You-Lin Wu

Time-to-Breakdown Weibull Distribution of Thin Gate Oxide Subjected to Nanoscaled Constant-Voltage and Constant-Current Stresses

In this paper, we report, for the first time, the statistical distribution of thin-gate-oxide breakdown characterized by using conductive atomic force microscopy (C-AFM) in conjuncdion with the semiconductor parameter analyzer Agilent 4156C. Nanoscaled constant-voltage stress (CVS) and constant-current stress (CCS) were applied to the samples, and the time-to-breakdown Tbd Weibull plots were obtained as a function of stress condition as well as oxide thickness. A different trend in TBD Weibull distribution dependence on the oxide thickness was found for the case of nanoscaled CVS and CCS. By examining the pre- and post-breakdown I-V characteristics as well as their curve fittings, we found that different degradation mechanisms are involved in the oxides subjected to CVS and CCS. For oxides subjected to nanoscaled CVS, the degradation follows the percolation model, whereas for those subjected to nanoscaled CCS, the degradation obeys the trap-assisted tunneling model. The Weibull slope beta value obtained in this paper is found to be consistent with those in the conventional oxide-breakdown tests.

Two-trap-assisted tunneling model for post-breakdown I-V characteristics in ultrathin silicon dioxide

This paper investigated the degradation and breakdown characteristics of an ultrathin silicon dioxide film by using conductive atomic force microscopy (C-AFM) with repetitive ramped voltage stress (RVS). Two-step oxide degradation was determined from the measured current-voltage (I-V) characteristics and topographies. In the first step, bond breaking and negative-charge accumulation near the SiO/sub 2//Si interface causes oxide thinning and an effective increase in SiO/sub 2//Si barrier height. In this step, hard breakdown (HBD) actually does not occur until permanent damage is produced within the oxide during the second step after several times of repetitive RVS. The permanent damage produced inside the oxide film is in the form of traps, which will cause the crooked I-V curves and a larger I-V shift along the voltage axis. A two-trap-assisted tunneling (TTAT) model was proposed to explain the postbreakdown I-V behaviors. In this model, two isolated traps were generated in the oxide after breakdown. The trap location of the nearer traps determines the bending of the postbreakdown I-V curves and that of the farther traps causes the I-V oxide voltage shift along the voltage axis. The model fits the measured postbreakdown I-V curves well when the locations of both the nearer trap and the farther trap are chosen correctly.

Polysilicon wire glucose sensor highly immune to interference

This study investigated the interference elimination ability of a glucose sensor made of polysilicon wire (PSW) with a surface modified by 3-aminopropyltriethoxysilane mixed with polydimethylsiloxane-treated hydrophobic fumed silica nanoparticles plus ultra-violet illumination (γ-APTES+NPs+UV). Glucose sensing of the PSW sensor in the presence of five common interferences such as ascorbic acid (AA), uric acid (UA), acetaminophen (AP), L-cysteine (Lys), and citric acid (CA) was performed. We found that the disturbance caused by the interferences was low for interference-to-glucose concentration ratios up to 600:1 if the PSW surface is modified with γ-APTES+NPs+UV. The outstanding interference immunity of this PSW glucose sensor is believed to be mainly due to the fact that it is a dry-type sensor and the extremely low leakage of the γ-APTES+NPs membrane which allows the PSW to show three orders of magnitude lower leakage current than with the γ-APTES membrane only. In addition to its excellent interference immunity, the PSW glucose sensor with a line width of 100 nm also exhibits a wide linear detection range, an ultra-high sensitivity, an ultra low detection limit, and it can be reused more than a thousand times without much sensitivity degradation.

Position-Dependent Nanoscale Breakdown Characteristics of Thin Silicon Dioxide Film Subjected to Mechanical Strain

This paper investigates the nanoscale breakdown characteristics of thin silicon dioxide (SiO2) films subjected to mechanical strain. A uniaxial compressive strain or a tensile strain was applied to the oxide samples using a homemade bending tool followed by the application of a ramped voltage stress (RVS) or a constant voltage stress to the oxide samples by means of a conductive atomic force microscope tip. The nanoscale current versus voltage (I-V) characteristics and the cumulative failure distributions of the oxide breakdown voltage for the RVS as well as the nanoscale current versus time (I-t) characteristics and cumulative failure distributions of time to breakdown at various surface positions along the strain axis were determined. The nanoscale breakdown characteristics of the strained oxide samples after Co-60 γ-ray irradiation were also investigated. It was found that the central region of both the preand postirradiated strained samples always exhibited a higher oxide leakage current, a lower oxide breakdown voltage, and a shorter time to breakdown than the side regions, regardless if they were under compressive or tensile strain. Our experimental results also showed that interfacial strain release as well as the nanoscale bias-annealing effect increased the Weibull slope β and 63%TBR in the center region of the postirradiated strained oxide samples, compared to the preirradiated ones.

An improved regulated cascode current mirror

Abstract Current mirrors are frequently used in analog and mixed signal circuit design and because they appear so simple, their importance is sometimes overlooked. This work reports the design of an improved regulated cascode current mirror that offers very higher resolution (up to 15 bits) and high speed (up to 400 MHz). The performance of the circuit was analyzed using simulations based on a 0.8 μm biCMOS technology.

