JP2013157587A - Compound semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of a large influence on practical use of an element substrate such as SiC for a high-voltage driver element, which is caused by a large number of crystal faults and a large amount of leakage current.SOLUTION: In a compound semiconductor of a present embodiment, by forming a single-crystal compound semiconductor such as a SiC film on an insulation film on a substrate to form a Schottky diode as an element substrate, an electric field from the substrate, and an electric field from a conductor formed in a groove which is formed as a trench in a part of the single-crystal semiconductor and which has oxide films on side walls, and an electric field from a field plate provided in a surface layer of the element through an insulation film ease an electric field applied to an anode of the Schottky diode. Accordingly, an influence of a crystal fault of the single-crystal compound semiconductor such as SiC is decreased.

Description

  The present invention relates to a substrate structure and an element structure of a semiconductor device using a power compound semiconductor, particularly a SiC substrate or a GaN substrate.

FIG. 1 shows a conventionally disclosed method for forming a single crystal SiC substrate. After the SiC film 2 is grown on the Si substrate 1 as shown in FIG. 1-a, the SiC film 3 is further grown on the SiC film 2 from which the Si substrate 1 has been removed as shown in FIG. It is a method to obtain a proper thickness. A Schottky diode comprising a cathode 111 and an anode 112 is formed thereon as shown in FIG.

However, the method of growing SiC based on Si as shown in FIG. 1 is suitable for increasing the diameter, but has a large leakage current when a device is formed due to many crystal defects in the vertical direction. Has become an issue. FIG. 2 conceptually shows how the crystal defects are generated. As reported in each paper, the crystal defect of the SiC substrate formed by the method shown in FIG. 1-a called 3C has an inclination angle of 54 degrees as shown in the conceptual diagram in FIG. 2-b. It has been known. Further, it is known that an SiC substrate grown by a technique called a sublimation method without using an Si substrate has many defects in a direction perpendicular to the substrate surface as shown in a conceptual diagram in FIG. Yes.

In FIG. 3A, a representative cross-sectional view of a Schottky diode is shown. If there is a crystal defect in the cathode electrode of the Schottky diode, a leak current flows along the defect, so the relationship between the reverse bias current and the applied voltage of the Schottky diode is as shown in FIG. That is, the leak is small up to a certain voltage without depending on the defect, and when the crystal defect breakdown voltage Vp is exceeded, the current along the defect starts to increase. Then, when the breakdown voltage of the Schottky junction is reached, current starts to flow due to a tunnel phenomenon and an electron avalanche. When the reverse bias voltage is applied in this way and the crystal defect breakdown voltage Vp is exceeded, the leakage current starts to increase, and it is a reality that a larger leakage current is generated before reaching the Schottky breakdown voltage Vq than this leakage current. It is. The element wants the leakage current to the breakdown voltage Vq of the Schottky junction to be extremely small, but because of the large number of crystal defects peculiar to the SiC substrate, the crystal defects existing on the Schottky junction plane exceed the crystal defect breakdown voltage Vp. The reality is that leakage current starts to occur from the applied voltage.

This data can be considered as follows: (A) There is a crystal defect that crosses the Schottky junction, and a voltage is applied to the crystal defect, and an electric field is generated along the crystal defect. (B) If the crystal defect has a Schottky junction surface only in a direction where no electric field is applied to the Schottky interface, the leak current due to the defect does not occur.

From the model shown in FIG. 3, what can be conceived for reducing the leakage based on the consideration as shown in FIG. 3A is to alleviate the electric field applied to the Schottky interface by some means. For this, a structure in which a compound semiconductor is formed on an insulating film, a Schottky diode is formed thereon, and the electric field from the anode is relaxed by the insulating film can be considered. In this case, there is also a method in which a trench is formed in the compound semiconductor on the insulating film, an oxide film is formed on the side wall thereof, and the electric field is relaxed through the oxide film from the poly semiconductor or conductor provided on the inside. Conceivable. In addition, a well-known means for providing a field plate for forming electrodes on the element surface via an insulating film is also effective.

