DE102021205315A1 - DIAPHRAGM SEMICONDUCTOR DEVICE AND METHOD OF MAKING THE SAME - Google Patents

Abstract

A membrane semiconductor component (100) with an outer area (81) and a membrane area (82) is provided. A gallium nitride layer system (15, 16, 17) is arranged on or above a first side of a substrate (61). A rear contact structure (52) is on or above a second side of the substrate (61), which is opposite the first side, and/or on or above the gallium nitride layer system (15, 16, 17) on the second side in the outer area (81 ) and arranged in the membrane area (82). At least part of the substrate (61) is arranged in the outer area (81). The substrate (61) is structured in such a way that a rear side trench (51) is set up in the membrane area (82). The backside trench (51) is free from the substrate (61). An electrically conductive rear side trench filling structure (56) is arranged in the rear side trench (51) at the second side and set up such that the rear side trench filling structure (56) electrically contacts the rear side contact structure (52) in the membrane area (82) and laterally from the substrate (61) and the back contact structure (52) in the outer region (81) is spaced.

Description

State of the art

Transistors based on gallium nitride (GaN) offer the possibility of realizing components with lower on-resistances and at the same time higher breakdown voltages than comparable components based on silicon or silicon carbide.

GaN transistors are primarily known for what are known as high-electron mobility transistors (HEMTs), in which the current flow takes place laterally on the top side of the substrate through a two-dimensional electron gas that forms the transistor channel. Such lateral components can be produced by heteroepitaxy of the functional GaN layers on silicon wafers. However, for high breakdown voltage with small on-resistance per unit area, vertical devices, in which the current flows from the front of the substrate to the back of the substrate, are more advantageous in terms of both the size and the electric field distribution inside the device. Such a component cannot be produced directly using heteroepitaxial GaN layers on silicon (Si), since insulating intermediate layers (a so-called buffer) are required to adapt the lattice mismatch between GaN and Si and to reduce the substrate curvature.

The buffer itself is mechanically strained in such a way that it just compensates for the strain of the GaN layers at room temperature. However, since the buffer is an insulator, the current flow from the front of the substrate to the back of the substrate is prevented by the buffer.

Native GaN substrates are also known on which the required additional epitaxial GaN layers of the device can be grown without the need for an insulating buffer. However, such GaN substrates are small (typically 50 mm in diameter) and expensive.

In order to reduce the transistor price per area element, it can be advantageous to use the available heteroepitaxial GaN layers on large silicon substrates. Vertical components (trench MOSFET, pn diode) are known for this purpose, in which the silicon substrate and the insulating buffer under the component are selectively removed, whereby a backside trench (backside trench) is formed in order to directly cover the backside of the drift zone of the component to be able to contact. 1 shows the basic structure of such a component 1 with an insulating buffer and rear side trench 51 (here based on a trench MOSFET 1). The rear side trench 51 can also be referred to below as a rear side cavern or rear side aperture.

As in 1 is illustrated, the following III-V nitride semiconductor layers (GaN with the exception of the buffer) are epitaxially grown on the silicon substrate 61 or in general the substrate 61: the insulating buffer 13, a highly doped contact semiconductor layer with n-type conductivity 14, the low-doped n-type conductive drift layer 15, a p-conductive body layer 16 and a highly doped n-conductive source contact layer 17.

Source contact layer 17 and body layer 16 are penetrated by a trench (trench), the side walls and bottom of which are separated from gate electrode 21 by a gate dielectric 22 . Source contact layer 17 and body layer 16 are contacted by a source electrode 41 which is separated from gate electrode 21 by an insulating layer 31 . At the rear, the silicon substrate 61 and the buffer 13 are removed by a rear-side trench 51, which ends in the highly doped contact semiconductor layer with n-type conductivity 14. This is contacted by a drain electrode 52 on the rear. In operation, a conductive channel is formed in the body layer 16 by applying a gate voltage to the gate electrode 21, through which a current flow from the source electrode 41 to the drain electrode 52 is permitted.

