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Lattice matching layer for use in a multilayer substrate structure

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Lattice matching layer for use in a multilayer substrate structure


A lattice matching layer for use in a multilayer substrate structure comprises a lattice matching layer. The lattice matching layer includes a first chemical element and a second chemical element. Each of the first and second chemical elements has a hexagonal close-packed structure at room temperature that transforms to a body-centered cubic structure at an α-β phase transition temperature higher than the room temperature. The hexagonal close-packed structure of the first chemical element has a first lattice parameter. The hexagonal close-packed structure of the second chemical element has a second lattice parameter. The second chemical element is miscible with the first chemical element to form an alloy with a hexagonal close-packed structure at the room temperature. A lattice constant of the alloy is approximately equal to a lattice constant of a member of group III-V compound semiconductors.
Related Terms: Semiconductor Lattice C Alloy Lattice Semiconductors

Browse recent Tivra Corporation patents - Pleasant Hill, CA, US
USPTO Applicaton #: #20130333611 - Class: 117 6 (USPTO) - 12/19/13 - Class 117 
Single-crystal, Oriented-crystal, And Epitaxy Growth Processes; Non-coating Apparatus Therefor > Processes Of Growth From Solid Or Gel State (e.g., Solid Phase Recrystallization) >At Pressure Above 1 Atmosphere

Inventors: Indranil De, Francisco Machuca

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The Patent Description & Claims data below is from USPTO Patent Application 20130333611, Lattice matching layer for use in a multilayer substrate structure.

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CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of provisional applications 61/662,918, filed on Jun. 22, 2012 and 61/659,944, filed on Jun. 14, 2012, the contents of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The example embodiments of the present invention generally pertain to semiconductor materials, methods, and devices, and more particularly to a multilayer substrate structure for epitaxial growth of group III-V compound semiconductors.

BACKGROUND

Group III-V compound semiconductor, such as gallium nitride (GaN), gallium arsenide (GaAs), indium nitride (InN), aluminum nitride (AlN) and gallium phosphide (GaP), are widely used in the manufacture of electronic devices, such as microwave frequency integrated circuits, light-emitting diodes, laser diodes, solar cells, high-power and high-frequency electronics, and opto-electronic devices. To improve throughput and reduce manufacturing cost it is desired to increase size (e.g., diameter) of substrates. Because growing III-V compound semiconductors of large size is very expensive a great number of foreign materials including metals, metal oxides, metal nitrides as well as semiconductors, such as silicon carbide (SiC), sapphire and silicon, are commonly used as substrates for epitaxial growth of III-V compound semiconductors.

However, epitaxy growth of group III-V compound semiconductors (e.g., GaN) on substrates (e.g., sapphire) poses many challenges on crystalline quality (e.g., grain boundaries, dislocations and other extended defects, and point defects) of the epitaxial layers due to lattice mismatch and coefficient of thermal expansion mismatch between the GaN layer and the underlying substrate, a foreign material. Differences in the coefficient of thermal expansion between the GaN layer and the underlying substrate result in large curvatures across the wafer, resulting during and post processing upon returning to room temperature, and the large mismatch in lattice constants leads to a high dislocation density, unwanted strain and defects propagating into the epitaxial GaN layer. In order to cope with these problems, stress relaxation strategies are employed, such as growing buffer layers between the GaN layer and the sapphire substrate, or counter balancing compressive and tensile strain by alternating appropriate material layers. However, by adding the buffer layer or stress relieving layers, the dislocation density may remain high and the manufacturing cost and complexity increases significantly because of the use of the same deposition techniques involved in growing the active device layers.

BRIEF

SUMMARY

According to one exemplary embodiment of the present invention, a multilayer substrate structure comprises a lattice matching layer. The lattice matching layer includes a first chemical element and a second chemical element. Each of the first and second chemical elements has a hexagonal close-packed structure at room temperature that transforms to a body-centered cubic structure at an α-β phase transition temperature higher than the room temperature. The hexagonal close-packed structure of the first chemical element has a first lattice parameter. The hexagonal close-packed structure of the second chemical element has a second lattice parameter. The second chemical element is miscible with the first chemical element to form an alloy with a hexagonal close-packed structure at room temperature. A lattice constant of the alloy is approximately equal to a lattice constant of a member of group III-V compound semiconductors.

According to one exemplary embodiment of the present invention, a method of fabricating a multilayer substrate structure comprises growing a lattice matching layer. The lattice matching layer includes a first chemical element and a second chemical element. Each of the first and second chemical elements has a hexagonal close-packed structure at room temperature that transforms to a body-centered cubic structure at an α-β phase transition temperature higher than room temperature. The hexagonal close-packed structure of the first chemical element has a first lattice parameter. The hexagonal close-packed structure of the second chemical element has a second lattice parameter. The second chemical element is miscible with the first chemical element to form an alloy with a hexagonal close-packed structure at room temperature. A lattice constant of the alloy is approximately equal to a lattice constant of a member of group III-V compound semiconductors.

