Patent Publication Number: US-2003224105-A1

Title: Apparatus and methods for forming films on substrates

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates generally to the formation of films on one or more substrates for screening and characterization of the film properties, and more particularly to apparatus and methods for forming such films from liquid samples.  
       [0002] Combinatorial synthesis and evaluation of arrays of films enables the rapid discovery of new materials with novel chemical and physical properties and the rapid optimization of previously known materials. Such techniques are currently employed to evaluate materials such as superconductors, zeolites, magnetic materials, phosphors, nonlinear optical materials, thermoelectric materials, and high and low dielectric materials. For example, U.S. Pat. No. 6,030,917 (Weinberg, et al.), the entire disclosure of which is incorporated herein by reference, discloses techniques for the combinatorial synthesis of arrays of organometallic compounds and catalysts. Using the various synthesis methods disclosed therein, arrays containing thousands or millions of different elements can be formed. Such techniques have met with success in, for example, screening various ligands such as peptides and oligonucleotides to determine their relative binding affinity to a receptor such as an antibody.  
       [0003] In the past, it has been disclosed that arrays of materials may be prepared by a variety of techniques, including chemical vapor deposition, physical vapor deposition or liquid dispensing. U.S. Pat. No. 6,004,617 (Schultz et al. and U.S. Pat. No. 6,333,196 (Willson et al.) disclose a variety of methods for synthesizing and screening arrays of materials for useful properties. However, when applying combinatorial techniques to a particular problem, the optimal techniques to apply to array or library design, synthesis, screening and/or informatics may not be straightforward. For example, Schultz et al. disclose using spin-coating to deposit components of materials onto a substrate in regions. As an additional example, U.S. Pat. Nos. 6,313,044 and 6,291,628 disclose that it is known in the semiconductor industry to coat the entire surface of a semiconductor wafer using what is commonly referred to as spin-coating technology. Conventional spin-coating techniques involve forming a liquid solution by dissolving a material in a volatile solvent and then depositing the liquid solution on the center of a wafer. The wafer is then rotated by a spin-coating device at a high speed to spread the material across the entire wafer surface and to facilitate evaporation of the solvent, thereby leaving a thin film coating on the wafer surface. The liquid solution is thus spread over the substrate surface without directly touching the solution, such as with a finger, doctor blade, brush or the like so as to minimize the risk of contaminating the solution. However, conventional spin-coating techniques are generally disadvantageous for use in synthesizing an array of films, primarily because only a relatively large (e.g., 3-6 inch diameter), single wafer is coated at a time or additional steps, such as masking schemes, must be used.  
       SUMMARY OF THE INVENTION  
       [0004] In general, a method of the present invention for forming a plurality of films on a surface of a substrate comprises depositing at least two liquid samples on the substrate surface in generally spaced relationship with each other. The substrate is moved so that the liquid samples on the substrate are subjected to a spreading force sufficient to cause each sample to spread over the substrate surface to form a respective film thereon. At least a portion of each film is discrete from one or more other films formed on the substrate surface.  
       [0005] In another embodiment, the method generally comprises depositing at least two liquid samples on the substrate surface in generally spaced relationship with each other. The liquid samples on the substrate surface are subjected to a non-contact spreading force sufficient to cause each sample to spread over the substrate surface to form a respective film thereon. At least a portion of each film is discrete from one or more other films formed on the substrate surface. At least one characteristic of at least one of the films formed on the substrate surface is then characterized.  
       [0006] A method of forming a film on a surface of a substrate generally comprises depositing a liquid sample on the substrate surface at a location generally offset from a center of the substrate surface whereby the liquid sample covers substantially less than the entire surface of the substrate. The substrate is moved so that the liquid sample is subjected to a spreading force sufficient to cause the liquid sample to spread over the substrate surface to form a film thereon whereby the film covers less than the entire surface of the substrate.  
       [0007] In another embodiment, the method generally comprises depositing a liquid sample on the substrate surface and oscillating the substrate to subject the liquid sample to a spreading force sufficient to cause the liquid sample to spread over the substrate surface to form a respective film thereon.  
       [0008] In yet another embodiment, the method generally comprises depositing a liquid sample on the substrate surface whereby the liquid sample covers substantially less than the entire surface of the substrate. A pressurized gas is directed to impact the liquid sample to apply a spreading force thereto sufficient to cause the liquid sample to spread over the substrate surface to form a film thereon.  
       [0009] In general, a method of forming an array of films for use in screening at least one characteristic of each of the films comprises depositing at least two liquid samples onto at least one substrate such that the at least two liquid samples are at least partially discrete from each other. The at least one substrate is moved so that the liquid samples are subjected to a spreading force during overlapping durations of time. The spreading force is sufficient to cause each liquid sample to spread over the at least one substrate to form a respective film thereon. At least a portion of each film is discrete from one or more other films formed on the at least one substrate.  
       [0010] In another embodiment, the method comprises depositing at least two liquid samples onto at least one substrate such that the at least two liquid samples are at least partially discrete from each other. The liquid samples are subjected to a non-contact spreading force during overlapping durations of time whereby the spreading force is sufficient to cause each liquid sample to spread over the at least one substrate to form a respective film thereon. At least a portion of each film is discrete from one or more other films formed on the at least one substrate.  
       [0011] In general, a method of effecting the parallel formation of films comprises depositing liquid samples of different compositions on an array of substrates wherein each substrate has a surface for receiving a respective sample. The liquid samples on at least two of the substrates are subjected to non-contact spreading forces during overlapping durations of time whereby the spreading forces are sufficient to cause the samples to spread over respective surfaces of the substrates to form films on the surfaces.  
       [0012] In another embodiment, the method comprises depositing liquid samples of different compositions on an array of substrates wherein each substrate has a surface for receiving a respective sample. At least two of the substrates of the array are moved during overlapping durations of time to subject the samples on the at least two substrates to spreading forces sufficient to cause the samples to spread over respective surfaces of the substrates to form films on the surfaces.  
       [0013] In yet another embodiment, movement of the at least two substrates is controlled by using a single controller programmed to vary the movement of the substrates according to a predetermined program.  
       [0014] In still another embodiment, the method generally comprises operating a robot system to deposit liquid samples on an array of substrates wherein each substrate has a surface for receiving a respective sample. At least two of the substrates of the array are moved during overlapping durations of time to subject the samples on the at least two substrates to spreading forces sufficient to cause the samples to spread over respective surfaces of the substrates to form films on the surfaces.  
       [0015] In another embodiment, the method comprises depositing liquid samples on an array of substrates occupying an area having a maximum dimension of no greater than about five feet, wherein each substrate has a surface for receiving a respective sample. At least two of the substrates of the array are moved during overlapping durations of time to subject the samples on the at least two substrates to spreading forces sufficient to cause the samples to spread over respective surfaces of the substrates to form films on the surfaces.  
       [0016] In another embodiment, the method generally comprises depositing liquid samples on an array of substrates wherein each substrate has a surface for receiving a respective sample. At least two of the substrates of the array are moved in different ways during overlapping durations of time to subject the samples on the at least two substrates to spreading forces sufficient to cause the samples to spread over respective surfaces of the substrates to form films on the surfaces.  
       [0017] Apparatus of the present invention for forming a plurality of films on a surface of a single substrate generally comprises a deposition device adapted for depositing a plurality of liquid samples on the surface of the substrate in generally spaced relationship with each other. A movement device is capable of supporting the substrate with the liquid samples deposited thereon and is operable to move the substrate to thereby subject the liquid samples to a spreading force sufficient to cause the samples to spread over the substrate surface to form respective films thereon.  
       [0018] In another embodiment, apparatus for forming a film on a surface of a substrate generally comprises a deposition device for depositing a liquid sample on the surface of the substrate. A movement device is capable of supporting the substrate with the liquid sample deposited thereon and is operable to subject the substrate to non-rotational movement whereby the non-rotational movement subjects the liquid sample to a spreading force sufficient to cause the liquid sample to spread over the substrate surface to form a film thereon.  
