by S. Wolf Chapter 5: GASES, LIQUID-CHEMICALS, & ULTRAPURE-WATER FOR ULSI
Chapter 5: Gases, Liquid-Chemicals & CHAPTER CONTENTS Basic Properties of Materials Temperature Thermal Expasio of Materials Liquid Chemicals Used i ULSI Acids Bases Solvets ph Scale Gases Used i ULSI Bulk Gases Specialty Gases Gas Storage ad Delivery Systems Ultrapure Water (UPW) Suset Beach CA 5-2
BASIC PROPERTIES OF MATERIALS: TEMPERATURE Drawig of a mercury thermometer, a example of a istrumet used to measure temperature TEMPERATURE SCALES: Celcius - ( C) Fahreheit - ( F) Kelvi (absolute) - (K) Suset Beach CA 5-3
BASIC PROPERTIES OF MATERIALS: THERMAL-EXPANSION OF MATERIALS The temperature-coefficiets-of-expasio (TCE) of materials used i semicoductor devices (i C -1 ). Thermal expasio differeces betwee Al ad Si, show i (a) give rise to stresses i the Al thi-film ad Si substrate [as show i (b)]. I this case, tesile-stress develops at the top of the Si-substrate, ad compressive- stress develops i the Al-film. Suset Beach CA 5-4
UTILITIES AND MATERIALS IN IC-FABRICATION Utility Flow-Diagram for a Wafer Fab Suset Beach CA 5-5
CHEMICALS USED IN IC FABRICATION: ACIDS, BASES, & SOLVENTS TABLE 5.1 - Acids Used i Chip-Makig Hydrofluoric acid HF Etchig SiO 2 films ad cleaig furace tubes Buffered Oxide Etch BOE Etchig SiO 2 films Nitric acid HNO 3 Used i mixtures of HF & HNO 3 to etch silico Sulfuric acid H 2 SO 4 Used i a mixture of H 2 SO 4 ad H 2 O 2 to clea wafers Hydrochloric acid HCl Used to clea wafers Phosphoric acid H 3 PO 4 Used to etch SiN & Al Acetic Acid CH 3 COOH Used i Al etch baths TABLE 5.2 - Bases Used i Chip-Makig Ammoium hydroxide NH 4 OH Used i wafer cleaig processes Potassium hydroxide KOH Positive-photoresist developer Tetramethyl-ammo- TMAH Positive photoresist ium hydroxide developer TABLE 5.3 - Solvets Used i Chip-Makig Ultrapure Water UPW Widely used to rise (H 2 O) wafers ad dilute aqueous chemical solutios Isopropyl Alcohol IPA Geeral-purpose (C 3 H 8 O) cleaig solvet Trichloroethylee TCE Cleaig solvet Acetoe Suset Beach CA Geeral-purpose cleaer Xylee PR edge-bead removal 5-6
CHEMICALS USED IN IC FABRICATION: ph SCALE Suset Beach CA 5-7
GASES USED IN IC FABRICATION: BULK-GASES Bulk gases used i chip-makig iclude: Iert (N2, Ar, He), Oxidizig (O2), & Reducig (H2) gases Bulk-gases are used i large quatities, ad their purity is cotrolled to a very-high degree (seve-ies - 99.99999%) Bulk gases are stored i large storage taks outside of the wafer fab. They are supplied to the work statios through a bulkgas distributio (BGD) system. Suset Beach CA 5-8
Gases, Liquid-Chemicals, & GASES USED IN IC FABRICATION: SPECIALTY GASES Chapter 5: There are may types of specialty gases used i chip-makig (see Chap. 5) Specialty-gas storage & delivery systems cosist of may differet compoets Suset Beach CA 5-9
ULTRAPURE WATER (UPW) Diagram of a ultra-pure-water (UPW) treatmet system used i ULSI wafer fabs The priciple of reverse osmosis Purity specificatios for ultrapure-water (UPW) iclude: a) 18 MW-cm resistivity; b) Low particle cocetratios; c) Low bacteria cocetratios; d) Small cocetratios of the followig cotamiats: oxyge; dissolved silica; Na; Cl; metal ios; ad total orgaic cocetratio (TOC) MICROCHIP MANUFACTURING Suset Beach CA 5-10
SUMMARY OF KEY CONCEPTS Importat materials properties ad process parameters i chip-makig iclude: temperature, pressure ad vacuum, desity, vapor pressure, thermal expasio ad stress, ad depositio rates. Liquid chemicals used i IC fabricatio ca be grouped ito three categories: 1) acids, 2) bases; ad 3) solvets. Gases used i IC fabricatio are grouped ito two classes: 1) bulk-gases; ad 2) specialty-gases. Gases must be stored ad delivered to the process chambers i a safe, clea, ad precisely-metered maer. Bulk-gases are simple & relatively o-toxic (such as O 2 ad N 2 ). Specialty-gases are ofte a chemical-hazard, ad are trasported ad stored i a fab i metal cyliders. The equipmet used for specialty-gas storage & delivery plays a key role i wafer fabs. Ultra-pure-water is eeded i large quatities for processig wafers. Such water is produced from the raw water-supply by a complex UPW-system at each wafer fab. The UPW that is produced is free of: ios, metals, bacteria, oxyge, ad particles. Suset Beach CA 5-11