Patent Application
20190252509
The present disclosure relates to electronic devices and processes of forming electronic devices, and more particularly to, electronic devices including a conductive layer that contacts another layer including a III-V material and processes of forming the same.
High electron mobility transistors can include a GaN channel layer and an overlying AlGaN barrier layer. Source and drain electrodes contact the barrier layer. Different metal stacks for conductive layers used in source and drain electrodes have been tried; however, one or more complications may arise including contamination concerns, relatively high temperature anneals, contact resistance being too high, or the like. Further improvement of contact resistance without other adverse complications is desired.
Embodiments are illustrated by way of example and are not limited in the accompanying figures.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention.
The following description in combination with the figures is provided to assist in understanding the teachings disclosed herein. The following discussion will focus on specific implementations and embodiments of the teachings. This focus is provided to assist in describing the teachings and should not be interpreted as a limitation on the scope or applicability of the teachings. However, other embodiments can be used based on the teachings as disclosed in this application.
A III-V material is intended to mean a material that includes at least one Group 13 and at least one Group 15 element. A III-N material is intended to mean a semiconductor material that includes at least one Group 13 element and nitrogen.
The term “power transistor” is intended to mean a transistor that is designed to normally operate with at least a 50 V difference maintained between the source and drain of the transistor or emitter and collector of the transistor when the transistor is in an off-state. For example, when the transistor is in an off-state, a 50 V may be maintained between the source and drain without a junction breakdown or other undesired condition occurring.
The terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive-or and not to an exclusive-or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).
Also, the use of “a” or “an” is employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one, at least one, or the singular as also including the plural, or vice versa, unless it is clear that it is meant otherwise. For example, when a single item is described herein, more than one item may be used in place of a single item. Similarly, where more than one item is described herein, a single item may be substituted for that more than one item.
Group numbers corresponding to columns within the Periodic Table of Elements based on the IUPAC Periodic Table of Elements, version dated Nov. 28, 2016.
Unless otherwise defined, all 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. The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent not described herein, many details regarding specific materials and processing acts are conventional and may be found in textbooks and other sources within the semiconductor and electronic arts.
An electronic device can include a first layer including a III-V material, and a conductive layer including a first film that contacts the first layer, wherein the first film includes Ta—Si compound. In an embodiment, the electronic device can be a high electron mobility transistor (HEMT), and the first layer can be a barrier layer between a channel layer and source and drain electrodes of the HEMT. The source and drain electrodes are formed from the conductive layer. In a particular embodiment, the barrier layer can include AlGaN, and TaSi can be the first film that contacts AlGaN within the barrier layer. The Ta—Si compound allows for relatively low contact resistance to be achieved without a relatively high anneal temperature seen with some metallurgies of conductive layers or contact resistance that is unusually sensitive to relatively small changes in thickness when Ta, rather than a Ta—Si compound, is used. The concepts are better understood after reading the specification in conjunction with the figures.
The semiconductor stack 120 can include a buffer layer 122, a channel layer 124, and a barrier layer 126. Each of the layers within the semiconductor stack 120 can include a III-N material, and in a particular embodiment include AlxGa(1-x)N, where 0≤x≤1. The composition of the buffer layer 122 may depend on the composition of the channel layer 124. The composition of the buffer layer 122 can be changed as a function of thickness, such that the buffer layer 122 has a relatively greater aluminum content closer to the substrate 110 and relatively greater gallium content closer to the channel layer 124. In a particular embodiment, the cation (metal atoms) content in the buffer layer 122 near the substrate 110 can be 10 atomic % to 100 atomic % Al with the remainder Ga, and the cation content in the buffer layer 122 near the channel layer 124 can be 0 atomic % to 50 atomic % Al with the remainder Ga. The buffer layer 122 can have a thickness in a range of approximately 1 micron to 5 microns.
The channel layer 124 can include AlyGa(1-y)N, where 0≤y≤0.1 and have a thickness in a range of approximately 20 nm to 4000 nm. In a particular embodiment, the channel layer 124 is a GaN layer that may be doped with an electron donor (n-type) dopant or an electron acceptor (p-type) dopant.
