Method for forming electrical contacts and method for forming semiconductor devices

Abstract

The invention relates to a method for forming an electrical contact (16). The method comprises grinding a silicon carbide surface (101) with a grinding disk having a grinding surface containing nickel or a nickel compound, such that particles (12) of nickel or a nickel compound from the grinding surface are deposited (210) in the ground silicon carbide surface; and tempering the ground silicon carbide surface (101g) by means of a laser, such that at least a portion of the deposited nickel particles (12) form (220) nickel silicide with the silicon of the silicon carbide.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for forming an electrical contact and to a method for forming a semiconductor device. BACKGROUND

[0002] Silicon carbide is a semiconductor material which is increasingly applied in the semiconductor industry, in particular in recent years.

[0003] In US patent 8,216,929 B2 a method for forming an electrical contact on a silicon carbide substrate is disclosed, wherein the surface of the silicon carbide substrate is first treated such that its average roughness value is less than 10 nm. Then the surface is damaged by means of a plasma, after which a thin metal layer is applied to the damaged surface in a subsequent process. Finally, the thin metal layer is irradiated with a laser. SUMMARY

[0004] It is the task on which the present invention is based to provide a method for forming an electrical contact on a silicon carbide surface which reduces the number of process steps.

[0005] In different embodiments a method for forming an electrical contact is provided. The method can comprise grinding a silicon carbide surface with a grinding disk having a grinding surface comprising nickel or a nickel compound. Here, the grinding can be carried out in such a way that particles of the nickel or the nickel compound from the grinding disk are deposited into the ground silicon carbide surface. Furthermore, the method can also comprise tempering the ground silicon carbide surface by means of a laser, which can be carried out in such a way that at least a portion of the deposited nickel particles form nickel silicide with the silicon of the silicon carbide.

[0006] In different embodiments the described method can be used for forming a silicon carbide semiconductor device, for example a transistor, for example a MOSFET, for example a power-MOSFET.

[0007] The above described method can form an ohmic contact on a silicon carbide (SiC) substrate. The electrical (ohmic) contact can be formed between silicon carbide and nickel silicide.

[0008] In different embodiments the damaging / roughening of the silicon carbide surface and the arranging of the metal on or in the damaged / roughened surface can be combined into one process. Here, the grinding means for treating the surface can be configured in such a way that the metal particles deposited in the damaged / roughened surface are released when the silicon carbide surface is treated.

[0009] In the following the term "grinding disk" is used for the grinding means. However, it is to be understood that the grinding means can have a disk shape which is different from the commonly used disk shape. The grinding means can for example be a grinding wheel, be belt-like or cylindrical or have any other suitable shape.

[0010] In different embodiments a manufacturing method for forming an electrical contact on silicon carbide is provided, wherein two separate processes for on the one hand preparing a surface and on the other hand depositing or embedding a metal into the surface can be dispensed with.

[0011] Combining the roughening / damaging of the surface with depositing nickel into the surface, in other words dispensing with a separate process for the metal deposition process, can mean a reduction in the manufacturing costs for forming the electrically conductive connection.

[0012] In different embodiments the manufacturing of the electrically conductive connection can be simplified by grinding the silicon carbide surface with a grinding disk containing nickel and laser tempering being able to be sufficient to form the electrically conductive connection to the silicon carbide.

[0013] The grinding can be carried out in such a way that the silicon carbide substrate is thinned to a thickness of about 50 μιη to 200 μιη, wherein the ground surface can have an average roughness of more than 10 nm and there are crystal defects and nickel particles introduced by means of the grinding disk below the ground surface up to a depth of at least about 100 μιη and at most about 500 nm.