According to one exemplary embodiment of the present invention, a multilayer substrate structure comprises a lattice matching layer. The lattice matching layer includes a first chemical element and a second chemical element. Each of the first and second chemical elements has a hexagonal close-packed structure at room temperature that transforms to a body-centered cubic structure at an α-β phase transition temperature higher than the room temperature. The hexagonal close-packed structure of the first chemical element has a first lattice parameter. The hexagonal close-packed structure of the second chemical element has a second lattice parameter. The second chemical element is miscible with the first chemical element to form an alloy with a hexagonal close-packed structure at room temperature. A linear relation exists between the first and second chemical elements and their associated lattice parameters at constant temperature to allow lattice constant of the alloy approximately equal to that of a group III-V compound semiconductor.

BRIEF DESCRIPTION OF THE DRAWING(S)

Having thus described the example embodiments of the present invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIGS. 1A-1D illustrate cross-sectional views of exemplary multilayer substrate structures in accordance with exemplary embodiments;

FIG. 2A illustrates a schematic of a hexagonal close-packed structure;

FIG. 2B illustrates a schematic of a unit cell showing lattice constants;

FIG. 3 illustrates a periodic table; and

FIG. 4 illustrates a phase diagram correlation between transition temperature and atomic percentage of constituent elements in accordance with an exemplary embodiment.

DETAILED DESCRIPTION

The various embodiments are described more fully with reference to the accompanying drawings. These example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to readers of this specification having knowledge in the technical field. Like numbers refer to like elements throughout.

FIG. 1A illustrates a cross-sectional view of an exemplary miltilayer substrate structure 100 in accordance with an exemplary embodiment. The miltilayer substrate structure 100 may include a substrate 102 and an epitaxial layer 104 epitaxially grown on the substrate 100. Depending on various applications, the substrate 102 may comprise a semiconductor material, a compound semiconductor material, or other type of material such as a metal or a non- metal. For example, the material may comprise molybdenum, molybdenum-copper, mullite, sapphire, graphite, aluminum-oxynitrides, silicon, silicon carbide, zinc oxides and rare earth oxides, and/or other suitable material.

The epitaxial layer 104 may include group III-V compound semiconductors, such as aluminum nitride (AlN), gallium nitride (GaN), indium gallium nitride (InGaN) and indium nitride (InN). As described above, there may be a lattice constant mismatch between the substrate 102 and the epitaxial layer 104. To decrease or eliminate the defects resulting from the lattice constant mismatch, the epitaxial layer 104 growth on the substrate 102 may use a lattice matching layer 106 with thickness in a range of 5 nm-100 nm to accommodate the lattice constant mismatch between the substrate 102 and the epitaxial layer 104. The lattice matching layer 106 may comprise two or more constituent elements, for example of two constituents, a first chemical element and a second chemical element, to form an alloy. The first chemical element is miscible with the second chemical element in this alloy. The constituent elements may have similar crystal structures at room temperature, such as hexagonal close-packed structure, as shown in FIG. 2A. Each of the constituent elements may have its respective lattice constants including lattice parameters along a-axis, b-axis and c-axis, and lattice parameters of interaxial angles α, β and γ, as shown in FIG. 2B. In addition to the crystal structures, the constituent elements may have similar chemical properties. In one embodiment, the first and second chemical elements may both belong to group four elements (namely, titanium (Ti), zirconium (Zr), hafnium (Hf) and rutherfordium (Rf)) in periodic table illustrated in FIG. 3. In this way, the alloy may be made from elements Ti and Zr, elements Ti and Hf, and elements Zr and Hf and may have similar crystal structure to the constituent elements at room temperature, or by any combination of 2. The alloy may comprise a third chemical element or more elements which have similar crystal structures and similar chemical properties.

A linear relation may exist between the first and second chemical elements and their associated lattice parameters at constant temperature to allow the lattice constant of the lattice matching layer 106 to be approximately equal to that of the epitaxial layer 104. The mole fraction in atomic percentage of the first chemical element to the second chemical element is P1 to (1-P1). The mole fraction may vary from application to application, as the composition will control the resulting lattice parameter value of the alloy. In one embodiment, when the epitaxial layer 104 includes GaN and the alloy includes Ti mixed with Zr, atomic percentage PZr of Zr may be greater than 75% and less than 90%. For example, PZr may be about 86%. It follows that atomic percentage PTi of Ti is (1-PZr). A first lattice parameter of Zr, e.g., a-axis lattice parameter aZr, is 3.23 Å. A second lattice parameter of Ti, e.g., a-axis lattice parameter aTi is 2.951 Å. As a result, lattice constant PA along a-axis of the alloy is PZr×aZr+(1-PZr)×aTi=86%×3.23+14%×2.951=3.19 Å which is approximately equal to the a-axis lattice constant PGaN of hexagonal close-packed GaN where PGaN=3.189 Å. Depending on the constituent elements and other factors, the atomic percentage of the first chemical element to the second chemical element may be about 43% to 57% or 99% to 1%.

