JP2007095785A - Field effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field effect transistor (FET) which is excellent in surface flatness with good embedding properties into large step differences and into complicated structures and with low stress to a gate portion, and which can be formed at a low temperature and can be completely covered and protected in its electrode with an application type resin film of relatively low dielectric constant that does not give a bad affection to the gate electrode also in a manufacturing process. <P>SOLUTION: In a field effect transistor including a control circuit board equipped with a gate electrode having a trapezoidal structure, a T type structure, and a Y type structure, the application type resin film is interposed between the control circuit board and the sealing resin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a field effect transistor (FET) such as a high electron mobility transistor (HEMT) or a heterostructure field effect transistor (HFET), and more particularly, a high performance field effect transistor having a low gate resistance. It relates to a transistor.

Research and development of field effect transistors (hereinafter, field effect transistors are appropriately abbreviated as FETs) using group 13/15 (formerly IIIB / VB) compound semiconductors such as GaAs has been actively conducted. In order to improve the performance of high-frequency devices using FETs, it is very important to reduce parasitic resistance and capacitance. In the prior art, in order to reduce the resistance of the gate electrode, trapezoidal gate electrode formation, T-type gate electrode formation, Y-type gate electrode formation, etc. using a multilayer photoresist film are carried out, and the gate electrode structure is devised. Has been done. Furthermore, in order to stabilize the characteristics of the gate electrode, the surface of the gate electrode is covered and protected with a nitride film such as a SiN film or an oxide film such as a SiO ₂ film. Patent Document 1 discloses a field effect transistor in which a gate control electrode provided above a channel is in contact with a semiconductor layer having a low impurity density and a high resistance in a region outside the channel. ing.

  In addition, when a device package by resin sealing is performed, since a resin having a high dielectric constant such as a liquid resin such as an epoxy resin, a fluororesin, a urethane resin, or a silicone resin is used as the sealing resin, the characteristics are reduced. Insufficient moisture resistance of the resin itself becomes a problem, and device characteristic deterioration due to internal stress of the resin is also highlighted.

  Furthermore, Patent Document 2 discloses the following general formula (I):

(Wherein R ^{1 to} R ⁴ are each a hydrogen atom or a lower alkyl group, R ⁵ and R ⁶ are each an aryl group, an alkyl group or an alkenyl group, and 2% or more of 2n R ⁵ and R ⁶ are 2% or more. 270 ° C., comprising a silicone ladder polymer represented by an alkenyl group, n represents an integer of 5 to 1600), 0.2 to 20.0% by weight (mass%) of a catalyst and an organic solvent with respect to the silicone ladder polymer The following silicone resin compositions that can be thermally cured at low temperatures are disclosed. Patent Document 3 discloses the following general formula (II):

Wherein R ₁ and R ₂ are an aryl group, a hydrogen atom, an aliphatic alkyl group or a functional group having an unsaturated bond, and may be the same or different. R ₃ , R ₄ , R ₅ and R ₆ are hydrogen An atom, an aryl group, an aliphatic alkyl group, a trialkylsilyl group or a functional group having an unsaturated bond, which may be the same or different, provided that R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ 1% by weight (mass%) or more is a functional group having photosensitivity, and n is a natural number.) Photosensitive silicone containing a silicone ladder polymer resin and a photosensitive crosslinking agent or photopolymerization initiator A ladder-based resin composition is disclosed.

JP-A-5-136177 JP-A-4-213364 Japanese Patent Laid-Open No. 10-319597

  However, an inorganic protective film such as the above-described nitride film or oxide film is usually formed by sputtering, CVD, or vapor deposition, and also protects the gate electrode as described in Patent Document 1. Since a semiconductor layer having a low impurity concentration and high resistance is formed by a crystal forming method such as selective epitaxial growth as a layer, film quality such as micro surface roughness and film composition is delicately determined depending on a film forming apparatus and film forming conditions. Change. Due to the difference in film quality, a variation of several percent was observed in transistor characteristics (for example, gain), and it was difficult to obtain stable characteristics with good reproducibility. Further, since these gate electrode structures are complicated, there are regions with poor coverage such as a rectangular portion or a back portion in the case of a T-type or Y-type. If the coverage is insufficient, moisture in the air enters and causes deterioration of the gate electrode characteristics. Furthermore, in order to supplement coverage, it may be possible to increase the thickness of the nitride film or oxide film. However, increasing the thickness increases the stress applied to the gate electrode region, or the dielectric constant of these films is high. As a result, there is a problem that, if the film thickness is increased, deterioration of the gain performance of the transistor is accelerated.

  Therefore, the object of the present invention is that the surface is excellent in flatness, has a high step and has a good embedding property in an intricate structure, has a low stress applied to the gate region, and can be formed at a low temperature. An object of the present invention is to provide an FET in which a gate electrode part is completely covered and protected by a coating resin film having a relatively low dielectric constant that does not adversely affect the electrode part.

