Jong Tae Baek

Characterization of anhydrous HF gas-phase etching with CH3OH for sacrificial oxide removal

Abstract One of the major issues in surface micromachining is process-induced failures of freestanding microstructures after the removal of sacrificial layers. This failure process consists of temporary deformation due to capillary force during drying and permanent stiction of the deformed microstructures to the substrate due to the residual product. In order to alleviate this failure, some researchers have investigated the use of low-surface-tension liquids, temporary support, sublimation of the final liquid, or the supercritical method. In this paper, we present the characteristics of newly developed anhydrous HF (hydrogen fluoride) gas-phase etching (GPE) technology to remove sacrificial TEOS (tetraethylorthosilicate) oxide. In order to minimize the capillary force of the gas-liquid interface and residual product, methanol of low vapor pressure and low surface tension is employed as a catalyst instead of water vapor. The effectiveness of HF GPE with methanol is verified by successfully fabricating polysilicon cantilevers up to 1000 μm in length with no stiction using photothermal radiometry. The etch rate is 10–15 μm h −1 for sacrificial TEOS oxide, and shows little deviation for a one-dimensional microchannel of 0.1–2 gmm height.

Modeling and Characterization of Gas‐Phase Etching of Thermal Oxide and TEOS Oxide Using Anhydrous HF and CH 3 OH

We propose a model for a gas-phase etching of silicon dioxide using anhydrous HF gas and methanol (CH 3 OH) vapor on the basis of its mechanism and characteristics which were reported by previous researchers. Here, the etch reaction rate was assumed to be determined by the formation step of HF 2 - resulting from the ionization reaction between HF and CH 3 OH adsorbed physcially on the oxide surface. The validity of this etch model was confirmed by the experimental data obtained from etching thermal oxide and tetraethylorthosilicate (TEOS) oxide at various etching conditions : HF partial pressure of 2 to 35 Torr, CH 3 OH partial pressures of 0.3 to 4.5 Torr, and wafer temperatures of 25 to 75°C. It was shown that the gas-phase etching of the oxides could be well characterized by the behaviors of physical adsorptions for HF and CH 3 OH molecules on the oxides, which were expected from the Brunauer-Emmett-Teller (BET) equation with the values of parameters in the etch model. Also, it was shown that the etch selectivities between the thermal oxide and the TEOS were mainly dependent on the wafer temperature and the reactant partial pressures, and could be in the range of 2 to 30 according to the etching conditions in the gas-phase regime.

Effect of temperature and substrate on the growth behaviors of chemical vapor deposited Al films with dimethylethylamine alane source

Abstract Al films were deposited by pyrolysis of dimethylethylamine alane on Si, SiO 2 and TiN substrates without a carrier gas. When Al was deposited on Si and SiO 2 below 160°C, the incubation time increased from 1 to 11 min as the substrate temperature decreased. But no incubation time was observed on TiN substrate. The nucleation activation energies ( E an ) of Al on Si and SiO 2 were 0.71 and 0.79 eV, respectively. The growth rate increased as the substrate temperature increased to 160°C and then it decreased with further increase in the substrate temperature. The maximum growth rate of 600 nm/min was observed on TiN substrate. Below 160°C, the growth activation energies ( E act ) of Al on Si, SiO 2 , and TiN were 0.23, 0.34, and 0.1 eV, respectively. The difference in the growth rate and activation energy might be related to substrate conductivity. The texture of Al film was affected by TiN orientation and Al thickness. When the Si substrate was biased at +100 V, the degree of Al(111) texture was greatly improved. Al film with low resistivity was denser than that with high resistivity.

Fabrication of surface micromachined polysilicon actuators using dry release process of HF gas-phase etching

The HF GPE (gas-phase etching) process was newly developed for the dry-release of sacrificial oxide in polysilicon surface micromachining. Using anhydrous HF gas and CH/sub 3/OH vapor, we successfully fabricated vibrating micro-gyroscope structures with virtually no process-induced stiction. Compared with conventional wet-release, HF GPE process showed more than eight times longer detachment length, which enables highly sensitive sensors.

INTERFACIAL REACTION IN THE SPUTTER-DEPOSITED SIO2/TI0.1W0.9 ANTIFUSE SYSTEM

The effects of annealing temperature on the interfacial reactions and the antifuse I‐V characteristics of ultra thin SiO2 layer deposited on Ti0.1W0.9 substrate were investigated. The interfacial reactions were analyzed using x‐ray photoelectron spectroscopy and Auger electron spectroscopy with the sample which is in situ annealed under ultra high vacuum or ex situ annealed in a nitrogen atmosphere. The surface of the Ti0.1W0.9 substrate was oxidized during sputter deposition of SiO2 layer. Ti, W oxides consist of Ti2O3 (Ti3O5), TiO2, WO2, and WO3. The WO3 and Ti2O3 decomposed into metallic W and Ti at 400 and 500 °C, respectively. The breakdown voltage of the antifuse decreased as the annealing temperature increased, due to the thinning of dielectric layer resulted from the decomposition of Ti, W oxides and the formation of metallic W and Ti. Annealing at 600 °C caused the reaction between metallic (Ti,W) and SiO2 layer and formed elemental silicon in the dielectric layer, where SiO2 layer completely los...

