WO2020245423A1 - Tunable stress compensation in layered structures - Google Patents

Tunable stress compensation in layered structures Download PDF

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Publication number
WO2020245423A1
WO2020245423A1 PCT/EP2020/065719 EP2020065719W WO2020245423A1 WO 2020245423 A1 WO2020245423 A1 WO 2020245423A1 EP 2020065719 W EP2020065719 W EP 2020065719W WO 2020245423 A1 WO2020245423 A1 WO 2020245423A1
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Prior art keywords
porous layer
layer
starting material
stress
over
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PCT/EP2020/065719
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French (fr)
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Richard Hammond
Rodney Pelzel
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Iqe Plc
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Priority to PCT/EP2020/075534 priority Critical patent/WO2021244769A1/en
Priority to TW109131247A priority patent/TW202147403A/en
Publication of WO2020245423A1 publication Critical patent/WO2020245423A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
    • H01L21/76—Making of isolation regions between components
    • H01L21/762—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers
    • H01L21/7624—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using semiconductor on insulator [SOI] technology
    • H01L21/76245—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using semiconductor on insulator [SOI] technology using full isolation by porous oxide silicon, i.e. FIPOS techniques
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02002—Preparing wafers
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/02373—Group 14 semiconducting materials
    • H01L21/02381—Silicon, silicon germanium, germanium
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02436—Intermediate layers between substrates and deposited layers
    • H01L21/02439—Materials
    • H01L21/02441—Group 14 semiconducting materials
    • H01L21/02447—Silicon carbide
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02436—Intermediate layers between substrates and deposited layers
    • H01L21/02439—Materials
    • H01L21/02441—Group 14 semiconducting materials
    • H01L21/0245—Silicon, silicon germanium, germanium
    • H—ELECTRICITY
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02436—Intermediate layers between substrates and deposited layers
    • H01L21/02439—Materials
    • H01L21/02455—Group 13/15 materials
    • H01L21/02458—Nitrides
    • H—ELECTRICITY
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02436—Intermediate layers between substrates and deposited layers
    • H01L21/02439—Materials
    • H01L21/02488—Insulating materials
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02436—Intermediate layers between substrates and deposited layers
    • H01L21/02494—Structure
    • H01L21/02496—Layer structure
    • H01L21/02502—Layer structure consisting of two layers
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02436—Intermediate layers between substrates and deposited layers
    • H01L21/02494—Structure
    • H01L21/02513—Microstructure
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02538—Group 13/15 materials
    • H01L21/0254—Nitrides
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    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02656—Special treatments
    • H01L21/02658—Pretreatments
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
    • H01L21/76—Making of isolation regions between components
    • H01L21/7605—Making of isolation regions between components between components manufactured in an active substrate comprising AIII BV compounds

Definitions

  • Deposition of semiconducting and/or dielectric layers on a semiconducting substrate may result in a significant stress of the finished wafer due to the differential thermal expansion of the deposited layers compared to the underlying substrate. In some cases, the stress may result in a bow in the wafer.
  • the deposition of epitaxial layers at high temperature may induce stress in either the underlying substrate or the epitaxial layer at room
  • the lithographic focal point used for lithographic techniques may not be coincident with the wafer surface because of curvature induced in the case of a wafer bow (i.e., regions of the wafer surface will be out of focus).
  • the present disclosure is directed to controlling stress in a layered structure.
  • a layered structure suitable for processing and manufacturing semiconductor devices, and techniques for compensating stress and subsequently setting layer properties in the layered structure, are described herein.
  • a porous semiconductor region may be tuned to control net stress in the layered structure.
  • the porous semiconductor region has an advantage of maintaining its crystalline structure and thereby supports any subsequent depositions (e.g., subsequent epitaxial growth of a semiconductor layer).
  • a tunable porous region may enable modification of preferred properties of subsequently deposited layers.
  • the layered structure includes a tunable porous layer over a layer of a starting material (e.g., a silicon wafer).
  • the porous layer may be tuned to modify layer properties of a layer deposited over the porous layer.
  • the porous layer may be tuned to set net stress in the layered structure to counter wafer cracking.
  • the porous layer may be tuned to modify one or more layer properties of an epitaxial layer over the porous layer.
  • the tunable porous layer induces a bow in the starting wafer. In such an implementation, the induced bow may be tuned using the porous layer to set the net stress in the layered structure.
  • the porous layer may be tuned to counterbalance a portion of the expected stress from a deposited layer. In some cases, the porous layer may be tuned to counterbalance most of the expected stress.
  • the layered structure can be designed to have some preferred properties that are dependent on net stress. For example, the layered structure can be designed to be planar or non planar.
  • the porous layer may be tuned by varying its porosity and/or thickness to compensate for a portion of stress in the layered structure. In some cases, most of the stress is compensated.
  • the layered structure having a tunable porous layer may support semiconductor device manufacturing and processing techniques which depend on layer properties influenced by net stress in the structure. As a result, semiconductor devices including the layered structure with a tunable porous layer may have improved performance because of modified properties from stress induced by the tunable porous layer.
  • Controlling stress in the layered structure includes forming a porous layer having tunable porosity and thickness over a layer of a starting material.
  • the starting material layer may be a substrate.
  • the starting material layer may be a silicon (Si) substrate.
  • the porous layer is formed from a portion of the starting material layer.
  • the starting material and the porous layer include the same Group IV element.
  • the starting material and porous layer may both include or be made of Si.
  • a porous layer may be formed from a portion of the starting material using any suitable technique such as electrochemical etching or anodization.
  • the porosity of the tunable porous layer may be uniform.
  • the porosity of the porous layer may be vertically graded and/or horizontally graded, which may result in regions of different porosities.
  • the tunable porous layer may have a first region of 10% porosity and a second region of 30% porosity.
  • Controlling stress in the layered structure may include tuning the degree of porosity, or the layer thickness, of the porous layer. For example, increasing duration of the electrochemical etching increases the porosity of the porous layer. Alternatively or additionally, adjusting the applied current density in the electrochemical etching may control the porous layer thickness and degree of porosity.
  • tuning the porous layer includes maintaining a crystalline structure in the tunable porous layer. The crystalline structure may enable subsequent deposition or growth of a layer over the tunable porous layer.
