JP5581471B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a structure of a semiconductor device using a nitride semiconductor and a manufacturing method thereof.

  In the conventional semiconductor device, the composition ratio of Al (aluminum) in the AlGaN (aluminum gallium nitride) layer (hereinafter simply referred to as “Al composition ratio”) is x%, the film thickness of the AlGaN layer is y nm, and x High electron mobility transistor (HEMT) in which y satisfies the formula [x + y <55, 25 ≦ x ≦ 40, y ≧ 10] and forms a two-dimensional electron gas at the junction interface between the AlGaN layer and the GaN (gallium nitride) layer An example of a technique called “mobility transistor” is disclosed (see, for example, Patent Document 1). According to this semiconductor device, since the film thickness of the AlGaN layer is made thinner than the critical film thickness to prevent the occurrence of cracks, the change in sheet resistance with time can be eliminated.

An example of a technique for growing an insulating film at a temperature of 750 ° C. or lower is disclosed (for example, see Patent Document 2). According to this semiconductor device, the maximum depth of the gaps existing between the columnar crystal masses is 65 [%] or less of the film thickness, the average depth is 30 [%] or less of the film thickness, and the average of each columnar crystal mass The diameter becomes 28 [nm] or less, and the leakage current generated between the gate electrode and the electron transit layer can be suppressed.
JP 2007-324363 A JP 2000-294768 A

  However, in the semiconductor device of Patent Document 1, the transistor is normally turned on under the influence of the high concentration two-dimensional electron gas generated at the hetero boundary surface, and the transistor is not turned off unless the gate voltage is made negative. When an inverter circuit is configured using this semiconductor device, for example, when the control signal of the gate voltage disappears (that is, becomes 0) during the operation of the inverter, two transistors connected in series are simultaneously turned on to supply power. There is a problem that a short circuit occurs and the inverter circuit is damaged. Therefore, in order to use the semiconductor device as a power device, it is necessary to make the semiconductor device normally off.

  Patent Document 2 describes a semiconductor device in which an insulating film made of undope-AlN or undope-AlGaN is grown on an electron transit layer made of n-type GaN. However, since the Al composition ratio and film thickness of the electron transit layer are not described, this semiconductor device may be normally-on as described above. Since a semiconductor device in which an insulating film is grown on an electron supply layer made of AlGaN is not described, it is unclear whether or not leakage current generated on the surface of the electron supply layer can be suppressed.

  The present invention has been made in view of these points, and an object thereof is to provide a semiconductor device that is normally off and that can suppress the occurrence of leakage current, and a method for manufacturing the same.

(1) Means for solving the problem (hereinafter, simply referred to as “solution means”) 1 is a nitride-based III-V group compound formed by epitaxial growth on a substrate and containing at least aluminum as a group III element. A semiconductor having an insulating film formed of aluminum nitride having a heterojunction structure of an electron supply layer formed and an electron transit layer formed of a nitride-based III-V group compound not containing aluminum as a group III element an apparatus, electron transit layer is formed by epitaxial growth on a substrate, the electron supply layer, the composition ratio of aluminum as a 10 to 18%, as 5~15nm thickness, epitaxially grown on the electron transit layer formed by the insulating film, by forming by epitaxial growth at a low temperature of about 700 ° C. on the electron supply layer, this electron supply layer And summarized in that where the structure are separated from each other with respect to the electron transit layer Ri.

The “electron supply layer” may be formed of a nitride III-V group compound containing at least aluminum as a group III element. That is, the group III element includes at least one of the group consisting of Ga (gallium), Al (aluminum), B (boron), and In (indium), and Al is an essential element. The group V element includes at least one of the group consisting of N (nitrogen), P (phosphorus), and As (arsenic).
The “electron transit layer” only needs to be formed of a nitride III-V group compound not containing aluminum as a group III element . That is, it is the same as the electron supply layer except that it does not contain Al as a group III element .
The “insulating film” may be formed of aluminum nitride .

