JP2912896B1 - Method for manufacturing detection element of platinum resistance thermometer and detection element manufactured by the method - Google Patents

Abstract

A method of manufacturing a detection element of a platinum resistance thermometer and a detection element manufactured by the method are provided. SOLUTION: A groove 34 having a predetermined pattern is formed on a silicon substrate 31 by chemical etching using a silicon dioxide layer 32 as a mask. After removing the mask, the silicon substrate 31 is thermally oxidized, and a silicon dioxide layer 35 grows on the substrate including the grooves 34. This silicon dioxide layer 35 is divided into a rough surface portion of the groove 34 and a portion of the original polished substrate surface. Sputtered, platinum layer 36
Is deposited on the surface of the silicon dioxide layer 35 and the substrate 31 undergoes light polishing. The platinum layer 36 deposited on the substrate surface is easily removed due to low adhesiveness, but the platinum layer 36 deposited on the groove 34 is firmly attached and is not removed. Therefore, the platinum layer portion remaining in the groove 34 forms a pattern of the platinum circuit 37 substantially similar to the pattern of the groove 34. Further, post-processes such as heat treatment and wiring are performed to form a platinum resistance detecting element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a detecting element of a platinum resistance thermometer and a detecting element manufactured by the method.

[0002]

2. Description of the Related Art A resistance thermometer (RTD) measures temperature by relating the resistance of its "sensing element" to temperature. The RTD detecting element includes a circuit mainly composed of a metal or an alloy, and the resistance value of the metal or the alloy depends on the temperature. The resistance value of the detection element is almost directly proportional to the absolute temperature, and the proportionality constant is the temperature coefficient of resistance (TCR) of the RTD.
Is defined. That is, RTDs with high TCR values are more sensitive than those with low TCR values. As is well known, the higher the concentration of impurities in the metal or alloy constituting the circuit, the lower the TCR value.

[0003] Since platinum has chemical inertness and physical stability, it is considered to be an important resistance value and temperature measuring device. In addition, as a material of the detection element circuit, platinum has a high T
An RTD having a CR value and configured has an advantage of high sensitivity to a temperature change.

The resistance value of the platinum circuit is -200 to 10
Since the temperature is almost directly proportional to the absolute temperature in the range of 00 ° C., an accurate temperature can be easily obtained in the above temperature range. Therefore, many people are engaged in research on platinum resistance thermometers, and their use is wide. The specification of the platinum resistance thermometer mentioned above is J
IS C-1604, DIN 43760, and IEC
Pub. 751 etc., among which DIN 4376
0 is most widely adopted as a standard, and the TCR value of the platinum resistance thermometer is 3850 ppm (° C.) ⁻¹ .

[0005] Even in the same platinum circuit, its T
CR value is different. In detail, comparing the thin-film platinum circuit with the bulk platinum circuit, the former has a lower TCR value than the latter, which is the so-called "bulk effect". Therefore, the sensitivity of a platinum RTD with a bulk platinum circuit is better than a platinum RTD with a thin film platinum circuit.

However, the conventional platinum RTD is very expensive because platinum itself is expensive and the manufacturing cost of the platinum detecting element is high. Typically, a conventional platinum RTD is
It is manufactured by forming a circuit pattern of a platinum detecting element on the surface of the dielectric layer. The drawback is that pure platinum exhibits poor adhesion to most dielectric materials, and the platinum circuit pattern deposited on the surface of the dielectric substrate is easily separated from the surface. Although some dielectric materials have good adhesion to platinum, each has drawbacks. For example, a silicon substrate has the advantages that it is inexpensive, has good smoothness, and is easy to process.
Since the silicon alloy is formed during the high-temperature heat treatment, the characteristics of the detection element are adversely affected. Although silicon dioxide substrates are inexpensive, they cannot provide good adhesion to platinum. Alumina substrates are inexpensive, heat-resistant, and have excellent adhesion to platinum, but their uneven surfaces hinder the formation of fine patterns. This uneven surface can be smoothed by polishing, but polishing an alumina substrate having high hardness leads to a large increase in the cost of the substrate material. The sapphire substrate has the advantages of good heat resistance and smoothness and good adhesion to platinum, but has the disadvantage of being very expensive and difficult to cut into small chips. Thus, a typical platinum resistance thermometer is made by forming a platinum pattern on the surface of the dielectric material using special manufacturing processes and / or equipment, thereby increasing manufacturing costs.

