Abstract:
One embodiment includes a sputtering system that includes a vacuum chamber; a substrate transport system configured to transport a substrate through the vacuum chamber; a cathode for supporting a sputtering target, the cathode at least partially inside the vacuum chamber; and a power supply configured to supply power to the cathode and the power supply configured to output a modulated power signal. Depending upon the implementation, the power supply can be configured to output an amplitude-modulated power signal; a frequency-modulated power signal; a pulse-width power signal; a pulse-position power signal; a pulse-amplitude modulated power signal; or any other type of modulated power or energy signal.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to power supplies and systems for sputtering.  
       BACKGROUND OF THE INVENTION  
       [0002]     Coated substrates are found almost everywhere and are critical for today&#39;s consumer products, solar products, and glass. For example, typical consumer products that utilize coated substrates include cell phone displays, flat-panel computer displays, flat-panel televisions, personal digital assistants, and digital watches. These coated substrates are generally formed by depositing a thin layer of material on a particular substrate. Often, this deposited material is a transparent conductive oxide (TCO), which transmits light and can conduct electrical current. Exemplary TCOs include indium tin oxide (ITO) and aluminum zinc oxide (AZO), but other TCOs are known to those of skill in the art.  
         [0003]     Manufacturers use a process known as “sputtering” to deposit TCOs and other films on substrates. Sputtering involves atomizing a target by bombarding it with ions. The atoms sputtered from the target are deposited on a substrate, which is generally moved past the target during the sputtering process. The sputtered atoms collect on the substrate and form crystals and eventually a film. High density and high-quality crystals are important to high-quality films.  
         [0004]      FIGS. 1 through 4  illustrate implementations of the sputtering process.  FIG. 1 , for example, illustrates a sputtering system known as a “rotatable magnetron.” This system is often used for a coating glass. The basic rotatable magnetron includes a rotatable cathode  10  and a target  15 , both of which are located inside a vacuum chamber  20 . The vacuum chamber  20  includes a gas inlet  25  and gas exit port  30  for introducing gas into and removing gas from the vacuum chamber  20 . The basic system also includes a power supply  35 , which could be, among other things, an AC, DC, or RF-based power supply. The power supply  35  provides energy to the cathodes  10  to ignite the gas inside the chamber  20  so that a plasma is formed around the cathode  10 . The gas ions produced by the plasma are focused by a magnet assembly  40  located inside the rotatable cathode  10  so that the ions bombard the target  15  and sputter atoms of the target  15 . Finally, this rotatable magnetron system includes a substrate transport system  45  that moves a substrate by the cathode  10  during the sputtering process. The atoms sputtered from the target  15  settle on the substrate and form a film.  
         [0005]      FIG. 2  illustrates a cross section of a portion of another sputtering system. This system is referred to as a “planar magnetron” because it uses a planar cathode  50  and planar target  55  rather than a rotatable cathode and target. Like the rotatable magnetron, the planar magnetron uses magnets  60  to force ions from the plasma to bombard the target  55 . The planar magnetron is commonly used for producing thin films for displays.  
         [0006]      FIG. 3  illustrates the magnetic fields  65  created by the magnet assembly  70  included in a planar magnetron. The magnetic fields confine the electrons and secondary electrons on and near the surface of the sputtering cathode generating ions as they move through drift around the race track. The Ions created bombard the target (shown in  FIG. 2  as element  55 ). As can be seen in  FIG. 2 , this bombardment is considerably more intense on certain portions of the target  55 . For example, two portions  75  of the target  55  have been significantly sputtered while the remaining portions of the target  55  are relatively untouched. The pattern formed by this sputtering process is known as a “race track.”  FIG. 4  illustrates a planar target  75  with a well-formed race track  80 . The target  75  was originally a rectangular block, and the sputtering process atomized the material in the race-track area  80  and deposited it on a substrate.  
