JP3867510B2 - Biosensor and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biosensor using a semiconductor field effect transistor and a method for using the biosensor. Biosensors are particularly expected to be applied to the medical field as ion sensors, enzyme sensors, DNA sensors, antigen / antibody sensors, protein sensors, and the like.
[0002]
[Prior art]
A conventional field-effect semiconductor biosensor has a structure in which a gate electrode is removed from a normal MOS FET and an ion-sensitive film is deposited on the gate insulating film. In particular, the ion sensor detects the ion sensor FET (Ion Sensitive FET). )is called. FIG. 8 is an explanatory diagram of a conventional example of ISFET. In the figure, 81 is a silicon (Si) substrate, 81S is a source, 81D is a drain, 82 is an isolation insulating film, 83 is a gate insulating film, and 84 is an ion sensitive film. Here, by immobilizing an oxidoreductase, various proteins, DNA, an antigen antibody, etc. on an ion sensitive membrane, it becomes applicable as various biosensors.
[0003]
However, the ISFET using bulk silicon needs to be sealed with a resin or the like in order to prevent the cross section of the sensor chip from being exposed in the electrolyte. There is a problem that it is difficult to seal a small ISFET and reliability is lowered. In addition, since the leakage current due to light and heat increases, accurate measurement is difficult.
[0004]
In response to these problems with ISFETs using bulk silicon, silicon-on-insulator (SOI) structure ISFETs have been proposed, but the price of the sensor itself is high because the SOI substrate is expensive in the first place. Was not suitable. On the other hand, Japanese Patent Publication No. 5-49187 proposes a polysilicon ISFET that can be fabricated on a glass substrate as a semiconductor layer using a polysilicon TFT structure.
[0005]
[Problems to be solved by the invention]
The ISFET having a conventional structure has a problem in that it is necessary to adjust the voltage applied to the reference electrode each time due to the difference in threshold voltage Vth for each element, temperature characteristics, and the like, which is troublesome. In particular, an ISFET having a polysilicon TFT structure is (1) a semiconductor layer is not exposed to the electrolyte, and therefore, leakage current is suppressed and reliability is high, compared with ISFETs using other structures. (2) Carriers in polysilicon are high. It has excellent characteristics such as a short lifetime that affects the transistor characteristics due to light irradiation, and (3) a glass substrate makes it possible to manufacture a sensor at a low cost. However, variations in threshold voltage are common. It tends to be big. That is, there is a problem that sensor sensitivity variation becomes large.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to a biosensor according to an aspect of the present invention, a substrate, a first semiconductor film formed on the substrate and having a source region and a drain region, and the substrate A first insulating film covering the first semiconductor film and the second semiconductor film, and the first insulating film corresponding to the first semiconductor film. Covering the first gate electrode provided on the film, the second gate electrode provided on the first insulating film corresponding to the second semiconductor film, and the first gate electrode A second insulating film; a source electrode connected to the source region through a first contact hole formed in the second insulating film; and a second contact formed in the second insulating film. A drain electrode connected to the drain region through a hole, and the second gate electrode And a ion-sensitive film formed on said second semiconductor film is used as a back gate.
[0007]
In the biosensor according to one embodiment of the present invention, the semiconductor film is a polysilicon film into which impurities are ion-implanted.
[0008]
The biosensor according to one embodiment of the present invention is characterized in that the semiconductor film is an amorphous silicon film.
[0009]
The biosensor according to one embodiment of the present invention is characterized in that the substrate is made of any one of a glass substrate, a plastic substrate, and an organic polymer material.
[0011]
According to the biosensor manufacturing method of one embodiment of the present invention, a step of forming a back gate in a predetermined region on the substrate, and a step of forming a first insulating film on the substrate and the back gate A step of forming a semiconductor film on the first insulating film; a step of forming a second insulating film on the semiconductor film; and ion implantation into a predetermined region of the semiconductor film to thereby form a source / drain Forming a region, removing the second insulating film on the channel region of the semiconductor film, and forming a third insulating film on the channel region of the semiconductor film and on the second insulating film And a step of forming an ion sensitive film on the third insulating film on the channel region of the semiconductor film.
