A.J.R. de Kock

The effect of doping on the formation of swirl defects in dislocation-free czochralski-grown silicon crystals

Abstract During the growth of macroscopically dislocation-free Czochralski silicon crystals three types of swirl defects (types A, B and C) can form. The effect of doping with electrically active impurities (B, Ga, Sb, P and As) and isoelectronic impurities (Sn) on the formation of these microdefects has been investigated by means of preferential etching, copper and lithium decoration, X-ray transmission topography and EBIC-mode SEM. Doping with donors (concentration > 10 17 cm -3 ) suppresses the formation of A swirl defects (dislocation loops). Doping with acceptors (concentration > 10 17 cm -3 ) eliminates the formation of B and C swirl defects, while doping with tin has no effect. The new experimental data strongly suggest that the formation of the different types of swirl defects is due to parallel condensation processes involving silicon interstitials and vacancies. The observed doping effects are explained in terms of complex formation as a result of coulomb attraction between dopants and charged thermal point defects.

VACANCY CLUSTERS IN DISLOCATION‐FREE SILICON

Dislocation‐free silicon crystals made by the floating zone technique contain vacancy clusters formed during cooling of the crystal after growth. The distribution and concentration of these defects have been determined. A model is presented describing the formation of these clusters. The influence of vacancy clusters on the leakage current of planar diodes is investigated.

Role of surface morphology in wafer bonding

The strain patterns detected by x‐ray topography in wafers bonded for silicon‐on‐insulator (SOI) technology were found related to the flatness nonuniformity of the original wafers. Local stresses due to the bonding process are estimated to be about 1×108 dynes/cm2. The stress is reduced about 100 times for the thin (0.5 μm) SOI films. Most of the wafer deformation occurs during room temperature mating of the wafers. The deformation is purely elastic even at 1200 °C. The magnitude of the stress appears insignificant for complimentary metal‐oxide‐semiconductor devices performance.

Effect of growth parameters on formation and elimination of vacancy clusters in dislocation-free silicon crystals

Abstract Dislocation-free Si crystals grown by floating-zone techniques generally contain two types of vacancy clusters located in a striated pattern (‘wisrls’). By means of a series of special growth experiments it was established that the formation sequence of both types of clusters predominantly depends on the crystal cooling rate, while the formation of one particular type is also related to the occurrence of remelt. It is suggested that remelt, due either to crystal rotation in an asymmetrical thermal environment or to melt turbulence promotes the trapping of non-equilibrium vacancy concentrations at the solid-liquid interface. The possible mechanisms of this trapping process are discussed.

The formation of interstitial swirl defects in dislocation-free floating-zone silicon crystals

Abstract Swirl defects in quenched dislocation-free floating-zone silicon crystals have been analyzed by transmission electron microscopy (TEM). The silicon crystals were quenched from the melt to prevent impurity clustering and precipitation and to minimize their effects on the swirl defect nucleation. The TEM analysis shows that the Type A swirl defects are perfect extrinsic dislocation loops elongated along 〈100〉 directions. The smaller B type swirl defects remained undetectable by TEM indicating that these defects cause very little lattice strain. From the present data it is concluded that the silicon self-interstitials are the dominant point defects during the crystal growth process. An impurity interstitial clustering mechanism is proposed for the swirl defect formation during the growth of floating zone silicon single crystals.

The influence of thermal point defects on the precipitation of oxygen in dislocation‐free silicon crystals

The precipitation of oxygen in regularly grown and in situ‐quenched dislocation‐free Czochralski silicon crystals has been investigated by means of infrared absorption spectroscopy, preferential etching, and x‐ray transmission topography. In addition, the effect of doping with acceptor or donor impurities on oxygen precipitation has been studied. The experimental results indicate that at oxygen supersaturation ratios smaller than 20 the formation of nuclei for precipitation predominantly occurs via a heterogeneous in which thermal point defects, in particular silicon interstitials, play an important role.

The introduction of dislocations during the growth of floating-zone silicon crystals as a result of point defect condensation

Abstract During growth of dislocation-free floating-zone crystals two types of “swirl defects” (A- and B-clusters) are formed as a result of point defect condensation. The diffusion coefficient of these point defects (vacancies, silicon interstitials) in the temperature interval 1050–1100 °C, is found to be 2 × 10 -5 cm 2 /sec. Section topographic analysis showed that the A-clusters (dislocation loops) rapidly increase in size with decreasing crystal cooling rate. This is attributed to a combined climb-glide process. Evidence is presented that the predominant cause for the loss of dislocation-free growth, particularly of large-diameter crystals, is due to emission of dislocation arrays from the A-clusters.

The effect of doping on microdefect formation in as‐grown dislocation‐free Czochralski silicon crystals

The influence of p‐ and n‐type doping on microdefect formation in macroscopically dislocation‐free as‐grown Czochralski silicon crystals has been studied using copper decoration, x‐ray transmission topography, preferential etching, and high‐voltage transmission electron microscopy. B‐doped crystals are found to contain undecorated perfect dislocation loops of an interstitial nature. In Sb‐doped crystals two other types of microdefects are present, one of which consists of a precipitate particle exhibiting a vacancy type of strain field. All defects are distributed in a striated pattern.

Formation and elimination of growth striations in dislocation-free silicon crystals

Abstract Growth striations due to inhomogeneous incorporation of dope impurities as well as residual carbon in dislocation-free floating-zone and Czochralski silicon crystals have been studied. The dope striations are detected by means of spreading resistance measurements and preferential etching, while the carbon striations are analysed using among other things a special type of X-ray transmission section topography. The relationship between various growth parameters and striation formation is determined. The influence of remelt phenomena and solid-state diffusion on striation formation is analysed and directives are obtained for the elimination of striations during crystal growth. Carbon striations are also eliminated by means of annealing treatments of the as-grown crystals.

Growth of dislocation-free gallium-phosphide crystals from a stoichiometric melt

Abstract The conditions required for dislocation-free growth of gallium-phosphide crystals by means of the LEC technique are investigated. Using X-ray topography of longitudinal crystal sections it is found that growth of the crystal cone after the necking-in procedure is the most critical stage. Dislocation-free crystals are grown in the Ga 〈111〉 direction up to a diameter of 15 mm at a pulling speed of 0.20 to 0.25 mm min -1 . Doped as well as undoped dislocation-free crystals show a striated distribution of microdefects after preferential etching of P {111} surfaces.