In 1 For simplicity, a transistor with three cells, ie three repeating structures, is illustrated. In a real transistor, there are typically a large number of such cells and are therefore effectively connected in parallel. Typical active areas are in the range of a few square millimeters, the remaining GaN layers have a thickness of a few micrometers. The drain electrode 52 can consist of multiple metallic layers.

In order to increase the electrical resistance of the drain contact 52 and the stability of the membrane semiconductor component 1, the rear side cavern 51 is filled with a conductive material 53, as in FIG 2 is illustrated.

When the rear side cavern 51 is completely filled with filling material 53, the reliability of the component is reduced due to the greatly different thermal expansion coefficients of the semiconductor materials in the membrane semiconductor component 1 (silicon (2.6*10 ^-6 K ^-1 ), GaN(3.2*10 ^-6 K ^-1 )) and the filling metals (e.g. copper (17*10 ^-6 K ^-1 ), silver (18*10 ^-6 K ^-1 )). On the one hand, this leads to reliability problems during production, for example due to high temperatures during sintering, and by temperature variations during operation.

Disclosure of Invention

Advantages of the Invention

The core of the invention is a vertical gallium nitride power component on a foreign substrate with a partially metallically filled back side cavity, the metal being arranged within the cavity in the form of one or more columns. The advantage of this arrangement is that a lateral expansion of the metal columns is possible in the event of a temperature change, which means that there is less mechanical stress on the component.

The membrane semiconductor component according to the invention with the features according to claim 1 has the advantage that a more reliable membrane semiconductor component can be provided, for example a vertical GaN-on-Si membrane semiconductor component with a low series resistance of the drain electrode and improved thermal stability. This is clearly made possible by a structured rear-side trench filling structure, which allows the electrically conductive filling material to expand thermally and to reduce or avoid the thermal stresses caused as a result.

As an illustrative example, a vertical gallium nitride power device is provided on a foreign substrate with a back side cavity partially filled with metal, the metal being arranged within the back side cavity in the form of one or more columns. This allows the metal columns to expand laterally when the temperature changes. As a result, lower mechanical loads can occur in the semiconductor component.

Developments of the aspects and advantageous configurations of the vertical semiconductor component are described in the dependent claims and the description.

character list

• 1 eine schematische Darstellung eines Membran-Transistors der bezogenen Technik;
• 2 schematische Darstellung eines vertikalen Feldeffekttransistors der bezogenen Technik; und
• 3 bis 5 schematische Darstellungen eines Membran-Halbleiterbauelements gemäß verschiedenen Aspekten.

Embodiments of the invention are shown in the figures and are explained in more detail below. Show it:

• 1 a schematic representation of a membrane transistor of the related art;
• 2 schematic representation of a vertical field effect transistor of the related art; and
• 3 until 5 schematic representations of a membrane semiconductor device according to various aspects.

In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. It is understood that the features of the various exemplary embodiments described herein can be combined with one another unless specifically stated otherwise. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. In the figures, identical or similar elements are provided with identical reference symbols, insofar as this is appropriate.

In the following description, various aspects and embodiments of a vertical semiconductor component are described using a trench MOSFET as an example. However, it goes without saying that the use of the stepped metal foil for processing the rear side of a semiconductor component is not limited to a trench MOSFET, so that in principle any vertical semiconductor components can be produced using this technology, such as Schottky diodes, pn diodes, vertical Diffusion MOSFETS (VDMOS), Current-Aperture Vertical Electron Transistors (CAVETs), vGroove Vertical High Electron Mobility Transistors (vHEMTs) or Fin Field Effect Transistors (FinFETs).

