High Temperature, High Accuracy Quartz Crystal (QCM)

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High Temperature, High Accuracy Quartz Crystal (QCM)
High Temperature, High Accuracy Quartz Crystal (QCM) Measurement Technology for ALD “Temperatur ist Alles“ Process control sensors for thin film manufacturing and research applicaCons ScoE Grimshaw, CTO Colnatec Gilbert, Arizona, USA October 2013 Common ALD Process and Measurement Issues o  Lack of affordable, accurate, real-­‐2me in-­‐situ metrology –  Thin film deposiCon is measured aPer the fact. –  Process variaCons or even cycle failures are not detected as they happen –  Daily calibraCon or set-­‐up is required. o  Precursor and reactor development is difficult and expensive –  KineCc parameters involved in the ALD gas–surface reacCons are hard to resolve –  Effects of pressure, temperature, flow rate and even surface chemistry are nearly impossible to measure in a dynamic environment o  Reactor maintenance cycles are difficult to quan2fy –  Lack of ability to predict when a chamber needs to be cleaned –  ParCculates become a major problem because of a “dirty” chamber –  Maintenance of the reactor condiCon, down stream vacuum plumbing, traps and pumps is a reacCve down Cme event. Use of Standard Quartz Crystal Microbalance (QCM) as SoluCon o  Inexpensive (~3.000 € starCng) o  Highly accurate (<0.001Å Possible) o  Reproducible o  Easy to install and Maintain o  Fast ( <1 sec/measurement) o  In-­‐Situ o  Easily Placed in System 10/8/13 ConfidenCal & Proprietary @2012 3 ConfidenCal & Proprietary @2013 ConfidenCal & Proprietary @2013 5 But There are Problems with Standard QCMs o  Current commercial systems are not ALD suitable (water cooled to 20°C) o  When sensor is heated, measurement is “noisy” o  SensiCve to temperature, pressure, mass and stress of film o  ALD vapors can penetrate sensor housing and “back side” coat sensor, leading to inaccurate readings o  Work-­‐arounds include complicated “back-­‐side” purge, epoxy sealed sensors and “home-­‐built” technology 10/8/13 ConfidenCal & Proprietary @2012 6 What is a Quartz Crystal Sensor? • 
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10/8/13 Crystal vibrates in the range of 5 or 6 MHz when hooked up to an electronic monitor Embedded in a metallic holder called a “sensor head” with electrical contacts Is only 0.025 mm thick and is fragile Is typically 12.5 or 14 mm diameter (but can be made smaller!) Is cut from a bar of syntheCc α-­‐quartz at a specific angle to minimize thermal or stress induced noise ConfidenCal & Proprietary 7 What are the Crystal Design ConsideraCons? o  OrientaCon of the crystal when it is manufactured is criCcal. One special angle (“AT-­‐cut”) is designed to minimize temperature effects (~ 35° 15’) o  AT-­‐cut crystals operate from 0° to 100 C very well. But you must maintain the temperature to insure accuracy! o  Crystals are “contoured” to maximize stability. One side is plano (flat), the other side is convex (curved) o  Contouring keeps crystal vibraCon in center. Electrode paEern does not maEer! o  Can use small crystals (8mm) the same as large (14 mm). No difference electrically. 10/8/13 ConfidenCal & Proprietary 8 What is the Measurement Algorithm ? From the frequency change , the thickness is then calculated by: tf = [(ρqvq/2πZfc) tan-­‐1{Z tan [π (fq-­‐fc)/fq]}]/ρf Where: o  tf = thickness of film o  ρq = density of quartz (or of the vibraCng crystal) o  vq = velocity of acousCc wave through quartz (a constant) o  Z = acousCc impedance factor (depends on the material coated) o  fq = frequency of uncoated quartz o  fc = frequency of coated quartz o  ρf = density of film being measured 10/8/13 ConfidenCal & Proprietary 9 But There are Thin Film Measurement LimitaCons The change in crystal frequency (ΔF) is driven by several factors (not only the coaCng!): ΔF = ΔfM+ ΔfT + ΔfS +ΔfP o 
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Mass of film on crystal “M” (or film thickness) Crystal temperature “T”, affected by process heat Stress of coaCng on crystal “S”, caused by film condensaCon Pressure on crystal “P”, new or old (coated) For accurate reading, we only want to measure ΔfM 10/8/13 ConfidenCal & Proprietary 10 So How Do We Fix Them? o  Start by Controlling the Temperature o  Use Low Temperature Coefficient Crystal o  Correct for Frequency vs. Temperature shiP by soPware algorithm o  Measure the Pressure vs. Frequency ShiP (use inert gas for pressure pulse) o  Correct for P vs. F shiP by soPware algorithm o  Measure Film Stress vs. Frequency o  Correct for S vs. F by soPware algorithm 10/8/13 ConfidenCal & Proprietary @2012 11 Tempe/Eon: The UlCmate ALD Tool 10/8/13 ConfidenCal & Proprietary @2012 12 High Temperature Controlled or Measuring Sensors o 
