JP5730511B2 - Manufacturing method of semiconductor device - Google Patents

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device having a nitride semiconductor.

  For example, a field effect transistor (FET) such as a high electron mobility transistor (HEMT) using a nitride semiconductor such as gallium nitride (GaN) is used as a power element that operates at high frequency and high output. It is known that a phenomenon called drain current collapse occurs in an FET using a nitride semiconductor (Patent Document 1).

JP-A-2005-286135

  In FETs using nitride semiconductors, it is required to suppress drain current collapse. An object of the present invention is to suppress drain current collapse.

The present invention includes a step of forming a source electrode, a gate electrode, and a drain electrode on a nitride semiconductor layer, a step of forming a silicon nitride film on the nitride semiconductor layer, the gate electrode, the drain electrode, Performing a heat treatment at 300 ° C. or higher in a state where the nitride semiconductor layer is not exposed from the silicon nitride film and an upper surface of the silicon nitride film is exposed between the gate electrode and the drain electrode And a step of treating the upper surface of the silicon nitride film between the gate electrode and the drain electrode with a solution containing hydrofluoric acid after the step of performing the heat treatment . It is a manufacturing method. According to the present invention, drain current collapse can be suppressed.

  The above structure can include a step of sealing without performing heat treatment at 300 ° C. or higher with the upper surface of the silicon nitride film exposed after the step of using the solution containing hydrofluoric acid.

  In the above structure, after the process using the solution containing hydrofluoric acid, the resin insulating film is in contact with the upper surface of the silicon nitride film without performing a heat treatment at 300 ° C. or higher with the upper surface of the silicon nitride film exposed. It can be set as the structure including the process of forming.

  In the above structure, the method includes a step of forming a field plate on the silicon nitride film between the gate electrode and the drain electrode, and the step of treating with a solution containing hydrofluoric acid is after the step of forming the field plate. It can be set as the process which is a process performed.

  In the above structure, the solution containing hydrofluoric acid may be buffered hydrofluoric acid or a hydrofluoric acid aqueous solution.

  According to the present invention, drain current collapse can be suppressed.

FIG. 1A to FIG. 1D are cross-sectional views (part 1) illustrating the method for manufacturing the semiconductor device according to the first embodiment. 2A to 2D are cross-sectional views (part 2) illustrating the method for manufacturing the semiconductor device according to the first embodiment. FIG. 3 is a sectional view (No. 3) illustrating the method for manufacturing the semiconductor device according to the first embodiment. FIG. 4A to FIG. 4C are diagrams showing drain voltage-current characteristics. FIG. 5 is a cross-sectional view illustrating the method of manufacturing the semiconductor device according to the second embodiment. FIG. 6 is a cross-sectional view illustrating the method of manufacturing the semiconductor device according to the third embodiment. FIG. 7A to FIG. 7D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to the fourth embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1A to FIG. 3 are cross-sectional views illustrating a method for manufacturing a semiconductor device according to the first embodiment. As shown in FIG. 1A, the buffer layer 12, the channel layer 14, the electron supply layer 16, and the cap layer 18 are sequentially formed as the semiconductor layer 19 on the substrate 10. The substrate 10 is SiC. The buffer layer 12 is an AlN layer having a thickness of 300 nm. The channel layer 14 is a GaN layer having a thickness of 1000 nm. The electron supply layer 16 is an n-type AlGaN layer having a thickness of 20 nm and an Al composition ratio of 0.2. The cap layer 18 is an n-type GaN layer having a thickness of 5 nm. A 2DEG (two-dimensional electron gas) 15 is formed at the interface of the electron supply layer 16 of the channel layer 14.

  As shown in FIG. 1B, a photoresist 40 having an opening is formed on the semiconductor layer 19. Using the photoresist 40 as a mask, the cap layer 18 is removed, and a recess reaching the electron supply layer 16 is formed. As shown in FIG. 1C, the photoresist 40 is peeled off. A two-layer photoresist 42 having an opening is formed. Ta and Al are vapor-deposited in the recess as the source electrode 20 and the drain electrode 22. The photoresist 42 is lifted off by removing it. Heat treatment is performed at a temperature of 550 ° C. Thus, the source electrode 20 and the drain electrode 22 are formed in the recess. As shown in FIG. 1D, a silicon nitride film 26 having a film thickness of 60 nm is formed by CVD (Chemical Vapor Deposition) so as to cover the semiconductor layer 19 and the source electrode 20 and the drain electrode 22. A photoresist 44 having a gate opening is formed.

As shown in FIG. 2A, the silicon nitride film 26 is etched using the photoresist 44 as a mask. As shown in FIG. 2B, the gate electrode 24 in contact with the semiconductor layer 19 is formed by using a vapor deposition method and a lift-off method. The gate electrode 24 is made of Ni and Au from the semiconductor layer 19 side. As shown in FIG. 2C, a silicon nitride film 28 having a thickness of 40 nm is formed on the silicon nitride film 26 so as to cover the gate electrode 24 by the CVD method. As shown in FIG. 2D, the silicon nitride films 26 and 28 on the source electrode 20 and the drain electrode 22 are removed. Au is formed by plating as the wiring 30 so as to be in contact with the source electrode 20 and the drain electrode 22. Heat treatment is performed at 350 ° C. for 30 minutes as a plating sinter.

