Selective Etching Of Wide Bandgap Nitrides

Abstract

High-density plasma etching has been an effective patterning technique for the group-I11 nitrides due to ion fluxes which are 2 to 4 orders of magnitude higher than more conventional reactive ion etch (RIE) systems. GaN etch rates exceeding 0.68 pdmin have been reported in Cl,/H,/Ar inductively coupled plasmas (ICP) at -280 V dc-bias. Under these conditions, the etch mechanism is dominated by ion bombardment energies which can induce damage and minimize etch selectivity. High selectivity etch processes are often necessary for heterostructure devices which are becoming more prominent as growth techniques improve. In this study, we will report high-density ICP etch rates and selectivities for GaN, AlN, and InN as a function of cathode power, ICP-source power, and chamber pressure. GaN:AlN selectivities > 8: 1 were observed in a Cl,/Ar plasma at 10 mTorr pressure, 500 W ICP-source power, and 130 W cathode rf-power, while the GaN:InN selectivity was optimized at -6.5: 1 at 5 mTorr, 500 W ICP-source power, and 130 W cathode rf-power.

Etch Processing of III-V Nitrides

“…As can be seen, the etch rates achieved with these methods is nearly an order of magnitude higher than in conventional RIE methods. The bulk of these efforts have involved halogen based chemistries including chlorine- [11][12][13][14][15][16][17], iodine- [18], and bromine-based [14,17] chemistries. There have also been efforts in mixed halogen chemistries such as ICl [19] and CCl 2 F 2 [17].…”

“…To date, most reports on etch damage in the III-V nitrides have centered on topographic or stoichiometric changes imparted to the surface [13,[20][21][22][23]. In these representative reports, smooth etched surfaces are identified as generally achievable, with the exception of "etch pit" formation on the surfaces of nitride films grown on basal plane sapphire [13]. Smooth sidewall surfaces are also reported to be contingent upon a robust mask -erosion of the mask edges leads to striations in the sidewall in these high fidelity processes [13].…”

Dry and Wet Etching for Group III – Nitrides

“…Etch rates for InN, AlN, and various mole fractions of AlInN and AlGaN have also been reported [33]. Etch selectivities between these various materials have been reported for different gas mixtures including Cl 2 /SF 6 [23]. Selectivities of 5 and 3 were reported for GaN on AlN and GaN on InN, respectively, using Cl 2 /Ar at -250 V [34].…”

“…They include ion milling [6,7], chemically assisted ion beam etching (CAIBE) [8,9,55], reactive ion beam etching (RIBE) [10], reactive ion etching (RIE) [11][12][13][14][15], electron-cyclotronresonance reactive ion etching (ECR-RIE) [16][17][18][19][20][21], and inductively-coupled-plasma reactive ion etching (ICP-RIE) [22][23][24][25][26][27]. Optical excitation sources with photon energies higher than the bandgap energies of the semiconductors have been applied to both dry and wet etching methods.…”

“…ICP-RIE sources are easier to scale up than ECR sources and are more economical to operate [25]. These factors have led to the investigation of ICP-RIE for III-nitrides in various plasmas [22][23][24][25][26][27]. As expected, high etch rates and etch profiles with high anisotropy have been demonstrated.…”