Localized annealing of metal-silicon carbide ohmic contacts and devices so formed
A contact for a semiconductor device can be formed by forming a metal on a Silicon Carbide (SiC) substrate and annealing an interface location of the metal and the SiC substrate to form a metal-SiC material thereat and avoiding annealing at a location on the SiC substrate to avoid forming the metal-SiC material thereat.
This application claims the benefit of U.S. Provisional Application No. 60/495,189, filed Aug. 14, 2003, entitled, Laser Annealing of Ohmic Contacts to SiC, and the benefit of U.S. Provisional Application No. 60/495,284, filed Aug. 15, 2003, entitled Laser Annealing of Ohmic Contacts to SiC, which are both assigned to the assignee of the present application, the disclosures of which are incorporated herein by reference in their entireties as if set forth fully herein.
FIELD OF THE INVENTIONThis invention relates to microelectronic devices, and more particularly, to the fabrication of light emitting devices (LEDs) and LEDs so formed.
BACKGROUNDIt is known that the thickness of Silicon-carbide (SiC) substrates in SiC-based light emitting devices can affect the forward voltage needed to operate the devices at a given current level. For example, the SiC-based light emitting diode C450-CB230-E1000 available from Cree, Inc. has a substrate thickness of about 250 μm (+/−25 μm) and has an associated forward operating voltage of about 3.5 volts at about 10 mA forward operating current. Moreover, reducing the thickness of the SiC substrate of an LED may reduce the forward voltage, which may yield reduced power consumption in such diodes.
It is also known that many small electronic devices may incorporate individual devices having reduced thicknesses so that the overall thickness of the electronic device may be reduced. For example, manufacturers of cellular phones may use surface-mounted LED chips to reduce the thickness of the component used to backlight a display of the cellular phone. Accordingly, reducing the thickness of the SiC substrate may also allow the device to be used in these types of small electronic devices.
It is known to form ohmic contacts on SiC at low/room temperature by, for example, implanting ions into a backside of a SiC wafer. However, if an implanted SiC substrate is thinned prior to formation of ohmic contacts, the doped region may be removed during the thinning, which may make the implant superfluous. Accordingly, metals deposited to form ohmic contacts may not have ohmic properties when deposited on the substrate as the implant may be performed in a later step. Ion implantation for the formation of ohmic contacts is discussed, for example, in U.S. patent application Ser. Nos. 09/787,189 and 10/003,331, the disclosures of which are incorporated herein by reference in their entireties as if set forth fully herein.
It is also known to form metal ohmic contacts by depositing a metal, such as nickel, and annealing the metal at a high temperature (such as temperatures greater than 900° C.). High temperature annealing may damage epitaxial layers of gallium nitride based materials included on the SiC substrate. Accordingly, there is a need for improved methods for forming ohmic contacts to substrates of materials such as SiC, GaN, InGaN or the like.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments according to the invention can provide localized annealing of metal-silicon carbide ohmic contacts in semiconductor devices and devices so formed. Pursuant to these embodiments, a contact can be formed by forming a metal on a Silicon Carbide (SiC) layer and annealing an interface location of the metal and the SiC layer to form a metal-SiC material thereat and avoiding annealing at a location on the SiC layer to avoid forming the metal-SiC material thereat. In some embodiments according to the invention, the layer can be a SiC substrate.
In some embodiments according to the invention, the annealing can include annealing at the interface location and annealing according to a pattern to avoid annealing at the location. In some embodiments according to the invention, the interface location can be a first interface location and the location on the SiC substrate can be a second interface location of the metal and the SiC substrate. The annealing can include impinging laser light through an opening in a mask layer onto the metal layer at the first interface location and blocking the laser light with the mask layer opposite the second interface location to avoid annealing at the second interface location.
In some embodiments according to the invention, the annealing can include activating a laser opposite the interface location to impinge laser light onto the metal layer at the interface location and de-activating the laser opposite the location to avoid annealing at the location. In some embodiments according to the invention, forming the metal can include forming the metal on the SiC substrate to form the location spaced-apart from the SiC substrate.
