Atomic Layer DepositionAtomic Layer Deposition

ENMA465ENMA46514 May 200314 May 2003

Nicole HarrisonBryan Sadowski

Anne SamuelKunal Thaker

Presentation OutlinePresentation Outline

•• ALD Theory and ProcessesALD Theory and Processes•• ApplicationsApplications

–– Focus on ALD applications in gate Focus on ALD applications in gate dielectricsdielectrics

•• EquipmentEquipment•• Comparisons to other ProcessesComparisons to other Processes•• Current and Future DevelopmentCurrent and Future Development•• QuestionsQuestions

What is ALD?What is ALD?•• ALD (Atomic layer deposition) previously ALD (Atomic layer deposition) previously

known by the name ALE (Atomic layer known by the name ALE (Atomic layer EpitaxyEpitaxy) was originated by ) was originated by T.SuntolaT.Suntola in in Finland.Finland.

•• Deposition method by which precursor Deposition method by which precursor gases or vapors are alternately pulsed on gases or vapors are alternately pulsed on to the substrate surface.to the substrate surface.

•• Precursor gases introduced on to the Precursor gases introduced on to the substrate surface will substrate surface will chemisorbchemisorb or surface or surface reaction takes place at the surface.reaction takes place at the surface.

ALD ALD •• Surface reactions on ALD are all selfSurface reactions on ALD are all self--

limiting.limiting.•• SelfSelf--limiting characteristics of the process limiting characteristics of the process

steps is the foundation of ALD.steps is the foundation of ALD.•• Two fundamental selfTwo fundamental self--limiting mechanisms limiting mechanisms

in ALD: CSin ALD: CS--ALD and RSALD and RS--ALD.ALD.•• CSCS--ALD: ALD: ChemisorptionChemisorption Saturation process Saturation process

followed by exchange reaction.followed by exchange reaction.•• RSRS--ALD: Sequential surface chemical ALD: Sequential surface chemical

reaction.reaction.

CSCS--ALD ProcessALD Process•• Substrate is exposed to the first Substrate is exposed to the first

molecular precursor. The first molecular molecular precursor. The first molecular precursor is retained on the surface by precursor is retained on the surface by chemisorptionchemisorption..

•• Second precursor is introduced on to the Second precursor is introduced on to the surface, which reacts on the surface of surface, which reacts on the surface of the first precursor.the first precursor.

•• Exchange reaction takes place between Exchange reaction takes place between the two precursors and bythe two precursors and by--products are products are formed.formed.

•• Exchange reaction continues till the Exchange reaction continues till the second precursor reacts with first second precursor reacts with first precursor: selfprecursor: self--limiting step.limiting step.

•• Final reaction is MLFinal reaction is ML22+AN+AN22→MA(filmMA(film) + 2 ) + 2 LNLN

•• Sequence is repeated to grow films.Sequence is repeated to grow films.

RSRS--ALD ProcessALD Process•• Promoted by chemistry between Promoted by chemistry between

reactive surface and reactive reactive surface and reactive molecular precursor.molecular precursor.

•• Deposition process is as a result of Deposition process is as a result of the chemical reaction between the chemical reaction between reactive molecular precursors and reactive molecular precursors and substrate.substrate.

•• Substrate surface is made reactive Substrate surface is made reactive by certain surface groups. And first by certain surface groups. And first precursor is introduced to this precursor is introduced to this surface.surface.

•• The reaction now looks like this The reaction now looks like this AN + MLAN + ML22 →→ AAMLML +NL(A) +NL(A) reaction selfreaction self--saturates until AN saturates until AN groups are converted to AML groups.groups are converted to AML groups.

RSRS--ALD Process ALD Process •• Followed by this reaction, the first precursor is removed by ineFollowed by this reaction, the first precursor is removed by inert rt

gas purging prior to the introduction of second precursor.gas purging prior to the introduction of second precursor.

•• Second precursor is introduced, which reacts with ML surface to Second precursor is introduced, which reacts with ML surface to formformAML + ANAML + AN22 →→ MMANAN + NL(B)+ NL(B)–– Self saturatesSelf saturates

•• The surface now looks like initial surface (AN) and surface is nThe surface now looks like initial surface (AN) and surface is now ow ready for reaction (A). The repetition of ABAB…sequence will ready for reaction (A). The repetition of ABAB…sequence will deposit films.deposit films.

•• During each halfDuring each half--reaction(A&B), surface functionality changes reaction(A&B), surface functionality changes from one surface species to another. from one surface species to another.

