Seiji Shiba

Systematic Investigation of Gettering Effects on 4th Row Element Impurities in Si by Dopant Atoms

The gettering of 4th row element impurities (K, Ca, 3d transition metals, and Zn) in Si crystals by dopant atoms was systematically investigated by first-principles calculation through evaluation of the diffusion barrier and the binding energy. The dopant atoms considered include p-type dopants (B), n-type dopants (P, As, Sb), or light elements (C, O). It was found that (1) the diffusion barrier of impurity atoms decreases with an increase in their atomic number up to Ni, (2) B atom becomes an efficient gettering center for metals except for Ni, (3) most of the metals except for Fe and Co cannot be gettered by n-type dopants, and (4) C and O atoms alone do not become efficient gettering centers for the metals used in actual LSI processes. The vacancy 𝑉𝑐 and n-type dopant complexes (P𝑉𝑐, As𝑉𝑐, Sb𝑉𝑐) can be efficient gettering centers for Cu in n/n

TEM Observation of the Dislocations Nucleated from Cracks inside Lightly or Heavily Doped Czochralski Silicon Wafers

The crack propagation from the indent introduced with a Vickers hardness tester at room temperature and the dislocation nucleation from the cracks at 900°C inside lightly boron (B), heavily B, or heavily arsenic (As) doped Czochralski (CZ) Si wafers were investigated with transmission electron microscopy (TEM) observations. It was found that the dopant concentration and the dopant type did not significantly affect the crack propagation and the dislocation nucleation. The slip dislocations with a density of about (0.8∼2.8) × 1013/cm3 were nucleated from the cracks propagated about 10 μm in depth. Furthermore, small dislocations that nucleated with very high density and without cracks were found around the indent introduced at 1000°C.

First principles calculation of stable structure and adhesive strength of plated Ni/Fe(100) or Cu/Fe(100) interfaces

Abstract A study the with first principles calculation of the interfaces of the Ni layer or Cu layer on the Fe(100) surface formed with metal plating was performed. Ni or Cu atoms were shown to adopt the corresponding position to the bcc structure of the Fe(100) substrate. Other calculations showed that the interfaces of Ni (5 atomic layers)/Fe(100) (5 layers) or Cu (5 atomic layers)/Fe(100) (5 layers) had square lattices. The orientation relationship of Ni/Fe(100) interface corresponds to fcc-Ni(100)//bcc-Fe(100), Ni[011]//Fe[010], and Ni[0 1]//Fe[001]. Similar results were obtained for Cu/Fe(100) interfaces. This structure was supported by TEM analysis of plated Ni layer on Fe(100) surfaces. The adhesion strength of the Ni/Fe(100) interface evaluated by first principles calculation was higher than that of the Cu/Fe(100) interface. The experimental results of Hull cell iron plated with Ni or Cu supported the results of the calculation. These results indicate that the first principles calculation, which deals with the ideal interface at the atomic scale, has the potential to evaluate the adhesion strength of metallic material interfaces.

First Principles Calculation for Cu Gettering by Dopantor Dopant-Vacancy Complex in Silicon Crystal

For finding the effective gettering center of cupper (Cu) atom in silicon (Si) crystal, an interaction between interstitial Cu atom and dopant (B, Sb, As, P), C or O atom was studied with first principles calculation. It was found that only B could be an effective gettering center. This result indicates that heavily B doped p/p+ epitaxial wafers will show a sufficient gettering efficiency for Cu contamination. In order to design the gettering center of Cu in n/n+ epitaxial wafers, the interaction between vanancy (V)-Sb, V-As or V-P complexes and Cu was investigated. It was found that these complexes could be effective gettering centers. The mechanism of Cu gettering by oxide precipitates was also studied with further calculations. It was found that the stabilities of Cu atom in β-crystobalite or in strained Si were not superior to that in strain-free Si. The trapping at the interface or the interaction with emitted interstitial Si (I) from oxide precipitates should be the possible mechanisms for Cu gettering.

First Principles Calculation for Point Defect Behavior, Oxygen Precipitation and Cu Gettering in Czochralski Silicon

Theoretical consideration for technologically important phenomena in defect engineering of Czochralski silicon was performed with first principles calculation. (i) Point defect behaviour during crystal growth, (ii) enhanced oxygen precipitation in p/p+ epitaxial wafers, and (iii) Cu gettering by impurities are main topics in this work. Following results are obtained. (i) Interstitial Si I is dominant in p type Si while vacancy V is dominant in n type Si during crystal growth when dopant concentration is higher than about 1x1019atoms/cm3. (ii) In initial stage of oxygen precipitation including a few interstitial oxygen (O) atoms, BOn complex is more stable than On complex. The diffusion barrier of O atom in p+ Si is reduced to about 2.2eV compared with the barrier of about 2.5eV in intrinsic Si. (iii) In substitutional B, Sb, As, P and C atoms, only B atom can be an effective gettering center for Cu.