JPH0625745B2 - Semiconductor sensor - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a semiconductor sensor, and more particularly to improvement of a field effect type chemical sensor for detecting a component in a solution.

[Technical background of the invention and its problems]

In a semiconductor sensor such as ISFET, a source region, a drain region, and an insulating film are formed on a surface of a silicon substrate, and a gate portion thereof is immersed in a solution, so that the source and the drain are separated between the source and the drain according to an ion concentration of a specific component in the solution. It detects a change in conductance. Thus ISFET
In the above, since the element directly contacts the solution, it is necessary to insulate at least the liquid contact surface. For this reason, an insulating film that also serves as a gate insulating film such as a silicon nitride film or a silicon oxide film and a protective film (passivation film) is used. However, a part of this insulating film is selectively etched in order to lead out from the source / drain diffusion layer, and a vapor-deposited metal film or a metal thin wire is formed in that part to provide a connection portion.

In order to prevent the source / drain connection part from coming into contact with the solution, conventionally, a structure has been adopted in which only the gate part is contacted with the solution or the connection part is resin-coated so that the solution is contacted with almost the entire surface. It is used. The semiconductor sensor having such a structure is as shown in FIG. 4 or FIG. 5, respectively.

In FIG. 4, n ⁺ type source and drain regions 2 and 3 are formed on the surface of the p-type silicon substrate 1. An insulating film (not shown) serving as a gate insulating film and a protective film is formed on the entire surface of the silicon substrate 1. One ends of the source and drain regions 2 and 3 are provided close to each other to form a channel region 4. The source, drain regions 2, 3, channel region 4 and insulating film form a gate portion of the field effect transistor. On the other end side of the source / drain regions 2 and 3, the insulating film is selectively etched, and metal films 5 and 6 are formed on those portions, respectively. Lead wires 7 and 8 are connected to the metal films 5 and 6, respectively. The semiconductor sensor having such a structure is used by immersing the gate portion in the solution 9.

However, since the semiconductor sensor having such a structure receives a fluid pressure on one end side of the substrate 1, there is a problem in strength and the wiring resistance is increased by the silicon layer, so that the total length of the semiconductor sensor cannot be increased, and the lead cannot be obtained. The distance between the connection with the lines 7 and 8 and the gate is usually a few mm. Therefore, in order to project the gate portion into the tube in order to measure the solution in the tube, the wall thickness of the tube must be limited to less than that, and there is a problem in selecting the tube. Further, in this structure, when an insulating film is formed on the liquid contact surface, the substrate 1
Inevitably, an insulating film must be formed over the entire circumference of the wafer, and for that purpose, the process of processing the outer shape of the sensor in advance at the time of manufacturing and then forming the insulating film is taken, making it impossible to process with a normal wafer size. is there. For this reason, there are drawbacks in that it requires careful handling during the manufacturing process and is easily damaged.

On the other hand, in FIG. 5, n ⁺ type source / drain regions 12 and 13 are formed on the main surface of the p-type silicon substrate 11,
Further, an insulating film 14 such as a silicon nitride film or a silicon oxide film, which will be a gate insulating film and a protective film, is formed on the main surface of the substrate 11. A channel region 15 is formed between the source / drain regions 12 and 13. The source and drain regions 12, 13, the channel region 15 and the insulating film 14 form a gate portion of the field effect transistor. Part of the insulating film 14 corresponding to the source and drain regions 12 and 13 is selectively etched, and metal films 16 and 17 connected to the source and drain regions 12 and 13 are deposited.
Further, lead wires 18 and 19 are connected to the metal films 16 and 17, respectively. In the semiconductor sensor having such a structure, a part of the measuring tube 20 is notched and the resin film 21 for bonding is used to bond the metal films 16 and 17 to the lead wires 18 and 19 in a state of being bonded to each other. Measurement is performed by immersing the gate portion in the solution inside.

