JPS60111950A - Preparation of semiconductor ion sensor - Google Patents

Abstract

PURPOSE:To obtain a sensor having stable characteristics, by thermally oxidizing the island shaped epitaxially grown Si-layers formed on a saphire substrate except the semiconductor ion sensor formed part of said Si-layer to convert the same to SiO2 layers and thickly providing SiO2 layers to the peripheries of the residual Si-layers. CONSTITUTION:B is diffused in a plurality of island shaped epitaxially grown Si- layers on a saphire substrate to form a P type SiO2 layers 2 low in impurity concn. In the next step, SiO2 layers 6' and Si3N4 layers 7' having predetermined shapes are formed as masks in this order. Next, the Si-layers 2 except ion sensor formed parts are etched to reduce the thickness thereof to about 1/2. Subsequently, steam oxidation is performed to remain island shaped Si-layers 2 under the layers 6' while converting other parts to SiO2 layers 6. Then, layers 6', 7' are removed and a P-ion is injected by using an Al-mask 10 to form a N type drain region 3 and a source region 4. In the next place, an earth region 5 is formed by using a separate mask and, thereafter, the SiO2 layers 6 are thickly left in the peripheries of the sensor parts by using a photoresist film 11 while the other parts are removed by etching. Then, a gate oxide layer is newly formed and an Si3N4 layer 7 is formed so as to include the surface of the substrate 1 to obtain a perfectly insulated sensor.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a semiconductor ion sensor.

In particular, the present invention relates to a method of manufacturing a field-effect semiconductor ion sensor that uses the outdoor effect of a semiconductor for chemical-electrical conversion.

Conventionally, there is an ion-sensitive field effect transistor (hereinafter referred to as ISFgT) using an rc field effect transistor, which is a type of semiconductor ion sensor that measures the concentration of ions in a solution. This ZSPG'R has a structure in which the gate electrode of the field-effect transistor is replaced with an iodine-sensitive membrane that can selectively detect ions and generate voltage sound.It is a silicon IC with low output impedance.
Since it can be manufactured using up to the same manufacturing technology, it has the characteristic of being able to be miniaturized.

When measuring the ion concentration in a solution using such a l5FET, it is important to insulate the silicon part where the l5FET is formed from the solution. Is there a hole in the silicone knee 71 that has been coated with epoxy resin or silicone rubber? A method has been adopted in which the needle-shaped silicon is provided in an open wafer and the silicon needle is completely insulated by covering the needle-shaped silicon with a silicon dioxide layer or a silicon nitride layer. However, the above method has the disadvantage that assembly becomes troublesome and the manufacturing process becomes complicated.

The present inventors have developed a semiconductor ion sensor (hereinafter referred to as "18FET"), which is formed using island-shaped silicon provided on a sapphire substrate, as an 18FET that has a simple manufacturing process and is easy to assemble, and is suitable for miniaturization and mass production. , SO8/l8FET.

) was devised and published in JP-A-57-191539 and JP-A-57-1915.
-151940 I suggested it. This SO8/l8F
In ET, the silicon part is surrounded by a sapphire substrate, which is a good insulator, and an insulating film on the surface in the wafer state, so the insulation of the silicon part is maintained even after the entire wafer is scribed, making manufacturing and assembly easy. The characteristic of being? have.

However, after etching, the taxially grown silicon on a conventional sapphire substrate is left in the form of scalar islands.
In this manufacturing method in which the island-like silicon layer is fully oxidized and the entire gate oxide layer is used, the oxidation layer at the end of the island-like silicon layer in contact with the sapphire substrate is thinner than other parts, forming a so-called figure-7 groove. A so-called depression was created at the interface between silicon and sapphire. Therefore, the end portion of the island-shaped silicon layer has a disadvantage that the silicon insulation is not sufficient compared to other portions. This drawback cannot be solved even if a silicon nitride layer is further provided as a protective layer by ycVD method after gate oxidation.

That is, the V-shaped groove at the end of the island-like silicon layer is formed by CVD.
However, even after the entire silicon nitride layer was formed, the problem remained that leakage between the silicon and the solution was likely to occur at the end of the island-shaped silicon layer.

