JPS6258456B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to an electrical resistance type humidity sensor that enables highly accurate detection and a method for manufacturing the same.

Conventionally, various mechanical and electrical resistance sensors have been used to measure relative humidity. Electrical resistance humidity sensors have a relatively fast response speed, a compact structure, and are superior to mechanical humidity sensors in terms of adaptability. A typical example is a humidity sensor that has a surface layer whose electrical resistance changes depending on the ambient humidity, such as the one described in Japanese Patent Publication No. 54-26913, which has a thin layer of sulfonated polyethylene as a moisture-sensitive layer. be.

Conventional electrical resistance humidity sensors measure the change in electrical resistance between a pair of thin electrodes that are placed in close contact with the moisture-sensitive layer while maintaining a distance from each other, but generally the electrical resistance of the moisture-sensitive layer is very low. Attempts have been made to reduce the electrical resistance value of the humidity sensor by increasing the facing area of the electrodes or by reducing the distance between the electrodes. The reason for reducing the electrical resistance value of the humidity sensor is as follows. In other words, if the electrical resistance value is large, the measurement circuit for the humidity sensor output becomes complicated, and moreover, it is susceptible to external noise and leakage resistance, making it difficult to detect the sensor output with high accuracy.

An example of a conventional electrical resistance type humidity sensor is shown in FIG. A is a plan view, b is a sectional view taken along line A-A' of a, and c is an equivalent circuit diagram of the humidity sensor. In FIG. 1A, 4 and 5 are a pair of electrodes made of polysilicon, and 7 and 8 are external lead electrodes of the polysilicon electrodes 4 and 5. In FIG. In b, 1 is a silicon wafer, 2 is a silicon oxide (SiO ₂ ) layer formed on the silicon wafer 1, and this silicon oxide layer has an electrical insulation function. 3 is a silicon nitride (Si ₃ N ₄ ) layer formed on the silicon oxide layer 2 . The electrodes 4 and 5 are formed of polysilicon implanted with phosphorus or boron ions formed on the silicon nitride layer 3, and form interlocking comb shapes. The electrodes 7 and 8 are made of, for example, titanium (Ti), palladium (Pd), gold (Au), or the like. 6 in b
A moisture-sensitive material coated across the comb-shaped electrodes 4 and 5, typically polyvinyl alcohol containing lithium chloride, sulfonated polystyrene, or the like. The equivalent circuit of such an electrical resistance type humidity sensor is represented by C. The resistance of the moisture sensitive material 6 is connected in series with the comb-shaped electrodes 4 and 5. 6 has a sensitive effect on humidity.

FIG. 2 shows the resistance change characteristics of the electrical resistance type humidity sensor shown in FIG. 1 with respect to relative humidity. In B, it is possible to detect relative humidity up to 100%, but as mentioned above, the electrical resistance of the humidity-sensitive layer is extremely high and it is susceptible to external noise and leakage resistance. Therefore,
For high-precision, high-sensitivity detection, the input impedance of the circuit must also be high, which imposes restrictions on the circuit configuration. B is a case where a different moisture-sensitive material is used and the resistance of the moisture-sensitive material is lowered, but at this time, as shown in the figure, between 60% and 100% relative humidity, the resistance of the moisture-sensitive material is greater than the total electrode resistance. This results in a dead zone A. Therefore, if a low-resistance moisture-sensitive material is used, the resistance of the moisture-sensitive material for all relative humidity cannot be lower than the total resistance of the polysilicon electrode shown by the broken line B.

Based on the above, it is possible to further lower the resistance of the polysilicon electrode in order to lower the resistance value of the moisture-sensitive material, but when forming the polysilicon electrode by ion implantation, there is a limit to the amount of ion implantation, so the sheet resistance can be reduced. There is a limit (usually 30Ω/□
).

Further, in the conventional example, only the sensor is constructed on a silicon substrate, which has disadvantages such as poor area efficiency and high cost of the sensor.

An object of the present invention is to obtain an electrical resistance type humidity sensor that can reduce electrode resistance and improve area efficiency.

