We report on the detection of very low oxygen concentration in silicon by a secondary-ion mass spectrometry (SIMS) method. Using a magnetic IMS 6F Cameca SIMS spectrometer and applying a very high primary Cs + ion flux, prolonged presputtering, extensive vacuum chamber baking, titanium sublimation pump, and an LN trap, we have reached a detection limit of~2 × 10 15 O atoms/cm 3 in chemical vapor deposition epitaxial Si films. This value appears to be at least 10 times lower than in any published or unpublished source known to the authors, including the reference sensitivities listed by the instrument manufacturer. Most likely, the key improvement that has allowed us to drive the detection limit to 10 15 at/cm 3 is the use of an ion pump in the analysis chamber. The working pressure in our analysis chamber is~10 −10 Thorr, ie, 1 decade lower than that the commercially equipped with a turbo pump. This paper demonstrates optimized analytical conditions for the oxygen measurements in Si, as a function of depth: (i) Very shallow profiles are practically impossible to measure accurately because of native oxide at the surface. (ii) Shallow-to-medium range profiles, up to~20 μm, are the most amenable to SIMS measurements. (iii) Mediumto-deep (~20-50 μm) range is required to follow interdiffusion and segregation in epitaxial layers when the oxygen-free layer is grown on a CZ Si substrate. (iv) Extremely deep profiles, up to full thickness of the wafer, definitely necessitate beveling. 1 | INTRODUCTION Oxygen, a ubiquitous gaseous element, plays a special role in semiconductor physics and technology. In silicon, stable planar SiO 2 films serve as insulators, masks, and gate barriers in metal-oxide semiconductor transistors. Czochralski-grown Si wafers usually contain oxygen in quantities 7 to 10 × 10 17 at/cm 3 . At room temperature, oxygen-supersaturated Si is stable as the oxygen atoms occupy predominantly bond-centered interstitial sites in the lattice. 1 At elevated temperatures, diffusion of oxygen leads to its aggregation into SiO x precipitates and to the migration of atomic oxygen toward the external boundaries of the sample. 2 If the oxygen content is sufficiently low, as in the float zone (FZ) silicon, it is possible to indiffuse oxygen into the semiconductor from thermally grown or deposited SiO 2 film. 3 To determine principal quantities characterizing the behavior of oxygen in Si, diffusivity (D) and solid solubility (C s ) have been subject to numerous investigations employing a wide spectrum of methods. Fourier transform infrared absorption (FTIR) allows the measurement of the oxygen content left in solution in CZ Si after completion of the precipitation process 3,4 ; X-ray analysis detects a lattice strain gradient induced by 16 O indiffused into FZ Si, 5 and β-decay rate of 18 F produced by a (p,n) nuclear reaction is proportional to the concentration of 18 O isotope atoms introduced from Si 18 O 2 films. 6 Early secondary-ion mass spectrometry (SIMS) analyses of the oxygen in Si suffered from insufficient...