Further, based on the consideration as in (B), when there are many vertical crystal defects, the Schottky junction surface only needs to be in the vertical direction on the insulating film isolation structure.

No Schottky diode based on such consideration has been disclosed so far.

As the use of high voltage driving elements expands, the cost reduction of those elements and the practical application of higher performance elements have become important issues. A Schottky diode formed on a SiC substrate or a GaN substrate meets this need. When the inductance is switched by a MOSFET or the like, this element eliminates the induced current of the inductance at high speed because there is no problem of reverse recovery time at the PN junction. The present invention discloses a method of eliminating or mitigating leakage current caused by a longitudinal crystal defect characteristic of SiC using a compound semiconductor such as SiC suitable for high breakdown voltage. In the following cases, the contents of the invention will be disclosed by taking a SiC substrate as an example, but the same applies to a GaN substrate and other compound semiconductor substrates.

The problem to be solved by the present invention is to make it possible to use an inexpensive substrate by eliminating or mitigating the influence of vertical crystal defects peculiar to compound semiconductors.

The structure of the present invention is formed in a single crystal SiC layer formed on an insulating film based on the consideration of FIG. 3 so that the interface of the Schottky diode is only in the vertical direction, and is applied to the interface of the Schottky diode. It is the development of a method to relax the voltage.

By forming the Schottky diode in the single crystal SiC layer formed on the insulating film, the electric field applied to the interface of the Schottky electrode can be reduced. This is because the potential at the lower surface of the insulating film isolation can relax the potential at the interface of the Schottky diode in the substrate direction. For this, a structure in which a compound semiconductor is formed on an insulating film, a Schottky diode is formed thereon, and the electric field from the cathode is relaxed by the insulating film can be considered. In this case, there is also a method in which a trench is formed in the compound semiconductor on the insulating film, an oxide film is formed on the side wall thereof, and the electric field is relaxed through the oxide film from the poly semiconductor or conductor provided on the inside. Conceivable. It is also effective to provide a field plate for forming electrodes on the element surface via an insulating film. The combination of these electric field relaxations greatly reduces the electric field applied to the Schottky interface.

In addition, in a SiC substrate in which vertical crystal defects are dominant, a trench is formed in the SiC film that is insulated and separated, and a Schottky diode is formed on the side wall (side surface) thereof, whereby a vertical crystal defect A Schottky interface that does not cross can be realized.

In this way, the element substrate is theoretically possible by diverting the substrate bonding technology, trench technology, smart cut technology, etc., which have been put into practical use in Si substrates, to SiC. . In addition, a plurality of Schottky diodes can be mounted on the substrate by performing trench isolation on the SiC portion on the insulating film as necessary.

Although there is great expectation for the practical use of SiC substrates suitable for high-voltage driving, so far the crystal defects in the vertical direction are so large that the influence cannot be eliminated, and efforts have been made to reduce crystal defects. As a result, crystal defects have been reduced to some extent, although it is still impossible to put into practical use. On the other hand, the production process becomes complicated, and the cost increases in terms of man-hours. A high voltage driving element substrate and an element structure in which a SiC layer is formed on an insulating film on a lateral element and a base substrate according to the present invention, and an SiC isolation area is used to effectively use an SiC area This is a simple and cost-effective method. According to the present invention, a SiC film is formed by a trench etching technique, SiC is removed, a silicon oxide film is exposed at the bottom of the groove, a Schottky diode is formed on the side wall of the groove, and a lateral element is obtained. The structure in which the longitudinal crystal defects do not cross the Schottky plane is epoch-making. Further, by separating each element by the trench groove, a plurality of independent elements can be simultaneously formed on one substrate. Furthermore, by forming an element such as a MOSFET there, the individual elements are completely separated, and a plurality of high voltage elements can be combined to form an integrated circuit. It is an epoch-making thing which can put the element substrate which enables the high voltage drive integrated circuit of SiC into practical use.