When the epitaxial layer 104 includes different compound semiconductors (e.g., AlN, InGaN, InN and/or other group III-V compound semiconductors), the constituent elements of the lattice matching layer 106 and/or the mole fractions of the constituent elements may be adjusted to make the lattice constant of the lattice matching layer 106 accommodate that of the epitaxial layer 104. For example, when the epitaxial layer 104 comprises AlN and the constituent elements of the lattice matching layer 106 are Zr and Ti, the atomic percentage of Zr may be adjusted to be lower than 75% and higher than 50%. In another embodiment using the same constituent elements, when the epitaxial layer 104 comprises InGaN, the atomic percentage of Zr may be greater than 90%. In addition to the material of the epitaxy layer 104, the thickness of the epitaxial layer 104 may cause the changes of the selection of the constituent elements as well as mole fraction of the constituent elements to achieve 100% lattice match. Despite the changes of the thickness of the epitaxial layer 104, it may be in a range of 5 nm-500 nm. In other words, the thickness and the material of the epitaxial layer 104 may determine the selection of the constituent elements and their mole fraction in forming the lattice matching layer 106. By using any epitaxial techniques, such as vacuum evaporation, sputtering, molecular beam epitaxy and pulsed laser deposition, metalorganic chemical vapor deposition, atomic layer deposition and/or any other suitable epitaxial deposition methods, the epitaxial layer 104 is epitaxially grown on the lattice matching layer 106 to transfer the crystallographic pattern of the lattice matching layer 106 to the epitaxial layer 104. The lattice matching layer 106 may be formed on the underlying layer, for example, the substrate 102 using one of deposition techniques, such as vacuum evaporation, sputtering, molecular beam epitaxy and pulsed laser deposition, atmospheric chemical vapor deposition, and atomic layer deposition.

Because hexagonal close packed phase (α phase) has potential superiority over the body centered cubic phase (β phase) for certain opto-electronic devices and power semiconductor applications, it may be desired to grow the epitaxial layer 104 in α phase to achieve similar crystallographic pattern of the lattice matching layer 106. FIG. 4 shows a correlation between the α-β phase transition temperature and the atomic percentage of Zr and Ti in accordance with an exemplary embodiment. For example, when PZr is 50%, PTi=1-PZr=50%, the α-β phase transition temperature is about 605° C. When PZr is 84%, an example that has been illustrated above, the α-β phase transition temperature may be about 780° C. In an application of fabricating multi-quantum-well (MQW) devices on the epitaxial layer 104 (e.g. ultra high brightness LEDs), the epitaxial deposition method, such as metal organic chemical vapor deposition and atomic layer deposition and/or any other suitable methods for epitaxial growth, may be performed in a temperature range of 700° C.-850° C. In this embodiment, the miltilayer substrate structure may be heated by any heating methods/heat sources under the α-β phase transition temperature 780° C. but greater than 700° C. in an attempt to transfer the crystallographic pattern of the lattice matching layer 106 to the epitaxial layer 104 in a phase, avoiding β phase transition. Then the temperature for heating the miltilayer substrate structure during subsequent MQW growth, along with any additional device layers, can be raised above or lowered below 780° C. since epitaxial layer 104 has been formed and is permanently set in the a phase. The temperature may be initially raised above the α-β phase transition and then immediately dropped below α-β phase transition temperature to invoke generating phase transition free energy to crystallize large lateral areas resulting in single crystal α-phase in the lattice matching layer.

By introducing the lattice matching layer 106, the stresses may be lowered that might otherwise occur in the epitaxial layer 104 developed during the epitaxy growth as a result of difference in lattice constants between the substrate 102 and the epitaxial layer 104, and by doing so, aids in the growth of a high crystalline quality epitaxial layer 104. If such stress is not relieved by the lattice matching layer, the stress may cause defects in the crystalline structure of the epitaxial layer 104. Defects in the crystalline structure of the epitaxial layer 104, in turn, would make it difficult to achieve a high quality crystalline structure in epitaxy for any subsequent device growth.

