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Using Electrons to Etch Nanoscale


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ing has been effective for decades, it fails to provide the precise, nano-sized structures and pathways required by next-generation devices. The process also generates significant amounts of heat that can damage underlying mate- rial layers. For compound semiconductor materials, such as GaN or SiC, it can also change the surface atomic ratios. VelvETch, along with PVA TePla, have commercialized a system called


I


Electron Enhanced Material Processing™ (EEMP™) that uses electrons — not ions — to precisely remove material at the nano level.


EEMP In EEMP, precisely controlled waves of electrons are accelerated to the


surface of the material at specific voltages, designed to create chemical reac- tions that release the surface atomic bonds, allowing surface material to be lifted away gently. The full-scale immersion by electrons allows the item being processed, such as a wafer, to be completed at an etch rate comparable to RF plasma etching. EEMP is flexible, allowing various factors to be precisely controlled to etch


essentially any material, including nano-layers and quantum well structures. EEMP can also be finetuned and controlled to achieve atomically smooth sur- faces to enable the fabrication of quantum computing devices. EEMP has unique applications for the current generation of high


bandgap compound semiconductors made of gallium nitride, gallium arsenide and silicon carbide. “This is not an electron-beam scanning technology,” says Samir Anz, co-


founder of VelvETch. “We emphasize this because when people hear ‘elec- trons,’ they think ‘electron beam.’ This is a full-scale immersion technology. The entire semiconductor wafer or substrate is processed at all points, at the same time.” With EEMP it is not the impact that drives the etching, but a chemical reaction induced by a loss of electrons from the bonds at the surface that causes surface atoms to be gently released. Now commercialized by VelvETch after decades of research and develop-


ment, EEMP is conducted in a jointly designed advanced plasma system plat- form provided by PVA TePla, utilizing a proprietary bias waveform signal that pulls the electrons down to the surface being processed. Since electrons have little mass, there is no impact damage to the sur-


For all your workbench needs.


face, and only nominal heat is generated as a result of the chemical reaction. The sample remains at room temperature.


Compound Semiconductor Materials Compound semiconductor materials comprise more than one element.


Current high-bandgap compound semiconductors include gallium nitride, gal- lium arsenide and silicon carbide. Gallium nitride is very important for tran- sistors to operate at high frequencies, voltages and temperatures, including the microwave power amplifiers used for 5G wireless base stations, satellite communications and military radar systems. Gallium arsenide allows for faster operation, a wider bandgap and operation at higher temperatures. Sil- icon carbide is used in semiconductor devices that operate both at high tem- peratures and high voltages. Reactive-ion etching removes different elements at different rates, mod-


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ifying the surface stoichiometry, or ratio, of compound semiconductor ele- ments. EEMP, however, preserves the stoichiometry of compound semicon- ductors by carefully controlling the energy of the electrons in the discharge. This advantage of EEMP also applies to quantum well structures, which sandwich a thin layer of one semiconductor between two layers of another semiconductor material with a wider bandgap. Quantum wells are used in laser diodes, LEDs, high electron mobility


transistors, infrared photodetectors, and infrared imaging arrays. Among the benefits of EEMP is the ability to achieve atomically smooth


surfaces, because it removes atoms layer by layer, beginning with any exist- ing peaks. “If there is any roughness on the surface, EEMP will smooth it down to within one lattice constant of atomic smoothness, which is less than 0.25 nanometers in silicon,” says Stewart Sando, a cofounder of VelvETch. In quantum computing, atomically smooth surfaces are required for op-


timal performance. EEMP can also be used to smooth a surface prior to grow- ing another material on top of it, using molecular beam epitaxy or chemical vapor deposition. The fact that EEMP generates almost no heat is a major benefit. RF-


based ion etching generates high temperatures that can cause physical and electrical damage to compound semiconductors and ICs. The minimal amount of heat generated by EEMP allows temperature to


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be used as an additional control, rather than something to be mitigated. Today, chambers are available for EEMP, along with contract processing


services through VelvETch’s partnership with PVA TePla. Contact: PVA TePla America, Inc., 251 Corporate Terrace, Corona, CA


92879 % 951-371-2500 E-mail: billm@pvateplaamerica.com Web: www.pvateplaamerica.com r


Semiconductor Devices By Jeff Elliott


n semiconductor fabrication, the traditional approach to dry etching has been to utilize RF plasma to bombard the surface of the wafer with posi- tive ions to remove material between masking layers. Although ion etch-


June, 2020


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