ChemicalMechanicalPolishing(CMP)Overview[化學(xué)機(jī)械研磨(CMP)概述](-54)

1、NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 1NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingChemical Mechanical Polishing (CMP) OverviewDr. Stephen BeaudoinArizona State UniversityDr. Duane Bon

2、ingMassachusetts Institute of TechnologyDr. Srini RaghavanThe University of Arizona 1999 Arizona Board of Regents for The University of ArizonaNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 2Outline CMP Basics CMP Process Optimization Envi

3、ronmental Issues in CMPNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 3NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingLearning ObjectivesGain the ability to discuss CMP with polishing expertsUnder

4、stand basic phenomena that occur during polishing and will be able to explain why these phenomena occurBecome aware of the processing and environmental challenges associated with CMPLearn how to assess the environmental consequences of manufacturing processes and how to compare the impacts of compet

5、ing processesGain experience in setting new, more environmentally sound polishing practicesNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 4NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing What is C

6、MP? How does CMP work? Why do we need CMP? How do we describe CMP? What are the problems associated with the CMP process? What are the environmental impacts of CMP? How can we alter the environmental impacts of CMP?QuestionsNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor

7、 Manufacturing Beaudoin, et al. 5NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingCMP Basics What is CMP? CMP is a physico-chemical process used to make wafer surfaces locally and globally flat. Chemical action hydroxyl ions attack SiO2 in oxide CMP, causing

8、surface softening and chemical dissolution oxidants enhance metal dissolution and control passivation in metal CMP Mechanical action polisher rotation and pressureNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 6CMP Basics (contd) How does

9、CMP work? A rotating wafer is pressed face-down against a rotating polishing pad; an aqueous suspension of abrasive (slurry) is pressed against the face of the wafer by the pad. A combination of chemical and physical effects removes features from the wafer surface.NSF/SRC Engineering Research Center

10、 for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 7CMP ApparatusNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 8NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingCMP Basics (co

11、ntd) Why do we need CMP? for precise photolithography for advanced devices for advanced multilevel metallization processes (Damascene) How is CMP described? key parameter: post-polish nonuniformity (NU) NU = ratio of the standard deviation of the post-polish wafer thickness to the average post-polis

12、h wafer thickness caused by variations in local removal rate important parameter is removal rate (RR) RR = average thickness change during polishing divided by polishing timeNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 9Metal Damascene P

13、rocessTrenches/vias etched into ILD (interlayer dielectric)Metal depositionMetal CMPRepeat for multiple levels of metalNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 10NSF/SRC Engineering Research Center for Environmentally Benign Semicond

14、uctor ManufacturingCMP Consumables Slurries for oxide (SiO2) polishing colloidal suspension of silica particles in alkaline medium hydroxyl ions attack SiO2, causing softening and chemical dissolution (mechanism unverified) particles range from 10 to 3000 nm, mean size 160 nm 12% (wt) particles, KOH

15、 used to set pH 11 other concerns: particle size distribution (scratching), particle shape, particle agglomerationNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 11NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor

16、 ManufacturingCMP Consumables (contd) Slurries for metal (W, Al, Cu) polishing oxidants cause metal dissolution and passivation (reactions to form protective layer on metal surface) typically alumina particles (a or g), 100 to 2000 nm in diameter, 12% (wt) particles, pH 3 to 4 alumina-peroxide 1 par

17、t slurry, 1 part 50% H2O2, pH 3.7-4.0 alumina-ferric nitrate 6% alumina solids, 5% ferric nitrate, pH 1.5 alumina-potassium iodate 6% alumina solids, 2-8% potassium iodate, pH 4.0NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 12NSF/SRC Eng

18、ineering Research Center for Environmentally Benign Semiconductor ManufacturingCMP Consumables (contd) W polishing pH 4 with H2O2 or KIO3 pH 1.5 with ferric nitrate pH 6 with potassium ferricyanide, potassium acid phosphate and ethylene diamine Al polishing peroxide or iodate-based slurries Cu polis

19、hing ammonia-based solutions, passivating agentsNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 13NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingCMP Consumables (contd) Polish pads cast polyurethan

