JP2018059780A - Method of manufacturing semiconductor humidity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor humidity sensor with which it is possible to generate polyimide as a moisture sensitive film the durability change of which can further be reduced.SOLUTION: When generating polyimide as a moisture sensitive film 17 that constitutes a moisture sensitive element 11, a solvent not including γ-butyrolactone and N-methyl-2-pyrrolidone such as TetraG, ethyl benzoate, methyl benzoate, etc., as a solvent by which polyimide can be synthesized. Thus, the residual amount of acid anhydride in the moisture sensitive film 17 that causes a durability change of the moisture sensitive element 11 is reduced, as compared with the case where a conventional NMP solvent is used. Accordingly, it is possible to generate polyimide as a moisture sensitive film 17 the durability change of which can be reduced.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a semiconductor humidity sensor including a step of producing polyimide as a moisture sensitive film.

  Conventionally, for example, Patent Document 1 proposes a method of manufacturing a moisture-sensitive film for a moisture-sensitive sensor including a step of generating polyimide as a moisture-sensitive film. In the step of producing polyimide, the precursor polyamic acid is diluted with a solvent such as N-methylpyrrolidone (hereinafter referred to as NMP solvent), and the NMP solvent is applied to the substrate. Thereafter, the coating film is heated, dehydrated and condensed to be cured. By producing polyimide in this way, fluctuations in the output value detected as a change in capacitance between the electrodes are suppressed.

Japanese Patent No. 4057036

  However, in recent years, the usage environment of semiconductor humidity sensors has become severe. For this reason, the request | requirement which further reduces durability fluctuation | variation has come out, and there exists a problem that the request | requirement cannot be satisfy | filled with the said conventional moisture sensitive film | membrane.

  An object of this invention is to provide the manufacturing method of the semiconductor humidity sensor which can produce | generate the polyimide as a moisture sensitive film which can further reduce a durable fluctuation in view of the said point.

  In order to achieve the above object, according to the first aspect of the present invention, there is provided a method for manufacturing a semiconductor humidity sensor including a step of forming polyimide as a moisture sensitive film (17) constituting the moisture sensitive element (11). In the step of producing polyimide, polyimide is produced using a solvent that can synthesize polyimide and does not contain γ-butyrolactone and N-methyl-2pyrrolidone.

  In the invention according to claim 4, in the step of producing polyimide, polyimide is produced by using any one of Tetra G, ethyl benzoate, and methyl benzoate as a solvent capable of synthesizing polyimide. .

  According to this, an NMP solvent such as N-methyl-2pyrrolidone that causes generation of residual acid anhydride in the moisture-sensitive film is not used at the time of polyimide production. For this reason, compared with the case where the conventional NMP solvent is used, the residual amount of the acid anhydride in a moisture sensitive film | membrane which becomes a durable fluctuation | variation factor of a moisture sensitive element can be reduced. Therefore, it is possible to produce polyimide as a moisture-sensitive film that can reduce endurance fluctuations.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a top view of the semiconductor humidity sensor which concerns on one Embodiment of this invention. It is II-II sectional drawing of FIG. It is the figure which showed the molecular structure of the polyimide which is a moisture sensitive film | membrane of FIG.1 and FIG.2. It is the figure which showed the durable fluctuation amount with respect to NMP ratio. It is the figure which showed the process in which an acid anhydride is produced | generated.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The semiconductor humidity sensor according to the present embodiment is configured as a capacitive humidity sensor that detects humidity based on a change in dielectric constant of a moisture sensitive film.

As shown in FIG. 1, the semiconductor humidity sensor 10 has a humidity sensitive element 11 for detecting the relative humidity of the atmosphere surrounding the semiconductor humidity sensor 10. Specifically, as shown in FIG. 2, the moisture sensitive element 11 is formed on a semiconductor substrate 12 such as Si. An insulating film 14 such as SiO ₂ is formed on the surface 13 of the semiconductor substrate 12.

