PROCESS FOR FORMING LOW DEFECT DENSITY HETEROJUNCTIONS
A method for forming a low defect density heterojunction between a first and a second compound, the first and second compounds each includes a group III element combined with a group V element in the periodic table, the method includes the steps of introducing in the deposition chamber the flux of the group III element for the first compound at substantially the same time while introducing in the deposition chamber a flux of the group V element for the second compound, stopping the flux of the group III element for the first compound after a first predetermined time period, stopping the flux of the group V element for the first compound after a second predetermined time period, and introducing in the deposition chamber a flux of the group III element the group V element for the second compound.
CLAIM OF PRIORITY UNDER 35 U.S.C. § 120
This application is a continuation of and claims the benefit and priority of U.S. application Ser. No. 11/521,330, now U.S. Pat. No. ______, entitled “PROCESS FOR FORMING LOW DEFECT DENSITY HETEROJUNCTIONS,” filed on Sep. 14, 2006, which is assigned to the assignee hereof and hereby expressly incorporated by reference herein.
STATEMENT REGARDING GOVERNMENT RIGHTSThis invention was made with Government support under contract N66001-01-C-8032 awarded by the Department of Defense, DARPA, US Navy, Space & Naval Warfare Systems (SPAWAR). The Government has certain rights in the invention.
BACKGROUND OF THE INVENTION1. Field of the Invention
The invention relates generally to a semiconductor fabrication method. More particularly, the invention relates to a process for forming low defect density heterojunctions in semiconductor devices.
2. Description of Related Art
In advanced semiconductor devices, junctions between two different semiconductor materials are typically used to improve the performance of the device. These junctions, composed of layers of dissimilar semiconductor material, are known in the art as heterojunctions. The semiconductor materials used at the heterojunctions generally have non-equal band gaps and electron affinities.
A heterojunction has two pieces of semiconductor materials directly in contact with one another. It is often desirable to induce a specific type of bonding at the heterojunction. For example, forcing the heterojunction to have indium antimonide (InSb)-like bonding at an aluminum antimonide (AlSb) to indium arsenide (InAs) heterojunction for improved electron mobility, as described in G. Tuttle, H. Kroemer and J. English, “Effects of Interface layer sequencing on transport properties of InAs/AlSb quantum wells”, J.A.P.- Vol. 67, No. 6, 15 Mar. 1990, pp. 3033. Another example is forcing the heterojunction to have InSb-like bonding in a gallium antimonide (GaSb) to indium arsenide (InAs) superlattice grown on a GaSb substrate for lattice strain compensation.
A common method for achieving this desired bonding is using Molecular Beam Epitaxy (MBE) for growth. One advantage of using MBE growth is low temperature processing, which minimizes out-diffusion and autodoping in the semiconductor material. Another advantage is the precise control of doping profiles and deposition thickness that MBE allows. The MBE process can be used to control the bonding of group III-V materials. For example, the MBE process can be used to produce a GaSb to InAs heterojunction with InSb bonding, as opposed to GaAs bonding, at the heterojunction.
The prior art process of forming a AlGaSb to InAs heterojunction includes the following steps. First, AlGaSb is deposited on a base substrate. During the growth of AlGaSb, the aluminum (Al) and gallium (Ga) fluxes are stopped, and the surface is soaked with the antimony (Sb) flux. This covers any exposed aluminum or gallium atoms with an antimony atom, and any excess antimony should re-evaporate under typical MBE growth temperatures and fluxes. Next, the antimony flux is stopped, and a monolayer of indium is deposited. This indium monolayer is bonded to the antimony atoms on the surface of the substrate. After the deposition of the monolayer of indium, the indium flux is continued and a suitable arsenic flux is initiated, resulting in the growth of InAs. This method of forming the heterojunction is called “forcing InSb-like bonding”.
This procedure of interrupting growth, depositing a monolayer of the desired group III material, and then continuing growth has been discussed in the prior art. Unfortunately, this procedure causes defects at certain heterojunctions. For example, forcing InSb-like bonding at an InAs to AlGaSb heterojunction has resulted in tiny oval defects 113 nucleated at the heterojunction, as shown in
The exact nature of this invention, as well as the objects and advantages thereof, will become apparent from consideration of the following specification in conjunction with the accompanying drawings in which like reference numerals designate like parts throughout the figures.