As a result of diligent research and development, the present inventors have achieved a relatively low dielectric constant and low stress as a protective layer between the FET sealing resin and the control circuit substrate (particularly the gate electrode region). By forming a coating type resin film having both high moisture resistance, it was found that resin sealing can be performed while preventing characteristic deterioration, and the present invention has been achieved.
That is, the present invention relates to a field effect transistor comprising a control circuit substrate having a gate electrode having a trapezoidal structure, a T-type structure, or a Y-type structure, and a sealing resin.
The present invention relates to an FET characterized in that a coating type resin film is interposed between the control circuit board and the sealing resin.

  According to the present invention, the surface is excellent in flatness, has a high step and has a good embedding property in an intricate structure, has a low stress applied to the gate region, and can be formed at a low temperature. It is possible to provide an FET in which a gate electrode portion is completely covered and protected by a coating resin film having a relatively low dielectric constant that does not adversely affect the structure.

  The FET of the present invention is characterized in that a gate electrode portion in an FET having a trapezoidal gate electrode, a T-type gate electrode or a Y-type gate electrode is completely covered with a coating type resin film. It should be noted that not only the gate electrode portion but also the adjacent substrate and peripheral circuit may be covered with a coating type resin film.

  This coating type resin film is composed of silicone polymer, polyimide polymer, polyimide silicone polymer, polyarylene ether polymer, bisbenzocyclobutene polymer, polyquinoline polymer, perfluorohydrocarbon polymer, fluorocarbon polymer, aromatic. It is preferably composed of a cured film of at least one polymer selected from the group consisting of a hydrocarbon-based polymer and a copolymer of fluorocarbon and silicone. These polymers preferably have a heat resistance of 200 ° C. or higher, can be synthesized with high purity, and have a relatively low dielectric constant.

Among the above-mentioned polymers, it is more preferable to use a silicone-based polymer, and it is most preferable to use a silicone-based polymer represented by the following general formula (1) or a silicone-based polymer represented by the following general formula (2).
General formula (1):

[Wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are an aryl group, a hydrogen atom, an aliphatic alkyl group, a hydroxyl group, a fluorine atom, a fluoroalkyl group, a trialkylsilyl group, or an unsaturated group. A functional group having a bond, which may be the same or different. k, l, m and n are all integers of 0 or more, 2k + (3/2) l + m + (1/2) n is a natural number, and the mass average molecular weight is 1000 or more. The molecular end group is an aryl group, a hydrogen atom, an aliphatic alkyl group, a hydroxyl group, a fluorine atom, a fluoroalkyl group, a trialkylsilyl group, or a functional group having an unsaturated bond. There may be. ]

  The general formula (1) can also be expressed as a structural formula as follows:

  General formula (2):

(Wherein R ⁷ and R ⁸ are an aryl group, a hydrogen atom, an aliphatic alkyl group, a fluorine atom, a fluoroalkyl group or a functional group having an unsaturated bond, and may be the same or different. R ⁹ , R ¹⁰ , R ¹¹ and R ¹² are a hydrogen atom, an aryl group, an aliphatic alkyl group, a trialkylsilyl group or a functional group having an unsaturated bond, and may be the same or different. N is an integer and the mass average molecular weight is 1000 or more)

Moreover, the silicone polymer represented by the general formula (1) or the general formula (2) may be a mixture. Since these silicone polymers are less degassed during heat treatment, they are less likely to contaminate the gate electrode part or its control circuit board. In particular, the silicone-based polymer represented by the general formula (2) having a ladder structure has a rigid structure as compared with the silicone-based polymer represented by the general formula (1). It is excellent, has a low stress when forming a coating type resin film, and has a higher pressure resistance. Further, since the reaction during the heat treatment occurs at the end groups (R ⁹ , R ¹⁰ , R ¹¹ , R ¹² ), the degassing during the heat treatment is further reduced.

Such silicone polymers include those that are crosslinked and cured by light such as ultraviolet light, and suitable examples thereof include 1% or more of the substituents of R ^{1 to} R ⁶ in the general formula (1). Is a functional group having an unsaturated bond, and in the general formula (2), 1% or more of the substituents of R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ , R ¹² What is a functional group which has an unsaturated bond is mentioned. The functional group having an unsaturated bond is a reactive group for crosslinking resin molecules by a crosslinking reaction or a radical reaction, and is preferably an alkenyl group, an alkylacroyl group, an alkylmethacryloyl group, or a styryl group, but is not limited thereto. Is not to be done. These functional groups having an unsaturated bond may be introduced singly or in combination of two or more. Such a photocrosslinkable silicone polymer can be used alone or in combination with a photosensitive crosslinking agent, a photopolymerization initiator, and a photosensitizer to allow the curing reaction to proceed at a lower temperature using light as a driving force. The transistor manufacturing advantage is provided in that the temperature applied to the control circuit formed below the film can be reduced or self-patterning can be performed without using a resist.

