METHOD AND APPARATUS FOR METAL OXIDE CHEMICAL VAPOR DEPOSITION ON A SUBSTRATE SURFACE

Abstract: A method and apparatus for improved metal oxide chemical vapor deposition on a substrate surface where the application boundary layer is reduced and where the uniformity of the application boundary layer is greatly enhanced in a reactor (14). Primary and secondary sonic or other disturbance sources (32, 34) are introduced to the interior chamber or an oscillating chuck (22) is incorporated to influence the boundary layer thickness and uniformity.

Description: METHOD AND APPARATUS FOR METAL OXIDE CHEMICAL VAPOR DEPOSITION ON A SUBSTRATE SURFACE CROSS REFERENCES TO CO-PENDING APPLICATIONS None. BACKGROUND OF THE INVENTION 1. Field of the Invention - The present invention is for a chemical vapor deposition (CVD) , and more particularly, pertains to a method and apparatus for metal oxide chemical vapor deposition (MOCVD) upon a substrate surface. 2. Description of the Prior Art - Several difficulties in prior art metal oxide chemical vapor deposition have been found to be prevalent in the deposition of metal oxide chemical vapors upon a substrate, such as utilized for micro-chip manuf cturing or other purposes. Difficulties encountered during deposition are created in the most by (a) undesirable topology on the substrate surface, (b) non-uniform heating of the substrate, and (c) by a non-uniform gas boundary layer along and about the substrate. The first problem in MOCVD is related to undesirable and inherent substrate topology where at low pressures, such as 1 Torr, MOCVD best takes place, the different vapor components necessary to thermally decompose on a wafer surface in perfect stoichiometry for a particularly useful compound must arrive at the wafer surface at the correct ratio. If the wafer substrate surface were always flat, this ratio could be achieved by simply altering the relative mixture of the vapors, i.e., 10/90 percent to 11/89 percent. However, in most useful cases in integrated circuit construction, inherent uneven topology is usually present, i.e., .50 micron high plateaus with .25 micron spaces. In this case, each vapor component must arrive not only at the top of the topology features at the correct ratio, but must also arrive at the bottom of the topology features at the same ratio. If the deposition ratio is not maintained, then the composition of the complex metal oxide will be non-uniform and will not be useful. Since a gas boundary layer is usually present for a chemical vapor deposition (CVD) reactor with flowing gases of about .80 cm at 760 Torr, for example, for an 8 inch wafer bl=2/3L(v/UL) A .50, each vapor component must replenish the boundary layer. Furthermore, different depths within the boundary layer must get the same ratio of vapors in order to allow uniform compositions to form from thermal decomposition. Generally, different metal containing Metalorganic vapors diffuse at different speeds, as to most gases in general. The basic problem with the current art and prior art is that on uneven topography, uniform compound electrical and crystalline control is difficult, at best. Since the use of the dozens of new complex metal oxides will become prevalent, it is important to develop production methods to deposit the compounds that have been studied in planar applications. The solution to the uneven topology problem, such as presented by the present invention, is to artificially reduce the boundary layer to significantly smaller and uniform thickness, such as in microns. The boundary layer thickness can be significantly reduced and the boundary layer uniformity can be enhanced and stabilized by any one method or combinations of methods including the use of an externally generated periodically disturbed gas motion in the form of a pressure wave, or by moving or oscillating the wafer itself, or by changing the pressure of the injected gas, any or all in the range of Hz through kilo Hz. With reference to reducing boundary layer thickness, Appendix A is attached. Eg. bl=(v/pi.fr.d) where v=viscosity, pi is 3.14, etc., fr=frequency , and d=density of the gas. Appendix A is a spreadsheet relating to various fluids and gases over an 8 inch wafer with no disturbance, and with either 40,000 Hz for water and 10 Hz for the N2 and Argon, where the change in boundary layer (bl) is orders of magnitude. If the boundary layer is made small, then the compound variation due to differential diffusion lengths will also be small, thereby offering a solution for the problem of two and three chemical component MOCVD. An additional benefit is the speeding up of the deposition rate since most MOCVD reactions are limited by the delivery to the surface through a thick boundary layer. The second and third prior art problems in MOCVD are the creation of