JPH0679009B2 - Chemical sensor - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a chemical 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]

A field effect type (FET type) chemical sensor forms a source and drain regions and an insulating film on the surface of a silicon substrate, and immerses the gate part in a solution to adjust the ion concentration of a specific component in the solution. The change in conductance between the source and drain is detected. In such a chemical sensor, 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. Then, in order to lead out from the source / drain diffusion layer, a part of this insulating film is selectively etched, and a vapor-deposited metal film or a metal thin wire is formed in that part to provide a connection portion.

Conventionally, such a chemical sensor is shown in FIG.
The structures shown in (b), FIG. 6 (a), (b) and FIG. 7 are known.

The ones shown in FIGS. 5 (a) and 5 (b) have a probe-like shape. In FIGS. 5A and 5B, for example, an n ⁺ type drain region 2 and an n ⁺ type source region 3 are formed so as to surround the drain region 2 on the surface of the p type silicon substrate 1. The entire surface of the silicon substrate 1 is covered with a silicon oxide film 4 and a silicon nitride film 5 which will be a gate insulating film and a protective film. In this structure, the source and drain regions, the channel region between them, and the insulating film on one end side of the silicon substrate 1 constitute the gate portion of the field effect transistor. On the other end side of the drain region 2 and the source region 3, the insulating film is selectively etched, and metal films 6 and 7 are formed on the insulating film, respectively, to make contacts.

However, in the chemical sensor having such a structure, if the substrate 1 is exposed, a leak occurs between the elements in the water. Therefore, an insulating film has to be formed over the entire circumference of the substrate 1. A process of processing the outer shape of the sensor and then forming an insulating film is taken, and a process with a normal wafer size is impossible. For this reason, there is a drawback in that the mass productivity is poor and it is easily damaged during manufacturing. Also,
Even if damage is avoided during manufacturing, there is a problem in strength since the fluid pressure is applied to one end side of the substrate 1.

On the other hand, the one shown in FIGS. 6A and 6B has the SOS structure. In FIGS. 6A and 6B, an island-shaped p-type silicon layer 12 is formed on a sapphire substrate 11, and n ⁺ -type source / drain regions 13 and 14 are formed on the surface thereof. The surface of the silicon layer 12 is covered with a silicon oxide film 15 and a silicon nitride film 16 which will be a gate insulating film and a protective film. In this structure, the source and drain regions, the channel region between them, and the insulating film on one end side of the silicon layer 12 form the gate portion of the field effect transistor. On the other end sides of the source / drain regions 13 and 14, the insulating film is selectively etched, and metal films 17 and 18 are formed at the portions to make contacts.

In such a chemical sensor having the SOS structure, all the processes can be performed by the planar process, which is excellent in mass productivity. Further, there is an advantage that element isolation is complete even when a plurality of elements are formed and the elements are multi-layered. However, a silicon layer epitaxially grown on the sapphire substrate 11
Since 12 is usually as thin as 1 μm or less, the wiring resistance of the source / drain regions 13 and 14 is particularly high, which causes a decrease in sensitivity.

Furthermore, in FIG. 7, the main surface of the p-type silicon substrate 21 is
N ⁺ type source and drain regions 22 and 23 are formed, and an insulating film 24 such as a silicon nitride film or a silicon oxide film to be a gate insulating film and a protective film is formed on the main surface of the substrate 21. A channel region 25 is formed between the source / drain regions 22 and 23. The source / drain regions 22, 23, the channel region 25 and the insulating film 24 constitute a gate portion of the field effect transistor. Source and drain regions of the insulating film 24
Corresponding portions on the layers 22 and 23 are selectively etched, metal films 26 and 27 connected to the source and drain regions 22 and 23 are vapor-deposited, and lead wires 28 and 29 are formed on the metal films 26 and 27.
Are connected. In the chemical sensor having such a structure, a part of the measuring tube 30 is cut out, and the resin film 31 for bonding is used to bond the metal films 26, 27 and the lead wires 28, 29 in a state of being covered, and the tube 30 is bonded. Measurement is performed by immersing the gate portion in the solution inside.

Such a chemical sensor can perform all processes in a planar process and is excellent in mass productivity. However, the lead wires 28 and 29 may be cut or peeled off from the metal films 26 and 27 during the resin curing during manufacturing. In addition, during use, the resin 31 on the same surface as the detection surface is often immersed in the solution and swells, and the insulation is often impaired.