  The coating resin film composed of the silicone polymer as described above is obtained by applying a silicone polymer solution represented by the general formula (1) and / or (2), that is, a so-called varnish, followed by heat curing. Can be formed. As the silicone polymer solution, alcohol, ketone, ether, halogen, ester, benzene, alkoxybenzene, and cyclic ketone solvent solutions are suitable. In the silicone polymer solution, there are added a polymerizable monomer or polymerization initiator for improving the density of the cured film, a crosslinking agent, a sensitizer, and a polymerization inhibitor for improving storage stability. It may be. Photosensitive crosslinking agents and photopolymerization initiators are additives for causing film curing by radical reaction or crosslinking reaction. Examples of photosensitive crosslinking agents include aromatic azide compounds, aromatic bisazide compounds, iminoquinone diazide compounds, aromatic compounds. Photosensitive compounds that generate radical active species upon irradiation with light, such as aromatic diazo compounds and organic halogen compounds, and photopolymerization initiators include carbonyl compounds, dicarbonyl compounds, acetophenones, benzoin ethers, acylphosphine oxides, thioxanthones , Aminocarbonyl compounds, nitrogen-containing compounds, and the like. In addition, what is disclosed by patent document 3 can be used as a silicone type polymer shown by General formula (2) containing these additives.

  The curing temperature varies depending on the type of polymer and the heat resistance temperature of the FET, but is usually 100 ° C. to 400 ° C., and in particular, when the above-mentioned photocrosslinkable polymer is used, it is 100 ° C. to 250 ° C. The curing process can be performed at a relatively low temperature.

  The coating resin film provided around and above the gate electrode is preferably composed of a polymer cured film having a melting point and exhibiting high fluidity (reflowability) by heat treatment at a temperature near the melting point. That is, after coating a polymer solution (varnish), the coating film melts and flows by a heat treatment at a temperature near the melting point (that is, a temperature higher than the melting temperature of the polymer and lower than the curing temperature). The hole-filling property for the step on the substrate is improved, and the periphery of the gate electrode can be covered more completely without a gap. In this case, as long as the polymer has reflowability, a polymer having a mass average molecular weight in an arbitrary range can be used. In particular, from the viewpoint of enhancing the reflow property, the mass average molecular weight of the above various polymers is preferably 100,000 or less, and more preferably 10,000 or less.

  The coating type resin film as described above is composed of a cured film formed from a polymer having reflow properties, and a second coating type resin film can be formed above the coating type resin film. The second coating type resin film is preferably composed of a cured film formed from an ultra-high molecular weight polymer that is poor in reflow property and capable of forming a thick film. By providing the second coating type resin film, in addition to covering and protecting the gate electrode, stress applied to the gate electrode from the sealing resin or the like can be relaxed, and reliability can be improved. That is, the polymer having a low mass average molecular weight constituting the coating type resin film has a melting point as described above, and has a high fluidity (reflow property). It is possible to cover the periphery of a certain gate portion more completely without gaps. On the other hand, the ultra-high molecular weight polymer having a high mass average molecular weight constituting the second coating type resin film has a high viscosity, and thus has a low fluidity during heat treatment, but has a high flexibility and a good crack resistance. By forming the film, the stress applied to the FET from the upper layer such as a sealing resin is absorbed, and there is also a moisture resistance preventing effect, so that stabilization of transistor characteristics and reliability can be improved. The mass average molecular weight of the ultrahigh molecular weight polymer is preferably 100,000 or more from the viewpoint of crack resistance, but is not particularly limited as long as it has crack resistance and film thickness forming ability.

Further, as the silicone polymer for forming the second coating resin film, for example of the side-chain substituent of the general formula ^{(1) (R 1 ~R 6} ), an aryl group or more 20% Crack resistance can be improved by using an introduced polymer or a polymer having an aryl group introduced into 20% or more of the substituents (R ⁷ , R ⁸ ) in the side chain of the general formula (2). In addition, a thick film exceeding 1 μm can be formed. This is effective regardless of the presence or absence of the reflow property of the silicone-based polymer, and when the gate electrode portion is relatively high, it is necessary to satisfy both the reflow property and the crack resistance, so this method is effective.

Hereinafter, the FET of the present invention will be further described with reference to the accompanying drawings.
FIG. 1 is a schematic structural sectional view showing an embodiment of the FET of the present invention. This FET includes a GaAs semi-insulating substrate 1, an undoped GaAs or InGaAs channel layer 2, which is a high-purity channel layer, an n-type AlGaAs electron supply layer 3, an n-type GaAs layer 4, a source electrode 5, and a drain electrode. 6 and a T-type gate electrode 7. A passivation film (not shown) made of an inorganic film (silicon nitride film, silicon oxide film, etc.) formed by sputtering or CVD can be formed on the outermost surface layer of the FET.