The barrier layer 126 can be used to help reduce the likelihood of migration of contaminants or other materials between one or more layers underlying the barrier layer 126 and the dielectric layer 140. In an embodiment, the barrier layer 126 includes a III-V material. In a particular embodiment, the barrier layer 126 can include AlzGa(1-z)N, wherein 0.02≤z≤0.5, and in a further embodiment 0.11≤z≤0.3. The barrier layer 126 can have a thickness in a range of approximately 2 to 30 nm.
The semiconductor stack 120 is formed using an epitaxial growth technique, and thus the channel layer 124 and barrier layer 126, and at least a portion of the buffer layer 122 can be monocrystalline. In a particular embodiment, metal-containing films can be formed using metalorganic chemical vapor deposition. In another embodiment, different composition for the semiconductor stack 120 may be used, e.g., InAlGaN, InP, or the like.
The dielectric layer 140 can have a thickness in a range of 5 nm to 500 nm. The dielectric layer 140 can be formed using a chemical or physical vapor technique.
In an embodiment, the semiconductor stack 120, and at least one of the films of the dielectric layer 140 are formed without exposing the workpiece to air or another oxygen-containing gas. Thus, the layers and films can be formed little or no oxide at an interface between any of the layers and films. In another embodiment, the workpiece may be exposed to air between forming any one or more of the films or layers. If an interfacial oxide is not to remain in the finished device, the interfacial oxide may be reduced in a reducing ambient or etched, for example, back sputtering, to remove the interfacial oxide before forming the subsequent layer or film. In still another embodiment, an oxide film may be formed and remain. For example, after forming the dielectric layer 140, the workpiece may be exposed to air before forming the capping film.
Referring to
A conductive layer 300 is formed over the dielectric layer 140 and within the contact openings 262 and 264. The conductive layer 300 can include a plurality of films, as illustrated in
The conductive layer 300 can include an optional intermediate film 364. The intermediate film 364 can include a Ti-containing material, such as Ti, TiW, TiSi, TiN, or the like. The intermediate film 364 can have any of the thicknesses previously described with respect to the lowermost film 362. When present, the intermediate film 364 can have the same thickness or a different thickness as compared to lowermost film 362.
The conductive layer 300 can further include a conductive bulk film 366. The bulk film 366 can include Al, Cu, or another material that is more conductive than other films within the conductive layer 300. In an embodiment, the bulk film 366 can include at least 90 wt % Al. The bulk film 366 can have a thickness that is at least as thick as the lowermost film 362. The bulk film 366 helps to keep RDSON relatively low, so the bulk film 366 is typically the thickest film within the conductive layer 300. In an embodiment, the bulk film 366 has a thickness of at least 20 nm or at least 50 nm. Although there is not a theoretical upper limit on the thickness, in an embodiment, the thickness may be at most 900 nm or at most 500 nm and, in a particular embodiment, at most 200 nm. In an embodiment, the bulk film 366 has a thickness in a range 20 nm to 900 nm and, in a more particular embodiment, in a range of 50 nm to 500 nm.
The conductive layer 300 can further include another optional film 368 overlying the bulk film 366. The film 368 can serve one or more functions. In an embodiment, the film 368 can be an anti-diffusion film, an antireflective film, or the like. The film 368 has a different composition as compare to the bulk film 366. In an embodiment, the film 368 can include TiN, W, TiW, Pd, or the like. The thickness of the film 368 may depend on the material and purpose it serves. The film 368 can have any of the thicknesses previously described with respect to the lowermost film 362. When present, the film 368 can have the same thickness or a different thickness as compared to lowermost film 362.
