Bunji Mizuno

New doping method for subhalf micron trench sidewalls by using an electron cyclotron resonance plasma

A new doping method for the vertical sidewall of a trench by electron cyclotron resonance plasma is described. The plasma was produced under a pressure of 5×10−4 Torr. A doped layer was formed uniformly along the sidewall of a trench with subhalf micron width and an aspect ratio of 6.2. By using a de‐ionized water cooling system, the wafer temperature was maintained below 120 °C and the boron dopant was introduced without damage to the photoresist.

Effects of gas phase absorption into Si substrates on plasma doping process

In the low energy plasma doping process, the contribution of not only ionised species but also neutral species to the doping process should be considered. In order to investigate such a contribution, experiments of gas phase doping combined with Ar plasma pre-treatment were carried out. Gas phase impurity absorption should be affected by the Si crystalline disorder caused by the plasma doping. Ar plasma was used to simulate this effect. As a result, significant increase of boron dose from the neutral gas phase was observed when the substrate surface was pre-treated by Ar plasma prior to exposure to neutral B/sub 2/H/sub 6//He gas. The boron was considered to be absorbed in the amorphous layer. Understanding and control of this phenomenon are important for plasma doping technology, in which ion irradiation and absorption of neutral species proceed simultaneously.

Plasma doping for silicon

Very shallow and dense doping was realized by using the plasma doping method. This method was applied to fabricate diodes and MOS transistors with photo-resist as a mask material. This method is likely to be an alternative to ion implantation due to its properties of low energy and high throughput. The brief history of plasma doping is also reviewed.

Activated boron and its concentration profiles in heavily doped Si studied by soft x-ray photoelectron spectroscopy and Hall measurements

The chemical bonding states of boron (B) in shallow P+/N junctions on Si substrates were studied by soft x-ray photoelectron spectroscopy (SXPES). This study revealed three chemical bonding states of B embedded in bulk Si. The concentration profiles of B were successfully determined by combining SXPES with step-by-step etching of Si substrates. The concentration profiles of B thus determined were in good agreement with those determined by secondary ion mass spectroscopy. The concentration profiles of holes were also determined by combining Hall measurements with the step-by-step etching of Si substrates. The concentration profiles of B having the lowest binding energy were found to agree well with the concentration profiles of holes. Therefore, B with the lowest binding energy can be assigned as activated B and those having the middle and highest binding energies can be attributed to deactivated B having chemical bonding states different from that of activated B.

Effective removal of oxygen from Si layer on buried oxide by implantation of hydrogen

Effects of implanted hydrogen on removal of oxygen from a Si top layer on buried oxide by the post‐implantation annealing were studied. The Si top layer and the buried oxide layer were analyzed by secondary ion mass spectroscopy (SIMS) and cross‐sectional transmission electron microscopy (X‐TEM). With implanted hydrogen, oxygen concentration in the Si top layer could be reduced below the SIMS detection limit by annealing at relatively lower temperature 1150 °C for 2 h in an ambient of N2. It is verified by X‐TEM that the Si top layer is precipitate‐free. An amount of hydrogen comparable to the amount of oxygen contained in the Si top layer is needed to remove the oxygen completely. This effective removal of oxygen is attributed to the suppression of oxygen precipitation and the enhanced dissolution of oxide precipitates by hydrogen.

Excitation-Induced Atomic Motion of Self-Trapped Excitons in RbCl: Reorientation and Defect Formation

Effects of electron excitation of self-trapped excitons on the π-luminescence and the optical absorption due to electron transition from their lowest excited states in RbCl have been investigated. Similarly to KCl and KBr, it is found that the yield of the F centers creation is the highest when the electron is excited to the 2 p π u orbital lying in the (100) plane. The experimental results are analyzed using kinetic equations involving the non-radiative transitions between the excited states of the self-trapped exciton and the transitions to the F - H pair and to the ground state. The general trend of the non-radiative de-excitation process in RbCl is found to be similar to that in KCl, except that the reorientation is induced when the electron is excited to the 2 p π u orbital lying in the (110) plane. It is suggested that the reorientation is induced by the configuration interaction or the Auger transition in which a hole excited state is involved.

Vacancy-Boron Complexes in Plasma Immersion Ion-Implanted Si Probed by a Monoenergetic Positron Beam

Vacancy-type defects in plasma immersion B-implanted Si were probed by a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation were measured and compared with spectra calculated using the projector augmented-wave method. For the as-doped sample, the vacancy-rich region was found to be localized at a depth of 0–10 nm, and the major defect species were determined to be divacancy–B complexes. After spike rapid thermal annealing at 1075 °C, the lineshape parameter S of Doppler broadening spectra corresponding to the high-B-concentration region (4–30 nm) was found to be smaller than the characteristic S value obtained for defect-free Si. From a detailed analysis of the Doppler broadening spectra, the origin of the decrease in the S value was attributed to the trapping of positrons by negatively charged B clusters such as icosahedral B12.

Doping Effects from Neutral B2H6 Gas Phase on Plasma Pretreated Si Substrates as a Possible Process in Plasma Doping

In a low-energy plasma doping process, the contribution of not only ionized species but also neutral species to the doping process should be considered. To investigate such a contribution, experiments involving gas phase doping combined with Ar plasma pretreatment were carried out. As a result, a significant increase in boron dose from a neutral gas phase was observed when the substrate surface was subjected to Ar plasma pretreatment prior to exposure to neutral B2H6/He gas. Through a comprehensive study of the effects of plasma pretreatment and gas exposure conditions on the boron dose from the neutral gas phase, the substrate temperature at which the surface was exposed to the neutral B2H6/He gas after the plasma pretreatment was observed to significantly increase the boron dose.

Estimation of ultra-shallow plasma doping (PD) layer's optical absorption properties by spectroscopic ellipsometry (SE)

We evaluated the optical absorption properties of ultra-shallow (<10 nm) plasma doping (PD) layers by spectroscopic ellipsometry (SE). The optical absorption coefficients of PD layers are much larger than that of crystalline Si (c-Si) substrate by one figure at maximum in the wavelength range from 400 nm to 800 nm. We also found that higher DC bias during PD resulted in higher optical absorption coefficient for the same PD time of 60 seconds.

De-Excitation Pathways of Highly-Excited Self-Trapped Exciton and Electron Plus Self-Trapped Hole

The yield of F - H pairs in KBr upon photo-excitation of the electron of the self-trapped excitons to n ≥3 orbitals is found to be much lower than that upon photoexcitation to the n =2 orbitals and than the overall yield of the F centers under ionizing radiation. The results imply that the de-excitation pathways of excited self-trapped excitons and the electron trapped by the self-trapped holes are different.