According to Solution 1, since the electron supply layer is formed with an aluminum composition ratio of 10 to 18% and a film thickness of 5 to 15 nm, a normally-off semiconductor device is obtained. Further, an insulating film formed of aluminum nitride was epitaxially grown on the electron supply layer at a low temperature of about 700 ° C., the electron transit layer contains no aluminum insulating film as a Group III element The electron supply layer it is possible to suppress Runode, generation of leakage current across the.

(2) Solution 2 is the semiconductor device described in Solution 1, which is a HEMT or MESFET (Metal-Semiconductor Field Effect Transistor) that forms a two-dimensional electron gas at the junction interface between the electron supply layer and the electron transit layer. The main point is that it is a metal-semiconductor field effect transistor.

  According to the solution 2, it is possible to provide a HEMT or MESFET semiconductor device that is normally off and can suppress the occurrence of leakage current.

(3) Solution 3 includes an electron supply layer formed on a substrate and formed of a nitride III-V compound containing at least aluminum as a group III element, and a nitride not containing aluminum as a group III element A method of manufacturing a semiconductor device having a heterojunction structure with an electron transit layer formed of a group III-V compound and having an insulating film formed of aluminum nitride , wherein the electron transit layer is formed on a substrate by epitaxial growth And forming the electron supply layer epitaxially on the electron transit layer while controlling the gas supply amount so that the composition ratio of aluminum becomes 10 to 18% and the film thickness becomes 5 to 15 nm. a step, by by epitaxial growth at a low temperature of about 700 ° C. on the electron transit layer forming the insulating film, the insulating film on the electron transit layer by the electron supply layer And and a step of the configuration that are separated from one another, MOCVD epitaxial growth in these three steps (Metal Organic Chemical Vapor Deposition; metalorganic chemical vapor deposition) method, MBE (Molecular Beam Epitaxy; molecular beam epitaxy) method Alternatively, the gist is to carry out using any one of HVPE (Hydride Vapor Phase Epitaxy) method.

According to the solution 3, similarly to the solution 1 described above, it is a normally-off semiconductor device, and the occurrence of a leakage current can be suppressed. In addition, since any of the MOCVD method, the MBE method, and the HVPE method is performed, the substrate being manufactured is not exposed to the air for replacing the apparatus. Therefore, the interface is prevented from being deteriorated and the reliability of the device is increased.
In addition to the method described above, it is also possible to perform epitaxial growth using, for example, an ALE (Atomic Layer Epitaxy) method.

  According to the present invention, it is possible to provide a semiconductor device and a manufacturing method thereof that can suppress the occurrence of leakage current while realizing normally-off by forming an insulating film grown at a low temperature on the electron supply layer. it can.

  The best mode for carrying out the present invention will be described with reference to the drawings.

First, FIG. 1 is a cross-sectional view showing a configuration example of a semiconductor device according to the present invention. In the semiconductor device 10 shown in FIG. 1, an electron transit layer 16 is formed on a substrate 17 by epitaxial growth, and an electron supply layer 12 is formed on the electron transit layer 16 by epitaxial growth. The electron transit layer 16 and the electron supply layer 12 have a heterojunction structure and are a HEMT capable of forming a two-dimensional electron gas channel 13 at the junction interface. An insulating film 11 is formed on the electron supply layer 12 by epitaxial growth, and electrodes (that is, a source electrode, a gate electrode, and a drain electrode) are further provided. Substrate 17 is formed of, for example, SiC (carbonization silicon).

  The electron transit layer 16 is formed of a nitride III-V group compound, for example, GaN. The electron transit layer 16 of this example is formed of a plurality of layers including an LT-GaN layer 15 (a GaN layer grown at a low temperature) and a GaN layer 14 grown on the LT-GaN layer 15.

The electron supply layer 12 is formed of a nitride III-V group compound containing at least aluminum as a group III element, and corresponds to, for example, AlGaN (Al _0.26 Ga _0.74 N in the example of FIG. 1). The electron supply layer 12 is formed with an Al composition ratio of 10 to 18 [%] and a film thickness of 5 to 15 [nm].