  On the surface of the control circuit substrate (FET) including the T-type gate electrode 7 site, a silicone-based polymer, a polyimide-based polymer containing the composition represented by the general formula (1) and / or (2) as described above, Polyimide silicone polymer, polyarylene ether polymer, bisbenzocyclobutene polymer, polyquinoline polymer, perfluorohydrocarbon polymer, fluorocarbon polymer, aromatic hydrocarbon polymer, copolymer of fluorocarbon and silicone, alcohol A varnish dissolved in a solvent such as a system, a ketone system, an ether system, a halogen system, an ester system, a benzene system, an alkoxybenzene system, or a cyclic ketone system is applied to a film thickness of 10 nm to 50 μm, By applying heat treatment at 350 ° C, -Type resin film 8.

When it is necessary to expose a bonding pad (not shown) or a dicing line (not shown), a reactive ion etching apparatus or an ion beam etching apparatus is used with a resist pattern obtained by photolithography as a mask. The coating type resin film 8 and the passivation film (if provided) are continuously removed by a dry etching method. The etching gas used in the reactive ion etching is not particularly limited as long as it is a gas species that can etch the resin film, but CF ₄ , CHF ₃ , C ₄ F ₈ , N ₂ , H ₂ , Ar, O _2, etc. It is preferable to use a mixed gas consisting of As described above, when the coating-type resin film 8 is removed by the dry etching method, the coating-type resin film 8 and the passivation film (when provided) can be continuously removed, so that the process can be simplified. The resist on the coating type resin film 8 is removed by wet removal or dry removal using a reactive etching apparatus, ion beam etching apparatus, ashing apparatus, or the like. When the resist is removed by an ashing apparatus, the oxidation of the surface layer of the coating type resin film 8 can be reduced if it is performed under a low pressure condition and a low power condition. In particular, the oxidation of the surface of the resin film can be further reduced under a low pressure condition of 1 Torr or less and a low power condition of 1 kW or less.

  The FET having the structure as shown in FIG. 1 is formed by completely covering the T-type gate electrode 7 site, which is the structure thereof, with the coating-type resin film 8, so that the gate site can be protected from package materials such as moisture resistance prevention and sealing resin. Can relieve the stress applied to it, thereby contributing to improvement of gain, suppression of deterioration of characteristics, stability of use under high humidity, and improvement of reliability. In many cases, it is often impossible to sufficiently cover the rectangular portion of the portion of the T-type gate electrode 7 or the back side of the T-type by using only a passivation film formed by the conventional sputtering or CVD method. However, these problems can be solved by covering with the coating type resin film 8.

  The coating-type resin film 8 composed of a cured polymer film as described above has a low dielectric constant and a high withstand voltage, and therefore can prevent malfunction due to an electric field caused by the control circuit and deterioration of characteristics such as gain. Further, since the coating type resin film 8 has a low residual stress and has a buffering action, when the whole FET is sealed with a sealing resin, the stress from the sealing resin is buffered, and the T-type gate electrode 7 It is possible to suppress cracks in the thin pillar portions of the FET, and to prevent malfunction of the FET due to cracks. In addition, it has heat resistance that can withstand the manufacturing process of the FET, and is excellent in environmental resistance, so it is also effective as a protective film for the control circuit. Furthermore, no abnormalities in the characteristics are observed even in the reliability evaluation by the pressure cooker test.

  Further, in order to further improve the characteristics and reliability of the FET, the coating type resin film 8 preferably has a low dielectric constant and low hygroscopicity. In particular, a coating type resin film 8 having a dielectric constant of 3.2 or less and a water absorption of 5% or less is preferable, and those values are preferably lower.

  In the case of using a cured film formed from a silicone-based polymer as the coating type resin film 8, in order to further improve the adhesion to the base or the T-type gate electrode 7 site, many hydroxyl groups are included in the molecular structure of the polymer. The inclusion is preferred.

Further, as the coating resin film 8, a polymer in which R ^{1 to} R ⁶ and the molecular end group of the general formula (1) are hydrogen atoms, aliphatic alkyl groups, and hydroxyl groups, or R ^{7 of the} general formula (2) is used. And a cured film composed of a polymer in which all of R ⁸ are hydrogen atoms or aliphatic alkyl groups, the filling property of the coating resin film 8 is improved, and the coating resin film 8 and the T-type gate electrode are improved. Compatibility with 7 sites is improved, and the characteristics can be improved. In particular, R ^{1 to} R ⁶ of the general formula (1), the molecular end group, and R ⁷ and R ⁸ of the general formula (2) are preferably a hydrogen atom, a methyl group, an ethyl group, or a hydroxyl group.