Sectional drawing which shows the structure of a well-known SiC substrate Conceptual diagram of crystal defects generated in SiC film Structure diagram of Schottky diode formed on SiC film and relationship between applied voltage and leakage current Sectional view and electric field relaxation diagram of Schottky diode formed on SiC film on insulating film on poly-SiC substrate of the present invention Sectional view of Schottky diode formed on SiC film on insulating film on poly-SiC substrate of the present invention, element isolation by trench structure, and structure diagram of electric field relaxation from trench layer Sectional drawing of the Schottky diode formed only in the longitudinal direction of the thin SiC film on the insulating film on the poly SiC substrate of the present invention Sectional drawing of the Schottky diode formed only in the longitudinal direction of the thick SiC film on the insulating film on the poly SiC substrate of the present invention Method for forming element substrate of silicon oxide film and SiC film on poly SiC substrate by smart cut technique used in the present invention Manufacturing process diagram of Schottky diode formed on SiC film formed on insulating isolation film of FIG. Manufacturing process diagram of Schottky diode in which electric field relaxation layer is provided in trench portion of SiC film formed on insulating isolation film of FIG. Manufacturing process diagram of Schottky diode provided on thin SiC film formed on insulating separation film of FIG. 6 of the present invention Manufacturing process diagram of Schottky diode provided on thick SiC film formed on insulating isolation film of FIG. 7 of the present invention

FIG. 4 shows a structure in which a Schottky diode is formed on a single crystal SiC 3 formed on a poly SiC substrate 5 via a silicon oxide film 4 as an embodiment of the present invention. The electric field applied to the Schottky interface is relaxed by the presence of the silicon oxide film as compared with FIG. Therefore, even if crystal defects exist, the voltage at which leakage current is generated shifts from Vp to the high voltage side. The state of the electric field due to the presence of the silicon oxide film is shown in FIG. The electric field strength in the SiC film near the anode is greatly relaxed due to the influence of the substrate potential under the oxide film. As a result, as shown by the broken line in FIG.

FIG. 5 shows an example in which a trench isolation structure is used for element isolation. Other parts are common.

FIG. 6 shows an example of a structure in which a shallow SiC film on a silicon oxide film has no lateral (plane direction) Schottky interface. The trench groove formed by the trench is filled with a Schottky metal so that the side wall of the trench becomes a Schottky interface, so that only the vertical direction is obtained. As a result, a structure independent of longitudinal crystal defects can be obtained. The breakdown voltage of the Schottky diode is the breakdown voltage Vq determined by the Schottky barrier.

FIG. 7 shows an example of a structure in which a thick SiC film on a silicon oxide film has no lateral (plane direction) Schottky interface. As a method of forming the Schottky metal on the side surface of the trench groove formed by the trench, it can be formed by sputtering or vapor deposition from an angle of 45 degrees to all directions. By this oblique deposition method and sputtering method, a thin Schottky metal can be formed and a Schottky diode can be formed on the side surface of the trench. In addition, the trench side wall is a Schottky interface so that only the vertical direction is obtained. Thereby, it can be set as the structure which does not depend on the crystal defect of the vertical direction. The breakdown voltage of the Schottky diode is the breakdown voltage Vq determined by the Schottky barrier.
In FIG. 7B, each element can be separated by making the trench formed by the trench into an insulating structure.

In FIG. 8, a method for forming a SiC film on a silicon oxide film will be described. FIG. 8A shows a SiC seed crystal substrate. A substrate having good crystallinity with reduced crystal defects serves as a seed substrate. FIG. 8B shows a state in which a silicon oxide film is formed on poly SiC 6. FIG. 8C shows a portion indicated by a smart cut layer 34 having a depth of 1 μm and indicated by a broken line when hydrogen ions are implanted into the seed crystal substrate 8 for smart cut. FIG. 8D shows a state in which the substrate in which the silicon oxide film is formed on the poly SiC of FIG. 8B is inverted and bonded to the seed substrate in this state. Although the seed crystal substrate has few crystal defects, warping is generated even with a small amount of crystal defects, so it is preferable to put it on an adsorption stage and bond it together. Since the bonding is performed through the interface of the silicon oxide film, the bonding can be easily performed at room temperature. Further, since there is no warp in poly SiC, there is no warp in the bonded state. Thereafter, by raising the temperature to several hundred degrees, a thin SiC layer 35 is formed on the silicon oxide film 4 of the poly SiC substrate 5 by cleaving from the smart cut surface 35. The state is shown in FIG. In this state, the surface of the thin SiC layer 35 is polished, the crystal defect portion is removed, and a thick SiC layer 38 having a necessary thickness is epitaxially grown thereon, as shown in FIG.