In such a semiconductor sensor, as shown in FIG. 5, since the detection surface (the surface with the gate portion) can be attached along the pipe wall so as to contact the solution, the semiconductor sensor shown in FIG. Problems are unlikely to occur. However, the lead wires 18 and 19 may be cut during the resin curing during manufacturing, or the metal film 1
There is a risk of peeling from 6 and 17. In addition, during use, the resin 21 on the same surface as the detection surface is often immersed in the solution and swells, thereby damaging the insulation. Also, the fifth
When mounting a semiconductor sensor on the pipe 20 as shown in the figure,
Actually, the pipe 20 is divided into two in a vertical division, and the resin 20 is adhered from the inside and the outside of one of the two divided bodies provided with the notch, and then the two divided bodies are bonded again to form the pipe 20. It requires complicated work. Moreover, there is a drawback that such a structure cannot withstand a large fluid pressure.

Furthermore, in order to obtain high measurement accuracy, it is required that solid matter does not adhere to the gate portion and bubbles do not occur near the gate portion. However, in the semiconductor sensor shown in FIG. 4 and FIG. Since the flow of the solution is disturbed in the vicinity of the portion, solid substances are likely to be attached and bubbles are easily generated, resulting in poor measurement accuracy.

[Object of the Invention]

The present invention has been made to solve the above-mentioned drawbacks, is easy to attach to a tube, does not cause a short circuit or leak at the connecting portion with a lead wire, and can measure a solution with high accuracy for a long period of time. It is intended to provide a semiconductor sensor that can be performed.

[Outline of Invention]

A semiconductor sensor of the present invention includes a first conductive type first semiconductor substrate and a second semiconductor substrate formed on one surface of the first semiconductor substrate.
A conductive type diffusion layer, a first conductive type second semiconductor substrate directly bonded to a surface of the first semiconductor substrate on which the second conductive type diffusion layer is formed, the first and second A second conductive type diffusion layer formed over the entire peripheral portion of the semiconductor substrate, and penetrating the first and second conductive type semiconductor substrates at positions other than the peripheral portions of the first and second semiconductor substrates. It is characterized in that it is provided with a through hole provided and an insulating film formed on the surfaces of the first and second semiconductor substrates including the inner surface of the through hole.

In the above semiconductor sensor, the first and second semiconductor substrates function as source and drain regions, and the second conductivity type diffusion layer sandwiched therebetween functions as a channel region, and an insulating film is formed on the surface of these regions. By forming, the inside of the through hole becomes a gate portion. When measuring the solution with this semiconductor sensor, pipes are joined to the upper and lower surfaces of the semiconductor sensor, the through hole is located inside the pipe, and the connection with the lead wire is located outside the pipe. Configure the measurement system.

According to such a semiconductor sensor, attachment to a pipe becomes very easy as compared with a conventional semiconductor sensor. Further, the connection between the source / drain region and the lead wire is outside the tube, and this connection is never immersed in the solution. Therefore, it is not necessary to cover the connecting portion with the resin, and naturally, the insulation failure due to the swelling of the resin does not occur. Furthermore, since the solution smoothly flows in the vicinity of the gate portion inside the through-hole which also serves as a flow path for the solution, solid matter does not adhere and bubbles are not generated, and the measurement accuracy can be improved.

In manufacturing the semiconductor sensor of the present invention, the first
The following method is used to directly bond the semiconductor substrate of 1 to the second semiconductor substrate. First, two silicon wafers are prepared, and the surfaces to be bonded are mirror-polished to have a surface roughness of 500 Å or less. At this time, depending on the surface state of the silicon wafer, pretreatment with hydrogen peroxide solution + sulfuric acid, hydrofluoric acid, and dilute hydrofluoric acid is continued to degrease and remove the stain film adhering to the surface of the silicon wafer. Next, this silicon wafer mirror surface is washed with clean water for about several minutes, and a dehydration treatment such as a spinner treatment is performed at room temperature. Since this treatment step is intended to leave the water assumed to be adsorbed on the mirror surface of the silicon wafer as it is and remove the excess water, heating at 100 ° C. or higher at which most of the adsorbed water is volatilized. Avoid drying. The silicon wafers that have undergone these treatments are placed in, for example, a clean atmosphere of class 1 or less, and are adhered and bonded to each other in a state where no foreign matter is present between their mirror surfaces. In addition,
The bonding strength can be increased by heating the silicon wafer bonded in this manner at 200 ° C. or higher, preferably at 1000 to 1200 ° C.