  The insulating film 11 is formed of a nitride III-V group compound containing at least aluminum as a group III element in the same manner as the electron supply layer 12 described above, and is made of, for example, AlN (aluminum nitride). Note that the temperature at which the insulating film 11 is formed by epitaxial growth is around 700 [° C.] (specifically, 650 to 750 [° C.]).

A method of manufacturing the semiconductor device 10 having the above-described configuration will be described with reference to FIG. FIG. 2 is a cross-sectional view schematically showing an example of the MOCVD apparatus. Specifically, a horizontal section is shown in FIG. 2A, and a vertical section is shown in FIG. The MOCVD apparatus 20 shown in FIG. 2 includes a supply port 21, a reaction unit 22, a discharge port 23, a turntable 25, a heater 26, a driving means 28, and the like. The supply port 21 is filled with a gas containing a raw material necessary for epitaxial growth. In this example, as shown in FIG. 2B, three supply ports 21a, 21b, and 21c are provided to supply three types of gases. In the example of FIG. 2B, N ₂ gas (nitrogen gas) is supplied from the supply port 21a, and a group III element and a carrier (for example, N ₂ gas or H ₂ gas (hydrogen gas)) are supplied from the supply port 21b. A gas containing a group V element and a carrier is supplied from the supply port 21c.

  In the reaction unit 22, as shown in FIG. 2B, a laminar flow region and a diffusion region are provided between the supply port 21 and the turntable 25. In the laminar flow region, a partition plate 22a is provided on the supply port side in order to stabilize the gas supplied from each supply port into a laminar flow. The diffusion region is between the laminar flow region and the turntable 25, and the gas supplied from each supply port is mixed because there is no partition plate 22a.

  The upper surface of the turntable 25 is formed in a concave shape, and the wafer 24 is placed in this concave portion. The turntable 25 is fixed to the rotary shaft 27 of the drive means 28 and is rotated by performing drive control of the drive means 28. The heater 26 is provided below the turntable 25 and heats the wafer 24 through the turntable 25. The drive unit 28 includes a drive source (for example, a motor) and a control circuit. The electron transit layer 16, the electron supply layer 12, the insulating film 11, and the like are formed on the wafer 24 by epitaxial growth while controlling the type of gas, the supply speed of each gas, and the rotation speed of the turntable 25. Below, the specific example of the process of forming each layer is demonstrated easily.

(Step 1) Formation of the LT-GaN layer 15 constituting the electron transit layer 16 The temperature in the reaction part 22 is adjusted to a low temperature (around 700 [° C.]), and TMG (trimethylgallium) gas and NH ₃ (ammonia) gas are used. To form an LT-GaN layer 15 on the substrate 17.

(Step 2) Formation of the GaN layer 14 constituting the electron transit layer 16 The reaction part 22 is adjusted to a high temperature (about 1100 [° C.]), and TMG gas and NH ₃ gas, and further SiH ₄ (monosilane) gas as impurities Then, a GaN layer 14 is formed on the LT-GaN layer 15.

(Step 3) Formation of an AlGaN layer corresponding to the electron supply layer 12 The temperature in the reaction unit 22 is adjusted to a high temperature (about 1100 [° C.]), and TMG gas, NH ₃ gas, and TMA (trimethylaluminum) gas are reacted. To form an AlGaN layer. However, in order to make the Al composition ratio 10 to 18%, the supply amount of each gas is controlled so that Al and Ga have a predetermined ratio. Further, the gas supply amount, growth time, and the like are controlled so that the film thickness becomes 5 to 15 [nm].

(Step 4) Formation of an AlN layer corresponding to the insulating film 11 The temperature in the reaction part 22 is adjusted again to a low temperature (around 700 [° C.]), and Al material gas and NH ₃ gas are supplied continuously or intermittently. An AlN layer is formed.