ALD Precursor ALD Precursor RequirementsRequirements

•• Must be volatile and thermally stableMust be volatile and thermally stable•• PreferrablyPreferrably liquids and gasesliquids and gases

–– Can be solids Can be solids •• no sintering related problemsno sintering related problems

•• Should Should ChemiChemi--sorbsorb on surface or react on surface or react agressivelyagressively with with surface groups and each othersurface groups and each other–– Short saturation time, good deposition rate, no gas phase Short saturation time, good deposition rate, no gas phase

reactionsreactions•• Should not selfShould not self--decomposedecompose

–– DestorysDestorys selfself--limiting propertylimiting property•• Affects thickness, uniformity, and Affects thickness, uniformity, and containationcontaination

•• Should not etch, dissolute into film or substrateShould not etch, dissolute into film or substrate–– Prevents selfPrevents self--limiting film growthlimiting film growth

•• Examples of substratesExamples of substrates–– Zn, Zn, CdCd, S, Se, metal halides like AlCl, S, Se, metal halides like AlCl33, TiCl, TiCl44,TaCl,TaCl55, Alkyls, , Alkyls, ββ--

DiketonatesDiketonates etc [2].etc [2].

ApplicationsApplications•• Transistor Gate Transistor Gate

DielectricsDielectrics•• MEMSMEMS•• OptoOpto--electronicselectronics•• Diffusion BarriersDiffusion Barriers•• FlatFlat-- Panel displays Panel displays

–– Organic Light Organic Light Emitting Diodes Emitting Diodes (OLED)(OLED)

•• Interconnect Interconnect BarriersBarriers

•• Interconnect seed Interconnect seed layerlayer

•• DRAM and MRAM DRAM and MRAM dielectricsdielectrics

•• Embedded Embedded capacitorscapacitors

•• All thin films All thin films (<90 nm)(<90 nm)

•• Electromagnetic Electromagnetic recording headsrecording heads

ApplicationsApplications

•• Transistor gate dielectricsTransistor gate dielectrics–– Smaller transistor sizesSmaller transistor sizes

•• Smaller channel lengthsSmaller channel lengths•• Thinner gate oxide (limit Thinner gate oxide (limit

of ~2.3 nm)of ~2.3 nm)•• Larger leakage currentLarger leakage current

–– Need for highNeed for high--K dielectrics K dielectrics for transistor gate dielectricsfor transistor gate dielectrics

•• Will allow for the use of Will allow for the use of thicker gate dielectricsthicker gate dielectrics

•• Lower leakage currentLower leakage current•• Lower power lossLower power loss

ApplicationsApplications•• New processes are concurrently being New processes are concurrently being

developed as new materials are being developed as new materials are being testedtested

•• ALD provides one of the best alternatives ALD provides one of the best alternatives for depositing these new materialsfor depositing these new materials–– ConformalityConformality–– UniformityUniformity–– Compositional Compositional

ControlControl–– Thickness controlThickness control

EquipmentEquipment

●● SemiSemi--Closed System chambersClosed System chambers-- A channel is used with the top and bottom surfaces consisting A channel is used with the top and bottom surfaces consisting of two separate wafers and the precursor gas is passed of two separate wafers and the precursor gas is passed through the center.through the center.

●● SemiSemi--Open System chambersOpen System chambers-- Similar to a semiSimilar to a semi--closed system except one side is a wafer closed system except one side is a wafer and the other side is gasand the other side is gas-- limited.

●● Closed System ChambersClosed System Chambers-- The Reaction chamber walls The Reaction chamber walls are such that they effect the are such that they effect the transport (trajectory, etc.) of transport (trajectory, etc.) of the precursors.the precursors.

● ● Open System ChambersOpen System Chambers-- Dimensions of reaction Dimensions of reaction chamber do not interfere with chamber do not interfere with ALD process (very large ALD process (very large relative to wafer position). relative to wafer position).

limited.

EquipmentEquipment•• CVD conversion to ALD CVD conversion to ALD

–– The installation of a module: facilitates fast gas switching The installation of a module: facilitates fast gas switching •• ALD specific equipmentALD specific equipment

–– Wafer outputWafer output–– Reaction volumeReaction volume–– Factory AutomationFactory Automation–– ConsistencyConsistency–– ConformalityConformality–– UniformityUniformity

ALD Mode

Basic ALD Mechanism

EquipmentEquipment•• Research into more efficient equipment design continuesResearch into more efficient equipment design continues

–– PEALD/ ALD reactor developed by Genitech PEALD/ ALD reactor developed by Genitech CorporationCorporation

● Hf[N(CH● Hf[N(CH33))22]]44 as the reactant as the reactant species with an Ospecies with an O22 plasma plasma and Hand H22O O

● Temperature in the range of ● Temperature in the range of 200200--350C 350C

● Ar is the carrier and purge ● Ar is the carrier and purge gasgas

● Allows for increase in the ● Allows for increase in the choice of reactantschoice of reactants

