Strained semiconductor materials, devices and methods therefore

Various applications are directed to a material stack having a strained active material therein. In connection with an embodiment, an active material (e.g. a semiconductor material) is at least initially and partially released from and suspended over a substrate, strained, and held in place. The release and suspension facilitates the application of strain to the semiconductor material.

FIELD OF THE INVENTION

The present invention relates generally to semiconductors, and more particularly to semiconductor devices involving strained semiconductor materials.

BACKGROUND OF THE INVENTION

A variety of electronic and optoelectronic fields and related devices use semiconductor materials to suit a variety of purposes. In many implementations, the properties of various materials used to make these devices are selected or otherwise tailored to suit specific applications.

One of many representative semiconductor fields that have been of significant interest in recent times is the field of optoelectronics. The field of optoelectronics includes those materials, structures, devices, circuits, and systems that have properties appropriate for facilitating optical-electrical energy and signal conversion, transmission, modulation, and detection. Most optoelectronic devices in production today use III-V materials to achieve high performance. However, in light of a number of drawbacks concerning III-Vs, including process/fabrication complexity, high material costs, and incompatibility with silicon (Si), among others, some researchers have begun exploring alternatives to these traditional approaches to optoelectronics problems.

Photodetectors, for example, are optoelectronic devices that convert optical signals into electrical signals. At a general level, a photodetector is at least partially comprised of a light-absorption medium that is in electrical contact with a set of electrodes. Light energy is absorbed in the medium by excitation of electrons from valence bands into conduction bands, while current is generated via the transport of these excited charge carriers to the electrodes and through an external circuit. In the case of light emission, light-emitting diodes (LEDs) and lasers are the optoelectronic counterparts to photodetectors, converting electrical energy into optical energy. At a general level, these light emitting devices are also at least partially comprised of an optically active medium, which may include a multiplicity of several materials with different characteristics, in electrical contact with sets of electrodes. In these types of devices, electrical energy is passed through the optical medium by the application of a potential difference via the electrodes. While current flows through the medium, some of the associated charge carriers recombine with each other as electrons drop from the conduction bands back to the valence bands. For radiative recombination events, the energy associated with these transitions is emitted in the form of light via photons. As a third category of optoelectronic devices, modulators modify light, converting electrical signals into optical signals. Generally, these types of devices are also at least partially comprised of an optically active medium, which may include a multiplicity of several materials with different characteristics, in electrical contact with sets of electrodes. The application of a potential difference across the optical medium via the electrodes changes its optical properties, modulating the properties of a beam of light passing through it.

Photodetectors, lasers, and modulators are some of the key components in optical communications systems and often operate at a wavelength range that is inclusive of about 1300 nm-1600 nm (i.e. they interact with light energy relatively efficiently at these wavelengths for these particular applications). For telecommunications, certain standards are defined around 1550 nm, where the 1528-1560 nm range is referred to as the “C-Band” and the 1561-1620 nm range is known as the “L-Band.”

Many commercially available optoelectronic devices, such as the photodetectors, LEDs, lasers, and modulators described above, use type III-V materials such as GaAs, InGaAs, and GaN, which have the subset of disadvantages mentioned previously. For the particular examples here of photodetection, emission, and modulation, germanium (Ge) has attractive properties and is a promising silicon-compatible alternative as an optically active medium.

Unlike the III-V materials and their associated drawbacks, germanium does not undermine the performance of other devices that are built on a shared silicon-compatible platform. Therefore, silicon-compatible substrates can be used in a system that integrates other silicon-compatible electronic and/or optoelectronic devices and germanium-based optoelectronics, for example. Moreover, germanium fabrication and processing technologies are very similar to those used in traditional silicon manufacturing, reducing fabrication costs and complexity significantly compared to the III-Vs.

However, while bulk germanium may represent an attractive alternative to III-V materials for applications at the lower wavelength range, it suffers from limitations at wavelengths larger than about 1500 nm. In particular, bulk germanium has an absorption coefficient at 1550 nm that is about 1/20th the absorption coefficients of some III-V materials (e.g. InGaAs), requiring a relatively thick germanium layer for comparable photodetection at this wavelength and resulting in low operating speeds. In terms of light emission, germanium's optical output is especially weak due to several competing phenomena. This less-than-optimal optoelectronic performance is directly related to the band structure of bulk germanium.

For the case of photodetection, when light is absorbed by a material, its energy is used to lift electrons above an energetic bandgap between the valence and conduction bands to higher-energy states. Thus, to first-order, if the incident light energy does not exceed the energy of the bandgap, the light cannot be absorbed and it passes through the medium undetected. In germanium, there are two particularly relevant bandgaps: the indirect L and the direct gamma. The indirect L bandgap is about 0.667 eV in energy, while the direct gamma bandgap represents an energy barrier of about 0.8 eV. In terms of light wavelength, these energies correspond to about 1860 nm and about 1550 nm, respectively.

Unfortunately, germanium cannot efficiently absorb light energy at the band edges for several reasons. Absorption leading to excitation above the indirect bandgap requires the co-action of a phonon-related momentum transfer along with the photon-related energy gain. The simultaneous occurrence of these two events at the right energy and momentum is relatively rare, resulting in small absorption coefficients for indirect gap transitions. For direct bandgap transitions at the germanium gamma point, the low density of available charge states near the conduction band edge limits the number of carriers that can be excited just above the direct gap. The density of such states increases beyond the band edge, but transitions to these states require higher-energy (smaller wavelength) photons. Photon absorptions and carrier excitations occur preferentially at the direct bandgap due to momentum conservation. Phonon-assisted momentum transfers are not necessary for such transitions.