       [0019] In yet another embodiment the apparatus generally comprises a deposition device adapted for depositing a liquid sample on the surface of the substrate. A support supports the substrate with the liquid sample deposited thereon. A gas delivery device is operable to direct a pressurized gas to impact the liquid sample to thereby cause the liquid sample to spread over the substrate surface to form a film thereon.  
       [0020] In general, apparatus of the present invention for effecting the parallel formation of films comprises an array of holders for holding a plurality of substrates wherein each substrate has a surface for receiving a liquid sample thereon. A robot system deposits liquid samples on the surfaces of the substrates in the holders. A drive system is operable to move at least two of the holders of the array during overlapping durations of time to subject the samples on the at least two substrates to spreading forces to cause the samples to spread over respective surfaces of the substrates to form films on the surfaces.  
       [0021] In another embodiment, the apparatus generally comprises an array of holders occupying an area having a maximum dimension of no greater than about five feet wherein each holder is adapted for holding a substrate having a surface for receiving a liquid sample thereon. A drive system is operable to move at least two of the holders of the array during overlapping durations of time to subject the samples to spreading forces sufficient to cause the samples to spread over respective surfaces of the substrates to form films on the surfaces.  
       [0022] In yet another embodiment, the apparatus generally comprises an array of substrates wherein each substrate has a surface for receiving a liquid sample thereon. A drive system operates to move at least two of the substrates of the array during overlapping durations of time to subject the samples on the at least two substrates to spreading forces sufficient to cause the samples to spread over respective surfaces of the substrates to form films on the surfaces. A programmable control system controls the drive system to move the substrates according to a predetermined program. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023]FIG. 1 is a schematic perspective of a first embodiment of apparatus of the present invention for forming films on substrates;  
     [0024]FIG. 2 is a photograph of films formed on a substrate using the apparatus of FIG. 1;  
     [0025]FIG. 3 is side elevation of a movement device of a second embodiment of apparatus of the present invention shown supporting a substrate;  
     [0026]FIG. 4 is a top plan view of the movement device of FIG. 3 with the substrate omitted;  
     [0027]FIG. 5 is a photograph of films formed on a substrate using the movement device of FIG. 3;  
     [0028]FIG. 6 is a perspective of a movement device of a third embodiment of apparatus of the present invention shown supporting a substrate;  
     [0029]FIG. 7 is a side elevation thereof with portions omitted to reveal internal construction and with other portions shown in cross-section;  
     [0030]FIG. 8 is a photograph of films formed on a substrate using the movement device of FIG. 6;  
     [0031]FIG. 9 is a schematic side view of a substrate holder and an air knife of a fourth embodiment of apparatus of the present invention, with the air knife shown in cross-section;  
     [0032]FIG. 10 is a top view of the substrate holder and air knife of FIG. 9;  
     [0033]FIG. 11 is a side elevation of apparatus of a fifth embodiment of the present invention;  
     [0034]FIG. 12 is a top plan view thereof of the apparatus of FIG. 11;  
     [0035]FIG. 13 is a perspective of a portion of the apparatus of FIG. 11 showing a drive system and an array of substrate holders of the apparatus;  
     [0036]FIG. 14 is a top plan view of the drive system and substrate holders of FIG. 13;  
     [0037]FIG. 15 is a side elevation of the drive system and substrate holders of FIG. 13;  
     [0038]FIG. 16 is a cross-section taken in the plane of line  16 - 16  of FIG. 14 with a control system for the drive system shown schematically;  
     [0039]FIG. 17 is a fragmented cross-section of one substrate holder of the apparatus of FIG. 11;  
     [0040]FIG. 18 is a perspective of one substrate holder driven by a corresponding motor;  
     [0041]FIG. 19 is an exploded perspective of the substrate holder and motor of FIG. 18;  
     [0042]FIG. 20 is a cross-section of an array of substrate holders and a second embodiment of a drive system for the substrate holders; and  
     [0043]FIG. 21 is a schematic side view of apparatus of a sixth embodiment of the present invention showing a heater for heating substrates on which films are formed. 
    
    
     [0044] Corresponding reference characters indicate corresponding parts throughout the drawings.  
     DETAILED DESCRIPTION OF THE INVENTION  
     [0045] With reference now to the drawings, and in particular to FIG. 1, apparatus of a first embodiment of the present invention for forming films on substrates is indicated it its entirety by the reference numeral  21 . The apparatus  21  is more particularly for forming an array of such films on the surface of a single substrate  23 , and even more particularly for the parallel formation of an array of such films on the substrate. The apparatus  21  comprises a deposition device, generally indicated at  25 , for depositing one or more liquid samples on the surface of the substrate  23 . A movement device, generally indicated at  27 , supports the substrate  23  and is capable of moving the substrate to subject the liquid samples to a spreading force, and more particularly to a non-contact spreading force, so as to spread the liquid samples on the substrate and thereby form relatively thin films on the substrate. As used herein, a non-contact spreading force is defined as a force acting on the liquid samples on the substrate  23  by means other than directly contacting the liquid samples with an implement (e.g., other than the substrate itself), such as a doctor blade or other spreading implement, or with a jetted media.  
     [0046] The substrate  23  may be constructed of substantially any material which allows for the formation of films thereon and the subsequent screening of various properties and characteristics of such films. For example, the substrate  23  may be organic, inorganic, biological, nonbiological, or a combination of any of these, and may have any convenient shape, such as a disc, square, sphere, circle, etc. The substrate  23  may be constructed of polymers, plastics, pyrex, quartz, resins, silicon, silica or silica-based materials, carbon, metals, inorganic glasses, inorganic crystals, membranes or other suitable materials which will be readily apparent to those of skill in the art. The substrate  23  has a surface  29  on which the films are to be formed and which may be composed of the same materials as the substrate or, alternatively, the substrate may be coated with a different material to define the exposed substrate surface. Moreover, the substrate surface  29  may be modified without departing from the scope of the invention. For example, for film formation on a hydrophilic silicon substrate using a hydrophobic liquid, the surface can be rendered hydrophobic, if desired, by treating it with Hexamethyldisilazane (HMDS). For other applications, the ambient atmosphere could be modified to further affect the liquid solution/substrate interface (e.g., wetting angle).  
     [0047] The substrate  23  of the illustrated embodiment is a conventional semiconductor wafer having a surface  29  processed to a mirror-like finish to facilitate uniformity of thickness of the films formed thereon. However, it is understood that the substrate surface  29  may have a variety of alternative surface characteristics, depending on the film properties and characteristics to be measured, without departing from the scope of this invention. For example, the substrate surface  29  may have raised or depressed regions on which the synthesis of diverse materials takes place. The wafer shown in FIG. 1 has a diameter of approximately five inches. However, the size of the substrate  23  may be substantially larger or smaller, such as down to about 0.5 inches, depending on the size and number of films to be formed on the substrate.  
     [0048] Still referring to FIG. 1, the deposition device  25  is a robotic device in which a pipette, or probe  31  of the device is manipulated over the substrate surface  29  using a 3-axis translation system. The probe  31  is connected by flexible tubing  33  to one or more sources of liquid from which the films are to be formed. One or more pumps  37  are located along the flexible tubing  33  to draw liquid from the liquid sources and to deliver the liquid to the probe  31 . Suitable pumps  37  include peristaltic pumps and syringe pumps. A multi-port valve  39  is disposed in the flexible tubing  33  downstream of the pump(s)  37  to control which liquid is drawn from the liquid sources and delivered to the probe  31  for dispensing onto the substrate  23 . The probe  31  includes a tip  41  which broadly defines an outlet of the probe through which small, metered samples of liquid are dispensed onto the substrate surface  29 . The tip  41  is preferably spaced above the substrate surface  29  about 0.1 cm to about 6 cm during deposition of liquid onto the substrate  23 . While the deposition device  25  of FIG. 1 is illustrated as having a single probe  31  and tip  41 , it is understood that the device may have multiple probes  31  and/or multiple tips  41  for delivering multiple liquid samples onto the substrate surface  29  without departing from the scope of this invention. For example, multiple probes  31  each having a corresponding tip  41  may be arranged in a single row or in an array, and may deliver liquid samples onto the substrate surface  29  either serially or concurrently.  
