JP3350867B2 - Ion-sensitive field-effect transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion-sensitive field effect transistor for detecting the concentration of ions in a liquid.

[0002]

2. Description of the Related Art FIG. 5A shows a conventional ion-sensitive field-effect transistor. FIG. B is an enlarged view of a cross section taken along line II-II of FIG. A source region 13 and a drain region 1 are formed on a main surface 12 of a semiconductor substrate 11 such as silicon.
4 are formed insulated from each other. That is, the substrate 11
For example, the source region 13 and the drain region 14 are made of P-type single-crystal silicon, and are formed by diffusing N-type impurities. These source region 13 and drain region 1
4 are close to each other, but these source and drain regions 13 and 1
4, the lead portions 15, 1 of the same conductivity type, respectively.
6 are formed.

A gate insulating film 17 is formed on the main surface 12 between the source region 13 and the drain region 14, and the gate insulating film 17 is a relatively thin film. And semiconductor 11
The insulating layer 18 is formed continuously over the entire outer peripheral surface of the substrate. For example, after the gate insulating film 17 and the insulating layer 18 are formed of silicon dioxide, and the insulating layer 18 is formed,
The portion between the source region 13 and the drain region 14 can be thinned to form the gate insulating film 17. An ion penetration preventing layer 19 is formed on the main surface 12 side of the gate insulating film 17 and the insulating layer 18. The ion intrusion prevention layer 19 is, for example, silicon nitride Si ₃ N ₄ . An ion sensitive layer 21 is formed on the ion intrusion prevention layer 19. When the ion-sensitive layer 21 comes into contact with the ions in the solution, an electric charge is generated, whereby the channel between the source region 13 and the drain region 14 is controlled according to the bias voltage between the solution and the source region 13, A current corresponding to the charge generated in the sensitive layer 21 and the bias voltage flows between the source region 13 and the drain region. In this manner, a current corresponding to the ion concentration in the solution flows between the source region 13 and the drain region 14, and the ion concentration in the solution can be detected.

[0004] Such an ion-sensitive field-effect transistor can detect the ion concentration in the solution, but the external light affects the respective junctions of the source region 13 and the drain region 14, so that the detection is impossible. Sensitivity is affected and correct measurement cannot be performed. From such a point, conventionally, a black polymer layer 22 is formed on the ion-sensitive layer 21 so that external light can be bonded to the semiconductor, that is, the PN junction between the source region 13 and the drain region 14 and the substrate, or the like. The light is prevented from being incident on the channel region between the source region and the drain region (Japanese Patent Laid-Open No.
3-146993). Alternatively, as shown in FIG. 6 by attaching the same reference numerals to portions corresponding to FIG. 5, a metal layer 23 for blocking light is formed on the ion intrusion prevention layer 19, and an ion intrusion prevention layer 24 is formed on the metal layer 23. Further, an ion sensitive layer 21 is formed thereon, and a metal layer 23 prevents external light from reaching the PN junction between the channel region, the source region and the drain region, and the substrate ( JP-A-2-167462 official report).

[0005]

In the case where the above-mentioned black polymer layer is formed on the ion-sensitive film, the black polymer layer 22 hinders the movement of ions existing on the ion-sensitive film, and thus the sensitivity is reduced. There is a problem that the response characteristics are poor, and the number of steps for forming the black polymer layer increases.
That complicates the manufacturing process. In addition, it is pointed out that the black polymer layer 22 may peel off because the black polymer layer has poor adhesion to the silicon semiconductor.

On the other hand, when light is shielded by the metal layer 23, the metal layer 23 is vulnerable to acids and alkalis, and if a pinhole is present in the ion-sensitive film, the metal layer 23 is attacked. And the main surface between the ion-sensitive film 21 and the source region 13 and the drain region 14, that is, the distance to the channel 25 is increased, and the sensitivity and the response time are reduced accordingly. I do. In addition, there are many layers to be formed, and the manufacturing process is accordingly complicated.

An object of the present invention is to provide an ion-sensitive field-effect transistor capable of blocking external light without delaying response speed, reducing sensitivity, and complicating a manufacturing process. Is to do.

[0008]

According to the present invention, Sn-Sb is formed so as to cover the entire area of the gate insulating film between the source region and the drain region on the main surface side of each junction of the source region and the drain region. An -O film is formed. According to the invention of claim 2, Sn-Sb is further provided in the invention of claim 1.
An ion-sensitive film, particularly a film sensitive to ions other than hydrogen ions, is formed on the -O film.

[0009]

According to the first aspect of the present invention, the Sn-Sb-O film has a dark color and is sensitive to hydrogen ions, so that an output corresponding to the hydrogen ion concentration is detected without providing an ion-sensitive film. be able to. According to the second aspect of the present invention, the Sn—Sb—O film functions only as a light-shielding film, but has good adhesion to the semiconductor, and has an interval between the ion-sensitive film and the channel, that is, intervenes therebetween. There are few layers, the spacing is small, the response speed is fast,
In addition, the sensitivity can be improved.

