JPS623655A - Semiconductor sensor - Google Patents

Abstract

PURPOSE:To measure a solution for a long time by providing a through hole in the recessed part of the first conductive type semiconductor substrate and forming the second conductive type source and drain area on both faces of the substrate, and forming an insulating film on both faces of the substrate including the inside face of the through hole. CONSTITUTION:A through hole 33 is provided in the recessed part of a p-type silicon substrate 31, and n<+> type source and drain areas 34 and 35 are formed on both faces of the substrate 31. An insulating film 37 is formed on both faces of the substrate 31 including the inside wall of the hole 33. A part of the insulat ing film 37 on the source area 34 and a p<+> type diffused layer 36 or on the drain area 35 is etched selectively to from contact pads 38 and 39. Lead wires 40 and 41 are connected to these pads 38 and 39. Consequently, connection parts between source and drain areas 34 and 35 and lead wires 40 and 41 are on the outside of a tube and are not immersed in the solution. It is unnecessary to coat connection parts with a resin therefore. Thus, insulation defects or the like due to swelling of the resin are not caused, and the solution is measured stably for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a semiconductor sensor, and particularly to an improvement in a field-effect chemical sensor for detecting components in a solution.

[Technical background of the invention and its problems]

Semiconductor sensors, such as 15FET, form source and drain regions and an insulating film on the surface of a silicon substrate, and by immersing the gate part in a solution, the distance between the source and drain is adjusted according to the ion concentration of a specific component in the solution. It detects changes in conductance. In this way l5FET
In this case, since the element comes into direct contact with the solution, it is necessary to insulate at least the surface in contact with the liquid. For this purpose, an insulating film such as a silicon nitride film or a silicon oxide film that also serves as a gate insulating film and a protective film (passivation film) is used. However, in order to lead out leads from the source and drain diffusion layers, a part of this insulating film is selectively etched, and a vapor-deposited metal film or thin metal wire is formed in that part to provide a connection part.

In order to prevent the above-mentioned source and doin connection parts from coming into contact with the solution, conventional structures have been used in which only the gate part is in contact with the solution, or the connection part is coated with a resin so that almost the entire surface is in contact with the solution. It was used. A semiconductor sensor having such a structure is shown in FIG. 5 or FIG. 6, respectively.

In FIG. 5, n+ type source and drain regions 2.3 are formed on the surface of a p-type silicon substrate 1. An insulating film (not shown) such 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 2.3 are provided close to each other and form a channel region 4. These source and drain regions 2.3, channel region 4, and insulating film constitute a gate portion of a field effect transistor. The insulating film is selectively etched on the other end side of the source and drain regions 2.3, and a metal film 5.6 is formed in each of those portions. Lead wires 7.8 are connected to these metal films 5.6, respectively. A semiconductor sensor having such a structure is used with the gate portion immersed in the solution 9.

However, semiconductor sensors with this structure are subject to fluid pressure at one end of the substrate 1, which poses strength problems, and the silicon layer increases wiring resistance, making it impossible to increase the overall length of the semiconductor sensor. The distance between the connection with line 7.8 and the gate part is usually a few meters. Therefore, in order to make the gate part protrude into the pipe, the wall thickness of the pipe must be limited to less than this, which also poses problems in the selection of the pipe. In addition, with this structure, if an insulating film is to be formed on the surface in contact with liquid, the insulating film must be formed all around the substrate 1. To do this, the outer shape of the sensor is processed in advance during manufacturing, and then the insulating film is It is impossible to process with a normal wafer size. For this reason, it has the drawback of requiring care in handling during the manufacturing process and being easily damaged.

On the other hand, in FIG. 6, n1 type source and drain regions 12 and 13 are formed on the main surface of the p type silicon substrate 11.
Furthermore, an insulating film 14 such as a silicon nitride film or a silicon oxide film, which serves as a gate oxide film and a protective film, is formed on the main surface of the substrate 11. A channel region 15 is formed between the source and drain regions 12 and 13. These source and drain regions 12, 13, channel region 15, and insulator g114 constitute the gate portion of the field effect transistor. A portion of the insulation g114 corresponding to the source and drain regions 12.13 is selectively etched, and a metal 1116.17 connected to the source and drain regions 12.13 is deposited, and these metal films 16.17 are further etched. There is a lead wire 18.
19 are connected.