     [0049] The robotic deposition device  25  of the illustrated embodiment is controlled by a processor  43  in which the operator inputs various operating parameters to the device using a software interface. Typical operating parameters include the substrate surface  29  coordinates at which each liquid sample is to be deposited thereon and the liquid sources from which liquid is delivered to the probe for deposition onto the substrate surface. General construction and operation of robotic deposition devices similar to the deposition device  25  of the illustrated embodiment is known in the art and will not be further described herein except to the extent necessary to describe the present invention.  
     [0050] It is also understood that other suitable deposition devices may be used to deposit small, metered liquid samples onto the substrate surface  29  without departing from the scope of the present invention. For example, the deposition device  25  may include a plurality of probes for delivering multiple liquid samples to multiple locations on the substrate surface  29  either sequentially or concurrently. Also, the substrate surface  29  may be moved relative to the probe  31  instead of, or in addition to, the probe being moved relative to the substrate  23 . Moreover, the deposition device  25  may be operated manually, instead of robotically, without departing from the scope of the present invention.  
     [0051] The probe tip  41  dispenses liquid therefrom generally in the form of droplets, or samples of liquid. The volume of each liquid sample deposited onto the substrate surface  29  generally depends on the amount of liquid needed to obtain a desired film size. For example, based on limitations inherent in existing film screening techniques and devices, each film is desirably sized to have a surface area of at least about 0.1 mm 2 , preferably in the range of about 0.1 mm 2  to about 700 mm 2 , and more preferably in the range of about 1 mm 2  to about 50 mm 2 . The volume of each liquid sample deposited on the substrate surface  29  is preferably in the range of about 0.1 microliters to 10 milliliters, more preferably in the range of about 0.5 microliters to about 500 microliters, still more preferably in the range of about 0.5 microliters to about 100 microliters, even more preferably in the range of about 0.5 microliters to about 50 microliters and most preferably in the range of about 1 microliter to about 10 microliters.  
     [0052] The liquid from which each film is formed may be substantially any liquid solution or dispersion from which a film remains upon evaporation of the liquid. For example, the liquid may be a material for which its evaporation, decomposition or otherwise reaction creates films formed of polyimide, silicon dioxide, organic polymers, ceramic materials, composite materials (inorganic composites, organic composites and combinations), photoresists, sol-gel solutions including polymeric metal (organic) oxoalkoxides, other metallo-organic compounds, polymer based light-emitting materials including plastic, solutions and suspensions of ferroelectric materials, and optical coatings. The liquid may also comprise biological materials including antibodies, antigens, DNA, RNA, proteins, enzymes, oligopeptides, polypeptides, oligosaccharides, mono and polysaccharides, and lipids.  
     [0053] The thickness of the films formed on the substrate surface  29  is generally a function of various properties of the liquid from which the film is formed, such as the viscosity, the wettability (e.g., how well the liquid coats the substrate surface) and the volatility (e.g., the vapor pressure) of the solution or dispersing medium, and the amount of spreading force applied to the liquid samples by the movement device  27  as will be described. Generally, the more viscous the liquid sample, the thicker the resulting film will be for a given spreading force. Alternatively, for a more viscous liquid sample, the spreading forces acting on the sample can be varied to obtain a desired film thickness. As an example, the viscosity of the liquid sample is preferably in the range of about 1E −4  to about 1E 4  Pa-sec, more preferably in the range of about 5E −4  to about 1E 3  Pa-sec, still more preferably in the range of about 1E −3  to about 1E 2  Pa-sec, and most preferably in the range of about 1E −2  to 1E 1  Pa-sec.  
     [0054] For some materials it may be desirable or even necessary to lower the viscosity of the material by dissolving or dispersing the material in a solvent to facilitate the formation of a thinner film. Such a solvent preferably has a boiling point in the range of about −100° C. to about 1,000° C., more preferably in the range of about −50° C. to about 500° C., and most preferably in the range of about 25° C. to about 200° C. However, the more volatile the solvent, the faster it will evaporate after the liquid is deposited onto the substrate surface  29 . Consequently, as the volatility of the solvent increases, the spreading force required to form the desired film size before the liquid stops spreading over the substrate surface  29  also increases.  
     [0055] The thickness of each film formed on the substrate surface  29  is preferably in the range of about 50 Å to about 1000 micrometers, and more preferably in the range of about 1,000 Å to about 10 micrometers, and even more preferably in the range of about 1,000 Å to about 10,000 Å. In one preferred embodiment, a portion of the surface area of each film formed on the substrate  23  has a substantially uniform thickness to facilitate more accurate screening of the film. For example, a portion of each film preferably has a thickness which is uniform to within a variation of about 0% to about 20%, more preferably to within a variation of about 0% to about 10%, still more preferably to within a variation of about 0% to about 5% and most preferably to within a variation of about 0% to about 3%. The size (e.g., surface area) of a region within each film formed on the substrate surface  29  is preferably at least about equal to the minimum size required by the measurement method used to characterize the film, and is more preferably up to about three times larger than the minimum size required by the measurement method.  
     [0056] With further reference to FIG. 1, the movement device  27  of the illustrated embodiment is a non-oscillatory, or non-reciprocating device, and is more particularly a spin-coating device capable of uni-directional rotation on a rotation axis thereof to subject the liquid sample to subject the liquid samples on the substrate surface  29  to a generally monotonic non-contact spreading force. The spin-coating device  27  comprises a cylindrical housing  51 , a motor (not shown) enclosed within a lower portion of the housing, a drive shaft (not shown) rotatably driven by the motor and defining the rotation axis of the device, and a chuck  53  mounted coaxially on the drive shaft for conjoint rotation therewith on the rotation axis of the device. General construction and operation of spin-coating devices similar to that of the illustrated embodiment is known in the art and will not be further described herein except to the extent necessary to describe the present invention.  
     [0057] For example, one preferred spin-coating device  27  is available from Laurell Technologies Corporation of Pennsylvania under the model designation WS-400A-6NPP. The cylindrical housing  51  has an internal diameter of about 8.5 inches and a height of about 12 inches. A closure  55  is hinged to the housing  51  to permit closing of the housing during operation of the device  27 . The chuck  53  of the illustrated embodiment is a vacuum chuck in fluid communication with a vacuum source (not shown) for suctioning the substrate  23  down against the chuck during operation of the spin-coating device  27 . However, it is understood that the substrate  23  may be supported on the drive shaft by means other than a vacuum chuck, such as by mechanical retainers (not shown) or other suitable means without departing from the scope of this invention. The spin-coating device  27  shown in FIG. 1 can support a substrate  23  having a diameter of about three to about six inches and is capable of uni-directional rotation at speeds of up to at least about 6000 rpm. It is contemplated that where a smaller substrate is used, the spin-coating device  27  may be substantially smaller than that shown in FIG. 1. For example, one of the spin-coating devices shown in FIG. 11 and described later herein may be used to rotate a smaller substrate, such as a substrate having a diameter (or width) of about 0.5 inches.  
     [0058] Still referring to FIG. 1, a control system  57  is in electrical communication with the spin-coating device  27  for controlling operation thereof. The control system  57  is preferably a computer based system capable of sending data to and receiving data from the spin-coating device  27  to monitor and control operation of the device. Such data preferably include a motor start time, rotational acceleration and speed, duration of motor operation and other relevant parameters. The control system  57  is also desirably programmable to permit a pre-determined parameter profile, such as a rate of acceleration, duration of operation, rotational speed and stop time to be pre-programmed. For example, the control system  57  may be programmed such that following deposition of one or more liquid samples on the substrate  23 , the substrate is subjected to rotation for an initial time period, such as about 5-10 seconds, at a relatively low rotational speed, such as about 500 rpm, to promote spreading of the liquid samples on the substrate surface  29 . The substrate  23  may then be accelerated to a higher rotational speed, such as about 2000 rpm for a longer duration, such as about 40 seconds, to promote further evaporation of the liquid. It is believed that the hardware and software components of the control system  57  will be readily apparent to those of ordinary skill in this field and therefore will not be described in more detail.  
