JP4161917B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a semiconductor device having a Schottky junction and a manufacturing method thereof.

  2. Description of the Related Art Conventionally, in a so-called field effect transistor using a gallium nitride based semiconductor, a configuration using nickel as a material as a gate electrode for obtaining Schottky characteristics is known.

For example, a high electron mobility transistor (HEMT, hereinafter simply referred to as HEMT) using a two-dimensional electron gas generated at an Al _x Ga _1-x N / GaN heterojunction interface is known (for example, Non-Patent Document 1). In this HEMT, Ni (nickel) is used as the material of the gate electrode.
W. Lu, J. Yang, MA Khan, I. Adesida, IEEE Transactions on Electron Devices, Vol. 48, No. 3, 581 (2001) "AlGaN / GaN HEMTs on SiC with over 100GHz fT and Low Microwave Noise"

  For example, according to the technique described in Non-Patent Document 1 described above, nickel is used as a material for the gate electrode. As described above, when the gate electrode is formed of nickel, a reverse current is generated in the nitride semiconductor particularly during operation. Therefore, the reliability of the operation of the semiconductor element is lowered.

  As described above, the present situation is that the configuration for effectively suppressing the generation of the reverse current of the semiconductor element has not yet been realized. Therefore, a technique for realizing a semiconductor element that effectively suppresses the generation of such reverse current is desired.

  The present invention has been made in view of the above problems. In solving the above-described problems, the semiconductor element of the present invention has the following structural features.

That is, a semiconductor element of the present invention includes a substrate, a stacked structure of compound semiconductors provided on the substrate and including an n-AlGaN layer as an outermost layer, and a ruthenium layer provided in contact with the n-AlGaN layer. And a Schottky electrode having a laminated structure .

In addition, according to the method for manufacturing a semiconductor device of the present invention, a step of preparing a substrate, a step of forming a compound semiconductor layer including an n-AlGaN layer as an outermost layer on the substrate, and ruthenium on the n-AlGaN layer Forming a Schottky electrode having a laminated structure including layers by bringing the ruthenium layer into contact with the n-AlGaN layer.

  According to the configuration of the semiconductor element of the present invention, a Schottky junction having good characteristics can be formed by the n-AlGaN layer and the ruthenium layer in contact with the n-AlGaN layer. Therefore, so-called reverse current can be effectively suppressed. Therefore, if such a configuration is applied, for example, as a gate electrode of a so-called field effect transistor, the loss of the amplification function of the transistor due to the difficulty in controlling the depletion layer due to the generation of reverse current is more effective. Can be reduced. That is, a higher-performance semiconductor element can be provided.

  Moreover, according to the method for manufacturing a semiconductor element of the present invention, a semiconductor element having the above-described effects can be efficiently manufactured.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, only the shapes, sizes, and arrangement relationships of the respective constituent components are schematically shown to such an extent that the present invention can be understood, and the present invention is not particularly limited thereby. In the following description, specific materials, conditions, numerical conditions, and the like may be used. However, these are merely preferred examples, and are not limited to these.

1. Configuration of Semiconductor Element A configuration example of a semiconductor element of the present invention will be described with reference to FIG.

  FIG. 1 is an explanatory view schematically showing a cut surface of a cut surface of an element for explaining a configuration of a semiconductor element 10 of the present invention. Here, an example of a Schottky diode structure using a stacked structure of GaN-based compound semiconductors provided with a so-called high electron mobility transistor (hereinafter also simply referred to as HEMT) will be described.

  The semiconductor element 10 of the present invention is formed on a substrate 12. In this example, the substrate 12 is a sapphire substrate.

  On one surface (also referred to as a substrate surface) 12 a of the substrate 12, a compound semiconductor stacked structure (also simply referred to as a compound semiconductor layer) 20 including a plurality of layers is provided.

  On the substrate 12, a GaN buffer layer is provided as the first buffer layer 22. The first buffer layer 22 may be, for example, an AlN layer.

  On the GaN buffer layer, a second buffer layer 24, that is, an i-GaN layer in this example, is provided.

On the second buffer layer 24, a spacer layer 26, that is, an i-Al _0.24 Ga _0.76 N spacer layer in this example is provided.

On the spacer layer 26, an n-Al _0.24 Ga _0.76 N donor layer 28 which is a donor layer (Schottky junction layer) 28 which is a layer for supplying carriers is provided.