  • tuning the porous layer can be used to induce an initial bow in the starting material and control net stress in the layered structure.
  • the initial wafer bow may be further tuned by oxidizing the tunable porous layer, which causes stress on the starting material that may result in curving the starting material.
  • the bow is induced to oppose a curvature resulting from a deposited layer over the tunable porous layer.
  • a substrate may be curved concave using the induced bow to counter an expected convex curve resulting from epitaxial growth of a semiconductor layer.
  • the deposited layer, over the porous layer includes a material that is thermally dissimilar to the starting material.
  • a material that is thermally dissimilar to the starting material For example, an epitaxial layer grown over the tunable porous layer may have a thermal coefficient of expansion different from the starting material.
  • the different rates of thermal expansion may cause nonzero net stress to the layered structure when forming the epitaxial layer at high temperature.
  • the nonzero net stress may curve the layered structure.
  • the porous layer can be tuned to balance stress that results, or is expected to result, from deposition of a layer over the oxidized porous layer.
  • the porous layer may be tuned to compensate for the stress resulting from differing thermal expansion due to a deposited layer having thermally dissimilar material than the starting material.
  • the porous layer is tuned to set the net stress in the layered structure.
  • the porous layer may be tuned before deposition of a layer over the porous layer.
  • the porous layer may be tuned when forming a layer over the porous layer.
  • an induced bow from tuning the porous layer is used to modify characteristics of the deposited layer over the porous layer. For example, stress during lithographic patterning over the porous layer may cause a modification of layer properties in the layered structure, such as moving the layer surface out of focus.
  • tuning of the porous layer may help maintain preferred properties of the layer surface for the lithographic process, such as maintaining the focus on the layer surface.
  • the layered structure includes a layer of a starting material, a porous layer having tunable porosity and thickness over the starting material, and a layer formed over the porous layer.
  • a portion of the tunable porous layer is oxidized to further tune the net stress.
  • most of the tunable porous layer is oxidized.
  • the porous layer may be tuned by varying porosity and/or thickness of the porous layer.
  • the porous layer induces a tunable bow in the starting material layer. In such an implementation, the induced bow may be tuned by varying porosity and/or thickness of the porous layer.
  • the layer formed over the tunable porous layer is a semiconductor layer epitaxially grown over the tunable porous layer.
  • the semiconductor layer may include or be gallium nitride (GaN).
  • the semiconductor layer may include an alloy of a rare earth (RE) and aluminum nitride (AIN).
  • the semiconductor layer may include scandium aluminum nitride (ScAIN).
  • any of the layers as described in the present disclosure may be formed using a suitable thin-film deposition technique or combination of techniques. Some non-limiting examples include chemical vapor deposition, molecular beam epitaxy, and atomic layer deposition.
  • FIG. 1 shows an example of a layered structure having controllable stress, in accordance with some implementations of the present disclosure
  • FIG. 2 shows examples of layered structures having controllable stress, in accordance with some implementations of the present disclosure
  • FIGS. 3 and 4 show examples of layered structures made from specific materials, in accordance with some implementations of the present disclosure
  • FIG. 5 shows plots comparing curvature resulting from a tunable porous layer with varying porosities, thicknesses, and oxidation, in accordance with some implementations of the present disclosure.
  • FIG. 6 is a flowchart of a process for controlling stress in a layered structure, in accordance with some implementations of the present disclosure.
  • the present disclosure is directed to controlling stress in a layered structure.
  • a layered structure suitable for integrated semiconductor devices and techniques for controlling stress and subsequently adjusting layer properties in the layered structure are presented herein.
  • the techniques may be used to compensate for stress in a substrate resulting from deposition of materials that are thermally dissimilar to the substrate.
  • the techniques described enable modification of layer properties that depend on net stress during subsequent processing and manufacturing of semiconductor devices.
  • FIG. 1 shows an example of a layered structure 100 having controllable stress, in accordance with some implementations of the present disclosure.
  • Layered structure 100 includes a starting material 102, a tunable porous layer 104 formed over the starting material 102, and a layer 106 deposited over the tunable porous layer 104.
  • Tunable porous layer 104 is oxidized in layered structure 100.
  • porous layer 104 has been tuned to balance the net stress in layered structure 100.
  • tuning the porous layer 104 to balance the net stress results in modifying layer properties of starting material 102 and/or layer 106.
  • tuning the porous layer results in starting material 102 remaining planar after depositing layer 106.
  • Such a layered structure may support semiconductor device manufacturing and processing techniques which depend on a flat substrate (e.g., lithographic patterning or epitaxial growth).
  • FIG. 2 shows examples of layered structures 200 and 210 having controllable stress, in accordance with some implementations of the present disclosure.
  • layered structure 210 with epitaxial semiconductor layer 216 may be the result of balancing the net stress in layered structure 100.
  • Layered structure 200 shows a porous layer 204 formed over a starting material 202.
  • Porous layer 204 is formed over starting material 202.
  • porous layer 204 is formed from a portion of starting material 202.
  • the starting material may be a silicon (Si) substrate.
  • a porous layer may be formed from the surface portion of the Si substrate using any suitable technique or combination of techniques such as electrochemical etching or anodization.
  • porous layer 204 and starting material 202 would start out with the same elemental composition.
  • starting material 202 could be Si, resulting in formation of a porous Si layer 204.
  • Starting material 202, and therefore porous layer 204 also could be other Group IV materials, or other materials more generally.
  • the porosity of the tunable porous layer may be uniform.
  • the porosity of the porous layer may be vertically graded and/or horizontally graded, which may result in regions of different porosities.
  • the tunable porous layer may have a first region of 10% porosity and a second region of 30% porosity.
  • Layered structure 210 shows a tunable porous layer 214 over starting material 202.
  • Porous layer 214 has been oxidized in this example.
  • Oxidized porous layer 214 may be porous layer 204 after an oxidation process or another suitable process. The process may be performed with any suitable technique or combination of techniques for oxidizing the porous layer (e.g., thermal oxidation, wet oxidation, etc.).
  • a porous Si layer may be oxidized using thermal oxidation to form a porous S1O2 layer.