uniform heating and a uniform gas boundary layer of any thickness. Improved uniformity of the gas layer boundary is accomplished in the present invention in part or wholly as previously described. Usually, a prior art rotating wafer in a downflow creates a uniform boundary layer, independent of scale. The speed of rotation controls, to a certain extent, the thickness. Physical rotation is limited by a vacuum rotating seal and particle problems in prior art devices. Rotation is also helpful or necessary in creating uniform lamp heating and is the subject of several existing patents, such as in Applied Materials, etc. If a prior art stationary platen is used to heat the wafer uniformly, then the gas boundary layer will be non-uniform from the center to the edge with the center being thicker and the edge being a thinner boundary layer or the gradient will either increase or decrease from left to right accordingly. The preferred embodiment of the present invention provides for crossflow longitudinally and laterally along the substrate structure. If prior art rotation is used to make the boundary layer uniform, then a rotating vacuum seal is necessary, and lamp heating is necessary which is inherently non-uniform due to re-radiation differences at the edges of the wafer where radiation emits from all sides instead of just one side. Usually prior art multiple heat zones and multiple pyrometer feedback zones are used to compensate for non-uniformities. As well as gas delivery uniformity, temperature drives the reaction, so temperature uniformity is critical. The present invention eliminates the need for pyrometry since it is non-rotating and allows the use of contacting thermocouples imbedded in the heated stage. Multiple heat zones are eliminated since a large mass-conducting heated static chuck is used. In the present invention, the new boundary layer created by the periodical disturbance gas motion stabilizes the boundary layer thickness and reduces the usual thick boundary layer to a mere fraction, and gas delivery and temperature uniformity are achieved utilizing simple reactor construction. The vapors or gases are sent into the reactor with associated pressure waves, transmitted pressure waves from a transducer, a vibrating or oscillating wafer chuck, or other suitable device. SUMMARY OF THE INVENTION The invention discloses and provides a method and apparatus for metal oxide chemical vapor deposition on a substrate surface providing a crossflow and a downflow reactor. The preferred embodiment of the present invention includes a crossflow reactor having a centrally located oscillatible static chuck for grasping a substrate. A gas inlet in the one end of the crossflow reactor is plumbed to a primary disturbance source which generates periodic disturbances in wave form. Generated periodic disturbances are transferred through a sealed chamber and bellows arrangement to influence boundary layer delivery of metal oxide chemical vapor to the substrate surface. The boundary layer is minimized by the periodic disturbances to provide for greatly reduced and desirable boundary layer thickness. The boundary layer uniformity is also enhanced by the generated periodic disturbance. Additional disturbance can also be provided by oscillating the static chuck to reduce boundary layer thickness and to favorably influence the boundary layer uniformity. The chuck also provides a uniformly heated surface which enhances the thermal boundary layer uniformity. An alternate disturbance source is also provided to generate periodic disturbances to the interior of the crossflow reactor by use of a transducer. The preferred embodiment of this invention is the crossflow reactor since (1) the crossflow reactor limits the volume of gas required, and (2) the crossflow reactor provides an even heating from wafer to opposite surface to produce uniform thermal gradients . One significant aspect and feature of the present invention is the reduction of boundary layer thickness to provide for improved deposition on and about the uneven topology surfaces of a substrate. Another significant aspect and feature of the present invention is improved uniformity of the boundary layer to provide for improved deposition on and about the uneven topology surfaces of a substrate. A further significant aspect and feature of the present invention is the use of primary and alternate disturbance sources either singularly or in unison to reduce boundary layer thickness and to provide for uniformity of the boundary layer. An additional significant aspect and feature of the present invention is the use of an oscillatible chuck to reduce boundary layer thickness and to provide for uniformity of the boundary layer. Still another significant aspect and feature of the present invention is the use of an evenly heated