In terms of light emission, the germanium band structure poses a more fundamental problem. The energy offset between the L and gamma bands and their relative difference in densities of states lead to preferential carrier occupation of the L valley and significantly stronger phonon-assisted non-radiative (rather than radiative) recombination. As a result, charge carriers that are injected into bulk germanium (e.g. via an applied potential difference) occupy the lower-energy L-valley states and can drop down to the valence band primarily only by recombining non-radiatively. Thus, it is very difficult to make bulk germanium emit light without injecting an inordinately large amount of charge carriers. Such high levels of carrier injection are impractical, requiring very high applied voltages and/or very low operating temperatures.

Applying different types of tensile strain to germanium alters its band structure, in part by reducing the direct bandgap relative to the indirect bandgap, thereby increasing the relative density of available states in the direct gamma valley and improving photon absorption and emission. In particular, reducing the direct bandgap via strain (e.g. biaxial tensile strain) can expand the useful range of light absorption and emission achievable by germanium-based photodetectors and emitters to include the L and C telecommunication bands, as well as the longer wavelengths. For instance, applying around 0.2% biaxial tensile strain to germanium increases its absorption coefficient at 1550 nm by about 7.5 times, compared to unstrained germanium.

However, approaches to applying tensile strain to germanium in a silicon-compatible manner have fallen far short of the levels desired, involved material configurations that introduce drawbacks for final device performance and capabilities, and/or have involved complex fabrication processes that require particularly tight controls. As a result of these complications and relative to telecommunications, for example, a large portion of the optical communications spectrum has been left relatively unsupported by germanium.

These and other matters have presented challenges to the design, manufacture and implementation of semiconductor devices, and in particular, of silicon-compatible devices such as those used in optoelectronics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide new and improved semiconductor devices and their methods of manufacture.

A further object of the present invention is to provide new and improved semiconductor devices such as those used in electronics and/or optoelectronics and their methods of manufacture.

A further object of the present invention is to provide new and improved silicon-compatible semiconductor devices and their methods of manufacture.

A further object of the present invention is to provide new and improved silicon-compatible semiconductor devices such as those used in electronics and/or optoelectronics and their methods of manufacture.

A further object of the present invention is to provide semiconductor devices that include materials with highly-tunable strains and their methods of manufacture.

A further object of the present invention is to provide semiconductor devices that include materials with highly-tunable strains and are used in electronics and/or optoelectronics and their methods of manufacture.

A further object of the present invention is to provide silicon-compatible semiconductor devices that include materials with highly-tunable strains and their methods of manufacture.

A further object of the present invention is to provide silicon-compatible semiconductor devices that include materials with highly-tunable strains and are used in electronics and/or optoelectronics and their methods of manufacture.

A further object of the present invention is to provide semiconductor devices with engineered electronic and/or optoelectronic characteristics and their methods of manufacture.

A further object of the present invention is to provide silicon-compatible semiconductor devices with engineered electronic and/or optoelectronic characteristics and their methods of manufacture.

These and other objects of the present invention are achieved in a semiconductor device that includes a substrate, an active material, materials configured and arranged to induce a strain in the active material, materials configured and arranged to mitigate relaxation of the strain induced in the active material, and a support structure that suspends the active material over a portion of the substrate.

The present invention is exemplified in a number of implementations and applications, only some of which are summarized below.

According to one aspect, the present invention is directed to an active material including a semiconductor material, such as germanium, that is partially released from at least part of the underlying materials and/or substrate and strained by an adjacent material or related process. The release is used to set or otherwise control the application of strain, such as by controlling the active material's amenability to strain and to maintaining the strain.

According to another example embodiment, a semiconductor device includes a substrate, a material stack, and a support structure to support the released material stack over a portion of the substrate. The material stack includes a first material over the substrate, an active material on the first material, and a second material on the active material. At least one of the first and second materials is configured and arranged to induce a strain in the active material, and at least one of the first and second materials is configured and arranged to mitigate relaxation of the strain induced in the active material.

Other embodiments are exemplified in the figures, including those in the Appendix, which forms part of this patent document.

The above summary of the present invention is not intended to describe each illustrated embodiment or every other possible implementation of the present invention. The figures and detailed description that follow more particularly exemplify only certain embodiments.

While the present invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not necessarily to limit the invention to the particular example embodiments described and claimed. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

DETAILED DESCRIPTION OF THE INVENTION AND DRAWINGS

The present invention is believed to be useful for a variety of different applications involving semiconductors, and the invention has been found to be particularly suited for semiconductor devices having strained active materials. While the present invention is not necessarily limited to such applications, various aspects of the invention may be appreciated through a discussion of several examples within this context.

The present invention can be utilized with a variety of different active materials with strained or straining active material-based layers and active materials that need not be in a layer structure, and further in connection with electronic and optoelectronic devices. The active material can actually include of a number of different materials grown on top of each other (e.g. several epilayers) or other materials arranged horizontally but in physical contact, or any of a variety of other material types, number, and configuration. By way of illustration, and without limitation, for a particular example laser configuration, including but not limited to, edge-emitter, VCSEL, and the like, SiGe, SiGeSn, or SiGeC quantum wells, or even the traditional III-V materials, can be deposited, and then the entire material stack can be strained after all the materials are formed.

As a non-limiting example, the active materials can be selected from one or more of, materials and film types including but not limited to, Si, Ge, SiGe, SiGeSn, SiGeC, III-V materials, graphene, nanotubes, nanowires, metals, and others. Applying strain to a material alters its band structure and electronic/optoelectronic properties. This opens up an entirely new space for devices across a variety of applications, not merely silicon-compatible optoelectronics.