Description of the embodiments

3 FIG. 1 shows a schematic cross-sectional view of a membrane semiconductor device 100 according to various embodiments. As in 3 is illustrated, the backside trench fill structure 56 can be a partial backfilling of the backside cavern 51 (see FIG 1 ) in the form of a plurality of metallic columns 54 (also referred to as an electrically conductive structure 54). The columns 54 can be completely separated from one another or connected to one another in the direction of the plane of the drawing, for example in the form of interconnected lamellae. The metallic columns 54 bring about a reduction in the electrical resistance of the rear-side contact structure, for example the drain electrode 52. For example, the electrical resistance through the additional conductive paths reduced compared to the case that current conductivity is given only by the drain electrode 52 in the outer region 81. The mechanical stress on the membrane semiconductor component 100 is reduced due to the possibility of lateral expansion of these metallic pillars in the event of a temperature change (due to the intermediate spaces or the spacing of the metallic pillars 54). The metallic pillars 54 can include or be formed from copper, silver or nickel, for example. The metallic pillars 54 can be formed using a galvanic growth or an additive process. A corresponding additive method can be a Direct Metal Deposition (DMD) process, for example. In the DMD process, fine metal powders with particle sizes of a few µm can be locally melted using a laser beam. A horizontal powder bed is not absolutely necessary for a DMD process and the metallic structure, ie the metallic columns 54, can be formed directly in the back side trench 51 in layers.

4 FIG. 1 shows a schematic cross-sectional view of a membrane semiconductor device according to various embodiments. In various embodiments, the space between adjacent metallic columns 54 is filled with a further material 55, for example with an electrically insulating material 55. The further material 55 is more elastic (mechanically softer) than the metallic columns 54. In other words: the modulus of elasticity of the further material 55 is lower than the modulus of elasticity of the metallic pillars 54. Complete filling of the rear side trench 51 with the metallic pillars 54 and the further material 55 allows the membrane region 81 of the membrane semiconductor component 100 to be stabilized.

In comparison to a filling material 53 of the related technology, i.e. a one-piece complete metal filling of the rear side trench 51, a thermally induced, lateral expansion of the metallic columns 54 can take place in the event of a temperature change due to the lower modulus of elasticity of the further material 55. The further material 55 can, for example, be an organic material, for example a plastic, for example a duromer, a thermoplastic, a polyurethane or the like, or an inorganic material, for example a ceramic, for example an aluminum oxide or silicon oxide. The further material 55 can be introduced into the spaces between the metallic columns 54 by means of dispensing, jetting, capillary filling, molding or the like, for example.

5 shows a schematic top view of a membrane semiconductor component according to various embodiments, for example according to an in 4 illustrated embodiment. Metallic pillars 54 and the further material 55 within the rear side trench 51 are illustrated. The metallic pillars 54 are here arranged in a regular arrangement. The arrangement can be adapted to the geometry of the rear trench 51 . The geometry of the metallic columns 54 can also be adapted to the geometry of the rear trench 51 . An alternative, regular arrangement of the metallic columns 54 is a hexagonal arrangement (honeycomb pattern) of metallic columns 54 or metallic laminations 54. In the arrangement in FIG 5 In addition, the metallic columns 54 are separated from the remaining substrate 61 located under the drain electrode 52 by the additional material 55 . As a result, for example, the silicon of the substrate 61 and the metal of the metallic columns 54 can expand largely independently of one another when the temperature of the membrane semiconductor component 100 changes. In various embodiments, other configurations of the metallic columns 54 may be provided, such as in the form of concentric rings. Alternatively or additionally, the cross-sectional area or the base area of the metallic columns 54 can have the shape of a rectangle, a square, a polygon, a circle or an ellipse. Alternatively or additionally, the metallic columns 54 can have a non-uniform lateral extension, for example the thickness of the metallic columns 54 can vary over their height, for example tapering.