[0014] Furthermore, the tempering can be carried out in such a way that the crystal defects in the layer below the surface are reduced, at least a part of the deposited nickel reacts with the silicon of the silicon carbide (for example forms nickel silicide) and an ohmic contact with a contact resistance of less than 1 mΩcm 2 is formed. BRIEF DESCRIPTION OF DRAWINGS

[0015] The dependent claims and the description set forth in the specification are intended to clarify the aspects of the application. Embodiments of the application are shown in the drawings and are set forth in more detail in the following description. The drawings show:

[0016] Figures 1A to 1C : a schematic diagram of a method for forming an electrical contact according to different embodiments;

[0017] Figure 2 : a flow chart of a method for forming an electrical contact according to different embodiments; and

[0018] Figure 3 : a flow chart of a method for forming a semiconductor device according to different embodiments, and

[0019] Figure 4 : a semiconductor device which has been manufactured by means of a method for forming a semiconductor device according to different embodiments. DETAILED DESCRIPTION

[0020] Figures 1A to 1C A schematic diagram of a method for forming an electrical contact 16 according to different embodiments is shown.

[0021] Figure 1A A silicon carbide substrate 10 (for short: substrate) having a surface 101 is shown. The silicon carbide substrate 10 can be a SiC wafer, for example. The substrate 10 can have a thickness T, for example a thickness between about 250 pm and about 430 pm or more. The surface 101 can be a first main surface 101 of the silicon carbide substrate 10. The silicon carbide substrate 10 can have a second main surface 102 opposite the first main surface 101. In the following, the formation of an electrical contact 16 on the entire surface 101 is described. In different embodiments, the electrical contact 16 can be formed on one sub-area of the surface 101 or on a plurality of sub-areas which are connected to each other or separated from each other. In different embodiments, the formation of the electrical contact 16 is alternatively or additionally realized on the second main surface 102, for example on the entire second main surface 102 or on one sub-area of the second main surface 102 or on a plurality of sub-areas which are connected to each other or separated from each other.

[0022] According to different embodiments, an electronic semiconductor structure element 11 (schematically shown in Figure 1A ; see also Figure 4 ) can be formed in the substrate 10. The semiconductor structure element 11 can be formed in the substrate 10 as a vertical structure element, for example, such that it extends from the second main surface 102 into the substrate 10 and to an electrode to be formed on the first main surface 101. For example, the electronic semiconductor structure element 11 can be a vertical transistor, and the electrical contact 16 on the first main surface 101 can be a drain or a contact layer for a drain. The transistor can be a (power) MOSFET or another suitable vertical structure element, for example. In different embodiments, the method for forming one electrical contact 16 can be used for forming at least one electrical contact 16, for example at least one electrode, for a lateral electronic semiconductor structure element.

[0023] Figure 1B A substrate 10 is shown after its surface 101 has been ground. The ground surface is provided with the reference 101g, accordingly.

[0024] By means of grinding, the thickness T of the substrate 10 can be reduced to a thinned thickness Tg. In different embodiments, the grinding can essentially have a grinding process which is usually performed anyway for thinning the substrate 10. Here, the silicon carbide substrate 10 can be thinned to a thinned thickness Tg of about 50 pm to about 200 pm. In different embodiments, the grinding can be a process for forming the electrical contact 16, for example in the case of an electrical contact 16 formed on a main surface 101 or 102 having an electronic structure element.

[0025] The grinding can be performed by means of a grinding disk or another suitable grinding tool. The grinding disk can have nickel and / or a nickel compound, for example a nickel alloy, on its grinding face. The nickel content of the grinding disk can be between about 0.1 wt.-% and 100 wt.-%. In other words, the grinding disk can consist entirely or only partially of nickel. A grinding disk consisting only partially of nickel can for example also have a glass or ceramic material, for example SiO2, ZnO and / or CaO. The nickel can be embedded in the glass or ceramic material, for example as nickel particles.