● Better film quality● Better film quality● Increased deposition rates● Increased deposition rates

Comparison of ALD to Comparison of ALD to CVD and PVDCVD and PVD

•• Process descriptionProcess description–– ALDALD

•• atomic layeratomic layer--byby--layer deposition process where precursor layer deposition process where precursor is introduced into system, allowed to react with substrate is introduced into system, allowed to react with substrate surface until saturation, remaining bysurface until saturation, remaining by--products or products or unreactedunreacted gases are purged, process is repeated to form a gases are purged, process is repeated to form a monolayer/film monolayer/film

–– CVDCVD•• chemical reaction between gaseous precursors in gas chemical reaction between gaseous precursors in gas

phase; solid product of reaction is deposited on surface of phase; solid product of reaction is deposited on surface of substrate.substrate.

–– PVDPVD•• deposition process in gas phase where source material is deposition process in gas phase where source material is

physically transferred in the vacuum to the substrate physically transferred in the vacuum to the substrate without any chemical reactions being involvedwithout any chemical reactions being involved

Comparison ContinuedComparison Continued

•• selfself--limiting: gaslimiting: gas--surface reactions occur till surface reactions occur till surface is saturated surface is saturated

•• Precursors are introduced into system separately Precursors are introduced into system separately •• reactions occur at the surface reactions occur at the surface •• precise thickness control precise thickness control •• 100% step coverage even at high aspect ratios 100% step coverage even at high aspect ratios •• Films are very uniform, smooth, and Films are very uniform, smooth, and stoichiometricstoichiometric

Comparison ContinuedComparison Continued

•• less contaminationless contamination•• low pressures low pressures

–– typically less than 10typically less than 10--66 torrtorr•• Film thickness can be as low as 1nmFilm thickness can be as low as 1nm•• produces amorphous films produces amorphous films •• lower deposition temperatureslower deposition temperatures

–– as low as 180as low as 180ooC for HfOC for HfO22

Comparison ContinuedComparison Continued•• slow deposition rates slow deposition rates

because have to form because have to form monolayer in two steps monolayer in two steps –– HfOHfO22: dep. rate of : dep. rate of

0.1nm/s @ 3000.1nm/s @ 300ooCC•• Growth rate Growth rate

–– increases, reaches increases, reaches a max, and a max, and decreases slightly decreases slightly as temperature is as temperature is increasedincreased

–– increases with increases with number of cyclesnumber of cycles

Thin Solid Films, 427(1-2), p.147-151.

Current DevelopmentsCurrent Developments

•• Materials being usedMaterials being used–– ZrOZrO2 2 , Al, Al22OO33, HfO, HfO22

•• All exhibit good qualitiesAll exhibit good qualities–– thickness controlthickness control–– good conformitygood conformity–– excellent step coverageexcellent step coverage

Current DevelopmentsCurrent Developments•• HighHigh--k materialsk materials

–– traps electrons between barrier gate and SiOtraps electrons between barrier gate and SiO22

–– prevents burrowing of electrons through SiOprevents burrowing of electrons through SiO22

•• High barrier heightHigh barrier height–– energy required for electrons to pass from gate to energy required for electrons to pass from gate to

SiOSiO22

material formula koxsilicon oxide SiO2 3.9silicon nitride Si3N4 7Oxynitrides SixNyOz 4 - 7aluminum oxide Al2O3 9tantalum pentoxide Ta2O5 25hafnium oxide HfO2 30 - 40zirconium oxide ZrO2 25barium strontium titanate (BST) BaSrTiO3 300

Future DevelopmentsFuture Developments•• HfOHfO22--AlAl22OO33

laminatelaminate–– Being Developed Being Developed

by Samsungby Samsung–– combines good combines good

qualities of bothqualities of both–– Reduced current Reduced current

leakageleakage•• due to highdue to high--k of k of

HfOHfO22 and high and high barrier height of barrier height of AlAl22OO33

Future Developments Future Developments

•• SiN/SiOSiN/SiO22 stack gatestack gate--dielectricdielectric–– SiOSiO22 experiences softexperiences soft--breakdownbreakdown

•• due to differences in thermal expansion, high due to differences in thermal expansion, high electric field, and strained electric field, and strained SiSi--O bondsO bonds

–– low thermal budget (low thermal budget (≤≤550550ooC)C)–– lower leakage currentlower leakage current–– higher reliabilityhigher reliability–– softsoft--breakdown freebreakdown free