However, these embodiments are exemplary and may be implemented in connection with different numbers and types of materials and with different types of devices. For instance, a silicon-based material or other semiconductor material may be used in place of the discussed active material. The materials, layers, and other structures discussed as implemented with optoelectronic devices may be implemented with a variety of other devices, such as transistors, thyristors, memory devices and others.

According to an example embodiment, an active material is used as part of an optoelectronic structure, with another material that strains the active material under conditions involving at least a partial suspension of the active material. The strained active material is held in a strained state. This approach is amenable to implementation with, for example, optical photodetectors, LEDs, lasers, modulators, and photonic crystals, as well as a wide variety of other devices and systems (including improvements to current ones).

In many implementations, the active material is suspended in a manner that avoids and/or removes a force-energy balance between a suspended portion of the active material and an underlying material. The material used to strain the active material has an internal stress that is transferred to the suspended active material due to a modified force-energy balance therebetween, altering the active material's band structure to adjust its electronic and/or optoelectronic properties. This stress transfer is particularly effective due to the suspended nature of at least part of the active material, in that the strain transfer and concomitant band structure alteration is not inhibited by physical contact between the suspended portion of the active material and at least one of the underlying materials.

The composition, dimensions (e.g. thickness), internal strain state, shape, or other geometrical arrangement of the suspended active material, the materials applying stress and/or other materials underlying or adjacent to the suspended material are used to set strain characteristics of the active material to suit particular applications. For instance, relatively large changes in atomic spacing can be achieved with a relatively thin active material (i.e. to induce high stress and/or strain).

In some implementations, a suspended region of the active material is sandwiched between two other materials to form a material stack that is supported at its ends and/or edges by an underlying substrate. The materials sandwiching the active material respectively apply strain to the active material, altering its band structure.

In some embodiments, the active material is formed on a substrate and subsequently suspended by removing a portion of the underlying substrate or materials, yet leaving some of the underlying materials or substrate in contact with at least part of the suspended active material to limit the amount of stress or strain applicable thereto, and to keep the structure intact and connected to the substrate. One such implementation involves using an active material-on-insulator (e.g. germanium-on-insulator (GOI) stack, in which an active material layer is formed on an insulator layer, and in which a portion of the material stack is suspended. In one of several process variations, another material layer, such as an insulator, is formed on top of the active material-on-insulator stack to induce strain in the active material layer. A region of an underlying substrate (e.g. silicon) is removed up to the bottom insulator to release the material stack, from the backside and/or from the topside in a certain pattern and using certain chemistries to etch under the region of interest. Removal of the substrate underneath the active material stack results in a thinner total material stack in the region of interest, to balance internal stresses of the insulators by much larger stresses in the active material than could have been achieved, absent the suspension (i.e. the active material will experience significant strain and a considerable alteration of its band structure).

In certain implementations, a portion of the substrate underlying the active material-on-insulator stack is left intact below the suspended material stack to set characteristics of the device. In other implementations, a portion of the insulator underlying the active material is removed as well, to similarly set characteristics of the device and of the active material. These approaches are readily implemented for a variety of different applications, to set or otherwise tune characteristics of the active material related to stress or strain therein and/or to tune or set device characteristics.

Turning now to the figures,FIG. 1depicts a cross-section of an active material-based structure010having a strained active material012vertically adjacent to an overlying material013and an underlying substrate011, a portion of which014is removed to a depth within the underlying substrate011under an area of the active material012, according to an example embodiment of the present invention.

To facilitate the application of strain to the active material012, a portion of the underlying substrate011is removed to expose a region014, over which the active material012is suspended. As discussed above, the amount of the underlying substrate011removed below the active material012is based upon desired characteristics of the active material012and device/application considerations. Accordingly, dashed line015defines a region of the underlying substrate011that is left intact below the active material012, as representing an exemplary approach to removing less than all of the substrate011underlying the suspended portion of the active material012. Further, the amount of the underlying substrate011removed below the active material012to a depth within the underlying substrate011may also be determined by other desired material and device characteristics, which may include structural integrity of the remaining underlying substrate011, device integration schemes, and others.

The overlying material013may include one or more of a variety of materials, which can be implemented to strain the active material012and/or to hold the active material012in a strained state. In some implementations, the overlying material013may be used to strain the active material012, with the underlying substrate011used to hold the active material012in place. In other implementations, the underlying substrate011may be used to strain the active material012, with the overlying material013used to hold the active material012in place. In still other implementations, both the overlying material013and the underlying substrate011may be used to both strain the active material012and hold the active material012in place. In still other implementations, other processing steps, such as thermal treatments, mechanical bending, and others, may be used to strain the active material012, with the overlying material013and/or the underlying substrate011used to hold the active material012in place.

The specific fabrication process for the structure010can be carried out in one or more of a variety of manners, depending upon the desired material and device characteristics. In some embodiments, an initial active material-on-substrate stack (represented by012and011) can be released from the underlying substrate011(e.g. as shown at region014with the region represented by dashed line015intact), followed by the formation of an overlying stressed material (represented by013). In other embodiments, an overlying stressed material (represented by013) is formed first, with the material stack released from the underlying substrate011afterwards. Different approaches to the final strained material stack may be useful for different embodiments.

In other example embodiments, the structure010is integrated with electronics and/or optoelectronics to facilitate the fabrication of electronic and/or optoelectronic devices, circuits, and systems in any of a variety of integration schemes. Optoelectronic devices with which the structure010may be used include, for example and without limitation, photodetectors, telecommunications devices, modulators, light-emitting diodes (LEDs), on-chip optical interconnects, lasers, quantum well modulators, waveguide lasers/modulators, photonic crystals and active material-based optoelectronics operating in the L and C telecommunications bands and at other wavelengths.