  • the tunable porous layer sets net stress to modify layer properties of the starting material layer.
  • porous layer 214 induces a bow in starting material 202.
  • the induced bow may be tuned by varying the porosity and/or thickness of the oxidized porous layer 214 to compensate for expected stress in layered structure 210 (e.g., due to expected future deposition of an epitaxial layer at high
  • a substrate may be curved concave using the induced bow to counter an expected convex curve resulting from epitaxial growth of a semiconductor layer over the oxidized porous layer.
  • Porous layer 214 has one or more tunable parameters (e.g., porosity, thickness, oxidation).
  • the porous layer may have thickness between 0.1-100 pm.
  • controlling stress in the layered structure includes tuning porosity and thickness of the porous layer. For example, increasing duration of the electrochemical etching increases the porosity of the porous layer. As another example, adjusting the applied current density during the electrochemical etching may control the thickness and degree of porosity of the porous layer.
  • Layered structure 210 has an epitaxial semiconductor layer 216 over oxidized porous layer 214 and starting material 202. Porous layer 214 is tuned to counteract stress introduced by deposition of epitaxial semiconductor layer 216 in layered structure 210. One result is that layered structure 210 remains planar.
  • tuning the porous layer includes inducing a bow.
  • inducing the bow may include oxidizing the porous layer (e.g., to form oxidized porous layer 214).
  • tuning the porous layer includes tuning the porosity and/or thickness of the porous layer. The porous layer may be tuned to counterbalance a portion of the expected stress from a deposited layer to be deposited later.
  • the porous layer may be tuned to counterbalance most of the expected stress. By counterbalancing expected stress, the layered structure can be designed to have some preferred properties that are dependent on net stress.
  • tuning the porous layer to induce the bow causes a curvature to the starting material (e.g., starting material 202) to oppose an expected curvature from a subsequently deposited layer.
  • the tunable porous layer maintains a crystalline structure. The crystalline structure may enable subsequent growth of an epitaxial.
  • oxidized porous layer 214 has a crystalline structure to support epitaxial layer 216 in layered structure 210.
  • the starting material and the tunable porous layer share the same elemental composition (e.g., a Group IV element).
  • starting material 202 and oxidized porous layer 214 may both include or be substantially made of Si.
  • the deposited layer, over the porous layer includes a material that is thermally dissimilar to the starting material.
  • epitaxial layer 216 grown over tunable porous layer 214 may have a thermal coefficient of expansion different from starting material 202.
  • the different rates of thermal expansion may cause nonzero net stress to layered structure 210 when forming epitaxial layer 216 at a high temperature.
  • the nonzero net stress may curve layered structure.
  • the porous layer can be tuned to balance stress that results, or is expected to result, from deposition of a layer over the porous layer.
  • the induced bow from oxidized porous layer 214 may be tuned to compensate for the stress resulting from differing thermal expansion due to epitaxial layer 216 having a material that is thermally dissimilar to starting material 202.
  • the porous layer is tuned to set the net stress in the layered structure.
  • the porous layer may be tuned before deposition of a layer over the porous layer.
  • the porous layer may be tuned when forming a layer over the oxidized porous layer.
  • an induced bow from tuning the porous layer is used to modify characteristics of the deposited layer over the tunable porous layer. For example, stress during lithographic patterning over the porous layer may cause a modification to layer properties in the layered structure, such as moving the layer surface out of focus.
  • tuning of the porous layer may help maintain preferred properties of the layer surface for the lithographic process, such as maintaining the focus on the layer surface.
  • FIGS. 3 and 4 show examples of layered structures 300 and 400 made from specific materials, in accordance with some implementations of the present disclosure.
  • Layered structure 300 has Si substrate 302, oxidized porous Si layer 304 over substrate 302, and gallium nitride (GaN) layer 306 over oxidized porous Si layer 304.
  • Layered structure 400 has Si substrate 402, oxidized porous Si layer 404 over substrate 402, and scandium aluminum nitride (ScAIN) layer 406 over oxidized porous Si layer 404.
  • Semiconductor layers 306 and 406 may have been formed using any suitable technique (e.g., chemical vapor deposition).
  • one or more intermediate layers may be formed over the tunable porous layer before deposition of a semiconductor layer over the porous layer.
  • an interlayer may be formed over porous Si layer 404 to improve support for deposition of Sc AIN layer 406.
  • the porous layer is tuned to balance the net stress of the layered structure that results from forming a layer over the tunable porous layer.
  • porous layers 304 and 404 may have been tuned differently to support their respective semiconductor layers 306 and 406.
  • Tuning the porous layer may enable epitaxial deposition of thermally dissimilar materials.
  • GaN and Si have different thermal coefficients of expansion. Epitaxial deposition of GaN layer 306 at high temperature may result in a curvature to Si substrate 302 at room temperature.
  • Oxidized porous Si layer 304 may be tuned by adjusting porosity and/or thickness.
  • layer 304 may have been tuned to have 15 pm thickness and 20% porosity to balance net stress in layered structure 300 and keep the surface of GaN layer 306 planar at room temperature.
  • the porous layer may be further tuned to compensate stress resulting from subsequent semiconductor device processing.
  • FIG. 5 shows plots 500 and 510 comparing curvature resulting from a tunable porous layer with varying porosities, thicknesses, and oxidation, in accordance with some implementations of the present disclosure.
  • Plot 500 shows curvature of a bow in a porous layer at 20% porosity and varying layer thickness and oxidation.
  • Curve 502 shows a trend of the bow curvature for an oxidized porous layer as compared to an unoxidized porous layer having same porosity and thickness.
  • Plot 510 shows curvature of a bow in a porous layer at 30% porosity and varying layer thickness and oxidation.
  • Curve 512 shows a trend of the bow curvature for an oxidized porous layer as compared to an unoxidized porous layer having same porosity and thickness.
  • curvature of the oxidized porous layer e.g., curves 502 and 512
  • FIG. 5 shows measurable induced bows in both an unoxidized and oxidized porous layer, but the induced bow of an oxidized porous layer has improved tunable characteristics suitable for controlling stress in a layered structure.