Further, as a problem common to the above-mentioned three methods, after forming a passivation film, it is necessary to partially etch it to form source and drain contact openings, so that a material that is difficult to etch as a passivation film is used. There is a point that can not be used. The silicon nitride film that is usually used as a passivation film can be easily etched by the reactive ion etching method or the like.
The passivation property and the ion sensitivity property are not always satisfactory. Therefore, it is desirable to form a film of Al ₂ O ₃ , Ta ₂ O ₅ or the like, which is excellent in these characteristics, but since these films are difficult to etch, it is necessary to mask the contact portion. In this case, a vapor deposition method that allows low temperature treatment is generally used, but the film characteristics are poor. On the other hand, the CVD method can obtain a film with good characteristics, but since it is a high-temperature treatment, there is often no suitable material as a masking material.

[Object of the Invention]

The present invention has been made to solve the above-mentioned drawbacks, can be manufactured by a planar process, is excellent in mass productivity, does not cause problems due to wiring resistance and resin swelling, and can use an arbitrary passivation film. The present invention aims to provide a chemical sensor that can be used.

[Outline of Invention]

The chemical sensor of the present invention comprises: a first and a second semiconductor substrate directly bonded via an insulating film; and a first semiconductor substrate formed over the entire thickness of the first and second semiconductor substrates separated from each other.
A source / drain region having a conductivity type opposite to that of the semiconductor substrate and a second semiconductor substrate, and a channel region between the source / drain region formed in the first semiconductor substrate and a part of the source / drain region. A groove formed so as to be exposed, a gate insulating film formed on the surface of the source, drain region, and channel region exposed in the groove and on the surface opposite to the inner surface of the groove and the bonding surface of the second semiconductor substrate; An insulating film serving as a passivation film, an insulating film covering an exposed surface other than the bonding surface of the first semiconductor substrate, and an opening provided in the insulating film on the surface opposite to the bonding surface of the first semiconductor substrate. It is characterized by comprising electrodes connected to the source and drain regions respectively.

In such a chemical sensor, after the first and second semiconductor substrates are directly bonded via an insulating film, all the processes are performed by a planar process, and the first semiconductor substrate on which elements are formed is covered with the insulating film. Since it can be a broken structure,
Excellent mass productivity. Further, unlike the case of the chemical sensor having the SOS structure, the film thickness of the first semiconductor substrate on which the source / drain regions are formed can be increased, so that the sensitivity is not deteriorated due to the increase of the wiring resistance. Moreover,
Since the elements are separated from each other by the dielectric, it is easy to form a multi-element, and in addition to the detection element, it is easy to form a temperature detection element, an amplification / arithmetic processing element / circuit, and the like. Further, since the gate portion and the contact portion are on opposite surfaces, it is not necessary to bring the contact portion into contact with the solution,
As a matter of course, the insulation failure due to the swelling of the resin does not occur. Furthermore,
Since the gate part and the contact part are on the opposite sides, a passivation film can be formed independently on the gate side,
Subsequent steps such as contact hole drilling become unnecessary.
Therefore, the surface of the gate portion is not restricted by etching processability and the like, and it is possible to form a passivation film using any material that focuses on water resistance when immersed in the test liquid, ion sensitivity, and the like. On the other hand, since the contact portion is sufficient in passivation characteristic that does not come into contact with normal water, a film made of a material in consideration of etching processability may be formed, so that the sensitivity characteristic and the like can be further improved. Further, unlike the case where the gate portion and the contact portion are on the same surface, when performing resin molding on the contact portion, it is not necessary to provide a predetermined space for exposing the gate portion, which is suitable for high integration of future devices. Can also respond.

The following method is used to manufacture the chemical sensor of the present invention. First, the first semiconductor substrate and the second
The method of directly joining the semiconductor substrate of 1) through the insulating film is as follows. First, two silicon wafers are mirror-polished to have a surface roughness of 500 Å or less, preferably 50 Å
Below. Next, standard washing with an organic solvent, hydrogen peroxide solution + sulfuric acid, aqua regia boil, hydrofluoric acid, etc. is performed while appropriately washing with water. Subsequently, at least one of the wafers is thermally oxidized to form an insulating film (oxide film) on the surface.
To form. After that, the wafer is washed again with hydrogen peroxide solution + sulfuric acid and aqua regia while performing appropriate washing with water. Then, the insulating film on the bonding surface is washed with clean water for about several minutes, and dehydration treatment such as spinner treatment is performed at room temperature. This treatment step is intended to remove excess water by leaving the water assumed to be adsorbed on the insulating film as it is. avoid. After these processes, the silicon wafer on which the insulating film is formed is placed in, for example, a clean air atmosphere of class 1 or less, and is adhered and bonded to each other without any foreign matter therebetween. It should be noted that, in the state of being joined in this way, 200 ° C or higher, preferably 1000
Bonding strength is 100kg / cm by heat treatment at ~ 1200 ℃
It can be increased to ² or more.