Other devices with which the structure010may be used in a variety of embodiments include devices that do not necessarily involve optoelectronics, such as transistor devices, memory devices, and others, with the application of strain used to set various properties of the active material012. For instance, strain may be used to set charge carrier mobility, ON current, operating speed, and other electronic characteristics of transistors that include strained active materials (represented by012).

Additionally, in some embodiments, the area of the removed portion014of the underlying substrate011is left as-is (i.e. empty as free space) after the portion014is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 2depicts a cross-section of an active material-based structure020, similar to that shown inFIG. 1, having a strained active material022vertically adjacent to an overlying material023and an underlying substrate021, a portion of which024is removed to the bottom of the underlying substrate021under an area of the active material022, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material022, a portion of the underlying substrate021is removed to expose a region024, over which the active material022is suspended. The amount of the underlying substrate021removed below the active material022is based upon desired characteristics of the active material022and device/application considerations. Accordingly, dashed line025defines a region of the underlying substrate021that is left intact below the active material022, as representing an exemplary approach to removing less than all of the substrate021underlying the suspended portion of the active material022.

As discussed above, in some embodiments, the structure020is integrated with electronics and/or optoelectronics to facilitate the fabrication of electronic and/or optoelectronic devices, circuits, and systems in any of a variety of integration schemes. In the structure020, removal of a portion024of the underlying substrate021to the bottom of the underlying substrate021also facilitates integration with backside electronics and/or optoelectronics. Backside electronic and/or optoelectronic access to the active material022is made possible via the backside at024to permit different device, circuit, and system integration schemes. In some embodiments, the structure020may be used for applications involving wafer stacking (e.g. 3D integrated circuits), where electronic and/or optoelectronic access to the backside of the active material022is desired.

Additionally, as discussed above, in some embodiments, the area of the removed portion024of the underlying substrate021is left as-is (i.e. empty as free space) after the portion024is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 3depicts a cross-section of an active material-based structure030having a strained active material033horizontally adjacent to other materials032and vertically adjacent to an underlying substrate031, a portion of which034is removed to a depth within the underlying substrate031under an area of the active material033, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material033, a portion of the underlying substrate031is removed to expose a region034, over which the active material033is suspended. The amount of the underlying substrate031removed below the active material033is based upon desired characteristics of the active material033and device/application considerations. Accordingly, dashed line035defines a region of the underlying substrate031that is left intact below the active material033, as representing an exemplary approach to removing less than all of the substrate031underlying the suspended portion of the active material033. Further, the amount of the underlying substrate031removed below the active material033to a depth within the underlying substrate031may also be determined by other desired material and device characteristics, which may include structural integrity of the remaining underlying substrate031, device integration schemes, and others.

The horizontally adjacent materials032may include one or more of a variety of materials, which can be implemented to strain the active material033and/or to hold the active material033in a strained state. In some implementations, the horizontally adjacent materials032may be used to strain the active material033, with the underlying substrate031used to hold the active material033in place. In other implementations, the underlying substrate031may be used to strain the active material033, with the horizontally adjacent materials032used to hold the active material033in place. In still other implementations, both the horizontally adjacent materials032and the underlying substrate031may be used to both strain the active material033and hold the active material033in place. In still other implementations, other processing steps, such as thermal treatments, mechanical bending, and others, may be used to strain the active material033, with the horizontally adjacent materials032and/or the underlying substrate031used to hold the active material033in place.

The specific fabrication process for the structure030can be carried out in one or more of a variety of manners, depending upon the desired material and device characteristics. In some embodiments, an initial active material-on-substrate stack (represented by033and031) can be partially released from the underlying substrate031(e.g. as shown at region034with the region represented by dashed line035intact), followed by the formation of horizontally adjacent stressed materials (represented by032). In other embodiments, horizontally adjacent stressed materials (represented by032) are formed first, with the material stack released from the underlying substrate031afterwards. Different approaches to the final strained material stack may be useful for different embodiments.

Additionally, as discussed above, in some embodiments, the area of the removed portion034of the underlying substrate031is left as-is (i.e. empty as free space) after the portion034is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 4depicts a cross-section of an active material-based structure040, similar to that shown inFIG. 3, having a strained active material043horizontally adjacent to other materials042and vertically adjacent to an underlying substrate041, a portion of which044is removed to the bottom of the underlying substrate041under an area of the active material043, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material043, a portion of the underlying substrate041is removed to expose a region044, over which the active material043is suspended. The amount of the underlying substrate041removed below the active material043is based upon desired characteristics of the active material043and device/application considerations. Accordingly, dashed line045defines a region of the underlying substrate041that is left intact below the active material043, as representing an exemplary approach to removing less than all of the substrate041underlying the suspended portion of the active material043.

Additionally, as discussed above, in some embodiments, the area of the removed portion044of the underlying substrate041is left as-is (i.e. empty as free space) after the portion044is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 5depicts a cross-section of an active material-based structure050having a strained active material053vertically adjacent to an overlying material054and an underlying material052over an underlying substrate051, a portion of which055is removed to a depth within the underlying substrate051under an area of the active material053, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material053, a portion of the underlying substrate051is removed to expose a region055, over which the active material053is suspended. The amount of the underlying substrate051removed below the active material053is based upon desired characteristics of the active material053and device/application considerations. Accordingly, dashed line056defines a region of the underlying substrate051that is left intact below the underlying material052, as representing an exemplary approach to removing less than all of the substrate051underlying the suspended portion of the active material053. Further, the amount of the underlying substrate051removed below the active material053to a depth within the underlying substrate051may also be determined by other desired material and device characteristics, which may include structural integrity of the remaining underlying substrate051, device integration schemes, and others.