chuck. Yet another significant aspect and feature of the present invention is the use of a downflow reactor. Still another significant aspect and feature of the present invention is the use of a crossflow reactor. Having thus described embodiments and significant aspects and features of the present invention, it is the principal object of the present invention to provide a method and apparatus for metal oxide chemical vapor deposition on a substrate surface. BRIEF DESCRIPTION OF THE DRAWINGS Other objects of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings , in which like reference numerals designate like parts throughout the figures thereof and wherein: FIG. 1 illustrates the method and a downflow reactor apparatus for metal oxide chemical vapor deposition on a substrate surface; and, FIG. 2, the preferred embodiment, illustrates the method and a crossflow reactor apparatus for metal oxide chemical vapor deposition on one or more substrate surfaces. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates the method and apparatus for Metal Oxide Chemical Vapor Deposition on a substrate surface. A downflow reactor 10 apparatus is incorporated and utilized for Metal Oxide Chemical Vapor Deposition (MOCVD) upon the upper surface of a substrate 12 positioned central to the downflow reactor 10. The downflow reactor 10 is a cold wall vacuum reactor having a surrounding vessel wall 14 about and to which related structure and devices are attached or extend therefrom. A gas inlet 16 for receiving a gas from the Mass Flow Controller (MFC) is located at the upper region of the downflow reactor 10. Opposing the gas inlet 16 and located at the lower region of the downflow reactor 10 is a gas outlet 18 to which a metering valve 20 for control of the transitting gases through the vessel 14 is attached. A static chuck 22, which is utilized to secure the substrate 12, is centrally located within the surrounding, vessel wall 14. The static chuck 22 of large and sufficient mass is resistively heated and can be vibrated or oscillated at a low frequency either vertically or horizontally, or in the alternative can be vibrated or oscillated at a low frequency simultaneously both vertically and horizontally to assist in control of reduced boundary layer thickness and to contribute to boundary layer uniformity control. The relatively large mass of the static chuck 22 is conducive to appropriate uniform and even temperature distribution across the static chuck 22 to enhance boundary layer control. A plurality of thermocouples 24a-24n and a suitable resistance heater 25 are embedded in the static chuck 22 for monitoring and control of the static chuck 22 temperature. A chamber 26 is located at and attached to the gas inlet 16 at the upper region of the downflow reactor 10. An isolation bellows 28 is located in the chamber 26. An inlet 30 is attached to the chamber 26 to receive a disturbance input from a primary disturbance source 32. The primary disturbance source 32 introduces periodic disturbances to the downflow reactor 10 through the inlet 30, the chamber 26, the isolation bellows 28 and the gas inlet 16. The periodic disturbances 29 emanating from the primary disturbance source 32 can be provided by, but not limited to, devices such as a pneumatic oscillator which provide a sinusoidal disturbance. One or more transducers 33 and alternate disturbance sources 34 are attached to the vessel wall 14 to provide additional periodic disturbance either acting as an additional single unit for imparting a disturbance to the downflow reactor 10 or acting in concert with the primary disturbance source 32 to impart multiple or reinforced disturbances to the downflow reactor 10. Both the primary and the alternate disturbance sources 32 and 34 respectively can include but are not limited to a pneumatic oscillator, a speaker, a piezo or other electromagnetic device, a bellows with a pneumatic source, a pneumatic oscillator or other device which generates an appropriate disturbance. FIG. 2, the preferred embodiment, illustrates the method and apparatus for Metal Oxide Chemical Vapor Deposition on a substrate surface. A horizontally aligned crossflow reactor 40 apparatus is incorporated and utilized for Metal Oxide Chemical Vapor Deposition (MOCVD) upon the upper surface of a substrate 42 positioned central to the crossflow reactor 40. The crossflow reactor 40 is a cold wall vacuum reactor having a surrounding vessel wall 44 about and to which related structure and devices are attached or extend therefrom. A gas inlet 46 for receiving a gas from the Mass Flow Controller (MFC) is located at one end of the crossflow reactor 40. Opposing the gas inlet 46 and located at the opposing end of the crossflow reactor 40 is a gas outlet 48 to which a metering valve 50 for control of the transitting