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Integral thermocouple to real Cme measure crystal temperature Integral Heater to maintain the crystal within +/-­‐1C Air or Water Cooling OperaConal from 20-­‐500ᵒC depending Specific design changes prevent “back side” coaCng and don’t require “purge gas” 10/8/13 ConfidenCal & Proprietary 13 Heated Crystal Sensor Head 10/8/13 ConfidenCal & Proprietary @2012 14 Colnatec Next GeneraCon Technology: Electronics Eon™ and EonLT™ Temperature Measuring and RegulaCng Film Thickness Monitors and Controllers 10/8/13 ConfidenCal & Proprietary 15 Eon™ Dual Channel Crystal Controller 10/8/13 ConfidenCal & Proprietary 16 Eon™ SoPware 10/8/13 ConfidenCal & Proprietary 17 Expanded Measurement CapabiliCes Frequency vs. Thickness
10/8/13 Thickness vs. Time
ConfidenCal & Proprietary @2012 Rate vs. Time
18 Colnatec Next GeneraCon Crystal Sensors Premium AT Quartz Crystals for Longer Life, Higher Accuracy
Thin Film Measurement
HT™ Quartz Crystals For High Precision and “Self Cleaning”
SQ™ Crystals for Ultra High Temperature Measurement (500ᵒC +)
10/8/13 ConfidenCal & Proprietary 19 Expanding the Range of Quartz Crystal Temperature Stability: Colnatec High Temperature HT™ Quartz Crystal (Good to 250+C Uncontrolled!) 10/8/13 ConfidenCal & Proprietary 20 Pushing the Limits of Crystal Sensors to the Max: Colnatec SuperQuartz™ (SQ™) Ultra-­‐High Temperature Crystals 10/8/13 ConfidenCal & Proprietary 21 Quartz Crystal OperaCng at 511°C 10/8/13 ConfidenCal & Proprietary 22 300 mm ALD tool (FHR – ALD 300) for low temperature PEALD Extended with customized Colnatec QCM Sensor OFEC97-­‐01 PEALD Courtesy Fraunhofer CNT
QCM hook-­‐up Courtesy Fraunhofer CNT
Satura2on Curves (Colnatec QCM data) Ozone Satura2on 7 6 |Δf| [Hz] 5 4 center 3 edge 2 1 0 0 5 10 15 20 25 30 35 40 tOZONE [s] Courtesy Fraunhofer CNT
45 50 SaturaCon Curves (Colnatec QCM data) TMA Satura2on 7 6 |Δf| [Hz] 5 4 center 3 edge 2 1 0 0 0.5 1 1.5 2 tTMA [s] Courtesy Fraunhofer CNT
2.5 Colnatec ALD Process SoluCons o  In-­‐Situ Thickness Metrology Enabled •  Eon™ DeposiCon Controller with the Tempe™ High Temperature Sensor to measure, real-­‐Cme: – 
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Thickness Å DeposiCon Rates Å/sec. Temperature Other process variables via the Cactus™ SoPware Pla}orm o  Precursor Development Accelerated MulC-­‐variable real Cme measurement to determine reacCon kineCcs is now possible Independent temperature control of sensor to determine the onset of precursor breakdown and even sCcking coefficient(!) •  Ability to integrate pressure, flow and other parameters to develop an accurate model of the ALD process, real Cme • 
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o  In-­‐situ Maintenance Monitor •  Reactor can be conCnuously monitored to determine chamber condiCon status. ( Film thickness accumulaCon). •  Down Stream Exhaust Monitor: –  Pre cold trap monitor. –  Exhaust line and vacuum tree monitor ( maintenance tool) ConfidenCal & Proprietary @2013 ResulCng ALD Process Benefits o  ConCnuous , high temperature, real-­‐Cme deposiCon measurement leads to: •  ReducCon in ex-­‐situ metrology sampling and the Cme associated with measurements. •  ReducCon in set-­‐up and/or development Cmes leading to higher throughput •  ReducCon in scrapped runs due to real Cme control of process and/or reactor condiCons. •  Increased accuracy in film deposiCon per wafer leading to higher process yield. •  Increase in film quality and therefore higher device yield •  Savings in engineering , operator and maintenance technician Cme . •  Accurate predicCon of maintenance cycles allowing scheduled maintenance and a reducCon in parCculates, system failures and yield decrease. •  ReducCon in Cme and materials waste due to the capability of the QCM to assist in DOE (and the ability to measure mulCple variables simultaneously) Contact InformaCon Colnatec LLC 511 West Guadalupe Road, Suite 23 Gilbert, AZ USA Tel: +1 480.634.1449 Fax: +1 480.634.4339 Email: [email protected] Web: www.colnatec.com [email protected] [email protected] 10/8/13 ConfidenCal & Proprietary 29 

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