     [0059] A heater (not shown in FIG. 1 but similar to a heater  353  shown in FIG. 21 and described later herein), may be positioned above the substrate  23  in opposed relationship with the substrate surface  29 , such as at a distance of about 1 mm up to about 100 mm, to heat the substrate, ambient environment and/or liquid samples deposited on the substrate  23  during operation of the spin-coating device  27 . The heater is preferably capable of generating heat at a temperature in the range of about 25° C. to about 500° C., more preferably in the range of about 50° C. to about 450° C., and most preferably in the range of about 100° C. to about 400° C. As an example, one preferred such heater is a flat panel infrared heater available from Ogden of Arlington Heights, Ill. under the model designation FP2017 and is operable to generate heat at a temperature of up to about 200° C. Alternatively, it is understood that a cooling device (not shown) may be used to cool the substrate, ambient environment and/or liquid samples without departing from the scope of this invention.  
     [0060] In operation according to a method of the present invention for forming films on a substrate surface  29 , and more particularly for forming thin films from liquid samples on the surface of a single substrate, a substrate  23  is secured to the chuck  53  of the spin-coating device  27  generally coaxially with the rotation axis of the device and with the mirror-finish surface of the substrate exposed (e.g., facing up as shown in FIG. 1). The deposition device  25  is then operated to deposit one or more liquid samples on the exposed substrate surface  29 . The samples may be deposited serially, such as by the device  25  shown in FIG. 1, or simultaneously, such as by a deposition device (not shown) having multiple probes. It is contemplated that if only one liquid sample is deposited on the substrate surface  29 , it may be located offset from the center of the substrate  23  (e.g., relative to the rotation axis of the spin-coating device). In the event more than one liquid sample is deposited on the substrate  23 , the liquid samples are preferably deposited thereon in spaced relationship with each other, with the samples all being generally offset from the center of the substrate or with one of the samples being deposited at the center of the substrate.  
     [0061] The spin-coating device  27  is then operated to rotate the substrate  23  on the rotation axis of the device. The rotation of the substrate  23  subjects the liquid samples on the substrate surface  29  to a non-contact spreading force, resulting in a shear stress at the liquid sample/substrate surface interface. When sufficiently large, this shear stress causes the liquid to spread or flatten on the substrate surface  29  to facilitate thinning of the liquid and evaporation thereof to thereby form corresponding thin films on the substrate surface. For example, uni-directional rotation of the substrate  23  by the spin-coating device  27  of FIG. 1 subjects the liquid samples to a generally monotonic spreading force sufficient to spread or flatten the samples generally tangentially and/or radially outward on the substrate surface  29  as illustrated by the films formed on the substrate shown in FIG. 2.  
     [0062] The liquid samples may be deposited on the substrate surface  29  with sufficient spacing therebetween such that the corresponding films formed on the substrate surface remain discrete from each other. However, it is understood that portions of adjacent films may overlap each other and remain within the scope of this invention, as long as a portion of each film remains sufficiently discrete from other films on the substrate surface to permit the desired screening of each different film. For example, an area of at least about 0.1 mm 2  of each film formed on the substrate  23  is preferably discrete from other films formed thereon. It is also understood that certain experimental designs may require overlap between films, e.g., to investigate multilayer phenomena. It is also contemplated that the liquid samples may alternatively be deposited onto the substrate surface  29  during operation of the spin-coating device  27  so that the substrate surface is already rotating as liquid samples are deposited thereon.  
     EXAMPLE 1  
     [0063] The above method was used to form a plurality of silica-based films for the evaluation of their dielectric, optical, mechanical and chemical properties. A liquid solution comprising a silica source, a catalyst, a surfactant and a solvent was prepared and used as a liquid source for the deposition device  25  of FIG. 1. A silicon wafer having a diameter of about three inches was suctioned down against the vacuum chuck of the spin-coating device  25  of FIG. 1. The deposition device  25  was operated to serially dispense thirteen liquid samples of the solution on the exposed surface  29  of the wafer in a generally circular pattern having a diameter of about two inches, with the center-to-center spacing between adjacent samples being about 8 mm. The volume of each liquid sample was in the range of about 2-5 microliters. The control system  57  was used to operate the spin-coating device  27  according to a predetermined program pursuant to which after the deposition of each sample of liquid on the substrate  23 , the substrate was rotated at an acceleration rate of about 2000 rpm/sec until the rotational speed reached about 3000 rpm (e.g., about 1.5 seconds), and rotation then continued at a speed of 3000 rpm for about 5-10 seconds.  
     [0064] The control system  57  then caused rotation of the substrate  27  to stop while another sample of liquid was deposited on the substrate surface  29 . Rotation of the substrate  23  subjected the liquid samples to a non-contact spreading force, resulting in the liquid samples spreading radially and tangentially outward on the wafer surface to form films thereon. FIG. 2 illustrates the pattern of corresponding films F formed on the wafer surface  29 .  
     [0065] A movement device  27  of a second embodiment of apparatus  21  of the present invention is shown in FIGS. 3 and 4. In this embodiment, the movement device  27  is an oscillatory movement device, and more particularly an orbital movement device capable of oscillating the substrate  27  along an orbital path. The orbital movement device  27  comprises a housing  61  and an orbital drive system (not shown) operatively connected to an orbiting member (FIG. 3) for driving eccentric orbital movement of the orbiting member. The orbiting member  27  of the illustrated embodiment extends up out of the housing  61  and has a substrate holder  65  mounted thereon for conjoint orbital movement with the orbiting member. General construction and operation of orbital movement devices is known in the art and will not be further described herein except to the extent necessary to describe the present invention.  
     [0066] As an example, one preferred orbital movement device  27  is available from IKA-Works, Inc. of Wilmington, N.C., U.S.A., under the model designation MS1 MINISHAKER. The device  27  is capable of driving orbital movement of the substrate holder  65  (and hence the substrate  23  supported by the holder  65 ) at a speed in the range of about 200 rpm to about 2500 rpm along an eccentric path of up to about 0.177 inches on a major axis and up to about 0.089 inches on a minor axis. In the particular embodiment shown, the holder  65  comprises a base  67  adapted for connection with the orbiting member  19 , and three arms  69  (FIG. 4), or spokes extending radially outward from a central hub  71  and secured to the base by suitable fasteners  73 . The base  67  of the holder  67  includes a skirt  75  formed integrally therewith and depending therefrom. The skirt  75  is tapered in accordance with the contour of the housing  61  to generally surround and shield the portion of the orbiting member  63  which extends outward of the housing. As seen best in FIG. 4, the arms  69  of the holder  67  are preferably in equiangular relationship with respect to one another (e.g., at angles of about 120° relative to each other). A retainer in the form of a pin  73 , for example, extends up from the upper surface of each arm  69  generally adjacent its outer end. The substrate  23  thus seats on the upper surfaces of the arms  69  with the peripheral edge of the substrate  23  generally centered within the pins  73  such that the pins inhibit lateral (e.g., sliding) movement of the substrate on the holder during operation of the orbital movement device  23 .  
     [0067] It is contemplated that the apparatus  21  of this second embodiment may also have a control system (not shown but similar to the control system  57  shown in FIG. 1) for controlling the drive system of the orbital movement device  27 . For example, the control system  57  may be used to monitor and control the drive system start time, the orbital path and speed of the device, the duration of operation of the drive system and other relevant parameters. It also contemplated that a heater (not shown but similar to the heater  353  shown in FIG. 21 and described later herein) or a cooling device (not shown) may be used to heat or cool the substrate  23  and/or liquid samples during operation of the orbital movement device  27 .  
