Thin Gate Oxide Integrity Research Articles

The effect of native oxide on thin gate oxide integrity

We have studied the effect of native oxide on thin gate oxide integrity. Much improved leakage current of gate oxide can be obtained by in situ desorbing the native oxide using HF-vapor treated and H/sub 2/ baked processes. Furthermore, an extremely sharp interface between oxide and Si is obtained, and good oxide reliability is achieved even under a high current density stress of 11 A/cm/sup 2/ and a large charge injection of 7.9/spl times/10/sup 4/ C/cm/sup 2/. The presence of native oxide will increase the interface roughness, gate oxide leakage current and stress-induced hole traps.

Internal oxidation of vacancy agglomerates in Czochralski silicon wafers during high-temperature anneals

Fast pulled Czochralski silicon crystals usually contain large octahedral vacancy agglomerates. These voids are known as D defects, which degrade the integrity of thin gate oxides by causing time zero dielectric breakdown. After annealing the wafers at temperatures above 1100 °C, the gate oxide integrity is clearly improved. We show by theoretical estimation, light-scattering tomography and transmission electron microscopy studies that the vacancy agglomerates can be filled with silicon oxide by internal oxidation. This is brought about by diffusion of interstitial oxygen to the voids, which can be regarded as internal surfaces. In this way they become less detrimental for thin gate oxides, because now they consist of silicon oxide itself. However, they are still present in an octahedral-like geometry and can be observed by Brewster angle infrared light-scattering tomography.

Effect of Ultra-Dilute RCA Cleans on the Integrity of Thin Gate Oxides

ABSTRACTComparative studies on the effect of Ultra-dilute RCA cleans, chemical ratios in excess of 300:1, and Dilute RCA cleans, chemical ratios around 50:1, on the integrity of thin gate oxides have been performed. Ultra-dilute RCA chemistries have shown particle removal efficiency, metallic contamination removal, surface roughness, Qbd, BVox and defect density equivalent to those obtained using dilute RCA chemistries. Furthermore ultra-dilute chemistries use less chemical leading to shorter rinse times and thus increased throughput as compared to the dilute RCA chemistries.

H2O2 Decomposition and Its Impact on Silicon Surface Roughening and Gate Oxide Integrity

In this study the impact of temperature and metal contamination on the stability of hydrogen peroxide in the two most common wet chemical cleaning mixtures for wafer process operations has been investigated. The stability of the caustic mixture ( NH4OH/H2O2/H2O) was found to be very sensitive to certain metallic contaminations in the sub-ppb range, while the stability of the acid mixture ( HCl/H2O2/H2O) is mainly influenced by non metallic, anionic components of the solution itself. We observed also a strong oscillating behaviour of the rate of the oxygen gas evolution caused by the decomposition of H2O2. Furthermore it was found, that the oxygen gas bubbles, formed by the decomposition of hydrogen peroxide cause a certain kind of micro-roughness on the silicon surface through a micro masking mechanism. In a series of experiments we could prove that this kind of surface roughness has a significant impact on the integrity of thin gate oxides.

Effects of wafer bow and warpage on the integrity of thin gate oxides

We have studied the effects of initial wafer bow and warpage on the integrity of thinner gate oxides grown by both furnace and rapid thermal processing (RTP) methods. There is evidence of a correlation between wafer warpage and bow to the charge-to-breakdown characteristics of the gate oxide. An almost linear increase in defect density was observed when plotted as a function of increasing wafer warpage. The lifetime (t50%) of the samples with initial warpage of 10 μm or less is reported higher than those with initial warpage of more than 60 μm for both furnace and RTP-grown oxides. The value of bow for the warped samples was taken for cases with the highest positive and negative values so both kinds of shape trends could be investigated. With initial wafer warpage ranging from 4 to 70 μm, we present the results of wafer dimensional analysis and correlate these to defect density and lifetime studies for thin gate oxides.

New Wet Cleaning Strategies for Obtaining Highly Reliable Thin Oxides

The effect of metal contamination and silicon surface defects on the gate oxide yield is investigated. The characteristics of various cleaning procedures are studied and correlated with the integrity of thin gate oxides. The standard wet cleaning recipe is optimized and a new cleaning strategy is proposed. Selective contamination experiments in chemicals and on Siwafers are used to investigate the effect of small amounts of metal contaminants on the gate oxide integrity. It is found that the characteristics of the silicon substrate play a dominant role in this. HF-last processes are investigated and a new wet cleaning strategy is proposed.

Cleaning technology for improved gate oxide integrity

The effect of metal contamination and silicon surface defects on the gate oxide yield is investigated. The characteristics of various cleaning procedures are studied and correlated with the integrity of thin gate oxides. The standard wet cleaning recipe is optimized and a new cleaning strategy is proposed. Selective contamination experiments in chemicals are used to investigate the effect of small amounts of metal contaminants on the gate oxide integrity. HF-last processes are investigated and a new wet cleaning strategy is proposed.

Effects of Silicon Ion Implantation upon Thin Gate Oxide Integrity

ABSTRACTIn this study, using oxide breakdown voltage and time-dependent-dielectric breakdown measurements, thermal wave modulated reflectance and chemical etching/optical microscopy, we investigated effects of Si ion implantation upon formation of D-defects and thin gate oxide integrity. Our data show that addition of Si ion implantation with a dose of up to 1013 ions/cm2 improves oxide integrity if the implantation is done at a certain step just before sacrificial oxidation in the Mb DRAM process. However, no improvement in oxide integrity is observed when the same implantation is done on the virgin wafer surfaces at the start of the same Mb DRAM process. We discuss our hypothesis that the improvement in oxide integrity is due to a reduction in the D-defect density in the near-surface region of the wafer.

Improvement in very thin gate oxide integrity by ion implantation

It has been found that implanting silicon substrates prior to oxidation considerably improves the quality of very thin gate oxides (70 A). Data is presented on leakage characteristics and breakdown distributions of these oxides.