A portion of the metal film 16.17 and the lead wire 18.19 are covered with a resin 20.21.

Since such a semiconductor sensor is arranged so that the detection surface (the surface with the gate portion) is in contact with the solution, it can be attached, for example, along the tube wall. Therefore, problems like the semiconductor sensor shown in FIG. 5 are unlikely to occur. However, there is a risk that the lead wires 18.19 may be cut or peeled off from the metal 1i 116.17 during the resin curing during manufacturing. In addition, when in use, the resin 20.2 on the same surface as the detection surface is
1 swells when immersed in a solution, often damaging its insulation. Furthermore, such resins 20, 21 cannot withstand large fluid pressures, and leakage current may occur during use.

[Purpose of the invention]

The present invention was made to eliminate the above-mentioned drawbacks, and it is easy to attach to a pipe, does not cause short-circuits or leaks at the connection with the lead wire, and can stably measure solutions over a long period of time. The aim is to provide a semiconductor sensor that can perform

[Summary of the invention]

The semiconductor sensor of the present invention includes a recess formed in a part of a semiconductor substrate of a first conductivity type, a through hole provided in the recess, and a source of a second conductivity type formed on both surfaces of the substrate. , a drain region, and an insulating film formed on the surface of the substrate including the inner wall of the through hole.

In such a semiconductor sensor, the inner wall surface of the through hole becomes a gate portion. In addition, when measuring a solution inside a tube with this semiconductor sensor, the tubes are joined to both the top and bottom of the sensor, and the through-hole part is located inside the tube, and the area around the sensor is exposed outside the tube. Configure the measurement system.

According to such a semiconductor sensor, the connection portion between the source and drain regions and the lead wire is located outside the tube, and this connection portion is not immersed in the solution. For this reason, there is no need to cover the connection portion with resin, and of course there is no occurrence of insulation defects due to swelling of the resin.

Furthermore, since the measurement system is constructed by connecting tubes to both the upper and lower surfaces of the sensor, there is no need to particularly consider the thickness of the tubes. Furthermore, a semiconductor sensor having such a structure can be manufactured using a normal semiconductor manufacturing process, and a large number of sensors can be manufactured using a wafer having a larger area.

Note that in the semiconductor sensor of the present invention, the recess is formed so that the channel length of the field effect transistor is a practical value, but the thickness of the remaining semiconductor substrate after the recess is formed and the thickness of the semiconductor substrate around the through hole are ) is preferably 200- or less.

Further, the sensitivity of a transistor is proportional to the ratio of the channel width (the inner peripheral length of the 11 holes) to the channel length, so if the channel length can be shortened, a highly sensitive transistor can be manufactured with a smaller channel width. In this case, it is desirable that the size of the through hole is 5 or less in length. Furthermore, in order to prevent damage to the insulating film at the corners of the through holes and recesses, it is desirable to round the corners of these corners. Such rounding can be easily performed by selecting an etching solution.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1(a) and (b), FIGS. 2(a) to (e), and FIG. 3. In addition,
FIG. 1(a) is a sectional view of a semiconductor sensor according to the present invention, FIG. 1(b) is a plan view of the semiconductor sensor, and FIGS.
e) is a sectional view showing a method of manufacturing the semiconductor sensor, and FIG. 3 is an explanatory view showing the usage state of the semiconductor sensor.

