JP2019186263A - Laminate comprising conductive layer, semiconductor device and method of manufacturing them - Google Patents

Abstract

To provide a conductive layer capable of being applied as a contact layer for a semiconductor device using a group-III nitride semiconductor, and of being formed with ease.SOLUTION: A laminate comprising a conductive layer comprises: a base member; and a conductive layer that is formed on the base member, has a carrier concentration equal to or more than 1×10/cm, and is composed of amorphous GaN.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laminate including a conductive layer, a semiconductor device, and a method for manufacturing the same.

  Group III nitride semiconductors such as gallium nitride are attracting attention, for example, as a material for semiconductor devices for high frequency and high withstand voltage applications, and for example, as a material for semiconductor devices for emitting light having a wavelength ranging from visible to ultraviolet. Yes. As a semiconductor device using a group III nitride semiconductor, for example, a high electron mobility transistor (HEMT) has been proposed.

  When manufacturing a semiconductor device using a group III nitride semiconductor, an electrode is formed on a member made of a group III nitride semiconductor. In order to reduce the contact resistance of the electrode, a contact layer is provided between the group III nitride semiconductor member and the electrode. For example, in the HEMT, contact layers are provided below the source electrode and below the drain electrode, respectively. As a technique for forming a contact layer of HEMT, for example, there is a technique in which an n-type GaN layer is regrown on an electron supply layer or an electron transit layer by metal organic chemical vapor deposition (MOVPE), molecular beam epitaxy (MBE), or the like. For example, a technique for ion-implanting n-type impurities into an electron supply layer or an electron transit layer is known (see Non-Patent Documents 1 and 2).

JP 2017-85062 A

J. Burm et al., “Ultra-low resistive ohmic contacts on GaN using Si implantation”, Appl. Phys. Lett. 70, p464 (1997) F. Recht et al., “Nonalloyed Ohmic Contacts in AlGaN / GaN HEMTs by Ion Implantation With Reduced Activation Annealing Temperature”, IEEE Electron Device Letters (Volume: 27, Issue: 4, April 2006) p. 205-207.

  Since the contact layer forming technique as described above requires a regrowth process or an ion implantation process, it is complicated and expensive.

  An object of the present invention is to provide a conductive layer which can be applied as a contact layer of a semiconductor device using a group III nitride semiconductor and can be easily formed.

According to a first aspect of the invention,
A base member;
A conductive layer formed on the base member and having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more and made of amorphous GaN;
A laminate comprising a conductive layer,
Is provided.

According to a second aspect of the invention,
A base member;
A conductive layer formed of GaN formed on the base member and having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more;
Have
A laminate comprising a conductive layer, wherein the carrier concentration is higher than a concentration of an n-type impurity contained in the conductive layer;
Is provided.

According to a third aspect of the invention,
A laminate comprising a conductive layer according to the first aspect or the second aspect;
An electrode formed on the conductive layer;
A semiconductor device having
Is provided.

According to a fourth aspect of the invention,
A step of preparing a base member;
Preparing a target composed of GaN;
Forming a conductive layer made of GaN on the base member by sputtering the target with a sputtering gas;
Have
In the sputtering gas, the content of the nitrogen-containing gas is kept low so that the conductive layer having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more is formed. Manufacturing method,
Is provided.

According to a fifth aspect of the present invention,
The manufacturing method of the laminated body provided with the conductive layer of the fourth aspect;
Forming an electrode on the conductive layer;
A method of manufacturing a semiconductor device,
Is provided.

The conductive layer according to the above-described aspect can be preferably used as a contact layer of a semiconductor device using a group III nitride semiconductor by having a high carrier concentration of 1 × 10 ²⁰ / cm ³ or more. Such a conductive layer can be easily formed by sputtering.

4 is a flowchart showing an outline of a method for manufacturing a semiconductor device according to an embodiment of the present invention. It is a schematic sectional drawing which shows the manufacturing method of the semiconductor device (HEMT) by embodiment. It is a schematic sectional drawing which shows an example of a sputtering device. It is a graph which shows the relationship between carrier concentration and sputtering gas composition by an experiment example. It is an X-ray diffraction profile for every sample from which a sputtering gas composition differs by an experiment example. It is a graph which shows the relationship between the mobility of a carrier and sputtering gas composition by an experiment example. It is sectional drawing which shows typically the semiconductor device (LED) by other embodiment.

<Embodiment>
A method for manufacturing a semiconductor device according to an embodiment of the present invention will be described. In the present embodiment, a high electron mobility transistor (HEMT) 100 is exemplified as a semiconductor device to be manufactured (see FIG. 2C). In this embodiment, as a characteristic process, the conductive layer 50 made of GaN having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more is formed by sputtering using a target 200 made of gallium nitride (GaN). Forming a step. The base member 40 on which the conductive layer 50 is formed in this process is a semi-finished product of the HEMT 100. In the completed HEMT 100, the conductive layer 50 constitutes a contact layer 51 of the source electrode 61 and a contact layer 52 of the drain electrode 62. Details will be described below.