• In verschiedenen Ausführungsformen wird ein Membran-Halbleiterbauelement 100 mit einem Außenbereich 81 und einem Membranbereich 82 bereitgestellt. Das Membran-Halbleiterbauelement 100 weist ein Galliumnitrid-Schichtensystem 15, 16, 17 auf oder über einer ersten Seite eines Substrats 61 auf. Eine Rückseitenkontaktstruktur 52 ist auf oder über einer zweiten Seite des Substrates 61, die der ersten Seite gegenüberliegt, und/oder auf oder über dem Galliumnitrid-Schichtensystem 15, 16, 17 bei der zweiten Seite in dem Außenbereich 81 und in dem Membranbereich 82 angeordnet. Mindestens ein Teil des Substrats 61 ist in dem Außenbereich 81 angeordnet. Das Substrat 61 ist derart strukturiert, dass ein Rückseiten-Trench 51 in dem Membranbereich 82 eingerichtet ist. Der Rückseiten-Trench 51 ist dabei frei von dem Substrat 61. Eine elektrisch leitfähige Rückseiten-Trenchfüllstruktur 56 ist in dem Rückseiten-Trench 51 bei der zweiten Seite angeordnet. Die elektrisch leitfähige Rückseiten-Trenchfüllstruktur 56 ist derart eingerichtet, dass die Rückseiten-Trenchfüllstruktur 56 die Rückseitenkontaktstruktur 52 im Membranbereich 82 elektrisch kontaktiert und lateral von dem Substrat 61 und der Rückseitenkontaktstruktur 52 in dem Außenbereich 81 beabstandet ist.

In other words:

• In various embodiments, a membrane semiconductor component 100 having an outer area 81 and a membrane region 82 is provided. The membrane semiconductor component 100 has a gallium nitride layer system 15, 16, 17 on or over a first side of a substrate 61. A backside contact structure 52 is arranged on or above a second side of the substrate 61, which is opposite the first side, and/or on or above the gallium nitride layer system 15, 16, 17 on the second side in the outer area 81 and in the membrane area 82. At least part of the substrate 61 is arranged in the outer area 81 . The substrate 61 is structured in such a way that a rear side trench 51 is set up in the diaphragm area 82 . The rear side trench 51 is free of the substrate 61. An electrically conductive rear side trench filling structure 56 is arranged in the rear side trench 51 on the second side. The electrically conductive back ten trench filling structure 56 is set up in such a way that the rear side trench filling structure 56 electrically contacts the rear side contact structure 52 in the membrane area 82 and is laterally spaced apart from the substrate 61 and the rear side contact structure 52 in the outer area 81 .

If the substrate 61 has been completely removed, at least locally, so that the GaN layer system 15, 16, 17 is exposed on the back, there can clearly no longer be a second side of the substrate 61. In this case, the rear-side contact structure of the semiconductor component 100 is formed from the direction of the second side of the substrate 61 (previously possibly present) or in other words “on the second side of the substrate 61 and/or on or above one side of the gallium nitride layer system 15 , 16, 17 facing the first side of the substrate 61 .

The rear side contact structure 52 is set up as an electrode layer, for example. The membrane semiconductor device may be a controlled semiconductor device, such as a vertical transistor, or an uncontrolled semiconductor device, such as a diode. The membrane semiconductor device 100 is, for example, a vertical transistor 100. In this case, a front-side contact structure with a source electrode 41 and a drain electrode, respectively, and with a gate electrode 23 is formed on or over the first side and the back-side contact structure 52 is a Has drain electrode 52 and a source electrode. The gallium nitride layer system 15, 16, 17 can have at least one drift layer 15, a p-doped gallium nitride layer 16 and an n-doped gallium nitride layer 17. The rear contact structure 52 is in direct contact with the gallium nitride layer system 15, 16, 17 in at least one area. If the membrane semiconductor component is a diode, the front contact structure is an anode electrode and the rear contact structure is a cathode electrode, or vice versa.