The semiconductor sensor of the present invention uses the above-mentioned direct bonding method, and if the through holes are provided, the other regions can be manufactured by a simple process using a normal semiconductor process, and the depth of the diffusion layer and the through holes can be improved. It is also possible to obtain the effect that the sensitivity can be controlled simply by appropriately setting the size of.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. 1 is a sectional view of the semiconductor sensor according to the present invention, FIG. 2 is a plan view of the semiconductor sensor, and FIG. 3 is an explanatory view showing a usage state of the semiconductor sensor.

In FIG. 1, a P ⁻ type diffusion layer 32 is formed on one surface of an n ⁻ type first silicon substrate 31, and a p ⁻ type diffusion layer 32 of the first silicon substrate 31 is formed. The n ⁺ -type second silicon substrate 33 is directly bonded to the existing surface. Further, p ⁺ type channel stopper regions 34 and 35 are formed over the entire peripheral portions of the first silicon substrate 31 and the second silicon substrate 33. Also,
The n ⁺ -type diffusion layer 3 is formed on the other surface of the first silicon substrate 31.
6 is formed. Then, the first silicon substrate 31
And the first portion is provided at the center of the laminated body of the second silicon substrate 33.
Through holes 37 are formed to penetrate the silicon substrate 31 and the second silicon substrate 33. An insulating film 38 serving as a gate insulating film and a protective film is formed on the surfaces of the first silicon substrate 31 and the second silicon substrate 33 including the inner surface of the through hole 37. Further, the first silicon substrate 3
A part of the insulating film 38 on the n ⁺ type diffusion layer 36 provided on the first semiconductor layer 1 and on the boundary between the second silicon substrate 33 and the p ⁺ type channel stopper region 35 is selectively etched, and electrodes are respectively formed on the part. 39 and 40 are formed. Lead wires 41 and 42 are connected to the electrodes 39 and 40, respectively.

In the semiconductor sensor shown in FIG. 1, the first silicon substrate 3
1 is the drain region, the second silicon substrate 33 is the source region, and the p-type diffusion layer 3 provided on the first silicon substrate 31.
2 functions as a channel region, and the inner surface of the through hole 37 serves as a gate portion by forming the insulating film 38 on the surface of these regions.

The semiconductor sensor shown in FIGS. 1 and 2 was manufactured as follows. First, an n ⁻ -type first silicon substrate 31 and an n ⁺ -type second silicon substrate 33, each having a diameter of 1 inch, were prepared and mirror-polished so that the concavities and convexities of these bonding surfaces were 500 Å or less. . Next, boron was diffused over the entire polished surface of the first silicon substrate 31 to a depth of 10 μm to form a p ⁻ -type diffusion layer 32 that became a channel region. Since the diffusion depth of the p ⁻ type diffusion layer 32 becomes the channel length, the diffusion conditions are controlled so that the diffusion depth becomes a predetermined value. Further, phosphorus was diffused on the surface of the first silicon substrate 31 opposite to the surface on which the p ⁻ type diffusion layer 32 was formed, except for the peripheral portion, to form the n ⁺ type diffusion layer 36. Since the n ⁺ -type diffusion layer 36 has a low impurity concentration as the first silicon substrate 31 for forming the p ⁻ -type diffusion layer 32 which becomes the channel region, it becomes the first drain region. It is formed for the purpose of lowering the resistance of the silicon substrate 31 and obtaining good contact.

Then, the bonding surfaces of the first and second silicon substrates 31 and 33 were respectively standard-cleaned with an organic solvent, sulfuric acid, an aqueous solution of hydrofluoric acid and the like, and then the surfaces were treated with deionized water. After that, the surfaces to be joined were superposed and joined by heating in an electric furnace at 1100 ° C. for 1 hour in air.

Then, a through hole 37 having a diameter of 3 mm was formed by machining so as to penetrate substantially the central portions of the first silicon substrate 31 and the second silicon substrate 33. Next, in the state where the layers are bonded as described above, a channel is also formed in the peripheral portion of the laminated body, so a thermal oxide film is formed on the entire surface and the portion formed on the outer periphery is selectively etched. After that, using this as a mask, boron was diffused to form p ⁺ type channel stopper regions 34 and 35 at the peripheral portions of the first and second silicon substrates 31 and 33.