Next, in a state where they are separated from each other in the first semiconductor substrate,
The following two methods are conceivable as methods for forming the source and drain regions over the entire film thickness. After directly bonding the first and second semiconductor substrates via the insulating film as described above, the first semiconductor substrate is lapped from the surface opposite to the bonding surface to a thickness allowing impurity diffusion, Then, impurities are selectively diffused from a surface opposite to the bonding surface to a part of the first semiconductor substrate until reaching the bonding surface side to form source and drain regions. Alternatively, a diffusion layer serving as a source / drain region is formed in advance on the bonding surface side of the first semiconductor substrate, and the second semiconductor substrate is directly bonded via an insulating film, and then the first semiconductor substrate is bonded. Etching is performed from the surface opposite to the surface until the diffusion layer is exposed. Note that methods other than these may be used.

Further, in order to form a groove penetrating the second semiconductor substrate and exposing a part of the channel region and the source / drain region formed between the source / drain regions in the first semiconductor substrate, A mask material is formed on the surface of the semiconductor substrate opposite to the bonding surface, and the second semiconductor substrate is etched to the bonding surface. This etching is preferably performed by an anisotropic etching method, but other etching methods may be used.

Example of Invention

An embodiment of the present invention will be described below along with the manufacturing method shown in FIGS. 1 (a) to 1 (g).

First, each has a diameter of 3 inches, a specific resistance of 10 Ω · cm, and a thickness of 40.
A first silicon substrate 41 and a second silicon substrate 42 having a 0 μm, p-type and surface crystal orientation (100) are prepared, and the surface roughness of each of these silicon substrates 41 and 42 is 50 Å or less. Polished. Next, while performing appropriate washing with water, washing was carried out by an ordinary standard process using an organic solvent, hydrogen peroxide solution + sulfuric acid, aqua regia boil, hydrofluoric acid aqueous solution and the like. Then, both silicon substrates 41 and 42 were oxidized in high temperature steam to form an oxide film 43 having a film thickness of about 1 μm on each surface. Continuing,
While appropriately washing with water, both silicon substrates 41 and 42 were washed again with hydrogen peroxide and aqua regia, and further thoroughly washed with deionized water for several minutes or more to treat the surfaces. After this,
The surfaces to be joined should be overlapped and placed in an electric furnace in air,
It heat-processed at 1100 degreeC for 2 hours, and joined. Subsequently, the unnecessary oxide film 43 was removed (shown in FIG. 1 (a)).

Then, the first silicon substrate 41 was lapped from the surface opposite to the bonding surface until the thickness became 10 μm, and mirror-finished (shown in FIG. 2B). Then, the first silicon substrate
An oxide film 44 serving as an etching mask was formed on each of the surfaces of the 41 and the second silicon substrate 42 on the opposite side to the bonding surface.
Subsequently, a part of the first silicon substrate 41 is etched by using an anisotropic etchant EPW (mixed solution of ethylenediamine-pyrocatechol-water), and second
A groove 45 is formed by etching a part of the silicon substrate 42 until the oxide film 43 on the bonding surface is exposed. When the above etchant was used, the etching proceeded along the (111) plane, and the etched surface became an inclined surface. In this case, the opening on the joint surface side of the groove 45 was designed to be a square with a side of 300 μm. (The same figure (c) is shown).

Then, an oxide film 46 serving as a diffusion mask was formed on a part of the first silicon substrate 41 and the exposed surface of the second silicon substrate 42. Subsequently, phosphorus is diffused from the opening of the oxide film 46 formed on the surface of the first silicon substrate 41 to reach the junction surface, and n ⁺ type source and drain regions 47 separated from each other are formed.
48 formed. A region sandwiched between these source / drain regions 47 and 48 becomes a channel region 49. A part of the channel region 49 and the source / drain regions 47, 48 is formed so as to be exposed in the groove 45 on the bonding surface side of the first silicon substrate 41 (shown in FIG. 3D). Then, an oxide film 50 serving as a diffusion mask was formed on a part of the first silicon substrate 41 and the exposed surface of the second silicon substrate 42. Subsequently, boron was diffused to form ap ⁺ type channel stopper region 51 on the surface of the first silicon substrate 41 opposite to the bonding surface (shown in FIG. 7E).