TiN barrier layer formation by the two-step rapid thermal conversion process

We formed TiN barrier layers on single‐crystalline silicon substrates by thermal conversion of Ti films at various temperatures in an ammonia ambient using a rapid thermal process with a sequential two‐step temperature cycle. The first‐step temperatures were held in the low‐temperature range of 400–450 °C for 60–300 s to minimize Ti/Si interaction while keeping reasonable interaction of Ti/NH3 and nitrogen diffusion through the Ti layer to maximize the thickness of the TiN layer. Then, the second‐step was carried out at relatively high temperatures, 700–1000 °C, for 5–90 s to reduce Ti/Si interaction during the silicidation process. By the first steps of the low temperature process, sheet resistances increased with annealing time up to 60 s due to the deep penetration and high concentration of nitrogen in the Ti film, followed by saturation at 60–120 s; they steadily decreased beyond 120 s. Sheet resistance increases were dominated by the nitrogen‐rich Ti layer formed during the first steps of long‐time n...

A new low-resistance antifuse with planar metal/dielectric/poly-Si/dielectric/metal structure

A new antifuse with metal/dielectric/poly-Si/dielectric/metal structure has been developed for use in FPGAs as a voltage programmable link. This structure has two thermally grown dielectrics with an 8.5nm thickness and a boron-doped poly-Si pad. Low programmed on-state resistance of ∼20 Ω was achieved by the formation of Al-Si metal alloy link in the doped poly-Si pad. The metal link was formed by the diffusion of Al from the positive electrode into poly-Si. The dielectric property of this antifuse might be reliable because of no hillocks on the bottom electrode and no interaction between the thermally grown SiO 2 and the bottom electrode.

Interfacial Reaction between Aluminum Metal and Boron-Doped Polysilicon in a Planar Type Antifuse Device

The interfacial reaction between Al metal and boron-doped polysilicon was investigated to understand the mechanism of link formation in the planar type antifuse with a polysilicon pad and two Al electrodes. In the antifuse, the Si–Al alloy filament with a low resistance was formed only on the boron-doped polysilicon pad, not on the phosphorus-doped or undoped polysilicon pads. After annealing Al/boron-doped polysilicon at 400°C for 20 min, an Al-B compound (AlB2) was found by the reaction between Al metal and solute borons at the grain boundaries of polysilicon using Auger electron spectroscopy, X-ray diffractometer, and X-ray photoelectron spectroscopy. In the planar type antifuse device, the formation of AlB2 at the grain boundaries might act as a seed for the conductive filament formation by supplying Al from the positive electrode. After forming a low resistance Si–Al alloy filament, it grows toward the negative electrode by the reaction between supplied Al and highly reactive solute borons segregated at the grain boundaries.

Characterization and removal of trace heavy metal contamination on Si-surface resulted from CHF3/C2F6 reactive ion etching

The characteristics of removal of trace heavy metal contamination on the silicon surface resulted from CHF3/ C2F6 reactive ion etching (RIE) was studied using total reflection X-ray fluorescence spectroscopy (TRXRF). In order to investigate the depth profile of metallic contaminants near the surface, TRXRF measurements containing glancing angle scans were performed after slightly etching of silicon surface by repeating the cleaning procedures that diluted HF (DHF) removed the oxide grown by the mixture of H2SO4 and H2O2 (SPM) or O2 plasma ashing treatment. RIE and O2 plasma ashing processes resulted in metal contamination such as Fe, Ni, Zn, etc. They were present as both of plate-type and bulk-type, and the large part of plate-type contamination was removed easily. Especially, Fe resulted from RIE was the most abundant contaminant and its concentration was ~1011 atoms/ cm2. Fe was mainly distributed within ~2 nm from silicon surface and could be effectively reduced below ~2×1010 atoms/ cm2 by etching of ~2.5 nm depth of the silicon substrate.

Investigation of link formation in a novel planar-type antifuse structure

Abstract A novel antifuse structure with planar-type polysilicon pad is described. The formation of a link between the aluminum electrodes after application of a programming voltage was also investigated. The structure consists of Al/SiO 2 poly-Si/SiO 2 /Al layers. The poly-Si pad was doped with boron and the thickness of the antifuse dielectric was 9 nm. When a programming voltage is applied, the electrodes are connected by the mass transfer of aluminum through the dielectric and the doped polysilicon pad. The on-state resistance of about 10 Ω, which is the lowest on-state resistance ever reported, is obtained after breakdown with 9.9 V programming voltage. Scanning Auger microscopy analyses show the propagation of a link, as mass transfer of aluminum in the boron doped polysilicon pad. The elliptical link has a maximum diameter of 1.0 μm in the horizontal direction and a minimum diameter of 320 nm in the vertical direction.