In some embodiments according to the invention, the metal can be formed in a pattern to expose a portion of the SiC substrate at the location and the annealing can include activating a laser opposite the interface location to impinge laser light onto the metal layer at the interface location. Activation of the laser can be maintained opposite the location.
In some embodiments according to the invention, the metal-SiC material at the interface location can be a metal ohmic contact on a back side of the substrate opposite a front side of the substrate having an epitaxial layer thereon. In some embodiments according to the invention, the annealing can include impinging laser light on the interface location to form at least one ohmic contact including opposing ohmic contact boundaries having a non-ohmic contact region therebetween.
In some embodiments according to the invention, the at least one ohmic contact can be a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining a striped pattern forming an oblique angle with a side of the device. In some embodiments according to the invention, the at least one ohmic contact can include a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining a striped pattern parallel to a side of the device.
In some embodiments according to the invention, the at least one ohmic contact can include a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining a circular pattern. In some embodiments according to the invention, the interface location can be a first interface location and the location on the SiC substrate comprises a second interface location of the metal and the SiC substrate. Annealing can include impinging an electron beam on the interface location and blocking the electron beam from impinging the second interface location.
In some embodiments according to the invention, forming a contact for a light emitting device can include forming a metal on a Silicon Carbide (SiC) substrate and laser annealing interface locations of the metal and the SiC substrate according to a pattern to form a metal-SiC material thereat corresponding to the pattern. In some embodiments according to the invention, forming the metal can include forming a blanket metal on the substrate. The laser annealing can include impinging laser light on the interface locations through openings in a mask, that defines the pattern, to form the metal-SiC material thereat. The laser light can be blocked with the mask opposite other interface locations of the metal and the SiC substrate.
In some embodiments according to the invention, forming the metal can include forming a blanket metal on the substrate, wherein laser annealing can include activating a laser opposite the interface locations, according to the pattern, to impinge laser light onto the blanket metal layer at the interface location. The laser can be de-activated opposite other interface locations to avoid annealing at the other locations.
In some embodiments according to the invention, the metal can be nickel, platinum, or titanium. In some embodiments according to the invention, laser annealing can include impinging laser light on the interface locations at an energy and wavelength sufficient to form a silicide of the metal and the SiC substrate.
In some embodiments according to the invention, the SiC substrate can be 6H SiC, wherein laser annealing can include impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 2.8 joules/cm2 in a single pulse having a duration of about 30 nanoseconds. In some embodiments according to the invention, the SiC substrate can be 4H SiC, wherein laser annealing can include impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 4.2 joules/cm2 in about five pulses each having a duration of about 30 nanoseconds. In some embodiments according to the invention, the laser light can be photon energies above a bandgap of the SiC substrate. In some embodiments according to the invention, the laser light can be pulsed or continuous wave laser light.
In some embodiments according to the invention, a contact for a light emitting device can include forming a metal on a Silicon Carbide (SiC) layer according to a pattern so that portions of the layer are exposed. Laser light can be impinged on the exposed portions of the SiC layer and on interface locations of the metal and the Si-C layer to form a metal-SiC material thereat corresponding to the pattern. In some embodiments according to the invention, the layer can be a SiC substrate.
In some embodiments according to the invention, the metal can be nickel, platinum, or titanium. In some embodiments according to the invention, the laser annealing can include impinging laser light on the interface locations at an energy and wavelength sufficient to form a silicide of the metal and the SiC substrate.
In some embodiments according to the invention, the SiC substrate can be 6H SiC, wherein the laser annealing can include impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 2.8 joules/cm2 in a single pulse having a duration of about 30 nanoseconds.
In some embodiments according to the invention, the SiC substrate can be 4H SiC, wherein the laser annealing can include impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 4.2 joules/cm2 in about five pulses each having a duration of about 30 nanoseconds.
In some embodiments according to the invention, the laser light can include photon energies above a bandgap of the SiC substrate. In some embodiments according to the invention, the laser light can be pulsed or continuous wave laser light.