  • FIG. 6 is a flow diagram of a process 600 for controlling stress in a layered structure, in accordance with some implementations of the present disclosure.
  • Process 600 starts from 602.
  • a porous layer is formed having tunable porosity and thickness over a starting material.
  • porous layer 204 is formed over starting material 202.
  • the porous layer is oxidized.
  • a bow is induced by oxidation of the porous layer.
  • a layer is formed over the oxidized porous layer using epitaxy or other suitable technique.
  • the induced bow in the starting material is tuned to set the net stress in the layered structure by varying the porosity and/or thickness of the oxidized porous layer.
  • Some non-limiting example results from process 700 may include layered structures 100-300.
  • semiconductor layer 216 is epitaxially grown over oxidized porous layer 214.
  • the induced bow is tuned to balance the net stress, maintaining flat semiconductor layer 216.
  • Porous layer 214 may have been tuned to modify other properties of layer 216 in this example.
  • the unoxidized porous layer may be tuned to modify layer properties for expected deposition at 608.
  • a layer means a substantially uniform thickness of a material covering a surface.
  • a layer can be either continuous or discontinuous (i.e., having gaps between regions of the material).
  • a layer can completely or partially cover a surface, or be segmented into discrete regions, which collectively define the layer (i.e., regions formed using selective- area epitaxy).
  • Monolithically-integrated means formed on the surface of the substrate, typically by depositing layers disposed on the surface.
  • Disposed on means “exists on” or “over” an underlying material or layer.
  • This layer may include intermediate layers, such as transitional layers, necessary to ensure a suitable surface.
  • intermediate layers such as transitional layers, necessary to ensure a suitable surface.
  • a material is described to be “disposed on” or “over a substrate,” this can mean either (1) the material is in intimate contact with the substrate; or (2) the material is in contact with one or more transitional layers that reside on the substrate.
  • Single-crystal means a crystalline structure that comprises substantially only one type of unit-cell.
  • a single-crystal layer may exhibit some crystalline defects such as stacking faults, dislocations, or other commonly occurring crystalline defects.
  • Single-domain means a crystalline structure that comprises substantially only one structure of unit-cell and substantially only one orientation of that unit cell. In other words, a single-domain crystal exhibits no twinning or anti-phase domains.
  • Single-phase means a crystalline structure that is both single-crystal and single domain.
  • Substrate means the material on which deposited layers are formed.
  • Exemplary substrates include, without limitation: bulk gallium nitride wafers, bulk silicon carbide wafers, bulk sapphire wafers, bulk germanium wafers, bulk silicon wafers, in which a wafer comprises a homogeneous thickness of single-crystal material; composite wafers, such as a silicon-on-insulator wafer that comprises a layer of silicon that is disposed on a layer of silicon dioxide that is disposed on a bulk silicon handle wafer; or the porous germanium, germanium over oxide and silicon, germanium over silicon, patterned germanium, germanium tin over germanium, and/or the like; or any other material that serves as base layer upon which, or in which, devices are formed.
  • a substrate may have a single bulk wafer, or multiple sub-layers.
  • a substrate e.g., silicon, germanium, etc.
  • Semiconductor refers to any solid substance that has a conductivity between that of an insulator and that of most metals.
  • An example semiconductor layer is composed of silicon.
  • the semiconductor layer may include a single bulk wafer, or multiple sub-layers.
  • a silicon semiconductor layer may include multiple non-continuous porous portions. The multiple non-continuous porous portions may have different densities and may be horizontally distributed or vertically layered.
  • a first layer described and/or depicted herein as “configured on,” “on,” “formed over,” or “over” a second layer can be immediately adjacent to the second layer, or one or more intervening layers can be between the first and second layers.
  • a first layer that is described and/or depicted herein as “directly on” or “directly over” a second layer or a substrate is immediately adjacent to the second layer or substrate with no intervening layer present, other than possibly an intervening alloy layer that may form due to mixing of the first layer with the second layer or substrate.
  • a first layer that is described and/or depicted herein as being “on,” “over,” “directly on,” or “directly over” a second layer or substrate may cover the entire second layer or substrate, or a portion of the second layer or substrate.
  • a substrate is placed on a substrate holder during layer growth, and so a top surface or an upper surface is the surface of the substrate or layer furthest from the substrate holder, while a bottom surface or a lower surface is the surface of the substrate or layer nearest to the substrate holder.
  • Any of the structures depicted and described herein can be part of larger structures with additional layers above and/or below those depicted. For clarity, the figures herein can omit these additional layers, although these additional layers can be part of the structures disclosed. In addition, the structures depicted can be repeated in units, even if this repetition is not depicted in the figures.

Abstract

A layered structure having controllable stress is described herein. The layered structure includes a starting material, a tunable porous layer formed over a starting material, and an epitaxial layer formed over the porous layer. The tunable porous layer induces a tunable bow in the starting material to set net stress in the layered structure. Additionally, techniques for controlling stress in the layered structure are described herein. A process for controlling stress in the layered structure includes forming a porous layer having tunable porosity and thickness over a starting material, inducing a bow in the starting material by oxidizing the porous layer, and tuning the induced bow to set net stress in the layered structure that results from a layer subsequently grown or deposited over the tunable porous layer.

Description

TUNABLE STRESS COMPENSATION IN LAYERED STRUCTURES
Cross-Reference to Related Applications
[0001] This disclosure claims the benefit under 35 U.S.C. § 119(e) of United States Provisional Patent Application No. 62/858,279, filed June 6, 2019, which is hereby incorporated by reference herein in its entirety.
Background
[0002] Deposition of semiconducting and/or dielectric layers on a semiconducting substrate may result in a significant stress of the finished wafer due to the differential thermal expansion of the deposited layers compared to the underlying substrate. In some cases, the stress may result in a bow in the wafer. The deposition of epitaxial layers at high temperature may induce stress in either the underlying substrate or the epitaxial layer at room
temperature. This can result in wafer cracking in the material system or unwanted modification of the inherent properties of the epitaxial layer. In addition, the resulting effects on the underlying substrate may be problematic for any subsequent device manufacture and/or device processing. For example, the lithographic focal point used for lithographic techniques may not be coincident with the wafer surface because of curvature induced in the case of a wafer bow (i.e., regions of the wafer surface will be out of focus).