The respective materials054and052may include one or more of a variety of materials, which can be implemented to strain the active material053and/or to hold the active material053in a strained state. In some implementations, the overlying material054may be used to strain the active material053, with the underlying material052used to hold the active material053in place. In other implementations, the underlying material052may be used to strain the active material053, with the overlying material054used to hold the active material053in place. In still other implementations, both the overlying material054and the underlying material052may be used to both strain the active material053and hold the active material053in place. In still other implementations, other processing steps, such as thermal treatments, mechanical bending, and others, may be used to strain the active material053, with the overlying material054and/or the underlying material052used to hold the active material053in place.

The specific fabrication process for the structure050can be carried out in one or more of a variety of manners, depending upon the desired material and device characteristics. In some embodiments, an initial active material-on-insulator stack (represented by053,052, and051) can be released from the underlying substrate051(e.g. as shown at region055), followed by the formation of an overlying stressed material (represented by054). In other embodiments, an overlying stressed material (represented by054) is formed first, with the material stack released from the underlying substrate051afterwards. Different approaches to the final strained material stack may be useful for different embodiments.

Additionally, as discussed above, in some embodiments, the area of the removed portion055of the underlying substrate051is left as-is (i.e. empty as free space) after the portion055is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 6depicts a cross-section of an active material-based structure060, similar to that shown inFIG. 5, having a strained active material063vertically adjacent to an overlying material064and an underlying material062over an underlying substrate061, a portion of which065is removed to the bottom of the underlying substrate061under an area of the active material063, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material063, a portion of the underlying substrate061is removed to expose a region065, over which the active material063is suspended. The amount of the underlying substrate061removed below the active material063is based upon desired characteristics of the active material063and device/application considerations. Accordingly, dashed line066defines a region of the underlying substrate061that is left intact below the underlying material062, as representing an exemplary approach to removing less than all of the substrate061underlying the suspended portion of the active material063.

Additionally, as discussed above, in some embodiments, the area of the removed portion065of the underlying substrate061is left as-is (i.e. empty as free space) after the portion065is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 7depicts a cross-section of an active material-based structure070having a strained active material074horizontally adjacent to other materials073and vertically adjacent to an underlying material072over an underlying substrate071, a portion of which075is removed to a depth within the underlying substrate071under an area of the active material074, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material074, a portion of the underlying substrate071is removed to expose a region075, over which the active material074is suspended. The amount of the underlying substrate071removed below the active material074is based upon desired characteristics of the active material074and device/application considerations. Accordingly, dashed line076defines a region of the underlying substrate071that is left intact below the underlying material072, as representing an exemplary approach to removing less than all of the substrate071underlying the suspended portion of the active material074. Further, the amount of the underlying substrate071removed below the active material074to a depth within the underlying substrate071may also be determined by other desired material and device characteristics, which may include structural integrity of the remaining underlying substrate071, device integration schemes, and others.

The respective materials073and072may include one or more of a variety of materials, which can be implemented to strain the active material074and/or to hold the active material074in a strained state. In some implementations, the horizontally adjacent materials073may be used to strain the active material074, with the underlying material072used to hold the active material074in place. In other implementations, the underlying material072may be used to strain the active material074, with the horizontally adjacent materials073used to hold the active material074in place. In still other implementations, both the horizontally adjacent materials073and the underlying material072may be used to both strain the active material074and hold the active material074in place. In still other implementations, other processing steps, such as thermal treatments, mechanical bending, and others, may be used to strain the active material074, with the horizontally adjacent materials073and/or the underlying material072used to hold the active material074in place.

The specific fabrication process for the structure070can be carried out in one or more of a variety of manners, depending upon the desired material and device characteristics. In some embodiments, an initial active material-on-insulator stack (represented by074,072, and071) can be released from the underlying substrate071(e.g. as shown at region075), followed by the formation of horizontally adjacent stressed materials (represented by073). In other embodiments, horizontally adjacent stressed materials (represented by073) are formed first, with the material stack released from the underlying substrate071afterwards. Different approaches to the final strained material stack may be useful for different embodiments.

Additionally, as discussed above, in some embodiments, the area of the removed portion075of the underlying substrate071is left as-is (i.e. empty as free space) after the portion075is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 8depicts a cross-section of an active material-based structure080, similar to that shown inFIG. 7, having a strained active material084horizontally adjacent to other materials083and vertically adjacent to an underlying material082over an underlying substrate081, a portion of which085is removed to the bottom of the underlying substrate081under an area of the active material084, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material084, a portion of the underlying substrate081is removed to expose a region085, over which the active material084is suspended. The amount of the underlying substrate081removed below the active material084is based upon desired characteristics of the active material084and device/application considerations. Accordingly, dashed line086defines a region of the underlying substrate081that is left intact below the underlying material082, as representing an exemplary approach to removing less than all of the substrate081underlying the suspended portion of the active material084.

Additionally, as discussed above, in some embodiments, the area of the removed portion085of the underlying substrate081is left as-is (i.e. empty as free space) after the portion085is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 9depicts a cross-section of an active material-based structure090having a strained active material093vertically adjacent to an overlying material094and an underlying material092over an underlying substrate091, where a portion095of the underlying material092is removed under an area of the active material093, according to another example embodiment of the present invention.

To facilitate the application of strain to the active material093, a portion of the underlying material092is removed to expose a region095, over which the active material093is suspended. The amount of the underlying material092removed below the active material093is based upon desired characteristics of the active material093and device/application considerations. Accordingly, dashed line096defines a region of the underlying material092that is left intact below the active material093, as representing an exemplary approach to removing less than all of the material092underlying the suspended portion of the active material093.

