Bo-Young Lee

Anomalous oxygen precipitation near the vacancy and interstitial boundary in CZ-Si wafers

The behavior of oxygen precipitation was investigated in radial direction using Si wafers with different generation area of vacancy-related defects. Oxygen precipitation is more enhanced in vacancy-rich region than in interstitial-rich region. The behavior of oxygen precipitation in the radial direction is strongly dependent on the size of vacancy-rich region which is related to crystal growth condition. Anomalous oxygen precipitation occurred in the marginal vacancy-rich region and the inner edge of interstitial rich region. In the marginal interstitial-rich region, however, oxygen precipitation is suppressed to nearly zero.

Observation of Micro-Oxygen Precipitates in the Vicinity of the Oxidation-Induced Stacking Fault Ring and Their Effects on Thin Gate Oxide Breakdown

Micro-oxygen precipitates and their effects on thin gate oxide breakdown have been investigated using a crystal-originated-particle (COP)-free wafer and a low COP wafer. After two-step annealing and subsequent repolishing, regions containing micro-oxygen precipitates were observed inside and outside the oxidation-induced stacking fault (OSF) ring. Delta [Oi] and near-surface microdefects (NSMDs) in those regions showed a reverse trend. It appears that micro-oxygen precipitates show a different precipitation behavior from the anomalous oxygen precipitation (AOP) behavior in the conventional Czochralski (CZ) silicon wafer with the OSF ring. The oxide breakdown electrical field was degraded in almost the same region as that where micro-oxygen precipitates were revealed. This indicates that micro-oxygen precipitates can affect the degradation of gate oxide integrity (GOI).

Evaluation of Citric Acid Added Cleaning Solution for Removal of Metallic Contaminants on Si Wafer Surface

We have investigated cleaning solutions based on citric acid (CA) to remove metallic contaminants from the silicon wafer surface. Silicon wafers were intentionally contaminated with Fe, Ca, Zn, Na, Al and Cu standard solution by spin coating method and cleaned in various CA-added cleaning solutions. The concentration of metallic contaminants on the silicon wafer surface before and after cleaning was analyzed by vapor phase decomposition/inductively coupled plasma-mass spectrometry (VPD/ICP-MS). And the surface micro-roughness was also measured by atomic force microscopy (AFM) to evaluate the effect of cleaning solutions. It was found that acidic CA/H2O solution has the ability to remove metallic contaminants from silicon surfaces. Fe, Ca, Zn and Na on silicon surface were decreased from the order of 1012 atoms/cm2 to the order of 109 atoms/cm2 even at low CA concentration, low temperature of CA solution and with short immersion time. CA was also effective in alkali cleaning solution. Fe, Ca, Zn, Na and Cu were reduced down to the order of 109 atoms/cm2 in CA added with NH4OH/H2O2/H2O solution without degradation of surface micro-roughness.

Effects of Bulk Microdefects and Metallic Impurities on p–n Junction Leakage Currents in Silicon

The effects of bulk microdefects and metallic impurities on leakage currents at p–n junctions have been evaluated quantitatively by relating leakage currents with bulk defects and metallic impurities, and the results are reported. Bulk defects and metallic impurities, which were introduced by appropriate thermal treatment and intentional contamination by spin-coating metal ion solutions onto the silicon surfaces, were shown to induce heavy leakage currents at p–n junctions, which had been manufactured by boron implantation and phosphorus diffusion. We found the bulk microdefects to be critical in causing leakage currents to flow and propose that their measurements be used as a means for the determination of the bulk defect densities. Die failure rates were also used for the evaluation of the effects of metallic impurities such as Cu, Ni, and Fe on the leakage currents.

Systematic Study of Thick Strained Silicon NMOSFETs for Digital Applications

This work investigates NMOSFETs on thick biaxially strained silicon for digital logic applications. Strain and long channel mobility enhancement are shown to be maintained for strained films as thick as 300 nm, 15 times thicker than the equilibrium critical thickness, and misfit-dislocation induced off-current leakage is shown to be completely eliminated for tSi equiv 100 nm. Significant performance enhancement is achieved: short channel DC NMOS drive current is up to 18% higher than comparable unstrained silicon devices and thin strained silicon devices

Formation of High Quality Strained-Si / Strained-SiGe Layers Grown on Relaxed SiGe Virtual Substrates for Advanced CMOS Application

In this work, we have fabricated 8-inch SiGe wafers with the dual channel through a direct production line and the samples were mostly characterized by the line equipment. Some characteristic methods and vital specification were presented for device makers

Gate-Oxide-Integrity Characteristics of Vacancy-rich Wafer Compared with Crystal-Originated-Pits-free Wafer as a Function of Oxide Thickness

The dielectric breakdown of oxides with various thickness between 5–70 nm on Czochralski (CZ)-grown silicon wafer had been investigated. To observe the effects of crystal-originated-particle (COP), vacancy-rich wafers and COP-free wafers were compared. In breakdown voltage (BV) measurement, breakdown fractions of vacancy-rich wafers were increased with the increase of oxide thickness (tOX) and showed a maximum value at the tOX range of 10–20 nm. On the other hand, COP-free wafers showed few breakdowns over all the range of tOX. Furthermore, time dependent dielectric breakdown (TDDB) of the vacancy-rich wafers showed higher extrinsic breakdowns than that of the COP-free wafers in the tOX below 20 nm. For the intrinsic breakdown, two groups showed the same charge-to-breakdown (QBD) along the strength of injection current over all the range of tOX. Especially, only in case of vacancy-rich wafer, abnormal increase of current, i.e., hump phenomena, was observed in the range of electric field below the Fowler-Nordheim (F-N) tunneling.

Determination of Flow Pattern Defect Area by µ-Photoconductivity Decay Lifetime Measurement

Flow pattern defects (FPDs), the decrease in interstitial oxygen concentration during heat treatment and µ-photoconductivity decay (µ-PCD) lifetime were measured precisely in the radial direction using samples with different grown-in defect densities and defect generation areas. In the inner and/or outer region adjacent to the rim of the FPD area where FPD density was zero, a peak and/or a valley of µ-PCD lifetime distribution were observed. It was found that the µ-PCD lifetime distribution depended on the behavior of oxygen precipitation, especially on anomalous oxygen precipitation (AOP). In the case of FPD area larger than about 175 mm in diameter, the edge effect became dominant and it was difficult to observe a peak or a valley in the µ-PCD lifetime distribution due to AOP. The FPD area, however, could be monitored by theµ-PCD lifetime measurement. The relationship between µ-PCD lifetime and oxygen precipitation rate was also interpreted.