Abstract:
Thin films are produced by a method wherein a material is heated in a furnace placed inside a vacuum system. An inert gas is flown over/through the heated material. The vapors of the material are entrained in the carrier gas which is then directed onto a substrate heated to a temperature below that of the furnace temperature and placed in close proximity to the exit of the furnace.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon provisional application Ser. No. 60/193,662, filed Mar. 31, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 5,945,163 discloses an apparatus and method for depositing a material on a substrate. In that patent a distributor is utilized which includes a heated permeable member through which a carrier gas and a material are passed to provide a vapor that is deposited on a conveyed substrate. The permeable member is tubular and has an electrical voltage applied along its length to provide the heating and the carrier gas and the material as a powder are introduced into the tubular permeable member for flow outwardly therefrom as the vapor. A shroud extends around the tubular permeable member and has an opening through which the vapor flows for the deposition. 
     It would be desirable if improved techniques could be provided for producing thin film. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide improved methods for producing thin film. 
     In accordance with this invention the material to be produced as a thin film is heated to a sufficient temperature T in a furnace placed inside of a vacuum system. An inert carrier gas is flown over/through the heated material and the vapors of the material are entrained in the carrier gas. Carrier gas containing the vapors of the material is directed onto a substrate heated to a temperature below that of the furnace temperature and placed in close proximity to the exit of the furnace. 
     Carrier gas flow is adjusted to give: 
     A sufficient degree of entrainment of the material during contact with the source, 
     A pressure inside the vacuum enclosure that would be high enough to suppress any re-evaporation from the substrate, 
     The desired deposition rate. 
     The vacuum system could be pressurized by a secondary inert gas inlet not going through the source to give more flexibility for the adjustment of the carrier gas flow going through the furnace. 
    
    
     THE DRAWINGS 
     FIG. 1 is a schematic showing of the inert carrier gas flow used for deposition in accordance with this invention; 
     FIG. 2 is an exploded isometric view of a prototype source in accordance with this invention; 
     FIGS. 3A and 3B are a side view and an end view, respectively, of the source shown in FIG. 2; 
     FIG. 4 is an end view with the substrate of the source shown in FIGS. 2-3; 
     FIG. 5 is an SEM Image of example  2002  at the center of the deposition zone; 
     FIG. 6 is an X-Ray diffraction pattern of example  2002 ; 
     FIG. 7 is an SEM Image of example  2008  at the center of the deposition zone; 
     FIG. 8 is an AFM Image of example  20089  a the center of the deposition zone; and 
     FIG. 9 is an X-Ray diffraction pattern of example  2008 . 
    