Further, as the coating type resin film 8, by using a cured film composed of a polymer in which all the substituents at the terminals of R ^{9 to} R ^{12 in} the general formula (2) are hydrogen atoms, adhesion to the base is achieved. Can be improved.

When a coating type resin film having a thickness of 1 μm or more is formed, 20% or more of R ^{1 to} R ^{6 in} the general formula (1), and R ⁷ and R ⁸ in the general formula (2). Among them, a polymer in which 20% or more is an aryl group such as a phenyl group is preferable, and a silicone polymer having a mass average molecular weight of 50,000 or more is more preferable because crack resistance at the time of thick film is improved.

  In addition, since the polymer having a mass average molecular weight of 100,000 or less has a melting point, the coating film is obtained by applying a heat treatment in the vicinity of the melting point (that is, higher than the melting temperature of the polymer and lower than the curing temperature) after applying the varnish. Since the melt flow (reflow) is performed in a direction where the level difference is low, the hole can be efficiently filled with the resin film, and the resin film can be completely inserted into the gap between the T-type gate electrode 7 and the base. . In particular, a polymer having a mass average molecular weight of 1,000 to 10,000 has a very high reflow property and can be preferably used. However, when the coating film thickness is thinner than the height of the T-type gate electrode 7, the coating-type resin film 8 may not be formed on the T-type gate electrode 7.

  If the application type resin film 8 is applied once and the gap between the T-type gate electrode 7 and the base cannot be sufficiently filled, it can be improved by applying a thick film or applying multiple layers. . In the case of multilayer coating, the same varnish may be used, or varnishes having different viscosities or different polymers may be used. However, during multi-layer coating, post-baking is performed each time the film is formed so that it does not mix with the previously formed coating resin film, or a solvent that does not dissolve the previously formed coating resin film. It is necessary to use a varnish that has been prepared.

  Moreover, before apply | coating the said varnish, the surface of a foundation | substrate can be processed with the solution etc. which contain a silane coupling agent, and the adhesiveness of a foundation | substrate and a coating type resin film can also be strengthened.

  FIG. 2 is a schematic structural sectional view showing another embodiment of the FET of the present invention. This FET has the same configuration as that shown in FIG. 1 except that the gate electrode of the control circuit is the Y-type gate electrode 9 before the coating type resin film is formed. On the control circuit, a coating-type resin film 8 that completely covers and protects the Y-type gate electrode 9 is provided. Further, on the coating-type resin film 8, a thick second coating-type resin is provided. A membrane 10 is provided.

  The FET manufacturing method shown in FIG. 2 differs from the above-described method in that the stress applied to the FET from the package material such as the sealing resin is provided by providing the second coating resin film 10 on the coating resin film 8. It is more relaxed and further improves the moisture resistance of the FET, thereby stabilizing the device characteristics and improving the reliability.

  First, in the same manner as described above, the control circuit forms the coating type resin film 8 on the surface by the method described above, and covers and protects the periphery of the Y-type gate electrode 9 portion as a structure without any gap. The second coating resin film 10 can also be formed using the varnish made of the above-described polymer, and may be the same as or different from the base polymer constituting the varnish of the coating resin film 8. Before applying the varnish of the second coating type resin film 10, the surface of the coating type resin film 8 serving as a base is treated with a solution containing a silane coupling agent, etc. Adhesiveness with the coating type resin film 10 can also be strengthened.

  The second coating resin film 10 is formed with a film thickness equal to or greater than that of the coating resin film 8. The film thickness is preferably 1 μm to 50 μm, and more preferably 3 μm to 10 μm from the viewpoint of the function of buffering the stress from the sealing resin and the processing process of the pad and dicing line. After the varnish is applied, heat treatment is performed at 100 ° C. to 350 ° C. on the hot plate to form the second coating resin film 10 on the coating resin film 8.

  The second coating-type resin film 10 needs a thick film, and does not need to fill holes like the coating-type resin film 8. Ultra high molecular weight polymer with high mass average molecular weight is high in viscosity, so fluidity during heat treatment is low, but flexibility is good and crack resistance is good, so by forming a thick film, upper layer such as sealing resin Therefore, the stress applied to the transistor can be absorbed, and the moisture resistance can be prevented, so that the transistor characteristics can be stabilized and the reliability can be improved. The mass average molecular weight of the ultrahigh molecular weight polymer is preferably 100,000 or more from the viewpoint of crack resistance, but is not particularly limited as long as it has crack resistance and thick film forming ability.