Summary
[0003] Accordingly, the present disclosure is directed to controlling stress in a layered structure. A layered structure suitable for processing and manufacturing semiconductor devices, and techniques for compensating stress and subsequently setting layer properties in the layered structure, are described herein. A porous semiconductor region may be tuned to control net stress in the layered structure. The porous semiconductor region has an advantage of maintaining its crystalline structure and thereby supports any subsequent depositions (e.g., subsequent epitaxial growth of a semiconductor layer). In addition, a tunable porous region may enable modification of preferred properties of subsequently deposited layers.
[0004] Specifically, the layered structure includes a tunable porous layer over a layer of a starting material (e.g., a silicon wafer). As noted, the porous layer may be tuned to modify layer properties of a layer deposited over the porous layer. For example, the porous layer may be tuned to set net stress in the layered structure to counter wafer cracking. In another example, the porous layer may be tuned to modify one or more layer properties of an epitaxial layer over the porous layer. In some implementations, the tunable porous layer induces a bow in the starting wafer. In such an implementation, the induced bow may be tuned using the porous layer to set the net stress in the layered structure.
[0005] The porous layer may be tuned to counterbalance a portion of the expected stress from a deposited layer. In some cases, the porous layer may be tuned to counterbalance most of the expected stress. By counterbalancing expected stress, the layered structure can be designed to have some preferred properties that are dependent on net stress. For example, the layered structure can be designed to be planar or non planar. The porous layer may be tuned by varying its porosity and/or thickness to compensate for a portion of stress in the layered structure. In some cases, most of the stress is compensated. The layered structure having a tunable porous layer may support semiconductor device manufacturing and processing techniques which depend on layer properties influenced by net stress in the structure. As a result, semiconductor devices including the layered structure with a tunable porous layer may have improved performance because of modified properties from stress induced by the tunable porous layer.
[0006] Controlling stress in the layered structure includes forming a porous layer having tunable porosity and thickness over a layer of a starting material. The starting material layer may be a substrate. For example, the starting material layer may be a silicon (Si) substrate.
In some implementations, the porous layer is formed from a portion of the starting material layer. In such an implementation, the starting material and the porous layer include the same Group IV element. For example, the starting material and porous layer may both include or be made of Si. A porous layer may be formed from a portion of the starting material using any suitable technique such as electrochemical etching or anodization.
[0007] In some implementations, the porosity of the tunable porous layer may be uniform. Alternatively, the porosity of the porous layer may be vertically graded and/or horizontally graded, which may result in regions of different porosities. For example, the tunable porous layer may have a first region of 10% porosity and a second region of 30% porosity.
[0008] Controlling stress in the layered structure may include tuning the degree of porosity, or the layer thickness, of the porous layer. For example, increasing duration of the electrochemical etching increases the porosity of the porous layer. Alternatively or additionally, adjusting the applied current density in the electrochemical etching may control the porous layer thickness and degree of porosity. In some implementations, tuning the porous layer includes maintaining a crystalline structure in the tunable porous layer. The crystalline structure may enable subsequent deposition or growth of a layer over the tunable porous layer.
[0009] As noted above, tuning the porous layer can be used to induce an initial bow in the starting material and control net stress in the layered structure. The initial wafer bow may be further tuned by oxidizing the tunable porous layer, which causes stress on the starting material that may result in curving the starting material. In some implementations, the bow is induced to oppose a curvature resulting from a deposited layer over the tunable porous layer. For example, a substrate may be curved concave using the induced bow to counter an expected convex curve resulting from epitaxial growth of a semiconductor layer.
[0010] In some implementations, the deposited layer, over the porous layer, includes a material that is thermally dissimilar to the starting material. For example, an epitaxial layer grown over the tunable porous layer may have a thermal coefficient of expansion different from the starting material. In this example, the different rates of thermal expansion may cause nonzero net stress to the layered structure when forming the epitaxial layer at high temperature. The nonzero net stress may curve the layered structure. The porous layer can be tuned to balance stress that results, or is expected to result, from deposition of a layer over the oxidized porous layer. For example, the porous layer may be tuned to compensate for the stress resulting from differing thermal expansion due to a deposited layer having thermally dissimilar material than the starting material.
[0011] In some implementations, the porous layer is tuned to set the net stress in the layered structure. As previously noted, the porous layer may be tuned before deposition of a layer over the porous layer. Additionally or alternatively, the porous layer may be tuned when forming a layer over the porous layer. In some implementations, an induced bow from tuning the porous layer is used to modify characteristics of the deposited layer over the porous layer. For example, stress during lithographic patterning over the porous layer may cause a modification of layer properties in the layered structure, such as moving the layer surface out of focus. In this example, tuning of the porous layer may help maintain preferred properties of the layer surface for the lithographic process, such as maintaining the focus on the layer surface.
[0012] As described in the present disclosure, stress in a layered structure is compensated by tuning a porous layer. The layered structure includes a layer of a starting material, a porous layer having tunable porosity and thickness over the starting material, and a layer formed over the porous layer. In some implementations, a portion of the tunable porous layer is oxidized to further tune the net stress. In some cases, most of the tunable porous layer is oxidized. The porous layer may be tuned by varying porosity and/or thickness of the porous layer. In some implementations, the porous layer induces a tunable bow in the starting material layer. In such an implementation, the induced bow may be tuned by varying porosity and/or thickness of the porous layer.
[0013] In some implementations, the layer formed over the tunable porous layer is a semiconductor layer epitaxially grown over the tunable porous layer. For example, the semiconductor layer may include or be gallium nitride (GaN). In another non-limiting example, the semiconductor layer may include an alloy of a rare earth (RE) and aluminum nitride (AIN). For example, the semiconductor layer may include scandium aluminum nitride (ScAIN).
[0014] Using any of the techniques described in the present disclosure, stress may be compensated by tuning the tunable porous layer in the layered structure. It should be noted that any of the layers as described in the present disclosure may be formed using a suitable thin-film deposition technique or combination of techniques. Some non-limiting examples include chemical vapor deposition, molecular beam epitaxy, and atomic layer deposition.