    
     DETAILED DESCRIPTION 
     All of the details of application Ser. No. 60/193,662 are incorporated herein by reference thereto. 
     The invention enables high substrate temperature deposition of materials that have high vapor pressure, which would otherwise not stick to the substrate. Material utilization rate is very close to 100%. Such high utilization rate would reduce operational cost by: 
     Reducing material cost—no wastage, 
     Low maintenance and reduced downtime. 
     The method of the present invention does not require capital cost intensive high vacuum system; rather a low cost, mechanical pump generated low vacuum system is acceptable. The invention allows precise control of deposition rate by controlling gas flows both into the furnace and/or into the system. In fact, the deposition can be initiated and stopped by respectively reducing and increasing the pressure inside the system. 
     The invention also allows deposition of multi-layer films by placing multiple furnaces one after another in a vacuum system without costly schemes of physically separating deposition zones from each other. This is because 100% material utilization in each zone prevents any possibility of cross-contamination. 
     The invention is particularly useful for the deposition of CdTe films at high rates and at high substrate temperature. Other possible uses include high substrate temperature deposition of: 
     Any other congruently evaporating compounds such as CdS, 
     Other high vapor pressure compounds such as In 2 Se 3 , CuCl, 
     Other high vapor pressure single component materials. 
     The following description provides first-order design calculations for CdTe deposition by a carrier gas. Following the description of the first-order design calculation is a description relating to vapor-resistant evaporation source in prototype experiment. 
     FIG. 1 schematically illustrates the furnace  10  which contains source material  12 . Inert carrier gas enters container  10  as shown by arrow  14  which exits furnace  10  as shown by arrow  16  to flow over substrate  18 . 
     As shown in FIGS. 2-4 the system for practicing the method of this invention includes a vacuum system in which the furnace  10  is located. The furnace is in the form of a cylindrical container which is covered by a cylindrical radiative shield  20 . The shield and the container have a longitudinal slot  22  through which the carrier gas would flow. Accordingly, the slot functions as a discharge opening. The source material  12 , such as CdTe, is located in a perforated quartz ampoule  24  which extends through a removable plug closing the upstream end of the container. The perforated ampoule  24  is located along the longitudinal axis of the container. The carrier gas enters the furnace through the tubular basket. A removable plug  25  is in the upstream end of the container  10 . A second removable plug  26  in the downstream end of the container is used for mounting the heating structure which is illustrated as being a thermocouple  28  having a plurality of filaments  30  equally spaced along an arc surrounding the ampoule  24 . A heated plate or platen  32  is located along one edge of the discharge opening  22  of the container still located within the vacuum system. A further heated plate  34  is mounted adjacent to the opposite side of the discharge opening  22 . The substrate  18  is mounted on a heated plate  36  and moves in a direction below and parallel to the heated platen  32  and heated plate  34  transverse to the longitudinal discharge opening. As illustrated in FIG. 4 one of the heated plates  34  has a downwardly extending flange  38  which is spaced slightly above the path of movement  40  of the substrate which would thereby direct the flow of the carrier gas toward the substrate. The carrier gas has a flow path between the heated platen  32  and the moving substrate  18 . 
     This document presents a methodology and quantitative results for the design of a CdTe deposition system using a carrier gas. In the design, the carrier gas is saturated with CdTe vapor (actually Cd and Te 2 ), the flowed through the deposition zone. By maintaining the CdTe source at a higher temperature than the substrate, the vapor above the substrate becomes supersaturated, and deposits on the substrate. A conceptual schematic of the process is shown in FIG. 1. A key advantage of an inert atmosphere CdTe process over a vacuum CdTe process is the suppression of film re-evaporation during substrate cooldown. 
     By maintaining T source &gt;T platen &gt;T substrate  CdTe vapor generated in the source becomes supersaturated in the deposition zone, and deposits on the substrate. Argon has been arbitrarily chosen as the carrier gas. 
     1. Mass-transfer Characterization 
     A first order design (to determine feasibility of the proposed process) requires the development of a mass balance and a worst-case estimate of the mass transfer rates in the system. 
     The following discussion has as its objective to demonstrate the viability of carrier-assisted CdTe deposition with grown rate of ˜0.1 to 1.0 μm/min at system pressures of 10 to 100 Torr. 
     1. Prototype Source Schematic Diagrams 
     FIGS. 2-4 are views of the prototype source equipment. 
     2. Power Ratings for 6 loop Kanthal filament, 90 cm L, 0.032 gauge (0.8 mm dia) 
     Initial resistance. R=3.5 Ω 
     After Heating @ 44V for 10 min in N 2 . R=4.5 Ω. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2.1 
               
             
             
               
                   
               
               
                 Filament power at different settings. 
               
             
          
           
               
                   
                 Measured 
                 Measured 
                 Measured 
                 Estimated 
               
               
                 Variac 
                 Voltage 
                 Current 
                 Power 
                 Current 
               
               
                 Setting 
                 (V) 
                 (A) 
                 (W) 
                 from P = I 2 R 
               
               
                   
               
             
          
           
               
                 10 
                 11 
                 3.3 
                  36 
                 2.8 
               
               
                 20 
                 22 
                 6.6 
                 145 
                 5.7 
               
               
                 30 
                 33 
                 9.7 
                 320 
                 8.4 
               
               
                 40 
                 44 
                 12.5 
                 550 
                 11.0 
               
               
                   
               
             
          
         
       
     