  If the process up to step 4 is performed, the insulating film 11 is formed, so that each electrode (source electrode, gate electrode, drain electrode) is formed on the insulating film 11. The material of the electrode is, for example, Ti (titanium) or Au (gold), and is formed by a vapor deposition method, a lift-off method, or the like. Thereafter, when it is appropriately cut, the semiconductor device 10 of FIG. 1 is obtained.

The characteristics of the semiconductor device 10 manufactured as described above will be described with reference to FIGS. FIG. 3 is a graph showing a relationship in which the horizontal axis represents the Al composition ratio [%] and the vertical axis represents the threshold voltage V _th [V] of the gate electrode. FIG. 4 is a graph showing the relationship where the horizontal axis is the film thickness [nm] of the AlGaN layer and the vertical axis is the threshold voltage V _th [V] of the gate electrode. FIG. 5 is a graph showing the relationship where the horizontal axis is the growth temperature [° C.] of the insulating film and the vertical axis is the source-drain current [mA / mm]. FIG. 6 is a graph showing a relationship in which the horizontal axis is the growth temperature [° C.] of the insulating film and the vertical axis is the mutual conductance [mS / mm].

FIG. 3 shows the threshold voltage V _th when the semiconductor device 10 is manufactured with the AlGaN layer thickness set to 5, 10, 15, 20, 26 [nm] and the Al composition ratio changed for each thickness. . FIG. 4 shows threshold voltages V _th when the Al composition ratio is 5, 10, 15, 20, 25, 35, 45, 55 [%] and the semiconductor device 10 is manufactured with the thickness of the AlGaN layer changed. Represents. In order for the manufactured semiconductor device 10 to be normally off, the threshold voltage V _th shown in FIGS. 3 and 4 must be 0 [V] or more. As shown by hatching, the film thickness of the AlGaN layer is in the range of 5 to 15 [nm], and the Al composition ratio is in the range of 10 to 18 [%].
Since the semiconductor device of Patent Document 1 has an AlGaN layer thickness of 10 [nm] or more and an Al composition ratio of 25 [%] or more, both are normally on when applied to FIGS. It is clear that

The semiconductor devices 10 in which the insulating film 11 (AlN layer) was formed at 500, 600, 700, 800, 900, 1130 [° C.] were produced. The maximum source-drain current I _DSmax in each semiconductor device 10 is shown in FIG. 5, and the maximum mutual conductance g _mmax is shown in FIG. Since the semiconductor device 10 in which the AlN layer is grown at 700 [° C.] can suppress the leakage current generated on the surface of the electron supply layer 12, as shown in FIGS. 5 and 6, the source-drain current I High characteristics were obtained for _DSmax and transconductance _gmmax .
Note that the semiconductor device 10 in which the insulating film 11 (AlN layer) is grown at 1130 [° C.] also has high source-drain current I _DSmax and mutual conductance g _mmax, but is not suitable because it is _{normally on} .

According to the embodiment described above, the following effects can be obtained.
(1) The electron supply layer 12 was formed by epitaxial growth with an Al composition ratio of 10 to 18 [%] and a film thickness of 5 to 15 [nm] (see FIG. 1). The produced semiconductor device 10 is normally off (see FIG. 3 and FIG. 4), preventing the occurrence of cracks and the like. Therefore, this semiconductor device 10 can be used as a power device.
In addition, since the insulating film 11 is formed by growing on the electron supply layer 12 at a low temperature of around 700 [° C.], leakage current generated on the surface of the electron supply layer 12 can be suppressed.

(2) The HEMT was formed as a two-dimensional electron gas channel 13 at the junction interface between the electron supply layer 12 and the electron transit layer 16 (see FIG. 1). Therefore, the HEMT semiconductor device 10 can be used as a power device.