The first feature of the present invention is that the electrode is formed with a conductive film (molybdenum or tungsten) lower than the sheet resistance of polysilicon, and this conductive film is covered with water-resistant and chemically stable polysilicon. The purpose is to reduce the total resistance of the electrode by forming the electrode in parallel with a conductive film and polysilicon.

A second feature of the present invention is that a humidity sensor and a driving circuit for this sensor are formed on the same silicon substrate, thereby improving area efficiency.

Embodiments of the present invention will be described below based on the drawings. FIG. 3 shows the structure of the electrical resistance type humidity sensor according to the present invention. Figure 3 a is a plan view, b is A-
It is a sectional view taken along line A'. In these figures, 11 is a silicon wafer, and a first insulating layer 12 made of silicon oxide is formed on the silicon wafer 11. Further, a second insulating layer 13 made of silicon nitride is formed on the first insulating layer 12, and a second insulating layer 13 is formed of silicon nitride.
Electrodes 14 and 15 made of molybdenum (Mo) or tungsten (W) are alternately arranged on the insulating layer 13 in a comb shape. Furthermore, electrodes 14, 15
Comb-shaped polysilicon electrodes 16 and 17 into which phosphorus ions or boron ions are implanted are formed on the top.
The ends of these comb-shaped electrodes 14, 15, 16, 17 are connected with connection terminals 1 made of titanium, palladium, gold, etc.
8 and 19 are formed.

Further, the comb-shaped electrodes 14, 15, 16, 17
is a moisture-sensitive material 2 whose resistance value changes depending on the surrounding humidity.
covered with 0.

Next, the manufacturing process of the electrical resistance type humidity sensor shown in FIG. 3 will be explained based on FIG. 4.

First, an n-type silicon wafer 1 with a specific resistance of about 10Ωcm
1, an oxide film 12 with a thickness of several hundred Å is formed by thermal oxidation (A). Next, a silicon nitride layer 13 with a thickness of several hundred Å is formed by chemical vapor deposition (hereinafter abbreviated as CVD method).
form (B). Here, silicon nitride is a material suitable for humidity sensors because it is a good electrical insulator and also has good water resistance. Next, molybdenum or tungsten with a thickness of several thousand Å to several μm is deposited as a conductive film, and the electrode 1 is etched using a known photoetching method.
Remove molybdenum or tungsten other than 4 and 15 (C). After that, polysilicon with a thickness of several hundred angstroms is formed by the CVD method as described above, boron or phosphorus ions are implanted into this polysilicon to reduce the electrical resistance, and the polysilicon electrode 1 is formed by photoetching.
Form 6, 17 (D). Here, polysilicon is suitable for electrodes of humidity sensors because its specific resistance can be reduced by implanting boron or phosphorus ions, and it is also water resistant and chemically stable. Next, electrodes 18 and 19 as shown in FIG. 3 are formed by vapor deposition using a mask using titanium, panadium, gold, etc., as external terminals used for displaying the detected amount, etc. Thereafter, each chip is cut out, mounted in a package, and external connection terminals and leads are attached.Finally, a moisture sensitive material 20 is applied to complete the humidity sensor (E).

Here, the electrode material of the humidity sensor must not be corroded by the environment in which it is used. Materials that have low resistance and satisfy the above conditions include gold, platinum (Pt), etc. in addition to those used in this embodiment, but these have problems in terms of cost. Note that if the humidity sensor electrode is made of aluminum (Al), the polysilicon on it is formed at a relatively high temperature, so the aluminum will diffuse during heat treatment and cause defects. Problems arise such as easy melting and cutting. For the same reason, the electrode terminals are made of vapor-deposited layers of titanium, panadium, and gold, and aluminum is not used.

Further, in this embodiment, if the resistance value of the moisture sensitive material is low, it may be possible that ion implantation may not be performed on the polysilicon provided on the conductive film.