(1) Preparation of base member FIG. 1 is a flowchart showing an outline of the present manufacturing method. In step S1, the base member 40 is prepared. FIG. 2A is a schematic cross-sectional view showing the base member 40. The base member 40 is a semiconductor laminate having a substrate 10, an electron transit layer (buffer layer, channel layer) 20, and an electron supply layer (barrier layer) 30.

  The substrate 10 is, for example, a silicon carbide (SiC) substrate. More specifically, for example, a polytype 4H or polytype 6H semi-insulating SiC substrate is used as the substrate 10. On the substrate 10, for example, a nucleation layer (not shown) is provided. The nucleation layer is composed, for example, of aluminum nitride (AlN) as a main component.

  The electron transit layer 20 is provided on the substrate 10 via a nucleation layer. The electron transit layer 20 is made of a group III nitride semiconductor, and is composed mainly of GaN, for example. The thickness of the electron transit layer 20 is, for example, not less than 500 nm and not more than 2500 nm. A region located on the nucleation layer side of the electron transit layer 20 mainly functions as a buffer layer that buffers a lattice constant difference between the nucleation layer and the electron supply layer 30. A region located on the electron supply layer 30 side in the electron traveling layer 20 functions as a region where electrons travel when the HEMT 100 is driven.

  The electron supply layer 30 is provided on the electron transit layer 20. The electron supply layer 30 is made of a group III nitride semiconductor having a wider band gap and a smaller lattice constant than the group III nitride semiconductor constituting the electron transit layer 2, and is composed mainly of AlGaN, for example. Yes. The thickness of the electron supply layer 30 is, for example, not less than 5 nm and not more than 50 nm. Due to the polarization action of the electron supply layer 30 provided on the electron transit layer 20, a two-dimensional electron gas is generated in the electron transit layer 20 and spatially confined in the electron transit layer 20. .

The base member 40 is manufactured as follows, for example, by metal organic chemical vapor deposition (MOVPE). As the substrate 10, a polytype 4H semi-insulating SiC substrate is prepared. A nucleation layer made of AlN is grown on the substrate 10 by supplying trimethylaluminum (TMA) gas as a group III source gas and supplying ammonia (NH ₃ ) gas as a group V source gas. On the nucleation layer, trimethylgallium (TMG) gas is supplied as a group III source gas, and NH ₃ gas is supplied as a group V source gas, whereby the electron transit layer 20 made of single-crystal GaN is epitaxially grown. An electron supply layer 30 made of single crystal AlGaN is epitaxially grown on the electron transit layer 20 by supplying TMG gas and TMA gas as group III source gas and supplying NH ₃ gas as group V source gas. In this way, the base member 40 is produced. The base member 40 may be prepared by manufacturing or may be prepared by obtaining from the outside.

(2) Preparation of GaN Target As described above, the conductive layer 50 is formed on the base member 40 by sputtering using the target (GaN target) 200 made of GaN. In step S2, the target 200 is prepared. The target 200 is not particularly limited as long as it is a target composed of GaN. For example, the target 200 may be formed by sintering GaN microcrystals, or may be integrally formed by growing GaN, for example. A method for integrally growing the target 200 is not particularly limited, and an example is hydride vapor deposition (HVPD). The target 200 formed integrally by growth may be composed of, for example, GaN polycrystal, or may be composed of, for example, GaN single crystal. The shape, size, thickness, and the like of the target 200 may be appropriately selected according to the specifications of the sputtering apparatus 300 (see FIG. 3) used for forming the conductive layer 50. The target 200 may be prepared by manufacturing or may be prepared by obtaining from the outside.

In this specification, “a target composed of GaN” means a target containing GaN, and may be composed of GaN containing some impurities. The target 200 may contain an n-type impurity, for example. Here, the n-type impurity is silicon (Si) or oxygen (O), and the overall n-type impurity concentration is evaluated by the sum of the Si concentration and the O concentration. For example, with respect to secondary ion mass spectrometry (SIMS), the lower detection limit concentration of Si is about 1 × 10 ¹⁵ / cm ³ , and the lower detection limit concentration of O is about 1 × 10 ¹⁶ / cm ³ . In this specification, it is evaluated that “the target 200 is substantially free of n-type impurities” when the overall n-type impurity concentration in GaN constituting the target 200 is 1 × 10 ¹⁶ / cm ³ or less. The Note that n-type impurities contained in GaN constituting the conductive layer 50 are similarly evaluated.

