The present technology is related to engineered substrates having mechanically weak structures and associated systems and methods. In particular, the present technology relates to engineered substrates for separating epitaxially grown semiconductor structures and methods of manufacturing that involve separating semiconductor layers and/or solid state transducers from an engineered substrate.
Solid state lighting (“SSL”) devices are designed to use light emitting diodes (“LEDs”), organic light emitting diodes (“OLEDs”), and/or polymer light emitting diodes (“PLEDs”) as sources of illumination, rather than electrical filaments, plasma, or gas. Solid-state devices, such as LEDs, convert electrical energy to light by applying a bias across oppositely doped materials to generate light from an intervening active region of semiconductor material. SSL devices are incorporated into a wide variety of products and applications including common consumer electronic devices. For example, televisions, mobile phones, tablets, digital cameras, MP3 players, and other portable and non-portable electronic devices utilize SSL devices for backlighting. Additionally, SSL devices are also used for traffic lighting, signage, indoor lighting, outdoor lighting, and other types of general illumination.
Semiconductor layers are often grown on substrates to make solid state transducers, such as LEDs, by epitaxially growing materials on sapphire or other types of growth substrates, such as engineered substrates.
It is sometimes desirable to remove the growth substrate 20 to improve the optical properties of the SST die 10 or to gain electrical access to the SST structure 22. For example, growth substrates, in particular engineered substrates, are typically opaque and thus will block emission of light produced by the SST structure 22 if the growth substrate 20 is not removed. However, since the epitaxial layers 12, 14, and 16 are extremely delicate and thin (e.g., less than 10 microns), the outer epitaxial layer 16 of the SST die 10 must first be attached to a transfer substrate 24 or die-attach tape before removing the growth substrate 20. As shown in
Conventional chemical etching lift-off processes often involve exposing the edge of a wafer assembly to a chemical etchant such that the chemical etchant travels toward the center of the wafer assembly through voids formed by a reaction between an epitaxial material and a growth substrate. To separate the epitaxial material from the substrate, the chemical etchant must reach the center of the wafer assembly, which often leads to relatively long etch times. For example, the chemical etchant must travel four inches radially inward along the epitaxial/wafer interface to reach the center of an eight inch diameter wafer assembly. Additionally, it is difficult to consistently deliver the chemical etchant through the voids along the entire epitaxial/growth substrate interface. Grinding processes are often used to mechanically remove substrates from the epitaxial materials as an alternative to chemical etching. Unfortunately, mechanical grinding can damage the epitaxial material and produce relatively large scratches which must be removed by a subsequent polishing process.
Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Instead, emphasis is placed on illustrating clearly the principles of the present disclosure. For ease of reference, throughout this disclosure identical reference numbers are used to identify similar or analogous components or features, but the use of the same reference number does not imply that the parts should be construed to be identical. Indeed, in many examples described herein, the identically-numbered parts are distinct in structure and/or function. Furthermore, the same shading may be used to indicate materials in a cross section that can be compositionally similar, but the use of the same shading does not imply that the materials should be construed to be identical.
Specific details of several embodiments of methods for making semiconductor devices are described herein along with related devices and systems. The term “semiconductor device” generally refers to a solid-state device that includes semiconductor materials. Examples of semiconductor devices include logic devices, memory devices, and diodes, among others. Furthermore, the term “semiconductor device” can refer to a finished device or to an assembly or other structure at various stages of processing before becoming a finished device. Specific details of several embodiments of solid-state transducers (“SSTs”) and associated systems and methods are described below. The term “SST” generally refers to solid-state components that include a semiconductor material as the active medium to convert electrical energy into electromagnetic radiation in the visible, ultraviolet, infrared, and/or other spectra. For example, SSTs include solid-state light emitters (e.g., LEDs, laser diodes, etc.) and/or other sources of emission other than electrical filaments, plasmas, or gases. SSTs can alternately include solid-state components that convert electromagnetic radiation into electricity.