  On the insulating film 14, a pair of electrodes 15 and 16 are formed. The pair of electrodes 15 and 16 are formed on the insulating film 14 so as to be opposed to each other on the same plane. Each of the electrodes 15 and 16 is formed of a conductive material such as Al, Al—Si alloy, Ti, Au, Cu, Poly-Si (polycrystalline silicon), for example.

  Further, as shown in FIG. 1, the pair of electrodes 15 and 16 each have a comb-teeth shape. Thereby, since the comb-tooth portions of the electrodes 15 and 16 are engaged with each other and face each other, the arrangement area is reduced as a whole, and the facing area is increased. For this reason, the detection accuracy of the relative humidity of the atmosphere surrounding the semiconductor humidity sensor 10 is improved.

  In addition, a moisture sensitive film 17 is formed on the insulating film 14 so as to cover the pair of electrodes 15 and 16 and between these electrodes. The moisture sensitive film 17 adsorbs and desorbs moisture contained in the atmosphere according to the humidity of the environment where the semiconductor humidity sensor 10 is placed. Such a moisture sensitive film 17 is made of polyimide. The polyimide has a molecular structure of the chemical formula (1) shown in FIG.

  The above is the configuration of the semiconductor humidity sensor 10. The semiconductor humidity sensor 10 includes a housing that accommodates the above-described components, terminals for electrical connection with other devices, and the like.

  Next, the operation of the semiconductor humidity sensor 10 will be described. When moisture contained in the atmosphere surrounding the semiconductor humidity sensor 10 is adsorbed and desorbed on the moisture sensitive film 17, the dielectric constant of the moisture sensitive film 17 changes. Here, since the dielectric constant of water is larger than that of polyimide, which is a polymer, when the moisture is adsorbed on the moisture sensitive film 17, the composite dielectric constant of the polymer is increased. Therefore, the humidity sensing element 11 detects this change in the composite dielectric constant as a change in capacitance between the pair of electrodes 15 and 16.

  The output of the moisture sensitive element 11 is input to a processing circuit (not shown). The processing circuit includes a switched capacitor circuit that converts a capacitance value between the pair of electrodes 15 and 16 into a voltage, an amplification circuit that amplifies a CV conversion value that is an output voltage value of the switched capacitor circuit at a predetermined amplification factor, and the like. It is configured. For example, the processing circuit may be formed on the semiconductor substrate 12 or the semiconductor substrate 12, or may be formed on an IC chip different from the semiconductor humidity sensor 10.

Then, the manufacturing method of the semiconductor humidity sensor 10 shown by FIG. 1 is demonstrated. First, a wafer such as Si is prepared as the semiconductor substrate 12, and the wafer is heat-treated in an oxygen atmosphere to form an insulating film 14 such as SiO _{2 on} the surface of the wafer. Note that a processing circuit or the like may be formed on the wafer before the insulating film 14 is formed.

  Next, a metal film such as Al is formed on the insulating film 14 by a method such as vapor deposition or sputtering, and is patterned in a comb-teeth shape by a method such as etching. Thereby, a pair of electrodes 15 and 16 are formed on the insulating film 14.

  Thereafter, the above-described polyimide that becomes the moisture sensitive film 17 is screen-printed on the wafer, that is, on the insulating film 14 and the pair of electrodes 15 and 16. As a result, a polyimide film as the moisture sensitive film 17 is formed on the wafer.

  When producing polyimide, the polyimide is produced using a solvent capable of synthesizing polyimide and not containing γ-butyrolactone and N-methyl-2pyrrolidone. That is, polyimide is produced without using a general solvent such as γ-butyrolactone or N-methyl-2pyrrolidone, that is, an NMP solvent. In other words, polyimide is produced using a solvent that does not contain raw materials or impurities of a lactone system that causes acid anhydrides.

  Specifically, diamine, which is one of polyimide raw materials, is dissolved in a solvent. As the solvent, TetraG (tetraglyme), ethyl benzoate (hereinafter referred to as BAEE), or methyl benzoate is used alone or in combination.

