Tai-Kyung Kim

Origin of hexagonal-shaped etch pits formed in (0001) GaN films

We report the origin of hexagonal-shaped etch pits generally observed by conventional wet etching processes on (0001) GaN-based films based on the investigation with transmission electron microscopy on GaN films after being etched with molten KOH. The origin of hexagonal-shaped etch pits is identified as nanopipes through careful characterization of abnormal contrast of nanopipe (open-core screw dislocation), “lobe contrast” of end-on edge and screw (full-core) dislocations, visible and invisible conditions of edge and screw dislocations. Consideration of energetics of these defects also suggests preferential etch pit formation at nanopipes because of much higher energy.

ETCH CHARACTERISTICS OF GAN USING INDUCTIVELY COUPLED CL2/AR AND CL2/BCL3 PLASMAS

In this study, Cl2/Ar and Cl2/BCl3 inductively coupled plasmas were used to etch GaN and the effects of etch parameters such as gas combination and operation pressure on the characteristics of the plasmas and etch properties of GaN were investigated. The characteristics of the plasmas were estimated using a Langmuir probe and optical emission spectroscopy. Surface residue remaining after the etch was investigated using x-ray photoelectron spectroscopy (XPS). The increase of Ar and BCl3 in Cl2 generally reduced GaN etch rates except for the small addition of Ar or BCl3. With the addition of 10% Ar or 10% BCl3  to Cl2, the GaN etch rates showed the maximum etch rates. Also, the increase of operational pressure up to 30 mTorr increased the GaN etch rates. By optimizing etch process parameters, etch conditions having smooth and nearly vertical etch profiles with the etch rates close to 8500 A/min and the selectivity over SiO2 higher than 3.5 could be obtained with Cl2-rich Cl2/BCl3 gas combinations. The chang...

Characteristics of inductively coupled Cl2/BCl3 plasmas during GaN etching

In this study, the characteristics of inductively coupled Cl2/BCl3 plasmas during GaN etching were estimated using plasma mass spectrometry by measuring the relative amounts of positive ions, neutrals, and etch products. The results showed that the enhancement of GaN etch rates for Cl2/BCl3 plasmas could be related to the formation of Cl radicals and reactive ions such as Cl2+ and BCl2+ measured by the mass spectrometry during GaN etching. These Cl radicals are responsible for chemisorption and BClx+ and Cl2+ for chemical and/or physical sputtering. Ion assisted chemical desorption seems to be generally enhanced by the addition of BCl3 to Cl2 and also with the increase of pressure. Also, the abundance of BCl2+ in the Cl2/10%BCl3 plasmas appears to be important in GaN etching compared to pure Cl2 plasma. Ga+, GaCl2+, and N2+ were observed during GaN etching as the etch products and the intensities of these ion etch products were correlated with the trend of the GaN etch rate.

Programming characteristics of phase change random access memory using phase change simulations

We present a new simulation methodology for analyzing programming characteristics of a chalcogenide based phase-change device, phase change random access memory (PRAM), which is a next-generation non-volatile memory. Using the new simulation methodology, we analyze the initialization of chalcogenide material (ICM) of the mechanism and propose the next generation PRAM scheme. From the results of the phase change simulation, the process conditions for ICM for stable operation are presented. Also, the self-heating confined structure to overcome the inherent limitation of high operation power is proposed that resolves the operating power limitation associated with PRAM development.

Effects of plasma conditions on the etch properties of AlGaN

Abstract In this study, etchings of III-nitrides such as GaN, AlGaN, and InGaN were performed using planar inductively coupled Cl 2 /BCl 3 plasmas. Especially, etch properties of Al x Ga 1− x N were investigated as a function of inductive power, bias voltage, substrate temperature, and pressure. Etch rates of GaN were higher than those of AlGaN and InGaN regardless of plasma conditions for the Cl 2 -rich plasmas. The increase of the Al composition in the AlGaN decreased the etch rate because of higher bond strength between Al and N and Al-oxidation. The enhancement of AlGaN etch rates could be obtained by the addition of BCl 3 to Cl 2 gas and the decrease of the pressure. Plasma diagnostics and surface analysis were performed to understand the etch mechanism of AlGaN. The effective removal of Al from the surface of AlGaN during the etching appears to be important in increasing the AlGaN etch rates.