The composition of the AlGaN layer constituting the spacer layer 26 and the donor layer 28 described above is merely an example. That is, the composition ratio of the AlGaN layer is defined as Al _x Ga _1-x N (0 ≦ x <1), and any suitable composition ratio can be set within this range. Considering the quality of the film to be formed (surface roughness) and the mobility of electrons in the two-dimensional electron layer (2DEG), x is preferably about 0.5 at most.

  As described above, the compound semiconductor layer 20 of this example has a structure in which the first buffer layer 22, the second buffer layer 24, the spacer layer 26, and the donor layer 28 are sequentially stacked on the substrate 12. is doing.

  On the surface 28a of the donor layer 28, a Schottky electrode 32 and an ohmic electrode 34 are formed apart from each other.

  The Schottky electrode 32 of the present invention includes a ruthenium layer 32a and an antioxidant film 32b provided on the ruthenium layer 32a. The ruthenium layer 32a comes into contact with the Schottky junction layer 28 and combines with each other to form a so-called Schottky junction. The antioxidant film 32b can be a general antioxidant film. The antioxidant film 32b is preferably a film made of, for example, gold (Au).

  In this example, the ohmic electrode 34 includes a first ohmic metal layer 34a selected from titanium (Ti) and a second ohmic metal layer 34b provided on the first ohmic metal layer 34a. The second ohmic metal layer 34b is preferably formed using, for example, aluminum (Al) as a material in order to reduce ohmic contact resistance.

  As apparent from the above description, the semiconductor element 10 of the present invention includes the n-AlGaN layer that is the donor layer 28 and the ruthenium layer 32a that forms a Schottky junction with the n-AlGaN layer as the Schottky electrode 32. It has a configuration.

  With such a configuration, a Schottky junction with excellent electrical characteristics can be obtained. Specifically, in the reverse bias state, the generation of so-called reverse current can be prevented, so that the loss of the amplification function of the transistor due to the difficulty in controlling the depletion layer due to the generation of reverse current. Can be reduced more effectively.

  The structure of the compound semiconductor element in which the ruthenium metal layer 32a is Schottky-bonded to the n-AlGaN layer is merely an example for evaluating the characteristics of the Schottky-junction. It can be applied to the bonding of electrodes of any compound semiconductor device to which the layer is applied. Specifically, for example, the present invention is suitably applied to the configuration of the gate electrode of the field effect transistor such as the HEMT described above.

2. Next, a method for manufacturing the semiconductor element 10 described with reference to FIG. 1 will be described with reference to FIG.

  2A, 2 </ b> B, 2 </ b> C, and 2 </ b> D are schematic views illustrating a cut surface of a semiconductor element that is being manufactured in order to explain the manufacturing process.

  First, as shown in FIG. 2A, in this example, a substrate 12 which is a sapphire substrate is prepared.

  Next, as illustrated in FIG. 2B, a compound semiconductor layer 20 including a plurality of layers is formed on the surface 12 a of the substrate 12. The stacked structure 20 is formed by sequentially epitaxially growing a plurality of compound semiconductor layers.

  In this example, first, the first buffer layer 22 which is a GaN layer is formed on the substrate 12. This formation can be performed by a conventionally known metal organic chemical vapor deposition (MOCVD) method performed under any suitable conditions. For example, a molecular beam epitaxial method (MBE method) can also be applied.

  A second buffer layer 24, which is an i-GaN layer in this example, is formed on the first buffer layer 22 by the same metal organic vapor phase growth process.

Next, a spacer layer 26 that is an i-Al _0.24 Ga _0.76 N layer is formed on the second buffer layer 24.

Next, the donor layer 28 which is an n-Al _0.24 Ga _0.76 N layer is formed on the spacer layer 26.

  In this way, the compound semiconductor layer 20 in which a plurality of layers are stacked is formed by sequentially forming a film.

  Thereafter, as shown in FIG. 2C, the ohmic electrode 34 is formed on the compound semiconductor layer 20. In this example, first, a conventionally known mask process and electron beam evaporation process are performed under any suitable conditions using titanium (Ti) and aluminum (Al). Specifically, using a mask such as a resist having an opening in the shape of an ohmic electrode, for example, a titanium film is laminated with a thickness of 15 nm, and then an aluminum film is laminated on the titanium film with a thickness of 200 nm.

