N-type Cz Research Articles

The evolution of hydrogen molecule formation in hydrogen-plasma-treated Czochralski silicon

The formation of H2 molecules in voids/platelets and their evolution upon annealing were studied. Standard p- and n-type Czochralski (Cz) silicon wafers have been treated by a hydrogen plasma at 250°C. After the plasma hydrogenation the samples were annealed at temperatures up to 600°C in air. Investigations were done by Raman spectroscopy. H2 did appear as nearly free molecules in the platelets/voids (Raman shift ∼4150cm−1), but not on the tetrahedral interstitial position in the Si lattice. The normalized Raman intensities of the H2 vibration modes exhibited significant sensitivity to the annealing temperature for both p- and n-type Cz Si. These peculiarities can be explained by the evolution of the platelets during annealing.

Carbon influence on γ-irradiation induced defects in n-type CZ Si

The study of irradiation effect of γ rays for 60Co source on n-type carbon-free and carbon-rich Czochralski silicon single crystals is presented, based on deep level transient spectroscopy technique. It is shown that generation of vacancy-related defects is significantly enhanced in carbon-rich silicon in respect to carbon-free samples. Divacancy and multivacancy-related defects were particularly enhanced. The observed behavior is discussed and related to the carbon presence in the bulk. Carbon trapping of self-interstitials significantly enhanced vacancy concentration that further caused observed behavior.

Hydrogen reactions with electron irradiation damage in silicon

We have irradiated n-type CZ silicon with 2MeV electrons at room temperature, and atomic hydrogen has been introduced either before or after irradiation from the surface by wet etching. Quantitative comparisons of vacancy-related defects before and after the hydrogen reactions have been made using high-resolution (Laplace) DLTS. A deep level appears after hydrogenation at EC — 0.311eV, with two components detected by Laplace DLTS. This has previously been reported to be due to either VOH or VOH2, and is accompanied by a decrease in the intensity of the A centre (VO). The Laplace DLTS shows that the A centre emission rate is modified by the hydrogen, and a slower emission rate from the A centre is observed in the presence of hydrogen. Depth profiling shows that this modification occurs in the expected spatial location of the introduced hydrogen.

The Conversion of Czochralski Silicon from P-Type to N-Type by Hydrogen Plasma Enhanced Thermal Donor Formation

ABSTRACTOur experiments show a hydrogen plasma assisted creation of p-n junctions in p-type Cz silicon due to a hydrogen enhanced thermal donor (TD) formation at temperatures ≤450 °C. Applying DC or HF plasma treatments a conversion of p-type into n-type Cz silicon by TD formation occurs. One can distinguish one step processes (p-n junction formation appears just after the plasma exposure) and two step processes (p-n junction formation requires subsequent post hydrogenation annealing). The samples are studied by depth resolved spreading resistance probe (SRP), capacitance-voltage (CV) and Hall measurements. For the one step processes a kinetic model for hydrogen enhanced TD formation is presented.

Annihilation Process of New Donors in N-Type Carbon-Rich CZ Silicon

It has been known that the new donor ND whose deep-level transient spectroscopy (DLTS) peak appears at about 33 K can be generated in two-step heat treated (723 and 923 K) carbon-rich n-type CZ silicon. In this study, the annihilation process of the new donor ND1 is studied by a combination of electrical measurement, DLTS and Fourier transform infrared spectroscopy (FTIR). The results show that the ND1 is annihilated by annealing at temperatures above 1073 K. The size of the ND1 cluster is not the same, but distributes in a certain range. The ND1 loses its electrical activity by both decomposition and growth of the ND1 cluster during the annealing. Annealing at a temperature between 1073 and 1273 K would delay the ND1 annihilation by decomposition and enhance that by growth in the subsequent annealing at a higher temperature.

Rapid Thermal Oxidation of Heavily Doped Silicon for Advanced Solar Cell Processing

AbstractCrucial steps in solar cell processing such as emitter diffusion and surface oxide passivation have been carried out by rapid thermal processing (RTP). Rapid thermal diffusion (RTD) of boron into silicon from APCVD borosilicates has been studied. Rapid thermal oxidation (RTO) of the heavily B-doped surfaces of these shallow junctions (0.2 μm) has been studied in view of applicability of this technique in solar cell processing. These shallow diffusions have excellent lateral uniformity over large areas and have high surface concentrations depending on the APCVD deposition conditions and on RTP conditions. The surface passivating oxides resulting from the RTO are exceptionally thick in case of heavy boron diffused surfaces. RTO does not cause considerable drive-in of the diffused junction profiles. In the contrary, the thick RTO oxides considerably reduce the surface concentration, thereby reducing the heavy doping effects in the junctions, making them more suitable emitters for devices such as solar cells. p+nn+ solar cells have been fabricated on n-type CZ silicon wafers by RTD of boron followed by RTO. The cells result in conversion efficiencies as high as 16.2% The passivation effect of RTO oxides have been investigated by analysing RTO MOS capacitors and are compared to conventional furnace oxides.

A Lifetime Study of Oxygen Agglomeration Induced Defects in Cz Silicon Crystal by Surface Photovoltage (SPV)

ABSTRACTIn this study the effect of oxygen agglomeration on minority carrier diffusion length in as-grown p-CZ silicon has been studied in detail. Oxygen-related defects were found acting as minority carrier traps in p-CZ silicon. These defects are not found in either oxygen-free FZ silicon or in n-type CZ silicon samples. The traps have profound effect on low excitation level diffusion length values leading to an apparent lifetime decrease by as much as an order of magnitude. This effect can be eliminated by a steady state “bias light” superimposed on the chopped excitation light. The traps can be annihilated and re-generated by thermal treatments.Our study has also revealed oxygen-induced recombination centers. Significant improvement in lifetime is realized in p-type CZ silicon after heat treatment between 550°C and 800°C.

Effectiveness of CVD thin Film Backside Gettering and Its Interaction with Intrinsic Gettering

AbstractThe effectiveness of CVD thin film backside gettering on n-type CZ silicon wafers for CMOS technology has been investigated using optical techniques for bulk microdefect analyses and transmission electron microscopy for interfacial structure study. The deposition of LPCVD polysilicon (500-2000 nm), silicon nitride (150 nm), or poly/nitride films on the backside of Si wafers was found to enhance the bulk precipitation. Bulk microdefect density increased as the thickness of polysilicon increased. At the polysilicon/silicon interface, no extended line defects from polysilicon were observed. Based on the results of minority carrier lifetime and oxide breakdown measurements, the best gettering efficiency was given by 1300 nm polysilicon backside gettering scheme.

Interaction Between Deposited Film Extrinsic Gettering and Intrinsic Gettering in CZ Silicon During Simulated CMOS Process Cycles

ABSTRACTThe gettering effectiveness of various thin film structures on n-type CZ silicon wafers has been investigated using electron microscopy, synchrotron radiation topography and optical techniques. Polysilicon, silicon nitride, and poly/nitride films were deposited on etched wafer backsurfaces. The various materials characteristics were correlated with gate oxide breakdown voltage, minority carrier lifetime and yield of MOS capacitors. These studies show that the poly/nitride configuration is superior as a gettering technique.