JPS6082846A - Electric field effect type semiconductor sensor - Google Patents

Abstract

PURPOSE:To enable stable high accuracy measurement and mass production in good yield, by using a specific semiconductor as the substrate of an electric field effect type semiconductor sensor provided with a layer selectively responding only to the substance to be measured on a gate part. CONSTITUTION:A III-V group semiconductor, for example, InP, of which the resistance is enhanced by doping Fe, is used as a substrate 10 and the surface thereof is doped with Zn to form a P<-> type InP layer 11. S is diffused in the layer 11 to form an N<+> layer 12 for drain and an N<+> layer 13 for source. By the diffustion of Zn into the P<-> layer 11, a P<+> layer 14 for facilitating electrical connection is formed while two metal layers for a drain contact 15 and a source P<-> layer common contact 16 are formed and a channel part 19 is formed by mesa-etching. The other than the parts of the P<-> layer 11, on which the N<+> layers 12, 13, the P<+> layer 14 and the channel part 19 are formed, are removed to provide an insulating layer 17 and a chemically responding insulating layer 18. By this method, stable high accuracy measurement and mass production in good yield are enabled.

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 technology Kate insulated field effect transistor (MI 5FET)
) Semiconductor sensors that measure the ion activity and the concentration of other chemical substances in an electrolytic solution have been known for a long time. There are descriptions regarding these in Ion 5 sensitive. However, all the sensors proposed to date use silicon as a base material.

The source (2) and drain (3) diffusion regions are formed spaced apart from each other with the channel region (4) in between, and the surface of this substrate is covered with an insulating layer (5) of a material such as 5i02. , a metal layer (6) for lead contact of the source and drain. In Figure 1, each number is 1000.
A thin film (7) impermeable to the atmosphere to be measured (about λ) and a chemically selective film (8) are formed, and in FIG. 2, a conductive material layer (9) of arbitrary thickness and a thin chemically selective film 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.

A method has been proposed. There are two main ways to do this:

(■) A silicon wafer is processed three-dimensionally by etching, and not only the surface of the sensor element but also most of the side and back surfaces are covered with an insulating film that is impermeable to the atmosphere to be measured. (For example, JP-A-55-24603) (11) A sensor is constructed by using an insulating sapphire substrate without using silicon as the substrate, and forming a minimum necessary silicon layer thereon, and
Most of it is covered with an insulating film that is impermeable to the atmosphere. (For example, JP-A-57-191539) Sensors made by these methods have stability and reproducibility that can withstand practical use, but both require extremely advanced technology in the manufacturing process, and the process is complicated. Since 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 The present invention proposes that although it is not possible to obtain a material with very high resistance in a homopolarly coupled crystal semiconductor that exhibits the properties as an element such as silicon (Si), a-V
In group compound semiconductors, GaAs contains Cr.

This paper focuses on the fact that by doping InP with an impurity such as Fe, a semi-insulating material with a high resistance of more than 107 Ω can be obtained.

In GaAs, in the MIS structure, the Fermi level at the interface is pinned near the center of the forbidden band, and the interface state density is 10
Since it is large, on the order of 110 l3" eV-1, it is impossible to invert the GaAs surface or accumulate it within the withstand voltage range of the insulating film.

On the other hand, in InP, the pinning position of the interface Fermi level in the MIS structure is close to the conduction band, and the interface state density is 1012cI.
It is about n-2eV-1, and an accumulation layer can be formed for an n-type substrate, and an inversion layer can be formed for a p-type substrate.

An 15FET using an InP substrate is shown in FIG. The cross-sectional structure along the A-N line, the B-B' line, and the C-σ line in the top view of FIG. 3(a) is shown in FIG. 3(b).
, shown in FIG. 3(c) and FIG. 3(d). However, this l
Let's talk about 5FET. Figures 4, 5, and 6 show (1) doping with Fe, with a specific resistance of 1070
The (100) plane of InP, which has a high resistance as described above, is
used as (Fig. 4(a), Fig. 6(a), Fig. 7(a)) (11) Zn on the surface of semi-insulating InP substrate OD
is doped to form a p-type InP layer 0η. (
(Fig. 4(b), Fig. 5(b), Fig. 6(b))) (iii) Diffusing S into the p layer 00 with the n10 layer @ for the drain and the n+N (13) as an impurity. Then, a p layer is formed by diffusion of Zn (Fig. 6 (
d)) (v) Form two metal layers: one for the F rain contact (I) and one for the source single layer common contact.

(Fig. 5(d), Fig. 6(e)) This formation method involves performing selective vapor deposition of AuGeNi and Au, and then depositing Ar
An effective method is to perform sintering at 350° C. for several minutes in an atmosphere.

(vl) Forming channel portion 0 by mesa etching (Fig. 4 (d)) The etching solution used is HCl: H20z: H20=4:1:
A mixture of No. 6 and the like is good.