9 shows a manufacturing process procedure of the Schottky structure having the structure shown in FIG. FIG. 9A shows a substrate prepared according to FIG. 8-F. FIG. 9B shows an N ⁺ layer formed on this substrate by a known resist 50, photolithography technique, and ion implantation technique. Further, FIG. 9C shows a state in which a trench is formed and the trench oxide film 52 is filled therein. FIG. 9D shows a state where the SiC of the Schottky anode portion 114 is exposed. Thereafter, the Schottky metal film 112 is formed as shown in FIG. Further, the state in which the cathode electrode 116 and the anode electrode 113 are formed is shown in FIG.

FIG. 10 shows a manufacturing process procedure of the Schottky structure having the structure shown in FIG. In contrast to FIG. 4, an oxide film is formed in the cross-sectional direction of SiC by a trench structure in the vicinity of the anode portion to create an electric field relaxation effect, and a field plate creates an electric field relaxation effect from the surface. 10-a and b are the same as FIGS. 9-a and b. FIG. 10C shows a state in which the trench groove 51 is formed. In this state, the narrow trench groove is filled with the trench oxide film 52 by oxidizing the exposed SiC side wall of the trench groove. A trench sidewall oxide film 53 is formed on the sidewall of the wide trench. In this state, the trench portion N ⁺ backfill layer 54 is formed of polysilicon by a known means. FIG. 10-c shows this state. Further, in FIG. 10-d, a Schottky anode metal film 112 is formed by the same process as in FIGS. 9-d and e. FIG. 10E shows that the field plate 120, the cathode electrode 116, and the anode electrode 113 are formed in this state.

FIG. 11 shows a manufacturing process procedure of the Schottky structure having the structure shown in FIG. A thin SiC film has no vertical Schottky electrode surface. 11A, 11B, 11C, and 11C show Schottky cathodes 111 and anodes 114 formed in the same manner as FIGS. 9A, 9B, 9C, and 9D. FIG. 11D shows a state where the thin SiC film in the anode portion is removed by etching up to the interface of the silicon oxide film 4. FIG. 11E shows a state where the Schottky metal film 112 is formed, and FIG. 11F shows a state where the cathode electrode 116 and the anode electrode 113 are formed. For reference, FIG. 11G is a structural diagram of an example in which a trench oxide film as shown in FIG. 9C is formed during the series of steps in FIG.

FIG. 12 shows a manufacturing process procedure of the Schottky structure having the structure shown in FIG. A thick SiC film does not have a vertical Schottky electrode surface. 11A, 11B, 11C, 11D, 11D, 11C, 11D, and 11D show Schottky cathodes 111 and anode portions 114 formed in the same manner as in FIGS. A state in which the thick SiC film is removed by etching up to the interface of the silicon oxide film 4 is shown. FIG. 11E shows a state in which the Schottky metal film 117 in the anode part is formed. Since the trench groove is deep, the metal film is formed by vapor deposition or sputtering from the oblique direction 121. Thereafter, the Schottky metal 117 is removed leaving only a necessary portion to form the Schottky metal film 112. FIG. 12F shows a state where the cathode electrode 116 and the anode electrode 113 are formed. Further, FIG. 12-g shows a state in which the field plate 120 is formed on the surface.

In the above examples, the case of a silicon oxide film as an insulating film was introduced. However, it is also effective to use alumina, aluminum nitride, or other highly insulating materials. As the insulator of the trench portion, not only the silicon oxide film but also alumina, aluminum nitride, or other insulators can be used.