gases through the vessel 44 is attached. A static chuck 52, which is utilized to secure the substrate 42, is centrally located and extends through the surrounding vessel wall 44. At least one or more wafers are flush to the surface of the crossflow reactor 40 to reduce gas flow while having good laminar flow. The static chuck 52 of large and sufficient mass is resistively heated and can be vibrated or oscillated vertically or horizontally, or in the alternative can be vibrated or oscillated simultaneously both vertically and horizontally to assist in control of reduced boundary layer thickness and to contribute to boundary layer uniformity control. The relatively large mass of the static chuck 52 is conducive to appropriate uniform and even temperature distribution and to having an even reaction across the static chuck 52 to enhance boundary layer control. One or more thermocouples 54a-54n and a resistance heater 55 are embedded in the static chuck 52 for monitoring and control of the static chuck 52 temperature. One or more transducers 56 and primary disturbance sources 58, preferably in a location opposite to the gas inlet 46, are attached to the end or other suitable site on the vessel wall 44 to provide periodic disturbance acting to impart a disturbance to the crossflow reactor 40. The periodic disturbances 60 emanating from the primary disturbance source 58 can be provided by, but not limited to, devices such as a pneumatic oscillator which provide a sinusoidal disturbance. With respect to an alternate disturbance source 62, a chamber 64 is located at and attached to the gas inlet 46 at the end of the crossflow reactor 40. An isolation bellows 66 is located in the chamber 64. An inlet 68 is attached to the chamber 64 to receive a disturbance input from the alternate disturbance source 62. The alternate disturbance source 62 introduces periodic disturbances to the crossflow reactor 40 through the inlet 68, the chamber 64, the isolation bellows 66 and the gas inlet 46. Both the primary and the alternate disturbance sources 58 and 62, respectively, and the additional transducer 70 can include but are not limited to a pneumatic oscillator, a speaker, a piezo or other electromagnetic device, a bellows with a pneumatic source, a pneumatic oscillator or other device which generates an appropriate disturbance. In use, the primary disturbance source 58 and transducer 56 can be used as a stand device for introduction of periodic disturbance, but in the alternative can incorporate the additional and simultaneous use of the transducer 70 located on the vessel wall 44. In a similar fashion, the alternate disturbance source 62, including the delivery components, can be used as a stand-alone device for introduction of periodic disturbances, but in the alternative can incorporate the additional and simultaneous use of the transducer 70 located on the vessel wall 44. Other combinations incorporating the use of one or more disturbance sources, transducers and the like are also included in the scope of the invention. METHOD AND APPARATUS FOR METAL OXIDE CHEMICAL VAPOR DEPOSITION ON A SUBSTRATE SURFACE PARTS LIST downflow reactor 46 gas inlet substrate 48 gas outlet vessel wall 50 metering valve gas inlet 52 static chuck gas outlet 54a-n thermocouples metering valve 55 resistance heater static chuck 56 transducer a-n thermocouples 58 primary disturbance resistance heater source chamber 60 periodic disturbances isolation bellows 62 alternate disturbance source periodic disturbances 64 chamber inlet 66 isolation bellows primary disturbance source 68 inlet transducer 70 transducer alternate disturbance source crossflow reactor substrate vessel wall Any suitable reactor can be utilized such as crossflow or downflow or even an atmospheric pressure reactor that uses gas and boundary layer technology. Any reactor that depends on a uniform and thin boundary layer can include CVD, MOCVD, MBE, LPE and VPE. Various modifications can be made to the present invention without departing from the apparent scope hereof. IT IS CLAIMED: APPENDIX A CHEMICAL VAPOR DEPOSITION AND EPITAXIAL GROWTH Dennis W. Hess Department of Chemical Engineering University of California Berkeley, California . 