(3) Formation of conductive layer by sputtering After the preparation of the base member 40 in step S1 and the preparation of the target 200 in step S2, the conductive layer 50 is formed by sputtering in step S3. In addition, as long as it is performed before step S3, either step S1 and S2 may be performed before, and step S1 and S2 may be performed simultaneously.

  A sputtering apparatus 300 used for forming the conductive layer 50 and its operation will be described. FIG. 3 is a schematic cross-sectional view showing the sputtering apparatus 300 and illustrates a radio frequency (RF) sputtering apparatus. The sputtering apparatus 300 includes a chamber 310, a target holding table 320, a base member holding table 330, and an AC power source 340. A target holding base 320 and a base member holding base 330 are provided in the chamber 310. The target holding base 320 holds the target 200, and the base member holding base 330 holds the base member 40. The target 200 and the base member 40 are arranged in a state of facing each other.

  The sputtering gas 400 introduced into the chamber 310 is interposed between the target 200 and the base member 40. The AC power source 340 applies an AC voltage between the target 200 and the base member 40. The sputtering gas 400 is turned into plasma by the AC voltage, and the target 200 is sputtered by the plasmad sputtering gas 400, so that the GaN material 210 is scattered from the target 200. The scattered GaN material 210 is deposited on the base member 40, whereby the conductive layer 50 is formed.

  FIG. 2B is a schematic cross-sectional view showing the base member 40 on which the conductive layer 50 is formed. In the present embodiment, the conductive layer 50 is formed as the contact layer 51 of the source electrode 61 and the contact layer 52 of the drain electrode 62 of the HEMT 100. For this reason, it is good to perform sputtering process with respect to the base member 40 in the state in which the mask 55 which has an opening in the area | region where the contact layer 51 and the contact layer 52 should be formed. Thereby, the conductive layer 50 can be selectively formed on the region.

  More specifically, the step of forming the conductive layer 50 by sputtering is performed as follows, for example. A mask 55 having an opening in a region where the contact layer 51 and the contact layer 52 are to be formed is formed on the electron supply layer 30 of the base member 40. The mask 55 is made of, for example, a resist, and is made of, for example, silicon oxide. The base member 40 on which the mask 55 is formed is held on the base member holding base 330 of the sputtering apparatus 300. Further, the target 200 is held on the target holding base 320 of the sputtering apparatus 300.

A sputtering gas 400 is introduced into the chamber 310 while the base member 40 and the target 200 are held. Then, the sputtering process is performed by applying an alternating voltage to the sputtering gas 400 at a predetermined temperature and pressure. Examples of the conditions for the sputtering treatment include the following.
Deposition temperature: 100 ° C to 250 ° C
Deposition pressure: 1 Pa to 5 Pa
Sputtering gas: a mixed gas of argon gas (Ar gas) and nitrogen gas (N ₂ gas), and the partial pressure of N ₂ gas (N ₂ / (N ₂ + Ar)) is 2% or less, more preferably Ar Gas RF power density: 0.37 W / cm ^{2 to} 12.3 W / cm ² (for example, 30 W to 1000 W as RF power for a target 200 having a diameter of 4 inches)

  The film forming temperature is preferably 100 ° C. or higher. This is to prevent moisture remaining in the chamber 310 from entering the conductive layer 50. When moisture is mixed into the conductive layer 50, the low resistance of the conductive layer 50 is impaired. In the case where the chamber 310 is open to the atmosphere, it is preferable to perform a baking process at 100 ° C. to 150 ° C. for about 2 hours before the sputtering process. In order to prevent moisture from entering the chamber 310, the chamber 310 is more preferably a load lock type. The film forming temperature is preferably 250 ° C. or lower. This is because the mask 55 has a low heat resistance compared to an inorganic material such as silicon oxide, so that the resist can be easily used.

As will be described in detail later, the carrier concentration of the conductive layer 50 to be formed can be increased as the number of nitrogen atoms (N) contained in the sputtering gas 400 is reduced. The carrier concentration of the conductive layer 50 used as the contact layers 51 and 52 is preferably 1 × 10 ²⁰ / cm ³ or more. Therefore, it is preferable that the content rate of the gas containing N in the sputtering gas 400 be kept low so that the conductive layer 50 having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more is formed.

As the sputtering gas 400, a gas containing a rare gas is preferably used, and a gas composed of a rare gas is more preferably used. Examples of the rare gas used for the sputtering gas 400 include Ar, krypton (Kr), and xenon (Xe). The sputtering gas 400 may contain a rare gas and a gas containing N if it is a small amount. Examples of the gas containing N used for the sputtering gas 400 include N ₂ gas. As the sputtering gas 400 containing a gas containing N, for example, it consists of a rare gas and a gas containing N, and the partial pressure of the gas containing N is preferably 2% or less, more preferably 1% or less. Gas can be used. Note that the sputtering gas 400 may contain other gas, for example, hydrogen gas, if necessary, as long as the carrier concentration of the conductive layer 50 to be formed does not decrease to less than 1 × 10 ²⁰ / cm ^3. .