     [0068] In operation, the substrate  23  is placed in the holder  65  of the orbital movement device  27  as described above, with the mirror-finish surface  29  exposed (e.g., facing up in the device of FIG. 3). The deposition device  25  is then operated to deposit one or more liquid samples on the exposed substrate surface  29 . The liquid samples may be deposited onto the substrate surface  29  serially, such as by the device shown in FIG. 1, or simultaneously, such as by a deposition device (not shown) having multiple probes. It is contemplated that if only one liquid sample is deposited on the substrate surface  29 , it may be located offset from the center of the substrate  23 . In the event more than one liquid sample is deposited on the substrate  23 , the liquid samples are preferably deposited thereon in spaced relationship with each other, with the samples all being generally offset from the center of the substrate or with one of the samples being deposited at the center of the substrate.  
     [0069] The orbital movement device  27  is then operated to drive movement of the substrate  23  along an orbital path. Orbital movement of the substrate  23  subjects the liquid samples on the substrate surface  29  to a non-contact spreading force, resulting in a shear stress at the liquid sample/substrate surface interface. When sufficiently large, this shear stress causes the liquid samples to spread or flatten on the substrate surface  29  to facilitate thinning of the liquid and evaporation thereof to thereby form corresponding thin films on the substrate surface. For example, orbital movement of the substrate  23  by the orbital movement device  27  of the illustrated embodiment causes each liquid sample to spread or flatten on the substrate surface  29  in a generally circular pattern to form generally circular films F on the substrate in FIG. 5.  
     [0070] The liquid samples are preferably deposited on the substrate surface  29  with sufficient spacing therebetween such that the films F formed on the substrate surface remain discrete from each other. However, it is understood that portions of adjacent films may overlap each other and remain within the scope of this invention, as long as a portion of each film remains sufficiently discrete from other films on the substrate surface  29  to permit the desired screening of each different film. For example, an area of at least about 0.1 mm 2  of each film formed is preferably discrete from other films formed on the substrate  23 . It also contemplated that the liquid samples may alternatively be deposited onto the substrate surface  29  during operation of the orbital movement device  27  so that the substrate surface is already moving as liquid samples are deposited thereon.  
     EXAMPLE 2  
     [0071] The apparatus  21  of the second embodiment was used to form a combinatorial array of silica-based films F for the evaluation of their dielectric, optical, mechanical and chemical properties. Different compositions of a liquid solution comprising a silica source, a catalyst, a surfactant and a solvent were prepared and used as liquid sources for the deposition device  25  (FIG. 1). A silicon wafer having a diameter of about 125 mm was placed in the holder  65  of the orbital movement device  27  of FIG. 3 in the manner described previously. The orbital movement device  27  was operated to move the wafer at a speed of about 2200 rpm along an orbital path having a major axis of about 4.5 mm and a minor axis of about 2.25 mm.  
     [0072] While the wafer was moving along its orbital path, the deposition device  25  was operated to serially dispense twenty-five samples of liquid on the wafer in a generally square pattern (e.g., a matrix of five rows of five samples each), with the center-to-center spacing between adjacent samples being about 17.5 mm. The volume of each liquid sample was in the range of about 2-5 microliters. Dispensing of the liquid samples on the wafer occurred over a period of about 12 minutes, and the substrate  12  was moved on its orbital path for a total duration of about 15 minutes (e.g., about 3 minutes longer than the time at which the last liquid sample is deposited on the substrate), after which orbital movement of the substrate was stopped. Orbital movement of the wafer subjected the liquid samples on the wafer surface  29  to a non-contact spreading force to facilitate spreading of the liquid samples on the wafer surface to form films thereon. FIG. 5 illustrates the pattern of corresponding films F formed on the wafer surface  29 . The diameter of each of the films formed on the wafer surface  29  was approximately 17 mm.  
     [0073]FIGS. 6 and 7 illustrate a movement device  27  of a third embodiment of apparatus  21  of the present invention in which the movement device subjects the substrate to oscillatory movement. In this embodiment, the movement device  27  is a reciprocating device and, more particularly, a linear reciprocating device capable of reciprocating the substrate  23  along a longitudinal path extending generally normal to the surface  29  of the substrate (e.g., up/down as indicated by the direction arrow in FIG.  6 ). The linear reciprocating device  27  generally comprises a housing  81 , a drive system generally indicated at  83  in FIG. 7, and a holder, generally indicated at  85 , operatively secured to the drive system for supporting the substrate  23  during operation of the device. The drive system  83  of the illustrated embodiment is an electromagnetic drive system including an armature  87  coaxially received within a central passage of an electromagnetic coil  89 . The armature  87  is movable axially (e.g., vertically) relative to the coil  89  on along a longitudinal path defined by the armature. Leaf springs  91  are secured to the armature  87  toward its upper end for controlling the axial displacement of the armature. The drive system  83  also includes a generally rectangular mounting block  93  secured to the top of the armature  87  for conjoint linear reciprocation therewith. A cover plate  95  is secured to the top of the mounting block  93  for conjoint movement therewith and generally defines the top of the housing  81 .  
     [0074] General construction and operation of linear reciprocation devices such as the device  27  described herein and illustrated in FIG. 7 as having an electromagnetic drive system  83  is known in the art and will not be further described herein except to the extent necessary to describe the present invention. For example, U.S. Pat. Nos. 3,155,853 and 4,356,911, the entire disclosures of which are incorporated herein by reference, disclose reciprocating devices having electromagnetic drive systems. One particularly preferred linear reciprocation device  27  is available from Union Scientific Corporation of Randallstown, Md., U.S.A., as a vertical electromagnetic shaker. The drive system  83  is capable of linear reciprocation at a frequency of up to about 60 Hz and an amplitude of up to about 0.15 inches.  
     [0075] As best seen in FIG. 6, the holder  85  comprises a support platform which, in this embodiment, comprises a plate  97  secured to the cover plate  95  and having a depression, or seat  99 , formed in its upper surface for receiving the substrate  23  therein. Preferably, the seat  99  has a size and shape closely conforming to the size and shape of the substrate  23  to provide a close clearance fit of the substrate  23  in the seat. A groove  101  is formed within the upper surface of the support plate  97  and extends from the seat  99  out to the peripheral edge of the support plate to facilitate handling of the substrate  23 , such as lifting the substrate out of the seat. A pair of retaining arms  103  is secured to the upper surface of the support plate  97  in spaced relationship with each other adjacent the peripheral edge of the seat  99 . Each retaining arm  103  is pivotally secured at a pivot end  105  thereof to the upper surface of the support plate  97  by a suitable fastener  107 . An opposite, free end  109  of each retaining arm  103  has an open slot  111  formed therein which is sized for receiving another fastener  113 . A central portion  115  of each retaining arm  103  is configured for extending over the peripheral edge margin of the seat  99  (and hence the substrate  23  seated therein) and has a thickness such that the retaining arm engages the substrate to urge the substrate down into the seat during operation of the device  27 .  
     [0076] To secure a substrate  23  on the device  27 , the fasteners  113  at the free ends  109  of the arms  103  are loosened and the arms are pivoted out to an open position (e.g., as shown by one arm in FIG. 6) in which the arms do not extend over any portion of the seat  99  formed in the upper surface of the support plate  97 . The substrate  23  is then placed in the seat  99  and the arms  103  are pivoted inward to a closed position (e.g., as shown by the other arm in FIG. 6) in which the shafts of the loosened fasteners  113  are received in the slots  111  formed in the free ends  109  of the arms  103 . In their closed position, the central portions  115  of the retaining arms  103  extend over a peripheral edge margin of the seat in engagement with the substrate  23  seated therein. The fasteners  113  at the free ends  109  of the arms  103  are then tightened, causing the central portions  115  of the retaining arms  103  to generally urge the substrate  23  down into the seat  99  to inhibit movement of the substrate during operation of the device  27 .  