Additionally, depending upon the context in which it is used, the term “substrate” can refer to a wafer-level substrate or to a singulated, die-level substrate. A person having ordinary skill in the relevant art will recognize that suitable steps of the methods described herein can be performed at the wafer-level or at the die-level. Furthermore, unless the context indicates otherwise, structures disclosed herein can be formed using conventional semiconductor-manufacturing techniques. Materials can be deposited, for example, using chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic material deposition (AMD), spin coating, and/or other suitable techniques. Similarly, materials can be removed, for example, using plasma etching, wet etching, chemical-mechanical planarization (CMP), or other suitable techniques. Further, features can be formed in structures, for example, by forming a patterned mask (e.g., a photoresist mask or a hard mask) on one or more semiconductor materials and depositing materials or removing materials in combination with the patterned mask. A person skilled in the relevant art will also understand that the technology may have additional embodiments, and that the technology may be practiced without several of the details of the embodiments described below with reference to
As discussed above in the background section, previous lift-off methods to remove the growth substrate from the semiconductor materials have relied on chemical etching which can be time and capital expensive and in not feasible in manufacturing settings. Also as discussed above, mechanical grinding processes can cause damage to the semiconductor layers and prohibit reuse of the growth substrates which increases manufacturing costs. In manufacturing a conventional semiconductor device, the substrate that provides a support surface for epitaxial growth of semiconductor layers or films and is used to form or “grow” the device is commonly referred to as a “handle” substrate. Because of the disadvantages illustrated above, the handle substrate is typically not removed because removal requires additional processing steps that complicate manufacturing and increase manufacturing costs. Rather, the handle substrate is singulated along with the other semiconductor materials to form the semiconductor device.
Methods and devices in accordance with embodiments of the present technology, however, can provide several advantages over these and other manufacturing techniques. A method can include, for example, providing a mechanically weak intermediary material (e.g., a sacrificial material) located between a semiconductor structure and a structural material or substrate to provide means for separating or isolating the semiconductor structure from the handle substrate. In some embodiments, the mechanically weak intermediary material can be compromised, broken or fractured to decouple the semiconductor structure from the handle substrate.
In general, the intermediary material can include a porous film or layer that can withstand processing in epitaxial chamber conditions, but will break when mechanical stress is induced or otherwise applied (e.g., during epitaxial transfer). In one embodiment, the intermediary material can be CVD or PVD polycrystalline Si that is wet etched to create pores (e.g., with desired pore diameters). In another embodiment, the mechanically weak intermediary material can be an inherently non-conformal film epitaxially grown on the handle substrate. During epitaxial transfer and removal of the handle substrate from the semiconductor structure, applied mechanical stress can compromise and cause a break or fissure in the intermediary material without damaging the semiconductor structure or the handle substrate.
The intermediary material 106 is a sacrificial material that can be broken or compromised under mechanical stress, for example, to facilitate the separation of the structural material 104 from a semiconductor structure (not shown). For example, the intermediary material 106 can include a deposited silicon (Si) material and/or a polycrystalline Si. In some embodiments, the Si material can be a CVD or PVD deposited material which can be etched (e.g., electrochemically, photoelectrochemically, etc.) to create pores with desired diameters (e.g., approximately less than 1 μm) to make the intermediary material 106 mechanically weakened compared to other materials used to form the handle substrate 102 (e.g., the structural material 104). In other embodiments, however, the intermediary material 106 can be composed of a material deposited in a manner that would inherently form or otherwise have suitable pores.
