JPS59225344A - Insulating gate electric field effect transistor for ion sensor - Google Patents

Abstract

PURPOSE:To enhance yield, reliability and mass-productivity, by encircling the side surfaces and bottom surface of a second semiconductor region, which surrounds the source region and the drain region of a sensor FET, by a first semiconductor region. CONSTITUTION:A second silicon semiconductor substrate 21 having a second conductive type semiconductor region 23 is prepared on a first conductive type semiconductor region 22 and an N<+> type diffusion region 24 is subsequently formed. In the next step, a first P<+> type channel stopper region 25 is formed in a ring form within a second semiconductor region and, succeedingly, an N<+> type source region is formed in a ring form within a second semiconductor region 23a while an N<+> type drain region 27 is simultaneously formed. Thereafter, a second P<+> type channel stopper region 28 is provided and, succeedingly, an SiO2 membrane 29, an Si3N4 membrane and an SiO2 membrane 33 are successively formed in the region surrounded by the broken line in the drawing while a protective insulating membrane 33 is formed to a part of the surface of the substrate 21. A source electrode 35 is formed so as to reach the upper surface of the second semiconductor region 23a to connect a bulk and a source. At last, a dot line position is cut to complete an indivisual sensor FET.

Description

Detailed Description of the Invention Technical Field The present invention relates to an insulated gate field effect transistor (hereinafter referred to as sensor FET) for an ion sensor that measures ion concentration or detects the presence or absence of ions based on ions attached to a gate insulating film. ).

Prior Art FIG. 1 is a front view showing a conventional sensor FET with an insulating film removed, and FIG. 2 is an enlarged sectional view corresponding to the AA cross section in FIG. 1. In this drawing, (1) is the silicon substrate, (2) is the P region (bulk), (3) is the source electrode, (6) is the drain electrode, (the force is the 5j02 film (thermal oxide film) , -・(8) is Si 3N4 film, (9) is 5i0
2 (vapor phase grown film. aω is an ion sensitive part, provided at the bottom of the silicon substrate (1), and has a gate insulating film I as shown in FIG. 2. Note that the gate insulating film is ,
The Si02 film (7) provided on the upper part of the channel region connecting the drain region (3) and the drain region (4) and the Si02 film (7)
It consists of a part of the 3N4 film (8). Ion sensing part (10)
is immersed in the liquid (I21) whose ion concentration is to be measured, so as shown in FIG.
), a 5iaN4 film (8), and a 5i02 film (9) (insulated from liquid α by one wrinkle).

By the way, if there are pinholes or cracks in the insulating film a3, and one or more of the internal forces of the P region (2), the source region (3), and the drain region (4) come into direct contact with the liquid (121), , the potential state of each part of the sensor FET changes, causing trouble in its operation as a sensor FET.For example, if the liquid (12) comes into contact with the P region (2) on the side or bottom surface of the silicon substrate (1), the back gate If it comes into contact with the source region (3), it will become a gate-source short circuit, and the sensor FET will go into an abnormal operation mode.Therefore, it is important to reliably insulate the sensor FET from the liquid (121). It is.

However, the conventional sensor FET shown in FIGS.
In this case, it was difficult to ensure insulation. That is, the outer peripheral surface of the P region (2) on which the insulating film Q31 must be formed not only has a large area, but also exists on the side and bottom surfaces of the substrate (1), and has a curved surface. Therefore, it was difficult to form the insulating film (13) on the entire outer peripheral surface with a low probability of pinholes or cracks occurring.

In addition, when mass producing the sensor FETs shown in FIGS. 1 and 2, it is necessary to mass produce the sensor FETs shown in FIG.
la) A large number of sensor FETs must be formed and divided along the dotted line -. In addition, before this division, the ion sensitive parts QO) of a large number of sensor FETs are etched in the form of slits penetrating from one main surface of the wafer to the other main surface, so that they are made independent of each other, and , a gate insulating film (111) and a protective insulating film (13+) must be formed as shown in FIG. This makes the process complicated and makes it difficult to manufacture FETs with a high yield.

OBJECTS OF THE INVENTION An object of the present invention is to provide a sensor FET that can reliably and easily insulate a liquid containing ions from the inside of the FET.

Structure of the Invention The present invention (house, semiconductor substrate eυ
A first ring formed to be exposed in an annular manner on one main surface of the
a first semiconductor region (22a) of a conductivity type, a second conductivity type opposite to the first conductivity type, and a portion exposed to one main surface of the semiconductor substrate H; a second semiconductor region (23a) surrounded by the first semiconductor region (22a) and having the first conductivity type and one of the semiconductor substrates eυ; A source region (23a) that has a portion exposed on the main surface and is surrounded by the second semiconductor region (23a) except for this exposed portion.
b), the semiconductor substrate (b) has the first conductivity type and the semiconductor substrate (b) has the first conductivity type;
1) has a portion exposed on one main surface and is surrounded by the second semiconductor region (23a) except for this exposed portion; and the source region (23a).
The semiconductor substrate (211
at least the second semiconductor region (23a) and the source region 0Q.
and a film formed to cover the exposed surface of the drain region (2) that is not covered by the gate insulating film when boiled, and provided so as to be continuous with the gate insulating film portion, and - and thicker than the gate insulating film 2. The present invention relates to an insulated gate field effect transistor for detecting ions in a liquid, which is characterized by having a thick protective insulating film.

