Czochralski-grown Silicon Wafers Research Articles

Thermal Warpage of Large Diameter Czochralski-Grown Silicon Wafers

Thermal warping of large diameter Czochralski-grown silicon wafers as affected by oxygen precipitation is investigated both experimentally and theoretically. The difference of wafer warpage and its shape between the heating and cooling processes is clarified by thermal stresses calculated from temperature gradients in wafers for each process. The critical temperatures for the slip occurrence are determined for the heating and cooling processes as a function of the microdefect density. Then, the optimized process conditions to avoid slip dislocations are obtained experimentally. The critical stress curve for the processed wafers in MOS devices is determined by comparison with the thermal stress curves calculated under various process conditions, and thereby predicting the slip-free conditions for wafers in a row with various diameters from 100 to 200 mm.

Nitrogen effect on oxygen precipitation in Czochralski silicon

The nitrogen effect on enhancement of oxygen precipitation in Czochralski-grown silicon wafers has been investigated by means of a preferential chemical etching technique and secondary ion mass spectroscopy. The precipitate enhancement is evident in an oxygen out-diffused region in which oxygen precipitation does not normally occur. Incorporation of the nitrogen atoms in substitutional sites to generate very stable microdefects in Czochralski-grown silicon crystals can explain the nitrogen effect on oxygen precipitation.

Dependence of Warpage of Czochralski-Grown Silicon Wafers on Oxygen Concentration and Its Application to MOS Image-Sensor Device

The resistance of precipitation-treated Czochralski-grown silicon wafers to warpage has been investigated using crystals containing oxygen at a concentration of 5.5-12.3×1017 atoms/cm3. The precipitation softening is effectively suppressed if the oxygen concentration is lower than a threshold value of about 8×1017 atoms/cm3. In wafers with oxygen concentrations of 5.5-8×1017 atoms/cm3, oxygen precipitation proceeds slowly, resulting in slow growth of bulk stacking faults and few dislocation sources. In MOS image-sensor devices, the wafers with such oxygen concentrations have few crystal defects within the area of the photodiodes after processing, which cause the fatal failure of white blemishes detected as white scratches on output pictures.

Determination of the denuded zone in Czochralski-grown silicon wafers through MOS lifetime profiling

A technique is presented that can determine whether a denuded zone exists in Czochralski-grown silicon wafers and, if so, how deep into the substrate it extends. Measurements taken after oxygen out-diffusion and precipitation anneals show agreement with denuded zone measurements taken using section topography and angle lapping/ chemical etching. The defect mechanisms that are being monitored by this technique include enhanced thermal generation due to defect states. They also include increased electron-hole pair generation due to impact ionization, which is caused by distortion of the potential lines near precipitates (oxide and/or metal precipitaties). Another defect mechanism, injection of unannihilated thermal donors, is shown to be less significant.

Warpage of Czochralski-Grown Silicon Wafers as Affected by Oxygen Precipitation

The warpage of Czochralski-grown silicon wafers was investigated in relation to oxygen precipitation caused by simulated heat-treatments at 1000°C and LSI processing, using specimens cut from measured positions along the crystal length. The warpage of the wafers due to simulated thermal stresses increases with the concentration of precipitated oxygen atoms associated with the formation of SiO2 precipitates observed in infrared spectra at around 1224 cm-1, reaching a maximum in the seed-end and a minimum in the tail-end wafers. LSI processing experiments showed that the microdefect density resulting from the nuclei in as-grown ingots must be equal to or lower than 5×109 cm-3 to reduce the warpage and improve the chip yield of devices, even if the microdefect density in the bulk is increased to aim at the intrinsic gettering effect.

Ultrasonic effects in the freeze-out and hopping regions of nInSb

Defect-related deep-level traps in two-step annealed Czochralski-grown silicon (Cz-Si) wafers are examined by the photoluminescence (PL) method. As interstitial oxygen reduction increases after the annealing, the deep-level emissions labeled by the D1 and D2 lines become stronger in the PL spectra at 4.2 K. The band-edge PL intensity at room temperature decreases with an increase in the D-line emission. The decay-time curve of the band-edge emission is successfully measured under the same excitation condition as the band-edge PL intensity measurement using an instrument we developed. Using this decay-time curve method, the band-edge PL intensity is correlated to the carrier lifetime for the two-step annealed Cz-Si wafers.

Exciton-neutral donor scattering and dynamics of the neutral donor bound exciton in nGaAs

Defect-related deep-level traps in two-step annealed Czochralski-grown silicon (Cz-Si) wafers are examined by the photoluminescence (PL) method. As interstitial oxygen reduction increases after the annealing, the deep-level emissions labeled by the D1 and D2 lines become stronger in the PL spectra at 4.2 K. The band-edge PL intensity at room temperature decreases with an increase in the D-line emission. The decay-time curve of the band-edge emission is successfully measured under the same excitation condition as the band-edge PL intensity measurement using an instrument we developed. Using this decay-time curve method, the band-edge PL intensity is correlated to the carrier lifetime for the two-step annealed Cz-Si wafers.