20、e or felt impregnated with polyurethane, thickness 1-3 mm hardness affects planarization and nonuniformity surface treatment (conditioning) required to control polish rate and slurry transport scraping pad surface with hard edge to remove debris, open pores pads wear out quickly (100-1000 wafers/pad

21、!) perforated, grooved pads coming into use (improved slurry transport/uniformity)NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 14NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingCMP Consumables (c

22、ontd) Carrier Films hold wafers onto polish head (carrier) porous polymeric materials held onto carrier by vacuum, thermal processing, adhesive average roughness 1-20 microns compressibility range 1-25% under 10 psi load (typical of CMP conditions) thickness 0.1-1 mm profound effect on polishing per

23、formanceNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 15NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingCMP Requirements Stable, predictable, reproducible process Removal rates 1700 /min for SiO2

24、and 2500 /min for W Independent of device/circuit design, substrate good selectivity between metal and dielectric and similar polishing rates for metals and liners Few defects (scratches, peeling, particles) Low NU less than 5% variation in film thickness across wafer 3-6 mm edge exclusionNSF/SRC En

25、gineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 16NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingPrestons Equation Simplest CMP model Expresses polishing rate in terms of applied pressure and relative veloci

26、ty between polishing pad and wafer RR = KpPS Kp = Preston coefficient (inversely proportional to elastic modulus of material being polished) P = down pressure S = pad-wafer relative speed can predict general trends observed RR usually proportional to P and S cannot predict within wafer NU, feature e

27、ffects, or variations due to pattern density effectsNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 17 CMP Process Variables Tool Pressure (down force) Platen and carrier speeds Platen temperature Slurry Flow rate (150-300 ml/min) Slurry ag

28、e Temperature Pad conditioningNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 18NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingCMP Processing Problems Particle contamination on wafers slurry partic

29、les, pad material, abraded films Chemical contamination on wafers metal ions (K+, Fe3+, Ni2+) anions (SiO32-, WO42-, IO32-) surfactants Mechanical damage to wafers Nonuniform polishing RR variations with time during processingNSF/SRC Engineering Research Center for Environmentally Benign Semiconduct

30、or Manufacturing Beaudoin, et al. 19NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingParticle Contamination Electrostatic effects can cause particles to be attracted to wafer depends on zeta potential of particle, pH, ionic strength of solution can be attract

31、ive or repulsive Once particles are near wafer, Van der Waals interactions (always attractive) enhance adhesion To minimize particle contamination, particle and surface must have same chargeNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 20

32、Minimization of Particle Contamination:Additives to Alumina Slurry Isoelectric point of: Alumina8 - 9 W 2.0 - 2.5 SiO22 - 3 Minimization of particulate contamination may be achieved by choosing a pH such that the surface charge (and zeta potential) of tungsten, silica, and alumina bear the same sign

33、. Two strategies possible: Both alumina and tungsten bear a positive surface charge (ferric nitrate based slurries pH 1.5 - 2.0) Both alumina and tungsten are negatively charged (anionic additives such as anionic surfactants and polyanions to slurries pH 3.5 - 4.0) NSF/SRC Engineering Research Cente

34、r for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 21NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingMechanical Contamination CMP can induce rearrangement of the structure of the metal or SiO2 wafer surface Can extend tens of nm into t

35、he wafer Highly strained structures, broken networks and loss of Si atom tetrahedral coordinationNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 22NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingChe

36、mical Contamination Chemicals in solution change oxidation state based on pH, potential of the solution Reactivity also changes Solubility and partitioning of chemical species can vary considerably with oxidation state and reactivity changes Corrosion may occur depending on redox potential of expose

37、d metals (TiN-W system of concern)NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 23NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingCMP Control Issues: Polishing Nonuniformities Dishing reduction in

38、 thickness of large metal features towards the center of the features caused by differences in polishing rates of metal, liner, and insulator Pattern erosion thinning of oxide and metal in a patterned area increases with pattern density Edge effect, “racetrack” NU variations in removal rate due to s

39、tress variations with radial distance across waferNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 24Pattern Erosion and Large Feature Dishing Dense SRAM Array Dishing Erosion is the thinning of oxide and metal in a patterned area, while dis

40、hing is a reduction in the thickness of a large tungsten feature toward the center of that feature.Support CircuitsNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 25NSF/SRC Engineering Research Center for Environmentally Benign Semiconducto