     [0077] It is understood that linear reciprocation of the substrate  23  along a path normal to the substrate surface  29  may be performed with other conventional linear reciprocating devices having drive systems other than an electromagnetic drive system. It is also understood that movement devices capable of reciprocating the substrate along an axis other than normal to the substrate surface are known in the art and may be used without departing from the scope of this invention. For example, a movement device in which the substrate is reciprocated generally in the plane of the substrate surface (e.g., side-to-side) may be used. Devices in which a combination of reciprocating movements within and out of the plane of the substrate supported thereby, such as a device in which the substrate is rocked back and forth on an arcuate path, may be used. It is also contemplated that a movement device in which the substrate is rotated, such as the spin-coating device of FIG. 1, may be adapted to oscillate the substrate back and forth about the rotation axis of the device (e.g., first in one direction and then in another) and remain within the scope of this invention.  
     [0078] The movement device  27  may also move the substrate  23  in different ways, either sequentially or concurrently, such as by reciprocating the substrate up and down while the substrate is moved in an orbital path or rotated, or by varying the operating parameters of the movement device, such as to vary the speed (e.g. rotational speed or frequency) or displacement (e.g., amplitude or orbital path) of the substrate, during operation of the device.  
     [0079] The apparatus  21  of this third embodiment may also comprise a control system (not shown but similar to the control system  57  shown in FIG. 1) for controlling the drive system of the reciprocating movement device  27 . For example, the control system may be used to monitor and control the drive system  83  start time, the amplitude and frequency of the device, the duration of operation of the drive system and other relevant parameters. It also contemplated that a heater (not shown but similar to the heater  353  shown in FIG. 21 and described later herein) or a cooling device (not shown) may be used to heat or cool the substrate  23  and/or liquid samples during operation of the reciprocating movement device  27 .  
     [0080] In operation, a substrate  23  is seated in the holder  85  of the linear reciprocating device  27  in the manner described previously, with the mirror-finish surface  29  of the substrate exposed (e.g., facing up in the device shown in FIG. 6). The deposition device  25  is then operated to deposit one or more liquid samples on the exposed substrate surface  29 . The liquid samples may be deposited serially, such as by the device  25  shown in FIG. 1, or simultaneously, such as by a deposition device (not shown) having multiple probes. It is contemplated that if only one liquid sample is deposited on the substrate surface  29 , it may be located offset from the center of the substrate. In the event more than one liquid sample is deposited on the substrate surface  31 , the liquid samples are preferably deposited thereon in spaced relationship with each other, with the samples all being generally offset from the center of the substrate or with one of the samples being deposited at the center of the substrate.  
     [0081] The reciprocating movement device  27  is then operated to effect a linear reciprocating movement of the substrate  23 , such as up and down for the device shown in FIG. 6. Linear reciprocation of the substrate  23  subjects the liquid samples to a non-contact spreading force (e.g., due to acceleration), resulting in a shear stress at the liquid sample/substrate surface interface. When sufficiently large, this shear stress causes the liquid samples to spread or flatten on the substrate surface  29  to facilitate thinning of the liquid and evaporation thereof to thereby form corresponding thin films on the substrate surface. Linear reciprocation of the substrate  23  facilitates a more controlled spreading or flattening of the liquid sample on the substrate surface  29 . For example, the vertical reciprocating movement of the substrate by the device  27  of the illustrated embodiment causes each liquid sample to spread or flatten on the substrate surface  29  in a generally circular pattern to form generally circular films F on the substrate  23 , as shown in FIG. 8.  
     [0082] The liquid samples are preferably deposited on the substrate surface  29  with sufficient spacing therebetween such that the films formed on the substrate surface remain discrete from each other. However, it is understood that portions of adjacent films may overlap each other and remain within the scope of this invention, as along as a portion of each film remains sufficiently discrete from other films on the substrate surface  29  to permit the desired screening of each different film. For example, an area of at least about 0.1 mm 2  of each film formed on the substrate surface  29  is preferably discrete from other films formed thereon. It also contemplated that the liquid samples may alternatively be deposited on the substrate surface  29  during operation of the reciprocating movement device  27  so that the substrate surface  29  is already moving as liquid samples are deposited thereon.  
     EXAMPLE 3  
     [0083] The apparatus  21  of the third embodiment was used to form a combinatorial array of silica-based films. Different compositions of a liquid solution comprising a silica source, a catalyst, a surfactant and a solvent were prepared and used as liquid sources for the deposition device (FIG. 1). A silicon wafer having a diameter of about 125 mm was placed in the holder  85  of the reciprocating movement device  27  of FIG. 6 in the manner described previously. The reciprocating movement device  27  was operated to reciprocate the wafer along a linear path normal to the wafer surface  29  at an amplitude of about 0.07 inches and at a frequency of about 60 Hz.  
     [0084] While the wafer was moving, the deposition device  25  was operated to serially dispense twenty-five samples of liquid on the wafer in a generally square pattern (e.g., a matrix of five rows of five samples each), with the center-to-center spacing between adjacent samples being about 17.5 mm. The volume of each liquid sample was in the range of about 2-5 microliters. Dispensing of the liquid samples on the wafer occurred over a period of about 12 minutes, and the wafer was reciprocated for a total duration of about 15 minutes (e.g., about 3 minutes longer than the time at which the last liquid sample is deposited on the substrate  23 ), after which movement of the substrate was stopped. Linear reciprocating movement of the wafer caused the liquid samples to spread over the wafer surface  29  to form films thereon. FIG. 8 illustrates a pattern of corresponding films F formed on the wafer surface. The diameter of each of the films formed on the wafer surface was approximately 17 mm. While not shown in the drawings, each of the films formed as a result of the vertical reciprocating movement has a generally concave cross section, with the center portion of the film being thinner than an annular area of the film toward the peripheral edge thereof.  
     [0085]FIGS. 9 and 10 illustrate a portion of a fourth embodiment of apparatus  21  of the present invention in which a spreading force is applied to the liquid samples by pressurized gas, such as air, directed toward the substrate  23  by an air knife (broadly, a gas delivery device), generally indicated at  121 . The substrate  23  is supported by a suitable holder  123  mounted on a stand  125 , and the air knife  121  is positioned above the substrate at a distance of from about 1 mm up to about 100 mm. The air knife  121  comprises a manifold  127  in fluid communication with a source (not shown) of pressurized gas via a suitable gas line  129 , and one or more nozzles  131  (two are shown in FIG. 10) secured to the manifold for receiving pressurized gas and directing the gas down toward the substrate surface.  
     [0086] Gas supplied to the nozzle(s)  131  is preferably at a pressure in the range of from about 1 psi to about 100 psi, and more preferably in the range of about 5 psi to about 20 psi. The nozzles  131  are preferably oriented to direct pressurized gas down toward the substrate surface  29  at an impact, or incident angle in the range of about 0° to about 90°, more preferably in the range of about 10° to about 80°, and most preferably in the range of about 30° to about 60°. General construction and operation of air knives is known in the art and will not be further described herein except to the extent necessary to describe the present invention. As an example, one preferred air knife  121  is available from Silvent of Sweden under the model designation  392  and comprises a pair of generally flat nozzles. Other conventional air knives  121  are shown and described in U.S. Pat. Nos. 2,135,406 and 5,505,995, the entire disclosures of which are incorporated herein by reference.  
     [0087] It is contemplated that the air knife  121  may be moveable relative to the substrate  23  during operation of the air knife to vary the direction at which air impacts the substrate surface (and hence the liquid samples deposited thereon). Also, the substrate  23  may be moveable instead of, or in addition to, the air knife  121 , such as by being rotated or moved laterally relative to the air knife, without departing from the scope of this invention.  
     [0088] In operation, a substrate  23  is supported by the holder  123  with the mirror-finish surface  29  of the substrate exposed (e.g., facing up in the device  27  shown in FIG. 9). The deposition device  25  is then operated to deposit one or more liquid samples on the exposed substrate surface  29 . The liquid samples may be deposited serially, such as by the device shown in FIG. 1, or simultaneously, such as by a deposition device having multiple probes. It is contemplated that if only one liquid sample is deposited on the substrate surface  29 , it may be located offset from the center of the substrate. In the event more than one liquid sample is deposited on the substrate surface  29 , the liquid samples are preferably deposited thereon in spaced relationship with each other, with the samples all being generally offset from the center of the substrate or with one of the samples being deposited at the center of the substrate.  