  For example, the solvent is ethyl benzoate. And after adding the acid anhydride which is another raw material, an imidation catalyst is thrown in and it heats and stirs and performs imidation and superposition | polymerization. After stirring until the desired degree of polymerization is reached, the temperature is lowered, and ethynylaniline, which is a terminal modifier, is added and stirred to conduct a terminal reaction to complete the reaction.

  Examples of raw materials include 4,4′-oxydiphthalic anhydride (ODPA), 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane (BIS-AF-A), 4-ethynylaniline Etc. can be used.

  As the solvent, in addition to the above, for example, aprotic polar solvents such as N, N-dimethylacetamide, N, N-dimethylformamide, 1,3-dimethylimidazolidinone, sulfolane, dimethylsulfoxide, dimethylsulfone, etc. Sulfur-containing solvents, high boiling ketone solvents such as cyclopentanone, cyclohexanone, methylcyclohexanone, glycol ethers such as ethylene glycol alkyl ether, diethylene glycol alkyl ether, propylene glycol alkyl ether, triethylene glycol alkyl ether, tetraethylene glycol alkyl ether Solvents, aromatic ester solvents such as methyl benzoate, ethyl benzoate, butyl benzoate, propylene glycol monomethyl ether acetate, diethylene glycol Ester solvents such as Roh butyl ether acetate can be used.

  Here, in a conventional NMP solvent, the main chain is subjected to amic acid (imide precursor) polymerization at room temperature, followed by heating and thermal imidization. Then, after cooling, it complete | finishes by terminal addition and a heating reaction. On the other hand, since the solubility of the monomer raw material in the solvent is low at room temperature, the reaction rate as BAmic acid does not advance. Therefore, the imidization reaction is started immediately by heating the raw material without taking time. There is no difference with the conventional terminal modification reaction.

  As described above, when a polyimide pattern is formed on a wafer by screen printing, the raw material is diluted with TetraG as a solvent so as to have a viscosity necessary for printing. The viscosity is, for example, 10,000 mPas. This produces a moisture sensitive polyimide ink. By using TetraG instead of dilution with BAEE, it is possible to obtain an ink that is less likely to evaporate during screen printing.

  When the moisture sensitive film 17 is formed by spin coating or other methods, dilution with BAEE may be used. That is, the viscosity of the solvent can be appropriately changed depending on the type of the solvent. The method for forming the polyimide film may be patterning, spin coating, dispensing, an inkjet method, or the like.

  Then, using a moisture sensitive film polyimide ink, a polyimide film is printed on the wafer by pattern printing by screen printing, and then cured at 350 ° C., for example, for both drying and crosslinking of acetylene end groups. In this step, for example, a coating agent is applied to the entire surface of the wafer with a dropper and spin-dried, a coupling agent baking at 150 ° C. for 30 minutes, a polyimide coating by screen printing, a reduced pressure of −0.1 MPa or more, 1 hour Vacuum degassing, nitrogen atmosphere, 350 ° C., polyimide curing for 1 hour.

  The molecular structure when a polyimide film is applied on the wafer is the same as the above chemical formula (1). In this way, a polyimide film is formed on the wafer, and the wafer is diced to complete the moisture sensitive element 11.

  The semiconductor humidity sensor 10 having polyimide as the moisture-sensitive film 17 has a characteristic that moisture absorption into the film proceeds in a high-temperature and high-humidity environment of 70 ° C., 80% RH, 5 V, and the output fluctuates positively. On the other hand, in a high-temperature standing environment of only 115 ° C., moisture is released and the output fluctuates negatively. The inventors have found through experiments that there is a correlation between the NMP ratio of the moisture-sensitive film solvent and the amount of variation in durability. The test time was 2000 h. The result is shown in FIG.