As shown in FIG. 3, the surface of the silicon nitride film 28 is immersed in a buffered hydrofluoric acid solution of NH ₄ F: HF 10: 1 for 30 seconds. Thereby, the surface of the silicon nitride film 28 is etched by 1 to 10 nm.

  FIG. 4A to FIG. 4C are diagrams showing drain voltage-current characteristics. The HEMT whose drain voltage-current characteristics were measured has a gate length of 1 μm, a gate width of 80 μm, and a gate-drain distance of 5 μm. The drain voltage / current characteristics were measured using a curve tracer. 4 (a) to 4 (c), the broken line indicates the drain voltage / current characteristics when the drain voltage is applied up to 10V and the gate voltage is applied in steps of 2V to -1V. The solid line shows the drain voltage-current characteristics when the drain voltage is applied up to 50V and the gate voltage is applied in steps of 2V to -1V.

  FIG. 4 (a) shows the results measured after the step of FIG. 2 (d). As shown in FIG. 4A, the drain current is reduced by applying a drain voltage of 50V. This phenomenon is a drain current collapse phenomenon. FIG.4 (b) shows the result measured after washing with water and drying after FIG.2 (d). As shown in FIG. 4B, the drain current collapse phenomenon is not improved. FIG.4 (c) shows the result measured after FIG. As shown in FIG. 4C, the drain current collapse phenomenon is hardly observed even when a drain voltage of 50 V is applied. Thus, it was found that the drain current collapse phenomenon can be suppressed by treating the surface of the silicon nitride film 28 with a solution containing hydrofluoric acid.

  The drain current collapse is considered to be a phenomenon that occurs because electrons of the channel (2DEG) are trapped in the surface of the semiconductor layer 19 or traps in the silicon nitride films 26 and 28. It is considered that when there are many Si dangling bonds on the surface of the silicon nitride film 28, electrons are easily trapped in the trap due to the influence of the dangling bonds. When the silicon nitride film 28 is heat-treated, Si—H bonds are released and a large number of Si dangling bonds are formed on the surface of the silicon nitride film 28. For this reason, the drain current collapse increases. In particular, between the gate electrode 24 and the drain electrode 22, the electric field is large and 2DEG electrons are easily trapped in the trap. When the surface of the silicon nitride film 28 is treated with hydrofluoric acid as shown in FIG. 4C, the dangling bonds of Si on the surface of the silicon nitride film 28 become Si—H bonds, and the drain current collapse is suppressed.

  According to the first embodiment, at least the upper surface of the silicon nitride film 28 between the gate electrode 24 and the drain electrode 22 is treated with a solution containing hydrofluoric acid. Thereby, Si dangling bonds on the surface of the silicon nitride film 28 become Si—H bonds, and the drain current collapse is suppressed.

As a solution containing hydrofluoric acid, buffered hydrofluoric acid or hydrofluoric acid aqueous solution can be used as in Example 1. The aqueous hydrofluoric acid solution, HF: of _{H 2} O for example 1: 10 to 1: can be 1000. Further, at least the upper surface between the gate electrode 24 and the drain electrode 22 of the silicon nitride film 28 may be treated with hydrofluoric acid. For example, as in Example 1, the silicon nitride film between the source electrode 20 and the drain electrode 22 The entire upper surface of 28 may be treated with hydrofluoric acid.

  Si dangling bonds on the surface of the silicon nitride film 28 are likely to occur by heat treatment at 300 ° C. or higher, and more likely to occur at 350 ° C. or higher. Therefore, it is preferable that the heat treatment at 300 ° C. or higher is performed with the upper surface of the silicon nitride film 28 exposed, and the treatment using the solution containing hydrofluoric acid is performed after the heat treatment. The temperature of the heat treatment is more preferably 350 ° C. or higher.

  FIG. 5 is a cross-sectional view illustrating the method of manufacturing the semiconductor device according to the second embodiment. After the process of FIG. 3 of the first embodiment, the semiconductor chip 60 is divided into pieces. As shown in FIG. 5, the package has a base 52 and a cap 50. The semiconductor chip 60 manufactured according to the first embodiment is mounted on the base 52. The base 52 has a cap 50, and the semiconductor chip 60 is sealed.

  As shown in FIG. 5, after the treatment with the solution containing hydrofluoric acid shown in FIG. 3, the silicon nitride film 28 is sealed without being subjected to heat treatment at 300 ° C. or higher with the upper surface of the silicon nitride film 28 exposed. For example, the upper surface of the silicon nitride film 28 is sealed with the upper surface of the silicon nitride film 28 exposed. As a result, it is possible to maintain a state where there are few dangling bonds on the surface of the silicon nitride film 28. The sealing is preferably hermetic sealing, and is preferably sealed using an inert gas such as nitrogen or argon.

