JPS6134617B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a field effect transistor (hereinafter referred to as ISFE) for an ion sensor. ISFET does not have a gate electrode (metal) on the gate insulating film, and when it is immersed in an electrolyte, such as blood, the semiconductor surface (source,
It is configured to detect the ionic activity in blood by utilizing the change in conductivity between the drains and drains. Generally, when ISFET is used as a biosensor, it is inserted into a syringe (needle) and immersed in blood within a blood vessel, so it is structurally delicate, especially the sensor part that is immersed in blood. It is desirable that the gate portion, etc.) be completely insulated from the blood, and that it be provided with an electrode structure (including lead wires) that allows the sensor output to be easily taken out to the outside. Figure 1 a and b show this type of ISFET.
1 is a plan view and a sectional view taken along the line A-A' of FIG. 3 is a P+ type channel stop region formed around the source region 2; 4 is a gate portion; 5 is an N+ type drain diffusion region; 6 is formed to cover the entire surface of the substrate 1. The insulating films S and D, such as a silicon oxide film (si02) or a silicon nitride film (siN), are connected to other external lead wires (not shown) at source and drain electrodes, respectively. In the ISFET having such a structure, the surface geometry of the source region 2 and drain region 5 is formed to be elongated so that the tips serve as the sensor (gate) section, and the rear ends serve as the source electrode section and the drain electrode section. The lead wire can be easily taken out without immersing the end in blood. However, since the surface of the intermediate portion between the tip and rear end of the source and drain regions is protected by an insulating film 6 and also serves as an internal wiring, it is required that the resistance value thereof be made low. . For this reason, it is necessary to diffuse impurities for a long time to achieve a high impurity concentration during diffusion, and as a result, the diffusion depth of the source and drain regions becomes deep, and the side (lateral direction) diffusion significantly shapes the geometry. It is difficult to downsize due to lack of space in dimensions, etc. Further, due to the high concentration and long-time diffusion, defects may occur in the crystals of the substrate (silicon) 1, resulting in lower product yields or longer process times. FIG. 2 is a schematic cross-sectional view showing another conventional structure of this type, in which the sensor part 4 and the lead wire extraction part are separated, and the internal wiring between them is connected to aluminum (A
), etc., and the surface of the other sensor parts and the metal wire 7 except for the gate part of the sensor part is coated with epoxy or insulating resin 8 such as RTV.
It was designed to be covered with In such a structure, the adhesion of the insulating resin 8 is insufficient, and since the insulating resin 8 has poor chemical resistance, it is not possible to maintain sufficient insulation from the electrolyte, and the resin is removed leaving only the gate portion. It has drawbacks such as difficulty in coating and increased size. In view of these points, the present invention uses a semiconductor insulating film such as a silicon oxide or nitride film to insulate the sensor part, etc. and the electrolyte, and the intermediate wiring part is made of polysilicon (polycrystalline silicon) doped with impurities. The present invention is to provide a new ISFET that eliminates the above-mentioned drawbacks at once.The present invention will be explained in detail below with reference to the drawings.
FIGS. 3a and 3b are a plan view showing the structure of an embodiment of the present invention, and a cross-sectional view taken along line A-A' in FIG. In the present invention, a source region 2 and a drain region 5 having the minimum required area are formed at the tip of a silicon substrate 1 by diffusion, and then a silicon oxide film (Si02) is formed on the entire surface of the substrate 1. Next, after removing the silicon film on the required surfaces of the source region 2 and drain region 5, a string-like or band-like polysilicon layer 9 is formed in the direction of the rear end of the base 1, covering the surface and the other silicon film Si02. do. This polysilicon layer 9 is formed using the CVD method (Chemical Vapor
The resistance value can be adjusted as desired by doping with impurities at a high concentration during formation. Next, a silicon oxide film Si02 is formed on the polysilicon layer 9,
Further, a silicon nitride film SiN is formed over the entire silicon film. Then, a required portion of the silicon nitride film and silicon oxide film is removed at the rear end of the base surface to expose the polysilicon layer, and a source electrode S and a drain electrode D are formed on the exposed surface. The present invention having such a configuration
With ISFET, the sensor part can be concentrated at the tip of the substrate, so the diffusion process can be omitted, there is no side diffusion during diffusion, the shape of the substrate can be made smaller, and there are no silicon crystal defects, which improves product yield. . In addition, the electrode wiring can be easily formed into any shape, and the insulation treatment of the wiring portion is easy, and the insulation treatment for delicate shapes and electrode extraction required for ISFETs, such as stability, are fully satisfied. FIGS. 4a and 4b are a plan view and a sectional view taken along line A-A' in FIG. 2 and 2' are formed, and a polysilicon layer 9 is formed from the required surfaces of the source regions 2 and 2' toward the rear end of the base 1, thereby constructing a composite sensor. According to this structure, after forming the diffusion region in advance in the structure of the composite sensor, it is possible to change the wiring shape of the polysilicon layer depending on the combination of the sensors, so that the sensor can be easily integrated. As is clear from the above description, according to the present invention, it is possible to provide a miniaturized ISFET with a simple structure, and therefore the practical effects are great.

[Brief explanation of the drawing]

1 and 2 are conventional structural diagrams, and FIGS. 3 and 4 are structural diagrams of an embodiment of the present invention. In the figure, 1 is a semiconductor substrate, 2 and 2' are source diffusion regions, 3 is a channel stop region, 4 is a gate portion, 5 is a drain diffusion region, 6 is an insulating film, 7 is a thin metal wire, and 8
9 is an insulating resin, 9 is a polysilicon layer, S is a source electrode, and D is a drain electrode.

Claims (1)

[Claims] 1. A source region and a drain region are formed on one surface of a semiconductor substrate, and a gate insulating film is formed on the semiconductor surface between the source region and the drain region, and a gate electrode (metal) is not formed on the insulating film. In the field effect transistor for an ion sensor, the ion sensor is characterized in that wiring is formed between at least one surface of the source region or the drain region and the source electrode or the drain electrode using polycrystalline silicon containing impurities. field effect transistor.