C. Y. Chang

The effects of plasma treatment for low dielectric constant hydrogen silsesquioxane (HSQ)

Abstract Low density materials, such as hydrogen silsesquioxane (HSQ), can offer lower dielectric constants. With HSQ, a low value of K can be achieved if the density of Si H bonding is maintained at a high level and the formation of –OH bonds and absorption or creation of water in the film is minimized. In this work, we have studied the use of hydrogen plasma to improve the quality of HSQ. In addition, the effects of N 2 and O 2 plasma post-treatments on HSQ are investigated. The leakage current of HSQ decreases as the H 2 plasma treatment time is increased. However, the leakage current of HSQ increases as the N 2 and O 2 plasma treatment time is increased. A model is proposed to explain the role of hydrogen in HSQ. The hydrogen passivates the surface of porous HSQ. The H 2 plasma treatment provides additional hydrogen passivation of the HSQ. On the other hand, the N 2 and O 2 plasma treatments reduce the hydrogen passivation of HSQ. As a result, both the leakage current and dielectric constant increase as the N 2 and O 2 plasma treatment time is increased. Finally, HSQ with H 2 plasma treatment is used as the intermetal dielectric in a multilevel interconnection structure. Consistent with our model, the via resistance decreases with increasing H 2 plasma treatment time.

Effects of isolation materials on facet formation for silicon selective epitaxial growth

Effects of isolation materials on facet formation for low temperature Si selective epitaxial growth (SEG) using Si2H6 have been demonstrated by ultrahigh vacuum-chemical molecular epitaxy (UHV-CME) system. The activation energy of the Si epitaxial growth is 47.35 Kcal/mol. The isolation material includes silicon nitride, wet oxide, and tetraethylorthosilicate (TEOS) oxide. Different isolation materials have different faceting behaviors for the Si epilayer. A silicon nitride mask and a wet oxide mask result in a preferred faceting plane of (111) and (311), respectively. Using a TEOS oxide mask, we obtain a low temperature Si SEG layer without facet and twin formation. The preferred faceting plane orientation for different isolation materials is ascribed to the difference in the interface free energy between the Si layer and the isolation material.

Pulsed KrF laser annealing of Ni/Si0.76Ge0.24 films

Pulsed KrF laser annealing can suppress the island structure formation and Ge segregation associated with the interfacial reactions of Ni/Si0.76Ge0.24. For the Ni/Si0.76Ge0.24 films annealed at an energy density of 0.1–0.3u2009J/cm2 nickel germanosilicide associated with the amorphous overlayer was formed, while at energy densities above 0.4u2009J/cm2 cellular structures of Ge-deficient Si1−xGex islands surrounded by Ni(Si1−xGex)2 due to the constitutional supercooling occurred. For the continuous Ni(Si1−xGex) films grown at 200u2009°C, subsequent laser annealing at a higher energy density of 0.6–1.0u2009J/cm2 caused transformation into homogeneous Ni(Si0.76Ge0.24)2 films without island structure and Ge deficiency which readily appeared on furnace annealing at temperatures above 400u2009°C. At energy densities above 1.6u2009J/cm2 the same cellular structures as described above were also noted.

High current gain, low offset voltage heterostructure emitter bipolar transistors

Heterostructure Emitter Bipolar Transistors (HEBTs) were fabricated with improved characteristics by employing the emitter edge-thinning technique. Optimum design for the n-GaAs emitter and the ledge thickness were used to remove the potential spike and to prevent ledge conduction simultaneously. Current gains as high as 720, which is the highest current gain ever reported for HEBTs, and offset voltages down to 70 mV were obtained. Very large improvement in current gain, especially at low collector current, was obtained by using the emitter edge-thinning technique.<<ETX>>

Phosphorus doping of Si and Si1−xGex grown by ultrahigh vacuum chemical vapor deposition using Si2H6 and GeH4

100 ppm PH3 diluted in hydrogen is used as the n‐type dopant gas in Si and Si1−xGex epilayers grown by ultrahigh vacuum chemical vapor deposition (UHVCVD) using Si2H6 and GeH4. The phosphorus concentration in Si increases linearly at a small PH3 flow rate and becomes nearly saturated at higher flow rates, while the phosphorus concentration in Si1−xGex only shows a nearly linear behavior with PH3 flow rate. The growth rates of Si and Si1−xGex epilayers decrease seriously (∼50%) and slightly (∼10%) with the increase of PH3 flow rate, respectively. These results can be explained by a model based on the enhancement of hydrogen desorption rate at smaller PH3 flow rates and different levels of the effects of phosphorus blocking of surface‐activated sites between Si and Si1−xGex epilayers at higher PH3 flow rates.