  When it is necessary to expose a bonding pad (not shown) or a dicing line (not shown), a reactive ion etching apparatus or ion using a resist pattern obtained by photolithography as a mask as described above. The coating type resin film 8, the second coating type resin film 10 and the passivation film (if provided) are continuously removed by a dry etching method using a beam etching apparatus.

  Instead of the continuous dry etching method, the second coating type resin film 10 is removed by development processing, and then the coating type resin film 8 and a passivation film (provided with the pattern of the coating type resin film 8 as a mask) are provided. Case) may be removed by dry etching. Pattern formation by development processing of the second coating type resin film 10 is performed by immersion development or spin development with a developer dedicated to the second coating type resin film 10 using a resist pattern obtained by photolithography as a mask. Thereafter, it can be carried out by washing with a rinse solution dedicated to the resin film.

  Further, when a varnish made of the above-described photosensitive polymer is used for film formation of the second coating type resin film 10, after applying the varnish, heat treatment is performed at 100 ° C. to 250 ° C., and then a desired pattern is formed. The glass coating mask is used to irradiate and expose from above, the second coating resin film 10 in the non-irradiated portion of the light is removed by development treatment, and finally post-baked at 100 ° C. to 450 ° C., The second coating resin film 10 is cured. As a result, a flattened second coating resin film 10 having a predetermined portion opened is obtained. The coating resin film 8 and the passivation film (if provided) may be removed by dry etching using the pattern of the second coating resin film 10 as a mask. When this photosensitive varnish cured film is used for the second coating type resin film 10, the resist pattern forming step can be omitted, and the pattern can be transferred stably in a short time, thus simplifying the process. Can contribute to cost reduction.

  The coating method of the coating type resin film 8 and the second coating type resin film 10 in the present invention is not particularly limited. For example, a spin coating method, a spray coating method, a screen printing method, a dip coating (dip pulling up) ) Method, potting (dropping) method, inkjet method and dispenser method can be applied.

  As the coated resin film 8 of the FET shown in FIG. 1, the following various resin varnishes are coated on the control circuit (the surface of the FET), the embedding property under the T-type gate electrode 7, the presence or absence of improvement in gain characteristics, heat A cycle test (−45 ° C. = 130 ° C., 1000 cycles) and a moisture resistance test (130 ° C./85% RH / 2 atm. 1000 hours) were carried out for evaluation.

<Example 1>
A varnish in which a fluorocarbon polymer (dielectric constant = 2.1) is dissolved in perfluorooctane so as to be 20% by mass is spin-coated at a speed of 3000 rpm and heat-treated on a hot plate at 120 ° C. for 1 minute. And dried and surface-treated. Further, post-baking was carried out at 350 ° C. for 1 hour in an oven to completely cure, thereby forming a coated resin film made of a cured fluorocarbon polymer film having a thickness of about 2 μm. From the cross-sectional evaluation by SEM, the T-type gate electrode could be covered except that a slight gap remained below the T-type gate electrode. This is considered to be due to the low reflow property (fluidity) of the fluorocarbon polymer and the high viscosity of the fluorocarbon polymer itself. The gain of this FET increased by 0.2 dB, the noise figure decreased by 0.05 dB, and the characteristics were remarkably improved. No deterioration of the characteristics was observed after the heat cycle test and moisture resistance test.

<Example 2>
In the above general formula (1), the side chains R ^{1 to} R ⁶ are all methyl groups, the weight average molecular weight is 25,000, and k / l / m / n = 0/75/25/0 silicone-based polymer (dielectric A varnish obtained by dissolving 20% by mass in methanol at a rate of 2.8; melting point = 90 ° C. was spin-coated at a speed of 2000 rpm to obtain a coating film thickness of about 0.6 μm. Thereafter, heat treatment was performed on the hot plate at 120 ° C. to 200 ° C. near the melting point of the silicone polymer, the silicone polymer was reflowed, and the periphery of the T-type gate electrode portion was covered without a gap. However, a slight step remained in the upper layer of the T-type gate electrode. Next, post-baking was performed in an oven under a nitrogen atmosphere at 250 ° C. for 1 hour to completely cure. The gain of this FET was increased by 0.4 dB, the noise figure was decreased by 0.1 db, and the characteristics were remarkably improved. No deterioration of the characteristics was observed after the heat cycle test and the moisture resistance test.

