David Hsu

Thermal stability of crystalline thin films

Abstract A simple model, free of any adjustable parameter, is introduced for the size-dependent melting of crystalline thin films. It predicts that the melting temperature of a crystalline thin film decreases as its thickness decreases. The prediction is supported by the available experimental results on Pb, In, Sn and Fe thin films.

Effect of Gastric Bubble as a Weight Reduction Device: A Controlled, Crossover Study

In spite of the widespread use of the Garren-Edwards gastric bubble as an adjuvant device in weight reduction, its efficacy has not been established. Therefore, our purpose was to conduct a randomized, double-blind, crossover study of this device in the management of exogenous obesity. The study group consisted of 23 patients, 21 women and 2 men, ranging in age from 21 to 53 yr. Patients were 25%-111% above their ideal body weight. They were studied for 24 wk, consisting of two separate 12-wk evaluation periods. Patients were randomly assigned either to receive the gastric bubble or to have a sham procedure. After the first 12-wk evaluation period, the gastric bubble and sham were administered in crossover fashion, so that those who had received the gastric bubble initially received the sham later and vice versa. The study coordinator remained blind to the kind of treatment, weighed each patient biweekly, enforced dietary counseling, and provided behavior modification. Those who had passed or were found to have a deflated bubble at the end of the treatment period were excluded from the study. Mean weight reduction in the two evaluation periods did not differ significantly. Patients lost 5.4 +/- 1.7 kg (mean +/- SE) during the gastric bubble period and 5.20 +/- 0.8 kg during the sham period. The order of administration of the gastric bubble and sham did not significantly affect the result. The time-course of mean biweekly values, however, revealed that with the gastric bubble, weight loss was significantly greater only during first (p less than 0.005) and second (p less than 0.025) 2-wk evaluation periods. This difference, however, disappeared after the initial 4 wk of treatment. These observations suggest that although gastric bubble implantation reduced weight significantly more than the sham procedure initially, the mean weight loss during 12 wk of evaluation was not different between the two periods. In our opinion, the gastric bubble is of no value as an adjuvant device in weight reduction.

Curing kinetics and optimal cure schedules for underfill materials

The curing reactions and optimal schedules of three promising flip-chip underfill materials under isothermal and nonisothermal treatments are reported. It is found that curing reactions for three-tested underfill materials are autocatalytic, and the cure rate can be well described by the corresponding model. The activation energy, the rate constants, as well as two reaction orders m and n are determined to describe the curing progress. The temperature dependence of the cure degree for each heating rate is also investigated. It is found that the extent of reactions at a given temperature is a function of the heating rate. The glass transition temperature for the underfill UF-II is determined as a function of cure degree. It is found that the glass transition temperature increases with the cure time.

ILD thermal stability in deep-submicron technologies : from thin to ultrathin dielectric films

Thermal stability is a critical issue for polymer thin films being used as interlevel dielectrics (ILDs) in deep- submicron multilevel interconnection. One of crucial parameters to predict thermal stability is the glass transition temperature (Tg). Unfortunately the glass transition in polymer thin films is still not clearly understood. In this work, a simple model is developed for the thickness dependence of Tg of polymer thin and ultrathin films. It is predicted that Tg of polymer thin films can either be reduced or enhanced in comparison with its bulk values, depending on the polymer-substrate and polymer-surface interactions. In addition, the thickness- dependent Tg of polymer thin films can exhibit a minimum as a function of thickness. Experimental data from technologically important ILD films are obtained to support the theoretical model.

Two limits of melting temperatures of nanocrystals

It is demonstrated that the melting temperature of nanocrystals embedded in a matrix exhibit two asymptotic limits as the size of the nanocrystal reaches its smallest value. The lower limit of melting temperatures is related to the disappearance of size-dependent entropy of melting and is considered as the lowest glass transition temperature which is located between Kauzmann temperature and glass transition temperature. The upper limit of a nanocrystal embedded in a matrix is determined by the ratio between the bulk melting temperature of the embedded nanocrystal and that of the matrix. The predicted thermodynamic melting temperature range and the lowest glass transition temperature are supported by available experimental evidences.