Effects of the invention According to the invention, the source region (26) of the sensor FET
and a second semiconductor region (23a) surrounding the drain region surface.
Since the side and bottom surfaces of the second semiconductor region (22a) are surrounded by the first semiconductor region (22a), the second semiconductor region (23a) is reliably separated from the ion-containing liquid Oη. Therefore, compared to the conventional structure in which the inside of the FET is separated from the liquid by an insulating film, it is possible to improve yield and reliability. Moreover, since it can be manufactured using normal planar technology, mass production becomes easy.

Embodiment Next, a sensor FET according to an embodiment of the present invention will be described with reference to FIGS. 4 to 6.

Figure 4 shows the manufacturing method of the sensor FET.
FIGS. 6 and 7 show the completed sensor FET and its usage state. When manufacturing a sensor FET, first, as shown in FIG. 4 (4), on an N-type (first conductivity type) semiconductor region (c) made of high-resistance silicon,
A Ueno-state silicon semiconductor substrate (21) having a P-type (second conductivity type) semiconductor region (23) made of a boron-doped high-resistance noebitaxial growth layer is prepared.

Next, by selective diffusion of phosphorus, an N-type diffusion region O reaches from the surface of the P-type semiconductor region (c) to an N-type semiconductor region (27J).
A is formed as shown in FIG. 4 CB). This results in N
A first semiconductor region (22a) of N type (first conductivity type) consisting of a type semiconductor region 4 and an N type diffusion region (24) is obtained, and a second semiconductor region annularly surrounded by this semiconductor region. A region (23a) is obtained.

Next, as shown in FIG. 4(C), a first P-type channel stopper region (two ring-shaped regions) is formed in the second semiconductor region (23a) by selective diffusion of boron. An N-type drain region (27) is formed in the second semiconductor region (23a) in an annular shape by selective diffusion of the sensor FET0.
As is clear from FIG. 5 showing the main surface, in the planar shape,
The source region (26) is the first channel stopper region 0!
51, and the drain region (2) is formed inside the source region (26).
The surface region from t271 to drain region t271 becomes a path for drain current, but in this embodiment, in order to prevent the entire region from becoming a channel, the source region (26) and drain region (271) are separated as shown in FIG. A second P type channel stopper region (two barrels is provided partially between the What is not shown is.

These are cross-sectional views of the portion corresponding to the line BB in FIG.

Next, as shown in FIG. 4, a 5i02 film (
29), an S t 3N4 film (30) by vapor phase growth, and a 5iQ2 film 01) by vapor phase growth are sequentially formed. however,
The gate insulating film portion consists of an Si02 film (29) and a Si3N4 film which are thinner than the others, and in this embodiment is formed in the region surrounded by the dotted line in FIG. Since the gate insulating film portion may be formed only on the upper part of the effective channel region, the upper part of the drain region opening may not be formed as a gate insulating film, but may be formed with the same thick protective insulating film C331 as other places, if necessary. Note that the protective insulating film C33) is formed on one main surface (2I) of the substrate (2I) excluding the gate insulating film (321, divided region indicated by a chain line, source electrode 0!51 and drain electrode OG).
(top surface). As shown in FIG. 5, the source electrode C351 is formed by At evaporation so as to reach not only the upper surface of the source region (26) but also the upper surface of the second semiconductor region (23a), thereby providing a connection between the bulk and the source.

Finally, the individual sensor FETs as shown in FIGS. 5 and 6 are completed by cutting along the chain line (b) at 00 in FIG.

Figure 5 shows the completed sensor FET and its usage state with the insulating film removed, and Figure 6 is B in Figure 5.
- It shows the part corresponding to the B line. As is clear from FIG. 5, in this embodiment, the entire sensor FET is not immersed in the ion-containing liquid t3'O, but only the lower ion-sensitive part (31O) including the gate insulating film (31O) is immersed. Measure the ion concentration by immersion.For example, hydrogen ions (H
”) When measuring pH by concentration, place the ion-sensitive part of the sensor FET in a liquid On containing ions, apply voltage VDs between the source electrode G51 and the drain electrode (G), A positive bias voltage VR is applied from a power supply (4I) to the bias electrode end in the liquid On.
Measure 1 from the drain current in the case of . After that, the bias power supply (4υ) is adjusted so that the drain current ID+ is maintained at the same value as at the standard ion concentration even at the ion concentration to be measured, and the bias voltage vR2 at this time is measured. Since the amount of change in bias voltage ΔVn=VRIVxt based on the change in concentration can be known, the ion concentration is calculated based on this.