By such sputtering treatment, a conductive layer 50 having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more and made of GaN is formed. In this specification, the conductive layer 50 “constituted of GaN” means that the conductive layer 50 includes GaN, and is not limited to the case where the conductive layer 50 is configured of GaN containing no impurities. This also means that the conductive layer 50 is made of GaN containing some impurities. GaN constituting the conductive layer 50 may contain an n-type impurity, for example. When the target 200 includes an n-type impurity, the conductive layer 50 includes an n-type impurity caused by the target 200. The n-type impurity concentration of the conductive layer 50 is less than or equal to the n-type impurity concentration of the target 200. In order to keep the resistance of the conductive layer 50 low, the thickness of the conductive layer 50 is preferably 100 nm or less, for example.

The conductive layer 50 may have a carrier concentration higher than the concentration of n-type impurities contained in the conductive layer 50, for example, a carrier concentration that is ten times or more higher than the concentration of n-type impurities contained in the conductive layer 50. For example, even if the concentration of the n-type impurity contained in the conductive layer 50 is 1 × 10 ¹⁹ / cm ³ or less, for example, even if the conductive layer 50 does not substantially contain the n-type impurity, that is, the conductive layer 50 The conductive layer 50 has a carrier concentration of 1 × 10 ²⁰ / cm ³ or more even when the concentration of the n-type impurity contained in the layer is 1 × 10 ¹⁶ / cm ³ or less. This is because the main carriers in the conductive layer 50 are not generated due to the n-type impurities, but are generated due to the properties of the GaN itself constituting the conductive layer 50.

In the sputtering process according to the present embodiment, N vacancies are generated in the GaN constituting the conductive layer 50 by sputtering the target 200 with the sputtering gas 400 in which the content of the N-containing gas is kept low. That is, in the GaN constituting the conductive layer 50, the ratio of the number of N atoms to the number of Ga atoms is made smaller than one. Thus, n-type carriers due to N deficiency can be generated as main carriers in the conductive layer 50, and a high carrier concentration of 1 × 10 ²⁰ / cm ³ or more can be realized.

  After the base member 40 on which the conductive layer 50 is formed is unloaded from the sputtering apparatus 300, only the inside of the opening of the mask 55 is lifted off by removing the unnecessary portion of the conductive layer 50 formed on the mask 55 together with the mask 55. In other words, the conductive layer 50 is left only in the region where the contact layer 51 and the contact layer 52 are to be formed.

(4) Formation of electrode on conductive layer and other processes for completing HEMT After formation of conductive layer 50 by sputtering in step S3, formation of electrode on conductive layer 50 is performed in step S4. , And other processes for completing the HEMT 100 are performed. FIG. 2C is a schematic cross-sectional view showing the completed HEMT 100.

  Specifically, a source electrode 61 and a drain electrode 62 are formed as electrodes on the conductive layer 50. The source electrode 61 is formed on the electron supply layer 30 via a conductive layer 50 that becomes the contact layer 51 of the source electrode 61. The drain electrode 62 is formed on the electron supply layer 30 via a conductive layer 50 that becomes the contact layer 52 of the drain electrode 62. On the other hand, the gate electrode 63 is formed on the electron supply layer 30 without the conductive layer 50 interposed therebetween.

  The source electrode 61, the drain electrode 62, and the gate electrode 63 are formed by appropriately using a known technique for forming the source electrode, the drain electrode, and the gate electrode of the HEMT. As the source electrode 61, the drain electrode 62, and the gate electrode 63, for example, a titanium (Ti) / aluminum (Al) electrode is formed.

  After the formation of the source electrode 61, the drain electrode 62 and the gate electrode 63, the protective film 70 is formed on the electron supply layer 30 so as to cover the source electrode 61, the drain electrode 62 and the gate electrode 63. The protective film 70 has openings on the upper surfaces of the source electrode 61, the drain electrode 62, and the gate electrode 63, and is configured so that external wiring can be connected to each of these electrodes 61 to 63. The protective film 70 is formed by appropriately using a known technique for forming a HEMT protective film. As the protective film 70, for example, a silicon nitride film is formed. Note that step S4 may include still another process performed to complete the HEMT 100, such as a nitrogen ion implantation process for element isolation. As described above, the HEMT 100 is manufactured. The HEMT 100 is an example of a stacked body including the conductive layer 50 and is an example of a semiconductor device including the stacked body including the conductive layer 50.