In some embodiments according to the invention, a method of forming an ohmic contact for a semiconductor device can include forming a photoresist on a SiC layer according to a pattern to expose first portions of the SiC layer and to cover second portions of the substrate. A blanket metal can be formed on the first portions and on the photoresist. Laser light can be impinged on interface locations of the blanket metal and the SiC layer corresponding to the first portions to form a metal-SiC material thereat, whereas impinging laser light on the blanket metal corresponding to the second portions can be avoided.
In some embodiments according to the invention, the method can further include removing metal from the photoresist so that metal-SiC material remains. An overlay can be formed on the metal-SiC material and the photoresist can be removed from the SiC substrate. In some embodiments according to the invention, the method can further include forming an overlay on the metal-SiC material and on the photoresist and removing the photoresist from the SiC layer.
In further embodiments according to the invention, the method can further include lifting-off the photoresist and the metal thereon leaving the metal-SiC material. An overlay can be formed on the metal-SiC material. In some embodiments according to the invention, the metal can be nickel, platinum, or titanium. In some embodiments according to the invention, the laser annealing can include impinging laser light on the interface locations at an energy and wavelength sufficient to form a silicide of the metal and the SiC substrate.
In some embodiments according to the invention, forming a contact can include impinging laser light on an interface location between a metal and a Silicon Carbide (SiC) layer to form a metal-SiC material to provide at least one ohmic contact on the device including opposing ohmic contact boundaries having a non-ohmic contact region therebetween.
In some embodiments according to the invention, a light emitting device (LED) can include at least one metal-Silicon Carbide (SiC) ohmic contact on a SiC layer, the at least one metal-SiC ohmic contact including opposing ohmic contact boundaries having a non-ohmic contact region therebetween.
In some embodiments according to the invention, the opposing ohmic contact boundaries are separated by about 10 um. In some embodiments according to the invention, the at least one ohmic contact can include a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining stripes in a striped pattern forming oblique angles with a side of the device.
In some embodiments according to the invention, the stripes are separated about 106 um. In some embodiments according to the invention, the at least one ohmic contact can include a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining stripes a striped pattern parallel to a side of the device.
In some embodiments according to the invention, the striped pattern defines a substantially circular shape having a diameter of about 95 um, wherein the stripes are separated by distance of about 4.0 um to about 5.0 um. In some embodiments according to the invention, the at least one ohmic contact can include a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining rings of a concentric circular pattern. In some embodiments according to the invention, the rings are separated by a distance of about 4.0 um to about 5.0 um.
In some embodiments according to the invention, a method of forming an ohmic contact for a semiconductor device can include forming a metal on a Silicon Carbide (SiC) layer and laser annealing the metal and the SiC layer to form a metal-SiC material at interface locations of the metal and the SiC layer. Portions of the metal-SiC material can be removed to expose the SiC layer according to a pattern to provide at least one ohmic contact on the semiconductor device.
DETAILED DESCRIPTION OF EMBODIMENTS ACCORDING TO THE INVENTIONThe present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. However, this invention should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It will be understood that when an element such as a layer, region or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Like numbers refer to like elements throughout the specification.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.
Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe-one element's relationship to another elements as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in the Figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower”, can therefore, encompasses both an orientation of “lower” and “upper,” depending of the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below.
Embodiments of the present invention are described herein with reference to cross-section (and/or plan view) illustrations that are schematic illustrations of idealized embodiments of the present invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the present invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an etched region illustrated or described as a rectangle will, typically, have rounded or curved features. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the present invention.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” another feature may have portions that overlap or underlie the adjacent feature.
As used herein the term “ohmic contact” refers to contacts where an impedance associated therewith is substantially given by the relationship of Impedance=V/I, where V is a voltage across the contact and I is the current, at substantially all expected operating frequencies (i.e., the impedance associated with the ohmic contact is substantially the same at all operating frequencies). For example, in some embodiments according to the invention, an ohmic contact can be a contact with a specific contact resistivity of less than about 10 e −03 ohm-cm2 and, in some embodiments less than about 10 e −04 ohm-cm2. Thus, a contact that is rectifying or that has a high specific contact resistivity, for example, a specific contact resistivity of greater than about 10 e −03 ohm-cm2, is not an ohmic contact as that term is used herein. As used herein, a “metal-SiC material” includes mixtures containing a metal and Silicon Carbide fused together or dissolving into each other when annealed. It will also be understood that, for example, a Ni—SiC material can be a mixture (or alloy) of nickel and silicon carbide when annealed so that a Ni-silicide is formed.