Copper electroplating for future ultralarge scale integration interconnection

Copper has received considerable attention during the past few years because of its low electrical resistivity, high melting temperature, and high electromigration resistance. Since electrochemical plating has several advantages compared to physical vapor deposition and chemical vapor deposition due to its low cost and low processing temperature, it becomes the most attractive technique for the implementation of Cu metallization. In this article, we report an electroplating scheme for Cu deposition and study aspects of copper electroplating related to chemical additives effected on Cu deposition. A low resistivity Cu film (∼2 μΩu200acm) could be obtained when metallic ion concentration is decreased or current density is increased. The detailed correlation between film resistivity, electrolyte concentration, current density, and film morphology is given in this study. In addition, chemical additives in electrolyte solutions also play important roles in copper electroplating. In this report, thiourea and polyet...

Heterojunction bipolar transistors with emitter barrier lowered by /spl delta/-doping

An npn heterojunction bipolar transistor with a Si-/spl delta/-doped layer at the emitter-base hetero-interface is demonstrated. The Si /spl delta/-doped layer reduces the potential spike at the emitter junction. This design reserves the abruptness of the heterojunction, reduces electron barrier and increases the hole barrier simultaneously. Experimental results show that the HBTs turn-on characteristics are greatly improved while the current gain remains high. The offset voltages as low as 44 mV have been obtained. Very high current gains at very low collector current densities are obtained.<<ETX>>

Characterization of multilayered Ti/TiN films grown by chemical vapor deposition

The resistivity of multilayered Ti/TiN films grown by chemical vapor deposition can be reduced from 240 μΩ cm (standard sample) to 120 μΩ cm with NH 3 plasma post-treatment for 300 s. Increasing the number of multilayered Ti/TiN films of reduced thickness and a plasma post-treatment technique contributed to reducing the resistivity of TiN films effectively. Smooth multilayered Ti/TiN films were observed by XTEM image. The content of chlorine in the multilayered Ti/TiN film was 1.6 at.%. Therefore, corrosion in the subsequent Al film should be minimized. SIMS depth profiles of the multilayered Ti/TiN sample showed that Ti atom distribution is fairly uniform. The result is in agreement with the observation of XTEM and the measurement of AES depth profiles. The resistivity of multlayered Ti/TiN films can be further reduced to 75 μΩ cm with an in situ NH 3 plasma post-treatment (500 W) for 300 s followed by RTA at 900°C for 60 s. Therefore, low resistivity (<100 μΩ cm) and low Cl concentration (<2 at.%) CVD TiN films can be achieved by a combination of forming a multilayered Ti/TiN structure, and using NH 3 plasma post-treatment and RTA.

Interfacial reactions of the Co/Si1−xGex system

Abstract Thermal reactions of Co(200)/Si0.76Ge0.24(1500)/Si and Co(200)/Si0.54Ge0.46(1000)/Si systems in a vacuum of 1−2×10−6 Torr were studied. At temperatures above 200 °C Ge segregation appeared even though no silicides and/or germanosilicides were formed. At a temperature of 225–550 °C Co(Si1 − yGey) was formed, in which the Ge concentration was deficient. The formation temperatures of CoSi2 in the Co/Si1 − xGex systems, where x = 0.24 and 0.46, were above 575 °C, being relatively higher than that in the Co/Si system. At temperatures above 500 °C the island structure, Ge segregation to the surface of the exposed Si1 − xGex films, and the penetration of reacted layer into the Si substrate occurred. At temperatures above 700 °C a SiC layer was grown on the film surface. For the Si0.54Ge0.46 films the penetration of the reacted layer into the Si substrate occurred even at 350 °C owing to the wave structure of the as-grown Si0.54Ge0.46 films. A Si layer interposed between Co and Si0.76Ge0.24 films is an effective scheme to grow a continuous CoSi2 contact at 550–600 °C without inducing Ge segregation and hence the strain relaxation in the Si0.76Ge0.24 films.

Interfacial reactions of Pd/Si0.76Ge0.24 by pulsed KrF laser annealing

The interfacial reactions of Pd/Si0.76Ge0.24 were studied by pulsed KrF laser annealing as a function of energy density and pulse number. At an energy density of 0.1–0.4u2002J/cm2, a continuous germanosilicide layer composed of a low-temperature phase, Pd2(Si1−xGex), and a high-temperature phase, Pd(Si1−xGex), was formed. In contrast to vacuum annealing, Ge segregation out of the germanosilicide layer and the strain relaxation of the residual Si0.76Ge0.24 film could be effectively suppressed by pulsed KrF laser annealing at 0.1u2002J/cm2. Multiple pulse annealing at 0.1 J/cm2 could further homogenize the Pd concentration of the germanosilicide layer and promote the growth of Pd(Si1−xGex). Concurrently, the smoothness of the germanosilicide layer was substantially improved in comparison with those grown by vacuum annealing at temperatures above 200u2009°C. The studies also revealed that for multiple pulse annealing at 0.1u2002J/cm2 with a low repetition rate, 1 Hz, the evolution of phase formation and Pd diffusion could b...