     3. Prototype Source #1—Circular Effusion Aperture, “Floating” Substrate Temperature 
     20001 
     Base Pressure=18 mTorr 
     Deposition Pressure 20-23 Torr 
     Carrier Gas Flow Rate=20 sccm Argon 
     Variac Setting=40% (44V, 12.5 A, 550 W) 
     “Steady-State.” Internal Source Temperature=945° C. 
     Sample to Orifice Distance=1.5 cm 
     Deposition time (at T&gt;880° C.)=2 minutes 
     Substrate=1″×2″ L.O.F. 3.5 mm SL/SnO 2    
     Comment: Sample touched heat shield and broke during deposition. Grey deposit 0.5 μm thick, XRD=&gt;CdTe; growth rate ˜0.25 μm/min. Rapidly raised system pressure to 200 Torr—seemed to stop deposition on exposed metal surface. 
     20002 
     Base Pressure=8 mTorr 
     Deposition Pressure 20-21 Torr 
     Carrier Gas Flow Rate=20 sccm Argon 
     Variac Setting=40% (44V, 12.5 A, 550 W) 
     “Steady-State” Internal Source Temperature=935° C. 
     Sample to Orifice Distance=1.7 cm 
     Deposition time (at T&gt;880° C.)=6.5 minutes 
     Substrate=2″×3″ Corning 1.5 mm 7059/ITO/CBD CdS 
     Comment: Sample remained intact, developed grey coating at minute 6 (T=899° C.). Central 2 cm diameter region measured 7.5 μm thick; growth rate ˜1.1 μm/min. Band of pinholes and progessively thinner towards edges.                τ   D                =                  h   2       D     CdTe   ,              Ar                 (     eqn   .              1     )                                
     where τ D  is the diffusion characteristic time (sec), h is the height of the gas phase above the CdTe source/sink (cm), and D CdTeAr  is the diffusivity of CdTe vapor in argon (cm 2 /sec). 
     An estimate of the diffusivity for a 2 component mixture is obtained using Chapman-Enskog theory:                D   AB                =                0.0018583                                      T   3            (       1     M   A                  +                1     M   B         )           P                   σ   AB   2                     Ω     D   ,              AB                     (     eqn   .              2     )                                
     where T is in K, P is the pressure in atm σ AB   2  is the effective molecular diameter in Å, M B  is the molecular weight of component i, and Ω D,AB  is a tabulated dimensionless correction factor which accounts for intermolecular attraction/repulsion. Ω D,AB  varies between 0.5 and 2 —for these calculations it has been assumed equal to unity. Values for the other parameters are shown in the section 3. 
     As a rule of thumb, a system reaches equilibrium after a time of about 4τ. Therefore, for a carrier gas either unsaturated or supersaturated, it will reach the saturation pressure of CdTe at a time of 4τ D . Since a continuously flowing system is under examination, the requirement for saturation is that 
     
       
         ⊖≧4τ D   (eqn. 3) 
       
     
     where ⊖ is the residence time given by 
     
       
         ⊖= L/v   (eqn. 4) 
       
     
     where v is the linear gas velocity (cm/sec), and L is the length. 
     In reality, the mass transfer of any system is typically enhanced by the presence of velocity gradients, thereby reducing the characteristic time. The approach exemplified by eqns. 3 and 4 therefore places an upper bound on the minimum required residence time. 
     At this stage, only two characterizations of the flow regime have been made, the Reynolds number              Re              =                  ρ                 vh     μ             (     eqn   .              5     )                                
     where ρ is the gas density (g/cm 3 ) and μ is the gas viscosity (g/cm/sec), and the mean free path              λ              =                RT       2                     πσ   AB   2                     pN   AV                 (     eqn   .              6     )                                
     where R is the ideal gas constant and N AV  is Avogadro&#39;s number, 6,022×10 23 /mol. The gas viscosity (g/cm/sec) is independent of the system pressure and is given by Chapman-Enskog theory:              μ              =                2.6693   ×     10     -   5                         MT         σ   2                     Ω   μ                   (     eqn   .              7     )                                
     As with Ω D,AB , Ω μ is a tabulated dimensionless value ranging from about 0.5 to 2. 
     The primary purpose in calculating Re is to determine whether the flow regime is turbulent or laminar. For flow through a smooth tube, turbulence occurs for Re&gt;10 3 , orders of magnitude greater than the situation here (the calculation will be shown in section 3). The presence of laminar flow allows a solution of the velocity and concentration profiles in the system. This is beyond the scope of this document, however. 
     Further useful characterizations are the Peclet number (Pe), which indicates whether mass transport is primarily diffusive or convective, and the Grashof number (Gr), which is used in estimating free convection driven by thermal gradients.                Pe   AB                =                hv     D   AB               (     eqn   .              8     )               Gr              =                    h   3                     ρ   2                   g                 βΔ                 T       μ   2               (     eqn   .              9     )                                
     where g is a gravitational constant and β is the thermal expansion coefficient (easily calculated for a gas). 
     2. Mass Balance 
     The mass balance relates the desired CdTe deposition rate (μm/cm 2 /min) to the physical design of the CdTe source and deposition zone, as well as the required flow rate of carrier gas. 
     The mass rate of CdTe carried to the deposition zone is given by 
     