As described above, the substrate 102 may comprise a semiconductor material, a compound semiconductor material, or another type of material such as a metal or a non-metal. In some embodiments, the substrate 102 may be in the form of a polycrystalline solid. Polycrystalline substrates may negatively impact the lattice matching layer 106 by making it polycrystalline instead of single crystal, thus enlarging the difference of lattice constants between the lattice matching layer 106 and the epitaxial layer 104 (an average lattice constant over multiple grains and multiple crystalline orientations), and causing extended defects such as threading dislocations or grain boundaries, leading to poor crystalline quality of the epitaxial layer 104. To reduce or eliminate the negative impact of a polycrystalline substrate, an amorphous layer 108 may be introduced between the polycrystalline substrate 102 and the lattice matching layer 106, as shown in FIG. 1B. By adding the amorphous layer 108 between the polycrystalline substrate 102 and the lattice matching layer 106, the impact of the polycrystalline substrate 102 on the lattice matching layer 106 may be reduced. In this way, only crystallography of the lattice matching layer 106 is transferred to the epitaxial layer 104. The amorphous layer 108 may comprise, but not limited to, one of silicon dioxide, silicon nitride, tantalum nitride, boronitride, tungsten nitride, glassy amorphous carbon, silicate glass (e.g., borophosphosilicate glass and phosphosilicate glass) and/or other suitable materials. The amorphous layer 108 may have a thickness of 5 nm to 100 nm.

In some embodiments, the coefficient of thermal expansion of the substrate 102 may be different than that of the above layers, resulting in large substrate curvatures. For example, when the coefficient of thermal expansion of the substrate 102 is greater than that of the above layers, biaxial compressive strain arises (e.g. when the substrate comprises sapphire). When the coefficient of thermal expansion of the substrate is less than that of the above layers, tensile strain arises (e.g. when the substrate comprises silicon). To overcome the drawback caused by the mismatch in the coefficient of thermal expansion, the substrate may be used as a thermal matching layer 102a (shown in FIGS. 1C and 1D) by including some chemical elements to accommodate the thermal mismatch between the substrate (namely, the thermal matching layer 102a in this embodiment) and the lattice matching layer 106 as shown in FIG. 1C, or between the substrate and the amorphous layer 108 as shown in FIG. 1D. In one embodiment, the thermal matching layer 102a may comprise molybdenum or its related alloys. The coefficient of thermal expansion of molybdenum is about 5.4×10−6/K which is approximately equal to that of some group III-V compound semiconductors, such as GaN. The substrate may be fabricated using a variety of methods for growth of metals, crystals, and their alloys. Example may include Czochralski, float zone (FZ), directional solidification (DS), zone melt recrystallization (ZMR), sintering, isostatic pressing, electro-chemical plating, plasma torch deposition, and/or other suitable methods. The thermal matching layer 102a has a thickness in a range of 5 nanometer to 1 millimeter. The thermal matching layer 102a is also disclosed in U.S. patent application entitled “A Multilayer Substrate Structure.”

By introducing the thermal matching layer and the lattice matching layer, the strain caused by the thermal expansion mismatch and lattice mismatch may be reduced or completely eliminated. As a result, the dislocation density may be less than 102/cm2 (<100 dislocations per square centimeter) in the resulting epitaxial layer 104. In development of light emitting diodes (LEDs), the reduction or elimination of the strain may fulfill requirements to overcome the so-called “green gap.” The “green gap” is an industry expression for a droop or decrease in LED light output from MQW LEDs that alloy indium with GaN to fabricate green LED\'s. This droop in green light outputted occurs for forward currents >50 mA in 1 to 5 square millimeter device areas due to defect density resulting from excessive strain from substrates, stress induced extended defects and point defects propagating into active MQW device layers.

Because the human eye is most sensitive to green and green light strongly affects the human perception to the quality of white light, the present embodiment enables high crystalline quality devices grown on layer 104. Moreover, exemplary embodiments of the present invention qualify a cost effective manner of manufacturing a green LED crystalline template. As such, the fulfilling of the “green gap” may enhance the high performance of white light emitting diodes based on mixing light from red, green and blue, having the highest theoretical efficacies over phosphor based down conversion LEDs used today.

Many modifications and other example embodiments set forth herein will bring to mind to the reader knowledgeable in the technical field to which these example embodiments pertain to having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the embodiments are not to be limited to the specific ones disclosed and that modifications and other embodiments are intended to be included within the scope of the claims. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions other than those explicitly described above are also contemplated as may be set forth in some of the appended claims.



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stats Patent Info
Application #
US 20130333611 A1
Publish Date
12/19/2013
Document #
13794285
File Date
03/11/2013
USPTO Class
117/6
Other USPTO Classes
423409, 2525191, 423412, 428220, 117 84, 117108, 117103, 117 88, 2041921, 117 13, 117 37, 117 81, 117/9, 117 95, 205188
International Class
/
Drawings
4


Semiconductor
Lattice C
Alloy
Lattice
Semiconductors


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