More or fewer films can be used in the conductive layer 300 as illustrated in
The films making up the conductive layer 300 can be serially deposited without exposure to air, without breaking vacuum, or both. In an embodiment, the films of the conductive layer 300 can be sputter deposited. The conductive layer 300 is patterned to form the source electrode 462 and the drain electrode 464, as illustrated in
Another opening can be formed in the dielectric layer 140, and a gate electrode 566 can be formed in within the opening as illustrated in
After forming the source and drain electrodes 462 and 464 or after forming the source, drain, and gate electrodes 462, 464, and 566, the workpiece can be annealed to form ohmic contacts between the barrier layer 126 and the source and drain electrodes 462 and 464. The anneal can be performed at a temperature in a range of 500° C. to 900° C. The contact resistance may be its lowest when the anneal temperature is in a range of 650° C. to 800° C. Below 650° C., the contact resistance may significantly increase, and above 800° C., the contact resistance may gradually increase. A lower anneal temperature is less likely to cause adverse affects to the device as compared to a higher anneal temperature. The anneal time can be in a range of 30 s to 300 s. In general, the contact resistance decreases significantly for an anneal time of 30 s to 60 s and gradually decreases from 60 s to 120 s. After 120 s, the contact resistance decreases slight and then become stable from 180 s to 300 s. In a particular embodiment, the anneal time is in a range of 120 s to 220 s. The anneal can be performed in a relatively inert gas, such as N2, Ar, He, or the like. An oxidizing gas, such as O2, N2O, H2O, or the like may be avoided. The anneal may not be significantly affected by pressure. In an embodiment, the anneal may be performed at approximately atmospheric pressure.
After the anneal, the contact resistance for the source electrode 462, the drain electrode 464, or the source and drain electrodes 462 and 464 may be at most 1.0 ohm·mm or at most 0.5 ohm·mm. When the anneal temperature is in a range of 650° C. to 800° C., and the anneal time is approximately 30 s, the contact resistance can be at most 0.4 ohm·mm. As the anneal time is increased to 60 s, the contact resistance can be at most 0.3 ohm·mm. A contact resistance of at most 0.25 ohm·mm can be achieved with an anneal temperature in a range of 650° C. to 750° C. with an anneal time in a range of 90 s to 150 s. Thus, good contact resistance can be achieved at a relatively low temperature as compared to other metal stacks used in conventional conductive layers.
One or more interconnect levels and a passivation layer may be formed over the workpiece. Each interconnect level can include an interlevel dielectric layer and interconnects. A conductive layer can be used at each interconnect level. The conductive layer may be the same or different from the other conductive layers described earlier in this specification. After forming the interconnect levels and the passivation layer, an anneal may be performed. Performance of the previously described anneal may be deferred until this time, or an anneal separate from the anneal previously described may be performed. If a separate anneal is performed, it may be performed using the same or different parameters as the anneal previously described. A substantially completed electronic device has been formed.
In another embodiment, the source electrode 462, the drain electrode 464, or the source and drain electrodes 462 and 464 may be recessed within a barrier layer 662, as illustrated in
Embodiments as described herein can help to achieve a relatively low contact resistance without other adverse complications. The relatively low contact resistance helps to reduce RDSON for the HEMT. The significance of the low contact resistance becomes more significant as the size of contacts decreases. For example, a HEMT designed for 650 V can have a contact resistance that makes up approximately 5% of the RDSON. Another HEMT designed for 200 V can have a contact resistance that makes up approximately 20% of the RDSON. The 650 V device has larger contact openings as compared to the 200 V device. Thus, the improvement in contact resistance helps both devices and will be more significant in keeping RDSON for the 200 V device.
The metal stack for the conductive layer previously described does not have or cause adverse complications as compared to other metal stack. A conductive layer having a metal stack of Ta/Si/Ti/Al/Ni/Ta or Ta/Ti/Al can require an anneal temperature of at least 800° C. to achieve low contact resistances as the previously described embodiments. A high anneal temperature may result in increased leakage in the GaN channel film or the buffer layer. The high anneal temperature can also significantly increase the roughness of the ohmic metal.
Another conductive layer can have a metal stack of Ta/Al/Ta or Ta/Al is believed to have a contact resistance that is sensitive to thickness of the Ta film. For example, when the Ta film contacting a barrier layer increases from 10 nm to 20 nm, the contact resistance increases by approximately 500%. When such Ta film is decreased from 10 nm to 5 nm, the contact resistance increases by approximately 50%. Therefore, such a conductive layer is not well suited for a manufacturing process.
The metal stack of the conductive layer previously described with respect to the source and drain electrodes 462 and 464 is well suited to provide good contact resistance, as the lowermost film 362 of the conductive layer 300 is not as sensitive to thickness variation as compared to the Ta/Al/Ta or Ta/Al conductive layer and can be annealed at a significantly lower temperature as compared to the Ta/Si/Ti/Al/Ni/Ta or Ta/Ti/Al conductive layer. Furthermore, the conductive layers as described herein do not include Au, and thus, contamination issues seen with Au are obviated.