       
           {dot over (N)}   CdTe   =c   Cd   q =2 c   Te     2     q   (eqn. 10) 
       
     
     where N CdTe  is in moles (dot above indicates rate), q is the volumetric flowrate in cm 3 /sec, and c i  is the concentration of species i in mol/cm 3 . The thickness deposition rate assuming 100% utilization of N CdTe  is given by.                       z   CdTe            t       =             N   *                  CdTe          MW   CdTe         ρ       CdTe   A                   substrate                 (     eqn   .              11     )                                
     Alternately, eqn. 11 can be easily modified to express the area per time that a film of Z CdTe  thickness can be deposited on:                       A   substrate            t       =         N   CdTe          MW   CdTe         P       CdTe   2        CdTe                 (     eqn   .              12     )                                
     where Z CdTe  is the film thickness and A substrate  is the substrate area. 
     The concentration of Cd and Te 2  are determined by the saturation pressure curve of CdTe: 
     
       
         log( P   CdTe   sat /bar)=−10650 /T− 2.56 Log( T )+15.80  (eqn. 13) 
       
     
     Where T is in K and 1 bar=1 atm=760 torr. Since the vapor phase stoichiometry is Cd:Te 2 =2:1, the saturation pressures of Cd and Te 2  respectively are 
     
       
           P   Cd   sat =0.67 P   CdTe   sat ( T )  (eqn. 14) 
       
     
     and 
     
       
           P   Te2   sat =0.33 P   CdTe   sat ( T )  (eqn. 15) 
       