94720 TOPICS INTRODUCTION FUNDAMENTALS OF CVD REACTOR CONFIGURATIONS AND COMPARISONS EPITAXIAL GROWTH OF SILICON SURFACE PREPARATION FOR EPI SELECTIVE EPITAXY EPITAXIAL DEFECTS LOW PRESSURE CVD PLASMA- AND PHOTON-ENHANCED CVD FUTURE CONSIDERATIONS GENERAL REFERENCES CHEMICAL VAPOR DEPOSITION (CVD) USES CHEMICALLY REACTTVE HOST IMPORTANT FACTORS FOR EPITAXIAL GROWTH VAPORS TO SYNTHESIZE OR DEPOSIT A FILM OR COATING. - SURFACE AND PROCESS CLEANLINESS A CVD PROCESS MUST FORM FILM MATERIALS WITH REPRODUCIBLE AND CONTROLLABLE PROPERTIES AT REASONABLE DEPOSITION RATES - ATTICE MATCH BETWEEN SUBSTRATE AND DEPOSIT AND COSTS WHILE MINIMIZING THE EFFECT OF DEPOSITION ON - THERMAL EXPANSION COEFFICIENT MATCH BETWEEN THE RESULTS OF PREVIOUS PROCESSING SUBSTRATE AND DEPOSIT FILM PROPERTIES TO CONTROL DURING CVD: - THICKNESS GENERAL ATTR1BUTES/ADVARTAGES OF CVD - COMPOSITION - PURITY VERSATILE - RYSTALLINITY/MORPHOLOGY HIGH PURITY, QUALITY VAPOR PHASE EPITAXY (VPE) is A SPECIAL CASE OF CVD WHEREIN A GOOD CONTROL OF FILM COMPOSITION CRYSTALLINE MATERIAL IS DEPOSITED ON TOP OF A CRYSTALRANGE OF OPERATING CONDITIONS POSSIBLE LINE SUBSTRATE DEPOSITION CAN BE ACTIVATED BY HEAT, PHOTONS, PARTICLES HOMOEPITAXY: SUBSTRATE IS THE SAME MATERIAL AS DEPOSIT HETEROGNEOUS/HOMOGENEOUS REACTIONS OCCUR HETEROEPITAXY: SUBSTRATE AND DEPOSIT DIFFER IN COMPOSITION Chemical vapour deposition (CVD) techniques Process Acronym Energy source Atmospheric pressure CVD APCVD Thermal Low-pressure CVD LPCVD Thermal Homogeneous CVD HOMOCVD Thermal Metallo-organic CVD MOCVD Thermal Plasma-enhanced CVD PECVD RF Photoiytic CVD UVCVD Photons Laser CVD LCVD Photons CVD Systems Deposition Pressure Temperature System Overall Reaction (Pascal) (K) SiH,.,Cl, + H, → Si + xHCl, x = 0, 2, 3, or 4 101 kPa 1050-1450 CVD SiHi→ Si + 2Hj 50 850-950 SiH, + N 2 ϋ-> SiO, + N t 50 . 900-1000 SiH,CI, + NHΪ→ Si.N 4 50 1000-1100 WF β + H.→ VV + HF 50 500-700 Very Low Pressure CVD SiH,-÷ Si + 2H 2 1 850-1150 Vapor-phase Epitaw 2HC1 + 2Ga- 2CaCI -t- H 2 (VPE) 12CaCl + 4A H, + 2As + As, i→ 12CaAs + 12HC1 101 kPa 800-1100 Mctallor^anic CVD Ga(CH 3 ) 3 + AsH 3 → CaAs + CH, 101 kPa 800-900 (MOCVD) CatCH a + Al,(CH.ι), + AsH 3 → Al,Ca,.,As + CH-, 101 kPa 800-1000 Plasma-enhanced CVD SiH,→ a.SiH 50 300-600 (PECVD) SiH., + NHi→ Si.N„:H 50 400-700 Photon-assisted CVD SiH, + N 2 0 → SiO, 50-500 300-600 In(CH 3 ) 3 + P(CHl → InP 60-500 600-700 FUNDAMENTAL PRINCIPLES IN CVD CVD CH 1. THERMODYNAMICS - EXTENT OF REACTION F(T, P.. Y j > • CVD Involves gas phase (ho aηd surface (heterogeneous) - SIDE REACTIONS - EQUILIBRIUM Silicon depositio 2. KINETICS - RATE - ADSORPTION OF REACTANT, SURFACE REACTION, BY-PRODUCT DESORPTI ON 3. MASS TRANSFER - DI FFUSI ON OF SPEC I ES TO/FROM SURFACE h. 5. 6. - FILM QUALITY, PURITY TRANSPORT AND REACTION PROCESSES IN CVD CVD REACTOR CONFIGURATIONS Horizontal CVD Reactor Vertical CVD Reactor (a) (b) f3as Inlet Barrel CVD Reactor Pancake CVD Reactor (c) (d) Exhaust Vertical LPCVD Reactor Horizontal LPCVD Reactor ( β ) (0 COMPARISON OF REACTORS GAS DEPLETION ATMOSPHERIC LOW PRESSURE PRESSURE REGION OF OPERATION MASS-TRANSPORT SURFACE-REACTION LIMITED CONTROLLED TEMPERATURE HIGHER LOWER PRESSURE 1 ATM (760 TORR) 0.1 - 1 TORR PRIMARY ADVANTAGE FLEXIBLE LARGE CAPACITY COMPENSATION FOR TILT TEMPERATURE COMPENSATION FOR GAS DEPLETION GAS DEPLETION SUSCEPTOR GRADIENT Operation in surface-reaction-limited regime allows close wafer spacing with radial thickness uniformity Low pressure increases reactant diffusion between closely-spaced wafers REYNOLD'S NUMBER CHOOSE LIMITING PROCESS FOR BEST CONTROL OF DEPOSITION, RE R E D T V P n Laminar flow for R E < 2000 STRUCTURE DEPENDS ON Turbulent flow for R E > 2000 • Substrate • Amorphous: eg, Siθ2, SΪ3N4 BOUNDARY-LAYER THICKNESS • Crystalline: eg, Si, Sapphire (AI2O3) S ( x ) = • Deposition pressure CVD REACTOR MODELING By combining VELOCITY DISTRIBUTION L continuity balances for momentum, species mass and energy D. expressions for mass and energy fluxes iil. kinetic rate expressions iv. thermochemical data. It Is possible to construct a model of a CVD reactor. Assumptions and simplifications are usually necessary to reduce the model complexity ana focus on essential features. Dislαnce Along Suscepfor (c m) Powerful numerical methods (e.g. collocation, finite differences, finite elements) and large supercomputers are available for solving complex problems. However, considerable insight can also be gained from simple, fundamental models. TEMPERATURE DISTRIBUTION The development of detailed CVD models are needed: • to provide a link between fundamental studies and process applications M E Coltrln, R J Kββ, end J A Miller, J. Elβctrochβ . Soc. 131, 425 (February 1984) • to develop process control strategies • to design process equipment SUBSTRATE PREPARATION TECHNIQUES FOR CVD o SUBSTRATE SURFACE CLEANLINESS - ESSENTIAL PREREQUISITE TO SUCCESSFUL CVD OR EPI - A CLEAN SURFACE HAS NO SIGNIFICANT UNDESIRABLE CONTAMINANTS, PARTICULATES, PHYSICAL ADSORBATES CHEMISORBED IMPURITIES o CLEANING APPROACHES - PREPARATORY TECHNIQUES - IN SITU TECHNIQUES (iN CVD REACTOR) o PHYSICAL METHODS - HIGH-PRESSURE SCRUBBING, HIGH-PRESSURE LIQUID SPRAYING - ULTRASONIC (20-80 KHZ) TECH IQUES - MEGASONIC (0.8 MHZ) TECHNIQUES - CENTRIFUGAL CLEANING TECHNIQUES - SOLVENT EXTRACTION, VAPOR DEGREASING, DISSOLUTION - THERMAL DESORPTION, SUBLIMATION, VACUUM HEATING - PHYSICAL SPUTTERING o PHYSICAL-CHEMICAL