JPS60228954A - Electric field effect type semiconductor sensor - Google Patents

Abstract

PURPOSE:To attain to reduce cost by mass production, by utilizing technique such that each element formed to the surface of a silicon substrate is separated electrically. CONSTITUTION:A source diffusion region 2 and a drain diffusion region 3 are formed in the region surrounded by an oxide layer 11 having a thickness sufficient to be separated electrically. The transmission of information is performed from said region by the conductive substance layer 9 for connecting a lead contacting metal layer 6 and a chemically responsive insulating layer 8 but, because not only the region other than said region but also the upper part thereof are perfectly protected by a protective layer 10, a sensor is made extremely stable as the operative characteristic of a transistor itself. As the conductive layer 9, Al or polysiloxane, to which conductivity is imparted by the injection of an ion, is used. As the protective layer 10, a monolayer structure comprising Si3N4 or Al2O3 formable at low temp. by plasma CVD or a polyimide resin or a multilayer struction by the combination of monolayer structures is considered. As the insulating layer 8, Si3N4 or Al2O3 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field The present invention relates to a field-effect semiconductor sensor used for measuring the concentration of chemical substances.

(2) Background Art Semiconductor sensors have been known that utilize the structure of a gate-insulated field effect transistor (MISFET) to measure the ion activity and the concentration of other chemical substances in an electrolyte. These are the Ion 5intensiveFie
ld Effect Transistor (ISF
ET), Chemical FET (CHEMFET)
This is called the Japanese Patent Publication No. 54-24817, and there are descriptions regarding them.

6 and 7 show the basic structure of the gate portion of the I5FET. For example, source (2) and drain (3) diffusion regions are formed on the surface of a p- silicon substrate (1) with a channel region (4) in between, and the substrate surface is
iOs+ is coated with an insulating layer (5) of material, and a metal layer (5) for source and drain lead contacts.
6) is a provision. In Fig. 6, each 1000λ
A thin membrane (7) impermeable to the atmosphere to be measured and a chemically selective membrane (8) are formed, and in FIG. It is formed.

During actual use, this sensor is directly immersed in an atmosphere to be measured, for example, a solution such as blood. For this reason, the part of the chemically selective membrane comes into direct contact with the solution, and the lead wires and contact metals must be insulated and protected so that they never come into contact with the solution. Conventionally, the most common method has been to use epoxy resin or silicone resin to provide impermeability to solutions, but these resins cannot withstand long-term use and swell.

Therefore, this method does not provide sufficient stability and reproducibility.

For this reason, a method has been proposed in which the sensor chip itself is made resistant to atmosphere. There are two main ways to do this:

(■) A silicon wafer is processed three-dimensionally by etching, and not only the front surface of the sensor chip but also most of the side surface and back surface are covered with an insulating film that is impermeable to the atmosphere to be measured. (
For example, JP-A-55-24603) (n) A sensor is constructed by using an insulating sapphire substrate without using silicon as the substrate, and forming a minimum necessary silicon layer on it, and most of it is placed in an atmosphere. Cover with an impermeable insulating film. , 4(
For example, sensors using these methods as disclosed in Japanese Patent Application Laid-Open No. 57-191589 have stability and reproducibility that can withstand practical use, but both require very advanced technology in their manufacturing process, and the process is complicated. Because it uses technology not found in general silicon IC manufacturing processes, it is currently almost impossible to mass-produce it with a high yield.

(3) Purpose of the invention The present invention enables stable and accurate measurement over a long period of time.
Another purpose of the present invention is to propose an ultra-small field-effect semiconductor sensor that can be mass-produced with high yield.

(4) Structure of the Invention In order to obtain stability and reproducibility that can withstand practical use, the field effect semiconductor sensor according to the present invention does not use any special technology that is not present in the currently commonly used silicon IC manufacturing process. The main feature is that it can be manufactured using only silicon wafer surface processing technology.

As mentioned above, since this sensor is directly immersed in the atmosphere to be measured, for example, a liquid such as blood, during actual use, the sensor chip itself needs to be resistant to the atmosphere. It is possible to protect the general silicon IC manufacturing process, although it involves some difficulties. However, when a silicon wafer is cut into chips and completed as a sensor chip, the cut surface, that is, the side surface of the chip, exposes the silicon single crystal substrate, which is a semiconductor, and is therefore extremely susceptible to the influence of the atmosphere being measured. It has an easy structure. For this reason, conventional technology protects not only the front surface but also the back and side surfaces of the sensor chip by performing eight-dimensional processing, or the substrate itself is made of insulating sapphire instead of silicon. The structure is unaffected by the measurement atmosphere.