(5) Effects obtained by the present embodiment According to the present embodiment, one or more effects shown below can be obtained.

(A) The conductive layer 50 having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more can be formed by the sputtering process as described above. The conductive layer 50 can be easily formed by sputtering using the target 200 made of GaN. Since the conductive layer 50 has a high carrier concentration of 1 × 10 ²⁰ / cm ³ or more, for example, as the contact layer 51 interposed between the electron supply layer 30 of the HEMT 100 and the source electrode 61, or for example, the electron supply of the HEMT 100 It can be preferably used as the contact layer 52 interposed between the layer 30 and the drain electrode 62.

  As a technique for forming a HEMT contact layer, for example, a technique for re-growing an n-type GaN layer on an electron supply layer or an electron transit layer by MOVPE, molecular beam epitaxy (MBE), or the like is known. A technique for ion-implanting n-type impurities into an electron supply layer or an electron transit layer is known. Since these techniques require a regrowth process or an ion implantation process, they are complicated and expensive. On the other hand, according to the present embodiment, the contact layers 51 and 52 of the HEMT 100 can be easily formed at low cost by sputtering. Note that sputtering can be easily applied to a process on a large-area member.

(B) The carrier concentration of the conductive layer 50 can be higher than the concentration of the n-type impurity contained in the conductive layer 50. For this reason, it is not necessary to add an n-type impurity to the conductive layer 50. That is, it is not necessary to prepare the target 200 to which the n-type impurity is added. Note that an n-type (or p-type) impurity may be added to the target 200.

(C) The sputtering process for producing the conductive layer 50 can be performed using a sputtering gas 400 in which the content of N-containing gas is kept low. As the sputtering gas 400, for example, Ar gas can be used. For example, a mixed gas of Ar gas and N ₂ gas, and the partial pressure of N ₂ gas is preferably 2% or less, more preferably 1%. The following gas can be used. Since it is not necessary to use a special gas as the sputtering gas 400, the conductive layer 50 can be easily manufactured.

<Other embodiments>
The present invention is not limited to the above-described embodiment, and various changes may be made without departing from the scope of the invention. Various embodiments and modifications may be combined as appropriate.

  In the above-described embodiment, the mode in which the conductive layer 50 is selectively formed on the region of the base member 40 using the mask 55 having an opening in the region where the contact layer 51 and the contact layer 52 are to be formed is illustrated. (See FIG. 2 (b)). As another method, after forming the conductive layer 50 on the entire surface of the base member 40 without using the mask 55, patterning is performed to remove the conductive layer 50 other than the regions to be the contact layer 51 and the contact layer 52 by etching. The conductive layer 50 may be left on the region. If necessary, a member in which the conductive layer 50 is formed on the entire surface of the base member 40 is prepared as a semi-finished product, and the HEMT 100 is processed by performing processing after the patterning of the conductive layer 50 on the member. You may make it produce.

  In the above-described embodiment, the structure as shown in FIG. 2C is illustrated as the HEMT 100 in which the conductive layer 50 formed by sputtering is applied as the contact layers 51 and 52 of the source electrode 61 and the drain electrode 62. However, the structure shown in FIG. The conductive layer 50 may be applied as the contact layers 51 and 52 in the HEMT 100 having another known structure. That is, in the HEMT 100 having another known structure, the conductive layer 50 formed by sputtering may be used as the contact layers 51 and 52 disposed under the source electrode 61 and the drain electrode 62.

  In the above-described embodiment, the HEMT 100 is exemplified as a semiconductor device to which the conductive layer 50 formed by sputtering is applied as the contact layers 51 and 52. The conductive layer 50 formed by sputtering is not limited to the contact layers 51 and 52 of the HEMT 100, and may be used as a contact layer in an electrode structure of another semiconductor device such as a light emitting diode (LED) or a semiconductor laser.

  FIG. 7 is a cross-sectional view schematically showing an LED 500 as an example of another embodiment. The LED 500 includes an n-type GaN substrate 510, an n-type GaN layer 520, a p-type GaN layer 530, a p-side electrode 540, an n-side contact layer 550, and an n-side electrode 560. Note that a light emitting layer having a quantum well structure may be provided between the n-type GaN layer 520 and the p-type GaN layer 530. The n-side contact layer 550 is configured as a conductive layer formed by sputtering as described above.

  FIG. 7 illustrates an element structure in which the n-side electrode 560 is disposed on the opposite side of the p-type GaN layer 530 and is disposed on the lower surface of the n-type GaN substrate 510 via the n-side contact layer 550. Not limited to this, an element structure in which the n-side electrode 560 is disposed on the same side as the p-type GaN layer 530 may be employed. In other words, an element structure in which an n-side electrode 560 is disposed via an n-side contact layer 550 on the upper surface of the n-type GaN layer 520 exposed by removing a part of the p-type GaN layer 530 is employed. Also good.