Then, after removing the thermal oxide film by hydrofluoric acid treatment, thermal oxidation is newly performed to form a SiO ₂ film having a film thickness of 500 Å, and further a Si ₃ N ₄ film having a film thickness of 1000 Å is deposited by the CVD method. The first including the inner surface of the through hole 37 depending on the process
And an insulating film 38 on the surfaces of the second silicon substrates 31 and 32.
Was formed.

Next, on the n ⁺ type diffusion layer 36 and the second silicon substrate 3
A part of the insulating film 38 on the boundary between 3 and the p ⁺ type channel stopper region 35 was selectively etched to open a contact hole. Then, after depositing a metal film on the entire surface, patterning was performed to form electrodes 39 and 40. Subsequently, lead wires 41 and 42 were connected to these electrodes 39 and 40 to manufacture the semiconductor sensor shown in FIGS. 1 and 2.

The semiconductor sensor as described above is used as shown in FIG. First, on the upper and lower surfaces of the semiconductor sensor 51 to which the lead wires 41 and 42 are connected, the through hole portion is located inside the pipe, and the connecting portion is located outside the pipe, for example, the inner diameter 500.
A tube in which the measuring tubes 52 and 53 of μm are joined by an adhesive or the like is prepared. The joining of the measuring tubes 52 and 53 need only be considered so as to prevent the test liquid from leaking to the outside. Next, one end of the measurement tube 52 is immersed in the test liquid 55 contained in the container 54, and the reference electrode 56 is immersed, and the measurement liquid 55 is sucked into the measurement tubes 52, 53 for measurement. The source follower circuit feeds back the current between the source and drain of the semiconductor sensor 51 to the reference electrode 56 so as to keep the current constant.

Actually, when a saturated calomel electrode was used as the reference electrode 56 in the measurement system shown in FIG. 3 and the gate potential was sequentially examined for buffer solutions having different pHs, a good sensitivity of 55 mV / pH was shown.

According to such a semiconductor sensor, as shown in FIG. 3, attachment to the measuring tubes 52 and 53 becomes very easy as compared with the conventional semiconductor sensor. Further, since the connecting portion between the source / drain regions and the lead wire is arranged outside the measuring tubes 52 and 53, the connecting portion is not immersed in the solution. Therefore, it is not necessary to cover the connecting portion with the resin, and naturally, the insulation failure due to the swelling of the resin does not occur. Further, since the test liquid 55 smoothly flows in the vicinity of the gate portion inside the through-hole 37 which also serves as the flow path of the test liquid 55, solid matters do not adhere and bubbles are not generated, thereby improving the measurement accuracy. be able to.

Further, the semiconductor sensor having the structure shown in FIG. 1 may possibly be manufactured by a method different from that used in the above embodiment. For example, after diffusing n-type impurities from both sides of a p-type silicon substrate to leave a thin p-type layer in the center, a channel stopper region, a through hole, an insulating film, and an electrode are sequentially formed, and finally a lead wire is connected. The process of doing is possible. However, since the silicon substrate usually has a thickness of about 300 μm, if a thin P-type layer is left in the central portion when the above method is used, the diffusion time of the n-type impurities is, for example, 2 days. It will be very long. Moreover, the diffusion of impurities is controlled by temperature and time, but if the thickness of the p-type layer left in the central portion of the silicon substrate is extremely smaller than the thickness of the n-type diffusion layers on both sides, it is difficult to control. The upper and lower n-type diffusion layers may come into contact with each other and the p-type layer may have a non-uniform thickness.

As described above, according to the method other than the method used in the above-mentioned embodiment, the diffusion time is long and the p-type layer thickness is difficult to control. In the case of using the method of utilizing the direct bonding of the two, the diffusion time for forming the p ⁻ type diffusion layer 32 is 1
It only takes ~ 2 hours, and its thickness is easy to control.

Further, the sensitivity of the semiconductor sensor using the field effect transistor as shown in FIG. 1 is governed by various factors, but it can be most simply expressed by the gate length 1 and the gate width w. That is, the input voltage sensitivity is an amount proportional to w / l. Here, the gate length 1 is the thickness of the p ⁻ type diffusion layer 32,
The gate width W corresponds to the inner peripheral length of the through hole 37, respectively.