  Next, a conventionally known lift-off process is performed to form, for example, a first ohmic metal layer 34a that is a titanium film and a second ohmic metal layer 34b that is an aluminum film. In this way, the ohmic electrode 34 is formed.

  Next, an annealing process is performed at 550 ° C. for 1 minute in a nitrogen atmosphere to form a good ohmic contact.

Next, as shown in FIG. 2D, a Schottky electrode 32 is formed. A ruthenium (Ru) layer having a film thickness of 50 nm is formed by electron beam evaporation in the same manner as in the above-described ohmic electrode 34 formation step. Next, a gold (Au) film having a thickness of 400 nm is formed on the ruthenium layer by electron beam evaporation. Next, a conventionally known lift-off process is performed to form a ruthenium layer 32a made of ruthenium and an antioxidant film 32b, for example, a gold film. Thus, in this example, the Schottky electrode 32 having a junction area of 2.50 × 10 ⁻⁵ cm ² is formed.

  Here, the film forming process of the ruthenium layer 32a will be described. As the apparatus used for film formation, a conventionally known film formation apparatus can be used. In the electron beam evaporation method, for example, a cup-shaped container called a hearth liner is filled with an evaporation material, that is, ruthenium (Ru) in this example, and this ruthenium is irradiated with an electron beam to evaporate it. Then, a ruthenium layer is deposited on the donor layer (Schottky junction layer) 28.

  The irradiation conditions of the electron beam applied to the ruthenium in the hearth liner are preferably an acceleration voltage of 8 keV, a filament current of 17 to 18 A (ampere), and an emission current of 0.18 to 0.27 A. A value within the range of (Ampere) is good. When the electron beam is irradiated under such conditions, a film formation rate within a range of 0.01 nm / second to 0.06 nm / second can be obtained.

  If the emission current of the electron beam is made larger than the above range in order to improve the film formation rate, ruthenium in the hearth liner may bump.

  The hearth liner described above is generally formed of copper (Cu), tungsten (W), or any other suitable metal material. For example, a hearth liner made of tungsten having excellent heat resistance is filled with ruthenium. Even when electron beam irradiation is performed, ruthenium and tungsten react with each other at a high temperature, and the hearth liner may be damaged.

  Therefore, when performing the electron beam evaporation process of the ruthenium layer under the above-described conditions, it is preferable to use a carbon hearth liner.

  Thus, if an electron beam vapor deposition process is performed, the ruthenium Schottky electrode which has a favorable Schottky characteristic can be formed efficiently. That is, it is possible to efficiently manufacture a semiconductor element in which generation of reverse current is effectively suppressed.

3. Electrical Characteristics of Semiconductor Element With reference to FIG. 3, the current-voltage characteristics of the semiconductor element having the above-described structure will be described. FIG. 3 is a graph for explaining current-voltage characteristics of the semiconductor element of the present invention. In FIG. 3, the horizontal axis represents voltage (unit: V), and the vertical axis represents the absolute value of current density (unit: A / cm ² ) as a logarithmic display.

  Graph (I) is a graph showing current-voltage characteristics of a Schottky diode having the same configuration as that of the semiconductor element described above, except that the material of the Schottky electrode is nickel (Ni) as a conventional control.

  Graph (II) is a diagram showing the current-voltage characteristics of a semiconductor element (Schottky diode) having the above-described structure of the ruthenium layer of the present invention as a Schottky electrode.

  As is apparent from the graph (II), when the applied voltage is a negative voltage, when looking from -8 volts to 0 volts, the reverse current is about -8 volts to -5 volts. Is reduced to about 1/100. From -5 volts to 0 volts, the reverse current further decreases to 1/1000 and approaches 0 (zero).

  As the applied voltage turns positive, the absolute value of the current density increases sharply.

  It can be understood from the shape of the graph (II) that the semiconductor element using the ruthenium layer of the present invention as a Schottky electrode has good Schottky characteristics.

  As is clear from the comparison between the graph (I) and the graph (II), the current value (II) of the semiconductor element using the ruthenium layer as a Schottky electrode when a negative voltage is applied to the semiconductor element is the same as the conventional nickel layer. As compared with the current value (I) of a semiconductor element having a Schottky electrode, it can be understood that the current value is reduced to 1/100 or less. Specifically, when the applied voltage is in the range of -8 volts to -6 volts, it can be seen that the reverse current is reduced to about 1/1000. In the range of the applied voltage from -5 volts to -3 volts, the difference in the generated reverse current is maximized and reduced to 1 / 10,000 or less. It can be seen that in the range of applied voltage from -3 volts to 0 volts, the difference in the generated reverse current is slightly reduced, but is reduced to about 1/100.