In the above-described embodiment, AlGaN is exemplified as the material of the surface layer portion (electron supply layer 30) of the base member 40 in contact with the conductive layer 50. The material of the surface layer portion of the base member 40 in contact with the conductive layer 50 is not limited to AlGaN, and a group III nitride semiconductor represented by Al _x In _y Ga _1-xy N (0 ≦ x + y ≦ 1) is preferably used. be able to.

  In the above-described embodiment, RF sputtering is exemplified as the sputtering method used for forming the conductive layer 50 (see FIG. 3), but various sputtering methods can be used for forming the conductive layer 50. For example, direct current (DC) sputtering may be used. For example, a magnetron may be used for both RF sputtering and DC sputtering. For example, ion beam sputtering may be used. Furthermore, the method is not limited to sputtering, and other physical deposition methods such as pulsed laser deposition (PLD) may be used.

<Experimental example>
Next, an experiment in which a GaN layer is formed by sputtering using a GaN target will be described. This experiment was performed under the following conditions. As a target, a polycrystalline GaN substrate integrally formed by growth by HVPD was used. This target has a Si concentration of about 1 × ¹⁰ 18 / cm ^3, has an O concentration of about 1 × ¹⁰ 19 / cm ^3, n-type impurity concentration of about 1 × ¹⁰ 19 / cm ³ as a whole It was what had. The diameter of this target was 4 inches (10.16 cm). Using this target, a GaN layer was formed on the base substrate by RF sputtering. A glass substrate was used as the base substrate.

The film formation temperature was 200 ° C., the film formation pressure was 2.4 Pa, and the RF power was 50 W to 80 W. It was investigated how the characteristics of the formed GaN layer change by changing the composition of the sputtering gas. Ar gas and N ₂ gas were used as the sputtering gas, and the composition of the sputtering gas was changed by increasing the partial pressure of N ₂ gas (N ₂ / (N ₂ + Ar)) from 0%. Ar is an example of a rare gas, and N ₂ gas is an example of a nitrogen-containing gas.

FIG. 4 is a graph showing the relationship between the carrier concentration and the sputtering gas composition. The carrier concentration is the concentration of n-type carrier obtained by hole measurement. The horizontal axis represents the partial pressure of N ₂ gas (N ₂ / (N ₂ + Ar)) in% units, and the vertical axis represents the carrier concentration in logarithmic cm ⁻³ units.

The logarithmically expressed carrier concentration varies linearly with respect to the partial pressure of N ₂ gas. The carrier concentration is higher as the partial pressure of N ₂ gas is lower, and is maximum when the partial pressure of N ₂ gas is 0%, that is, when the sputtering gas is made of Ar gas. By setting the partial pressure of N ₂ gas to 0%, a very high carrier concentration of about 1 × 10 ²¹ / cm ³ can be obtained. Further, by setting the partial pressure of N ₂ gas to preferably 2% or less, more preferably 1% or less, a high carrier concentration of 1 × 10 ²⁰ / cm ³ or more can be obtained. Thus, by using a sputtering gas with a low content of N-containing gas, a GaN layer having a high carrier concentration of 1 × 10 ²⁰ / cm ³ or more and suitable as a conductive layer such as a contact layer can be obtained. It was found that it can be formed.

Since the n-type impurity concentration of the target is about 1 × 10 ¹⁹ / cm ³ , the n-type impurity concentration of the formed GaN layer is about 1 × 10 ¹⁹ / cm ³ at most. However, as can be seen from the results shown in FIG. 4, a carrier concentration higher than the concentration of the n-type impurity contained in the GaN layer can be obtained by keeping the partial pressure of the N ₂ gas low. Since the content of the gas containing N in the sputtering gas is low, n-type carriers due to N deficiency are generated in the formed GaN layer, and such high carriers are caused by n-type carriers due to N deficiency. It is assumed that the concentration has been achieved. For example, the n-type impurity concentration is about 1 × 10 ¹⁹ / cm ³ at most compared to the carrier concentration of about 1 × 10 ²¹ / cm ^{3 when the} N ₂ gas partial pressure is 0%. Little contribution to overall carrier concentration. From this result, it is considered that the high carrier concentration as described above can be obtained even if the formed GaN layer does not substantially contain n-type impurities.