  As shown in FIG. 4, it can be seen that the endurance fluctuation amount decreases as the NMP ratio in the moisture sensitive film solvent decreases from 100%. And when NMP rate in a moisture sensitive film | membrane solvent was 0%, ie, when the polyimide was produced | generated using the solvent which concerns on this embodiment, the endurance fluctuation amount in a high temperature / humidity environment and a high temperature environment decreased most. Therefore, by producing the polyimide using the solvent according to the present embodiment, it was possible to reduce the durability variation without depending on the environment of the moisture sensitive element 11.

  This is considered to be due to the fact that when the NMP content of the solvent used for polyimide formation is lowered, the acid anhydride in the moisture sensitive film 17 is reduced and the moisture is more difficult to be adsorbed, so that the durability is improved. Further, the reason why the residual amount of the acid anhydride in the moisture sensitive film 17 increases as the NMP content is higher can be estimated as follows. That is, as shown in FIG. 5, γ-butyrolactone, which is a raw material of NMP, is present as an impurity in the NMP solvent. NMP is produced by condensing γ-butyrolactone and methylamine. Furthermore, it is considered that the reaction proceeds through the route shown in FIG. 5 and finally dehydrates at a high temperature when the moisture sensitive film 17 is formed, so that the acid anhydride remains in the moisture sensitive film 17.

  However, in the present embodiment, polyimide is generated without using the NMP solvent that causes generation of residual acid anhydride in the moisture sensitive film 17, so that the moisture sensitive film is compared with the case where a conventional NMP solvent is used. The residual amount of acid anhydride in 17 can be reduced, and as a result, durability fluctuations due to high temperature and high humidity can be reduced. Therefore, it is possible to generate polyimide as the moisture sensitive film 17 that can reduce the durability fluctuation of the moisture sensitive element 11.

(Other embodiments)
The configuration of the semiconductor humidity sensor 10 shown in the above embodiment is an example, and the present invention is not limited to the configuration shown above, and other configurations that can realize the present invention can be used. For example, the configuration shown in FIGS. 1 and 2 is an example, and the shape and arrangement of the electrodes 15 and 16 may be appropriately changed.

  The molecular structure of polyimide is not limited to that shown in FIG. 3, and other polyimides may be used. Furthermore, in the above-described embodiment, a method is employed in which polyimide is directly synthesized for convenience of raw material solubility and applied and formed on the wafer. However, imidization may be performed by applying it to the wafer in an amic acid state. As described above, the effect of reducing the durability fluctuation can be obtained regardless of the type of polyimide or the formation of the polyimide moisture sensitive film via the amic acid.

DESCRIPTION OF SYMBOLS 10 Semiconductor humidity sensor 11 Humidity sensitive element 12 Semiconductor substrate 14 Insulating film 15, 16 Electrode 17 Moisture sensitive film

Claims (4)

A method for producing a semiconductor humidity sensor comprising a step of producing polyimide as a moisture sensitive film (17) constituting the moisture sensitive element (11),
In the step of producing the polyimide, a method for producing a semiconductor humidity sensor, wherein the polyimide is produced using a solvent that is capable of synthesizing the polyimide and does not contain γ-butyrolactone and N-methyl-2pyrrolidone.   2. The method for producing a semiconductor humidity sensor according to claim 1, wherein, in the step of producing the polyimide, any one of Tetra G, ethyl benzoate, and methyl benzoate is used alone or in combination as the solvent.   In the step of producing the polyimide, as the solvent, an aprotic polar solvent, a sulfur-containing solvent, a high-boiling ketone solvent, a glycol ether solvent, an aromatic ester solvent, or an ester solvent is used alone or in combination. The manufacturing method of the semiconductor humidity sensor of Claim 1 used. A method for producing a semiconductor humidity sensor comprising a step of producing polyimide as a moisture sensitive film (17) constituting the moisture sensitive element (11),
In the step of producing the polyimide, as a solvent capable of synthesizing the polyimide, manufacturing of a semiconductor humidity sensor producing the polyimide by using any of TetraG, ethyl benzoate, and methyl benzoate alone or in combination. Method.

Images