Papers

AVS2001 Session AS-TuA: Depth Profiling I

Tuesday, October 30, 2001 2:00 PM in Room 134

Tuesday Afternoon

Start	Invited?	Item
2:00 PM		AS-TuA-1 Sputtering-induced Effects in Ultra Shallow Depth Profiling A.T.S. Wee, C.M. Ng, R. Liu (National University of Singapore) Following the increasingly stringent requirements in the characterization of sub-micron IC devices, a good understanding of various factors affecting ultra shallow depth profiling in secondary ion mass spectrometry (SIMS) becomes crucial. Achieving high depth resolution (of the order of 1 nm) is becoming critical in the semiconductor industry today, and various methods have been developed to optimize depth resolution. In this paper, I will discuss ultra shallow SIMS depth profiling in several important semiconductor systems, namely B delta-doped Si, SiGe heterostructures and ultrathin oxynitride gate films. Results from both dynamic SIMS (Cameca IMS 6f) and TOF-SIMS (ION-TOF IV) will be presented. By using low energy (e.g. 500 eV) O₂⁺ and Cs⁺ beams, the relationship between depth resolution of the delta layers and surface topography measured by atomic force microscopy (AFM) is studied. The effects of oxygen flooding and sample rotation, used to suppress surface roughening, have also been investigated. X-ray photoelectron spectroscopy (XPS) is used to characterize the surface chemical composition of the crater bottom and a direct relationship between the surface chemical state and surface roughness is established. The various factors that limit the depth resolution in ultra shallow SIMS depth profiling are discussed.
2:40 PM		AS-TuA-3 Low Energy Ion-surface Interactions in Ultrashallow Profiling Investigated with In-situ Medium Energy Ion Scattering Spectroscopy D.W. Moon, H.I. Lee (Korea Research Institute of Standards and Science); H.J. Kang (Chungbuk National University, Korea) For ultrashallow junction profiling with secondary ion mass spectrometry (SIMS), low energy ions have been used successfully. However, detailed understanding on the low energy ion-surface interactions have been lacking for quantitative ultrashallow junction SIMS profiling. Especially the transient surface sputtering effect in the pre-equilibrium region is one of the important phenomena to be understood. In this report, low energy ion-surface interactions are studied with in-situ medium energy ion scattering spectroscopy (MEIS) which provide quantitative composition and structural information with better than 1nm depth resolution. Damage profiles in Si(100) surfaces due to 100~500 eV O₂⁺ ion bombardment were measured with in-situ MEIS as a function of dose, energy, and angle. The thickness of the damaged layer can be decreased down to 1nm with 80° grazing incidence. The transient sputtering yield change of an amorphous Si layer on a Si(100) could be measured quantitatively as a function of the ion dose for normal incident 500 eV O₂⁺ ion bombardment. At the initial stage of 500 eV O₂⁺ ion bombardment before the surface oxidation, the sputtering yield of Si was 1.4 (Si atoms/O₂⁺). With sputtering, the Si sputtering yield decreased rapidly down to 0.06 (Si atoms/O₂⁺) at the ion dose of 3x10¹⁶ O₂⁺ cm_-2. An initial Si surface swelling was observed due to the higher oxygen incorporation rate than the Si sputtering rate. Transient sputtering yield decrease of Si due to 500eV Ar⁺ is also observed, in contrary.
3:00 PM		AS-TuA-4 Low Energy Dual Beam Depth-Profiling: Influence of Sputter- and Analysis-Beam Parameters on Profile Performance using TOF-SIMS T. Grehl, R. Moellers, E. Niehuis (ION-TOF GmbH, Germany) In general TOF-SIMS measurements are carried out in the so-called quasi static mode where the fluence of the analysis beam is so low that the sample damage or the erosion caused by the primary ions is regarded to be negligible. A common way to take depth profiles with a TOF-SIMS instrument is the operation in the so-called dual beam mode. In this mode sample erosion and sample analysis are carried out with two different ion beams. Whereas sample erosion is performed with a quasi DC-beam, the sample analysis is done with a pulsed ion beam of relatively low current density. This mode offers great flexibility to optimize the sputter conditions (i. e. erosion rate, energy, sputter species, angle of incidence, etc.) for the specific analytical task independent from the analytical conditions. Typically sputter ions such as Cs⁺ or O₂⁺ are used to optimize the secondary ion yield. For the sample analysis a Ga liquid metal ion gun with high brightness and high lateral resolution is preferable. This combination is most suitable for applications such as micro area depth profiling or 3D-analysis where the analysis is taken from a small raster field within the sputter crater. Since the contribution of the high energy analysis beam to the atomic mixing becomes more significant for small areas, the influence of the analysis beam on the depth resolution requires a more detailed study. In this paper we investigate how the ion energy of the sputter gun as well as the analysis gun affects the depth profile. The sputter ion energy is varied from 200 eV to 1000 eV for Cs⁺ as well as for O₂⁺ while the erosion rate is kept constant during these measurements. In addition, the current density of the analysis gun will be changed while keeping constant sputter conditions.
3:40 PM		AS-TuA-6 Reference Materials for SIMS: Philosophy, Development, and Results D.S. Simons (National Institute of Standards and Technology) NIST has been developing reference materials for calibration of secondary ion mass spectrometers for approximately 10 years. The choice of materials was not only dictated by their potential market and economic impact, but also by the availability of independent analytical methods to perform certification measurements in a traceable manner. For these reasons, a decision was made to target materials of use to the semiconductor industry that were routinely analyzed by SIMS and for which good measurement calibration was important. Specifically, a program was undertaken to produce ion implants of the common dopants boron, arsenic, and phosphorus in silicon. The retained dose of the dopants would be certified by nuclear analytical methods that were available at the NIST research reactor. The first such reference material, SRM 2137, was a ¹⁰B implant in Si certified by a neutron reaction method known as neutron depth profiling. Lessons learned in this first project were incorporated into the production and certification by instrumental neutron activation analysis of a ⁷⁵As implant in Si, SRM 2134. NIST is currently validating certification procedures for a ³¹P implant in Si by radiochemical neutron activation analysis. We will show examples of the level of improvement in SIMS measurements that has been achieved by use of these reference materials.