To solve the above problem, a special platinum RTD is shown in US Pat. No. 4,129,848. As shown in FIG. 1A, the silicon dioxide layer 12 is grown on the upper surface of the substrate 11 by heating the substrate 11 in an environment containing oxygen. The exposed surface of the silicon dioxide layer 12 is roughened by sputter etching, thus extending down from the exposed surface, producing a plurality of microscopic holes that do not reach the substrate 11 (FIG. 1 (b)). Next, a platinum layer 13 is sputter deposited on the surface of the silicon dioxide layer 12 in a two step process. Due to the uneven interface between the silicon dioxide layer 12 and the platinum layer 13, the adhesion of the platinum layer 13 to the silicon dioxide layer 12 is improved (FIG. 1 (c)). Next, a quartz layer is deposited on the platinum layer 13 by sputtering and a photoresist mask for chemical etching is applied. The chemically etched quartz layer forms a quartz mask 14 having a positive pattern similar to the desired platinum circuit pattern (FIG. 1).
(D)). The exposed platinum layer 13 and a part of the crystal mask 14 are etched by sputter etching. As a result, platinum is formed in a predetermined pattern (that is, platinum circuit pattern 1).
5) Protected by crystal mask 14. Subsequently, the quartz mask 14 is removed, and subsequent procedures such as heat treatment proceed. However, the sputter etching procedure tends to introduce impurities, which blurs the resolution of the edges of the platinum pattern. That is, sputter etching of silicon dioxide deposits silicon dioxide molecules as impurities in the platinum, thus affecting the platinum structure and degrading edge resolution. Since the selectivity of the sputter etching procedure is poor,
The exposed surface of the silicon dioxide layer 12 will also be etched. As described above, since the introduced impurities lower the TCR value of the platinum detection element, a high-purity platinum circuit is required to maintain a high TCR value.

In a commercialized platinum resistance thermometer, a platinum circuit is generally arranged on the surface of a dielectric substrate such as alumina. This is due to the excellent adhesion of alumina to platinum. US Patent No. 4,805,296
Discloses a method of manufacturing a platinum resistance thermometer, in which a platinum layer is deposited by sputtering on an alumina film on the surface of a silicon substrate, and a platinum circuit pattern is also formed by sputter etching. However, etching the platinum film in the undesired area with a mask is
This causes a problem that a pattern having the required accuracy and uniformity cannot be obtained. Before the end of the etching procedure,
The mask layer tends to deteriorate and impurities tend to be introduced into the platinum. Accordingly, patents relating to most platinum resistance thermometers (eg, US Pat.
2,4103275, 4469717, 462790
2 and 4649364) describe only the processing conditions for platinum and the substrate, but do not show a detailed procedure for forming a platinum pattern.

A method of forming a platinum resistance thermometer without using a sputter etch mask is disclosed in US Pat.
9293, in which an alumina (or sapphire) substrate with excellent adhesion to platinum is used. As shown in FIG. 2A, a lifting medium (lift)
off medium), a silicon dioxide layer 22
Deposited on the upper surface of After the desired pass pattern is exposed on the photoresist and the photoresist is developed,
A photoresist pattern 24 is formed, thus leaving a strip pattern in the photoresist on top of the silicon dioxide layer 22 (FIG. 2 (b)). In the underlying silicon dioxide layer 22, a photoresist pattern 24
Unprotected areas are chemically etched, thus producing the desired puzz. That is, a positive pattern for depositing a platinum circuit pattern is formed on the upper surface of the substrate 21 (FIG. 2).
(C)). After the photoresist pattern 24 had been completely stripped from the remaining negative patterned silicon dioxide layer 22, the platinum deposition was ready (FIG. 2 (d)). Next, platinum is deposited by sputtering on the negatively patterned silicon dioxide layer 22 and the exposed surface of the substrate 21 to form a platinum layer 23 (FIG. 2 (e)). The thickness of the silicon dioxide layer 22 is at least 1.3 to 1.
5 times. Referring to FIG. 2F, a silicon dioxide layer 22 is formed.
An interconnecting step 23A on the side of the substrate connects the platinum layer on the silicon dioxide layer 22 to the platinum layer on the substrate 21. The deposition conditions are controlled so that this interconnecting step 23A has a porous thin film structure. Note that the interconnecting stage 23A is sufficiently porous to allow the etching solution to pass through the thin film. Next, hydrofluoric acid is introduced and the remaining portion of the silicon dioxide layer 22 between the substrate 21 and the platinum layer 23 is etched. After all of the silicon dioxide layer 22 has been etched, the portion of the platinum layer above the silicon dioxide layer can be mechanically separated from the portion of the platinum layer above the substrate 21 in the area of the interconnection step 23A. Since the platinum layer deposited on the substrate 21 is firmly bonded to the substrate surface, the platinum circuit pattern 25 of the resistance thermometer is
(FIG. 2 (g)). In the above procedure, appropriate materials and processing procedures are determined so as not to contaminate the platinum.

