Anisotropic etching of deep trenches in single-crystal Si has been obtained using reactive ion etching with SFdO2 gas mixtures for the first time. The influence of wafer temperature, total gas pressure, and O2 content on profile control and etch selectivity (Si:SiO2) has been determined. A high anisotropy and selectivity (18:1) have been achieved at 25% O2 content. Scanning electron microscopy and Auger electron spectroscopy techniques have been used to study the trench profile and surface roughness. Methods for post-reactive ion etching surface treatment have been explored to remove surface roughness.Reactive ion etching using gas mixtures has been investigated extensively and successfully applied to the mask pattern transfer in the fabrication of semiconductor devices. Properties such as precise line width control, proper vertical profile control, and high etching selectivity have been obtained with this technique. Both ion bombardment and chemical reaction play a major role in reactive ion etching. Basically, directional etching resulting from the reaction between the active gas-phase species and the etched surface is dominated by the ion sputter etching and selectivity from the competition of different materials is determined by chemical plasma etching (1). Generally, it is difficult to achieve both high anisotropy and selectivity at the same time.Anisotropic etching of deep Si trenches have been considered as a useful technology for use in the fabrication of modern semiconductor devices such as device isolation (2), DRAM capacitor (3), and power devices (4, 5). For these applications, chlorine-based plasmas have been extensively utilized for anisotropic etching of trenches. Problems observed with this process include sharp trench corners that create reliability concerns due to field crowding and the deposition of black silicon on the surface which interferes with the etching. The fluorine-based plasmas such as SFs (6) and NF3 (7) have also been previously studied. It has been found that these gases provide a high Si etch rate and high silicon/oxide etch selectivity, but the previous reports have indicated that these methods are not suitable for formation of trenches because the etching is isotropic. Flamm et al. (8) have demonstrated that the isotropic etching behavior of these gas plasmas is due to the poor efficiency of ion bombardment in the etching reaction. A large amount of investigation for surmounting this obstacle has been proposed: the loading effect at low pressure (9), microwave multipolar plasma (10), RF double cathode (11), dilution of SFs with nonactive gases JAr (6, 12), He (13), or N2 (12, 14)], or dilution of SF6 with reactive gases [CC14, HC1 (15), CFC13, C12 (16), H2 (12), 02 (12,(17)(18)(19), C2C1F5, or CBrF3 (20)]. From these experiments, reactive ion etching with combined isotropic and anisotropic reactions has been observed for silicon. The best results for fulfilling the requirements of high anisotropy and high selectivity for the trenches have been obtained using SF6 with the addit...

Temperature-gradient zone melting has been utilized to study growth kinetics in InSb. Indium and lead were used as zone metals. In the temperature region between 410° and 460°C, the rate of zone migration was observed to be dependent on both the thickness of the zone and the orientations of the solids at the bounding interfaces. Interface velocities as large as 2×10−6 cm/sec were observed during In:InSb growth runs for liquid zones having an average temperature gradient of 30°C/cm. During Pb:InSb growth runs, interface velocities as large as 0.9×10−6 cm/sec were observed for liquid zones having an average temperature gradient of 60°C/cm. Photomicrographs of growth surfaces obtained after In:InSb growth runs clearly indicated that growth proceeded by a two-dimensional nucleation mechanism. A best-fit comparison with theory of the observed dissolution interface velocity as a function of zone thickness also indicates a two-dimensional nucleation growth mechanism for both the In:InSb and the Pb:InSb systems.

Ionic diffusion of two mobile alkali earth impurities, calcium and magnesium, has been observed in thin vitreous silicon dioxide (silica) films at temperatures as low as 80~ A metal oxide semiconductor MOS capacitor has been utilized as the test structure for this device investigation. Controlled amounts of each impurity were introduced onto thermally oxidized surfaces of p-type silicon wafers prior to device contact metallization through immersion in strongly basic solutions, then the impurities were driven into the silica films during final metal sintering. Initially, transient ion diffusion currents have been measured during elevated temperature device stressing under both unbiased (shorted) and biased stress conditions; then the currents were integrated to determine the time dependence of mobile charge transferred from the gate interface to the substrate interface. Capacitor C-V flatband voltage shifts have also been examined to verify the amount of mobile charge transferred through the silicon dioxide films under biased as well as unbiased stress conditions. Negative flatband voltage shifts have been observed under unbiased (shorted) stress conditions, indicating the calcium and magnesium were present in the silica films as :mobile cations. These observations were subsequently supported by secondary ion mass spectroscopy impurity concentration profiles within the silica films. Finally, impurity diffusion activation energies have been determined for both ions from time dependent charge flux curves between 80 and 180~ Both activation energies were observed to exhibit strong dependencies upon applied electric field intensity during device stressing. These results are in agreement with an existing mobile ion transport model that includes both an emission-limited (interface boundary layer) activation energy term as well as a drift-limited (bulk trapping) term.Diffusion of mobile impurity ions within thin vitreous silicon dioxide (silica) films thermally grown on crystalline silicon substrates has been studied extensively over the past several decades. In 1986, a detailed review article on this subject by Hillen and Verwey ~ summarized the results of an extensive number of mobile ion transport experiments by numerous authors on a variety of impurities as well as discussed several different measurement techniques that were utilized in many of these investigations.To a great extent, mobile charge characterization activities in silica device films were initiated after threshold voltage instabilities were observed by silicon metal oxide field effect transistor (MOSFET) device manufacturers. 2' 3 Such device instabilities were identified as being primarily due to mobile alkali cations, in particular sodium, that could contaminate exposed silica dielectric films (e.g., gate or field regions) during normal device processing, a s Migration of mobile cations through a gate o1: field oxide to the substrate interface of a MOSFET device could then lead to instability by causing either inversion or accumulation of the...

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