In FIGS. 1(a) and 1(b), a p-type silicon substrate 3
A recess 32 is formed on one surface of the substrate 1, and a through hole 33 penetrating to the other surface of the substrate 31 is provided on the bottom surface of the recess 32. Further, on both sides of the substrate 31, n
++ Source and drain regions 34 and 35 are formed. Between these source and drain regions 34 and 35, that is, the inner wall of the through hole 33 becomes a channel region. In addition, in order to prevent channel action at the end surface of the substrate 31, p+
A wide diffusion layer 36 is formed. Further, on both surfaces of the substrate 31 including the inner wall of the through hole 33, an insulation 1 [37] serving as a gate insulation film and a passivation film is formed. This insulation 1137 is selectively etched on the source region 34, a part on the p+ type expansion layer 36, and a part on the drain region 35, and a contact pad 3 is formed in each of these regions.
8.39 is formed. These contact pads 3
Lead wires 40 and 41 are connected to 8 and 39, respectively.

A semiconductor sensor as shown in FIGS. 1(a) and (b) is manufactured by a method as shown in FIGS. 2(a) to (e).

First, an oxide film 51 is formed as an etching mask on both sides of a commonly used p-type silicon substrate 31 having a thickness of 450 mm and a surface crystal orientation (100). Next, the substrate 31 is etched at 110 DEG C. in a nitrogen atmosphere using EPW (ethylenediamine-pyrocatechol-water mixture) as an etching solution to form the recesses 32. When this etching solution is used, anisotropic etching is performed, and if the crystal orientation of the surface of the substrate 31 is (100) as described above, a recess having a surface inclined at an angle of about 55 degrees with respect to the surface of the substrate 31 will be formed. 32 is formed. Note that one side of the bottom of the recess 32 was 300 m, and the remaining thickness between the bottom surface of the recess 32 and the other surface of the substrate 31 was 100 m (as shown in FIG. 2(a)).

Next, after removing the oxide film 151, an oxide film 52 is formed only on the peripheral edge of the substrate 31 to serve as a mask for impurity diffusion. Next, n++ source and drain regions 34 and 35 are formed by diffusing phosphorus. The phosphorus concentration on the surface of these source and drain regions 34 and 35 is approximately 101
The diffusion depth of the 8/c layer 3 was 20 m (as shown in the same figure (b)).

Next, after removing the oxide film 52, an oxide film 53 is formed on the source and drain regions 34 and 35. Next, a p++ channel stopper region 36 is formed by diffusing boron using the oxide film 53 as a mask (see FIG.
C) As shown).

Next, after removing the oxide film 53, the center of the bottom of the recess 32 is selectively etched to form a through hole 33 having a diameter of 150 m. Subsequently, an insulating film 37 made of a thermal oxidation film and a silicon nitride film formed by CVD is formed on the entire surface (as shown in FIG. 3(d)).

Next, the source region 34 near the periphery of the substrate 31 and the p+ type scattering layer 36 adjacent thereto, and the drain region 3
A contact hole is formed by selectively etching a portion of the insulating film 37 corresponding to the top of the contact hole. Subsequently, a metal film is deposited on the entire surface, and then patterned to form contact pads 38 and 39 (as shown in FIG. 3(e)).

The wafer on which elements have been formed as described above is cut and divided by a dicer. Subsequently, lead wires are connected to the contact bands 38 and 39 using micro soldering paste to manufacture the semiconductor sensor shown in FIGS. 1(a) and 1(b).

The semiconductor sensor as described above is used as shown in FIG. First, prepare measurement tubes 62 and 63 with an inner diameter of 500mm, for example, bonded with adhesive or the like on both the upper and lower surfaces of the semiconductor sensor 61 so that the through-hole portion is located inside the tube and the connecting portion is located outside the tube. do. When connecting the measurement tubes 62 and 63, it is only necessary to take into consideration that the test liquid will not leak outside. Next, the test liquid 6 contained in the container 64
5, one end of the measuring tube 62 is immersed in the reference electrode 6.
Soak 6. Then, for measurement, the test liquid 65 is transferred to the measuring tube 62.
．． 63 and feedback to the reference electrode 66 using a source follower circuit to keep the current between the source and drain of the semiconductor sensor 61 constant.