A method for forming a low defect density heterojunction between a first semiconductor compound (i.e. InAs) and a second semiconductor compound (i.e. AlGaSb). The method controls the sequential deposition of the materials to control the detailed bonding at the heterojunctions, and minimize the nucleation of morphological defects. The method comprises depositing the first semiconductor compound on a substrate by introducing in a deposition chamber a flux of the group III element and the group V element for the first semiconductor compound, covering the deposited first semiconductor compound with a layer of the group V element for the first semiconductor compound to prevent the group III element for the first semiconductor compound from being exposed, and depositing the second semiconductor compound on the layer of the group V element for the first semiconductor compound by introducing in the deposition chamber a flux of the group III element and the group V element for the second semiconductor compound. This may produce an unforced heterojunction between the first and second semiconductor compounds.
In one embodiment, the group III and V elements of the first semiconductor compound is indium (In) and arsenic (As), respectively, while the group III and V elements of the second semiconductor compound is aluminum (Al), gallium (Ga) and antimony (Sb), respectively. In another embodiment, the group III and V elements of the first semiconductor compound is gallium (Ga) and antimony (Sb), respectively, while the group III and V elements of the second semiconductor compound is in https://exweb.panasonic.co.jp/ipro/ceeh01/dium (In) and arsenic (As), respectively.
Methods and systems that implement the embodiments of the various features of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. Reference in the specification to “one embodiment” or “an embodiment” is intended to indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least an embodiment of the invention. The appearances of the phrase “in one embodiment” or “an embodiment” in various places in the specification are not necessarily all referring to the same embodiment. Throughout the drawings, reference numbers are re-used to indicate correspondence between referenced elements. In addition, the first digit of each reference number indicates the figure in which the element first appears.
In Step 305, a substrate 411 is prepared for growth by placing it in an MBE deposition chamber 413. The base substrate 411 can be a silicon or gallium arsenide (GaAs) wafer. A cross-sectional view of the apparatus with the base substrate 411 is illustrated in
Next, in step 310, a constant flux of group III and V elements are introduced into the chamber at inlets 415, 416 and 417, respectively. In this example, the group III elements are aluminum (Al) and gallium (Ga), and the group V element is antimony (Sb). These elements react with one another to form an aluminum gallium antimonide (AlGaSb) layer 510.
After a predetermined period, which is a function of the desired thickness of the AlGaSb, the fluxes of the group III elements, aluminum (Al) and gallium (Ga), are stopped in Step 315. Since there are no longer aluminum (Al) or gallium (Ga) fluxes in the deposition chamber 413, only the group V flux of antimony (Sb) is impinging on the surface of the AlGaSb, step 320. This covers any exposed aluminum (Al) or gallium (Ga) with antimony (Sb) layer 610, as shown in
In one method embodying the invention, a monolayer of the group III element, indium (In), is deposited on AlGaSb at the heterojunction in step 330. To create an InSb-like bonding at the AlGaSb to InAs heterojunction, a flux of the group III element, indium (In), is introduced in the deposition chamber 413 https://exweb.panasonic.co.jp/ipro/ceeh01/. The indium reacts with antimony 610 to form an InSb layer 710 on the surface of the multilayer 600, as shown in
After the deposition of a monolayer of indium (In), a group V element, arsenic (As) flux, is initiated to grow an InAs layer 810 at step 335.
At step 340, the growth of the InAs layer 810 is terminated and the surface is soaked with group V element, arsenic (As), as shown in
Next, in step 345, the arsenic flux is stopped and fluxes of group III elements, aluminum (Al) and gallium (Ga), and group V element, antimony (Sb) are introduced into the deposition chamber 413. The elements, Al, Ga and Sb, react with one another to form an AlGaSb layer 1010, as shown in
To form a low defect density InAs to AlGaSb heterojunction, the indium flux is stopped, and the arsenic flux continues, to fully bond the surface of the InAs layer 810. Next, the arsenic flux is stopped, and aluminum, gallium and antimony fluxes are introduced in the chamber 413 to react and deposit AlGaSb. Finally, the aluminum, gallium and antimony fluxes are stopped.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other changes, combinations, omissions, modifications and substitutions, in addition to those set forth in the above paragraphs, are possible. For example, other compounds can be used at the unforced heterojunction from those described above to achieve a low defect density at the interface. Those skilled in the art will appreciate that various adaptations and modifications of the just described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.