As described herein in greater detail, embodiments according to the invention may provide methods of annealing interface locations of a metal and a silicon carbide substrate to form a metal-silicon carbide material thereat and avoid annealing other locations on the silicon carbide substrate so as to avoid forming a metal silicon carbide material. It will be understood that the interface locations where the metal-silicon carbide material is formed can include boundaries at or near the outer area where the laser light impinges the metal and the substrate. For example, as described in further detail herein in reference to
Annealing at one location with, for example a laser beam, while avoiding annealing at another location on the silicon carbide substrate may avoid the type of damage caused by a conventional rapid thermal anneal to an epitaxial layer. For example, in some embodiments according to the invention, metal-silicon carbide ohmic contacts can be formed by annealing the interface locations on the substrate using laser light while avoiding annealing other locations on the substrate (by masking or modulating the laser light) after an epitaxial layer has been formed on the front side of the substrate.
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According to
Regarding “moving” the laser beam described above, it will be understood that in some embodiments according to the invention, the laser beam can be moved in discreet steps according to the pattern whereas in other embodiments according to the invention, the laser beam is moved continuously and activated/deactivated at the appropriate intervals according to the pattern. It will be further understood that the laser beam can be “moved” by, for example, moving a mirror above the metal layer 110 to reflect the laser beam. Alternatively, the laser that generates the laser beam may be moved above the metal layer.
In still other embodiments according to the invention, the substrate can be moved beneath a “fixed” laser beam. For example, the substrate can be moved in increments of the mask pitch and stopped at each location where the laser is activated for a number of pulses (or duration) at each location. In some embodiments according to the invention, a 1.8 mm×1.8 mm field is used for a 6×6 array of 300 μm pitch die. Alternatively, the substrate can be moved beneath a fixed beam continuously along one axis, with activation of the laser beam being synchronized at every die pitch, which may vary by device. The number of pulses delivered to each site can be based on the number of die positions in the mask along the axis along which the substrate is moved. The wafer may then be indexed by the mask pitch along the non-scanned axis, whereupon the scanning can be repeated.
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It will be understood by those skilled in the art, given the benefit of this disclosure, that the laser light 1025 should preferably not damage the boundaries of the metal-SiC ohmic contacts 1135a-1135d that are formed as described above. In particular, if un-addressed, laser light 105 that impinges on the exposed portions of the SiC substrate 105 could damage the adjacent metal-SiC ohmic contacts 1135a-1135d. As described in reference to
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It will be understood that in some embodiments according to the invention, the laser light 1425 described above in reference to
Therefore, in some embodiments according to the invention, the ohmic contact boundaries 2101 and 2102 define the annealed metal-SiC ohmic contact where the non-ohmic contact region 2103 is included between the opposing ohmic contact boundaries 2101, 2102. It will be understood that the non-ohmic contact region, 2103 is also impinged by the laser light that anneals the interface location to form a metal-SiC at the opposing ohmic contact boundaries 2101, 2102. It will also be understood that the shape of the opposing ohmic contact boundaries 2101, 2102 can vary with the properties of the laser light used. For example, the laser light may be de-focused to provide the un-even contours shown in
In still other embodiments according to the invention, some edges in the laser mask can include features that measure less than a resolution of a lens (e.g., about 2 um) used to direct the laser light, which is sometime referred to as “softening” the edges of the mask. In particular, the softening of the edges can cause the energy of the laser light to be gradually reduced toward the edges of the image produced by the mask. Reducing the energy near the edges can increase the density of the feature edges produced by the laser light projected through the mask. Exemplary mask features are shown in
It will be understood that in some embodiments according to the invention, the stripes or rings included in the metal-SiC ohmic contacts described above in reference to
It will be understood that the laser light used to anneal the metal-SiC ohmic contacts described herein can be a laser light having a wavelength and intensity sufficient to form the metal-silicide material at the interface of the metal layer and the SiC substrate. For example, in embodiments using 6H SiC as the substrate, laser annealing may be accomplished by impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 2.8 joules per square centimeter in a single pulse having a duration of about 30 nanoseconds. In other embodiments according to the invention where, for example, the SiC substrate is 4H SiC, the laser light may have a wavelength of about 248 nanometers to about 308 nanometers and an energy of about 4.2 joules per square centimeter applied in about 5 pulses, each having a duration of about 30 nanoseconds. In still other embodiments according to the invention, other wavelengths and energies may be used to provide annealing at the interface location of the metal layer and the SiC substrate via absorption of light including photon energies that are above the bandgap of the SiC substrate. It will be understood that pulse and/or continuous loop lasers may also be utilized.