     [0089] The air knife  121  is then operated to direct pressurized gas toward the substrate surface  29  to impact the liquid samples. The pressurized gas impacting the liquid samples subjects the liquid samples to a spreading force, resulting in a shear stress at the liquid sample/substrate surface interface. When sufficiently large, this shear stress causes the liquid samples to spread or flatten on the substrate surface  29  to facilitate thinning of the liquid and the gas flow further facilitates evaporation of the liquid samples to thereby form corresponding thin films on the substrate surface.  
     [0090] The liquid samples are preferably deposited on the substrate surface  29  with sufficient spacing therebetween such that the films formed on the substrate surface remain discrete from each other. However, it is understood that portions of adjacent films may overlap each other and remain within the scope of this invention, as along as a portion of each film remains sufficiently discrete from other films on the substrate surface  29  to permit the desired screening of each different film. For example, an area of at least about 0.1 mm 2  of each film formed on the substrate surface  29  is preferably discrete from other films formed thereon.  
     [0091] It is contemplated that liquid samples on the substrate  23  may be subjected to non-contact spreading forces other than by the movement devices  27  described previously or by the air knife  121  without departing from the scope of this invention. For example, liquid samples may be dispensed onto the substrate  23  and the substrate may be tilted, or the substrate may be tilted prior to the delivery of liquid samples thereon, such that the liquid samples on the substrate are subjected to a gravitational force sufficient to spread the liquid samples on the substrate surface  29 . The tilt of the substrate  23  may also be varied as the liquid samples spread over the substrate surface  29 . It is also contemplated that the substrate may be moved, such as by the movement devices  27  described previously, or by the air knife  121 , concurrently with tilting the substrate.  
     [0092] FIGS.  11 - 19  illustrate yet another embodiment of apparatus of the present invention for forming films on substrates. More particularly, apparatus of this embodiment, generally designated  221 , effects the parallel formation of films on an array of substrates  223  each having the characteristics described above. However, each of the substrates  223  on which the films are formed by apparatus  221  of this embodiment are substantially smaller, such as preferably having a surface area of no greater than about one square inch, and more preferably a surface area of about 0.25 in. 2 . In the embodiment shown, the substrates  223  are held by holders, each of which is generally indicated at  251 . The apparatus  221  also includes a drive system, generally designated  253 , operable for moving at least two of the substrates  223  (and preferably all of the substrates) of the array during overlapping durations of time to subject samples deposited on the substrates to non-contact spreading forces to thereby cause the samples to spread over the respective surfaces of the substrates to form films on the surfaces. The drive system  253  is preferably under the control of a programmable control system, generally designated  255 , which controls the drive system to move the substrates  223  according to a predetermined program.  
     [0093] In the particular embodiment shown, the aforementioned drive system  253  is mounted on a frame having a base  257 , side walls  259  extending up from the base, and a top wall  261  which spans the side walls (FIG. 13). The drive system  253  includes at least one and preferably a plurality of electric motors  263 , one per substrate  223 , mounted below the top wall  261  of the frame by suitable fasteners. An output shaft  265  of each motor  263  projects up into a hole  267  through the top wall  261  of the frame and is connected to a respective substrate holder  251  by a shaft assembly comprising a cylindric rotor and drive shaft designated  269  and  271 , respectively. The rotor  269  is secured, as by a press fit, on the output shaft  265  of the motor  263  and has an outside dimension smaller than the hole  267  in the top wall  261  to provide the clearance necessary for the rotor to freely rotate as it is driven by the output shaft  265  of the motor. The drive shaft  271  has a lower end  273  of reduced diameter press fit (or otherwise secured) in the upper end of the rotor  269  and an upper end  275  of reduced diameter formed with a bore  277  which extends down into the body of the drive shaft.  
     [0094] The drive shaft  271 , rotor  269  and output shaft  265  of the motor  263  preferably have a common vertical axis of rotation. The spacing between adjacent motors  263  and drive shaft assemblies will depend primarily on the size of the holders  251 , which in turn will depend on the size of the substrates  223  to be held by the holders. In general, however, the centerline spacing between adjacent drive shafts  271  is preferably in the range of about 1 mm to about 500 mm, more preferably in the range of about 10 mm to about 100 mm, and even more preferably in the range of about 20 mm to about 80 mm. The construction of the drive shaft assembly may vary. For example, the rotor  269  and drive shaft  271  could be formed as a single piece, or as more than two pieces.  
     [0095] Given that the substrates  223  and holders  251  are relatively small in size, the motors  263  can also be relatively small. For example, each motor  263  may be a DC electric motor having a power output of about 3.5 W, a maximum speed of about 7000 rpm, a continuous torque of about 4.95 mNm and a stall torque of about 15.5 mNm. Other types of motors may also be used.  
     [0096] In the particular embodiment of FIGS.  11 - 19 , each substrate holder  251  has a base  281  with openings  283  therein adjacent the periphery of the base, a circular rim  285  extending up from the base, and a recess  287  or depressed area in the upper surface of the base for receiving a substrate  223  therein. The recess  287  is sized and shaped to hold the substrate  223  in a substantially fixed position against lateral movement during rotation of the drive shaft  271 . A central hub  289  projects down from the base  281  generally co-axially with respect to the respective drive shaft assembly. The hub  289  and drive shaft  271  are removably and drivingly connected by a connector  291  having an enlarged upper end received and secured (as by a press fit) in an opening in the hub and a lower end received and secured (as by a press fit) in the bore  277  in the drive shaft. The connector  291  is formed with one or more keys  293  receivable in keyway slots  295  extending down from the upper end  275  of the drive shaft  271  to prevent relative rotation of the drive shaft and the connector. The construction of the holder  251  and connector  291  may vary. For example, the holders  251  may have a construction similar to that of the holders  53 ,  65 ,  85 ,  123  of the various embodiments discussed above.  
     [0097] The substrates  223  are typically held in their respective seats by gravity and friction. Where necessary, other mechanisms can be used, such as vacuum, mechanical retainers, or other suitable means.  
     [0098] The number of substrate holders  251  and substrates  223  in the array may range from 2 to 96 or more. The configuration of the array may also vary. For example, the array shown in the drawings includes eight holders  251  and associated components, all arranged in the form of a 1×8 matrix. However, the holders  251  could be arranged in a matrix having any number of columns and rows, or they could be arranged in a geometric formation (e.g., a circle), or even randomly, without departing from the scope of this invention. For efficiency of space, it is preferred that the substrate holders  251  (and substrates  223  therein) be relatively closely spaced in an array which occupies an area (i.e., footprint) having a maximum dimension of less than about five feet by five feet, and more preferably occupies an area of about 1000 mm by about 300 mm, and even more preferably an area of about 100 mm by about 30 mm. If a robotic deposition system  225  is used to deposit samples on the substrates  223 , the array should be confined to an area capable of being serviced by the robot system. By way of example, the footprint of the array shown in FIG. 13 is generally rectangular, having a length of about 300 mm and a width of about 125 mm.  
     [0099] It is contemplated that the drive system  253  could have configurations other than those described above without departing from the scope of this invention. For example, the motors  263  could be mounted on multiple frames instead of a single common frame. Further, the motors  263  can be mounted so that their axes are other than vertical. A single motor  263  can also be used to move more than one substrate  223 , as exemplified by the system  253  shown in FIG. 20. In this embodiment, a single motor  263  is drivingly connected to more than one (e.g., all) of the drive shaft assemblies, as by a gear  301  on the corresponding drive shaft  271  in mesh with a gear train comprising a plurality of gears  303  attached to the remaining drive shafts. In this embodiment, the drive shafts  271  are rotatably supported by suitable bearings  297  in the frame. The arrangement is such that rotation of the drive shaft  271  by the motor  263  causes the other drive shafts and associated holders  251  to rotate in unison.  