According to the biosensor manufacturing method of one embodiment of the present invention, the step of forming the back gate includes a step of forming a metal film on the substrate and a step of patterning the metal film. The patterning is performed by wet etching.
In addition, according to the method for manufacturing a biosensor according to one embodiment of the present invention, a step of forming a semiconductor film on a substrate, a patterning of the semiconductor film, and a first semiconductor film region and a second semiconductor film region Forming a first insulating film on the first semiconductor film region and the second semiconductor film region, and on the channel region of the first semiconductor film region and the second semiconductor film Forming a gate electrode so as to cover the region, forming a second insulating film on the first insulating film and on the gate electrode, and the second semiconductor film on the second semiconductor film region. Removing the insulating film to form a first opening exposing a portion of the gate electrode on the second semiconductor film region; and covering the second insulating film and the first opening. Forming a third insulating film in the same manner, and the third in the first opening Removing the insulating film to form a second opening exposing a part of the gate electrode on the second semiconductor film region, and the second semiconductor exposed by the second opening Forming an ion sensitive film on the gate electrode on the film region.
According to the biosensor manufacturing method of one embodiment of the present invention, the substrate is made of any one of a glass substrate, a plastic substrate, and an organic polymer material.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
(1) First Embodiment Next, an ISFET type biosensor of the present invention will be described with reference to the drawings. FIG. 1 is a plan view and a cross-sectional view for explaining a first embodiment of the present invention. Here, FIG. 1B is a cross-sectional view taken along AB in the plan view of FIG.
[0013]
In this embodiment, the structure of the sensor will be described taking a case where a glucose sensor is manufactured as an example. As shown in FIGS. 1A and 1B, a polysilicon layer or a metal layer as a back gate 12 is formed by patterning on a glass substrate 11, and a gate insulating film is formed on the back gate 12. A silicon oxide film 13 is formed, and a polysilicon layer 14 as a semiconductor layer is formed thereon. Further, an N-type polysilicon layer 15 as a source region of the ISFET and an N-type polysilicon layer 16 as a drain region are provided at both ends of the polysilicon layer 14.
[0014]
A silicon oxide film 17 is provided so as to cover the polysilicon layer 14 including the N-type polysilicon layers 15 and 16. A part of the silicon oxide film 17, that is, the silicon oxide film 17 on the channel region of the polysilicon layer 14 which is an ion sensitive region is removed. Further, a silicon nitride film 18 as a protective insulating film is formed on the silicon oxide film 17. The silicon nitride film 18 in direct contact with the channel region of the polysilicon layer 14 is used as an ion sensitive region.
Therefore, here, in order to measure glucose, an enzyme-immobilized film 19 on which glucose oxidase (GOD) is immobilized is formed on the ion-sensitive region of the silicon nitride film 18. Since the entire ISFET is covered with the silicon nitride film 18, there are few pinholes and the reliability is high. Even in the case of a multi-sensor structure in which a plurality of sensors are manufactured on the same chip at the same time, the leakage current between the sensors can be kept small, so that highly accurate measurement is possible.
[0015]
Here, since the silicon nitride film 18 on the channel region of the polysilicon layer 14 is used as a gate insulating film of an ISFET, its thickness is set to an appropriate thickness for obtaining appropriate sensitivity as an ISFET. . Further, not only a silicon nitride film but also a silicon oxide film may be stacked and used. Although not shown, the N-type polysilicon layers 15 and 16 are connected to respective electrodes through contact holes opened in the silicon oxide film 17.
[0016]
The glass substrate used in the embodiment shown here may be Pyrex glass or quartz glass. Further, although the polysilicon layer is used as the semiconductor layer, amorphous silicon may be used. Further, the same effect can be obtained by using a tantalum oxide film, an aluminum oxide film, or the like in addition to the protective insulating film and the silicon nitride film as the gate insulating film.
[0017]
Next, the manufacturing method of the ISFET type biosensor described in the first embodiment will be described with reference to FIGS. FIG. 2 is a manufacturing process cross-sectional view of an ISFET type biosensor. As shown in FIG. 2, a chromium film 12 as a back gate, for example, is formed on a glass substrate 11 to a thickness of, for example, 2000A using a CVD method, and then patterned. At this time, it is desirable that the cross-sectional shape of the chromium film is trapezoidal by using wet etching so that the polysilicon film is not cut at the edge of the chromium film when the polysilicon film is formed in a later step. Or you may planarize using application | coating glass.