It will be also understood that electron beam annealing may be used as an alternative to laser light. Accordingly, in each of the embodiments described above, an electron beam may be used to anneal the interface locations of the metal layer and the SiC substrate to form the metal-SiC material thereat. It will be understood that the metal-SiC ohmic contacts can be a contact for any SiC device and may be included on a SiC epitaxial layer.
Many alterations and modifications may be made by those having ordinary skill in the art, given the benefit of the present disclosure, without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of example, and that it should not be taken as limiting the invention as defined by the following claims. The following claims are, therefore, to be read to include not only the combination of elements which are literally set forth but all equivalent elements for performing substantially the same function in substantially the same way to obtain substantially the same result. The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and also what incorporates the essential idea of the invention.
Claims
1. A method of forming an ohmic contact for a semiconductor device, comprising:
- forming a metal on a Silicon Carbide (SiC) layer; and
- annealing an interface location of the metal and the SiC layer to form a metal-SiC material thereat and avoiding annealing at a location on the SiC layer to avoid forming the metal-SiC material thereat.
2. A method according to claim 1 wherein the SiC layer comprises a SiC substrate.
3. A method according to claim 2 wherein annealing comprises:
- annealing at the interface location; and
- annealing according to a pattern to avoid annealing at the location.
4. A method according to claim 2, wherein the interface location comprises a first interface location and the location on the SiC substrate comprises a second interface location of the metal and the SiC substrate, wherein annealing comprises:
- impinging laser light through an opening in a mask layer onto the metal layer at the first interface location and blocking the laser light with the mask layer opposite the second interface location to avoid annealing at the second interface location.
5. A method according to claim 1 wherein annealing comprises:
- activating a laser opposite the interface location to impinge laser light onto the metal layer at the interface location; and
- de-activating the laser opposite the location to avoid annealing at the location.
6. A method according to claim 2 wherein forming a metal comprises:
- forming the metal on the SiC substrate to form the location, wherein the location is spaced-apart from the SiC substrate.
7. A method according to claim 2 wherein the metal is formed in a pattern to expose a portion of the SiC substrate at the location, wherein annealing comprises:
- activating a laser opposite the interface location to impinge laser light onto the metal layer at the interface location; and
- maintaining activation of the laser opposite the location.
8. A method according to claim 2 wherein the metal-SiC material at the interface location comprises a metal ohmic contact on a back side of the substrate opposite a front side of the substrate having an epitaxial layer thereon.
9. A method according to claim 1 wherein annealing comprises:
- impinging laser light on the interface location to form at least one ohmic contact including opposing ohmic contact boundaries having a non-ohmic contact region therebetween.
10. A method according to claim 9 wherein the at least one ohmic contact comprises a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining a striped pattern forming an oblique angle with a side of the device.
11. A method according to claim 6 wherein the at least one ohmic contact comprises a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining a striped pattern parallel to a side of the device.
12. A method according to claim 6 wherein the at least one ohmic contact comprises a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining a circular pattern.
13. A method according to claim 2, wherein the interface location comprises a first interface location and the location on the SiC substrate comprises a second interface location of the metal and the SiC substrate, wherein annealing comprises:
- impinging an electron beam on the interface location and blocking the electron beam from impinging the second interface location.
14. A method of forming an ohmic contact for a semiconductor device, comprising:
- forming a metal on a Silicon Carbide (SiC) layer; and
- laser annealing interface locations of the metal and the SiC layer according to a pattern to form a metal-SiC material thereat corresponding to the pattern.