(viDp 1 layer 0]) on top of it with n 10 layers (12, 13)
The p layer is removed by etching except for the part where the bonded channel portion is formed. (Fig. 16 Illustration to f)) Now, this chip except for the contact part,
The lower part is a semi-insulating substrate oQ1, and the upper part is covered with an insulating film α, which has sufficiently high insulation properties.

Possible types of this insulating film are listed together with their formation methods shown in brackets: native oxide,
e C thermal oxidation, plasma oxidation, anodic oxidation in molten residue)
P3N5 (CVD), Sing (CVD, plasma CVD) SigN+ (plasma CVD:) A
12O5 (CVD, reduced pressure CVD.

AI! plasma anodization, solution anodic oxidation, electron beam evaporation], etc.

(1x) Form a chemically sensitive insulating layer (18). (4th
(Figure (g)) The material can be various types depending on the substance to be measured. For example, inorganic materials such as Ta205°Al20a for H+ ions, glass whose composition has been changed to have selectivity for specific ions, and even membranes with fixed crown ethers can be used. In addition, we can measure not only ions, but also enzymes, pile bodies, binding cells (if we choose the quality, etc.), we can also use biofunctional materials that selectively respond to them (e.g., glucose oxidase for glucose, 08 for urea). If AA'20g is used for the insulating layer 07), the insulating layer (17) can also serve as an H+ ion sensitive film without any special formation.

(5) Effects of the Invention The greatest effect of the present invention is that it is possible to manufacture a sensor with a highly insulating sensor element itself through a significantly simpler process compared to conventional field effect semiconductor sensors that use single crystal silicon as a substrate. It is in.

That is, there is no need to process a silicon wafer eight-dimensionally by etching, and there is no need to epitaxially grow silicon on the sapphire substrate. In particular, when using AJgO++ as the gate insulating film, this Al
By making the 2Os layer serve the three roles of (1) gate insulating film, (li) H+ ion sensitive film, and (lii) solution impermeable film, a stable pH sensor can be realized with an extremely simple structure. .

Simplifying the structure and simplifying the process to achieve this will lead to improved yields during manufacturing and ultimately to lower costs. Furthermore, compared to the method of three-dimensionally processing a silicon wafer by etching, the effective usable area of the wafer is greatly different as the etching area is unnecessary.
Despite the difference in nP, the number of chips that can be manufactured from a wafer of the same area increases significantly. - Another major effect of the present invention is that the high electron mobility improves the response speed of the sensor. This is a great advantage when real-time performance is required, such as when this sensor is applied to various control and monitoring systems.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views of the basic configuration of the gate portion of a conventional field-effect semiconductor sensor using silicon as a substrate, and Figure 1 is a diagram showing a multilayer structure with only a thin insulating layer.
FIG. 2 is a diagram showing a multilayer structure including a conductor layer. FIGS. 3(a), (b), (C) and (d) are diagrams showing the structure of a field effect semiconductor sensor using InP as a substrate, which is an embodiment of the present invention. Figure 4 (
a), (b), (C), (d), (e
), (f) and value), Figure 5 (a), (b)
, (C), (d), (e) and (f), and FIG. 6(a). (b), (C), (d), (e), (
f) and (g) are A A' in FIG. 3(a), respectively.
Parts corresponding to r B B' and c-c' in Fig. 3 (b
), FIG. 3(C), and FIG. 3(d) are diagrams showing the manufacturing procedure for making the structures shown in FIG. 1 Silicon single crystal substrate 2 Source diffusion region 8 Drain diffusion region 4 Channel portion 5 Insulating layer (Part 1) 6 Metal layer for lead contact 7 Insulating layer (Part 2) 8 Insulating layer for chemical sensitization 9 Conductive material such as metal J・10 Semi-insulating InP substrate 11 P-type 1nP layer] 2 N10 layer for drain 13 N10 layer for source 14 P10 layer for p single layer connection 15 Metal layer for drain contact 1G For source/p single layer common contact Metal layer 17 Insulating layer 18 Insulating layer for chemical sensitivity 19 Channel part 71 hole to hole 2 side electric side 4 side (L”I) 7 18 1i knee, ”2 island

Claims (1)

[Scope of Claims] (]) A sensor substrate in a field-effect semiconductor sensor characterized in that a layer selectively sensitive only to a specific substance to be measured is provided on the gate portion of a gate-insulated field-effect transistor. A field-effect semiconductor sensor characterized in that a group IV compound semiconductor is used as a semiconductor. (2) The field-effect semiconductor sensor according to claim 1, wherein the substrate constituting the field-effect semiconductor sensor is a high-resistance semi-insulating material with a specific resistance of 10 7 Ω·m or more. (3) Sensor base...- Among V group compound semiconductors, In
Claims 1 and 2 are characterized in that P.
The field-effect semiconductor sensor described in .