In general, as a method to prevent insulation leakage between the gate electrode and the silicon due to the V-shaped groove generated in the MOSFET formed in the silicon layer on the sapphire substrate in the IC manufacturing method, silicon other than the island-shaped silicon layer where the transistor is formed is used. Manufacturing methods are known in which the layer is converted into a silicon dioxide layer by thermal oxidation. In this manufacturing method, the island-shaped silicon layer has a structure in which the entire periphery is surrounded by a thick silicon dioxide layer, so that a figure-7 groove is not generated and insulation leakage can be prevented.

However, in the case of l81T used in a solution, since there is no metal gate electrode, it is necessary to provide a silicon nitride layer as a protective layer on the entire surface of the silicon dioxide layer, but the silicon layer other than the above-mentioned island-like silicon layer is thermally oxidized. In the method of forming the entire island-shaped silicon layer using the method described above and then forming the silicon nitride portion entirely in the solution, the silicon layer and the silicon dioxide layer are covered with the silicon nitride layer at the wafer stage.

When the wafer is cut into chips, the silicon dioxide layer that is not covered by the silicon nitride layer is exposed at the cut surface. As a result, the silicon dioxide layer not covered by the silicon nitride layer melts into the solution, or ions in the solution enter, causing the characteristics of the 18FET to fluctuate. In particular, when I8FgTi is miniaturized, the width of the silicon dioxide layer that separates the silicon part from the entire solution is small and mobile ions easily reach the sensor part, resulting in a drawback that deterioration occurs quickly.

An object of the present invention is to provide an island-like structure provided on a sapphire substrate that can sufficiently insulate the silicon portion from the solution by removing the defective gold, and that can easily manufacture and assemble an I5FET 2 with stable characteristics. An object of the present invention is to provide a method for manufacturing a semiconductor ion sensor formed using a silicon layer.

A method for manufacturing a semiconductor ion sensor according to the present invention is a method for manufacturing a field effect semiconductor ion sensor formed using an island-like silicon layer provided on a sapphire substrate. Among them, the silicon layer in the inactive region where the ion sensor is not formed is thermally oxidized to become a silicon dioxide layer, and the entire silicon dioxide layer of the hind limb is left only in the peripheral area of the island-like silicon layer and removed by etching, and the gate oxidation is performed. forming a silicon nitride layer on the island-like silicon layer and then forming a silicon nitride layer on the top surface of the silicon island layer, the top surface of the silicon dioxide layer, and the top surface of the sapphire substrate region around the silicon dioxide layer.

Embodiments of the present invention will be described below with reference to all the drawings.

First, a semiconductor ion sensor manufactured according to the present invention will be explained. FIG. 1 is a plan view of a semiconductor ion sensor for hydrogen ions manufactured by an embodiment of the semiconductor ion sensor manufacturing method of the present invention, and FIGS. a'.

It is a bb' cross-sectional view. In these figures, l is a sapphire substrate, 2 is a p-type image impurity concentration silicon region which becomes a gate region, 3 is an n-type drain region of high impurity concentration silicon, and 4 is a source region of n-type high impurity concentration silicon.
numeral 6 is a silicon dioxide layer, 7 is a silicon nitride layer, 8 is a drain electrode made of aluminum, and 9 is a source electrode made of aluminum.

4(a) to 4(f) are cross-sectional views showing the main parts of the process sequence for explaining one embodiment of the present invention for making the entire semiconductor ion sensor of FIG. This corresponds to the -b' cross-sectional view. Next, the manufacturing process will be explained in detail.

As shown in FIG. 4(a), a p-type impurity such as boron is completely diffused into a silicon layer epitaxially grown on a sapphire substrate l with a thickness of approximately 0.6 μm, and approximately 5×101
After the p-type image impurity fIk of sctr1' is completely formed in the silicon region 2, a silicon dioxide layer 6' having a predetermined shape and a silicon nitride layer 7' are completely formed as a mask for silicon etching and silicon oxidation.

Next, as shown in FIG. 4(b), the silicon layer in the inactive region where the sensor portion is not formed is etched by about 0.3 μm using an anisotropic etching solution.

Subsequently, as shown in FIG. 4C, the entire silicon layer in the cine active region is converted into a silicon dioxide layer by steam oxidation to form an island-like silicon layer.

Thereafter, as shown in FIG. 4(d), a silicon dioxide layer 6 used for steam oxidation is applied to the anisotropic elastin of silicon.
' and silicon nitride layer 7' are removed by etching.
Predetermined shape? Aluminum mass 7io'4 mask, phosphorus? Highly doped by ion implantation to form a drain region 3 of n-type silicon with high impurity concentration and a source region 4t of silicon with n-type high impurity concentration.