15. A method according to claim 14 wherein the SiC layer comprises a SiC substrate.
16. A method according to claim 15 wherein forming a metal comprises forming a blanket metal on the substrate, wherein laser annealing comprises:
- impinging laser light on the interface locations through openings in a mask, that defines the pattern, to form the metal-SiC material thereat; and
- blocking the laser light with the mask opposite other interface locations of the metal and the SiC substrate.
17. A method according to claim 14 wherein forming a metal comprises forming a blanket metal on the substrate, wherein laser annealing comprises:
- activating a laser opposite the interface locations, according to the pattern, to impinge laser light onto the blanket metal layer at the interface location; and
- de-activating the laser opposite other interface locations to avoid annealing at the other locations.
18. A method according to claim 14 wherein the metal comprises nickel, platinum, or titanium.
19. A method according to claim 15 wherein laser annealing comprises impinging laser light on the interface locations at an energy and wavelength sufficient to form a silicide of the metal and the SiC substrate.
20. A method according to claim 19, wherein the SiC substrate comprises 6H SiC, wherein laser annealing comprises impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 2.8 joules/cm2 in a single pulse having a duration of about 30 nanoseconds.
21. A method according to claim 19, wherein the SiC substrate comprises 4H SiC, wherein laser annealing comprises impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 4.2 joules/cm2 in about five pulses each having a duration of about 30 nanoseconds.
22. A method according to claim 19 wherein the laser light comprises photon energies above a bandgap of the SiC substrate.
23. A method according to claim 19 wherein the laser light comprises pulsed or continuous wave laser light.
24. A method of forming an ohmic contact for a semiconductor device, comprising:
- forming a metal on a Silicon Carbide (SiC) layer according to a pattern so that portions of the layer are exposed; and
- impinging laser light on the exposed portions of the SiC layer and on interface locations of the metal and the Si-C layer to form a metal-SiC material thereat corresponding to the pattern.
25. A method according to claim 24 wherein the SiC layer comprises a SiC substrate.
26. A method according to claim 24 wherein the metal comprises nickel, platinum, or titanium.
27. A method according to claim 25 wherein laser annealing comprises impinging laser light on the interface locations at an energy and wavelength sufficient to form a silicide of the metal and the SiC substrate.
28. A method according to claim 25 wherein the SiC substrate comprises 6H SiC, wherein laser annealing comprises impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 2.8 joules/cm2 in a single pulse having a duration of about 30 nanoseconds.
29. A method according to claim 25 wherein the SiC substrate comprises 4H SiC, wherein laser annealing comprises impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 4.2 joules/cm2 in about five pulses each having a duration of about 30 nanoseconds.
30. A method according to claim 25 wherein the laser light comprises photon energies above a bandgap of the SiC substrate.
31. A method according to claim 25 wherein the laser light comprises pulsed or continuous wave laser light.
32. A method of forming an ohmic contact for a semiconductor device, comprising:
- forming a photoresist on a SiC layer according to a pattern to expose first portions of the SiC layer and to cover second portions of the substrate;
- forming a blanket metal on the first portions and on the photoresist;
- impinging laser light on interface locations of the blanket metal and the SiC layer corresponding to the first portions to form a metal-SiC material thereat and avoiding impinging laser light on the blanket metal corresponding to the second portions to avoid forming the metal-SiC material thereat.
33. A method according to claim 32 wherein the SiC layer comprises a SiC substrate.
34. A method according to claim 32 further comprising:
- removing metal from the photoresist so that metal-SiC material remains;
- forming an overlay on the metal-SiC material; and
- removing the photoresist from the SiC substrate.
35. A method according to claim 32 further comprising:
- forming an overlay on the metal-SiC material and on the photoresist; and
- removing the photoresist from the SiC layer.
36. A method according to claim 32 further comprising:
- lifting-off the photoresist and the metal thereon leaving the metal-SiC material; and
- forming an overlay on the metal-SiC material.
37. A method according to claim 32 wherein the metal comprises nickel, platinum, or titanium.
38. A method according to claim 32 wherein laser annealing comprises impinging laser light on the interface locations at an energy and wavelength sufficient to form a silicide of the metal and the SiC layer.
