Melting of silicon surfaces by high-power pulsed microwave radiation

Abstract

We have measured the microwave-induced melting and damage to the near-surface region of arsenic-implanted silicon for 1–2 μs pulses at a frequency of 2.856 GHz and an incident pulse power of up to 9 MW. Rectangular samples were irradiated by single-pass TE10 traveling wave pulses inside a WR-284 waveguide, and time-resolved in situ and post-irradiation studies were performed to characterize the material modifications induced by the microwave pulses. The test chamber where the specimens were irradiated was either evacuated to a pressure of 10−7–10−6 Torr or filled with a 30-psig pressure of Freon-12. Incident, transmitted, and reflected powers were monitored with directional couplers and fast diodes. The results of the time-resolved optical measurements for samples irradiated in vacuum show that melting of the near-surface region occurs for pulse powers exceeding 3 MW, and that the surface melting is accompanied by a large increase in the reflected microwave power. The onset of the enhanced reflectivity is measured at an earlier time as the microwave power is increased, and once the abrupt increase in the reflectivity is observed, it persists throughout the remainder of the pulse. Simultaneous with the onset of surface damage, we observe a large enhancement in the emission of light from the sample. Results are presented for the temporal behavior and spectral components of the fluorescence as a function of the incident microwave power. The gas pressure in the test cell was also monitored, and a large increase in the gas pressure was detected at the same pulse power as the threshold for the sudden increase in the microwave reflectivity. The large increments in the reflected microwave power, light emission, and gas pressure are attributed to the formation of a plasma due to gas breakdown at (or near) the sample surface. Examination of the irradiated specimens shows that the melting and damage are not homogeneous over the surface, and the degree of energy deposition from the microwave pulses depends on the ambient gas in the test cell. Using secondary ion mass spectrometry, we find that microwave pulses at a power of 8 MW cause melting and vaporization of the near-surface region up to depths that exceed 1 μm.

Deconvoluting the Mechanism of Microwave Annealing of Block Copolymer Thin Films

“…That silicon wafers can absorb microwave radiation and generate heat has been known for many decades. In the 1980s, a specially designed microwave device (given the name “microwave drill”) was designed to melt silicon wafers in a spatially defined, localized fashion . This work, and others, built upon the established observation that high resistivity silicon wafers heat more rapidly with microwave irradiation (frequencies of 2.45, 2.856, and 28 GHz), while low resistivity wafers are slow to heat up. , For BCP annealing, the relationship between silicon wafer resistivity and geometry and the heating profiles during irradiation under the conditions applied for BCP annealing remain unknown.…”

“…In the 1980s, a specially designed microwave device (given the name “microwave drill”) was designed to melt silicon wafers in a spatially defined, localized fashion . This work, and others, built upon the established observation that high resistivity silicon wafers heat more rapidly with microwave irradiation (frequencies of 2.45, 2.856, and 28 GHz), while low resistivity wafers are slow to heat up. , For BCP annealing, the relationship between silicon wafer resistivity and geometry and the heating profiles during irradiation under the conditions applied for BCP annealing remain unknown. To examine the influence of the resistivity and dopant type over the temperature profile of silicon, wafers of similar thicknesses (525 ± 25 μm) but of different resistivities and dopant types (Table ) were cut into 1.5 × 1.5 cm 2 pieces.…”

“…Microwave heating is well-established in industrial, academic, and domestic settings as a rapid, non-classical heating technique. − It was first used primarily in the food industry in the 1960s, but thereafter, its use rapidly expanded to other large-scale manufacturing, including the curing of rubber and wood products, ceramics, and semiconductors . Microwave heating is commonly used in academic laboratory settings since the rate of many reactions can be dramatically increased, often leading to higher yields and product purities. ,, Since microwave irradiation can heat and even melt silicon wafers, the typical substrate used for self-assembly of BCP thin films, our group proposed in 2010 that a research grade microwave oven could be used to anneal BCP thin films on silicon wafers . BCP thin films on silicon wafer shards of known resistivities were sealed in a glass vial, with or without a solvent, and heated in a research grade microwave oven.…”

“…70 Microwave heating is commonly used in academic laboratory settings since the rate of many reactions can be dramatically increased, often leading to higher yields and product purities. 68,71,72 Since microwave irradiation can heat and even melt silicon wafers, 73 the typical substrate used for self-assembly of BCP thin films, our group proposed in 2010 that a research grade microwave oven could be used to anneal BCP thin films on silicon wafers. 21 BCP thin films on silicon wafer shards of known resistivities were sealed in a glass vial, with or without a solvent, and heated in a research grade microwave oven.…”

Sol−Gel Synthesis and Characterization of Magnesium Silicate Thin Films

“…Microwave Processing. Since silicon absorbs microwave energy, coatings on silicon wafers were heated in a microwave oven as a means of rapid thermal annealing. − Coated substrates were heated in four stages as described in the Experimental Section; a container of water placed inside the oven was used to regulate the power absorbed by the wafer. The temperature of the silicon wafer reached at least 373 °C (but probably higher) after the final stage.…”