SPV Monitoring of Near Surface Doping - Role of Boron-Hydrogen Interaction; Boron Passivation and Reactivation
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SPV Monitoring of Near Surface Doping – Role of Boron-Hydrogen Interaction; Boron Passivation and Reactivation D. Marinskiy and J. Lagowski Semiconductor Diagnostics, Inc., 3650 Spectrum blvd., Ste 130 Tampa, FL 33612, U.S.A. ABSTRACT Hydrogen is known to cause the passivation of boron acceptors after such processing steps as wet etching, reactive ion etching, sputter deposition of metal contacts, and Ar ion beam etching. Previous studies of this effect employed CV profiling, spreading resistance profiling, and SIMS measurements on samples diffused with deuterium. These methods are either destructive to the Si surface or require deposition of metal contact. In the present study we used a non-contact small signal ac-surface photovoltage technique, currently available in commercial diagnostic tools. Simultaneous measurements of the semiconductor surface barrier, Vsb, and the capacitance of the surface depletion layer, CD, give the concentration of boron acceptors in a submicron distance from the Si surface or Si/SiO2 interface. The technique has proven very successful in monitoring low dose implants and also near surface doping in oxidized wafers. In bare silicon wafers the method occasionally indicated surface boron concentration noticeably below the bulk value. We found such behavior in wafers after the chemical cleaning, used to prepare a hydrogen terminated surface. Thermal annealing at temperatures from 150°C to 200°C reactivates the boron dopant. We will discuss the effect of various cleaning and annealing conditions on passivation and reactivation of boron acceptors in the near surface region. The results obtained with the non-contact SPV technique show excellent agreement with previous studies. They also provide a basis for reliable measurement of the boron concentration free of interference from hydrogen passivation. INTRODUCTION Hydrogen is known to cause impurity passivation in silicon [1,2] and other crystalline semiconductors. It can diffuse into Si and SiO2 during such processing steps as wet chemical cleaning, reactive ion etching, Ar ion beam etching, and sputter deposition of metal contacts. Hydrogen can be released from Al-H, AlO-H, Si-H, SiO-H sites in the Al gate, the SiO2 film, and Al/SiO2 and SiO2/Si interfaces [3,4]. The released hydrogen can diffuse into Si and can cause unintentional changes in the electrically active dopant profile near the surface or Si/SiO2 interface. The passivation of boron by hydrogen was studied previously using spreading resistance, C-V profiling, and SIMS measurements on samples diffused with deuterium [5,6,7]. In this work we study the passivation of boron by hydrogen introduced during typical surface treatments used in silicon IC fabrication. The electrically active boron concentration is monitored with a noncontact small signal ac-SPV technique, to be referred to as Near Surface Doping (NSD) [8,9,10]. In this method the simultaneous measurements of the semiconductor surface barrier, Vsb, and the capacitance of the surface depletion layer, CD, measured by ac-SPV, gi
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