Young Hoon Lee

Reactive ion etching related Si surface residues and subsurface damage: Their relationship to fundamental etching mechanisms

The role of silicon near‐surface modifications caused by reactive ion etching in obtaining oxide‐to‐silicon etch selectivity has been studied by combining Si etch rate and plasma optical emission spectroscopy data with results from the analysis of etched Si surfaces. The nature of the near‐surface modifications was established from the study of Si crystals subjected to overetching during CF4/x% H2 selective reactive ion etching of SiO2 on Si. The experimental techniques used included x‐ray photoemission spectroscopy, He ion channeling, nuclear reaction techniques, and ellipsometry. Impurity penetration has been verified by nondestructive depth profiling using nuclear reaction and angular dependent core level photoemission techniques. Fluorocarbon film deposition, a highly disordered near‐surface region (∼30 A), and etching gas related impurity penetration into the Si lattice are among the Si substrate modifications observed. By nuclear reaction analysis, hydrogen at concentrations of the order 0.1 at. % h...

Study of silicon contamination and near‐surface damage caused by CF4/H2 reactive ion etching

Silicon surfaces which had been exposed to a CF4 /H2 plasma have been characterized by x‐ray photoelectron spectroscopy, ellipsometry, He ion channeling, and H profiling techniques. Plasma exposure leads to the deposition of a thin (∼30 A thick) C,F‐polymeric layer. Hydrogen and/or damage (displaced Si atoms) can be detected in the near‐surface region up to a depth in excess of 400 A from the Si surface.

Silicon di-interstitial in ion-implanted silicon

A new Si di-interstitial model is derived from the Si-P6 electron paramagnetic resonance spectrum observed in neutron-, proton-, or ion-implanted silicon. Two Si interstitials lie in the {100} plane at a position considerably off from two tetrahedral interstitial sites nearby, sharing one Si lattice atom. The di-interstitial disappears at 170 °C annealing and can form the 〈110〉 interstitial chains which are considered to be a “building block” of the {311} extended defects frequently observed in ion-implanted Si.

Silicon etching mechanism and anisotropy in CF4+O2 plasma

From measurements of optical emission and silicon etch rate, we are able to separate contributions due to the chemical etching and the ion‐bombardment enhanced etching in the CF4+O2 reactive ion etching process. The chemical etching part of undoped polysilicon etch rates is linearly proportional to the ground state fluorine population and the ion bombardment part is proportional to the dc self‐bias voltage (V2.3bi). The chemical etching predominates during plasma etching, giving rise to the isotropic etch profile, while both the chemical etching and the ion‐bombardment enhanced etching mechanisms coexist during reactive ion etching. A degree of the etch anisotropy in reactive ion etching is determined by competition between the chemical etching and the ion‐bombardment enhanced etching, and can be expressed by an equation which only involves two physical quantities, etch rate and fluorine concentration, experimentally measurable in plasma etching and reactive ion etching. The silicon loading effect leads t...

Doping effects in reactive plasma etching of heavily doped silicon

Etch rates of heavily doped silicon films (n and p type) and undoped polycrystalline silicon film were studied during plasma etching and also during reaction ion etching in a CF4/O2 plasma. The etch rate of undoped Si was lower than the n+‐Si etch rate, but higher than the p+‐Si etch rate, when the rf inductive heating by the eddy current was minimized by using thermal backing to the water‐cooled electrode. This doping effect may be explained by the opposite polarity of the space charge present in the depletion layer of n+‐Si and p+‐Si during reactive plasma etching.

Plasma characterization of an electron cyclotron resonance–radio‐frequency hybrid plasma reactor

Langmuir probe measurements have been carried out for Ar, O2, and CF4 plasmas generated by an electron cyclotron resonance–radio‐frequency (ECR–rf) hybrid plasma reactor. The resonance width of electron cyclotron resonance, defined at one‐half of the maximum plasma density, is measured to be ∼200 G below 1 mTorr and increases with gas pressure for all three gases. No enhancement in the plasma density was observed in the ECR region at or above 70 mTorr for all three gases. The mean electron energy was measured to be 7.2 eV for a microwave power level of 700 W and the energy distribution is nearly Maxwellian. Plasma density increases with the magnetic field. The magnetic field effect becomes more prominent when rf bias is applied to the substrate electrode. The rf bias not only extracts ions from ECR‐generated plasmas, but also generates a plasma more effectively due to the magnetic field.

Exact description and data fitting of ion‐implanted dopant profile evolution during annealing

We solve analytically the problem of dopant redistribution from an arbitrary initial implanted profile. The diffusivity, assumed concentration independent, can be an otherwise arbitrary function of temperature. Next, we derive a closed‐form expression for the annealed concentration distribution in the special case of an initial truncated Gaussian. Our solution is valid over a much wider range of experimental conditions than is Seidel and MacRae’s approximation [Trans. AIME 245, 491 (1969)]. We offer a simple, yet precise, criterion for the validity of this approximation, and we guard against its indiscriminate use. Last, we fit short‐time annealed P profiles in implanted Si to get an average diffusivity D≂3×10−12 cm2/s. We describe simple and accurate one‐parameter data‐fitting procedures.

Sidewall damage in n+‐GaAs quantum wires from reactive ion etching

Electron cyclotron resonance and radio frequency reactive ion etching have been used to fabricate narrow n+‐GaAs wires employing CCl2F2/He as the etch gas. A comparison of the induced sidewall damage is made using room‐temperature conductivity measurements of the etched structures and the effect of overetching is investigated. In addition, preliminary analysis of low‐temperature transport reveals that the amplitude of universal conductance fluctuations is extremely sensitive to sidewall damage.

Silicon near‐surface disorder and etch residues caused by CCIF3/H2 reactive ion etching

The effects of SiO2 reactive ion etching (RIE) in CClF3/H2 on the surface properties of the underlying Si substrate have been studied by photoemission and He ion scattering/channeling techniques. We find that RIE introduces a F, C, and Cl containing layer on the Si surface. Furthermore, displacement damage is introduced in the Si near‐surface region during RIE processing. The efficacy of O2 plasma or rapid thermal annealing RIE post‐treatments for removal of contamination and/or displacement damage has been investigated.

Comparison of damage in the dry etching of GaAs by conventional reactive ion etching and by reactive ion etching with an electron cyclotron resonance generated plasma

We have developed a high‐resolution etch for GaAs in an electron cyclotron resonance‐radio frequency (ECR‐rf) hybrid reactor using CCl2F2/He as the etch gas. Surface contamination from the gas and from the electrodes was found to affect the etching process as well as etched substrate. Surface damage studies using Schottky diode and x‐ray photoelectron spectroscopy analysis and sidewall damage characterization using room‐temperature conductance measurements of n+‐GaAs quantum wires indicate that very little damage is caused by ECR‐rf reactive ion etching compared with conventional rf reactive ion etching (RIE). In addition, the small residual damage after ECR‐rf RIE is measured to increase with etching time.