FIG. 5 shows an X-ray diffraction profile for each sample having a different sputtering gas composition. The partial pressure of N ₂ gas shows the results of 0% results and 10% of the sample of the sample. The horizontal axis represents 2θ in degrees, and the vertical axis represents intensity in arbitrary units. In the sample having a N ₂ gas partial pressure of 10%, the (10-10) plane peak and (10-11) plane peak are observed as relatively strong peaks, and the (0002) plane peak and ( The peak of the 11-20) plane is observed. That is, GaN formed under the condition of N ₂ gas partial pressure of 10% shows a certain degree of crystallinity. On the other hand, no peak corresponding to the crystal plane of GaN is observed in the sample having a N ₂ gas partial pressure of 0%. That is, GaN formed under the condition of the N ₂ gas partial pressure of 0% does not show crystallinity and is amorphous.

Thus, it was found that an amorphous GaN layer was formed when the N ₂ gas partial pressure was 0%. For this reason, it is presumed that an amorphous GaN layer may be similarly formed under a low N ₂ gas partial pressure of 2% or less or 1% or less. If a high carrier concentration of 1 × 10 ²⁰ / cm ³ or more can be obtained, the formed GaN layer is not essential to be amorphous and may have some crystallinity. That is, you may show the X-ray-diffraction peak corresponding to any surfaces, such as the above-mentioned (10-10) plane. However, even if it is amorphous or has some crystallinity, a high carrier concentration of 1 × 10 ²⁰ / cm ³ or more exhibited by the formed GaN layer is high due to the n-type impurity contained in the GaN layer. Higher than concentration.

FIG. 6 is a graph showing the relationship between carrier mobility and sputtering gas composition. The carrier mobility is the mobility of the n-type carrier obtained by hole measurement. The horizontal axis represents the partial pressure of N ₂ gas (N ₂ / (N ₂ + Ar)) in% units, and the vertical axis represents carrier mobility in units of logarithm cm ² / (V · s).

In a sputtering gas composition that provides a high carrier concentration of 1 × 10 ²⁰ / cm ³ or more, that is, in a range where the N ₂ gas partial pressure is 2% or less, for example, mobility is as low as 0.1 cm ² / (V · s) or less. It shows. On the other hand, the resistance of the GaN layer used as the conductive layer is preferably 1 × 10 ⁻⁸ Ω / cm ² or less, for example. Accordingly, the thickness of the GaN layer used as the conductive layer is preferably not excessively thick, and is preferably 100 nm or less, for example. In addition, the minimum of the thickness of the GaN layer used as a conductive layer is not specifically limited, What is necessary is just the thickness which can be formed into a film and functions as a conductive layer.

<Preferred embodiment of the present invention>
Hereinafter, preferred embodiments of the present invention will be additionally described.

(Appendix 1)
A base member;
A conductive layer formed on the base member and having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more and made of amorphous GaN;
A laminate including a conductive layer.

(Appendix 2)
The laminate including the conductive layer according to appendix 1, wherein the carrier concentration is higher than the concentration of the n-type impurity contained in the conductive layer.

(Appendix 3)
A base member;
A conductive layer formed of GaN formed on the base member and having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more;
Have
The laminate including a conductive layer, wherein the carrier concentration is higher than the concentration of n-type impurities contained in the conductive layer.

(Appendix 4)
The laminate including the conductive layer according to Supplementary Note 3, wherein the conductive layer is made of amorphous GaN.

(Appendix 5)
The laminate including the conductive layer according to any one of appendices 1 to 4, wherein the carrier concentration is 10 times or more higher than the concentration of the n-type impurity contained in the conductive layer.

(Appendix 6)
The laminated body provided with a conductive layer according to any one of appendices 1 to 5, wherein the concentration of the n-type impurity contained in the conductive layer is 1 × 10 ¹⁹ / cm ³ or less.

(Appendix 7)
The said electrically conductive layer is a laminated body provided with the electrically conductive layer as described in any one of Additional remarks 1-6 which do not contain an n-type impurity substantially.

(Appendix 8)
In the GaN constituting the conductive layer, the ratio of the number of N atoms to the number of Ga atoms is a laminate including the conductive layer according to any one of appendices 1 to 7, which is smaller than 1.

(Appendix 9)
The mobility of GaN which comprises the said conductive layer is a laminated body provided with the conductive layer as described in any one of the supplementary notes 1-8 which are 0.1 cm < ² > / (V * s) or less.

(Appendix 10)
The laminate including the conductive layer according to any one of Supplementary notes 1 to 9, wherein the conductive layer has a thickness of 100 nm or less.

(Appendix 11)
In the base member, the surface layer portion in contact with the conductive layer is formed of Al _x In _y Ga _1-xy N (where 0 ≦ x + y ≦ 1) A laminate comprising layers.

(Appendix 12)
A laminate comprising a conductive layer according to any one of appendices 1 to 11, and
An electrode formed on the conductive layer;
A semiconductor device.

(Appendix 13)
HEMT,
The semiconductor device according to appendix 12, wherein the electrode is a source electrode or a drain electrode.