     
     Concentration is directly correlated to pressure by the ideal gas law:              c              =                    N   AV     V                =                P   RT               (     eqn   .              16     )                                
     In the source and deposition zone, the rate of accumulation/depletion of CdTe into/out of the carrier gas behaves exponentially: 
     Source:                P       Cd                 Te     ,   exit                  =                    P     Cd                 Te     sat          (     T   source     )       [                1              -                exp        (     -       θ   source       τ     D   ,              source           )         ]             (     eqn   .              17     )                                
     Dep. zone:                  P       Cd                 Te     ,   exit                  =                  (         P     Cd                 Te     sat          (     T   source     )                  -                  P     Cd                 Te     sat          (     T   substrate     )         )     [                1              -                exp        (     -       θ     dep   ·   zone         τ     D   ,                dep   ·   zone             )         ]                          (     eqn   .              18     )                                
     These equations assume no pressure drop through the system. These equations are coupled by the requirement that the volumetric flow rate of carrier gas be the same for the source and deposition zone (this assumes that the partial volume of CdTe vapor is negligible). 
     3. Sample Calculations 
     Clearly, a spreadsheet is best used to study the influence of the design variables (P, T, h, L, q) on the deposition rate. The following sample calculations are useful in placing an order of magnitude estimate on the design variables, however. 
     The diffusion coefficient was calculated using the following values:                D   AB     =     0.0018583                         T   3          (       1     39.9                 g        /        mol       +     1     200                 g        /        mol         )               P        (     3.5                 Å     )       2          (   1   )                   (     eqn   .              19     )                                
     For T=600° C.=873 K and P=50 torr=0.066 atm, D AB =10.3 cm 2 /sec. Note that the diffusivity is determined primarily by argon, since it is much lighter than Cd or Te—as a result, the vapor phase stoichiometry of CdTe does not have a significant influence on the diffusivity. 
     The viscosity of the Ar carrier gas (neglecting the CdTe vapor) is easily calculated:              μ   =     2.6693   ×     10     -   5                  (     39.9                 g        /        mol     )        T             (     3.5                 Å     )     2          (   1   )                   (     eqn   .              20     )                                
     For T=600° C.=873 K, m=4.07×10 −4  g/cm/sec. 
     For a gas velocity of v=10 cm/sec, a zone height of h=1 cm, and a pressure of 50 torr, the gas density and Re are calculated as follows:              ρ   =           (     50                 torr     )          (     39.9                 g        /        mol     )           (     6.24   ×     10   4                     cm   3          torr   /   mol          /        K     )          (     873                 K     )         =     3.66   ×     10     -   5                     g        /          cm   3                 (     eqn   .              21     )               Re   =           (     3.66   ×     10     -   5                     g        /          cm   3       )          (     10                 cm        /        sec     )          (     1                 cm     )         (     4.07   ×     10     -   4                     g        /        cm        /        sec     )       =   0.90             (     eqn   .              22     )                                
     Now that the basic physical constants have been estimated, it is possible to proceed with the source design. The first-cut design assumes that the CdTe vapor exits the source at its saturation pressure—this condition is approximated by          θ     τ   D       ≥   4.                          
     This condition is met by limiting the velocity of the carrier gas through the source to sufficiently increase the residence time. Since this is a worst case design, the physical situation is a carrier gas flowing above a planar source. The source could be designed for better performance by flowing the carrier gas through a packed bed of CdTe chunks, for example. After the saturation condition has been implemented, the velocity and maximum theoretical deposition rate (based on assumption of 100% utilization of CdTe in the deposition zone) can be estimated as a function of source geometry (height, width, and length), system pressure, and CdTe saturation pressure. 
     Assuming a source width of 10 cm and height of 1 cm, the following estimate for gas velocity, flow rate, and deposition rate were calculated: 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Effect of design variables on deposition rate. 
               
             
          
           
               
                 cm 
                 torr 
                 torr 
                 ° C. 
                 cm2/sec 
                 sec 
                 cm/sec 
                 cm3/sec 
                 sccm 
                 μm/min/cm2 
                 100 cm2 basis 
               
               
                 L 
                 pCdTe 
                 pT 
                 Tsource 
                 DAB 
                 char.time 
                 velocity 
                 q 
                 qSTP 
                 dep rate 
                 dep rate, μm/min 
               
               
                   
               
             
          
           
               
                 1 
                 1 
                 10 
                 775 
                 67.83318 
                 0.014742 
                 16.95829 
                 169.5829 
                 38.31931 
                 42.57248477 
                 0.425725 
               
               
                 1 
                 1 
                 50 
                 775 
                 13.56664 
                 0.07371 
                 3.391659 
                 33.91659 
                 38.31931 
                 8.514496955 
                 0.085145 
               
               
                 1 
                 1 
                 100 
                 775 
                 6.783318 
                 0.14742 
                 1.695829 
                 16.95829 
                 38.31931 
                 4.257248477 
                 0.042572 
               
               
                 1 
                 10 
                 50 
                 900 
                 16.0645 
                 0.062249 
                 4.016126 
                 40.16126 
                 40.5399 
                 90.07910192 
                 0.900791 
               
               
                 1 
                 10 
                 100 
                 900 
                 8.032252 
                 0.124498 
                 2.008063 
                 20.08063 
                 40.5399 
                 45.03955096 
                 0.450396 
               
               
                 10 
                 1 
                 10 
                 775 
                 67.83318 
                 0.014742 
                 169.5829 
                 1695.829 
                 383.1931 
                 425.7248477 
                 4.257248 
               
               
                 10 
                 1 
                 50 
                 775 
                 13.56664 
                 0.07371 
                 33.91659 
                 339.1659 
                 383.1931 
                 85.14496955 
                 0.85145 
               