METHODS - CHEMICAL SPUTTERING (PLASMA ETCHING, REACTIVE ION ETCHING) - GLOW DISCHARGE PLASMA TECHNIQUES, PLASMA OXIDATION ("ASHING") - SHORT-WAVELENGTH UV IRRADIATION o CHEMICAL METHODS - THERMAL OXIDATION AND STRIPPING - CHELATING, COMPLEXING - VAPOR PHASE CHEMICAL ETCHING - WET CHEMICAL OXIDATION WITH OXIDIZING REAGENTS, SUCH AS H2O2- HNO3, AQUA REGIA, H2SO/-H2O2, H2SO -CRO3 ETC. - WET CHEMICAL ETCHING TO REMOVE SURFACE LAYERS - ELECTROCHEMICAL ETCHING 0 FINAL RINSING, DRYING, AND STORAGE - DISTILLED AND DEIONIZED WATER - HIGH-PURITY ALCOHOLS - CENTRIFUGAL SPIN-DRYING, BLOW-DRYING - STORAGE (IF NECESSARY) IN CLEANED, CLOSED GLASS CONTAINERS WHY GROW SI EPITAXIAL FILMS ? • MAKE POSSIBLE UNIQUE DEVICE STRUCTURES: - CONTROL OF DOPANT CONCENTRATION, DISTRIBUTION, AND TYPE INDEPENDENT OF SUBSTRATE - "ENCLOSE" BURIED LAYERS - USE OF INSULATING SUBSTRATES AN EPITAXIAL PROCESS SEQUENCE Step Estimated Time Load clean wafers into reactor 2 - 4 in Purge with inert gas and Gil with F carrier. 3 - 5 nun (Also pumpdown if reduced pressure epitaxy process is being conducted). 3. Heat to hydrogen balce temperature (1200° 10 - 12 min to remove oxide layer. (Note: this step can remove 50- lOOA of an SiC layer.) 4. a) Heat to HCl etch temperature; b) Introduce anhydrous HCl (or SF ) to etch surface Si layer. 5 - 7 min c) Purge to clear HCl and dopants from system. a) Cool to deposition temperature; b) Introduce silicon 10 - 12 min source and dopants to deposit desired layer; c) Clear out silicon source and dopants by purging with H2. 6. Cool to room temperature. 10 - 12 min 7. Purge out H2 and backfill with N2 3 - 5 min Unload wafer 2 - 4 min Total Process Time 45 + min Total Heated Process Time 25 + min SILICON EPITAXY • Silicon expitaxial films are deposited on single crystal silicon <100> or <111> oriented substrates; typically 0.5 - 20μm thick. • The overall deposition reaction is S1CI4-X H x + (4-x)/2 H 2 → Si + (4-x) HCl • The deposition temperature increases with Cl content In the chlorosilanes: Chemical Nominal Temperature Allowed- Dβposilon growth rale (μ ln) range (*C) oxlcttzβr level (ppm) S.CI4 0.4-1.5 1150-1250 5-10 SWCI3 0.4-2.0 1100-1200 5-10 SiH 2 C-2 0.4-3.0 1050-1150 <S SiH 4 0.2-0.3 850-1050 <2 Slow growth at high temperature with Chlorosilane favors crystal perfection since the mobility is high and the reverse etching reaction preferentially attacks defects. If auto doping is an issue and sharp junctions are required, low temperature growth is desirable. PH 3 OR B 2 H 6 CONCENTRATION (ppm) Doping of the films can be done in situ with ppm additions of Pl- , B2Hg Boron and phosphorus concentrations in cpi silicon as a function and ASH3 in H2. of diborane and phosphine partial pressures. -i 1 1 1 1 1 r- TRANSITION LINE SMOOTH-PITTED H 2 / HCl (111) SILICON EPITAXY PROCESS GAS Problem: autodooinπ Autodoping is caused by two factors: i. Solid-state out diffusion of dopants from the bulk substrate into the growth epitaxial film. ϋ. Solid-state out diffusion and release of dopants into the gas stream followed by incorporation into the film. PROCESS GAS S A. AUTODOPING FROM BACK SIDE B. DOPANT LOST TO FREE STREAM A. Vertical Autodoping B Lateral Autodoping C. Dopant lost to free stream VERTICAL DEPTH Gas phase autodoping is reduced with lower pressure. Solid-state diffusion decreases exponentially with decreasing temperature. Probl 10 100 1000 Pattern shift is substantially reduced as the reactor pressure is PRESSURE (TORR) lowered. Resistivity of sputtering epltαxlol silicon Silicon Substrate • Epitaxial Silicon HF SiOx film Crystal Sheet cleaning thickness (A) structure β resistivity * (x>0.5) (Q/D) 1N-SITU SURFACE PREPARATION FOR EPI GROWTH Before Poly- cleaning 7 crystal 5x10* 1-2Z HCL FOR VAPOR CLEAN Wet Single- cleaning 0.4 crystal 100 • PROBLEMS Dry cleaning 0.3 Amorphous. 3-5x10* 1. THI N EP I LAYERS => CONTROL 2. METALLI C TRANSPORT AND CONTAMINAT I ON I) Pretreσtmβnt H2Sθ4+teC«(4!lvol) — ► Dl water — »IPA vapor drying 3. CHLOROS I LANE ETCH PRODUCTS DEGRADE VACUUM Q UALI TY 2) Crystal structure : Reflection electron diffraction 3) Sheet resistivity : Four point probe method o H2 CLEAN AT HI GH ( > 1100°C) TEMPERATURE H PASS IVATI ON FOLLOWED BY UHV-CVD ETCHING RATE OF Si0 2 BY H 2 ANNEALING 1 H2 OX K Kug i miya and Y. Hiroiujl. Japanese Journal 0! Applied Physics Vol 24. No 5. May. 19B5 pp 516-523 OXYGEN AND CARBON CONCENTRATION OF THE ECR DEPOSITED SILICON FILM BULK AND THE INTERFACE BETWEEN THE FILM AND THE SILICON SUBSTRATE DETERMINED BY SIMS. Film bulk Interface Cleaning procedure oxygen carbon oxygen carbon 17 3 17 3 of substrate (x 10 atoms/cm ) (x 10 atoms/cm This work UV/HF cleaning 60 1000 ** conventional 0.5 10 500 cleaning Previous works HF dipping by 100 <10 6000 Kumii HF dipping by 300 80 500 Hung Hg lamp for UV cleaning; samples at 200°C in 0- for 10 min. HF dip (50% HF) ECR with SiH (2 x IO -4 torr) at 540, 630, 710°C. UHV at 810°C. after Ohmi , 1990 UHV/CVD FOR EPITAXIAL GROWTH T,(C) nx suvw-a . ruRoe AMO FIDW OASES WΛCTIVt OASCI ON KEΛC-IOH ( TOβ M-E-Cr REΛ---T --H 1-22-H μ≤Ξ.