[0010]

FIG. 1 shows an embodiment of the invention of claim 1, and FIG.
The parts corresponding to are denoted by the same reference numerals. In this example, the ion intrusion preventing layer 19 is formed on the gate insulating film 17 between the source region 13 and the drain region 14 and also on the source region and the drain region. 19 on top of Sn-Sb-O
A film 31 is formed. This film 31 includes not only the portion on the gate insulating film 17 but also the portion on the main surface 12 side of the PN junction between the source region 13, the drain region 14 and the substrate 11. The film 31 is formed so as to extend over the entire region of the drain region 14 to the outside thereof, and covers portions including the PN junction of the terminal lead-out portions 15 and 16 with the substrate 11 for the source region and the drain region so as to shield them. Is formed.

The formation of the Sn—Sb—O film 31 is based on Sn
Tin chloride and antimony chloride mixed in a molar ratio of Sb to 0.15 to 0.4 are dissolved in hydrochloric acid diluted ten times with pure water, and dissolved in oxygen gas or oxygen-nitrogen mixed gas as carrier gas. Is formed on the substrate 11 heated to 500 ° C. or higher by a spray method. The thickness of this film 31 is preferably 0.3 μm or more. The transmittance at a wavelength of 500 nm of the Sn—Sb—O film thus formed is as shown in FIG. 2A. In FIG. 2A, the horizontal axis is the molar ratio of Sb to Sn, and the vertical axis is the light transmittance. From the characteristics of FIG. 2A, it is understood that when the molar ratio is 0.15 or more, the light transmittance becomes extremely small and blocks light. In the case of this spray method, tin chloride and antimony chloride are difficult to dissolve when the molar ratio is 0.4 or more, so that it is difficult to form a high concentration region with a molar ratio of 0.4 or more. . Therefore, when the spray method is used, the molar ratio is 0.15 to 0.4.

FIG. 2B shows a Sn—Sb— film having a thickness of 0.5 μm.
4 shows the light wavelength transmission characteristics of the O film. In this characteristic, the parameter is the Sn-Sb molar ratio, which is 15%
Alternatively, in the case of 39%, the wavelength is 200 to 260.
The light transmission is quite small over the range of 0 nm, ie it can block light, but this molar ratio is 3.8
%, Light is blocked at a relatively long wavelength, but in a region where the wavelength is short, the light blocking characteristic is degraded. When the molar ratio is 0, that is, when the component of antimony is 0, light is blocked. The blocking characteristic is completely lost. As can be seen from FIG. 2B, the film 31 is formed of Sn-S
It is understood that the molar ratio of b is preferably from 0.15 to 0.4. However, according to another manufacturing method, it is known that even if the molar ratio is 0.5, there is a light blocking property.

In manufacturing such a film 31, an Sn— film is formed on the entire surface of the semiconductor substrate 11 on the main surface 12 side.
An Sb-O film is formed, and the extraction electrode portions of the source region 13 and the drain region 14 are removed by a so-called photo-etching method. In that case, the etching solution is HBr
By heating a mixed acid of (hydrobromic acid, 47%): H ₂ O = 1: 1 to about 90 ° C., adding metal chromium powder, and immersing the entire substrate 11 in a solution of the oxidation reaction. Sn-
Unnecessary portions of the Sb-O film are removed.

The Sn—Sb—O film 31 does not dissolve even in the presence of a strong acid or strong alkali, and is sensitive to hydrogen ions.
The thickness of the film 31 is 0.5 μm, and the molar ratio is 0.3
In the case of No. 9, the response characteristic to the hydrogen ion concentration, so-called pH, that is, the characteristic of obtaining an output between the source region and the drain region, as shown in FIG. 3A, the output decreases linearly in inverse proportion to the hydrogen ion concentration. . That is, the response is linear in the range of pH 2 to 12, and the sensitivity is 40 to 55 mV / pH, such that the output voltage is high when the hydrogen ion concentration is low, and the output voltage is low when the concentration is high. That is, according to the embodiment shown in FIG. 1, Sn-Sb-
The O film 31 functions as a hydrogen ion sensitive layer and also functions as a light shielding layer for the semiconductor, that is, the channel 25 or the PN junction.

FIG. 3B shows the light shielding characteristics. In the figure, a line 33 is a characteristic of the present invention, and a line 34 is a characteristic without a conventional light shielding layer. The horizontal axis is the illuminance of the external light, and the vertical axis is the output. As a result, when the illuminance increases, the output increases. However, according to the present invention, the output is lower than that of the related art, that is, it is understood that the output is less affected by external light. In this case, the thickness of the film 31 of the present invention is 0.5 μm, and the molar ratio is 0.39. Thus S
When the n-Sb-O film 31 is provided, light-shielding characteristics can be obtained, hydrogen ion-sensitive characteristics can be obtained by itself, and adhesion to a semiconductor such as the silicon substrate 11 can be greatly improved because the film is a metal oxide. Good.