Additionally, in some embodiments, the area of the removed portion095of the underlying material092is left as-is (i.e. empty as free space) after the portion095is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 10depicts a cross-section of an active material-based structure100having a strained active material103vertically adjacent to an overlying material104and an underlying material102over an underlying substrate101, where a portion105of the underlying material102and underlying substrate101is removed to a depth within the underlying substrate101under an area of the active material103, according to another example embodiment of the present invention.

To facilitate the application of strain to the active material103, a portion of the underlying material102and underlying substrate101is removed to expose a region105, over which the active material103is suspended. The amount of the underlying material102and underlying substrate101removed below the active material103is based upon desired characteristics of the active material103and device/application considerations. Accordingly, dashed line106defines a region of the underlying material102that is left intact below the active material103, as representing an exemplary approach to removing less than all of the material102underlying the suspended portion of the active material103. Further, the amount of the underlying substrate101removed below the material102to a depth within the underlying substrate101may also be determined by other desired material and device characteristics, which may include structural integrity of the remaining underlying substrate101, device integration schemes, and others.

Additionally, in some embodiments, the area of the removed portion105of the underlying material102and underlying substrate101is left as-is (i.e. empty as free space) after the portion105is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 11depicts a cross-section of an active material-based structure110, similar to that shown inFIG. 10, having a strained active material113vertically adjacent to an overlying material114and an underlying material112over an underlying substrate111, where a portion115of the underlying material112and underlying substrate111is removed to the bottom of the underlying substrate111under an area of the active material113, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material113, a portion of the underlying material112and underlying substrate111is removed to expose a region115, over which the active material113is suspended. The amount of the underlying material112and underlying substrate111removed below the active material113is based upon desired characteristics of the active material113and device/application considerations. Accordingly, dashed line116defines a region of the underlying material112that is left intact below the active material113, as representing an exemplary approach to removing less than all of the material112underlying the suspended portion of the active material113.

Additionally, as discussed above, in some embodiments, the area of the removed portion115of the underlying material112and underlying substrate111is left as-is (i.e. empty as free space) after the portion115is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 12depicts a cross-section of an active material-based structure120having a strained active material124horizontally adjacent to other materials123and vertically adjacent to an underlying material122over an underlying substrate121, where a portion125of the underlying material122is removed under an area of the active material124, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material124, a portion of the underlying material122is removed to expose a region125, over which the active material124is suspended. The amount of the underlying material122removed below the active material124is based upon desired characteristics of the active material124and device/application considerations. Accordingly, dashed line126defines a region of the underlying material122that is left intact below the active material124, as representing an exemplary approach to removing less than all of the material122underlying the suspended portion of the active material124.

Additionally, in some embodiments, the area of the removed portion125of the underlying material122is left as-is (i.e. empty as free space) after the portion125is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 13depicts a cross-section of an active material-based structure130having a strained active material134horizontally adjacent to other materials133and vertically adjacent to an underlying material132over an underlying substrate131, where a portion of the underlying material132and underlying substrate131is removed to a depth within the underlying substrate131under an area of the active material134, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material134, a portion of the underlying material132and underlying substrate131is removed to expose a region135, over which the active material134is suspended. The amount of the underlying material132and underlying substrate131removed below the active material134is based upon desired characteristics of the active material134and device/application considerations. Accordingly, dashed line136defines a region of the underlying material132that is left intact below the active material134, as representing an exemplary approach to removing less than all of the material132underlying the suspended portion of the active material134. Further, the amount of the underlying substrate131removed below the material132to a depth within the underlying substrate131may also be determined by other desired material and device characteristics, which may include structural integrity of the remaining underlying substrate131, device integration schemes, and others.

Additionally, in some embodiments, the area of the removed portion135of the underlying material132and underlying substrate131is left as-is (i.e. empty as free space) after the portion135is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

FIG. 14depicts a cross-section of an active material-based structure140, similar to that shown inFIG. 13, having a strained active material144horizontally adjacent to other materials143and vertically adjacent to an underlying material142over an underlying substrate141, where a portion145of the underlying material142and underlying substrate141is removed to the bottom of the underlying substrate141under an area of the active material144, according to another example embodiment of the present invention.

As discussed above, to facilitate the application of strain to the active material144, a portion of the underlying material142and underlying substrate141is removed to expose a region145, over which the active material144is suspended. The amount of the underlying material142and underlying substrate141removed below the active material144is based upon desired characteristics of the active material144and device/application considerations. Accordingly, dashed line146defines a region of the underlying material142that is left intact below the active material144, as representing an exemplary approach to removing less than all of the material142underlying the suspended portion of the active material144.

Additionally, as discussed above, in some embodiments, the area of the removed portion145of the underlying material142and underlying substrate141is left as-is (i.e. empty as free space) after the portion145is removed. In other embodiments, this area is refilled with another material to satisfy any of a variety of desired material, device, circuit, and system characteristics.

The strained-material structures as described herein may be formed in one or more of a variety of shapes and arrangements, including but not limited to those shown inFIGS. 1-14and in the Appendix, which forms part of this patent document.

The following describes various embodiments, which may be applicable to one or more of the figures as described above, as well as to other embodiments described herein.

In one embodiment, a three-layer active material structure includes a 30 nm-thick diamond-like carbon (DLC) layer on a 100 nm-thick active material film, which is on a 100 nm-thick DLC layer. The material stack is partially suspended over a 5 μm hole in a silicon substrate, which facilitates the application of tensile strain to the active material film, by one or both DLC layers. In some implementations, greater than about 0.3% biaxial tensile strain is induced in the active material layer, which corresponds to a direct bandgap reduction in excess of 30 meV and a greater than 60 nm shift in the absorption edge towards longer wavelengths for the specific exemplary case of a germanium active layer.