               
                 10 
                 1 
                 100 
                 775 
                 6.783318 
                 0.14742 
                 16.95829 
                 169.5829 
                 383.1931 
                 42.57248477 
                 0.425725 
               
               
                 10 
                 10 
                 50 
                 900 
                 16.0645 
                 0.062249 
                 40.16126 
                 401.6126 
                 405.399 
                 900.7910192 
                 9.00791 
               
               
                 10 
                 10 
                 100 
                 900 
                 8.032252 
                 0.124498 
                 20.08063 
                 200.8063 
                 405.399 
                 450.3955096 
                 4.503955 
               
               
                   
               
             
          
         
       
     
     These results suggest that sufficient deposition rates can be achieved using a carrier gas system. Furthermore, the results suggest that successful operation is achievable over a wide range of pressures. 
     Determination of actual operating parameters will be based on further analysis. Calculation of Pe, for example, indicates the ability of the carrier gas to “confine” the flow of the CdTe. This is useful not only in confining the CdTe vapor during source heat up, but also in reducing re-evaporation of the CdTe film after the substrate has passed through the deposition zone. 
     4. Conclusions 
     The results of this simple analysis indicate that a CdTe/carrier gas deposition process is very robust—that is, there is sufficient room for error in both the design and operation of such processes. 
     
       
         
               
             
               
               
               
               
             
               
             
               
               
             
           
               
                 APPENDIX 
               
             
             
               
                   
               
               
                 Values Used in Calculations 
               
             
          
           
               
                 Variable 
                 Value 
                 Units 
                 Name 
               
               
                   
               
               
                 R 
                  0.08206 
                 L-atm/mol-K 
                  Ideal gas constant 
               
               
                   
                  62.4 
                 L-torr/mol-K 
               
               
                   
                  6.24 × 10 4   
                 cm 3 -torr/mol-K 
               
               
                 N AV   
                  6.022 × 10 23   
                 l/mol 
                 Avogadro&#39;s number 
               
               
                 MW Ar   
                  39.95 
                 g/mol 
                 Molecular weight - Argon 
               
               
                 MW Cd   
                 112.4 
                 g/mol 
                 Molecular weight - 
               
               
                   
                   
                   
                 Cadmium 
               
               
                 MW Te   
                 127.6 
                 g/mol 
                 Molecular weight - 
               
               
                   
                   
                   
                 Tellurium 
               
               
                 MW CdTe   
                 240.0 
                 g/mol 
                 Molecular weight - 
               
               
                   
                   
                   
                 CdTe 
               
               
                 ρ CdTe   
                  5.85 
                 g/cm 3   
                 CdTe density 
               
               
                 σ 
                  3.5 
                 Å 
                 Molecular diameter 
               
               
                   
                   
                   
                 (assumed same for all gas- 
               
               
                   
                   
                   
                 phase species) 
               
               
                 Ω μ   
                  1 
                 [dimensionless] 
                 Intermolecular interaction 
               
               
                   
                   
                   
                 correction for 
               
               
                   
                   
                   
                 viscosity calculations 
               
               
                 Ω AB   
                  1 
                 [dimensionless] 
                 Intermolecular interaction 
               
               
                   
                   
                   
                 correction for 
               
               
                   
                   
                   
                 diffusivity calculations. 
               
               
                   
               
             
          
           
               
                 Other Variables 
               
             
          
           
               
                 P 
                 Pressure 
               
               
                 T 
                 Temperature 
               
               
                 v 
                 linear velocity 
               
               
                 q 
                 True volumetric flow rate 
               
               
                 q STP   
                 Standardized volumetric flowrate (sccm) 
               
               
                 N 
                 Molar mass 
               
               
                 L 
                 Length 
               
               
                 h 
                 Height of atmosphere above CdTe source/sink 
               
               
                 Θ 
                 Residence time 
               
               
                 τ D   
                 Charateristic time for diffusion 
               
               
                 λ 
                 Mean free path 
               
               
                 ρ 
                 Density 
               
               
                 μ 
                 Viscosity 
               
               
                 D AB   
                 Diffusivity of mixture of A and B 
               
               
                 Re 
                 Reynold&#39;s number 
               
               
                 Pe 
                 Peclet number 
               
               
                 Gr 
                 Grashof number 
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3.1 
               
             
             
               
                   
               
               
                 X-ray diffraction peak data and assignments of 20002. 
               