Change in chemical state of fluorinated polyimides after the electroless Cu deposition solution treatment

Integrated circuit (IC) miniaturization continues to scale down to fulfill the demand for higher speed and greater efficiency in the high performance ultra-largescale (ULSI) applications. At such reduced dimensions, long RC time delay, excess power dissipation, and undesirable crosstalk between adjacent metal lines will limit performance of devices [1–6]. Therefore it is desirable to introduce new materials for conductive layers and low-dielectric-constant (low-k) interlayer dielectrics (ILDs) [7, 8]. The combination of Cu-based metallization and the low-k materials is considered promising for future integrated circuit fabrication. The present work is directed to investigate the compatibility between promising low-k materials and the electroless Cu deposition developed for sub-quarter-micron interconnect applications [9, 10]. Fluorinated polyimides have been increasingly used in the microelectronic applications due to their low dielectric constant, high glass transition temperature, low moisture absorption and high thermal stability. In this work, the low-k materials selected are two fluorinated polyimides, FPI-45M and FPI-136M, whose dielectric constants are 2.8 and 2.64 respectively [11]. Fourier transform infrared (FTIR) spectroscopy was employed to examine the possible chemical reactions between the low-k materials and electroless Cu deposition solution under different treatment solution temperatures and times. The electroless Cu deposition solution contained cupric sulfate, ethylenediaminetetraacetic acid (EDTA) and formaldehyde. The pH of the solution was in the range of 12.3–12.7, adjusted by tetramethylammonium (TMAH). Stabilizers and surfactants were also added to the solution to increase the solution stability and to decrease the surface tension of the solution [10]. The detailed composition of the electroless Cu deposition solution is shown in Table I. Two low-k fluorinated polyimide polymers with different proprietary formulations (FPI-45M and FPI-136M) developed by DuPont [11] were used as samples for the investigation of their compatibility with the electroless Cu deposition solution. FPI-45M and FPI-136M are two copolymers which mainly consist of pyromellitic dianhydride (PMDA) and 2,2-bis(trifluoromethoxy)benzidine (TFMOB), p-phenylenediamine (PPD) and different flexibilizing comonomers which can improve the mechanical properties of copolymers. The generalized structures for FPI-136M and FPI-45M are schematically shown in Fig. 1 [11]. As shown in Fig. 1, the flexibilizing comonomers for FPI-136M and FPI-45M are, respectively, 6FDA and BPDA. Generally, the bath of the electroless Cu deposition solution employed in this work is operated at temperatures ranging between 50 and 80 ◦C for Cu deposition. Therefore 57 and 77 ◦C were selected as low and high experimental temperatures at which the FPI-45M and FPI-136M supported on Si substrates were investigated, specifically to investigate whether they would chemically react with the electroless Cu deposition. In the experiments, the sample films were immersed in the electroless Cu solution at two different solution temperatures, 57 and 77 ◦C, for 5, 10, and 15 min. During the immersion of sample films in the electroless Cu deposition solution under the real deposition conditions, copper deposition did not occur because there was no Cu seed layer initially deposited onto the polyimide films.

Electroless copper deposition solution induced chemical changes in low-k fluorinated dielectrics

Abstract It is demonstrated that the electroless Cu deposition solution can lead to a significant chemical change in FLARE ™ 1.51, as indicated by the observed disappearance of the 1726 cm −1 absorption band from IR spectra. Two possible reaction mechanisms are suggested for the observed change in FLARE ™ 1.51.

Supercooling vs overheating in the III-V semiconductor compound InSb: an abrupt-discontinuous relationship

The dependence of supercooling level ((Delta) T-) of InSb melt preceding on its melt overheating ((Delta) T+) above the equilibrium melting temperature, is investigated for the first time on a III-V semiconductor compound. The dependence of (Delta) T- on (Delta) T+ in the InSb melt is shown to be abrupt-and-discontinuous. The observation can be linked to the semiconductor-metal transition upon melting, and is probably general, occurring also for other III-V and group IV semiconductors.