Claims
1. A method for forming a low defect density heterojunction between a first compound and a second compound, the first and second compounds each including a group III element and a group V element in the periodic table, the method comprising:
- simultaneously depositing a first group III element and a first group V element to form a first compound layer including the first compound during a first period of time;
- continuously depositing the first group V element while stopping the depositing of the first group III element to form a first junction surface substantially covering the first compound layer during a second period of time, the first junction surface including the first group V element and substantially free of the first group III element; and
- simultaneously depositing a second group III element and a second group V element to form a second junction surface and a second compound layer including the second compound during a third period of time, the second junction surface substantially covering the first junction surface, the second compound layer formed on the second junction surface, such that the first and second junction surfaces combine to form the low defect density heterojunction.
2. The method of claim 1, wherein the first group III element is indium (In).
3. The method of claim 1, wherein the second group V element is antimony (Sb).
4. The method of claim 1, wherein the first group V element is arsenic (As).
5. The method of claim 1, wherein the second group III element is selected from a group consisting of aluminum (Al), gallium (Ga), and combinations thereof.
6. The method of claim 1, wherein the first group V element is chemically bonded to the first group III element to form the first compound, and wherein the second group V element is chemically bonded to the second group III element to form the second compound.
7. The method of claim 1, wherein the second period of time comes after the first period of time, and the third period of time comes after the second period of time.
8. The method of claim 1, wherein the second junction surface consists essentially of the second group III element.
9. The method of claim 1, wherein the first group III element is different from the second group III element, and wherein the first group V element is different from the second group V element.
10. A method for forming a low defect density heterojunction between a first compound and a second compound, the first and second compounds each including a group III element and a group V element in the periodic table, the method comprising:
- simultaneously introducing a first flux of a first group III element and a second flux of a first group V element to form a first compound layer including the first compound;
- stopping the first flux of the first group III element while continuing the second flux of the first group V element to form a first junction surface substantially covering the first group III element of the first compound layer; and
- stopping the second flux of the first group V element while introducing a third flux of a second group III element and a fourth flux of a second group V element to form a second junction surface and a second compound layer including the second compound.
11. The method of claim 10, wherein the second junction surface substantially covers the first junction surface, and the second compound layer is formed on the second junction surface, such that the first and second junction surfaces combine to form the low defect density heterojunction.
12. The method of claim 10, wherein the first group III element is indium (In) and the first group V element is arsenic (As).
13. The method of claim 10, wherein second group V element is antimony (Sb), and the second group III element consists of an element selected from a group consisting of aluminum (Al), gallium (Ga), and combinations thereof.
14. The method of claim 10, wherein the second junction surface consists essentially of the second group III element.
15. The method of claim 10, wherein the first group III element is different from the second group III element, and wherein the first group V element is different from the second group V element.
16. The method of claim 10, further comprising:
- stopping the third flux of the second group III element and the fourth flux of the second group V element.
17. A hetrostructure field effect transistor (HFET) device comprising:
- a first compound layer having a first chemical compound;
- a group V element junction surface covering the first compound layer; and
- a second compound layer having a second chemical compound, and forming on the group V element junction surface.
18. The device of claim 17, wherein the first chemical compound includes a first group III element and a first group V element, wherein the second chemical compound includes a second group III element and a second group V element.
19. The device of claim 17, further comprising a group III element junction surface covering the group V element junction surface, the group III element junction surface combining with the group V element junction surface to form a low defect density heterojunction between the first compound layer and the second compound layer.
20. The device of claim 18, wherein:
- the first group III element is indium (In),
- the first group V element is arsenic (As),
- the second group III element is selected from a group consisting of aluminum (Al), gallium (Ga), and combinations thereof, and
- the second group V element is antimony (Sb).
Type: Application
Filed: Sep 24, 2010
Publication Date: Feb 10, 2011
Inventors: Gerard J. Sullivan (Newbury Park, CA), Amal Ikhlassi (Thousand Oaks, CA), Joshua I. Bergman (Thousand Oaks, CA), Berinder Brar (Newbury Park, CA), Gabor Nagy (Thousand Oaks, CA)
Application Number: 12/890,526
International Classification: H01L 29/772 (20060101); C30B 25/16 (20060101);