[0026] The nickel-containing grinding face can be configured, for example in terms of its roughness, such that the surface 101 is roughened and the crystal structure of the silicon carbide is destroyed by means of the grinding. Furthermore, nickel particles 12 can be introduced into the surface 101 or 101g during the grinding. In other words, craters 13 and lattice damage 14, for example microcracks, dislocations and / or pores, can be formed in the surface 101g by means of the grinding and nickel particles 12 can also be introduced onto and / or into the surface 101g of the substrate 10. The nickel particles 12 can for example be arranged in the craters 13 and at locations where the lattice damage 14 is present. The grinding can be performed such that the craters 13, the lattice damage 14 and the nickel particles 12 extend into the substrate 10 up to a depth d of about 10 nm to about 500 nm. The surface-adjacent region in which the lattice damage 14, the craters 13 and the deposited nickel 12 are present is also referred to as the damage region.

[0027] In order to achieve a predetermined damage region depth and a desired amount of nickel 12 deposited therein, parameters relating to the grinding process can be adapted, for example the nickel content and the roughness of the grinding disk, the grinding duration, the pressing pressure during the grinding process, etc. In different embodiments, for example, a maximum depth of the damage region (for example between 200 nm and 500 nm) can be pursued if the formed electrical contact 16 is to be used directly as an electrode and / or if this electrical contact 16 forms a backside electrode of a semiconductor component. Conversely, a minimum depth of the damage region (for example between 10 nm and 200 nm) can be pursued if it is provided that the formed electrical contact 16 is to be used only as a seed layer for depositing a further electrically conductive layer and / or if the electrical contact 16 forms at least one frontside electrode.

[0028] The average roughness value Ra of the ground surface 101g can be between about 10 nm and about 500 nm, for example between about 10 nm and about 50 nm.

[0029] In different embodiments, the substrate 10 can have all of the above-mentioned properties after grinding, i.e. the thickness Tg of the substrate 10 is about 50 pm < Tg < 200 pm, the average roughness value Ra is about 10 nm < Ra < 500 nm and the damage region has a thickness of between about 10 nm and about 500 nm, and nickel and / or a nickel compound 12 is arranged in the ground surface 101 g and / or in the damage region.

[0030] In Figure 1C is shown a silicon carbide substrate 10 having a ground surface 101 g during a tempering process. The tempering can be performed by means of a laser, the laser light 18 of which is irradiated onto the ground surface 101 g. The irradiation (tempering) by means of the laser 18 can be performed such that the defects (pits 13 and lattice damage 14) are reduced or eliminated, such that at least a part of the nickel or nickel compound 12 reacts with the silicon of the silicon carbide substrate 10 (e.g. forms nickel silicide) and forms an ohmic contact 16 on the surface 101 g, wherein the contact 16 can have a contact resistance of less than 1 mWcm 2 . The surface having the ohmic contact 16 obtained after tempering is designated by reference sign 101 g in Figure 1C .

[0031] In Figure 1C is shown on the left-hand side that the defects can be reduced or eliminated after irradiation of the ground surface 101 g with the laser 18. In different embodiments, the laser 18 can have a wavelength of less than 400 nm and an energy density of more than 2 J cm -2 .

[0032] During the laser tempering recrystallization can occur. This recrystallization leads to a change (reduction) of the surface roughness. For example, the average roughness Ra after tempering can be less than half of the average roughness Ra before tempering.

[0033] Furthermore, the laser tempering can also lead to a chemical bonding of the nickel 12 present in the layer near the surface (e.g. formation of nickel silicide) and also to the evaporation of a part of the silicon. The nickel silicide compound formed by the laser tempering can form an electrically conductive layer and thereby form an electrical connection (contact) 16. The thickness of the electrically conductive connection 16 can be in the range from about 10 nm to about 500 nm, for example between about 10 nm and about 50 nm.

[0034] If the electrical connection (as described above) is formed only on a partial area of the surface of the substrate 10, this can be achieved by grinding only a partial area of the surface 101 and subsequently irradiating with the laser 18, and / or by grinding the entire surface 101 but tempering only on a partial area of the surface 101. If the entire surface 101 is ground but the electrical connection is formed only in a partial area of the surface 101, a protective layer (not shown) can be arranged on the ground, non-irradiated area.