When the applied voltage between the solution for detecting ions and the source region 13 is relatively low, or when the thickness of the gate insulating film 17 is relatively large, as shown in FIG. 19 can be omitted. That is, if there is no possibility that the charges based on the ions adhering to the Sn—Sb—O film 31 pass through the gate insulating film and reach the channel layer without the ion intrusion prevention layer 19, the ion intrusion can be performed in this manner. The prevention layer may be omitted.

FIG. 4B shows an embodiment of the second aspect of the present invention.
1 and 4A are denoted by the same reference numerals.
In this example, on the gate insulating film 17 and the source region 1
3. S on the drain region 14 via the insulating layer 18
The n-Sb-O film 31 is formed, that is, the structure is as shown in FIG. 4A. The ion intrusion prevention layer 19 is further formed thereon, and the ion sensitive film 21 is formed thereon. . In this case, the Sn—Sb—O film 31 merely functions as a light shielding layer, and the conditions for the light shielding layer are the same as those in FIG. In this case, the ion-sensitive membrane 21 may be one that is sensitive to hydrogen ions,
As described above, the film 31 itself is sensitive to hydrogen ions, and thus the film 31 is usually a film that is sensitive to ions other than hydrogen ions without any special purpose. For example, immobilized urease can be used as the one that responds to urea ions.

Further, in the present invention, the ion intrusion preventing layer 19 inside the metal layer shown in FIG. 6 can be omitted, so that the ion sensitive layer 21 can be closer to the channel 25 than that shown in FIG. Can be. Further, even if the ion sensitive layer 21 has a pinhole, the Sn—Sb—O film 31 is not liable to be attacked by an acid or an alkali, and has a function of preventing intrusion of ions. May be. Therefore, if the ion intrusion prevention layer 19 is also omitted, the ion sensitive layer 21 can be brought closer to the channel 25. Further, in the conventional light shielding using a metal layer, the shorter the wavelength, the lower the light shielding property.
The b-O film 31 does not have such a thing, and a light shielding property superior to that of the metal layer can be obtained.

In the above description, the Sn—Sb—O film 31 has a molar ratio of 0.15 to 0.4. However, according to another known manufacturing method other than the spray method, the molar ratio can be further increased. It is recognized that sufficient light-shielding properties can be obtained even at 0.6 at present. Semiconductor substrate 1
1 may be of N type, and the source region 13 and the drain region 14 may be of P type.
As 1, an intrinsic semiconductor may be used. In addition, Sn-Sb
The -O film may shield only the gate region, that is, the channel region from the outside.

[0020]

As described above, according to the present invention, by using the Sn—Sb—O film as the ion-sensitive film, it can be used not only as a hydrogen ion-sensitive film but also as a light-shielding film, so that it is not affected by light. In addition, the hydrogen ion concentration can be correctly detected, and the distance between the ion-sensitive membrane and the channel can be made shorter than before, so that the sensitivity is good and the response characteristics are good. In addition, this film has good adhesion to the semiconductor, and there is no fear of peeling. In addition, since the structure is simple, the manufacturing process is also simple.

According to the invention of claim 2, the Sn-Sb
Since the -O film is used as a light-shielding film, the adhesiveness to the semiconductor is good, and since it is strong against acid and alkali, the ion-sensitive film can be closer to the channel than before, and there is no fear of peeling. , Which have good stability and sensitivity and responsiveness as compared with the prior art.

[Brief description of the drawings]

FIG. 1A is a plan view showing an embodiment of the invention of claim 1; FIG.
FIG. 2 is an enlarged cross-sectional view taken along line II of FIG.

FIG. 2A is a diagram illustrating light transmittance characteristics of a Sn—Sb—O film with respect to a Sb—Sn molar ratio, and FIG. 2B is a diagram illustrating wavelength characteristics of light transmission with respect to various molar ratios of the film.

FIG. 3A is a diagram showing an output characteristic with respect to a hydrogen ion concentration in an embodiment of the first aspect of the present invention, and FIG. 3B is a diagram showing an output change characteristic with respect to an external light input.

FIG. 4A is a sectional view showing another embodiment of the invention of claim 1, and FIG. 4B is a sectional view showing an embodiment of the invention of claim 2;

FIG. 5A is a plan view showing a conventional ion-sensitive field-effect transistor, and FIG. 5B is an enlarged cross-sectional view taken along the line II-II.

FIG. 6 is a cross-sectional view showing a conventional ion-sensitive field-effect transistor showing a metal film as a light-shielding layer.

Claims (2)

(57) [Claims] 1. A source region and a drain region are respectively formed on a main surface of a semiconductor substrate, a gate insulating film is formed on the main surface so as to extend between the source region and the drain region, and the source region is formed on the main surface. And an Sn-Sb-O film formed over the entire junction surface portion of the drain region and the gate insulating film. 2. The ion-sensitive field-effect transistor according to claim 1, wherein an ion-sensitive film is formed on the Sn—Sb—O film.