Brief Description of the Drawings
[0015] The present disclosure, in accordance with one or more various implementations, is described in detail with reference to the following drawings. The drawings are provided for purposes of illustration only and merely depict typical or example implementations. These drawings are provided to facilitate an understanding of the concepts disclosed herein and shall not be considered limiting of the breadth, scope, or applicability of these concepts. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.
[0016] FIG. 1 shows an example of a layered structure having controllable stress, in accordance with some implementations of the present disclosure; [0017] FIG. 2 shows examples of layered structures having controllable stress, in accordance with some implementations of the present disclosure;
[0018] FIGS. 3 and 4 show examples of layered structures made from specific materials, in accordance with some implementations of the present disclosure;
[0019] FIG. 5 shows plots comparing curvature resulting from a tunable porous layer with varying porosities, thicknesses, and oxidation, in accordance with some implementations of the present disclosure; and
[0020] FIG. 6 is a flowchart of a process for controlling stress in a layered structure, in accordance with some implementations of the present disclosure.
Detailed Description
[0021] The present disclosure is directed to controlling stress in a layered structure. A layered structure suitable for integrated semiconductor devices and techniques for controlling stress and subsequently adjusting layer properties in the layered structure are presented herein. In some implementations, the techniques may be used to compensate for stress in a substrate resulting from deposition of materials that are thermally dissimilar to the substrate. In some aspects of the present disclosure, the techniques described enable modification of layer properties that depend on net stress during subsequent processing and manufacturing of semiconductor devices.
[0022] FIG. 1 shows an example of a layered structure 100 having controllable stress, in accordance with some implementations of the present disclosure. Layered structure 100 includes a starting material 102, a tunable porous layer 104 formed over the starting material 102, and a layer 106 deposited over the tunable porous layer 104. Tunable porous layer 104 is oxidized in layered structure 100.
[0023] In layered structure 100, porous layer 104 has been tuned to balance the net stress in layered structure 100. In some implementations, tuning the porous layer 104 to balance the net stress results in modifying layer properties of starting material 102 and/or layer 106. In layered structure 100, tuning the porous layer results in starting material 102 remaining planar after depositing layer 106. Such a layered structure may support semiconductor device manufacturing and processing techniques which depend on a flat substrate (e.g., lithographic patterning or epitaxial growth).
[0024] FIG. 2 shows examples of layered structures 200 and 210 having controllable stress, in accordance with some implementations of the present disclosure. For example, layered structure 210 with epitaxial semiconductor layer 216 may be the result of balancing the net stress in layered structure 100. Layered structure 200 shows a porous layer 204 formed over a starting material 202.
[0025] Porous layer 204 is formed over starting material 202. In some implementations, porous layer 204 is formed from a portion of starting material 202. For example, the starting material may be a silicon (Si) substrate. In this example, a porous layer may be formed from the surface portion of the Si substrate using any suitable technique or combination of techniques such as electrochemical etching or anodization. In such implementations, porous layer 204 and starting material 202 would start out with the same elemental composition. For example, starting material 202 could be Si, resulting in formation of a porous Si layer 204. Starting material 202, and therefore porous layer 204 also could be other Group IV materials, or other materials more generally.
[0026] In some implementations, the porosity of the tunable porous layer may be uniform. Alternatively, the porosity of the porous layer may be vertically graded and/or horizontally graded, which may result in regions of different porosities. For example, the tunable porous layer may have a first region of 10% porosity and a second region of 30% porosity.
[0027] Layered structure 210 shows a tunable porous layer 214 over starting material 202. Porous layer 214 has been oxidized in this example. Oxidized porous layer 214 may be porous layer 204 after an oxidation process or another suitable process. The process may be performed with any suitable technique or combination of techniques for oxidizing the porous layer (e.g., thermal oxidation, wet oxidation, etc.). For example, a porous Si layer may be oxidized using thermal oxidation to form a porous S1O2 layer.
[0028] In some implementations, the tunable porous layer sets net stress to modify layer properties of the starting material layer. In layered structure 210, porous layer 214 induces a bow in starting material 202. The induced bow may be tuned by varying the porosity and/or thickness of the oxidized porous layer 214 to compensate for expected stress in layered structure 210 (e.g., due to expected future deposition of an epitaxial layer at high
temperatures), thereby counteracting an expected undesirable bow of the finished structure. For example, a substrate may be curved concave using the induced bow to counter an expected convex curve resulting from epitaxial growth of a semiconductor layer over the oxidized porous layer.
[0029] Porous layer 214 has one or more tunable parameters (e.g., porosity, thickness, oxidation). For example, the porous layer may have thickness between 0.1-100 pm. In some implementations, controlling stress in the layered structure includes tuning porosity and thickness of the porous layer. For example, increasing duration of the electrochemical etching increases the porosity of the porous layer. As another example, adjusting the applied current density during the electrochemical etching may control the thickness and degree of porosity of the porous layer.
[0030] Layered structure 210 has an epitaxial semiconductor layer 216 over oxidized porous layer 214 and starting material 202. Porous layer 214 is tuned to counteract stress introduced by deposition of epitaxial semiconductor layer 216 in layered structure 210. One result is that layered structure 210 remains planar.
[0031] In some implementations, tuning the porous layer includes inducing a bow. In such implementations, inducing the bow may include oxidizing the porous layer (e.g., to form oxidized porous layer 214). In some implementations, tuning the porous layer includes tuning the porosity and/or thickness of the porous layer. The porous layer may be tuned to counterbalance a portion of the expected stress from a deposited layer to be deposited later.
In some cases, the porous layer may be tuned to counterbalance most of the expected stress. By counterbalancing expected stress, the layered structure can be designed to have some preferred properties that are dependent on net stress. In some implementations, tuning the porous layer to induce the bow causes a curvature to the starting material (e.g., starting material 202) to oppose an expected curvature from a subsequently deposited layer. By tuning the induced bow to have curvature opposing that of epitaxial semiconductor layer 216, layered structure 210 can be formed with zero net stress following deposition of epitaxial layer 216. In some implementations, the tunable porous layer maintains a crystalline structure. The crystalline structure may enable subsequent growth of an epitaxial. For example, oxidized porous layer 214 has a crystalline structure to support epitaxial layer 216 in layered structure 210. In some implementations, the starting material and the tunable porous layer share the same elemental composition (e.g., a Group IV element). For example, starting material 202 and oxidized porous layer 214 may both include or be substantially made of Si.