Next, as shown in FIG. 3, in order to make the chromium film function as a back gate, a silicon oxide film 13 having a thickness of, for example, 1000 A is formed by a CVD method. Thereafter, an amorphous silicon film 14 is formed by a CVD method, and an excimer laser beam generated from an excitation gas containing XeCl or the like is irradiated on the entire surface of the substrate in order to convert this into polysilicon. By this laser irradiation, the amorphous silicon film 14 becomes a polysilicon film 14. Next, as shown in FIG. 4, a silicon oxide film 17 as a protective insulating film is formed with a thickness of 4000 A, and impurity ions containing phosphorus are implanted using a photoresist as a mask in order to form source and drain regions. In this way, N-type polysilicon layers 15 and 16 as the source and drain are formed. Thereafter, etching is performed using a photoresist as a mask so that the silicon oxide film on the channel region of the polysilicon layer 14 has an appropriate thickness as a gate insulating film.
Although not shown, an aluminum film as an electrode is formed on the N-type polysilicon layers 15 and 16 through contact holes opened in the silicon oxide film and patterned. Next, as shown in FIG. 5, a silicon nitride film 18 is formed as a protective insulating film and a gate insulating film. Since this silicon nitride film 18 is used as a gate insulating film of an ISFET, it is set to an appropriate film thickness so as to have a desired sensitivity as an ISFET.
[0018]
Next, as shown in FIG. 6, after patterning so as to mask the region other than the ion sensitive region of the ISFET, that is, the region other than the channel portion with a photoresist, a mixed solution of glucose oxidase, albumin aqueous solution, and glutaraldehyde is applied to the entire surface of the substrate. To be applied. After the mixed solution is solidified, the immobilized enzyme film 19 is formed on the channel region of the ISFET by removing the photoresist in acetone.
[0019]
Through the steps as described above, an ISFET type biosensor having a polysilicon TFT structure having a back gate is manufactured.
[0020]
(2) Second Embodiment Next, a second embodiment will be described with reference to FIG. FIG. 7B is a cross-sectional view taken along AB in the plan view of FIG. The difference from the first embodiment is that the ion sensitive region is provided directly on the gate electrode via the gate insulating film, not on the channel portion of the polysilicon layer as the semiconductor layer, The back gate is provided not under the channel portion of the semiconductor layer but under the gate electrode. The manufacturing process of the ISFET having this structure is almost the same as that of the first embodiment, but the process of forming the back gate which is necessary in the first embodiment is not required. That is, in the second embodiment, the polysilicon layer ion-implanted at a high concentration can function as a back gate. The method for forming the immobilized enzyme membrane may be the same production method as in the first embodiment.
[0021]
Using the ISFET biosensor of this example, the channel potential is adjusted by the back gate to adjust the sensitivity as a sensor.
[0022]
The manufacturing method according to this embodiment requires fewer steps. In addition, since the setting range of the coupling capacitance between the back gate, gate, and channel is expanded, the sensitivity design as an ISFET is facilitated, and the sensitivity adjustment range is expanded.
[0023]
The biosensor described in the above embodiment has a structure in which an enzyme-immobilized film is formed on an ion sensitive film of ISFET using a polysilicon TFT. However, the present invention is not limited to this structure, and the same effect can be obtained even when the polysilicon film is an amorphous silicon film.
[0024]
In the above embodiment, the ISFET having the polysilicon TFT structure is formed on the glass substrate. However, the same effect can be obtained even if it is formed on a plastic substrate or another polymer material substrate.
[0025]
In this embodiment, the glucose sensor in which glutar oxidase is immobilized as the immobilized enzyme membrane has been described. However, the present invention can also be applied to other enzymes. Further, the gist of the present invention is not limited to an enzyme as an ion-sensitive membrane, but may be used as a protein sensor for detecting a reaction between other proteins, or a DNA sensor for detecting a reaction between nucleic acids. The same effect can be obtained as an antibody sensor for detecting an antigen-antibody reaction.
[0026]
【The invention's effect】
As described above, according to the biosensor of one embodiment of the present invention, the back gate is located in the lower layer of the channel region, and thus does not require a special area for arranging the back gate.