  Furthermore, the electrical characteristics when the forward voltage of each of the semiconductor elements having the current-voltage characteristics shown in the graph (I) and the graph (II) is applied are evaluated based on the so-called thermionic emission theory. did.

  The details of the thermionic emission theory and the ideal factor (n value) derived from the theory are not the gist of the present invention, and the description thereof will be omitted.

  As a result, the barrier height of the semiconductor element having the ruthenium layer as a Schottky electrode was 1.1 eV (electron volts), and the ideal factor (n value) was 1.6.

  On the other hand, the barrier height of the semiconductor element using nickel as a Schottky electrode was 0.77 eV, and the ideal factor (n value) was 1.7.

  As described above, the barrier height of the semiconductor element using the ruthenium layer as the Schottky electrode is larger than the barrier height of the semiconductor element using the nickel as the Schottky electrode. This means that the Schottky electrode of the ruthenium layer generates more reverse current. It means that it can be effectively suppressed.

  In addition, the ideal factor of a semiconductor element using a ruthenium layer as a Schottky electrode is closer to 1 than the ideal factor of a semiconductor element using nickel as a Schottky electrode. This means that ideal Schottky characteristics have been obtained.

  That is, for example, if a field effect transistor is manufactured using an n-AlGaN layer as a Schottky junction layer and a ruthenium Schottky electrode as a gate electrode, a good Schottky with a reduced gate leakage current can be obtained. An element having characteristics can be obtained.

  According to the configuration of the Schottky electrode suitable for application to the field effect transistor or the like of the present invention, a Schottky electrode having a Schottky junction with more excellent electrical characteristics can be obtained. Specifically, the Schottky electrode of the present invention can suppress the generation of reverse current in the so-called reverse bias state of the element. That is, the loss of the amplification function of the transistor due to the difficulty in controlling the depletion layer due to the generation of reverse current can be more effectively reduced.

  In addition, according to the manufacturing method of the present invention, a semiconductor element including a Schottky electrode that exhibits such an effect can be efficiently formed.

It is explanatory drawing which showed roughly the cut end of the cut surface of an element, in order to demonstrate the structure of the semiconductor element of this invention. (A), (B), (C) and (D) are schematic diagrams showing a cut surface obtained by cutting a semiconductor element being manufactured in order to explain the manufacturing process. It is a graph for demonstrating the current-voltage characteristic of the semiconductor element of this invention.

Explanation of symbols

10: Semiconductor element 12: Substrate (sapphire substrate)
12a: surface 20: compound semiconductor layer 22: first buffer layer 24: second buffer layer 26: spacer layer 28: donor layer (Schottky junction layer)
32: Schottky electrode 32a: Ruthenium layer 32b: Antioxidation film 34: Ohmic electrode 34a: First ohmic metal layer 34b: Second ohmic metal layer

Claims (5)

A substrate,
A stacked structure of compound semiconductors provided on the substrate and including an n-AlGaN layer as an outermost layer;
A semiconductor device comprising: a Schottky electrode having a laminated structure including a ruthenium layer provided in contact with the n-AlGaN layer.   The substrate is a sapphire substrate, and the stacked structure of the compound semiconductor is provided on a buffer layer provided on the substrate, an i-GaN layer provided on the buffer layer, and the i-GaN layer. 2. The semiconductor device according to claim 1, further comprising: an i-AlGaN layer, and an n-AlGaN layer provided on the i-AlGaN layer. Preparing a substrate;
Forming a compound semiconductor stacked structure including an n-AlGaN layer as an outermost layer on the substrate;
And a step of forming a Schottky electrode having a laminated structure including a ruthenium layer on the n-AlGaN layer by bringing the ruthenium layer into contact with the n-AlGaN layer. 4. The method of manufacturing a semiconductor device according to claim 3, wherein the step of forming the ruthenium layer is a step performed by an electron beam evaporation method using a carbon hearth liner. The step of forming the ruthenium layer is performed with an acceleration voltage of 8 keV, a filament current within a range of 17 to 18 amperes, and an emission current within a range of 0.18 to 0.27 amperes. 3 is a method for producing a semiconductor device as described in 4 above.

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