39. A method according to claim 33 wherein the SiC substrate comprises 6H SiC, wherein laser annealing comprises impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 2.8 joules/cm2 in a single pulse having a duration of about 30 nanoseconds.
40. A method according to claim 33 wherein the SiC substrate comprises 4H SiC, wherein laser annealing comprises impinging laser light having a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 4.2 joules/cm2 in about five pulses each having a duration of about 30 nanoseconds.
41. A method according to claim 33 wherein the laser light comprises photon energies above a bandgap of the SiC substrate.
42. A method according to claim 32 wherein the laser light comprises pulsed or continuous wave laser light.
43. A method of forming a contact for a light emitting device (LED), comprising:
- impinging laser light on an interface location between a metal and a Silicon Carbide (SiC) layer to form a metal-SiC material to provide at least one ohmic contact on the LED including opposing ohmic contact boundaries having a non-ohmic contact region therebetween.
44 A method according to claim 43 wherein the SiC layer comprises a SiC substrate.
45. A method according to claim 43 wherein the at least one ohmic contact comprises a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining a striped pattern forming an oblique angle with a side of the device.
46. A method according to claim 43 wherein the at least one ohmic contact comprises a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining a striped pattern parallel to a side of the device.
47. A method according to claim 43 wherein the at least one ohmic contact comprises a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining a circular pattern.
48. A method according to claim 44 wherein the SiC substrate comprises 6H SiC, wherein the laser light comprises a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 2.8 joules/cm2 in a single pulse having a duration of about 30 nanoseconds.
49. A method according to claim 44 wherein the SiC substrate comprises 4H SiC, wherein the laser light comprises a wavelength of about 248 nanometers to about 308 nanometers at an energy of about 4.2 joules/cm2 in about five pulses each having a duration of about 30 nanoseconds.
50. A method according to claim 44 wherein the laser light comprises photon energies above a bandgap of the SiC substrate.
51. A method according to claim 43 wherein the laser light comprises pulsed or continuous wave laser light.
52. A method of forming an ohmic contact for a semiconductor device, comprising:
- forming a metal on a Silicon Carbide (SiC) layer;
- laser annealing the metal and the SiC layer to form a metal-SiC material at interface locations of the metal and the SiC layer; and
- removing portions of the metal-SiC material to expose the SiC layer according to a pattern to provide at least one ohmic contact on the semiconductor device.
53. A method according to claim 52 wherein the SiC layer comprises a SiC substrate.
54. A contact in a semiconductor device, comprising:
- at least one metal-Silicon Carbide (SiC) ohmic contact on a SiC layer, the at least one metal-SiC ohmic contact including opposing ohmic contact boundaries having a non-ohmic contact region therebetween.
55. A contact according to claim 54 wherein the SiC layer comprises a SiC substrate.
56. A contact according to claim 54 wherein the opposing ohmic contact boundaries are separated by about 10 um.
57. A contact according to claim 54 wherein the at least one ohmic contact comprises a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining stripes in a striped pattern forming oblique angles with a side of the device.
58. A contact according to claim 54 wherein the stripes are separated about 106 um.
59. A contact according to claim 54 wherein the at least one ohmic contact comprises a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining stripes a striped pattern parallel to a side of the device.
60 A contact according to claim 54 wherein the striped pattern defines a substantially circular shape having a diameter of about 95 um, wherein the stripes are separated by distance of about 4.0 um to about 5.0 um.
61. A contact according to claim 54 wherein the at least one ohmic contact comprises a plurality of ohmic contacts including respective opposing ohmic contact boundaries defining rings of a concentric circular pattern.
62. A contact according to claim 54 wherein the rings are separated by a distance of about 4.0 um to about 5.0 um.
63. A contact according to claim 54 wherein, the device comprises a light emitting diode.
Type: Application
Filed: Aug 11, 2004
Publication Date: May 19, 2005
Inventors: David Slater (Durham, NC), John Edmond (Cary, NC), Matthew Donofrio (Raleigh, NC)
Application Number: 10/916,113