By the method disclosed in the aforementioned US Pat. No. 5,089,293, a platinum resistance thermometer having a predetermined platinum pattern and a pure platinum circuit can be obtained. However, since alumina and sapphire are used as the material of the substrate and their hardness is very high, it is difficult to treat alumina and sapphire themselves, and it is also difficult to perform subsequent steps and treatment. Also,
Etching the lift-off medium hindered through the porous platinum thin film requires special manufacturing procedures and equipment, which increases manufacturing costs.

[0011]

SUMMARY OF THE INVENTION From the above prior art, a batch production of platinum sensing elements with high purity platinum circuits using standard procedures and equipment commonly used in the semiconductor industry (ba).
If tch producing can be performed, the manufacturing cost of the platinum detecting element will be greatly reduced, and the price of the platinum detecting element will also be significantly reduced. When a silicon substrate is used, the platinum detection element and other integrated circuits can be made on a single chip, thus simplifying the assembly of the RTD,
The size is also reduced.

It is an object of the present invention to provide a method of manufacturing a detecting element of a platinum resistance thermometer by forming the detecting element on, for example, a silicon substrate by using materials and manufacturing procedures generally used in the semiconductor industry. Is to provide a way to Another object of the present invention is to provide a detection element of a platinum resistance thermometer manufactured by this method. This greatly reduces the manufacturing cost and the price of the configured platinum resistance thermometer.

In addition, a high-purity platinum circuit is formed so that the TCR value of the platinum resistance thermometer becomes high, and a detection element having a bulk platinum circuit is formed so that the sensitivity of the platinum resistance thermometer becomes high. This is also an object of the present invention.

[0014]

In the embodiment of the present invention, a silicon wafer is used as a substrate of a platinum resistance detecting element. First, grooves having a desired circuit pattern are formed on a silicon substrate by chemical etching using a silicon dioxide layer as a mask. Next, the mask is removed and the etched silicon substrate with the upper surface groove is thermally oxidized to grow a layer of silicon dioxide over the silicon substrate and the groove. The silicon dioxide layer can be divided into two parts: a concave part grown on the rough surface with the grooves recessed and a smooth part grown on the surface of the original polished substrate. Next, sputtering is performed and a platinum layer is deposited on the surface of the silicon dioxide layer. The substrate portion with the silicon dioxide layer on top and the substrate portion with the platinum layer on top are lightly polished. Since platinum has poor adhesion to the surface of the smooth silicon dioxide layer, the platinum layer deposited on the smooth portion of the silicon dioxide layer is easily removed from the silicon dioxide layer. On the other hand, the platinum layer deposited on the concave portion of the silicon dioxide layer adheres firmly to the silicon dioxide layer because of the groove, that is, the platinum layer has good adhesion to the rough surface of the concave portion. . The platinum layer portion in the groove forms a platinum circuit pattern substantially similar to the groove pattern. Next, after a subsequent procedure such as heat treatment and wiring is performed, a platinum resistance detecting element is formed.

By using a specific etching solution so that the cross section of the groove becomes V-shaped (referred to as V-shaped groove), platinum deposited in the V-shaped groove is spread uniformly on the surface of the groove. At the bottom of the groove. As a result, a platinum circuit having a substantially bulk structure is formed, so that the TCR value of the platinum resistance detecting element is increased, and the sensitivity of the platinum RTD is also improved.

