-_.-~ Sample. HIGH SENSITIVITY TYPE TOTAL REFLECTION X-RAY SPECTROMETER SYSTEM Wafer Surface Analysis System --

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1 THE RIGAKU JOURNAL VOl. 8 / NO. 1 / 1991 HIGH SENSITIVITY TYPE TOTAL REFLECTION X-RAY SPECTROMETER SYSTEM Wafer Surface Analysis System Introduction System 3726 utilizes the total reflection characteristic of X- rays to analyze a wafer surface. The system can achieve lower detection limits in the 10 9 atomsjcm 2 level. This enables the analysis of heavy metal contaminants like Fe, Ni, Cu, Zn, etc. deposited on silicon wafers. It also permits the analysis of W, Au, As and the like elements, so far considered impossible to analyze. The system 3726 was designed based on Rigaku's years of experience of some thousands of installations of X-ray spectrometers. It is equipped with a highly reliable 18 kw X-ray generator; a source of high sensitivity, to assure stable use in the process line. 2. Principle When X-rays are incident at very low angles on the surface of a material with a mirror finish they may be reflected similar to the total reflection of visible light on a mirror surface. Only some of the X-rays will penetrate into the extreme surface area of the material. By utilizing this total reflection characteristic Fluorescent Se miconductor detector Re\\ec1ed 'f.,.-!ays ~ -_.-~ Sample X-ray spectrometry can detect an X-ray fluorescent spectrum with very low backgrounds. Thus, it is possible to analyze trace elements in the extreme surface of materials. This technique is called the total reflection X- ray fluorescent method. 3. Features.High Sensitivity Analysis: An 18 kw rotating anode X- ray source, coupled with a high-efficiency hybrid monochromator (patented), enables the analysis of surface con- 40 The Rigaku Journal

2 taminating heavy metals at a level of below 2.5 x 10 9 atoms/cm 2, as the lower limit of detection..w, As, Au, Ga, etc. a/so ana/yzable: The use of the hybrid monochromator (patented) enables the analysis of W, Au, Pt, Ga, Ge and the like elements, formerly considered unanalyzable with the tungsten target. (As-implanted Wafer at 5 x 10'0 atoms/cm') (Wafer Contaminated at a 1.25 x 10" atoms/cm').fu//y Automated Ana/ysis: Such conditions as measurement points in the wafer plane (mapping), the angle of incidence, etc. can be preset in a fully automatic analysis program. Printout of quantitative analysis results and profiles can be made during continuous measurement. Further, measurement is performed by automatically adjusting the optimum condition of total reflection with respect to the very small thickness, inclination and so on that vary according to each wafer and each measurement point in the plane. The operator has only to install wafers or a cassette for un- attended, automatic analysis of up to 25 wafers to be made automatically. (Automatic Measurement Program).Corre/ation of Contaminant E/ements: Mapping of a multi-element (up to 4) distribution is displayed simultaneously. "Since a superimposed display of elements is also possible, their correlation can be easily obtained..depth Ana/ysis: 1 nformation on the density of contamination versus depth can be obtained non-destructively, in a short time, by varying the X-ray incident angle. A series of angles are also programmable in the fully automatic (unattended) analysis program..c/ean Chamber: Design considerations are given to minimizing the generation of particles in the sample chamber. Wafers are kept from particle contamination from dust caused by the driving section of the chamber interior and the vacuum/leak system. A dry vacuum pump is used and the gas purge is made first at slow then high speeds. Selection of piping materials and treatment of the internai surfaces are also based on particle-free concept..clean Samp/e Ho/ding Robotics: The system employs a handing robot characterized by high wafer positioning reproducibility and havi ng a non -contact orientation fiat adj usting mechanism. Thorough care is taken, moreover, to prevent particle contamination on the rear side of the wafer by carefully selecting the shape and material of the chuck. Accommodation of 8" Wafer (Standard): The system as standard can cope with wafers ranging from 4" to 8" in size. The system also allows measurement of abnormal-shape samples like rectangular or semi-divided wafers or pieces. Vol. 8 No

