Worth B. Henley

Non-contact mapping of heavy metal contamination for silicon IC fabrication

The authors present the principles and application examples of a recently refined, computerised, surface photovoltage (SPV) method. This new method is capable of wafer-scale, non-contact mapping of metal contaminants in the bulk and on the surface with sensitivities as high at 1010 atoms cm-3. They demonstrate the unique ability of SPV to measure product wafers with finished integrated circuits.

Iron detection in the part per quadrillion range in silicon using surface photovoltage and photodissociation of iron-boron pairs

The photodissociation of iron‐boron pairs in p‐type silicon produces lifetime killing interstitial iron and may be combined with noncontact surface photovoltage (SPV) measurement of the minority carrier diffusion length to achieve fast detection of iron. We found that, for iron concentrations ranging from 8×108 to 1×1013 atoms/cm3, the pair dissociation using a white light (10 W/cm2) was completed within 15 s. Surface recombination was a major rate limiting factor. Passivation of the surface enhanced the rate by as much as a factor of 20. The photodissociation rate increased with increasing temperature, however, the increase was smaller than that of the thermal dissociation rate. These characteristics are consistent with a previously proposed recombination enhanced dissociation mechanism. For practical iron detection, it is important that the detection limit of the approach is close to one part per quadrillion.

Detection of copper contamination in silicon by surface photovoltage diffusion length measurements

Surface photovoltage minority carrier lifetime/diffusion length analysis of copper contaminated silicon was performed. It was observed that copper and copper associated defects degrade minority carrier lifetime more in n-type than in p-type silicon. This finding is explained by analysis of copper related defect levels identified by other deep level transient spectroscopy studies. In copper contaminated p-type silicon, an optical or thermal activation procedure significantly degrades the diffusion length. A process similar to that of Fe–B in p-type silicon is proposed. The activation process dissociates the Cu–Cu pairs, a weak recombination center in p-type silicon, and the copper forms extended substitutional defects in silicon, which have much greater recombination activity. No recovery of diffusion length was observed following such an activation procedure. The difference in copper and iron diffusion length recovery properties after activation can be used to differentiate iron contamination from copper ...

Diffusion of Iron in Silicon Dioxide

A quantitative analysis of diffusion of iron in silicon dioxide is presented. A source of iron deposited on the surface of thermally oxidized silicon wafers was diffused at temperatures ranging from 700-1100°C in an inert (nitrogen) ambient. The iron concentration in SiO 2 and Si was measured using total reflection X-ray fluorescence, deep level transient spectroscopy, and surface photovoltage techniques. A two-boundary diffusion model was applied to the experimental data to determine the diffusivity and segregation coefficient of iron in SiO 2 . It is observed that iron diffusivity in SiO 2 follows the Arrhenius relationship and has a thermal activation energy of 1.51 eV. Iron exhibits a strong tendency to segregate into silicon dioxide and has a value of k = 1.1 × 10 -7 at 1000°C, where k = N Si /N oxide .

Effects of Copper Contamination in Silicon on Thin Oxide Breakdown

Effects of copper contamination on the breakdown and reliability characteristics of thin silicon gate oxides are discussed. Gate oxide integrity is measured for thermal oxides of 45, 75, 120, and 200 A grown on silicon wafers intentionally contaminated with 10 10 -10 15 cm -3 of copper. Copper doping of silicon was performed according to solubility data considerations. The oxide breakdown voltages as a function of copper concentration for the various oxide thicknesses are reported. For 45 A oxide, copper concentration cannot exceed 10 13 cm -3 without severe degradation in oxide quality. The threshold contamination level for 75 A oxides is ten times higher. Premature oxide breakdown is proposed to occur due to copper silicide precipitation, which locally enhances the electrical field. It is concluded that the impact of copper contamination on oxide breakdown is not as severe as that of iron contamination on oxide breakdown. This is due to the difference in segregation properties of the two metals at the Si/SiO 2 interface.