The present invention utilizes technology for electrically isolating each element formed on the surface of a silicon substrate (hereinafter referred to as element isolation technology), which is used in silicon IC and LSI manufacturing processes, to create a basic sensor. By electrically separating the gate insulated field effect transistor section from the back and side surfaces of the sensor chip, even if the back and side surfaces of the sensor chip are affected by the atmosphere being measured, the effect will not affect the transistor section. Therefore, it is possible to operate stably as a transistor and, in turn, to operate stably as a sensor. Further, at this time, it is preferable that the gate structure not only consist of an insulating layer as shown in FIG. 6, but also include a conductive layer as shown in FIG. This is because, as proposed in Japanese Patent Application No. 59-59946, the positions of the chemically sensitive portion and the transistor portion can be physically separated. If the chemically sensitive part is located above the transistor part, the chemically sensitive part is directly immersed in the atmosphere to be measured, so even though element isolation technology eliminates the influence from the side of the sensor chip, the chemically sensitive part is separated. Although there is a high risk that the transistor part itself will be affected by the atmosphere to be measured, if the chemically sensitive part and the transistor part are separated, it becomes easier to protect the transistor part, and long-term stability of the characteristics can be expected.

In addition, there are the following methods for element isolation technology:
These may be used alone or in combination,
It is also conceivable that it will be even more effective.

(1) Selective oxidation method (LOGO5: Local 0xi
(dation of Silicon)... A thick oxide film is formed between each element region, and each element is isolated by the oxide film, which is an insulator.

(II) Pn junction method: Insulate by pn junction.

(m) a Plate etching method: grooves are formed between each element region by etching to structurally separate the element regions.

OV) Selective epitaxial growth method: First, an insulating layer such as an oxide film is selectively formed only in regions not used as element regions, and then single crystal silicon is epitaxially grown in a state separated into the element regions.

(V) Insulator isolation method: A groove similar to the substrate etching method is formed, and the groove is filled with an insulator such as Si3N4, or an insulator thin film is first formed and then polysilicon or the like is filled.

(5) Example 1 of the invention Hereinafter, the present invention will be explained with reference to drawings of embodiments.

One of the most effective combinations of element isolation methods is to use selective oxidation to prevent the effects from the side surfaces of the sensor chip, and to prevent effects from the back side using a pn junction, but here we use selective oxidation for simplicity. This paper describes a field-effect semiconductor sensor in which elements are separated using only the method. FIG. 1 is a plan view showing the structure of a field-effect semiconductor sensor according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the dashed line a-a' in FIG. 1, and FIG. b', Figure 4 is c
-c', FIG. 5 is a cross-sectional view at d-d'.

The size of the sensor chip in this example is 1. Qmx5. Qm
It is x. As shown in Figure 1, the transistor section is formed intensively at one end of the chip, and the chemically sensitive layer (
8) is formed at the other end, and is spaced apart by about 8 centimeters in plan view. The most important feature of this embodiment is that the transistor section is electrically isolated from the periphery of the sensor chip by an oxide layer αD for element isolation.

That is, an oxide layer σ with sufficient thickness to provide electrical isolation.
A source diffusion region (2) and a drain diffusion region (3) are formed in the region surrounded by D. From this area, there is a metal layer for lead contact (6) and an insulating layer for chemical sensitivity (8).
Information is transmitted through the conductive material layer (9) for connection with the transistor, but other than this, the upper part is also completely protected by the protective layer, so the operating characteristics of the transistor itself are very stable. becomes.

As the conductive layer (9), Al or polysilicon made conductive by ion implantation is used.

In addition, as the protective layer αO, 5isN4y klsosm SiOxNy+, which can be formed at low temperatures such as by plasma CVD, is used.
AI! 0xNy, PSG (Phospho-5il
icate PgOs Sing )+ Pb0-AA
'gOa・Sing (Lead-Alumino-5
ilinate ) # PbO・BgOs・Sing
(Lead-Boro-5ilinate) +
PbO-Al! gos・BgOa・5iOs+ (Le
ad-Alumino-Boro-3ilicate)
Alternatively, a single layer structure of polyimide resin or a multilayer structure made of a combination of these can be considered, and the film thickness is 1 μm.
The above is desirable.