-) <D REMOTE H2/H ETCHING OF Si SURFACE Di β jr j-α of RFCYD cxpenaiea- uJ system tfc nnag ii-t-u-dedu-mt of sam * pic beater. rcuduaj fas a-aslyxcr (ROΛ) ta acpara-tctl from the proαc M chamber by a threc-po tom vabn. Tha vm w al m sαuor bead M saαψk the dumber bacfcfn-wad a f Uy opca po β uαa And a-bo i-Qows t- tcna-or bead to s-unpk ibc process naa | di-βer- e ut pumptαf beα n poai- sent ent low rts Auger spectrum of the silicon surface showing the silicon, oxygen and carbon peaks before in um remote hydrogen plasma clean (top), after m situ remote hydrogen plasma dean ( ottom ) The incident beam cncrgj » 3 cV and the peak-to-peak modulation voltage is 2 e V, except for Si KLL. which is recorded at 4-eV modulation voltage IMPURITIES IN HYDROGEN Hydrogen Purified 6-9's' 5-9V H 3 0 (ppb) 50 50 > 12000 O. (ppb) < 2 20 nominally 99.9999% pure nominally 99.999% pure Low temperature epi (650 C) can be grown KJ at atmospheric pressure if an extremely clean environment is provided. At higher T (800 C) selective epi can be grown - load-locked system - hydrogen purifier (Nanoche lithium- phenyl based unit) - transition from epi to poly at 750 C occurs when H2O > 0 ppb and 0 2 > 20 ppb SELECTIVE SILICON DEPOSITION (SSD) - SELECTIVE EP ITAXIAL GROWTH (SEG) • DEVICE I SOLATION SELECTIVE SILICON GROWTH (SSG) OR SELECTIVE POLYSILICON SELECTIVE EPITAXY DEPOSITION (SPD) • RENCH FILLING FOR PLANARIZATION BARRIER TO NUCLEATION ON OXIDE (NON-ACTIVE AREA) DIFFERENT BONDING ON Si AND Si0 2 SIMULTANEOUS SINGLE/POLY DEPOSITION (SSPD) DEPOSITION ON Si WITHOUT DEPOSITION • SIMULTANEOUS BASE FORMATION AND POLY ON OXIDE DEPOSITION OVER OXIDE FAVORED IF CHLORINE SPECIES PRESENT "ETCHES" INCIPIENT NUCLEI ON OXIDE SELECTIVITY CONTROL SILICON NUCLEATION AND GROWTH OCCUR SIMULTANEOUSLY OVER SILICON INCUBATION PERIOD OCCURS IF NATIVE OXIDE OR THICKER S1O2 LAYER IS PRESENT (INCUBATION TIME DEPENDS UPON SILICON SOURCE GAS, DEPOSITION TEMPERATURE, DEPOSITION PRESSURE, AND OXIDE SURFACE CONDITION) The temperature dependence of select con on silicon slices portly coated with oxide or Si (ON OXIDE)+2HCL— >SICL2+H2 tion of temperature and supersaturation, express in hydrogen as a carrier gas. SILICON NUCLEATION DENSITY OVER OXIDE 1E4/T(K) S1H4 S1H4*HCI SIH2CI2 SIHCJ3 1. Oild* Itleπ 4. Coalaacβnc* 2. SβWcthr-. Ep4 V«rttcW Growth 5. Ptwu.rtz--.Uon W///,*W//M SI Substrate — V/////^W/λ 3. Epttax t tan-- Owgrowtti 0«*ic* Fabrication MOtaαna-) P-Ctumai Epitaxial Lateral Overgrowth (ELO) for siliαon on insulator (SOI) technology Common defects occuring silicon epitaxial layers are: E P I D E F E C T S 1. Line or edge dislocations intially present in the substrate extending Into the epitaxial layer (these can be caused by nonuniform heating of the substrate). Z Stacking faults nucleated by impurity precipitates on the • DISLOCATIONS substrate surface. 3. Impurity precipitates in the epitaxial layer. - SLIP DISLOCATIONS (THERMAL STRESS) 4. Growth hillocks, their density decrease with increasing - MISFIT DISLOCATIONS (INTERFACE STRESS temperature, and decreasing growth rate. CAUSED BY LATTICE PARAMETER MISMATCH) 5. Bulk stacking faults extending into the epitaxial layer. o • STACKING FAULTS (DEFECTS AND IMPURITIES) • PRECIPITATES - OXYGEN - METAL CONTAMINANTS Thermally induced slip EFFECT OF TRANSITION METALS ON EPITAXIAL STACKING FAULT DENSITIES o CONTAMINATED WAFER BACKSIDE WITH EITHER - METAL WIRE SCRATCHING - METALS IN SOLUTION o IN SOME CASES, RTA (1000°C FOR 30 SEC) WAS PERFORMED TO PREC I P I TATE THE METAL ON WAFER FRONTSIDE o EPI WAS GROWN AT 1070°C USING SICLJJ Ni Cu> FE FOR METAL PRECIPITATES 0 LOW DENSITIES OF STACKING FAULTS WERE OBSERVED FOR SOLUTION- CONTAMINATED WAFERS o AN IN-S ITU HCL ETCH AT 1070°C PR I OR TO EP ITAXIAL GROWTH LOWERED STACKING FAULT DENSITIES AFTER SPARKS ET AL., IN "ADVANCED MATERIALS FOR ULSI," ED. BY SCOTT, AKASAKA, AND REIF, ELECTROCHEM. SOC, 1988. LPCVD OF POLY-SILI CON SiH 4 ► SI + 2H 2 600 < T < 650 β C 0.1 < P < 1.0 TORR SIH 4 PARTIAL PRESSURE (Pa) Typical reations for depositing dielectrics and polysilicon. Product Reactants Deposition temperature, °C Silicon dioxide SiH 4 + C0 2 + H 2 850-950 Silicon nitride SiH 4 + NH 3 700-900 SiCl 2 H 2 + NH 3 650-750 Plasma silicon nitr de SiH 4 + NH 3 200-350 SiH + N 200-350 Plasma silicon dioxide SiH., + N 2 0 200-350 Ftolysiiicon SiH 4 575-650 POLYCRYSTALLINE SI Poly-Si films from SiH 4 can be doped insitu by addition of B 2 H 6 , J. Electrochem. Soc. 131 , 2361 (1984) The enhanced growth rate in B Hg doping is most likely due to a surface electronic effects. The