(3) Steps 1 and 2 for forming the electron transit layer 16, Step 3 for forming the electron supply layer 12 having an Al composition ratio of 10 to 18 [%] and a film thickness of 5 to 15 [nm], and 700 And the step 4 of forming the insulating film 11 at a low temperature around [° C.], and epitaxial growth in these steps 1 to 4 was performed using the MOCVD method. The produced semiconductor device 10 is normally off (see FIG. 3 and FIG. 4), preventing the occurrence of cracks and the like. Therefore, this semiconductor device 10 can be used as a power device. Since the insulating film 11 is formed by growing on the electron supply layer 12 at a low temperature of about 700 [° C.], leakage current generated on the surface of the electron supply layer 12 can be suppressed, and the source / drain with high characteristics can be suppressed. Current I _DSmax and transconductance g _mmax are obtained (see FIGS. 5 and 6).
In addition, since the steps 1 to 4 are performed by the MOCVD method (that is, performed in the same MOCVD apparatus 20), it is not necessary to expose the substrate 17 in the process of production to the air for replacing the apparatus. Therefore, the interface is prevented from being deteriorated and the reliability of the device is increased.

[Other Embodiments]
Although the best mode for carrying out the present invention has been described above, the present invention is not limited to this mode. In other words, various forms can be implemented without departing from the scope of the present invention. For example, the following forms may be realized.

(1) In the above-described embodiment, the insulating film 11 is made of AlN (see FIG. 1). Instead of this form, it may be composed of any one of SiO ₂ (silicon dioxide), SiON (silicon oxynitride), borazine-silicon polymer (a polymer having a network structure in which borazine and silicon compounds are alternately connected), and the like. Good. By forming it by growing on the electron supply layer 12 at a low temperature around 700 [° C.], leakage current generated on the surface of the electron supply layer 12 can be suppressed.

(2) In the above-described embodiment, AlGaN is applied to the electron supply layer 12 (see FIG. 1 and the like). Instead of this form, other nitride-based III-V group compounds may be applied although it is a condition that at least aluminum is included. That is, the group III element may include at least one of the group consisting of Ga (gallium), Al (aluminum), B (boron), and In (indium), and the group V element includes N (nitrogen), P (phosphorus). ) And As (arsenic) may be included. For example, AlGaAs (aluminum gallium arsenide), AlGaP (aluminum gallium phosphide), and the like are applicable.
Further, a compound in which indium is used instead of gallium contained in these compounds, for example, AlInN (aluminum indium nitride), AlInAs (aluminum indium arsenide), AlInP (aluminum indium phosphide), or the like may be applied.
Regardless of the compound, by setting the film thickness in the range of 5 to 15 [nm] and the Al composition ratio in the range of 10 to 18 [%], it is possible to obtain the same effects as the above-described embodiment. it can.

(3) In the above-described embodiment, the electron transit layer 16 is formed of GaN (see FIG. 1 and the like). Instead of this form, other nitride III-V compounds may be applied. Group III elements and Group V elements are the same as in (2) above. For example, GaAs (gallium arsenide), GaP (gallium phosphide), and the like are applicable. Further, a compound in which indium is applied instead of gallium contained in these compounds, for example, InN (indium nitride), InAs (indium arsenide), InP (indium phosphide), or the like may be applied. Whichever compound is used, the same effect as that of the above-described embodiment can be obtained.

  The electron transit layer 16 is formed of a plurality of layers including the LT-GaN layer 15 and the GaN layer 14 (see FIG. 1 and steps 1 and 2). Instead of this form, it may be formed of a single layer consisting only of the GaN layer 14. In this case, since step 1 is not necessary, it is possible to reduce labor and cost for manufacturing the semiconductor device 10.

(4) In the embodiment described above, the substrate 17 is made of SiC (see FIG. 1 and the like). Instead of this form, Al ₂ O ₃ (sapphire), Si (silicon), or the like may be used. Even in this case, the same effects as those of the above-described embodiment can be obtained.