Modeling of cumulative thermo-mechanical stress (CTMS) produced by the shallow trench isolation process for 1 Gb DRAM and beyond

The defects induced by the thermo-mechanical stress in the device fabrication process are correlated with device characteristics of 1 Gb DRAM. To identify the defect formation in the thermal process, we modeled the cumulative thermo-mechanical stress (CTMS) throughout the shallow trench isolation (STI) integrated DRAM process, and performed computer simulation using ABAQUS. The defect-free stress level was extracted from the relationship between the cumulative shear stress and electrical device characteristics, and then applied to optimizing thermal annealing process to obtain the defect-free process condition for the fabrication of 1 Gb DRAM and beyond.

Magnetized inductively coupled plasma etching of GaN in Cl2/BCl3 plasmas

In this study, Cl2/BCl3 magnetized inductively coupled plasmas were used to etch GaN, and the effects of magnetic confinements of inductively coupled plasmas on the GaN etch characteristics were investigated as a function of Cl2/BCl3. Also, the effects of Kr addition to the magnetized Cl2/BCl3 plasmas on the GaN etch rates were investigated. The characteristics of the plasmas were estimated using a Langmuir probe and quadrupole mass spectrometry (QMS). Etched GaN profiles were observed using scanning electron microscopy. The small addition of BCl3 (10%–20%) in Cl2 increased the GaN etch rates for plasmas both with and without magnetic confinements. The application of magnetic confinements to the Cl2/BCl3 inductively coupled plasmas increased the GaN etch rates and changed the Cl2/BCl3 gas composition of the peak GaN etch rate from 10% BCl3 to 20% BCl3. It also increased the etch selectivity over the photoresist, while slightly reducing the selectivity over SiO2. The application of the magnetic field signi...

CMP profile simulation using an elastic model based on nonlinear contact analysis

Recently, simulation of Chemical Mechanical Polishing (CMP) is becoming more important because planarity and uniformity which are dependent on many dynamic factors are difficult to control. In this paper, a profile simulation environment based on the linear elastic material and nonlinear contact analysis that considers equipment parameters, such as pad hardness, thickness and down pressure is presented. In transient CMP simulation using the elastic model, the contact stress on the wafer surface is the dominant factor in polishing rate during the CMP process. The profiles of CMP simulation agree well with the measured data. This simulation can be used to optimize the CMP process and to generate design rules for filling dummy patterns which are used to improve planarity.

Reduction of Ohmic Contact Resistivity on p‐Type GaN by Surface Treatment

The contact resistivity of transparent Pt contact on p-type GaN was drastically decreased by four orders of magnitude through the surface treatments in sequence using aqua regia and (NH4)2Sx solution. The surface oxide on p-type GaN formed during epitaxial growth was removed in the boiling aqua regia, and the formation of native oxide on the oxide-free surface during air exposure prior to metal deposition was suppressed by the (NH4)2Sx treatment. This suggests that the reduction of contact resistivity is due to direct contact of Pt on the clean surface of p-type GaN, via shift of the Fermi level to a energy level of acceptors near the valence band, resulting in the reduction of barrier height for holes at the interface of Pt/p-type GaN.

Etch Properties Of Gallium Nitride Using Chemically Assisted Ion Beam Etching (CAIBE)

Dry etching properties of GaN were investigated using chemically assisted ion beam etching (CAIBE) with Cl2, BCl3, and HCl gases. The measured GaN etch rate with increasing tilt angle showed the maximum at a 30° tilt angle, similar to the effect of tilt angle on sputter yield. The GaN etch rate was the highest with Cl2 and the lowest with BCl3. In the case of GaN etching with BCl3, the GaN etch rate was even lower than that in the case of GaN etched with Ar ion source only. The lower etch rate appears to be related to the higher binding energy of BCl3 and high degree of condensation on the substrate maintained at 0°C. A highly anisotropic etch profile with smooth sidewalls could be obtained with Cl2. The addition of Cl2 to BCl3 did not improve GaN etch profile. The lowest roughness value of about 10 A was obtained for the etching with Cl2. The GaN surface etched by Cl2 and BCl3 showed an N-rich surface possibly due to the removal of Ga preferentially by forming GaClx, and GaN surface etched by HCl showed near-stoichiometric surface possibly due to the removal of Ga by forming GaClx and N by forming NHx.