Furthermore, as shown in FIG. 4(e), an aluminum layer with a different shape (not shown) is doped with a high concentration of boron (all boron ions are implanted) using the entire mask, and then removed. A photoresist film 11 is provided in the area covering the island-shaped silicon layer, and this is used as a mask to remove the silicon dioxide layer in the inactive area by etching, leaving only the periphery of the island-shaped silicon layer.

Next, as shown in Figure 4(f) of VC1, the remaining silicon dioxide layer on the surface of the island-shaped silicon layer is completely removed by etching, and a new gate oxidation layer is formed by thermal oxidation.
A silicon nitride layer is then formed to a thickness of approximately 1,000 nm by CVD over the entire surface.

Next, in order to provide a source electrode and a drain electrode, after completely removing the silicon nitride layer and gate oxide layer in the electrode area, the aluminum layer was vaporized and etched into a predetermined shape. A drain electrode 8 and a source electrode 9 are formed by heating in a gas for about 30 minutes.

With this, the process at the wafer stage is completed, and the wafer stage 2 is completed.
By this process, the semiconductor ion sensor shown in FIG. 1 is obtained.

The semiconductor ion sensor manufactured according to this example has a third
As shown in the figure, the side surfaces of the island-like silicon layer are covered with a thick silicon dioxide layer 6, and the sapphire substrate l on the side surfaces is further covered with a thick silicon dioxide layer 6.
The interface region is covered only with the silicon nitride layer 7. Therefore, conventionally, when the island-like silicon layer provided on the sapphire substrate was completely oxidized and the silicon dioxide layer was completely formed, the silicon dioxide layer was not thin at the silicon-sapphire interface at the end of the island-like silicon layer, which was a problem)7 The formation of grooves can be prevented, and the silicon dioxide layer is sufficiently covered by the silicon nitride layer and sapphire without exposing the silicon dioxide layer on the scribing surface of the wafer, preventing contact with the solution. Since the silicon part is sufficiently insulated from the solution and the characteristics are stable, SO8/l5
FET' can be obtained.

In this example, a hydrogen ion sensor using a silicon nitride counterfeit was described, but an ion sensor equipped with an ion-sensitive membrane for detecting specific ions on the gate bottom IC of an 18FET by the manufacturing method of the present invention, an enzyme, etc. It is also possible to create a biosensor by providing a membrane in which antibodies and microorganisms are completely immobilized, and it is clear that multiple sensors can be easily provided on the same chip.

As described above in detail, the method for manufacturing a semiconductor ion sensor of the present invention has the following features: The island-like silicon/layer has a structure in which the entire side surface is a thick silicon dioxide layer, and the sapphire substrate interface on the side surface is covered only with a silicon nitride layer. This eliminates the occurrence of figure-97 grooves due to thin layers, and the silicon dioxide layer is not exposed during chipping, so the silicon dioxide layer is not immersed in the solution and the silicon portion is removed. It is possible to obtain a semiconductor ion sensor that is sufficiently insulated from the solution and has stable characteristics, which is highly effective.

[Brief explanation of drawings]

FIG. 1 is a plan view of a semiconductor ion sensor manufactured according to an embodiment of the present invention, and FIGS. 2 and 3 are sectional views taken in the order of steps. l... Sapphire substrate, 2... P-type low impurity concentrated silicon region, 3... Drain region, 4... Source region, 5... ...Earth area, 6. 6'...Silicon dioxide layer, 7.
7'...Silicon nitride layer, 8...Drain electrode, 9...Source electrode, 10...
・Jie 1 wa 1 Bore 2 plaster ・I' figure

Claims (1)

[Claims] In a method for manufacturing a field effect semiconductor ion sensor formed using an island-like silicon layer provided on a sapphire substrate, a portion of the island-like silicon layer epitaxially grown on the sapphire substrate on which the ion sensor is not formed is provided. a step of thermally oxidizing the silicon layer in the active region to convert it into a silicon dioxide layer, and then removing the silicon dioxide layer by etching, leaving only the peripheral region of the island-like silicon layer; and forming a silicon nitride layer on the upper surface of the silicon dioxide layer and the upper surface of the sapphire substrate region around the silicon dioxide layer.