The rear side trench filling structure 56 can have at least a first electrically conductive structure 54 and a second electrically conductive structure 54, for example. The first electrically conductive structure 54 and the second electrically conductive structure 54 are arranged in the rear side trench 51 at a distance from one another and from the substrate 61 . At least one electrically conductive structure 54 of the backside trench fill structure 56 may extend from the backside contact structure 52 such that the electrically conductive structure 54 has a surface that is coplanar with a surface of the backside contact structure 52 in the outer region 81 . At least one electrically conductive structure 54 of the rear-side contact structure 52 may include or be formed from a metal. At least one electrically conductive structure 54 of the rear-side contact structure 52 can have a column structure or a lamellar structure, for example, which extends from the surface of the rear-side contact structure 52 .

The backside trench fill structure 56 may further include an electrically insulating material 55 . The electrically insulating material 55 can be arranged laterally between the first electrically conductive structure 54 and the second electrically conductive structure 54 . The rear side trench filling structure 56 can have, for example, an electrically insulating material 55 that is arranged laterally between the substrate 61 or laterally between the rear side contact structure 52 in the outer area 81 and at least one electrically conductive structure 54 . The electrically insulating material 55 can include or be formed from a plastic or a ceramic.

Rear-side trench filling structure 56 can have, for example, an electrically insulating material 55 that is located laterally between substrate 61 and at least one electrically conductive structure 54 of rear-side trench filling structure 56 and/or laterally between a first electrically conductive structure 54 and a second electrically conductive structure 54 of the back side trench fill structure 56 is arranged. The electrically insulating material 55 and at least one of the first electrically conductive structure 54 and the second electrically conductive structure 54 may extend from the backside contact structure 52 such that the electrically conductive structure 54 and the electrically insulating material 55 have a surface that is coplanar with a Surface of the rear contact structure 52 in the outer area 81 is.

In various embodiments, a method for producing a membrane semiconductor component 100 with an outer area 81 and a membrane region 82 comprises: forming a gallium nitride layer system 15, 16, 17 on or over a first side of a substrate 61; Forming a backside contact structure 52 on or over a second side of the substrate 61, which is opposite the first side, and/or on or over the gallium nitride layer system 15, 16, 17 on the second side in the outer area 81 and in the membrane area 82, wherein at least a part of a substrate 61 is arranged in the outer area 81, the substrate 61 being structured such that a rear side trench 51 is established in the membrane area 82, the rear side trench 51 being free of the substrate 61, and forming a electrically conductive back side trench filling structure 56, which is in the back side trench 51 at is arranged on the second side and is set up such that the rear-side trench filling structure 56 electrically contacts the rear-side contact structure 52 in the membrane region 82 and is laterally spaced apart from the substrate 61 and the rear-side contact structure 52 in the outer region 81 .

The procedure can be carried out in the order mentioned above. In various embodiments, the method can have further features, for example one or more intermediate steps before, after or between the aforementioned method steps.

The embodiments described and shown in the figures are only chosen as examples. Different embodiments can be combined with one another completely or in relation to individual features. An embodiment can also be supplemented by features of a further embodiment. Furthermore, method steps described can be repeated and carried out in a different order than in the order described. In particular, the invention is not limited to the specified method.

Claims (14)