In the examples of FIGS. 5 to 12 described above, SiC is described as an example of a single crystal compound semiconductor, but the same applies to other compound semiconductors such as GaN. In addition to Si and SiC, a material having a lattice constant close to that of a compound semiconductor such as Ge can be used as the substrate, and an insulating substrate such as a sapphire substrate can also be used.

Industrial applicability

High-voltage drive elements using SiC substrates, GaN substrates, and the like are becoming increasingly important with the spread of hybrid vehicles and electric vehicles. In addition, with the spread of smart grids in homes, the role of high voltage elements becomes important for the electrification and energy management of home appliances. A single crystal SiC thin film is formed on an Si substrate or a poly SiC substrate according to the present invention via an insulating film, elements are formed therein, and crystal defect leakage at the junction that serves as a reverse bias of these elements is reduced in electric field. This creates a great effect of reducing the amount of the element and greatly contributes to the popularization of elements in the field. There are similar expectations for other compound semiconductors such as GaN. In addition, a method capable of forming an isolation element by an oxide film isolation structure is epoch-making as a compound semiconductor such as SiC or GaN, and is a base for practical application of an integrated circuit of a compound semiconductor.

DESCRIPTION OF SYMBOLS 1 ... Si substrate 2 ... SiC film 3 ... SiC substrate 4 ... Silicon oxide film 5 ... Poly SiC substrate 8 ... Seed SiC crystal substrate 20 ... Planarization stage 21 ... Intake hole 34 of flattening stage ... Smart cut layer 35 ... Thin SiC layer 37 ... Thin SiC layer 38 ... Thick SiC layer 50 ... Resist mask 51 ... Trench groove 52 ... Trench oxide film 53 ... trench side wall oxide film 54 ... trench portion N ⁺ backfill layer 67 ... element boundary 68 ... element isolation portion 103 ... vertical defect 104 ... 54 Degree of crystal defect 105... PN junction surface crystal defect 111... Schottky diode cathode (N ⁺ layer)
DESCRIPTION OF SYMBOLS 112 ... Schottky metal film 113 ... Schottky diode anode electrode 114 ... Schottky diode anode part 115 ... Crystal defect current 116 ... Cathode electrode 117 ... Schottky metal film 120 ... Field plate 121 ... An oblique deposition

Claims (4)

A compound semiconductor having a single crystal compound semiconductor layer through an insulating film layer using a material such as a Si substrate, a SiC substrate, or a Ge substrate that is close to the lattice constant of the single crystal compound semiconductor layer formed over the insulating film as a base substrate A trench is formed in the single crystal compound semiconductor layer formed on the insulating film layer of the substrate or on the insulating film layer of the substrate, the trench reaches the insulating film layer, and an insulating film is formed on the sidewall of the trench. In a semiconductor element in which a conductor is provided on the side surface of the oxide film or a field plate layer is provided on the element surface via an oxide film, at least a reverse bias is applied when a Schottky diode formed in a single crystal compound semiconductor layer is used. A semiconductor element having means for relaxing an electric field on the Schottky junction surface and a semiconductor device using the same. 2. The means for applying an electric field through an oxide film according to claim 1, wherein at least one of an insulating film between the base substrate and the compound semiconductor layer, an insulating film on the trench sidewall, and an insulating film on the element surface is used. Semiconductor element having means for relaxing electric field and semiconductor device using the same A compound semiconductor having a single crystal compound semiconductor layer through an insulating film layer using a material such as a Si substrate, a SiC substrate, or a Ge substrate that is close to the lattice constant of the single crystal compound semiconductor layer formed over the insulating film as a base substrate A trench is formed in a single crystal compound semiconductor layer formed on the insulating film layer of the substrate or on the insulating film layer of the substrate, the trench reaches the insulating film layer, and an insulating film is formed in the trench portion. Using an element substrate having a single-crystal compound semiconductor layer with one or a plurality of insulating separation shapes, the Schottky electrode interface of the Schottky diode formed on the single-crystal compound semiconductor layer is not parallel to the substrate. A semiconductor device characterized by an element structure. 4. A semiconductor device according to claim 1, wherein the single crystal compound semiconductor is single crystal SiC, and the base substrate is SiC or silicon.

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