In another embodiment, a four-layer active material structure includes a 30 nm-thick DLC layer on a 100 nm-thick active material layer, which is on a 100 nm-thick silicon nitride layer (Si3N4) on a 30 nm-thick silicon dioxide (SiO2) layer, and the material stack is partially suspended over a 5 μm hole in a silicon substrate. In some implementations for the case of a germanium active layer, a tensile strain that is greater than about 0.4% is induced in the active material layer, which corresponds to a 40 meV reduction in the direct bandgap and at least an 80 nm absorption edge shift towards longer wavelengths. In one implementation, the DLC-active material-Si3N4—SiO2material stack is supported by beams at four locations from an underlying silicon substrate. In other implementations, such as those involving the use of horizontally-located stressor materials (e.g. as073ofFIG. 7), well over 2% strain is induced upon an active material layer. In fact, for such a configuration as well as others, arbitrary amounts of strain can be applied depending on structure geometries, material compositions, and other characteristics. For these and other implementations, the amount of strain applied to a material can be set up to a threshold including and below which the material is capable of remaining intact under the strain, where such a threshold depends upon characteristics and arrangement of the material and its interactions with surrounding materials.

The materials as described herein may be formed and stressed using one or more of a variety of approaches. In some embodiments, an active material in a suspended material stack is relaxed, prior to stressing with another adjacent material as discussed above. In other embodiments, the active material is pre-stressed, prior to further stressing with another adjacent material. These approaches may be used with a variety of configurations, including an active material-on-insulator configuration, with a stressing material formed over the starting material stack after pre-relaxation or pre-stressing.

The substrate material over which the active material stack is formed can also be formed and/or arranged using one or more of a variety of approaches. In some embodiments, an underlying substrate is chosen to induce different properties in the active material. For example, an underlying substrate or material may be selected and used to set the crystal orientation and/or the initial strain state of the active material, where the active material is first formed on the substrate and subsequently suspended via removal of a portion of the substrate.

In addition, the shape and amount of substrate material that is etched or otherwise removed to suspend the active material stack can also be used to set the strain experienced by the active material. For instance, substrate material may be left in certain regions to add structural integrity to the active material stack while reducing the strain therein.

In addition, subsequent to the etching or otherwise removal of materials underlying an active material to allow for strain transfer, other materials may be formed to reconnect the active material to the underlying materials and/or substrate in whole or in part. For instance, a material may be used to refill the space underneath a strained active material stack in order to provide enhanced structural integrity, improved thermal conductivity, or any of other desired characteristics once strain has been introduced in the active material.

Different types of materials can be used to set the strain of active materials as described herein. For example, one embodiment is directed to using a transparent film on one or opposing sides of an active material film (e.g. as064and/or062ofFIG. 6) to permit optical detection or emission from the active material film. In another embodiment, a highly stressed metal is deposited on an active material film as a capping layer (e.g. as064ofFIG. 6) with a transparent dielectric (e.g. as062ofFIG. 6) underneath the active material film. In this embodiment, the top metal could both induce strain in the active material and serve as electrode(s), while the optical absorption/emission is accomplished from the backside. In other embodiments, the size and geometry of a capping layer (e.g. as013ofFIG. 1) is set to induce highly localized strains (e.g. with varying thickness, composition and/or location of a top layer), or to induce small, uniform strains (e.g. with a layer013across an entire active material film, or extending beyond such a film).

Suspended material stacks including an active material as discussed herein may be formed in one or more of a variety of shapes. In some implementations, the shape of the suspended material stack is set to correspondingly set characteristics of the active material, such as those relating to strain, stress gradient, light absorption, light emission, charge carrier mobility, and charge carrier scattering statistics, among others.

Devices Built on Strained Active Layers

An active-on-other material stack (e.g. germanium-on-insulator) is prepared by any of several methods. The starting material stack may be part of a semiconductor (e.g. silicon) wafer that includes fabrication of CMOS or other circuitry thereon. The active layer is patterned using photolithographic techniques common in semiconductor fabrication. In one example, this could include the coating, exposure, and development of a photoresist material that serves as a protective mask during subsequent etch and removal of the exposed active layer areas. The starting active layer may have a thickness determined by the need to satisfy any of various material, mechanical, and device specifications for a given application. For example, the range of active layer thicknesses appropriate for one such application may be 100 Å-10000 Å.

Another material under internal tensile stress is then deposited non-selectively on the patterned active layer and surrounding wafer surface. In one example, this deposited material may be a silicon nitride film deposited using any of several available techniques, including low-pressure chemical vapor deposition (LPCVD), plasma-enhanced chemical vapor deposition (PECVD), sputtering, etc. The thickness of the deposited stressed film is also determined by material, mechanical, and device specifications depending on the application. For example, for a 2500 Å-thick active layer, a stressor layer with thickness in the range of 2500 Å-10000 Å may be appropriate, depending on the application and other factors. The salient feature of the deposited film is the presence of internal tensile stress due to thermal considerations, internal atomic structure, or other factors. The deposited stressor layer is then patterned and etched to form structures physically connected to and overlapping the patterned active layer in some areas. In one example, a patterned active region may be rectangular, with the stressor layer etched to form two separate stressor regions on the wafer surface near opposite ends of the active region and partially overlapping the opposite active area ends in direct physical contact (e.g. similar to070inFIG. 7).