3 4. Composition Diagram X'ray gener~ Monochromator Shutter open/ close mechanlsm Rotating anode X'ray tube Sample r::=:::===s=ta=g=e~ ~.._--j r. 8. <p. positionmg mechanism ~ Z. ad,ust'ng mechanism Electrostallo chuck Sample cham ber X -ray shutter Hea t exohanger Vacuum system :. TMP & rotary pump (diagram) 5. Measurement Example Wafer contaminated by spin coater at 2.5E1 0 atoms/cm 2 40 kv--450 ma sec Calibration Curve of wafer contaminated by spin coater, 40 kv--450 ma sec P wafer, 40 kv--450 ma sec 42 The Rigaku Journal

4 6. Composition. Specifications Composition Specifications X-ray Tube X-ray Generator Heat Exchanger Optical System Sam pie Chamber Detector Counting Circuit Data Processor Software Type Target Material Maximum Loading Vacuum System Voltage & Current Safety Circuit Overflow type direct cooling system Chiller-equipped circulation system Monochromator Slit System Sam pie Stage Atmosphere Measurement Point Intraplanar movement Wafer Plane Height Adjustment Optimum condition setting for incident angle and total reflection Cassette-to- Cassette Detector Liquid N 2 Dewar Vessel Liquid N 2 Automatic Feed System Pulse Processor Multi-Channel Analyzer Microcomputer HV Power Supply for Personal Computer Graphie Printer Color Piotter Measurement Program Waveform Processing Program Qualitative Analysis Program Quantitative Analysis Program Fully Automatic Analysis Program Mapping Program Rotating Anode X-ray Tube Tungsten (W) (other materials are also available) 18 kw, 40 kv ~450 ma Turbomolecular Pump & Rotary Pump 20~40kV, 10~450mA Voltage, current, filament current water cutout, vacuum degree, etc. Requires installation outside of clean room environ ment Hybrid type (patented) 1 st 2nd slit systems Wafer Size: 4~8" Vacuum, N 2, He r, e driving, (X-Y) or (r, e) input system Sample stage driving in 2 directions (automatie setting by laser displacement detection) Sample stage automatic setting in cf> direction Si (Li)Semiconductor Detector 15/ With dead time correction 2048 channels Multi-task monitor 0~1000V Also available is system 3726A which uses a sealed-off X-ray tube as the X-ray source. PC9801 RA Allows 15" wide hard copy Allows simultaneous data analysis Smoothing Automatic qualitative analysis, search function, background subtraction and comparison analysis Peak separation, background subtraction, calibration curve preparation and calibration curve quantitation Measurement, quantitative analysis, data saving and result output (including the incident angle and intraplanar measurement). Multi-element simultaneous display, superposing display and three-dimensional display Vol. 8 NO

5 7. Utility Requirements Power Supply 200 VAC, 3- phase (50/60 Hz). 100 A (for X-ray generator, spectrometer controller, vacuum system and heat exchanger) 100 VAC, single phase (50/60 Hz), 10 A (for computer, etc.) Earth Ground Independent Grounding. Resistance should be below 300 Cooling Water Quality Tap water or equivalent, non-corrosive industrial water Pressure 3~5kgf/cm2 Temperature 25 C (77 F) maximum Flow 201/min or more Room Temperature 18 ~30 C, daily variation Relative Humidity Below 80% Atmosphere No corrosive gas or dust particles. Installation in a clean room is recommended. N 2 Gas 1 ~ 1.2 kgf/cm" for sample chamber purge, 401/min or more Installation Example 850 r=-l X-ray ~[D / ge~~~t or... (H) [ ~IJ )~~i~~~ i t [bd /' (H ) ~ C 10 C Personal ~~~puter (Hl 73~ N, o 510 H D J H. V. transformer.:1 750 (H) 560 H O:n Vacuum pump Clean room Water feed and 0 drain 0 Power supply [ Maintenance rqom 44 The Rigaku Journal