(Appendix 14)
A step of preparing a base member;
Preparing a target composed of GaN;
Forming a conductive layer made of GaN on the base member by sputtering the target with a sputtering gas;
Have
In the sputtering gas, the content of the nitrogen-containing gas is kept low so that the conductive layer having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more is formed. Manufacturing method.

(Appendix 15)
The sputtering gas is a gas composed of a rare gas, or a partial pressure of a gas composed of a rare gas and a nitrogen-containing gas is preferably 2% or less, more preferably 1% or less. The manufacturing method of the laminated body provided with the conductive layer of Additional remark 14 which is gas.

(Appendix 16)
The film forming temperature when forming the conductive layer is the method for producing a laminate including a conductive layer according to appendix 14 or 15, wherein the temperature is in the range of 100 ° C. or higher and 250 ° C. or lower.

(Appendix 17)
The said conductive layer is a manufacturing method of the laminated body provided with the conductive layer as described in any one of Additional remarks 14-16 comprised with amorphous GaN.

(Appendix 18)
The method for producing a laminate including a conductive layer according to any one of appendices 14 to 17, wherein the carrier concentration is higher than a concentration of n-type impurities contained in the conductive layer.

(Appendix 19)
The method for producing a laminate including a conductive layer according to any one of appendices 14 to 18, and
Forming an electrode on the conductive layer;
A method for manufacturing a semiconductor device, comprising:

(Appendix 20)
A method of manufacturing a HEMT,
20. The method for manufacturing a semiconductor device according to appendix 19, wherein the electrode is a source electrode or a drain electrode.

DESCRIPTION OF SYMBOLS 10 Substrate 20 Electron travel layer 30 Electron supply layer 40 Base member 50 Conductive layer 51, 52 Contact layer 55 Mask 61 Source electrode 62 Drain electrode 63 Gate electrode 70 Protective film 100 HEMT
200 GaN target 300 sputtering equipment

Claims (15)

A base member;
A conductive layer formed on the base member and having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more and made of amorphous GaN;
A laminate including a conductive layer.   The laminate having a conductive layer according to claim 1, wherein the carrier concentration is higher than the concentration of n-type impurities contained in the conductive layer. A base member;
A conductive layer formed of GaN formed on the base member and having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more;
Have
The laminate including a conductive layer, wherein the carrier concentration is higher than the concentration of n-type impurities contained in the conductive layer. The concentration of the n-type impurity contained in the conductive layer, 1 × 10 19 ^/ cm according to ³ 1, wherein one to claims 1 to 3 or less is a laminate comprising a conductive layer.   The said conductive layer is a laminated body provided with the conductive layer of any one of Claims 1-4 which does not contain an n-type impurity substantially.   In the GaN which comprises the said conductive layer, the ratio of the number of N atoms with respect to the number of Ga atoms is smaller than 1, The laminated body provided with the conductive layer of any one of Claims 1-5.   The thickness of the said conductive layer is 100 nm or less, The laminated body provided with the conductive layer of any one of Claims 1-6. Wherein the base member, the surface layer portion in contact with the conductive _{layer, Al x In y Ga 1-} x-y N (0 ≦ x + y ≦ 1) according to any one of claims 1 to 7, it is composed of A laminate comprising a conductive layer. A laminate comprising a conductive layer according to any one of claims 1 to 8,
An electrode formed on the conductive layer;
A semiconductor device. A step of preparing a base member;
Preparing a target composed of GaN;
Forming a conductive layer made of GaN on the base member by sputtering the target with a sputtering gas;
Have
In the sputtering gas, the content of the nitrogen-containing gas is kept low so that the conductive layer having a carrier concentration of 1 × 10 ²⁰ / cm ³ or more is formed. Manufacturing method.   11. The sputtering gas according to claim 10, wherein the sputtering gas is a gas composed of a rare gas or a gas composed of a rare gas and a nitrogen-containing gas and having a partial pressure of the nitrogen-containing gas of 2% or less. The manufacturing method of a laminated body provided with a conductive layer.   The method for producing a laminate including a conductive layer according to claim 10 or 11, wherein a film formation temperature when forming the conductive layer is a temperature in a range of 100 ° C or higher and 250 ° C or lower.   The method for producing a laminate including a conductive layer according to any one of claims 10 to 12, wherein the conductive layer is made of amorphous GaN.   The method for producing a laminate including a conductive layer according to any one of claims 10 to 13, wherein the carrier concentration is higher than a concentration of an n-type impurity contained in the conductive layer. The manufacturing method of the laminated body provided with an electroconductive layer of any one of Claims 10-14,
Forming an electrode on the conductive layer;
A method for manufacturing a semiconductor device, comprising:

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