[0027]
According to the biosensor of one embodiment of the present invention, since the back gate is disposed below the gate electrode, a coupling capacitance with respect to the gate electrode can be arbitrarily set.
[0028]
According to the biosensor of one embodiment of the present invention, the sensitivity of the ion sensor is adjusted because the potential of the channel region or the potential of the gate electrode can be adjusted by changing the voltage applied to the back gate. be able to.
[0029]
In addition, according to the biosensor of one embodiment of the present invention, the current flowing through the polysilicon TFT greatly changes with a slight change in the interface potential in the ion sensitive region of the polysilicon TFT. And the dynamic range is expanded. Polysilicon TFTs have high-performance transistor characteristics, so that not only sensor elements but also circuits can be configured, and intelligent sensors can be fabricated that have a CPU, memory, amplifier circuit, etc. built into the sensor chip at the same time. .
[0030]
In addition, according to the biosensor of one embodiment of the present invention, a biosensor that is inexpensive and suitable for mass production can be obtained.
[0031]
In addition, according to the biosensor of one embodiment of the present invention, a biosensor suitable for “disposable” that can be easily discarded by incineration can be obtained. Moreover, since a soft (flexible) sensor is obtained, it is suitable for the use which monitors a health condition, for example by implanting a sensor in a body.
[Brief description of the drawings]
1A and 1B are a plan view and a cross-sectional view of an ISFET type biosensor illustrating a first embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a manufacturing process according to the first embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a manufacturing process according to the first embodiment of the present invention.
FIG. 4 is a cross-sectional view illustrating a manufacturing process according to the first embodiment of the present invention.
FIG. 5 is a cross-sectional view illustrating the manufacturing process of the first embodiment of the present invention.
FIG. 6 is a cross-sectional view illustrating the manufacturing process of the first embodiment of the present invention.
FIGS. 7A and 7B are a plan view and a cross-sectional view of an ISFET type biosensor illustrating a second embodiment of the present invention. FIGS.
FIG. 8 is an explanatory diagram of a conventional example.
[Explanation of symbols]
11 Glass substrate 12 Back gate 13 Gate insulating film 14 Polysilicon layer 15 Source 16 Drain 17 Silicon oxide film 18 Silicon nitride film 19 Ion sensitive film

Claims (7)

A substrate,
A first semiconductor film formed on the substrate and having a source region and a drain region;
A second semiconductor film formed on the substrate;
A first insulating film covering the first semiconductor film and the second semiconductor film;
A first gate electrode provided on the first insulating film corresponding to the first semiconductor film;
A second gate electrode provided on the first insulating film corresponding to the second semiconductor film;
A second insulating film covering the first gate electrode;
A source electrode connected to the source region through a first contact hole formed in the second insulating film;
A drain electrode connected to the drain region through a second contact hole formed in the second insulating film;
An ion sensitive film formed on the second gate electrode;
With
The second semiconductor film is a biosensor used as a back gate.   The biosensor according to claim 1, wherein the semiconductor film is a polysilicon film into which impurities are ion-implanted.   The biosensor according to claim 1, wherein the semiconductor film is an amorphous silicon film.   The biosensor according to any one of claims 1 to 3, wherein the substrate is made of any one of a glass substrate, a plastic substrate, and an organic polymer material. Forming a back gate in a predetermined region on the substrate;
Forming a first insulating film on the substrate and the back gate;
Forming a semiconductor film on the first insulating film;
Forming a second insulating film on the semiconductor film;
Forming a source / drain region by ion implantation into a predetermined region of the semiconductor film;
Removing the second insulating film on the channel region of the semiconductor film;
Forming a third insulating film on the channel region of the semiconductor film and on the second insulating film;
Forming an ion sensitive film on the third insulating film on the channel region of the semiconductor film;
A method for manufacturing a biosensor comprising: The step of forming the back gate includes:
Forming a metal film on the substrate;
Patterning the metal film;
With
The biosensor manufacturing method according to claim 5, wherein the patterning is performed by wet etching.   The biosensor manufacturing method according to claim 5, wherein the substrate is made of any one of a glass substrate, a plastic substrate, and an organic polymer material.

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