The advantages of the platinum resistance detecting element according to the present invention will be described below. First, silicon substrates widely used in the semiconductor industry are fairly inexpensive, abundantly available, have excellent smoothness, are well studied, and can be easily processed. Next, the physical and chemical properties of the silicon are properly defined. It should be noted that all the equipment for manufacturing the platinum resistance detecting element according to the present invention is generally adopted in the semiconductor industry, and the manufacturing procedure is also a general procedure, so that both the equipment cost and the development cost are considerably reduced. Furthermore, since the platinum resistance detecting element having uniform quality can be mass-produced by batch production, the production cost is further reduced. Since the platinum circuit of the platinum resistance thermometer according to the present invention is not contaminated during the manufacturing process, the TCR value of the platinum RTD detecting element can be determined accurately, and batch fluctuation can be reduced considerably. In addition, a bulk platinum circuit can be obtained with a special groove structure, thereby further increasing the TCR value of the platinum resistance thermometer. Further, the present invention differs from the prior art in that the platinum circuit of the platinum resistance thermometer according to the present invention is arranged in a groove extending downward from the surface of the substrate, whereas the platinum resistance temperature according to the prior art is different. The point is that the platinum circuit of the meter is located above the surface of the substrate.
Therefore, the present invention can easily form a platinum circuit pattern by removing an undesired portion of the platinum layer by a mechanical method such as polishing, and the platinum circuit is protected by the groove structure.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIGS. 3A and 3B, first, a silicon dioxide layer 32 is formed on the surface of a silicon substrate 31. Next, a photoresist pattern 33 substantially similar to the negative pattern of the desired platinum circuit pattern
Is formed on the surface of the silicon dioxide layer 32. Using the photoresist pattern 33 as a mask, the photoresist pattern 3 in the silicon dioxide layer 32
Portions not protected by 3 are etched. Therefore, a contact hole is formed in the silicon dioxide layer 32, and a part of the surface of the silicon substrate 31 is exposed by the contact hole. After the etching has been performed, FIG.
As shown in (c), the exposed surface of the silicon substrate 31 is substantially similar to the desired platinum circuit pattern.

Next, the surface of the silicon substrate 31 is etched using the photoresist pattern 33 and the etched silicon dioxide layer 32 as a mask. A special etching solution (for example, a solution containing potassium hydroxide) is used so as to etch the silicon substrate 31 in a direction-dependent manner. Since the etching rate of this etching solution for (100) plane silicon is much higher than that for (111) plane silicon, V-grooves (grooves having a “V” cross section) are formed on the surface of the silicon substrate 31. (FIG. 3D). The reason for forming the V-groove using the direction-dependent etching procedure will be described later. Although the above-described groove has a V-shape as an example, it is not limited to this shape.
After the etching procedure is performed, the mask on the surface of the silicon substrate 31 is removed, and a silicon substrate having the V-shaped groove 34 is obtained (FIG. 3E). As shown in FIG. 4 which is a partially enlarged view of FIG. 3E, the surface of the silicon substrate 31 is divided into two parts, namely, a smooth surface 31A of the original silicon substrate 31 and a concave surface 31B of the V groove 34. Split. Since the concave surface 31B is formed by etching, the surface is rough.

Next, the etched silicon substrate 31
Is thermally oxidized by high-temperature oxygen in a heating furnace, so that a thermal oxide (silicon dioxide layer 35) grows on the surface as a dielectric layer (FIG. 3 (f)). Other than silicon dioxide, the dielectric layer may be formed of another dielectric material, for example, silicon nitride Si ₃ N ₄ . Subsequently, the silicon substrate 31 and the overlying silicon dioxide layer 35 are treated to remove impurities and platinum contamination is thereby minimized. The cross-section of the V-groove 34 is still "V" shaped. Next, as shown in FIG. 3 (g), platinum is deposited on the surface of the silicon dioxide layer 35 by sputtering to form a platinum layer 36. FIG. 5 is a partially enlarged view of FIG. 3G, and is a view showing a detailed structure of the platinum layer 36, the silicon dioxide layer 35, and the silicon substrate 31. As shown in FIG. 5, the silicon dioxide grown from the smooth surface 31A of the silicon substrate 31 is a smooth portion 35A.
On the other hand, the silicon dioxide grown from the rough concave surface 31B of the silicon substrate 31 is a rough concave surface 35B. The portion of the platinum layer 36 deposited on the smooth surface 35A becomes a flat thin film, while the portion of the platinum layer 36 deposited in the V-groove 34 is more evenly distributed over the concave surface 35B. Rather, they tend to accumulate at the bottom of the V-groove 34. The platinum layer 36 accumulated at the bottom of the V groove 34 has a substantially bulk structure.

Next, the platinum-coated silicon substrate 31
Undergoes light polishing. By choosing the appropriate slurry and polishing pad, the polished platinum will be free of contaminants. The portion of the platinum layer 36 above the smooth surface 35A adheres loosely to the silicon dioxide layer 35 and is easily scraped off because it is directly exposed to the slurry and polishing pad. On the other hand, the portion of the platinum layer 36 above the V-groove 34 adheres firmly to the concave surface 35B because the concave surface 35B has a rough surface, and is not directly exposed to the polishing pad because it is protected by the V-groove 34. . Therefore, even if the polishing is performed, it still adheres to the concave surface 35B. As shown in FIG. 6, by the process described above, the undesired portions of the platinum layer 36 can be easily removed from the substrate, and the remaining platinum layer (the portion adhering to the concave surface 35B), that is, the portion forming the platinum circuit 37. Is not contaminated. The pattern of the formed platinum circuit 37 is substantially the same as the pattern of the V groove 34, that is, the desired platinum circuit pattern. Since the platinum circuit 37 has a substantially bulk structure, the platinum resistance thermometer according to the present invention has a high TCR value and has excellent sensitivity.