             
          
           
               
                   
                   
                 Raw 
                 2θ 
                 d 
                   
               
               
                   
                 Peak 
                 Counts 
                 (± 0.05 deg) 
                 (Å) 
                 Assignment 
               
               
                   
                   
               
               
                   
                  1 
                  48 
                 21.40 
                 4.15 
                 111 k β   
               
               
                   
                  2 
                  169 
                 22.80 
                 3.90 
                 W 
               
               
                   
                  3 
                 6566 
                 23.75 
                 3.74 
                 111 
               
               
                   
                  4 
                  385 
                 39.30 
                 2.29 
                 220 
               
               
                   
                  5 
                  605 
                 46.45 
                 1.953 
                 311 
               
               
                   
                  6 
                  58 
                 56.80 
                 1.619 
                 400 
               
               
                   
                  7 
                  313 
                 62.45 
                 1.486 
                 331 
               
               
                   
                  8 
                  504 
                 71.25 
                 1.322 
                 422 
               
               
                   
                  9 
                  315 
                 76.30 
                 1.247 
                 511 
               
               
                   
                 10 
                  43 
                 84.55 
                 1.145 
                 440 
               
               
                   
                 11 
                  109 
                 89.40 
                 1.095 
                 531 
               
               
                   
                   
               
               
                   
                 Texture coefficient = 1.76 (111) =&gt; slight (111) texture.  
               
               
                   
                 Precision lattice parameter = 6.478 Å ± 0.002 Å.  
               
             
          
         
       
     
     4. Prototype Source 2—Slit Effusion Orifice, “Floating” Substrate Temperature 
     20003 
     Base Pressure=15 mTorr 
     Deposition Pressure 20-21 Torr 
     Carrier Gas Flow Rate=20 sccm Argon 
     Variac Setting=40% (44V, 12.5 A, 550 W) 
     “Steady-State” Internal Source Temperature=694° C. 
     Sample to Orifice Distance=1.5 cm 
     Deposition time (at T&gt;880° C.)=0 minutes 
     Substrate=3″×3  LOF TEC-15 SL/SnO 2 /Double Coat CBD CdS (P041+P028)/CdCl 2  HT 
     Comment: Sample shattered after 4 minutes, run aborted. 
     20004 
     Base Pressure=15 mTorr 
     Deposition Pressure 20-21 Torr 
     Carrier Gas Flow Rate=20 sccm Argon 
     Variac Setting=40% (44V, 12.5 A, 550 W) 
     “Steady-State” Internal Source Temperature=880° C. 
     Sample to Orifice Distance=1.7 cm 
     Deposition time (at T&gt;850° C.)=6 minutes 
     Substrate=4″×2.5″ Solarex 7059/SnO 2 /Single Coat CBD CdS (P038) 
     Comment: Non-uniformly Colored Deposit. Average Thickness Based on Mass Gain=2 μm. 
     Prototype Source 2—Slit Effusion Orifice, “Controlled” Substrate Temperature 
     20005 
     Base Pressure=10 mTorr 
     Deposition Pressure 20-21 Torr 
     Carrier Gas Flow Rate=20 sccm Argon 
     Variac Setting=40% (44V, 12.5 A, 550 W) 
     Target “Steady-State” Internal Source Temperature=880° C. 
     Sample to Orifice Distance=1.7 cm 
     Deposition time (at T&gt;850° C.)=0 minutes 
     Substrate Temperature: Monitored at edge with wide-gauge TC, set ˜500° C. (Variac ˜12%). 
     Substrate=3″×3″ Solarex 7059/SnO 2 /Single Coat CBD CdS (P045) 
     Comment: Sample shattered during substrate heat-up, run aborted 
     20006 
     Base Pressure=10 mTorr 
     Deposition Pressure 20-21 Torr 
     Carrier Gas Flow Rate=20 sccm Argon 
     Variac Setting=40% (44V, 12.5 A, 550 W) 
     Target “Steady-State” Internal Source Temperature=880° C. 
     Sample to Orifice Distance=1.7 cm 
     Deposition time (at T&gt;850° C.)=0 minutes 
     Substrate Temperature: Monitored at edge with wide-gauge TC, set ˜500° C. (Variac ˜12%). 
     Substrate=3″×3″ Solarex 7059/SnO 2 /Single Coat CBD CdS (P044) 
     Comment: Sample shattered during substrate heat-up, run aborted. Thermal gradient across sample judged to be excessive—sample touched heater clips. 
     20007 
     Base Pressure=15 mTorr 
     Deposition Pressure 20-21 Torr 
     Carrier Gas Flow Rate=20 sccm Argon 
     Variac Setting=40% (44V, 12.5 A, 550 W) 
     Target “Steady-State” Internal Source Temperature=900° C. 
     Sample to Orifice Distance=1.7 cm 
     Deposition time (at T&gt;850° C.)=6 minutes 
     Substrate Temperature: Monitored at edge with wide-gauge TC, set ˜465° C. (Variac ˜12%). 
     Substrate=1″×1″ and 1″×0.5″ IEC 7059/ITO/Evap CdS samples. 
     Comment: Samples directly on Vycor heater plate. Deposit thicker in edge band—we don&#39;t know the exact temperature in deposition zone. Also, there is significant thermal coupling between source and substrate. 
     20008 
     Base Pressure=10 mTorr 
     Deposition Pressure 20-21 Torr 
     Carrier Gas Flow Rate=20 sccm Argon 
     Variac Setting=40% (44V, 12.5 A, 550 W) 
     Target “Steady-State” Internal Source Temperature=880° C. 
     Sample to Orifice Distance=1.7 cm 
     Deposition time (at T&gt;850° C.)=8 minutes 
     Substrate Temperature: Monitored at center with narrow gauge TC, set ˜500° C. (Eurotherm). Rose to 600° C. during deposition. 
     Substrate=1″×1″ and 1″×0.5″ IEC 7059/ITO/Evap CdS samples. Comment: Deposition observed from left side to right (left 3 cm is where sparge nozzles are located inside source). Mass gain thickness of longitudinally-centered substrates=2.9 μm; growth rate ˜0.4 μm/min. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 5.1 
               
