半导体蚀刻技术获重大突破

Creating semiconductor¹ structures for high-end optoelectronic（光电子的） devices just got easier, thanks to University of Illinois researchers. The team developed a method to chemically etch（蚀刻） patterned arrays in the semiconductor gallium arsenide（砷化镓） , used in solar cells, lasers, light emitting diodes (LEDs), field effect transistors² (FETs), capacitors and sensors³. Led by electrical and computer engineering professor Xiuling Li, the researchers describe their technique in the journal Nano Letters.

A semiconductor's physical properties can vary depending on its structure, so semiconductor wafers（半导体薄片） are etched into structures that tune⁴ their electrical and optical properties and connectivity before they are assembled into chips.

Semiconductors⁵ are commonly etched with two techniques: "Wet" etching uses a chemical solution to erode⁶ the semiconductor in all directions, while "dry" etching uses a directed beam of ions to bombard the surface, carving⁷ out a directed pattern. Such patterns are required for high-aspect-ratio nanostructures, or tiny shapes that have a large ratio of height to width. High-aspect-ratio structures are essential to many high-end optoelectronic device applications.

While silicon⁸ is the most ubiquitous（普遍存在的） material in semiconductor devices, materials in the III-V (pronounced three-five) group are more efficient in optoelectronic applications, such as solar cells or lasers.

Unfortunately, these materials can be difficult to dry etch, as the high-energy ion blasts damage the semiconductor's surface. III-V semiconductors are especially susceptible⁹ to damage.

To address this problem, Li and her group turned to metal-assisted chemical etching (MacEtch), a wet-etching approach they had previously¹⁰ developed for silicon. Unlike other wet methods, MacEtch works in one direction, from the top down. It is faster and less expensive than many dry etch techniques, according to Li. Her group revisited the MacEtch technique, optimizing¹¹ the chemical solution and reaction conditions for the III-V semiconductor gallium arsenide (GaAs).

The process has two steps. First, a thin film of metal is patterned on the GaAs surface. Then, the semiconductor with the metal pattern is immersed in the MacEtch chemical solution. The metal catalyzes¹² the reaction so that only the areas touching¹³ metal are etched away, and high-aspect-ratio structures are formed as the metal sinks into the wafer. When the etching is done, the metal can be cleaned from the surface without damaging it.

"It is a big deal to be able to etch GaAs this way," Li said. "The realization¹⁴ of high-aspect-ratio III-V nanostructure arrays by wet etching can potentially transform the fabrication of semiconductor lasers where surface grating is currently fabricated by dry etching, which is expensive and causes surface damage."