Membrane semiconductor component (100) with an outer area (81) and a membrane area (82), having: a gallium nitride layer system (15, 16, 17) on or over a first side of a substrate (61); a rear contact structure (52) on or over a second side of the substrate (61) opposite the first side and/or on or over the gallium nitride layer system (15, 16, 17) at the second side in the outer area (81) and in the membrane area (82), wherein at least part of the substrate (61) is arranged in the outer region (81), the substrate (61) being structured in such a way that a rear side trench (51) is set up in the membrane area (82), the rear side trench (51) is free from the substrate (61), and an electrically conductive rear side trench filling structure (56) which is arranged in the rear side trench (51) on the second side and is set up such that the rear side trench filling structure (56) electrically contacts the rear side contact structure (52) in the membrane region (82). and spaced laterally from the substrate (61) and the backside contact structure (52) in the outer region (81). Membrane semiconductor component (100) according to claim 1 , wherein the rear contact structure (52) is set up as an electrode layer. Membrane semiconductor component (100) according to claim 1 or 2 , wherein the backside trench filling structure (56) has at least a first electrically conductive structure (54) and a second electrically conductive structure (54) which are spaced apart from one another and from the substrate (61) in the backside trench (51). Membrane semiconductor component (100) according to claim 3 , wherein the back side trench filling structure (56) further comprises an electrically insulating material (55) that is arranged laterally between the first electrically conductive structure (54) and the second electrically conductive structure (54). Membrane semiconductor component (100) according to claim 1 until 4 , wherein the rear side trench filling structure (56) has an electrically insulating material (55) that is arranged laterally between the substrate (61) and at least one electrically conductive structure (54). Membrane semiconductor component (100) according to one of claims 3 until 5 , wherein at least one electrically conductive structure (54) of the backside trench filling structure (56) extends from the backside contact structure (52) in such a way that the electrically conductive structure (54) has a surface which is coplanar with a surface of the backside contact structure (52) in the outside area (81). Membrane semiconductor component (100) according to one of Claims 1 until 6 , wherein the rear side trench filling structure (56) has an electrically insulating material (55) that is laterally between the substrate (61) and at least one electrically conductive structure (54) of the rear side trench filling structure (56) and/or laterally between a first electrically conductive structure and a second electrically conductive structure (54) of the rear side trench filling structure (56), wherein the electrically insulating material (55) and at least one of the first electrically conductive structure (54) and the second electrically conductive structure (54) extend from the backside contact structure (52) such that the electrically conductive structure (54) and the electrically insulating material (55) have a surface that is coplanar with a surface of the backside contact structure (52) in the outer region (81). Membrane semiconductor component (100) according to one of claims 3 until 7 , wherein at least one electrically conductive structure (54) of the rear-side contact structure (52) comprises a metal or is formed therefrom. Membrane semiconductor component (100) according to one of Claims 4 until 7 , wherein the electrically insulating material (55) comprises or is formed from a plastic or a ceramic. Membrane semiconductor component (100) according to one of claims 3 until 9 , wherein at least one electrically conductive structure (54) of the backside contact structure (52) has a column structure or a lamellar structure, which extends from the surface of the backside contact structure (52). Membrane semiconductor component (100) according to one of Claims 1 until 10 , wherein the membrane semiconductor component (100) is set up as a vertical transistor (100), wherein a front-side contact structure having a source electrode (41) or a drain electrode and having a gate electrode (23) on or above the first Side is formed and the rear contact structure (52) has a drain electrode (52) and a source electrode. Membrane semiconductor component (100) according to one of Claims 1 until 11 , wherein the gallium nitride layer system (15, 16, 17) has at least one drift layer (15), a p-doped gallium nitride layer (16) and an n-doped gallium nitride layer (15). Membrane semiconductor component (100) according to one of Claims 1 until 12 , wherein the rear-side contact structure (52) is in direct contact with the gallium nitride layer system (15, 16, 17) at least in one area. Method for producing a membrane semiconductor component (100) with an outer area (81) and a membrane area (82), the method having: forming a gallium nitride layer system (15, 16, 17) on or over a first side of a substrate (61); Forming a rear contact structure (52) on or over a second side of the substrate (61), which is opposite the first side, and/or on or over the gallium nitride layer system (15, 16, 17) on the second side in the outer area (81 ) and in the membrane area (82), wherein at least part of a substrate (61) is arranged in the outer area (81), the substrate (61) being structured in such a way that a rear side trench (51) is set up in the membrane area (82), the rear side trench (51) is free from the substrate (61), and Forming an electrically conductive rear side trench filling structure (56), which is arranged in the rear side trench (51) on the second side and is set up in such a way that the rear side trench filling structure (56) electrically contacts the rear side contact structure (52) in the membrane area (82). is contacted and laterally spaced from the substrate (61) and the rear contact structure (52) in the outer region (81).

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