Characterization and reliability of low dielectric constant fluorosilicate glass and silicon rich oxide process for deep sub-micron device application

Abstract Fluorosilicate Glass (FSG) with low dielectric constant currently has been replaced as an alternative to SiO2 for device speed improvement. However, several integration aspects, such as Fluorine (F) distribution, F thermal stability, gap fill capability, capacitance reduction and via resistance of FSG prepared by the high density plasma (HDP) chemical vapor deposition (CVD) method are of concern for sub-0.18-μm devices. In this study, HDP–FSG films show different F concentrations at different locations on an 8-inch wafer. In addition, the FSG film shows poor thermal stability and F diffuses out of the film after high temperature annealing and the pressure cook test (PCT). However, the thermal stability of FSG film can be improved by capping with an oxide layer. The results indicate that silicon rich oxide (SRO) has a better effect at blocking the F diffusion out of FSG films at high temperature than plasma enhanced oxide (PE-OX). For the gap fill capability, HDP-FSG can fill all 0.23-μm gaps and some of the 0.21-μm gaps with an aspect ratio

Polysilicon Wire for the Detection of Label-Free DNA

In this paper, we report the use of polysilicon (poly-Si) wire for label-free DNA sequence detection. Both single-strained (ss) homopolymers, polyadenine [poly(A)], polythymine [poly(T)], polycytosine [poly(C)], and polyguanine [poly(G)], and doublestranded (ds) heteropolymers (one homopolymer with its complement homopolymer), (A-T) [poly(A-T)] and (C-G) [poly(C-G)], were detected. These polymers, with different lengths and concentrations, were dropped onto the poly-Si wire surface, and then the currents flowing through the poly-Si wire channel were determined. The absolute value of the amount of current change ΔI in the channel for ss homopolymers with fixed length and fixed concentration is as follows: poly(T) > poly(C) > poly(G) > poly(A). For ds heteropolymers, it was observed that poly(A-T) has a ΔI that is higher than that of poly(C-G). This study also showed that the poly-Si wire is useful for detecting single- and multiple-base changes in the ss homopolymers as well as single-and multiple-matched-pair changes in ds heteropolymers. A single-pair mismatch in ds poly(C-G) was also investigated in this work.

Integration methodology of chemical vapor deposition TiN, chemical vapor deposition W and W chemical mechanical planarization for sub-quarter micron process application

Chemical vapor deposition (CVD) W plugs have been widely used for device metallization with excellent conformity in small contacts/vias with high aspect ratio [J. E. J. Schmitz, Chemical Vapor Deposition of Tungsten and Tungsten Silicides (Noyes, 1991)]. However, some unexpected plug fill such as plug loss and key hole exposing post tungsten chemical mechanical planarization (WCMP) still happened while going to smaller plug size and using metalorganic chemical vapor deposition (MOCVD) TiN barrier. In this study, MOCVD TiN and CVD W fill followed by WCMP for plug metallization were investigated. Extensive analysis had been conducted on various types of defective W plugs. Organic contaminants (hydrocarbon by-products) in MOCVD TiN deposition would prevent W deposition taking place inside the plug. For W wise, lower process temperature, carefully adjusted WF6/SiH4 and WF6/H2 partial pressure ratios had demonstrated better plug fill and electrical performance [T. E. Clark et al., J. Vac. Sci. Technol. B 9, 14...

Improvement in radiation hardness of reoxidized nitrided oxide (RNO) in the absence of post-oxidation anneal

A simple radiation-hard process for rapid thermal reoxidized nitrided oxide (RNO) structures is proposed. This process involves fast pulling (FP) of samples out of the furnace in a mixture of oxygen and nitrogen immediately after the oxidation has been completed. Samples with starting oxides prepared by conventional postoxidation annealing (POA) are also compared. It is found from CV curves that the initial interface property of an RNO structure with a fast pulled starting oxide (RNO/sub FP/) is almost the same as that with a postoxidation annealed starting oxide (RNO/sub POA/); however, after being exposed to Co-60 irradiation, the former becomes superior to the latter. Excess oxygen left at interface in the starting oxide during the fast pulling procedure might be the origin of the radiation-hard property for RNO/sub FP/ structures. >

Nanoscale Bias-Annealing Effect in Postirradiated Thin Silicon Dioxide Films Observed by Conductive Atomic Force Microscopy

This paper investigated the reliability of thin silicon dioxide (SiO2) subjected to irradiation followed by stress, using conductive atomic force microscopy (C-AFM). The I-V characteristics of localized spots on thin oxide films were measured before and after Co60gamma-ray irradiation. The oxide films were then subjected to a ramped voltage stress simultaneously during the I-V measurements. By taking advantage of a small contact area, we report for the first time the nanoscale postirradiation bias-annealing effect in thin SiO2 film using C-AFM. Based on the number of fluctuating current peaks appearing in the I-V curves of the pre- and posttreatment oxide films, as well as the calculated effective barrier height from the Fowler-Nordheim tunneling theory, we found that the trapped charge in the oxide films, but not the charge at the interface caused by Co60gamma-ray irradiation, can be effectively annealed out by a postirradiation ramped voltage.