Tae-Hyuk Ahn

HIGH TEMPERATURE PLATINUM ETCHING USING TI MASK LAYER

Platinum is a strong candidate for an electrode material of the high dielectric capacitors in highly integrated dynamic random access memory devices. However, it is extremely difficult to etch the fine patterns of Pt due to an inherently low etch slope. This characteristic comes from the physical sputtering nature of the Pt etching process. This article reveals that the Pt etching profile depends on the change of the Ti mask layer caused by the increase of wafer temperature during etching. The Pt etching slope of 80° in 0.40 μm pitch was attained by heating the wafer substrate up to 220° with plasma-on. From the transmission electron microscopy analysis the Ti mask is considered to be deformed to TiOx layer in oxygen plasma at high wafer temperature, elevated either by high electrode temperature or plasma irradiation.

Effects of fluorocarbon polymer deposition on the selective etching of SiO2/photoresist in high density plasma

A new periodic two-step process composing SiO2 etching with high bias radio frequency (rf) power and fluorocarbon deposition with low bias rf power was studied for the highly selective etching of SiO2 to photoresist (PR). In this experiment, the time scale of each step is longer than the conventional time-modulation technique in order to maximize the protection layer on PR and prevent the etch stop. Many works have focused on the gaseous chemical species especially CF2 radicals for selective surface reaction. However, normally utilizing only the difference of stoichiometric surface reaction, they inherently limit the etching conditions such as dependence on the chemical composition of PR, densities, and impurities of SiO2 layers. And these conventional processes severely suffer reactive ion etching lag or etch stop in high selective etching. The new process utilizes fluorocarbon deposition with low bias rf power to increase the mask selectivity by enhancing the difference between the polymer thickness on ...

Suppression of topography dependent charging using a phase-controlled pulsed inductively coupled plasma

The topography dependent charging (TDC) potential on the bottom of an oxide contact is measured with an in-situ charge-up monitoring wafer during plasma processing. The effects of the contact aspect ratio and the bias power on the TDC are investigated from the potentials measured on that wafer. By analyzing the potentials, we correlate the TDC to the difference of the charging potentials between a shading and a blank probe. We can suppress TDC considerably using a phase-controlled pulsed inductively coupled plasma, especially when the phase delay of the bias power relative to the source power is near 180/spl deg/ (out-of-phase condition).

Charge-up damage of dual gate transistor during RF pre-cleaning of metal contact before barrier metal deposition

The damage of dual gate (p-gate PMOS and n-gate NMOS) transistors during RF pre-cleaning of their metal contacts before barrier metal deposition has been investigated in logic devices by varying the aspect ratio of metal contacts and RF source power. With higher aspect ratios and a higher source power for RF pre-cleaning, the gate leakage current of PMOS increases, while that of NMOS stays constant. We present a possible explanation for this difference in damage behaviour.

Evaluation of plasma-induced charging damage on metal contact process

The evaluation of plasma-induced charging damage in a metal contact process has been studied with a two dimensional Monte-Carlo simulation and related experiments. From the simulation, it is concluded that the linear shrinkage of the design rule possibly evokes exponential plasma-induced charging damage on the gate oxide during the plasma process. We also confirmed the simulation results with the two different experiments, in-situ charge-up monitoring wafers and fully fabricated test wafers. A phase-controlled pulsed inductively coupled plasma is proposed to suppress the plasma-induced charging damage. Preliminary results show that charging damage is strongly suppressed when the phase delay of the bias power to the source power is near to 180 degrees.

Ellipsometric inspection of the inner surface of pellicle-covered masks

Crystal growth and haze formation on photomasks become serious problems in UV lithography. As the wavelength becomes shorter, photons carry more energy, so the chances of having a photochemical reaction become much higher. Pellicle, adhesive, residue from cleaning or resist strip process, and any contaminant in air can react with UV to form unwanted crystals and a haze layer on reticles. These will reduce the light transmission during exposure process. Thus, frequent mask inspection and periodic mask cleaning are needed to overcome these problems. However, these will in turn increase manufacturing cost and reduce mask life. Thus, a proper mask inspection tool is required to provide early warning of haze formation. In this work, we devised a new ellipsometric technique to investigate the inner surface of mask without removing pellicle. Ellipsometry is known to have mono-layer sensitivity and it can be used to measure any film or partial film formed on non-patterned spot in early stage of growth. However, when a pellicle covers the surface of mask, the ellipsometric data reflected from surface are extremely distorted due to the non-normal transmission through the pellicle. Thus, data analysis becomes extremely difficult without knowing the optical properties of pellicles. In order to solve this problem we developed compensation technique in which two blank pellicles are situated in the optical path in a way to compensate the polarization changes caused by the pellicle on mask. With this method, the conventional ellipsometry spectra of {Δ, Ψ} are deduced.