The bonding material 114 can comprise materials that grow native oxides (e.g., amorphous polymers, amorphous silicon, oxides, etc.). In one particular example, the bonding material 114 can include an oxide of silicon, such as silicon dioxide (SiO2). The bonding material 114 can be formed on the donor substrate using PVD, CVD, ALD, spin on coating and/or other suitable formation methods. The bonding material 114 may undergo an additional polishing step (e.g., using chemical-mechanical polishing (“CMP”)) to thin the bonding material 114 and to form a substantially smooth surface and/or to reduce a thickness of the bonding material 114 to about 250-350 Å (e.g., 300 Å). Accordingly, conventional bonding of the donor substrate to the handle substrate 102 via the bonding material 114 followed by exfoliation and optional CMP polishing can produce the engineered substrate assembly 100 shown in
The semiconductor structure 202 can have a plurality of dies or other structures that include integrated circuitry or other types of semiconductor devices. As such, the semiconductor structure 202 can include a single semiconductor material, a stack of different semiconductor materials, and/or other suitable materials. In a particular example, the semiconductor structure 202 can include epitaxial layers, such as those layers described with reference in
The semiconductor structure 202 can be formed via metal organic chemical vapor deposition (“MOCVD”), molecular beam epitaxy (“MBE”), liquid phase epitaxy (“LPE”), hydride vapor phase epitaxy (“HVPE”), and/or other suitable epitaxial growth techniques. In other embodiments, the semiconductor structure 202 can also include other suitable components, such as a buffer material that facilitates the formation of semiconductor materials and the active region (not shown individually) on the epitaxial formation structure 110. In further embodiments, the semiconductor structure 202 can include additional bonding and seed layers to facilitate bonding and/or epitaxial growth.
Although omitted for purposes of clarity, a person having ordinary skill in the art will appreciate that the semiconductor structure 202 can include a variety of materials. For example, in addition to materials that are semiconductive, the semiconductor structure 202 can include conductive materials (e.g., metallic materials) and insulative materials (e.g., dielectric materials). Also, the semiconductor structure 202 can include a variety of features formed throughout the structure. For example, the semiconductor structure 202 can include a through-substrate interconnect (not shown) that extends through the semiconductor structure 202. Such a through-substrate interconnect can electrically connect opposite sides of a finished semiconductor device, for example.
Once formed, the semiconductor structure 202 can be integrated into an SST device. For example, the method can further include forming other features of an SST device, such as forming a lens over the semiconductor structure 202, a mirror on a back side of the semiconductor structure 202, electrical contacts on or in the semiconductor structure 202, and/or other suitable mechanical/electrical components (not shown). In various embodiments, the semiconductor structure 202 can be removed from the engineered substrate assembly 100 before being integrated into an SST device. In further embodiments, the structural material 104 can be used in subsequent processes. For example, the structural material 104 can be used to grow additional structures (e.g., semiconductor structures 202 such as LEDs, transducers, etc.) to reduce fabrication costs.
As shown in
As shown in
Following separation of the semiconductor structure 202 from the handle substrate 102, the remaining intermediary material portions 106a and 106b can be removed via polishing (e.g., CMP), grinding, chemical etching, or other suitable method for removing the intermediary material. For example, the intermediary portions 106a and 106b can be removed via etching media selected based on desired etching rates and the type of etching process (e.g., wet etching, vapor etching, dry etching, etc.). The etching media can be a liquid suitable for wet etching (e.g., a liquid containing hydrofluoric acid, buffers, additives, etc.), or a vapor (e.g., vapor hydrofluoric acid). The etching media can selectively etch the intermediary portions 106a and 106b without etching the structural material 104 or any portions of the semiconductor structure 202. Once the intermediary portion 106b is removed via wet, dry or vapor etch for example, the structural material 104 can be used to grow further semiconductor structures 202. For example, an additional mechanically weak intermediary material 106 can be formed on the upper surface 105 of the structural material 104 to form the handle substrate 102. In other embodiments, the structural material 104 can accommodate additional or other materials to form an alternative type of engineered substrate assembly 100 suitable for epitaxy of semiconductor structures 202.
Once released, the handle substrate 102 having the structural material 104 and the intermediary material portion 106b can be etched (e.g., wet, dry, vapor, etc.) to remove the remaining intermediary material 106 left adhered to the upper surface 105 of the structural material 104. The structural material 104 can then be recycled and used to form other semiconductor structures as described above. Alternatively, the recovered structural material 104 can be discarded depending on the life-cycle of the structural material 104. For example, the structural material 104 (or handle substrate 102 with remaining intermediary material portion 106b) can be discarded if it has become too thin, contaminated, and/or cycled more than a pre-determined number of times.
The substrate assemblies and semiconductor devices described above with reference to
From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from the disclosure. For example, the engineered substrate assembly 100 shown in