IRON PRECIPITATION IN FLOAT ZONE GROWN SILICON

Temperature dependent iron precipitation in float zone grown silicon wafers has been experimentally investigated. Results of iron precipitation experiments over a wide thermal process temperature range and time are presented. Precipitation of iron in silicon was analyzed by a quantitative assessment of change in interstitial iron using a surface photovoltage minority carrier lifetime analysis technique. Contamination levels of iron in the range 1011–1013 atoms/cm3 are investigated. It is concluded that maximum iron precipitation occurs in the temperature range of 500–600 °C. Iron precipitation is rapid in this region where more than 90% of the interstitial iron precipitates in a period of 30 min.

Infrared photoluminescence from Er doped porous Si

Intense infrared photoluminescence with the characteristic maximum at about 1.55 μm was observed at room temperature in Er-doped porous silicon [Er related infrared photoluminescence (ErIR PL)]. Porous Si layers of different controlled porosity were fabricated by electrochemical anodization of n and p Cz–Si wafers as well as at p+/n silicon junction. Er was introduced into the porous Si using a spin-on doping technique. Rutherford backscattering spectroscopy measurements show that annealing up to 1000 °C does not influence the Er depth distribution in the porous silicon, although it strongly influences the oxygen content of the Si skeleton and the ErIR PL intensity. For the spin-on-doped samples annealed at 1000 °C, the ErIR PL intensity is increased by two orders of magnitude compared to Er implanted and annealed porous Si layers. It was found that a strong ErIR PL intensity was only observed in the spin-on-doped porous Si layers formed on p and p+/n substrates, which exhibit, simultaneously, an intense ...

Stability of Iron‐Silicide Precipitates in Silicon

A quantitative analysis of iron-silicide precipitate stability with respect to time and temperature is presented. Iron precipitation and dissolution in silicon was analyzed by a quantitative assessment of change in interstitial iron using a surface photovoltage minority carrier lifetime/diffusion length analysis technique. Interstitial iron is shown to rapidly precipitate to the silicide phase between 500 and 600°C. Iron-silicide precipitates were found to dissolve above a temperature of 760°C. Dissolution of FeSi 2 precipitates releases iron back to an interstitial position in the silicon matrix. The amount of precipitate dissolved was found to be a function of dissolution process temperature and time. It is concluded that the precipitate phase of iron, FeSi 2 , is thermally unstable above a temperature of 760°C.

Surface photovoltage analysis of copper in p-type silicon

Surface photovoltage minority carrier lifetime/diffusion length analysis of copper-doped p-type silicon was performed. Minority carrier recombination behavior of the deep level induced by copper and its thermal stability in the temperature range of 25–300 °C was investigated. This defect is attributed to interstitial copper pairs in p-type silicon. Isochronal annealing to a temperature of 150 °C results in improvement in diffusion length. This change in recombination behavior is attributed to precipitation of copper. At temperatures higher than 150 °C, copper forms extended substitutional defects in silicon, which results in a decrease in diffusion length. Interstitial copper concentration is estimated using the change in recombination behavior with isochronal annealing. Since copper is known to precipitate rapidly during cooling from high temperatures, it is observed that less than 0.01% of the total copper dissolved in silicon occupies an interstitial position.

Improvement of Diffusion Length in Polycrystalline Photovoltaic Silicon by Phosphorus and Chlorine Gettering

Results of chlorine and phosphorus gettering of photovoltaic (PV) polycrystalline silicon are presented. Using surface photovoltage (SPV) diffusion length (L) measurements, it has been established that PV polysilicon is very in homogeneous and gettering only improves L values in regions in which L is relatively high and a large amount of non precipitated Fe and Cr is present. In regions with low L, nonprecipitated Fe and Cr were not detected in as-grown polysilicon and gettering did not cause any substantial improvement in L values. It is conceivable that recombination in these regions is controlled by grown-in defects.