Many different aspects and embodiments are possible. Some of those aspects and embodiments are described below. After reading this specification, skilled artisans will appreciate that those aspects and embodiments are only illustrative and do not limit the scope of the present invention. Embodiments may be in accordance with any one or more of the items as listed below.
An electronic device can include a first layer including a III-V material; and a conductive layer including a first film that contacts the first layer, wherein the first film includes Ta—Si compound.
The electronic device of Embodiment 1, wherein the Ta—Si compound has a formula of Ta(2-x)Six, wherein x is in a range of 0.5 to 1.5.
The electronic device of Embodiment 1, wherein the first film has a thickness in a range of 5 nm to 100 nm.
The electronic device of Embodiment 1, wherein the first and conductive layers has a corresponding contact resistance of at most 1 ohm·mm.
The electronic device of Embodiment 1, wherein the conductive layer further includes a second film that includes at least 90 wt % Al.
The electronic device of Embodiment 5, further including a Ti-containing film between the first film and the second film.
The electronic device of Embodiment 5, wherein the conductive layer further includes a third film, wherein the second film is disposed between the first and third films.
The electronic device of Embodiment 7, wherein the third film has a composition different from each of the second film.
The electronic device of Embodiment 7, wherein the third film includes TiN, W, TiW, or Pd.
The electronic device of Embodiment 1, wherein the first layer includes AlzGa(1-z)N, where 0.02≤z<0.5.
The electronic device of Embodiment 1, including a high electron mobility transistor that includes the first layer.
The electronic device of Embodiment 11, wherein the high electron mobility transistor includes a channel layer that includes a III-V compound, wherein the first layer is disposed between the channel layer and the conductive layer.
The electronic device of Embodiment 12, wherein the channel layer is a GaN layer.
The electronic device of Embodiment 12, a source electrode of the high electron mobility transistor, a drain electrode of the high electron mobility transistor, or both the source and drain electrodes include the conductive layer.
The electronic device of Embodiment 14, wherein the high electron mobility transistor further includes a gate electrode having a different composition as compared to the source and drain electrodes.
An electronic device can include a high-electron mobility transistor, the high-electron mobility transistor including: a channel layer including GaN; a barrier layer overlying the channel layer and including AlxGa(1-x)N, where 0.05≤x<0.3; a source electrode contacting the barrier layer; and a drain electrode spaced apart from the source electrode and contacting the barrier layer, wherein the source electrode, the drain electrode, or both the source and drain electrodes include a conductive layer that includes a first film contacting the barrier layer and including TaSi, a second film that includes at least 90 wt % Al, and a third layer that is relatively inert with respect to Al.
The electronic device of Embodiment 16, wherein a contact resistance for the barrier layer and either or both of the source and drain electrodes is at most 0.3 ohm·mm.
A process of forming an electronic device including providing a first layer including a III-V material over a substrate; and forming a conductive layer contacting the first layer, wherein the conductive layer includes a first film that includes Ta—Si compound.
The process of Embodiment 18, wherein forming the conductive layer further includes forming the first film; forming a second film over the first film, wherein the second film includes at least 90 wt % Al; and forming a third film over the second film.
The process of Embodiment 18, further including annealing the first and conductive layers at a temperature in a range of 500° C. to 900° C., wherein a contact resistance for the first and conductive layers is at most 0.3 ohm·mm.
Note that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described. Still further, the order in which activities are listed is not necessarily the order in which they are performed.
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims.
The specification and illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The specification and illustrations are not intended to serve as an exhaustive and comprehensive description of all of the elements and features of apparatus and systems that use the structures or methods described herein. Separate embodiments may also be provided in combination in a single embodiment, and conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Further, reference to values stated in ranges includes each and every value within that range. Many other embodiments may be apparent to skilled artisans only after reading this specification. Other embodiments may be used and derived from the disclosure, such that a structural substitution, logical substitution, or another change may be made without departing from the scope of the disclosure. Accordingly, the disclosure is to be regarded as illustrative rather than restrictive.