In other words, even if the resistance of polysilicon is high, the distance of the polysilicon part is short and wide, so the structure of the humidity sensor is equivalently composed of a moisture sensitive material and an electrode made of a conductive film. The impact is negligible.

With the structure described above, a humidity sensor with long-term stability can be obtained.

Next, the effects of this embodiment will be described. An equivalent circuit of the electrode structure of the present invention is shown in FIG. If the resistance of polysilicon and the resistance of the conductive material are R _pply - _si and R _M respectively, the total resistance of the electrode part is It is expressed as R _M /R _pply - _si is usually <<1, and R _M is on the order of several tens of mΩ, so
Compared to conventional polysilicon electrode resistance (>100Ω), an electrode resistance of less than two orders of magnitude can be obtained. Therefore, it is possible to reduce the resistance change of the moisture sensitive material by more than two orders of magnitude, and the influence of external noise and leakage resistance can be reduced.

Next, another embodiment for improving the chip area efficiency will be described with reference to FIGS. 6 and 7.

Figure 6 shows a cross-sectional structure based on CMOS (complementary type) in which a humidity sensor is formed on the surface of a MOS/IC. In Figure 6, 1
1 is a silicon wafer, in which a buried layer 51 for element isolation is formed, and further diffusion layers 56, 5 for driving MOS/IC.
8 and a gate electrode 54 are formed.
Further, on the surface on which the element is formed, a conductive film 60 made of molybdenum or the like, a phosphorous glass layer 61 as an interlayer insulating film, a silicon nitride layer 62, a molybdenum or tungsten electrode 63, a polysilicon electrode 64, a Wet material 67 is sequentially formed. Formed around the wafer 11 are electrodes 65 for connection to external terminals used for displaying detected amounts, electrodes 66 for connection to an external power source for driving the elements, and the like.

In such an element structure, the resistance change of the humidity sensor is input to the gate electrode 54, calculated internally, and taken out to the outside via the external connection terminal 65.

Next, the manufacturing process of the humidity sensor shown in FIG. 6 will be explained using FIG. 7. The drive circuit part is normal
Manufactured using almost the same method as MOS/IC manufacturing process. In this embodiment, a CMOS (complementary type) case will be described.

First, as in the previous example, an n with a specific resistance of about 10 Ω-cm
After forming an oxide film 50 with a thickness of several thousand angstroms on the wafer surface by thermal oxidation on the mold silicon wafer 11, a photoresist 100 is applied on the surface of the oxide film 50, and unnecessary oxide film is removed by a known photoetching method. (A). Next, a photoresist film 100 and an oxide film 5
After boron ion implantation is performed using 0 as a mask and the resist film is removed, a p-type buried layer 51 is formed by a diffusion method (B). Thereafter, a silicon nitride layer 52 of several thousand angstroms is formed on the surface of the oxide film 50, and unnecessary portions of the silicon nitride are removed by photoetching (C). Next, a local oxide film L _pcps ) 53 is formed by thermal oxidation for the purpose of forming a field oxide film and alleviating the step difference in the surface portion, and then the silicon nitride is removed (D). After that, the wafer is cleaned, a gate oxide film of several hundred Å is formed, and then a polysilicon layer of several thousand Å is formed by CVD, and this polysilicon layer is diffused using phosphorus as an impurity source to reduce electrical resistance. Then, unnecessary polysilicon is removed by photoetching to form a gate electrode 54 (E). next,
An oxide film 55 of several thousand angstroms is formed by the CVD method, unnecessary oxide film is removed by a photoetching method, and then a p-type layer 56 is formed by a diffusion method using boron as an impurity source (F). After that, the boron glass film formed on the surface and the oxide film 55 formed by the CVD method are all removed, and the oxide film 55 of several thousand Å thick is removed again by the CVD method.
After forming 7, an unnecessary oxide film is removed by photoetching, and an n-type layer 58 is formed in the p-type buried layer 51 by a diffusion method using phosphorus as an impurity source (G).
Next, after removing all the phosphorous glass film formed on the surface and the oxide film 57 formed by the CVD method, a thermal oxide film 59 of several hundred angstroms is formed, and the unnecessary oxide film is removed by the photoetching method (H). . Thereafter, a wiring molybdenum layer 60 having a thickness of several hundred to several thousand angstroms is formed by vapor deposition, and unnecessary molybdenum is removed by photoetching. Further, unnecessary oxide films are removed (I).
Next, a phosphorus glass layer 61 (PSG) of several thousand angstroms is formed as an interlayer insulating film using a mixed gas of phosphine (PH ₃ ), monosilane (SiH ₄ ), and oxygen (O ₂ ), and unnecessary phosphorus is removed by photo-etching. After removing the glass, heat treatment is continued in a nitrogen (N ₂ ) atmosphere (J).