Next, the oxide film formed on the gate portion and the inner surface of the groove 45.
After selectively removing a part of 50, a gate oxide film 52 having a film thickness of 800 Å is formed, and a silicon nitride film 53 having a film thickness of 800 Å to be a passivation film is further deposited on the entire surface by the LPCVD method. ) Illustration). Then, the first silicon substrate 41
Part of the corresponding silicon nitride film 53 and oxide film 50 on the source / drain regions 47 and 48 on the surface opposite to the junction surface were selectively etched to open contact holes. Subsequently, Cr and Au were sequentially deposited on the entire surface and then patterned to form contact pads 54 and 55. Subsequently, in this state, each element was cut out from the wafer using a dicer. In addition, the contact pads 54 and 55 have lead wires respectively.
56 and 57 were connected to manufacture a chemical sensor (shown in FIG.

As shown in FIG. 2, this chemical sensor is mounted by cutting a part of a flow cell 58 and sealing it with a resin 59, and measuring a specific ion in a solution flowing in the flow cell 58.

Such a chemical sensor includes a first silicon substrate and a second silicon substrate.
After directly bonding 41 and 42 via the oxide film 43, all the processes are performed by a planar process to form a dielectric isolation structure in which the first silicon substrate 41 on which elements are formed is covered with an insulating film. Therefore, it is excellent in mass productivity.

Further, unlike the case of the chemical sensor having the SOS structure shown in FIG. 6, the film thickness of the first silicon substrate 41 on which the source / drain regions 47 and 48 are formed is large (in the above embodiment, the film thickness after lapping is 10 μm), there is no reduction in sensitivity due to an increase in wiring resistance. Moreover, since the elements are separated from each other by dielectric, it is easy to make multiple devices,
In addition to the detection element, it is easy to form a temperature detection element, an amplification / arithmetic processing element / circuit, and the like. It should be noted that the cost can be reduced because an epitaxial growth apparatus is not required and expensive sapphire or the like is not required.

Further, since the gate portion and the contact portion are on the opposite sides of each other and the contact portion does not have to be brought into contact with the solution, naturally, insulation failure due to swelling of the resin does not occur. Similarly, the gate portion and the contact portion are on the opposite surfaces, not the silicon nitride film 53 as in the above embodiment,
It is also possible to form a passivation film, such as Al ₂ O ₃ or Ta ₂ O _5, which has good passivation characteristics and ion sensitivity characteristics but is difficult to etch, only on the surface of the gate portion, while considering the etching characteristics at the contact portion. Since the passivation film may be formed, the sensitivity characteristics and the like can be further improved. Unlike the case where the gate step and the contact portion are on the same surface, the surface of the gate portion does not need to be resin-molded at all, and the entire surface of the contact portion can be resin-molded. Therefore, it is not necessary to provide a predetermined space to expose the gate portion as in the conventional case, and when the detection element is multi-elemented, a temperature detection element other than the detection element, an amplification / arithmetic processing element / circuit, etc. Since the elements can be formed with the shortest distance therebetween even when the element is formed, it is possible to cope with the future high integration of the element.

Furthermore, as shown in FIG. 2, since the method is implemented along the wall surface of the flow cell, the flow path resistance can be reduced.

Actually, as shown in FIG. 2, the pH response characteristic was measured by a source follower circuit using a saturated calomel electrode as a reference electrode, and a linear response of about 58 mV / pH was shown at pH 2 to 11, and The drift was also good.

The chemical sensor of the present invention can have selectivity not only for hydrogen ions (pH) as described above but also for other ions by forming various sensitive films on the gate portion. In the chemical sensor of the present invention, these sensitive films are formed in the groove, so that the adhesive strength of the sensitive film can be improved. That is, these sensitive films are often made of an organic material, are generally difficult to adhere to the surface of the inorganic material of the device, and are swelled in an aqueous solution. Therefore, when applied to a chemical sensor having a planar structure, the sensitive film is easily peeled off, and the durability of the element is often determined by the peeling of the sensitive film. On the other hand, in the structure in which the sensitive film is formed in the groove as in the chemical sensor of the present invention, the contact area with the sensitive film is large, and when the sensitive film swells, the force that presses it against the substrate facing the groove. Does not easily peel off the sensitive film.