The thickness of the p-type layer which can be controlled by the method other than the method used in the above-mentioned embodiment is about 50 μm at the most, whereas the method used in the embodiment can sufficiently control the thickness of 5-10 μm. Therefore, when the diameters of the through holes 37 are the same, it is possible to expect good sensitivity 5 to 10 times.

In the semiconductor sensor of the present invention, by covering the gate portion with various modifiers, not only the hydrogen ions (pH) measured in the above-mentioned examples but also other ions can be made selective. For example, a resin and a valinomycin film can be used as a K ⁺ sensor, or a resin and crown ethers can be used as a Na ⁺ sensor. When these modifiers are used, the resin swells, and when applied to the conventional semiconductor sensor shown in FIG. 4 or 5,
Peeling or breakage occurred in water. On the other hand, in the semiconductor sensor of the present invention, even if the resin swells, it acts in the direction of expanding the through-hole, so that the resin has high adhesion strength and does not easily peel off, so that the life is two to three times that of the conventional one. .

Further, if a plurality of semiconductor sensors having different functions obtained by the above method are laminated in a watertight structure so that the positions of the through holes are made to coincide with each other and then the measurement system is configured in the same manner as in FIG. Sensor assembly.

Further, the steps for obtaining the semiconductor sensor of the present invention can be changed as appropriate. For example, the first and second silicon substrates are not limited to n-type and p-type may be used. Also,
The processing temperature at the time of direct bonding can be selected in the range of 400 to 1200 ° C. The through holes may be formed not only by machining but also by etching. The insulating film may be a SiO ₂ film alone or a Si ₃ N ₄ film alone. Furthermore, the order of each step can be changed as appropriate.

〔The invention's effect〕

As described in detail above, according to the semiconductor sensor of the present invention, it has an extremely great industrial value such that it can be easily attached to a pipe, the connection portion is highly reliable, and the measurement accuracy can be improved. is there.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a semiconductor sensor according to an embodiment of the present invention, FIG. 2 is a plan view of the semiconductor sensor, and FIG. 3 is an explanatory view showing a usage state of the semiconductor sensor. FIG. 4 is a front view of a conventional semiconductor sensor, and FIG. 5 is a sectional view showing a usage state of another conventional semiconductor sensor. 31: first silicon substrate, 32: p ^- type diffusion layer,
33 ... Second silicon substrate, 34, 35 ... P ⁺ type channel stopper region, 36 ... N ⁺ type diffusion layer, 37 ...
... through holes, 38 ... insulating film, 39, 40 ... electrodes, 4
1, 42 ... Lead wire, 51 ... Semiconductor sensor, 52,
53 ... Measuring tube, 54 ... Container, 55 ... Test liquid, 56
...... Reference electrode.

Claims (5)

[Claims] 1. A first semiconductor substrate of a first conductivity type, and the first semiconductor substrate.
Second conductivity type diffusion layer formed on one surface of the first semiconductor substrate and a first conductivity type diffusion layer directly bonded to the surface of the first semiconductor substrate on which the second conductivity type diffusion layer is formed. A second semiconductor substrate, a diffusion layer of the second conductivity type formed over the entire peripheral portions of the first and second semiconductor substrates, and a second semiconductor substrate at a position other than the peripheral portions of the first and second semiconductor substrates. A semiconductor comprising: a through hole provided through the first and second semiconductor substrates, and an insulating film formed on the surfaces of the first and second semiconductor substrates including the inner surfaces of the through hole. Sensor. 2. A first semiconductor substrate having a low impurity concentration is used, and a first-conductivity-type high-concentration diffusion layer is formed on the other surface of the first semiconductor substrate. The semiconductor sensor according to item 1. 3. The semiconductor sensor according to claim 1, wherein the insulating film is a SiO ₂ film. 4. The semiconductor sensor according to claim 1, wherein the insulating film is a Si ₃ N ₄ film. 5. The semiconductor sensor according to claim 1, wherein the insulating film is formed by sequentially laminating a SiO ₂ film and a Si ₃ N ₄ film.