Next, the sensor portion is formed by forming a silicon nitride layer 62, a molybdenum or tungsten electrode 63, a polysilicon electrode 64, titanium, panadium, gold electrodes 65, 66, and a moisture sensitive material 67, as in the previous embodiment.
are formed one after another to complete the humidity sensor (K)
(L).

According to this embodiment using the above manufacturing method, the sensor portion and the drive circuit can be integrated in the same chip, so that area efficiency can be improved, and the sensor can be miniaturized and costs can be reduced.

The electrode structure of the present invention can be applied to devices that detect resistance changes in a sensor portion in response to physical changes.

In addition, in this embodiment, the case where the structure of the drive circuit part is formed of CMOS shown in FIGS. 6 and 7 has been described, but this is not limited to this embodiment.
Of course, even if the drive circuit portion is configured with a single channel such as NMOS or PMOS, it is within the scope of the present invention.

According to the present invention, since electrode resistance can be reduced and area efficiency can be improved, a highly accurate and highly sensitive electrical resistance humidity sensor can be obtained.

[Brief explanation of the drawing]

Figure 1 shows the structure of a conventional electrical resistance humidity sensor, where a is a plan view, b is a sectional view taken along line A-A' of a, c is an equivalent circuit diagram of the electrode structure, and Figure 2 is a conventional relative humidity sensor. A graph showing changes in electrical resistance with respect to humidity, FIG. 3 shows the structure of an electrical resistance type humidity sensor according to the present invention, a is a plan view, b is a cross-sectional view taken along line A-A' of a, and FIG. 5 is an equivalent circuit diagram of an electrode structure, FIG. 6 is a sectional view of another embodiment according to the present invention, and FIG. 7 is a diagram showing the manufacturing process. 11... Silicon wafer, 12... First insulating layer,
13... Second insulating layer, 14, 15... Electrode (metal), 16, 17... Electrode (polysilicon).

Claims (1)

[Claims] 1. An electrical insulating layer made of a semiconductor oxide and a semiconductor nitride is provided on a semiconductor wafer, a comb-shaped electrode is formed using a metal conductive film on the electrical insulating layer, and a comb-shaped electrode is formed on the metal electrode. is covered with a polycrystalline semiconductor implanted with phosphorus ions or boron ions, and a pair of interdigitated electrodes with a narrow gap are provided in a state of engagement with each other, and the interdigitated electrodes are formed into a moisture-sensitive material whose resistance changes depending on the surrounding humidity. An electrical resistance type humidity sensor characterized by being coated with a material. 2. An electrical resistance humidity sensor according to claim 1, characterized in that an integrated circuit is formed within a semiconductor wafer. 3. A step of forming a silicon oxide layer on a silicon semiconductor wafer, a second step of forming a silicon nitride layer on the silicon oxide by chemical vapor deposition, and a step of forming a silicon nitride layer on the silicon nitride layer by vapor deposition. a third step of forming a conductive layer, a fourth step of removing unnecessary portions of the metal layer by etching to form a pair of electrodes, and depositing polysilicon on the metal layer by chemical vapor deposition. The fifth forming
a sixth step of implanting phosphorus ions or boron ions into the polysilicon layer; and a seventh step of removing unnecessary portions of the polysilicon layer by etching and covering the metal layer. A method of manufacturing a resistive humidity sensor.