A photolithography process is then done to expose regions of the wafer surface near the active layer and stressor structures while protecting the rest of the wafer surface. Any of several etch procedures can then be done to free the active layer and part of the stressor structures from the underlying materials. In one example, a selective etch can be done to isotropically remove the material that was immediately underneath the active layer in the starting film stack (e.g. the oxide underlayer in a GOI wafer) while leaving all other materials intact (e.g. as125ofFIG. 12). In another example, an etch through the underlying material layer (e.g. the oxide underlayer in a GOI wafer) can be done to expose the wafer substrate or second underlying material, which is then isotropically etched underneath the active layer and part of the stressor structures (e.g. as075ofFIG. 7).

The stressor structures that are connected to the patterned active regions and have been freed from the underlying materials then relax and release their internal tensile stress through contraction. Provided the active layer is relatively more compliant, the internal stress in the released stressor regions is then transferred to the suspended patterned active regions. The void left underneath an active region and part of the stressor structures as a result of the release etch can be left as-is or refilled using another material if desired, depending on application specifics. Electronic and/or optoelectronic devices can then be built on the strained active layer using a combination of fabrication steps, including but not limited to ion implantation steps, metal electrode deposition and patterning, and other processes used to fabricate various devices.

Following the general method of Example 1, a photodetector can be made on an active layer that is strained either prior to device fabrication or as the final step in the device fabrication process.

For example, a strained metal-semiconductor-metal (MSM) photodetector can be fabricated by adding a metal evaporation and photoresist lift-off lithography process after the method of Example 1 is followed to apply strain to an active layer meant to serve as the absorption medium in the device. In one specific process example, a spray-coating system can be used to deposit photoresist on all accessible material surfaces after the release etch is done for the strain transfer. Then, after photoresist exposure and developing to form electrode patterns, a metal electrode stack (e.g. 150 Å of Titanium followed by 350 Å of Gold) can be evaporated non-selectively on the wafer surface. A metal lift-off process consisting of soaking the wafer in a solvent (e.g. acetone) to dissolve the remaining photoresist and remove the metal films lying on top of the dissolving photoresist can be done to leave the desirable electrode pattern in electrical contact with the strained active material. In an alternate process example, the above metallization steps can be inserted into the fabrication process of Example 1 before the release etch is performed. In this case, the MSM photodetector is first formed on the active material prior to the introduction of strain via the removal of underlying materials and/or substrate in the regions of interest.

As another photodetector device example, a strained pin photodetector can be fabricated by combining the metallization steps described above for the MSM photodetector device and engineering of the active material itself. For example, the pin device fabrication process may commence with the active material comprised of several layers of doped semiconductor arranged either vertically or horizontally to obtain a region of intrinsic semiconductor sandwiched between regions of n-type and p-type semiconductors (e.g. via the epitaxial growth of three layers of semiconductor under different in-situ doping conditions). The metallization and electrode definition steps would then be designed to yield electrical contact to the n- and p-type regions. As an alternate process, the pin doping arrangement of the active layer could be achieved by starting with an intrinsic semiconductor that is subsequently doped via patterned ion implantation steps at any of various points in the rest of the device fabrication process.

Following the general method of Example 1, a light-emitting diode (LED) can be made on an active layer that is strained either prior to device fabrication or as the final step in the device fabrication process. For example, a strained pin LED can be fabricated by combining the methods of Example 1 and Example 2 for the case of a pin photodetector.

As an alternate device example, a pn LED can be fabricated by combining the methods of Example 1 and Example 2 for the case of a pin photodetector but removing the intrinsic semiconductor from the material stack. In the case of epitaxially-obtained films, the starting active layer in this case could be comprised of two epitaxially-grown semiconductors, one of n-type doping and the other of p-type doping. Alternately, the starting active layer could be a single semiconductor of either n- or p-type doping. A subsequent ion implantation or other doping process can be done to introduce the opposite doping species to desired regions of the active layer to selectively change the electrical character of those regions. For example, in the case of an n-type starting film, p-type dopants could be ion implanted into certain regions of the active layer. In this case, enough of the implanted species would need to be introduced to counter the dopants already present and invert the character of the active layer in those regions.

Photonic Crystals

Following the general method of Example 1, a photonic crystal can be made on an active layer that is strained either prior to device fabrication or as the final step in the device fabrication process.

For example, a strained photonic crystal can be fabricated by incorporating in the active layer pattern of Example 1 an additional pattern of holes of a desired size and arrangement to yield a photonic crystal in the active layer. In this approach, the hole pattern comprising the photonic crystal and the containing active layer pattern in which the holes are to be incorporated would be defined and etched simultaneously. Subsequent processing could proceed as normally described in the method of Example 1, with release etching done as normal or modified to also act through the photonic crystal holes in the active layer. The latter approach may be chosen to enhance the release etch rate, uniformity, mechanical integrity, and other factors of the active layer and device.

In an alternate process example, the photonic crystal hole pattern may be incorporated in the active layer after the release etch is performed. In this case, a spray-coating system may be used to deposit photoresist on the strained active layer. Exposure and develop steps following by etching would then be done to transfer the desired hole pattern onto the active layer, yielding a strained photonic crystal.

Without limitation, a variety of embodiments are directed to implementations consistent with those presented in the attached Appendix, which forms part of this patent document. For instance, one or more embodiments as described herein and/or as part of the claims may be implemented with one or more embodiments shown in and/or described in connection with the Appendix, alone, in combination with other embodiments, or in connection with other embodiments not described here.

The various embodiments described above are provided by way of illustration and should not be construed to limit the invention. Based upon the above discussion and illustrations, those skilled in the art will recognize that various modifications and changes may be made to the present invention without strictly following the exemplary embodiments and applications illustrated and described herein. Such modifications and changes do not depart from the true spirit and scope of the present invention, including that set forth in the following claims.