<Example 3>
Of the side chains R ⁷ and R ^{8 in} the general formula (2), 10 mol% is a vinyl group, the remainder is a phenyl group, and R ⁹ , R ¹⁰ , R ¹¹ and R ¹² are hydrogen atoms (hydroxyl groups). , A silicone polymer having a mass average molecular weight of 2000 (dielectric constant = 3.1; melting point = 100 ° C.) was dissolved in methoxybenzene so as to be 10% by mass, and 0.5% by mass of γ A varnish to which-(acryloxypropyl) trimethoxysilane was added was prepared. This varnish was spin-coated at a rate of 2500 rpm, and was reflowed by heat treatment at 150 ° C. for 30 minutes in a clean oven under a nitrogen atmosphere. A silicone polymer coating film having a thickness of 1.3 μm was formed. Thereafter, post-baking was performed at 250 ° C. for 1 hour in a clean oven under a nitrogen atmosphere to completely cure. As a result, the periphery of the T-type gate electrode portion can be covered without a gap, and sufficient flattening can be obtained in the upper layer of the T-type gate electrode. The gain of this FET was increased by 0.8 dB, the noise figure was decreased by 0.15 dB, the characteristics were remarkably improved, and no deterioration of the characteristics was observed after the heat cycle test and the moisture resistance test.

  Next, as the coating resin film 8 and the second coating resin film 10 in FIG. 2, the following various resin varnishes are coated on the control circuit to improve the embedding property and gain characteristics under the Y-type gate electrode. Presence / absence, heat cycle test (−45 ° C. = 130 ° C., 1000 cycles), and moisture resistance test (130 ° C./85% RH / 2 atm, 1000 hours) were carried out for evaluation.

<Example 4>
First, the side chain R ⁷ and R ^{8 in the} general formula (2) are all methyl groups, terminal R ^{9 to} R ¹² are hydrogen atoms, and a silicone-based polymer having a weight average molecular weight of 7000 (dielectric constant = 2.7). The melting point = 85 ° C.) and the varnish (a) for the coating type resin film 8 dissolved in butyl acetate so as to be 10% by mass, and the side chains R ⁷ and R ^{8 in the} general formula (2) are all phenyl In the second coating resin film 10, R ^{9 to} R ¹² at the terminals are hydrogen atoms and a silicone polymer having a mass average molecular weight of 17,000 is dissolved in methoxybenzene so as to be 20 mass%. Varnish (b) and an aqueous solution (c) containing 1% by mass of γ-aminopropyltrimethoxysilane were prepared in advance.

  The varnish (a) was spin-coated on the control circuit at a rate of 1500 revolutions per minute, and heat-treated in a clean oven under a nitrogen atmosphere from room temperature to 300 ° C. while raising the temperature at 10 ° C. per minute. It was kept at 300 ° C. for 1 hour. A coating type resin film 8 having a thickness of 0.8 μm was formed. The coating-type resin film 8 could cover the periphery of the Y-type gate electrode 9 without any gap, and sufficient flattening was obtained in the upper layer of the Y-type gate electrode 9.

  Next, in order to reinforce the adhesion, the aqueous solution (c) is spin-coated on the coating type resin film 8 at a speed of 2,000 revolutions per minute, heat-treated at 110 ° C. for 2 minutes on a hot plate, and then varnish ( b) was spin-coated at a speed of 1800 revolutions per minute so as to have a film thickness of about 10 μm, and a heat treatment at 135 ° C. was performed on the hot plate. Thereafter, post-baking was performed at 320 ° C. for 1 hour in a clean oven under a nitrogen atmosphere, and the film was completely cured to form a second coating type resin film 10. By forming this thick second coating type resin film 10, the stress received from the sealing resin can be greatly buffered, the gain of this FET increases by 1.5 dB, and the noise figure becomes 0.3 dB. There was a significant improvement in properties. In addition, no deterioration of the characteristics was observed after the heat cycle test and the moisture resistance test. Furthermore, the characteristic variation of each chip in the wafer surface was significantly reduced.

<Example 5>
Of the side chains R ^{1 to} R ⁶ of the general formula (1), 15% are allyl groups, the rest are phenyl groups, the weight average molecular weight is 15,000, k / l / m / n = 10/60 / A varnish (a) obtained by dissolving a 25/5 silicone polymer (dielectric constant = 3.2; melting point = 130 ° C.) in dimethoxybenzene so as to be 12% by mass, and a side chain R ^{7 of the} above general formula (2) And R ⁸ , a silicone polymer having a weight average molecular weight of 280,000, wherein 20 mol% is a methacryloylpropyl group, the rest is a phenyl group, and R ^{9 to} R ^{12 at the} terminals are methyl groups is converted to N-methylpyrrolidone. A varnish (b) in which 5% by mass of 2,6-bis (4′-azidobenzal) methylcyclohexanone was added to the polymer and dissolved in an amount of 10% by mass was prepared in advance.

  Varnish (a) was spin-coated on the control circuit at a speed of 3000 rpm, and heat-treated in a clean oven under a nitrogen atmosphere from room temperature to 350 ° C. while raising the temperature at 10 ° C./min. It was kept at 300 ° C. for 1 hour. A coating resin film 8 having a thickness of 1.2 μm was formed. The coating-type resin film 8 could cover the periphery of the Y-type gate electrode 9 without any gap, and sufficient flattening was obtained in the upper layer of the Y-type gate electrode 9.