  FIG. 6 is a cross-sectional view illustrating the method of manufacturing the semiconductor device according to the third embodiment. As shown in FIG. 6, after the step of treating with the hydrofluoric acid solution of FIG. An insulating film 32 is formed in contact with the substrate. As a result, it is possible to maintain a state where there are few dangling bonds on the surface of the silicon nitride film 28. For example, the insulating film 32 can be a resin insulating film made of an epoxy resin. The step of forming the resin insulating film is a step of curing the epoxy resin at a temperature of about 200 ° C. after applying the epoxy resin. The insulating film 32 is preferably a film other than a silicon nitride film, and is preferably an insulating film that hardly generates dangling bonds on the surface.

  Example 4 is an example of a method for manufacturing a semiconductor device having a field plate. FIG. 7A to FIG. 7D are cross-sectional views illustrating a method for manufacturing a semiconductor device according to the fourth embodiment. As shown in FIG. 7A, after FIG. 2C of the first embodiment, the wiring 30 is formed on the source electrode 20 and the drain electrode 22. At this time, a field plate 34 is formed on at least the silicon nitride film 28 between the gate electrode 24 and the drain electrode 22. In the example of FIG. 7A, a field plate 34 is formed on the silicon nitride film 28 between the source electrode 20 and the gate electrode 24 and the drain electrode 22.

  As shown in FIG. 7B, a silicon nitride film 36 having a thickness of 600 nm is formed on the field plate 34 and the silicon nitride film 28 by the CVD method. As shown in FIG. 7C, a photoresist 46 having an opening is formed on the silicon nitride film 36. Using the photoresist 46 as a mask, the silicon nitride films 36 and 28 are etched using a solution containing hydrofluoric acid. As shown in FIG. 7D, the photoresist 46 is removed.

  After the field plate 34 is formed as in the fourth embodiment, the upper surface of the silicon nitride film 36 between the field plate 34 and the drain electrode 22 is processed using a solution containing hydrofluoric acid. Thereby, the dangling bonds of Si on the surface of the silicon nitride film 36 are reduced, and the drain current collapse is suppressed.

  In the first to fourth embodiments, the HEMT in which AlGaN is the electron supply layer 16 and GaN is the channel layer 14 has been described as an example. However, as the semiconductor layer 19, other nitride semiconductors can be used. The nitride semiconductor is a semiconductor containing nitrogen, such as InN, AlN, InGaN, InAlN, or AlInGaN.

  Further, in Examples 1 to 4, the example in which the cap layer 18 is provided has been described. However, the gate electrode 24 may be directly formed on the electron supply layer 16 without providing the cap layer 18. Moreover, although the example of SiC was demonstrated as the board | substrate 10, the board | substrate 10 may be a sapphire or a Si substrate.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

19 Semiconductor layer 20 Source electrode 22 Drain electrode 24 Gate electrode 26, 28 Silicon nitride film 34 Field plate 36 Insulating film

Claims (6)

Forming a source electrode, a gate electrode, and a drain electrode on the nitride semiconductor layer; and
Forming a silicon nitride film on the nitride semiconductor layer;
In a state where the nitride semiconductor layer between the gate electrode and the drain electrode is not exposed from the silicon nitride film and an upper surface of the silicon nitride film between the gate electrode and the drain electrode is exposed, Performing a heat treatment at 300 ° C. or higher;
After the step of performing the heat treatment, treating the upper surface of the silicon nitride film between the gate electrode and the drain electrode with a solution containing hydrofluoric acid;
A method for manufacturing a semiconductor device, comprising: After the step of treating with a solution containing the hydrofluoric acid, the semiconductor of claim 1, wherein the upper surface of the silicon nitride film is characterized in that it comprises a step of sealing without 300 ° C. or more heat treatment while exposed Device manufacturing method. After the process using the solution containing hydrofluoric acid, a process of forming a resin insulating film in contact with the upper surface of the silicon nitride film without performing a heat treatment at 300 ° C. or higher with the upper surface of the silicon nitride film exposed. the method of manufacturing a semiconductor device according to claim 1, comprising a. Forming a field plate on the silicon nitride film between the gate electrode and the drain electrode;
Method of manufacturing steps, the semiconductor device according to any one claim of claims 1 to 3, characterized in that the step performed after the step of forming the field plate is treated with a solution containing hydrofluoric acid. The solution containing the hydrofluoric acid, buffered hydrofluoric acid or a method of manufacturing a semiconductor device according to any one of claims 1, wherein 4 to be a hydrofluoric acid solution. Forming a wiring on each of the source electrode and the drain electrode by plating,
6. The method of manufacturing a semiconductor device according to claim 1, wherein the heat treatment is a plating sinter of the wiring.

Images