41、r ManufacturingCMP Control Issues: Removal Rate Drift As pads wear, RR decreases Occurs even with conditioning Coincident with increasing NU over time Solutions substantial use of monitor wafers to check performance increase polish time over time to achieve desired removalNSF/SRC Engineering Researc

42、h Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 26NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingPost CMP Cleaning Remove particles and chemical contamination following polishing Involves buff, brush clean, megasonic clean,

43、spin-rinse dry steps Buffing after main polish , wafers “polished” using soft pads used following metal CMP oxide slurries, DI water, or NH4OH used changes pH of system to reduce adhesion of metal particles removes metal particles embedded in wafers can reduce cleaning loadsNSF/SRC Engineering Resea

44、rch Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 27NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingPost CMP Cleaning (contd) Brush cleaning brushes made from PVA with 90% porosity usually double sided scrubbing, roller or di

45、sk-type brushes probably make direct contact with wafer NH4OH (1-2%) added for particle removal (prevents redeposition), citric acid (0.5%) added for metal removal, HF etches oxide to remove subsurface defects Megasonic cleaning sound waves add energy to particles, thin boundary layers cleaning chem

46、icals added (TMAH, SC1, etc.) “acoustic streaming” induces flow over particles importance uncertainNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 28Brush BoxChemical Drip ManifoldUpper Brush AssemblyLower Brush AssemblyRollerRotating Wafer

47、Water InletsNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 29Double Side Scrubbing (DSS)System ConfigurationWet Sand IndexerDual Brush ModuleRinse, Spin Dry Station (Megasonic)Edge Handling Receive StationUser Interface(OnTrak Systems, Inc

48、.)NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 30NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingPost CMP Cleaning (contd) Spin-rinse drying following cleaning, wafers rotated at high speed water

49、 and/or cleaning solution (SC1) sprayed on wafer at start hydrodynamics drain solutions from wafer probably no effect on cleaning, but ensures that particles dislodged from wafer during preceding steps do not resettle on waferNSF/SRC Engineering Research Center for Environmentally Benign Semiconduct

50、or Manufacturing Beaudoin, et al. 31NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingCMP Environmental Problems Huge quantities of waste generated Polishing consumables (slurry, pads, water, chemicals) monitor wafers (used for testing purposes) killed wafers

51、rinse water used during process Post-CMP cleaning consumables (chemicals, water, brushes, buff pads) post-CMP cleaning rinse water killed wafersNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 32NSF/SRC Engineering Research Center for Enviro

52、nmentally Benign Semiconductor ManufacturingWaste Problems Slurry solids present in waste highly basic or acidic solutions cause pH changes in natural waters kills organisms enhances sediment dissolution, diminishes precipitation oxidizers toxic to wildlife Rinse waters large volumes tax wastewater

53、treatment systems water purification wastes are significant (ion exchange wastes, membranes, energy)NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 33NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing

54、Quantities of Wastes Typical polisher processes 40 wafers/hr. with 65% overall equipment efficiency Aqueous process wastes 190 gallons slurry/day/machine 180 gallons DI rinsewater/day/machine Solid wastes 3-4 monitor wafers/pad for break in (RR drift?) 1-2 pads/machine/day (not including buff pads)

55、Cleaning wastes 190 gallons rinsewater/day/machine cleaning chemicals highly variableNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 34NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor ManufacturingSubtle Concerns

56、 Energy, materials required to manufacture consumables Energy, materials required to manufacture monitor and lost wafers Long and short term environmental impacts Effects of process improvementsNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al

57、. 35Evaluating Environmental Aspects of ManufacturingNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 36The Million Dollar QuestionsNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 3

58、7NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing$1,000,000 Questions How does one assess environmental “soundness” of exisiting processes? Waste Audit How does one assess environmental consequences of processes? Environmental Impact Assessment (EIA) How doe

59、s one assess and compare environmental impacts of real and proposed/improved processes? Life Cycle Analysis (LCA)NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Beaudoin, et al. 38NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor

60、ManufacturingWaste Audits - Objectives Develop understanding of the actual operating processes in a facility or unit operation Identify regions where waste is generated Guide to environmental optimization of process 6 stepsNSF/SRC Engineering Research Center for Environmentally Benign Semiconductor