According to such a semiconductor sensor, the connection between the source and drain regions 34, 35 and the lead wires 40° 41 is located outside the measurement tube 62, 63 during measurement, and this connection cannot be immersed in the solution. do not have. Therefore, unlike the conventional semiconductor sensor shown in FIG. 6, there is no need to cover the connecting portion with resin, and of course there is no possibility of insulation failure due to swelling of the resin. Furthermore, since the area around the connection part is covered with the insulation 1137, even if the lead wires 40, 41 are broken at the connection part, it can be repaired any number of times. Furthermore, since the measurement system is constructed by connecting measurement tubes 62 and 63 to both the upper and lower surfaces of the sensor, unlike the conventional semiconductor sensor shown in FIG. 5, it is necessary to particularly consider the thickness of the measurement tubes 62 and 63. do not have. Furthermore, in a semiconductor sensor having such a structure, there is no need to form an insulating film 37 on the side surface of the substrate 31. Therefore, unlike the case of manufacturing the conventional semiconductor sensor shown in FIG. can be manufactured.

Therefore, a large number of sensors can be manufactured with a larger area wafer.

When a buffer solution was actually measured using the measuring device shown in FIG. 3, the gate potential showed good pHM response of about 55 mV/pH, and no dielectric breakdown was observed even after long-term use.

Incidentally, in the above embodiment, anisotropic etching was performed when forming the recessed portion in the step shown in FIG. 2(a), but the present invention is not limited to this, and isotropic etching may be performed.

When isotropic etching is used in this way, debris is generated under the oxide film 51 that serves as an etching mask, but the bottom surface of the recess can be made smoother than when anisotropic etching is used. It has the advantage of being Also,
In the above embodiment, the recesses 32 were formed only on one surface of the substrate 31, but the recesses may be formed on both surfaces. Figure 2 (
The through holes 33 formed in step d) may also be formed by anisotropic etching or isotropic etching. Furthermore, the shape of the recess and the through hole is not limited to a square, but may be of any shape.

Furthermore, since the semiconductor sensor of the present invention can use a normal semiconductor manufacturing process, a plurality of sensors can be formed on one substrate. A plan view of such a semiconductor sensor is shown in FIG.

In FIG. 4, the substrate and the source region are common, and four through holes 33, . . . are formed in the center of the substrate. N+ type drain regions 35... are formed around these through holes 33, . Contact pads 39, . . . are formed in each drain region 35, .

In such a semiconductor sensor, each sensor can be used for, for example, H+ ions, Na+ ions, K+ ions, etc., and simultaneous measurement of multiple components is possible.

(Effects of the Invention) As detailed above, according to the semiconductor sensor of the present invention, a specific component in a solution can be stably detected over a long period of time without causing insulation failure, and its manufacture is extremely easy. The industrial value is extremely great.

[Brief explanation of drawings]

FIG. 1(a) is a cross-sectional view of a semiconductor sensor according to an embodiment of the present invention, FIG. 1(b) is a plan view of the semiconductor sensor, and FIGS. 3 is an explanatory diagram showing the state of use of the semiconductor sensor, FIG. 4 is a plan view of a semiconductor sensor according to another embodiment of the present invention, and FIG. 5 is a front view of a conventional semiconductor sensor. 6 are cross-sectional views of other conventional semiconductor sensors. 31...p-type silicon substrate, 32... recess, 33.
...Through hole, 34.35...n++ source, drain region, 36...p+ type expansion layer, 37...insulating film, 3
8.39... Contact pad, 40.41... Lead wire, 51.52.53... Oxide film, 61... Semiconductor sensor, 62.63... Measuring tube, 64... Container , 65... Test liquid, 66... Reference electrode. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 5 Figure 6rlA

Claims (4)

[Claims] (1) A recess formed in a part of the semiconductor substrate of the first conductivity type, a through hole provided in the recess, and source and drain regions of the second conductivity type formed on both surfaces of the substrate, respectively. A semiconductor sensor comprising: an insulating film formed on a surface of a substrate including an inner wall of the through hole. (2) The semiconductor sensor according to claim 1, wherein the thickness of the semiconductor substrate around the through hole is 200 μm or less. (3) The semiconductor sensor according to claim 1, wherein the size of the through hole is 5 mm or less in length. (4) The semiconductor sensor according to claim 1, wherein the corners of the through hole and the recess are rounded.