•• fewer wasted samplesfewer wasted samples

•• Reduces Boron penetration in SiOReduces Boron penetration in SiO22

Future DevelopmentsFuture Developments

Future DevelopmentsFuture Developments

•• Zr(tZr(t--OCOC44HH99))44, commonly called , commonly called ZTB being used to replace ZrClZTB being used to replace ZrCl44as a precursor when making as a precursor when making ZrOZrO22–– ClCl supposed to be purged once supposed to be purged once ZrZr

has been reactedhas been reacted–– sometimes reacts with substratesometimes reacts with substrate–– can cause damage to whole can cause damage to whole

systemsystem

ReferencesReferences•• LeskelaLeskela MarkkuMarkku, , RitalaRitala MikkoMikko. " Atomic Layer Deposition (ALD): From Precursors to . " Atomic Layer Deposition (ALD): From Precursors to

Thin Film Structures". Thin Solid films, 2002 Thin Film Structures". Thin Solid films, 2002 VolVol 409. PP 138409. PP 138--139. 139. •• RitalaRitala MikkoMikko. "Fundamentals of ALD Chemistry" presented at AVS Topical Confe. "Fundamentals of ALD Chemistry" presented at AVS Topical Conference rence

on Atomic layer deposition, May 14on Atomic layer deposition, May 14--15. 2001 Monterey, California.15. 2001 Monterey, California.•• SnehSneh OferOfer, Phelps Robert et.al. “ Thin film , Phelps Robert et.al. “ Thin film atomiclayeratomiclayer deposition equipment for deposition equipment for

semiconductor processing” . Thin solid films, 2001 semiconductor processing” . Thin solid films, 2001 VolVol 402. PP 248402. PP 248--261.261.•• Scott Thompson, Portland Technology Development, Intel Corp. PauScott Thompson, Portland Technology Development, Intel Corp. Paul Packan, l Packan,

Technology Computer Aided Design, Intel Corp. Mark Technology Computer Aided Design, Intel Corp. Mark SohrSohr, Portland Technology , Portland Technology Development, Intel Corp. Intel Technology Journal. MOS Scaling: Development, Intel Corp. Intel Technology Journal. MOS Scaling: Transistor Challenges Transistor Challenges for the 21st Century. 10 April for the 21st Century. 10 April 2003.<2003.<http://www.intel.com/technology/itj/q31998/articles/art_3.htmhttp://www.intel.com/technology/itj/q31998/articles/art_3.htm>.>.

•• HoHo--KyuKyu Kang. Samsung Electronics Co., LTD. ALD high k materials for gaKang. Samsung Electronics Co., LTD. ALD high k materials for gate and te and capacitor gate dielectrics. ALD Conference 2002.capacitor gate dielectrics. ALD Conference 2002.

•• ASM. The process of innovation. Pulsar. Single Wafer Atomic LayeASM. The process of innovation. Pulsar. Single Wafer Atomic Layer CVD. 10 April r CVD. 10 April 20003. <20003. <http://http://www.asm.com/prod_pulsar.aspwww.asm.com/prod_pulsar.asp>.>.

•• MooMoo--Han Corporation. ALD System. ELFRA 7000 Series. 10 April 2003.<Han Corporation. ALD System. ELFRA 7000 Series. 10 April 2003.<http://www.moohttp://www.moo--han.com/eng/html/product_ald_2.htmlhan.com/eng/html/product_ald_2.html>.>.

•• DaeDae--YounYoun Kim, KyungKim, Kyung--Il Hong, Il Hong, JeongseokJeongseok Ha, Ha, CheolCheol--Min Chang, Min Chang, SeungSeung--Woo Woo ChoiChoi, , HyungHyung--Sang, Park, YongSang, Park, Yong--Min Min YooYoo, , WonyongWonyong KohKoh and and ChoonChoon--SooSoo Lee.Plasma Enhanced Lee.Plasma Enhanced Atomic Layer Deposition of HfO2.Genitech, Inc. ALD Conference 20Atomic Layer Deposition of HfO2.Genitech, Inc. ALD Conference 2002.02.

•• HoHo--KyuKyu Kang, Samsung Electronics Co., LTD, San#24 Kang, Samsung Electronics Co., LTD, San#24 NongseoNongseo--RiRi, , GiheungGiheung--EupEup, , YonginYongin--City, City, GyeonggiGyeonggi--Do, Korea 449Do, Korea 449--711711

•• AnriAnri Nakajima and Shin Yokoyama, Research Center for Nakajima and Shin Yokoyama, Research Center for NanodevicesNanodevices and Systems, and Systems, Hiroshima University 1Hiroshima University 1--44--2 2 KagamiyamaKagamiyama, Higashi, Higashi--, Hiroshima, Hiroshima 739, Hiroshima, Hiroshima 739--8527, 8527, JapanJapan

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