FIG. 7 is an overall view of the platinum circuit of the platinum resistance thermometer according to the present embodiment. Referring to FIG.
At both ends are bonding pads 38 and a platinum circuit 37
Is connected to an external circuit through a bonding pad 38.

In addition to the advantages described above, the platinum resistance thermometer according to the present invention has a small size because a circuit is formed on a silicon substrate by a general integrated circuit technique, and therefore, the integration of the circuit is improved. I do.

Using a silicon substrate, the platinum resistance detecting element and other integrated circuits according to the present invention can be formed on a single chip. Further, the line width of the platinum wiring is reduced, and the cutting procedure is facilitated.

In addition, since the platinum circuit 37 is hidden in the V-groove 34, it is protected in subsequent procedures such as heat treatment and bonding.

[Brief description of the drawings]

1 (a) to 1 (e) are cross-sectional views in respective steps until a platinum circuit of a conventional platinum resistance thermometer is formed.

2 (a) to 2 (g) are cross-sectional views in respective steps until a platinum circuit of another conventional platinum resistance thermometer is formed.

3 (a) to 3 (h) are cross-sectional views in respective steps until a platinum circuit of a platinum resistance thermometer according to one embodiment of the present invention is formed.

FIG. 4 is a partially enlarged view of FIG. 3E, showing a rough surface of a V groove.

FIG. 5 is a partially enlarged view of FIG. 3 (g), showing a detailed structure of a platinum layer, a silicon dioxide layer and a substrate.

FIG. 6 is a partially enlarged view of FIG. 3 (h), showing a part of a cross section of the platinum circuit according to one embodiment of the present invention.

FIG. 7 is an overall perspective view of a platinum circuit of the platinum resistance thermometer according to one embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11 substrate 12 silicon dioxide layer 13 platinum layer 14 quartz mask 15 platinum circuit pattern 21 substrate 22 silicon dioxide layer 23 platinum layer 24 photoresist pattern 25 platinum circuit pattern 31 silicon substrate 32 silicon dioxide layer 33 photoresist pattern 34 V groove 35 Silicon dioxide layer 36 Platinum layer 37 Platinum circuit 38 Bonding pad

Claims (8)

(57) [Claims] 1. A method for manufacturing a sensing element of a platinum resistance thermometer, comprising: forming a mask having a pattern substantially similar to a negative pattern of a platinum circuit of the sensing element on a surface of a substrate; Etching the substrate such that a groove having a pattern substantially similar to the positive pattern of the platinum circuit of the detection element is formed on the surface of the substrate through the portion; and completely removing the mask from the substrate. Forming a dielectric layer on the surface of the substrate, the dielectric layer being divided into a first portion on the surface of the groove and a second portion on the other surface, and the first portion of the dielectric layer and the Depositing a platinum thin film with a first platinum layer and a second platinum layer, respectively, on the surface of the second portion of the dielectric layer; and removing the second platinum layer, the first platinum Forming the platinum circuit of the sensing element by polishing the substrate so that a layer adheres to the first portion of the dielectric layer. How to manufacture. 2. The method according to claim 1, wherein the substrate is a silicon substrate. 3. The method according to claim 2, wherein the dielectric layer is a silicon dioxide layer or a silicon nitride layer. 4. The method of claim 1, wherein a cross section of the groove is V-shaped. 5. A method for manufacturing a sensing element of a platinum resistance thermometer, comprising: forming a mask having a pattern substantially similar to a negative pattern of a platinum circuit of the sensing element on a surface of a dielectric substrate; Through the opening of the surface of the dielectric substrate,
Etching the dielectric substrate so as to form a groove having a pattern substantially similar to the positive pattern of the platinum circuit of the detection element; and completely removing the mask from the dielectric substrate. Depositing a platinum thin film with a first platinum layer and a second platinum layer on a first portion corresponding to the groove and a second portion, respectively, on the surface of the dielectric substrate; and removing the second platinum layer. Forming the platinum circuit of the detection element by polishing the dielectric substrate so that the first platinum layer adheres to the first portion of the dielectric substrate. Of manufacturing a detection element of a platinum resistance thermometer. 6. The method of claim 5, wherein a cross section of the groove is V-shaped. 7. A detecting element of a platinum resistance thermometer manufactured by the method according to claim 1. 8. A sensing element for a platinum resistance thermometer manufactured by the method according to claim 5.