Next, the varnish (b) is spin-coated on the coating type resin film 8 at a speed of 2000 rpm so as to have a film thickness of about 6 μm, and heat treatment is performed on the hot plate at 135 ° C. for the second coating. A mold resin film 10 was formed. Furthermore, contact exposure was performed at a power of 500 mJ / cm ² using an ultrahigh pressure mercury lamp as a light source through a photomask having a required pattern such as a contact hole or a dicing line.
Subsequently, patterning of the silicone-based resin film was completed by dissolving and removing unexposed portions with a developing solution of methoxybenzene / xylene = 1/4 (volume ratio) and washing with xylene. Thereafter, post baking was performed at 250 ° C. for 1 hour in a nitrogen atmosphere in an oven, and the film was completely cured to form a pattern of the coating type resin film 10.
Next, using the pattern of the second coating resin film 10 as a mask, the coating resin film 8 and the passivation film (when installed) were continuously removed by a dry etching method. The dry etching method is not particularly limited as long as it does not affect the silicone-based resin film, but the reactive ion etching method or the ion beam etching method is used, and the dry etching gas is CF ₄ / O ₂ / Ar. Was performed using a gas having a mixing ratio of 5/3/2. In this way, the pattern formation of the coating resin film 8 and the second coating resin film 10 having a two-layer structure was completed.

  The gain of this FET was reduced by 2.0 dB, and the characteristics were significantly improved. In addition, no deterioration of the characteristics was observed after the heat cycle test and the moisture resistance test. Furthermore, the characteristic variation of each chip in the wafer surface was significantly reduced. While the same effects as those of the fourth embodiment can be obtained and the resist pattern forming step can be omitted, the process can be simplified and the cost can be reduced.

It is a typical structure sectional view showing one embodiment of FET of the present invention. It is a typical structure sectional view showing other embodiments of FET of the present invention.

Explanation of symbols

  1 GaAs semi-insulating substrate, 2 GaAs or InGaAs channel layer, 3 n-type AlGaAs layer, 4 n-type GaAs layer, 5 source electrode, 6 drain electrode, 7 T-type gate electrode, 8 coated resin film, 9 Y-type gate electrode 10 Second coating type resin film.

Claims (5)

In a field effect transistor comprising a control circuit substrate having a gate electrode having a trapezoidal structure, a T-shaped structure or a Y-shaped structure, and a sealing resin,
A field effect transistor comprising a coating resin film interposed between the control circuit substrate and the sealing resin.   The coating resin film is composed of a silicone polymer, a polyimide polymer, a polyimide silicone polymer, a polyarylene ether polymer, a bisbenzocyclobutene polymer, a polyquinoline polymer, a perfluorohydrocarbon polymer, a fluoroavone polymer, an aromatic 2. The field effect transistor according to claim 1, wherein the field effect transistor comprises a cured film of at least one polymer selected from the group consisting of an aromatic hydrocarbon polymer and a copolymer of fluorocarbon and silicone.   3. The coating resin film according to claim 1, wherein the coating resin film is configured so as to fill and cover the periphery of the gate electrode without any gap by flowing the polymer by heat treatment in the vicinity of the melting point of the polymer. The field effect transistor described. The coating resin film is composed of a cured film of a silicone-based polymer,
The silicone polymer has the general formula (1):

[Wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ are an aryl group, a hydrogen atom, an aliphatic alkyl group, a hydroxyl group, a fluorine atom, a fluoroalkyl group, a trialkylsilyl group, or an unsaturated group. A functional group having a bond, which may be the same or different. k, l, m and n are all integers of 0 or more, 2k + (3/2) l + m + (1/2) n is a natural number, and the mass average molecular weight is 1000 or more. The molecular end group is an aryl group, a hydrogen atom, an aliphatic alkyl group, a hydroxyl group, a fluorine atom, a fluoroalkyl group, a trialkylsilyl group, or a functional group having an unsaturated bond. There may be. Or general formula (2):

(Wherein R ⁷ and R ⁸ are an aryl group, a hydrogen atom, an aliphatic alkyl group, a fluorine atom, a fluoroalkyl group or a functional group having an unsaturated bond, and may be the same or different. R ⁹ , R ¹⁰ , R ¹¹ and R ¹² are a hydrogen atom, an aryl group, an aliphatic alkyl group, a trialkylsilyl group or a functional group having an unsaturated bond, and may be the same or different. (N is an integer and the mass average molecular weight is 1000 or more)
The field effect transistor according to claim 2, wherein   The electric field according to any one of claims 1 to 4, wherein the coating type resin film is a laminated film composed of a plurality of layers, and each layer is composed of a cured film of a different polymer. Effect transistor.

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