     [0100] Also, the drive system  253  can be operable to move the holders  251  in ways other than uni-directional movement. As described previously, other drive mechanisms can be employed to effect oscillatory movement, such as orbital movement, reciprocating movement (linear or otherwise) or rocking movement, or other forms of movement effective for subjecting liquid samples on the substrates  223  to non-contact spreading forces. By way of example, an array of holders  251  mounted on a common frame may be operably secured to the orbiting member of an orbital movement device similar to that shown in FIGS. 3 and 4, so that operation of the device effects orbital movement of the entire array of holders and substrates  223  held thereby. Alternatively, each holder  251  can be mounted on a separate orbital movement device. The drive system  253  can also be operable to move two or more of the substrates  223  in different ways, such as through different types of movement (e.g., rotational, orbital, linear) or at different rates and displacements.  
     [0101] The control system  255  for controlling the drive system  253  is preferably a computer based system capable of sending data to the drive system and receiving data from the drive system to monitor and control the operation of the system. Such data preferably includes, for each motor  263 , a motor start time, amplitude and/or frequency of movement, duration of motor operation, and any other relevant parameters. The control system  255  is also programmable to permit a pre-determined parameter profile, such as a rate of acceleration, duration of operation, rotational speed and stop time to be pre-programmed. For example, the control system  255  may be programmed such that following deposition of one or more liquid samples on each substrate  223 , the particular substrate is subjected to rotation for an initial time period, such as about 5-10 seconds, at a relatively low rotational speed, such as about 500 rpm, to promote spreading of the liquid samples on the substrate. The substrate  223  may then be accelerated to a higher rotational speed, such as about 2000 rpm for a longer duration, such as about 40 seconds, to promote further evaporation of the liquid. The system  255  can be used to control the operation of each motor  263  independent of the operation of the other motors (if more than one motor is used), so that different substrates  223  can be subjected to different movement conditions during the same run of experiments occurring during overlapping durations of time. It is believed that the hardware and software components of the control system  255  will be readily apparent to those of ordinary skill in this field and therefore will not be described in more detail.  
     [0102] Liquid samples may be deposited on the substrates  223  manually, or more preferably, by the robotic deposition system  225 . It is also contemplated that a robotic system (not shown) may be provided for automatically (instead of manually) mounting the substrates  223  on and removing the substrates from the substrate holders  251  without departing from the scope of this invention.  
     EXAMPLE 4  
     [0103] The above method was used to form a combinatorial array of silica-based films. Liquid solutions comprising a silica source, a catalyst, a surfactant and a solvent were prepared and used as liquid sources on the deposition device  25  of FIG. 1. Square silicon wafers each having a length and width of about 0.5 inches (e.g., a surface area of about 0.25 in. 2 ) were individually placed in each of the eight substrate holders  251  of the apparatus  221  of FIG. 11. The deposition device  25  was operated to dispense a sample of liquid generally centrally on one of the wafers. The volume of the liquid sample was approximately 10 microliters. The control system  255  was used to operate the motor  263  corresponding to the wafer on which the liquid sample was dispensed according to a predetermined program pursuant to which the wafer was rotated at an acceleration rate of about 2000 rpm/sec until the rotational speed reached about 3000 rpm (e.g., about 1.5 seconds), and rotation then continued at a speed of 3000 rpm for about 5-10 seconds.  
     [0104] Rotation of the wafer subjected the liquid sample to a non-contact spreading force, resulting in the liquid sample spreading out over the wafer surface to form a film thereon. The control system  255  then caused rotation of the wafer to stop and the deposition device  25  was moved to the next wafer over a time period of about thirty seconds to dispense another liquid sample thereon. This process was repeated until a film was formed on each of the eight wafers.  
     [0105]FIG. 21 illustrates yet another embodiment of apparatus  321  of the present invention which is similar to the apparatus  221  of FIG. 11 but with a heating system, generally designated  351 , positioned above the substrates for heating the substrates and the liquid samples deposited thereon. The heating system  351  of the illustrated embodiment comprises an infrared heater  353  positioned a distance of about 1 mm up to about 100 mm above the substrate. The heater  353  is preferably capable of generating heat at a temperature in the range of about 30° C. to about 500° C., more preferably in the range of about 50° C. to about 450° C., and most preferably in the range of about 100° C. to about 400° C. As an example, one preferred such heater  353  is a flat panel infrared heater available from Ogden of Arlington Heights, Ill. under the model designation FP2017 and is operable to generate heat at a temperature of up to about 200° C. If desired, a separate heater may be provided above each substrate holder  251  so that the temperature of one substrate  223  can be varied relative to the temperatures of the other substrates. The heating system can also be under the control of the control system  255  described above. It is also contemplated that a cooling device (not shown) may used instead of the heater  353  where cooling of the substrates  223 , ambient environments or liquid samples is desired.  
     [0106] The apparatus  221 ,  321  described above can be used for forming thin films in the same manner previously described, the only differences being that liquid samples are deposited on more than one substrate  223 , and more than one substrate is moved during overlapping durations of time. Liquid samples of the same or different composition and/or volume may be deposited on different substrates  223  and at the same or different locations on different substrates. Further, different numbers of samples may be placed on different substrates  223  (e.g., one sample on one substrate and more than one sample on other substrates), and the conditions under which the films are formed may be varied by varying the amplitude and/or frequency of movement(s), the duration of movement, etc. This is facilitated in certain embodiments by the use of the control system  255  described above. If a heater  353  or cooling device is used, the temperatures of the substrates  223  may also be controlled.  
     [0107] Following the formation of films on the substrates  23 ,  223  in accordance with any of the apparatus and methods described previously, the substrates are removed from their respective holders. It is contemplated that for some films, such as dielectric films, the substrates  23 ,  223  may be subjected to an annealing process in which the substrates are heated, such as to about 400° C., to promote decomposition of any organic material remaining in the film. However, annealing of the substrates  23 ,  223  may be omitted without departing from the scope of the invention.  
     [0108] The films formed on the substrates  23 ,  223  are then subjected to screening processes to determine, measure or otherwise characterize various properties of the films. As an example, U.S. Pat. No. 6,004,617 (Schulz et al.) discloses a number of such film properties which can be screened from a film formed on a substrate. As an additional example, mechanical properties such as the thickness, hardness and modulus of elasticity of each film may be measured. In one preferred technique for measuring the thickness of the film, commonly referred to as profilometry, the thickness of the film is determined using a stylus (not shown) in physical contact with the film. One machine (not shown) for determining the film thickness in such a manner is available from KLA/Tencor Corp. of San Jose, Calif., U.S.A. under the model designation P-15.  
     [0109] A preferred technique for determining the hardness and modulus of elasticity of each film is commonly referred to as nanoindentation, wherein a diamond tip (not shown) is driven down into the film and the resistance of the film to indentation by the diamond tip is measured. One preferred device (not shown) for carrying out such a screening is available from Hysitron Inc. of Minneapolis, Minn. and designated as a triboindentor nanomechanical test system. To use such a device, the films formed on the substrate  23 ,  223  are each preferably sized to have a width and length (or diameter) of at least about 50 nm to about 100 nm.  
     [0110] Electrical properties of each film, such as the capacitance and the dielectric constant (k) thereof, may also be determined. For example, a device (not shown) available from Solid State Measurements Inc. of Pittsburgh, Pa., U.S.A. under the model designation SSM 495 measures the capacitance of a film and, based on the thickness of the film (e.g., as determined by using the techniques described previously), determines the dielectric constant thereof. To use such a device, the films formed on the substrate  23 ,  223  are each preferably sized to have a surface area of at least about 3 mm 2 . The films may also be screened for various optical properties such as the refractive index (n) and the extinction coefficient, which is a measurement of the amount of light absorbed by the film. One device (not shown) for determining these optical properties is available from n&amp;k Technology of Santa Clara, Calif., U.S.A. under the model designation n&amp;k Analyzer 1500.  
     [0111] Construction and operation of the screening devices described above are well known in the art and will not be further described herein. Moreover, it is contemplated that other conventional screening devices may be used to screen the films formed on the substrate  23 ,  223 , including devices capable of screening for properties other than those described previously, without departing from the scope of this invention.  
     [0112] When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.  
     [0113] As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.