The effect of BCl₃ pretreatment on the etching of AlN in Cl₂-based plasma

Abstract

The effect of BCl3 and BCl3/Ar pretreatment on Cl2/Ar and Cl2/Ar/BCl3 dry etching of AlN is investigated using inductively coupled plasma reactive ion etching. The native AlN oxide can be effectively removed by a short exposure to BCl3 or BCl3/Ar plasma. Compared to the chlorine based plasma etching, BCl3/Ar is found to have the highest etch rate for both AlN and its native oxide. Following removal of the native oxide, Cl2/Ar/BCl3 plasma etching with 15% BCl3 fraction results in a high etch rate ˜ 87 nm/min and modest increases in the surface roughness.

High quality AlN for deep UV photodetectors

“…The onset of epitaxial growth was three dimensional ͑3D͒. AlN films are grown at a substrate temperature of 900°C and ammonia flux of 12 SCCM with growth rate of ϳ200 nm/ h. 7 We observed 1 ϫ 1 streaky RHEED pattern ͑not shown here͒ corresponding to a two dimensional growth mode after deposition of ϳ10-20 nm thick AlN. Streaky 2 ϫ 2 RHEED pattern corresponding to Al-polar surface 8 was observed at room temperature.…”

ICP-RIE etching of polar, semi-polar and non-polar AlN: comparison of Cl2/Ar and Cl2/BCl3/Ar plasma chemistry and surface pretreatment

“…ICP etching of polar (0001) c-plane GaN has been thoroughly investigated and is well understood [2][3][4][5][6][7]. However, very few reports exist on the etching of semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN, non-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) aplane GaN and high aluminum content Al x Ga 1−x N alloys of polar, semi-polar and non-polar orientations [8][9][10][11]14]. ICP etching of Al-based materials is mostly carried out using a chlorine plasma (mainly Cl 2 and BCl 3 ) with Ar used as an ion bombardment agent to increase desorption of volatile etch products from the etched surface [9] and thus increasing the etch rates.…”

“…Plasma etching of AlGaN is also associated with a time lag between the ignition of the plasma and the actual start of removal of materials [11,12]. This 'etch delay time' arises due to the surface aluminum oxide in high Al-content materials.…”

“…This 'etch delay time' arises due to the surface aluminum oxide in high Al-content materials. This delay can be as long as 1-2 min [11,12], poses a challenge in achieving high and reproducible etch rates and has been shown to affect device performance; for example transconductance and leakage current in HEMTs [13]. The non-uniform thickness of aluminum oxide across the wafer [15] leads to a very rough surface morphology.…”

“…The non-uniform thickness of aluminum oxide across the wafer [15] leads to a very rough surface morphology. A few reports have shown that adding BCl 3 to Cl 2 /Ar plasma actually improves surface morphology [9] but shows a peak in etch depths for BCl 3 concentration of 10-30% in Cl 2 /Ar mixtures [8,11]. Some reports have investigated the effect of plasma condition on the etch properties of AlGaN using quadrapole mass spectroscopy and optical emission spectroscopy [6,8].…”