decreased growth rate in PH 3 and ASH 3 doping are due to surface poisoning by PH X and AsH x species. The large non uniformities in this case are caused by the rapid SiH chemistry initiated in the gas phase. HALIDE AND HYDRIDE PROCESSES FOR CVD OF lll-V COMPOUND SEMICONDUCTORS GaAs deposition Hafide Process; WITH G0A1 CRUST CH 3 * + CH 3 « + Over-all reactions CH 3 « + AsH 3 → Zone 1 6AsCI 3 + 9H 2 → As + As 2 + 18HCI H« + AsH 3 → Zone 2 As 4 + As 2 + 6Ga -» GaAs Zone 3 6GaAs + 6HCI → As + As 2 + GaCI + 3H 2 Ga(CH 3 ) χ + AsHy → Hvdride Process: Ove LPCVD OF TUNGSTEN START 300°C 2WF« + 3Si 2W + 3SiF 4 \ STEP 1 : 300°C WF β + 3H 2 W + 6HF \ TUNGSTEN STEP 2: (~15θθA) Si0 Si LPCVD OF ALUMINUM AND Al-Si ALLOYS PYROLYSIS OF TRMSOBUTYL ALUMINUM. THEN ALLOYING: 200-300" C Al(C 4 H g ) 3 - Al + 3 2 H 2 + 3 C 4 H g 460* C Al + ~. ς:il ) _ β Al-Si + 2 H 2 1. REACTOR SS TUBE LPCVD FURNACE 2. Al SOURCE TEMP. 140*0 3. WAFER POSITIONING VERTICALLY. 2cm SPACES. 25 WAFERS 4. PUMP DOWN 50 TORR 5. HEAT-UP AMBIENT 0.5 ran H 2 β. FLUSH GAS PURE Ar 7. NUCLEATION EXPOSURE TO TiCI 4 VAPOR a. Al DEPOSITION TEMP. 260 β C 9. Al DEPOSITION RATE 100-200 A/min 10. THICKNESS UNIFORMITY ± 10% on 7.5 on WAFERS 11. CONFORMALITY EXCELLENT. BUT ROUGH SURFACE 12. POST DEPOSITION ALLOYING 10% SiH Λ IN H 2 . 0.5 TORR, 460 β C 13; ALLOYING STEP TOTAL PRESSURE 10-15 TORR 14. FILM COMPOSITION 0-0.8 wt% Si IN PURE Al Cooks at al.. Solid State Technαi. 25 (12). 62 (1982) PECVD PLASMA _ A PARTIALLY I ON I ZED GAS COMPOSED OF IONS, ELECTRONS, AND A VAR I ETY OF NEUTRAL SPEC I ES LP-CVO-LT.HT PROCESSES TEMP.. PRESSURE. OEP. RATE, FILM RE ACT ANTS • c TORR A/min COMMENTS RF GLOW DISCHARGE = NON-EQUILIBRIUM PLASMA ' SiO j SiH 4 /O j /N 2 466. 0.7 120 V6RY SPACING SENSITIVE F = 50 KHZ - 40 MHz Si(OC 2 H j ) 4 740 1.0 200 EXCELLENT SIH 4 /N 2 0 N j 860 1.0 50 LOW DEP. RATE p = 0.02 - 5 TORR SiH j d j ^ j O 910 OJ 120 EXCELLENT PSG SJH 4 PHJ/OJ/N 2 466 0.7 160 VERY SPACING SENSITIVE N E = IO 9 - IO 12 CM "3 SHOC j H^/ -V 740 xo 3S0 EXCELLENT PO(OCH 3 ) j /(0 2 ) N N ≡ IO 15 CM "3 S 3 N A SIHJCIJ/NHJ 73 0.5 40 EXCELLENT UNIFORMITY S»H 4 /NH j N 2 830 0-5 30 SPACING SENSITIVE T E « 1-10 EV SiH 2 2 /NH 3 910 0.06 80 EXCELLENT T, = 0.04 EV SiH 4 + Nil 3 — ► S1NH + 3H 2 T = 300°C (<J) STEP COVERAGE CONSIDERATIONS 893 Table I— The Need for interface Management Impact on Trend Barrier Equipment Smaller design Smaller contact openNeed to reduce exposure rules ings. Higher contact to particles, moisture, resistance. Need for chamber integration of contact etch and interconnect deposition. Need for higher throughput Low temperature Lowered thermal budget Need to integrate surface processing makes it difficult to preclean and epitaxial remove native oxide and deposition. and contamination before epitaxial deposition. Sensitivity to oxygen and moisture. Thinner gate Thermal oxide more Need to integrate. surface dielectrics susceptible to surface preclean, CVD oxide contamination and formation, and subsequent interface degradation. anneal. Sensitivity to oxygen and moisture. MULTICHAMBER REACTOR Wafer CVD or other ss chambers GENERAL REFERENCES VLSI Technology, ed. by S. M. Sze, McGraw-Hill, 1983; second edition, 1988. Silicon Processing for the VLSI Era. S. Wolf and R. Tauber, Lattice Press, 1986. Semiconductor Silicon 1986, ed. by H. R. Huff, T. Abe, and B. Kolbesen, The Electrochemical Society, Inc., 1986. Chemical Vapor Deposition 1987. ed. by G. W. Cullen, The Electrochemical Society, Inc., 1987. Advanced Materials for ULSI, ed. by M. Scott, Y. Akasa a, and R. Reif, The Electrochemical Society, Inc., 1988. ULSI Science and Technology 1989, ed. by C. M. Osburn and J. M. Andrews, The Electrochemical Society, Inc., 1989. K. F. Jensen, in, Microelectronics Processing: Chemical Engineering Aspects, e . by D. W. Hess and K. F. Jensen, ACS Advances in Chemistry Series No. 221, American Chemical Society, 1989. McD. Robinson, in Microelectronic Materials and Processes, ed. by R. Levy, NATO ASI Series; Series E: Applied Sciences - Vol 164; Kluwer Academic Publishers, 1989. Semiconductor Silicon 1990. ed. by H. R. Huff, K. Barraclough, and J. Chikawa, The Electrochemical Society, Inc., 1990. "Selective Silicon Deposition for the Megabit Age", J. O. Borland and I. Beinglass, Solid State Technol., Jan., 1990, p. 73.

Claims: 1. A method for improved chemical vapor deposition on a substrate surface where the application boundary layer is reduced and where the uniformity of the application boundary layer is greatly enhanced in a reactor comprising the step of introducing a primary and/or alternate sonic or other disturbance sources to the interior chamber of the reactor.

Inventors: GRANT ROBERT W, GRANT, ROBERT, W.
Applicants: PRIMAXX INC, PRIMAXX, INC.
Application year: 2000
Main classification: B05D3
IPC codes: C23C16, H01L21