High Dose Implantation of Nickel into Silicon

ABSTRACTSeveral silicon wafers were implanted with 58Ni+ at an energy of 170 keV and a current density of 12 μA cm-2 to doses between 5 × 1015 and 1.8 × 1018 ions cm-2. The substrates were phosphorus doped n-type <100> Czochralski grown silicon wafers. The wafers were water cooled during implantation and the surface temperatures was monitored with an infrared pyrometer and controlled to < 70°C. Samples were subsequently furnace annealed at 900°C for 30 min in nitrogen. The as-implanted and annealed samples were analyzed using cross-sectional transmission electron microscopy (XTEM), Rutherford backscattering (RBS) spectroscopy, spreading resistance depth profiling (SRP), and scanning electron microscopy (SEM). Micro-crystallites of NiSi2 (2–5nm) buried within an amorphous matrix formed during the 1.5 × 1017 ions cm-2 dose implantation. For higher doses above 3 × 1017 Ni+ cm-2, ion beam sputtering occurred. After annealing, rapid diffusion of nickel and solid-phase recrystallization of the amorphous regions occurred.

Determination of the oxygen precipitate-free zone width in silicon wafers from surface photovoltage measurements

A procedure has been developed for applying the surface photovoltage technique to the measurement of the width of the oxygen precipitate-free zone present at the surface of a thermally processed, Czochralski-grown silicon wafer. This procedure was developed through the use of a numerical simulation program which models the experimental determination of an effective diffusion lenght, L 0, from surface photovoltage measurements on silicon wafers. The program predicts L 0 for a given precipitate-free zone diffusion length and thickness and bulk diffusion length. Results of the simulations show that for bulk diffusion lengths of 2 μ or less and a precipitate-free zone diffusion length greater than the thickness of the zone, W, the W ≡ 2.5 L 0. Experimental results are presented which support the numerical findings.

Chemical impurities and structural imperfections in semiconductor silicon. Part I : Howard R. Huff. Solid St. Technol., 89 (February 1983)

This paper reviews recent development of X-ray techniques, which cover laboratory experiments and synchrotron radiation (SR) applications, to detect crystal imperfections and surface contamination in large-diameter Czochralski-grown silicon (CZ-Si) wafers. While process-induced defects can be easily detected by a large-sized Lang camera, it is difficult to observe grown-in microdefects and slight impurity-inhomogeneity even when the double-crystal method is applied. SR plane-wave X-ray topography has overcome this difficulty, except for observing void defects, with the help of its high strain sensitivity although it cannot be directly applied to large Si wafers because of their warpage. Recently, SR X-ray topography using a 300-mm-wide monochromatic beam has been employed for measuring the warpage of 200- and 300-mm wafers as well as inspecting surface damage caused by various steps of wafer-manufacturing.Although energy-dispersive total-reflection X-ray fluorescence analysis using a rotating-anode X-ray generator is now widely used for detecting traces of metallic impurities on the surface of 300-mm Si wafers, the requirement of a large scale integrated circuit miniaturization has promoted the combination of a vapor-phase decomposition technique and the TXRF for lowering the lower-limit of detection (LLD). SR-TXRF using an ED solid-state detector is effective in nondestructive and low LLD features, while newly developed wavelength-dispersive (WD) SR-TXRF in good energy resolution. The combined use of the laboratory and SR experiments leads to precise information about crystal perfection and surface contamination in large-diameter Si wafers.

A new intrinsic gettering technique using microdefects in Czochralski silicon crystal: A new double preannealing technique

A new intrinsic gettering technique using microdefects in Czochralski-grown silicon wafers is proposed where a new double preannealing technique is applied to the wafer before the conventional silicon process. In the first step, high temperature (∼1000 °C), nonoxygen ambient annealing is carried out in order to diffuse dissolved oxygen from near the wafer surface. In the second step, extremely low-temperature (∼650 °C) annealing is added to introduce a high density of microdefects in the inner part of the wafer. This produces a wafer having both a nearly perfect denuded zone near the surface and a gettering site region in its bulk, regardless of the original quality of the wafer. This technique has proved to be effective in eliminating ion-implanation oxidation-induced stacking faults.

Warpage of Silicon Wafers

High temperature processing of Czochralski grown silicon wafers can create temperature gradients high enough to generate slip. The generation of slip and the slip patterns have been found to depend on three factors: the temperature and the temperature gradient, the amount and form of the precipitated oxygen, and the direction of the initial bow and the wafer diameter over thickness ratio. A model is presented to fit experimental data of critical stress in silicon, temperature gradients, and wafer curvature to predict the critical temperature above which warpage will occur. An important result is that increased wafer diameter over thickness ratio makes the wafers more sensitive to warpage. When this is the case the difference in stresses on both sides of the wafer, because of the bending, makes the area affected by slip on the concave side much larger than on the convex side.

Lifetime improvement in Czochralski-grown silicon wafers by the use of a two-step annealing

Minority-carrier lifetime improvement by a two-step annealing has been demonstrated using MOS capacitors fabricated on Czochralski-grown (CZ) silicon wafers. It is shown that an intrinsic gettering effect does not always follow a single annealing in an oxygen-free ambient, even in the wafers containing high oxygen content (∼1018 cm−3). This is probably because nuclei of precipitate-dislocation complexes (PDC) are two small in size to grow into PDC during a single annealing of recent high-grade CZ wafers. In the present study, an additional low-temperature annealing at 800 °C is performed in order to improve the situation. A few critical conditions to the effectiveness of the intrinsic gettering are discussed in connection with the crystalline quality of the wafer.