[0032] In some implementations, the deposited layer, over the porous layer, includes a material that is thermally dissimilar to the starting material. For example, epitaxial layer 216 grown over tunable porous layer 214 may have a thermal coefficient of expansion different from starting material 202. In this example, the different rates of thermal expansion may cause nonzero net stress to layered structure 210 when forming epitaxial layer 216 at a high temperature. The nonzero net stress may curve layered structure. The porous layer can be tuned to balance stress that results, or is expected to result, from deposition of a layer over the porous layer. For example, the induced bow from oxidized porous layer 214 may be tuned to compensate for the stress resulting from differing thermal expansion due to epitaxial layer 216 having a material that is thermally dissimilar to starting material 202.
[0033] In some implementations, the porous layer is tuned to set the net stress in the layered structure. As previously noted, the porous layer may be tuned before deposition of a layer over the porous layer. Additionally or alternatively, the porous layer may be tuned when forming a layer over the oxidized porous layer. In some implementations, an induced bow from tuning the porous layer is used to modify characteristics of the deposited layer over the tunable porous layer. For example, stress during lithographic patterning over the porous layer may cause a modification to layer properties in the layered structure, such as moving the layer surface out of focus. In this example, tuning of the porous layer may help maintain preferred properties of the layer surface for the lithographic process, such as maintaining the focus on the layer surface.
[0034] FIGS. 3 and 4 show examples of layered structures 300 and 400 made from specific materials, in accordance with some implementations of the present disclosure. Layered structure 300 has Si substrate 302, oxidized porous Si layer 304 over substrate 302, and gallium nitride (GaN) layer 306 over oxidized porous Si layer 304. Layered structure 400 has Si substrate 402, oxidized porous Si layer 404 over substrate 402, and scandium aluminum nitride (ScAIN) layer 406 over oxidized porous Si layer 404. Semiconductor layers 306 and 406 may have been formed using any suitable technique (e.g., chemical vapor deposition). In some implementations, one or more intermediate layers may be formed over the tunable porous layer before deposition of a semiconductor layer over the porous layer. For example, an interlayer may be formed over porous Si layer 404 to improve support for deposition of Sc AIN layer 406.
[0035] In some implementations, the porous layer is tuned to balance the net stress of the layered structure that results from forming a layer over the tunable porous layer. For example, porous layers 304 and 404 may have been tuned differently to support their respective semiconductor layers 306 and 406. Tuning the porous layer may enable epitaxial deposition of thermally dissimilar materials. For example, GaN and Si have different thermal coefficients of expansion. Epitaxial deposition of GaN layer 306 at high temperature may result in a curvature to Si substrate 302 at room temperature. Oxidized porous Si layer 304 may be tuned by adjusting porosity and/or thickness. For example, layer 304 may have been tuned to have 15 pm thickness and 20% porosity to balance net stress in layered structure 300 and keep the surface of GaN layer 306 planar at room temperature. The porous layer may be further tuned to compensate stress resulting from subsequent semiconductor device processing.
[0036] FIG. 5 shows plots 500 and 510 comparing curvature resulting from a tunable porous layer with varying porosities, thicknesses, and oxidation, in accordance with some implementations of the present disclosure. Plot 500 shows curvature of a bow in a porous layer at 20% porosity and varying layer thickness and oxidation. Curve 502 shows a trend of the bow curvature for an oxidized porous layer as compared to an unoxidized porous layer having same porosity and thickness. Plot 510 shows curvature of a bow in a porous layer at 30% porosity and varying layer thickness and oxidation. Curve 512 shows a trend of the bow curvature for an oxidized porous layer as compared to an unoxidized porous layer having same porosity and thickness. In particular, curvature of the oxidized porous layer (e.g., curves 502 and 512) is greater than the unoxidized porous layer with the same porosity and thickness. FIG. 5 shows measurable induced bows in both an unoxidized and oxidized porous layer, but the induced bow of an oxidized porous layer has improved tunable characteristics suitable for controlling stress in a layered structure.
[0037] FIG. 6 is a flow diagram of a process 600 for controlling stress in a layered structure, in accordance with some implementations of the present disclosure. Process 600 starts from 602. At 602, a porous layer is formed having tunable porosity and thickness over a starting material. For example, porous layer 204 is formed over starting material 202. At 604, the porous layer is oxidized. At 606, a bow is induced by oxidation of the porous layer.
[0038] At 608, a layer is formed over the oxidized porous layer using epitaxy or other suitable technique. At 610, the induced bow in the starting material is tuned to set the net stress in the layered structure by varying the porosity and/or thickness of the oxidized porous layer. Some non-limiting example results from process 700 may include layered structures 100-300. For example, semiconductor layer 216 is epitaxially grown over oxidized porous layer 214. In this example, the induced bow is tuned to balance the net stress, maintaining flat semiconductor layer 216. Porous layer 214 may have been tuned to modify other properties of layer 216 in this example. Alternatively at 604-606, the unoxidized porous layer may be tuned to modify layer properties for expected deposition at 608.
[0039] The growth and/or deposition described herein may be performed using one or more of chemical vapor deposition (CVD), metalorganic chemical vapor deposition (MOCVD), organometallic vapor phase epitaxy (OMVPE), atomic layer deposition (ALD), molecular beam epitaxy (MBE), halide vapor phase epitaxy (HVPE), pulsed laser deposition (PLD), and/or physical vapor deposition (PVD). [0040] As described herein, a layer means a substantially uniform thickness of a material covering a surface. A layer can be either continuous or discontinuous (i.e., having gaps between regions of the material). For example, a layer can completely or partially cover a surface, or be segmented into discrete regions, which collectively define the layer (i.e., regions formed using selective- area epitaxy).
[0041] Monolithically-integrated means formed on the surface of the substrate, typically by depositing layers disposed on the surface.