It should be noted that the combination of the bias voltage based on the electrode 431 and the voltage based on the ions in the liquid 07) acts on the gate insulator as the operating gate voltage (G). And S
Since the i3N4 membrane (30) has the property of easily adhering to hydrogen ions (H), the ion concentration in the liquid can be detected with relatively high sensitivity. In the above measurement method, the drain current I11. Although the bias voltage VR was changed to keep V11 constant, it is also possible to keep the bias voltage V11 constant and measure the ion concentration by changing the drain current corresponding to the change in ions.

As is clear from the above, this embodiment has the following effects.

(a) The second semiconductor region (23a
) is surrounded by an N-type first semiconductor region (22a) except for the portion exposed to the surface of the substrate (211).

Further, a negative voltage is applied to the P-type second semiconductor region (23a) by the extension of the source electrode 09, while a bias voltage is applied to the N-type first semiconductor region (22a) at the electrode (3→ It is in contact with the applied liquid I3'O.Therefore,
The PN junction (4) is in a reverse bias state, and the second semiconductor region (23a) is reliably isolated from the liquid η.

(b) If pinholes or cracks occur in the thick insulating film G3 on the second semiconductor region (23a), channel stopper region (25), source region (a), and drain region (2), it will be the same as before. However, the area of the insulating film (1331) in this part is smaller than that of the conventional insulating film (1331) in FIG.
Since the area is significantly smaller than the area of 1, the probability of its occurrence is low.

Therefore, the yield can be improved.

(C) Since the insulating film (33) is only provided on the upper surface of the conductive plate (21), it is easy to form the gate insulating film 6 and the protective insulating film C33).

(d) Channel stopper region (2~ is provided, so
Operation using only the ion sensing section □□□) becomes possible.

(e) Since the channel stopper region (25) is provided, formation of a channel between the source region (261 and the first semiconductor region (22a)) can be prevented.

(f) Sensor F using planar technology as shown in Figure 4.
Since ET is formed, mass productivity can be improved.

Modifications Although the embodiments of the present invention have been described above, the present invention is not limited thereto, and, for example, the following modifications are possible.

(b) It may be an N-channel sensor FET.

(b) Source electrode (39) and drain electrode (5th column)
In the figure, it is provided on the top of the substrate CD, but it may extend to the ion sensing section (38). In this case, electrode C35
) Provide an insulating coating over l).

(c) When using a structure with high sensitivity to ions or when high measurement accuracy is not required, a bias electrode (
39) and the bias power supply (41) may be omitted.

) the first semiconductor region (22a) and the second semiconductor region (22a);
An electrode for applying a voltage higher than 23a) may be provided in the first semiconductor region (22a).

(e) A protective insulating layer may be provided to surround the side and bottom surfaces of the first semiconductor region (22a). However, even if a pinhole or the like is formed in this insulating layer and the liquid C37) IJ: comes into contact with the N-type first semiconductor region (22a), no problem will occur.

[Brief explanation of the drawing]

Figure 1 is a front view of a conventional sensor FET, Figure 2 is an enlarged cross-sectional view of a portion corresponding to line A-A in Figure 1, and Figure 3 is a wafer used to make the FET in Figure 1. Floor plan, 4th
The figures are cross-sectional views showing the sensor FET according to the embodiment of the present invention in the order of steps, FIG. 5 is a front view showing the sensor FET obtained in the steps shown in FIG. 4 and its usage state, and FIG. FIG. 2 is an enlarged sectional view of a portion corresponding to line BB of FIG. (21)...Semiconductor substrate, (22a)...First semiconductor region, (23a)...Second semiconductor region, (Two...Channel stopper regions, (C)...Source region, (2η...drain region, GZ...gate insulating film, G(to)...protective insulating film.

Claims (1)

[Claims] (1) A first semiconductor region of the first conductivity type formed so as to be exposed in an annular manner on one main surface of the semiconductor substrate eυ (
22a), having a second conductivity type opposite to the first conductivity type and having a portion exposed on one main surface of the semiconductor substrate (2I), and excluding this exposed portion, the semiconductor substrate (2I) has a second conductivity type opposite to the first conductivity type; Semiconductor area (2
2a); a second semiconductor region (23a) having the first conductivity type and having a portion exposed on one main surface of the semiconductor substrate (2υ and excluding this exposed portion) a source region (a) surrounded by the second semiconductor region (23a); and a source region (a) having the first conductivity type and having a portion exposed on one main surface of the semiconductor substrate (21); The drain region (2'0), which is surrounded by the second semiconductor region (23a) except for this exposed part, and the ion-sensitive channel region connecting the source region (26I) and the drain region (2'0) are at least a gate insulating film C32+ formed on the main surface of the semiconductor substrate (2υ) so as to cover the gates of at least the second semiconductor region (23a), the source region (26), and the drain region (2); a protective insulating film C331 formed to cover the exposed surface not covered with the insulating film 621, continuous with the gate insulating film C33, and having a thickness greater than that of the gate insulating film C33; An insulated gate field effect transistor for detecting ions in a liquid, characterized by having the following characteristics: