer deposited on a sapphire substrate. 5. A SIMOX in which an SOI substrate has an oxide layer formed by implanting oxygen ions into a silicon substrate.
The optical scanning potentiometric sensor according to claim 1, which is a substrate.