             
             
               
                   
               
               
                 X-ray diffraction peak data and assignments of 20008. 
               
             
          
           
               
                   
                   
                 Raw 
                 2θ 
                 d 
                   
               
               
                   
                 Peak 
                 Counts 
                 (± 0.05 deg) 
                 (Å) 
                 Assignment 
               
               
                   
                   
               
             
          
           
               
                   
                  1 
                 6566 
                 23.75 
                 3.74 
                 111 
               
               
                   
                  4 
                  385 
                 39.25 
                 2.29 
                 220 
               
               
                   
                  5 
                  605 
                 46.45 
                 1.953 
                 311 
               
               
                   
                  6 
                  58 
                 56.80 
                 1.619 
                 400 
               
               
                   
                  7 
                  313 
                 62.40 
                 1.487 
                 331 
               
               
                   
                  8 
                  504 
                 71.25 
                 1.322 
                 422 
               
               
                   
                  9 
                  315 
                 76.30 
                 1.247 
                 511 
               
               
                   
                 10 
                  43 
                 84.50 
                 1.145 
                 440 
               
               
                   
                 11 
                  109 
                 89.40 
                 1.095 
                 531 
               
               
                   
                   
               
               
                   
                 Texture coefficient = 0.31 (111) and 1.19 (311) =&gt; slight (311) texture.  
               
               
                   
                 Precision lattice parameter = 6.478 Å ± 0.002 Å.  
               
             
          
         
       
     
     6.0 SUMMARY AND CONCLUSIONS 
     For source to substrate distance ˜1-2 cm, achieved depositions at 0.2 to 1 μm/min (20001, 20002, 20008); 
     Deposits in central band are pure CdTe films having ˜5 μm grains and ˜random texture (20002 and 20008); 
     Sparge holes inside source DO affect longitudinal film thickness (all runs); 
     Deposition can be quickly halted by increasing total system pressure (20001).