[0035] In different embodiments, the electrically conductive contact 16 can directly form an electrode of the electronic semiconductor component. In different embodiments, the electrically conductive contact 16 can be the lowermost layer of a layer stack forming the electrode. In other words, the electrically conductive contact 16 can serve as a base layer or seed layer for applying at least one further electrically conductive layer, e.g. galvanically.

[0036] Figure 2 A flow chart of a method 200 for forming an electrical contact according to different embodiments is shown.

[0037] The method can comprise grinding a silicon carbide surface with a grinding disk having a grinding face containing nickel or a nickel compound such that particles of nickel or the nickel compound from the grinding disk are deposited (210) to the ground silicon carbide surface, and tempering the ground silicon carbide surface by means of a laser such that at least a portion of the deposited nickel particles form (220) nickel silicide with silicon in the silicon carbide.

[0038] Figure 3 A flow chart of a method 300 for forming a semiconductor device according to different embodiments is shown.

[0039] The method can comprise (310) forming a semiconductor structural element in a silicon carbide substrate, wherein the forming of an electrode of the semiconductor structural element comprises a method (320) for forming an electrical contact according to one of the above-described embodiments.

[0040] The method can be implemented on wafer level. The same applies to the method for forming an electrical contact according to different embodiments.

[0041] In different embodiments, the semiconductor structural element can be a transistor.

[0042] Figure 4 A semiconductor device 400 manufactured by means of a method for forming a semiconductor device according to different embodiments as detailed above is shown.

[0043] The semiconductor device 400 comprises a silicon carbide substrate 10 having an electrical contact 16 formed thereon, which forms a surface 101gt of the semiconductor device 400.

[0044] Furthermore, the semiconductor device 400 also comprises a semiconductor structural element 11 formed in the substrate 10, which extends, for example, from the second surface 102 into the substrate 10. The electrical contact 16 can be, for example, a backside electrode of the semiconductor structural element 11.

Claims

1. A method for forming an electrical contact (16), comprising: · Grinding a silicon carbide surface (101) using a grinding disk having a grinding surface containing nickel or a nickel compound, such that particles (12) of nickel or the nickel compound from the grinding disk are deposited (210) in the ground silicon carbide surface; and · Tempering the ground silicon carbide surface (101g) by means of a laser, such that at least a portion of the deposited nickel particles (12) form (220) nickel silicide with the silicon of the silicon carbide.

2. The method according to claim 1, in, The nickel silicide forms a surface layer (101gt).

3. The method according to claim 1 or 2, in, The grinding of the silicon carbide surface includes thinning a silicon carbide substrate (10) to a thickness between 50 μm and 200 μm.

4. The method according to claim 1 or 2, in, The ground silicon carbide surface (101g) has an average roughness value Ra of 10 nm < Ra < 500 nm.

5. The method according to claim 1 or 2, in, The grinding disk contains between 0.1% and 100% by weight of nickel.

6. The method according to claim 1 or 2, in, The tempering includes irradiation by means of a laser (18) having a wavelength of less than 400 nm.

7. The method according to claim 1 or 2, in, The tempering includes using a material with a diameter greater than 2 J / cm. -2 And less than 5 Jcm -2 Irradiation is performed using a laser with an energy density of (18).

8. The method according to claim 2, in, The surface layer (101gt) has an average roughness value of 10 nm < Ra < 500 nm.

9. The method according to any one of claims 1, 2 and 8, in, The method is implemented at the wafer level.

10. A method for forming a semiconductor device (400), comprising: · Forming a semiconductor structural element (11) in a silicon carbide substrate (310), having: Forming (320) an electrode (16) of the semiconductor structural element (11) by means of the method for forming an electrical contact according to any one of claims 1 to 9.

11. The method according to claim 10, in, The semiconductor structural element (11) is configured as a transistor.

12. The method according to claim 10 or 11, in, [[ID=

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