The chemically sensitive layer (8) is also shown as a single layer in Figure 7 for simplicity, but in reality it may have a multilayer structure with the chemically sensitive film as the outermost layer due to problems such as adhesion between films. many.

Possible types of this sensitive film are listed together with the measurement target shown in brackets: 5iaN*+A1g
Oay Tag's (H+ ion), various NAS (
Na sO-AlgOa-5ing synthesis) glass [K+
ion Na+ ion] palinomycin fixed membrane [K+ ion], various crown ether fixed membranes [K+ ion, 8g+ ion, TI+ ion, etc.] urease fixed membrane [urea], lipase fixed membrane [neutral lipid], benicillinase fixed membrane [penicillin] ] Anti-albumin antibody fixed membrane [albumin], a7tylcholinesterase fixed membrane (acetylcholine), etc.

(6) Effects of the Invention The present invention utilizes a general silicon IC and LSI manufacturing process that uses conventional technology to manufacture field-effect semiconductor sensors with stability, reproducibility, and reliability that can withstand practical use. Special technologies not found in Japan, such as three-dimensional processing technology for silicon wafers and SO3 (Si-1icon on 5apph)
The biggest feature is that it can be manufactured using only surface processing technology without requiring any other technology. For this reason, although it is a special device that is used in a harsh environment as a semiconductor device such as blood, it can be manufactured in large quantities with high yield because it can be manufactured using only the established and highly reliable PROS, just like general silicon ICs. This makes it possible to produce at a lower cost, resulting in lower costs.

In addition, element isolation technology was introduced to stabilize sensor characteristics, but element isolation technology itself was originally developed to increase the degree of integration of devices formed on silicon wafers, so it is difficult to implement it earlier. This is a great advantage in realizing multi-functionality rather than just a single-function sensor as in the example. In other words, when multiple chemically sensitive layers are formed on the same sensor chip, even if gate insulated field effect transistors corresponding to each layer are formed in a concentrated manner, it is difficult to separate these transistors from the periphery. Similarly, if the components are insulated and separated, the respective measured values will not interfere with each other, at least in the transistor section.

Furthermore, it is fully applicable to integrating on the same chip electric circuits for compensating sensor characteristics and analyzing measurement results of multiple items in the case of a multi-functional sensor.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the structure of a field effect semiconductor sensor in which a gate insulated field effect transistor section is electrically isolated from a peripheral structure by a selective oxidation method according to an embodiment of the present invention. FIG. 2 is a sectional view taken along dashed line a-a' in FIG. 1, FIG. 8 is a sectional view taken along b-b', FIG. 4 is a sectional view taken along c-c', and FIG. It is a sectional view taken along d-d'. 6 and 7 are cross-sectional views of the basic configuration of the gate portion of a conventional field-effect semiconductor sensor using silicon as a substrate.
The figure shows a case of a multilayer structure including a conductor layer. 16 Single crystal silicon substrate 2, source diffusion region 3, drain diffusion region raw channel section 5, insulating layer (part 1) 6, metal layer for lead contact 7, insulating layer (part 2). 8. Insulating layer for chemical sensitivity 9, layer of conductive material such as metal 10, protective layer 11, oxide layer for element isolation (Fig. 6, W7)

Claims (5)

[Claims] (1) In a field-effect semiconductor sensor in which a layer selectively sensitive only to a specific substance to be measured is provided on the gate part of a gate-insulated field-effect transistor, the transistor part, which is the basic structure, is exposed to an atmosphere containing the substance to be measured. A field-effect semiconductor sensor characterized in that the peripheral structure that is directly exposed and the layer that is sensitive to the substance to be measured are electrically isolated using element isolation technology. (2) The field-effect semiconductor sensor according to claim 1, which is formed on a silicon single crystal substrate. (3) The device isolation technique is one of a selective oxidation method, a pn junction method, a substrate etching method, a selective epitaxial growth method, and an insulator isolation method other than oxide, or a combination thereof. A field-effect semiconductor sensor according to claims 1 and 2. (4) A plurality of the gate insulated field effect transistors are provided, and the composition of each sensitive layer is changed to provide selection characteristics for a plurality of substances. Field-effect semiconductor sensor according to Items 2 and 3. (5) In the area where the above-mentioned gate insulated field effect transistor is formed or around it, electricity is provided for sensitivity compensation, temperature compensation, information processing, etc. in a state that is electrically isolated from the surrounding structure like this transistor. Claims 1 and 2, characterized in that a circuit is formed.
The field-effect semiconductor sensor according to items 3 and 4.