Actually, as a chemical sensor using a sensitive film, a K ⁺ sensor using a valinomycin-containing PVC film, a Na ⁺ sensor using a crown ether-containing PVC film, and a Cl ⁻ sensor using a quaternary ammonium salt-containing PVC film Was manufactured. We investigated the characteristics of these chemical sensors and found that K ⁺ and Na ⁺ contained 10 ^-1 to 10 ^-5 mol.
In / range, also Cl ^- in the 10 ^-1 to 10 ^-4 mol / range,
Each showed a linear response of about 50 mV / pX. Further, when the Na ⁺ sensor having the structure of the present invention and the conventional planar type structure were respectively immersed in an aqueous solution and the time-dependent change in the output was examined, as shown in FIG. It was confirmed that stable output was obtained, the adhesiveness of the sensitive film was improved, and the life was long.

As shown in FIG. 4, an insulating film formed on the surface of the second silicon substrate 42 opposite to the bonding surface (for example, an oxide film serving as an etching mask and a nitride film serving as a passivation film formed thereafter). A peeling strength of the sensitive film 60 can be further improved by forming a silicon film) on the groove 45 so as to project upward.

As the sensitive membrane, in addition to the ion sensitive membrane described above, an enzyme membrane or a microbial membrane sensitive to glucose, urea, penicillin and the like may be used.

Further, the outside of the groove may be covered with a gas permeable film, and the inside of the groove may be filled with an electrolyte solution or gel to be used as a gas sensor for CO ₂ or the like.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to manufacture by a planar process, is excellent in mass productivity, does not cause a problem due to wiring resistance or resin swelling, and can use an arbitrary passivation film. It is possible to provide a chemical sensor which has a good sensitivity, has a wide application range, and has a long life.

[Brief description of drawings]

1 (a) to 1 (g) are cross-sectional views showing a manufacturing process for obtaining a chemical sensor in an embodiment of the present invention, FIG. 2 is a cross-sectional view showing a usage state of the chemical sensor, and FIG. examples and characteristic diagram showing changes with time of the output obtained by the conventional Na ⁺ sensor, Figure 4 is a sectional view of a chemical sensor according to another embodiment of the present invention, FIG. 5 (a) is a plan of a conventional chemical sensor FIG. 6B is a sectional view taken along the line VV ′ of FIG. 6A, FIG. 6A is a plan view of another conventional chemical sensor, and FIG. Sectional view taken along line VI-VI 'in a), No. 7.
The figure is a cross-sectional view showing a usage state of another conventional chemical sensor. 41 …… first silicon substrate, 42 …… second silicon substrate, 43,44,46,50 …… oxide film, 45 …… groove, 47,48 ……
n ⁺ type source / drain region, 49 …… channel region, 51…
... Channel stopper region, 52 ... Gate oxide film, 53 ...
… Silicon nitride film, 54, 55 …… Contact pad, 56,
57 …… Lead wire, 58 …… Flow cell, 59 …… Resin, 60…
… Sensitive membrane.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location 7363-2J G01N 27/30 301 W 9054-4M H01L 29/78 301 U

Claims (6)

[Claims] 1. A first semiconductor substrate and a second semiconductor substrate which are directly bonded to each other via an insulating film, and a first semiconductor substrate which is separated from the first semiconductor substrate and formed over the entire thickness thereof. A channel region between the source and drain regions of the opposite conductivity type, which penetrates the second semiconductor substrate and the source and drain regions, and a part of the source and drain regions are exposed. The gate insulating film and the passivation film are formed on the formed groove and the surfaces of the source, drain region and channel region exposed in the groove, and the inner surface of the second semiconductor substrate and the surface opposite to the bonding surface. The insulating film, the insulating film that covers the exposed surface other than the bonding surface of the first semiconductor substrate, and the source through the opening provided in the insulating film on the surface opposite to the bonding surface of the first semiconductor substrate, Drain region Chemical sensor characterized by comprising a respective connecting electrodes. 2. The chemical sensor according to claim 1, wherein a sensitive film is formed in the groove. 3. A second member so as to project like a canopy into the groove.
Form an insulating film on the surface opposite to the bonding surface of the semiconductor substrate,
The chemical sensor according to claim 2, wherein a sensitive film is formed in the groove. 4. The chemical sensor according to claim 1, wherein the first semiconductor substrate is divided into a plurality of island-shaped semiconductor layers. 5. A diode or transistor for temperature detection or an element or circuit for amplification / arithmetic processing is formed on the first semiconductor substrate or a semiconductor layer obtained by dividing the first semiconductor substrate. Alternatively, the chemical sensor according to item 4. 6. A silicon nitride film as a passivation film,
The chemical sensor according to claim 1, wherein at least one of silicon oxide, alumina oxide, tantalum oxide, titanium oxide, zirconium oxide, niobium oxide, and hafnium oxide is used.