(5) In the above-described embodiment, the epitaxial growth was performed by the MOCVD method (see FIG. 2 and steps 1 to 4). Instead of this form, epitaxial growth may be performed by other methods. For example, the MBE method and the HVPE method are applicable. In any method, since the steps 1 to 4 are performed in the same apparatus, it is not necessary to expose the substrate 17 being manufactured to the air for replacing the apparatus. Therefore, the interface is prevented from being deteriorated and the reliability of the device is increased.

(6) In the above-described embodiment, the semiconductor device 10 is a HEMT that forms a two-dimensional electron gas at the junction interface between the electron supply layer 12 and the electron transit layer 16 (see FIG. 1 and the like). Instead of this form, the semiconductor device 10 may be a MESFET. That is, after the electron supply layer 12 and the electron transit layer 16 are epitaxially grown on the substrate 17, the electron supply layer 12 and the like are etched to form a mesa, and a metal electrode (ie, source electrode, gate electrode, drain electrode) is formed on the mesa. ) To produce. Even when the MESFET is formed in this way, the same effects as those of the above-described embodiment can be obtained as a normally-off semiconductor device.

(7) In the above-described embodiment, all three electrodes of the source electrode, the gate electrode, and the drain electrode are formed on the insulating film 11. Instead of this form, only the gate electrode may be formed on the insulating film 11, and the source electrode and the drain electrode may be formed after removing a part of the insulating film 11 and the electron supply layer 12. Even in this case, the same effects as those of the above-described embodiment can be obtained.

It is sectional drawing which represents typically the structural example of a semiconductor device. It is sectional drawing showing an example of a MOCVD apparatus typically. It is a graph showing the relationship between Al composition ratio and threshold voltage. It is a graph showing the relationship between the film thickness of an electron supply layer and a threshold voltage. It is a graph showing the relationship between the growth temperature of an insulating film and the source-drain current. It is a graph showing the relationship between the growth temperature of an insulating film and mutual conductance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor device 11 Insulating film 12 Electron supply layer 13 Two-dimensional electron gas channel 14 GaN layer (electron transit layer)
15 LT-GaN layer (electron transit layer)
16 Electron travel layer 17 Substrate 20 MOCVD apparatus 21 (21a, 21b, 21c) Supply port 22 Reaction unit 22a Partition plate 23 Discharge port 24 Wafer 25 Turntable 26 Heater 27 Rotating shaft 28 Driving means

Claims (3)

An electron supply layer formed on a substrate and formed of a nitride III-V compound containing at least aluminum as a group III element, and a nitride III-V compound containing no aluminum as a group III element A semiconductor device having an insulating film formed of aluminum nitride and having a heterojunction structure as an electron transit layer,
The electron transit layer is formed on the substrate by epitaxial growth,
The electron supply layer is formed by epitaxial growth on the electron transit layer with a composition ratio of aluminum of 10 to 18% and a film thickness of 5 to 15 nm.
The semiconductor device is configured such that the insulating film is formed by epitaxial growth on the electron supply layer at a low temperature of about 700 ° C., and is separated from the electron transit layer by the electron supply layer . A semiconductor device according to claim 1,
A semiconductor device that is a HEMT or MESFET that forms a two-dimensional electron gas at a junction interface between an electron supply layer and an electron transit layer. An electron supply layer formed on a substrate and formed of a nitride III-V compound containing at least aluminum as a group III element, and a nitride III-V compound containing no aluminum as a group III element A method of manufacturing a semiconductor device having a heterojunction structure with an electron transit layer and having an insulating film formed of aluminum nitride ,
Forming by epitaxial growth the electron transit layer on the substrate,
A step of epitaxially growing the electron supply layer on the electron transit layer while controlling the gas supply amount so that the composition ratio of aluminum is 10 to 18% and the film thickness is 5 to 15 nm;
The insulating film is formed by epitaxial growth on the electron supply layer at a low temperature of around 700 ° C., whereby the insulating film is separated from the electron transit layer by the electron supply layer. A process,
A method for manufacturing a semiconductor device, in which epitaxial growth in these three steps is performed using any one of the MOCVD method, the MBE method, and the HVPE method.

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