[0042] Disposed on means "exists on" or "over" an underlying material or layer. This layer may include intermediate layers, such as transitional layers, necessary to ensure a suitable surface. For example, if a material is described to be "disposed on" or "over a substrate," this can mean either (1) the material is in intimate contact with the substrate; or (2) the material is in contact with one or more transitional layers that reside on the substrate.
[0043] Single-crystal means a crystalline structure that comprises substantially only one type of unit-cell. A single-crystal layer, however, may exhibit some crystalline defects such as stacking faults, dislocations, or other commonly occurring crystalline defects.
[0044] Single-domain means a crystalline structure that comprises substantially only one structure of unit-cell and substantially only one orientation of that unit cell. In other words, a single-domain crystal exhibits no twinning or anti-phase domains.
[0045] Single-phase means a crystalline structure that is both single-crystal and single domain.
[0046] Substrate means the material on which deposited layers are formed. Exemplary substrates include, without limitation: bulk gallium nitride wafers, bulk silicon carbide wafers, bulk sapphire wafers, bulk germanium wafers, bulk silicon wafers, in which a wafer comprises a homogeneous thickness of single-crystal material; composite wafers, such as a silicon-on-insulator wafer that comprises a layer of silicon that is disposed on a layer of silicon dioxide that is disposed on a bulk silicon handle wafer; or the porous germanium, germanium over oxide and silicon, germanium over silicon, patterned germanium, germanium tin over germanium, and/or the like; or any other material that serves as base layer upon which, or in which, devices are formed. Examples of such other materials that are suitable, as a function of the application, for use as substrate layers and bulk substrates include, without limitation, alumina, gallium-arsenide, indium-phosphide, silica, silicon dioxide, borosilicate glass, and pyrex. A substrate may have a single bulk wafer, or multiple sub-layers. Specifically, a substrate (e.g., silicon, germanium, etc.) may include multiple non-continuous porous portions. The multiple non-continuous porous portions may have different densities and may be horizontally distributed or vertically layered.
[0047] Semiconductor refers to any solid substance that has a conductivity between that of an insulator and that of most metals. An example semiconductor layer is composed of silicon. The semiconductor layer may include a single bulk wafer, or multiple sub-layers. Specifically, a silicon semiconductor layer may include multiple non-continuous porous portions. The multiple non-continuous porous portions may have different densities and may be horizontally distributed or vertically layered.
[0048] A first layer described and/or depicted herein as "configured on," "on," "formed over," or "over" a second layer can be immediately adjacent to the second layer, or one or more intervening layers can be between the first and second layers. A first layer that is described and/or depicted herein as "directly on" or "directly over" a second layer or a substrate is immediately adjacent to the second layer or substrate with no intervening layer present, other than possibly an intervening alloy layer that may form due to mixing of the first layer with the second layer or substrate. In addition, a first layer that is described and/or depicted herein as being "on," "over," "directly on," or "directly over" a second layer or substrate may cover the entire second layer or substrate, or a portion of the second layer or substrate.
[0049] A substrate is placed on a substrate holder during layer growth, and so a top surface or an upper surface is the surface of the substrate or layer furthest from the substrate holder, while a bottom surface or a lower surface is the surface of the substrate or layer nearest to the substrate holder. Any of the structures depicted and described herein can be part of larger structures with additional layers above and/or below those depicted. For clarity, the figures herein can omit these additional layers, although these additional layers can be part of the structures disclosed. In addition, the structures depicted can be repeated in units, even if this repetition is not depicted in the figures.
[0050] From the above description it is manifest that various techniques may be used for implementing the concepts described herein without departing from the scope of the disclosure. The described implementations are to be considered in all respects as illustrative and not restrictive. It should also be understood that the techniques and structures described herein are not limited to the particular examples described herein, but can be implemented in other examples without departing from the scope of the disclosure. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

Claims

What is Claimed is:
1. A method of controlling stress in a layered structure, the method comprising:
forming a porous layer having tunable porosity and thickness over a starting material;
inducing a bow in the starting material, wherein the inducing the bow comprises oxidizing the porous layer; and
tuning the induced bow in the starting material to set net stress in the layered structure that results from an epitaxial layer grown over the oxidized porous layer, wherein the tuning the induced bow comprises tuning at least one of the porosity or the thickness of the oxidized porous layer.
2. The method of claim 1, wherein the tuning the induced bow comprises setting the net stress to modify characteristics of the epitaxial layer grown over the oxidized porous layer.
3. The method of claim 1, wherein the inducing the bow comprises inducing a first curvature opposite to a second curvature that results from the epitaxial layer formed over the oxidized porous layer.
4. The method of claim 1, wherein the tuning the induced bow to set the net stress comprises compensating stress that results from the starting material and the epitaxial layer having different thermal coefficients of expansion.
5. The method of claim 1, wherein the oxidizing the porous layer comprises maintaining a crystalline structure in the oxidized porous layer.
6. The method of claim 1, wherein the forming the porous layer over the starting material comprises forming the porous layer from the starting material.
7. A layered structure having controllable stress comprising:
a starting material;
an oxidized porous layer over the starting material, wherein a porosity and a thickness of the oxidized porous layer are tunable, and wherein the oxidized porous layer induces a bow in the starting material; and an epitaxial layer over the oxidized porous layer, wherein the induced bow is tuned by tuning at least one of the porosity or the thickness of the oxidized porous layer to set net stress in the layered structure that results from the epitaxial layer grown over the oxidized porous layer.
8. The structure of claim 7, wherein the induced bow is tuned to set the net stress to modify characteristics of the epitaxial layer over the oxidized porous layer.
9. The structure of claim 7, wherein the induced bow has a first curvature opposite to a second curvature that results from the epitaxial layer over the oxidized porous layer.
10. The structure of claim 7, wherein the starting material and the epitaxial layer have different thermal coefficients of expansion.
11. The structure of claim 7, wherein the oxidized porous layer maintains a crystalline structure.
12. The structure of claim 7, wherein the epitaxial layer comprises Ga.
13. The structure of claim 7, wherein the epitaxial layer comprises an alloy of a rare earth and aluminum nitride (AIN).
14. The structure of claim 13, wherein the rare earth is Sc.
15. The structure of claim 7, wherein the starting material and the oxidized porous layer comprise the same Group IV element.
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