Borophosphosilicate glassy ͑BPSG͒ films, used as a premetal dielectric in metal-oxide-semiconductor field-effect transistor devices, can be a serious constraint in the device technology due to the nucleation and growth of boron-phosphate phase ͑BPO 4 ͒, especially in BPSG films grown with a high boron-to-phosphorous ratio. It has been commonly believed that BPO 4 forms during the film flow/annealing process. This investigation focused on the mechanism of possible BPO 4 nucleation in the films, deposited by means of plasma-enhanced chemical vapor deposition ͑PECVD͒ before high-temperature annealing and its evolution during heating. Our study indicates that the dopant-related precipitates in the as-deposited films are a key factor for the ultimate manifestation of BPO 4 during high-temperature annealing. B 2 O 3 and P 2 O 3 /P 2 O 5 compounds, in conjunction with H 2 O, are essential for BPO 4 materialization in SiO 2 matrix. The impacts of each of the above reactants on the film instability are discussed. The optimization of the PECVD BPSG film structure to improve the film reliability is proposed.

High temperature nitrogen annealing induced interstitial oxygen (Oi) precipitation has been investigated in silicon epitaxial layers (epilayers) grown on heavily arsenic-doped Czochralski silicon wafers. Both transmission electron microscopy and secondary ion mass spectrometry data indicate a strong Oi precipitation and/or segregation in the subsurface of epilayers annealed in N2 at 1200°C. The Oi precipitates have needlelike morphology with {111} habit planes along ⟨110⟩ directions. This precipitation is facilitated by thermal nitridation-produced vacancies or nitrogen-vacancy complexes and is sensitive to annealing conditions. Annealing in Ar or in N2 at temperature <1125°C results in no epilayer subsurface Oi precipitation.

The precipitation of interstitial oxygen (Oi) in heavily arsenic doped Czochralski (CZ) silicon wafers (As-wafer) has been studied for both polysilicon and damaged back surfaces. After annealed at 1200°C for 45 minutes and 950°C for 15hrs sequentially, the As-wafers with polysilicon show no Oi precipitation in the bulk while polyhedral Oi precipitates are observed at the interface between polysilicon and the silicon substrate. They exhibit a habit plane of {100}. The lack of the Oi precipitation in the bulk may reduce the total gettering efficiency of the polysilicon layer on the As-wafer. The same annealing led to rod-like SiOx precipitates in the wafers with damaged back surface. These precipitates extended about 1um into the bulk and had a habit plane of {111}. This morphology has high interfacial energy and is only possible when strain relief is dominant. The Oi outdiffusion has been observed to be same for both backside surface conditions and is only determined by annealing process.

Articles you may be interested inAnalysis of the effect of germanium preamorphization on interface defects and leakage current for high-k metaloxide-semiconductor field-effect transistor J. Vac. Sci. Technol. B 29, 01AA05 (2011); 10.1116/1.3521479 Effect of oxygen precipitates and induced dislocations on oxidation-induced stacking faults in nitrogen-doped Czochralski silicon J. Appl. Phys. 96, 3031 (2004); 10.1063/1.1777804Complementary infrared and transmission electron microscopy studies of the effect of high temperature-high pressure treatments on oxygen-related defects in irradiated silicon Electrical effects of a single stacking fault on fully depleted thin-film silicon-on-insulator P-channel metal-oxide-semiconductor field-effect transistors

Silicon single crystals are known as the most perfect material that mankind has ever created. Even in such a perfect material, the concentration of oxygen as an impurity is generally higher than those of doping impurities, and they critically affect the electrical and mechanical properties of Si wafers. Therefore, oxygen in silicon has been being one of the hottest subjects in the field of silicon-based materials science and technology [1,2]. In the present work, we study the oxygen precipitation in Si wafers as a method to remove oxygen from the Si matrix. The precipitation behavior of oxygen in two kinds of backside treatments are compared, i.e. the deposition of polycrystalline Si back layer and the damaged back surface by sand blasting.The wafers were made of Czochralski silicon crystals and were heavily arsenic doped, with resistivity at 3 mΩ⋅cm and interstitial oxygen concentration of 7×10 17 /cm 3 . After the deposition of the polycrystalline Si layer of about 1.3 µm thick, or damaged with sand blasting, the wafers were annealed at 1200°C for 45 minutes and 900°C for 15 hrs under nitrogen ambient. Cross-sectional TEM samples were examined using JEM3010 and CM200-FEG microscopes, operating at 300 keV and 200 keV, respectively. Images were recorded digitally with CCD cameras. FIG. 1 (a) and (b)show the morphology and the selected area diffraction pattern for the wafer with backside poly-Si layer. It is found that the oxide precipitates formed only at the poly-Si/substrate interface. The diameter of the precipitates is about 10-20 nm. The poly-Si layer is heavily twinned. No precipitates can be found in the Si substrate and the poly-Si layer. The high resolution (FIG. 1 ((c)) indicates that the precipitates are amorphous silicon oxide columns, which lie in (001) plane, with the longitudinal axis inclined with respect to the electron beam direction [1][2][3][4][5][6][7][8][9][10], resulting in elongated shape at the interface.For the Si wafer with the backside damaged by sand blasting, oxide precipitates formed as elongated rods extending into the Si substrate, as shown in FIG. 2 (a). The precipitates lie in <110> directions, and are enclosed by the {111} planes of Si. The high resolution image of such a precipitate rod is shown in FIG. 2 (b). Due to the heat treatments in nitrogen ambient, Si-O-N precipitate also formed in the substrate, as confirmed by EDS (not shown here) and the extra diffraction spots seen in diffraction pattern (FIG. 2 (c)).