         [0007]     Due to the increase in products requiring thin films, the thin-film industry has recently placed increased emphasis on thin-film quality. Poor-quality films often result from unwanted debris collecting on the substrate and/or from films poorly forming on the substrate. The thin-film industry has addressed these film-quality issues in a variety of ways, including modifying power supplies and introducing ion-assisted deposition processes. But the industry has not yet developed reliable, efficient, and commercially practical solutions to its debris and film formation problems for these new thin film requirements.  
         [0008]     The debris problem facing the film industry (both thick and thin) involves two debris types. The first debris type includes debris that comes from the target, and the second debris type comes from the growing film itself and the substrate carrier. This second type of debris is often created after debris from the target impacts the film. Debris that comes from the target is often the result of nodules and electrical arcing. (Nodules are build ups of material on a target, and are often formed when sputtered material is deposited on the target or cathode rather than on the substrate.)  
         [0009]      FIG. 5  illustrates an example of a typical nodule  85  that forms on a cathode  90  and/or a target  95 . In this example, the cathode  90  and target  95  are shown as separate components that are adjacent. For example, the target  95  could be formed of ITO, and it could be bonded or otherwise coupled to the cathode  90 . Generally, the system should sputter the ITO target  95  but not the cathode  90  supporting the target  95 . In other embodiments, the cathode  90  and target  95  could be integrated as a single unit or be the rotatable type.  
         [0010]     The plasma in this sputtering system is formed from Argon gas  100 . The power supply (not shown) provides power to the cathode  90  to ionize the gas—thereby forming positively-charged ions  105  that are attracted to the negatively charged cathode  90  and target  95 . The power applied to the cathode  90  is steady-state DC in this implementation—although those of skill in the art could use other types of power.  
         [0011]     Once ions  105  are formed, the electrical attraction between the ions  105  and the negatively charged target  95  results in the target&#39;s bombardment and sputtering of the target material. The sputtered material is for the most part deposited on the substrate  110  as a film  115 . But some sputtered material redeposits on the cathode  90  and/or target  95  and forms nodules  85 .  
         [0012]     Nodules can cause significant problems—the most serious of which is arcing and debris. Positively charged ions that are attracted toward the negatively-charged target collect on a nodule and cause it to physically grow or be grown over. And as the ions build on the nodule, a potential develops between the nodule and the target surface and current flows along its surface. At some point, either through thermal stress or dielectric breakdown, an arc forms between the nodule and the target surface. This arc essentially causes the nodule to explode and blow particles toward the substrate creating debris. These particles can impact the growing film much as a meteor impacts the moon.  
         [0013]     Target particles that impact the film can cause three problems. First, they can disrupt the crystals growing on the film. In some instances, the impact can cause large scars and craters on the film surface. Second, the debris from the target can break loose existing film particles—leaving film shadows during the deposition process. These particles are then redeposited on other portions of the film. Finally, high temperature debris blown from the target can burn the growing film, especially if it has been grown on a polymer  
         [0014]     Even if film growth is not disrupted by debris, films may still not form properly. A significant problem plaguing film manufactures relates to micro-crystalline quality, nonuniform film growth, and stoichiometry. Some of these properties can be measured and the bulk resistance calculated, which is a measure of bulk-material conductivity. One method for solving this film-equality problem includes ion-assisted deposition. Ion-assisted deposition systems generally add a separate ion source to a sputtering system. The ions from this extra ion source help to settle or pack a film as it is growing. The ion source is distinct from the cathode and target, and it is very expensive. This expense has prevented ion-assisted deposition from being widely adopted.  
         [0015]     Accordingly, a system and method are needed to assist with film growth and to address the problems with present technology, including, but not limited to, the problems listed above.  
       SUMMARY OF THE INVENTION  
       [0016]     Exemplary embodiments of the present invention that are shown in the drawings are summarized below. These and other embodiments are more fully described in the Detailed Description section. It is to be understood, however, that there is no intention to limit the invention to the forms described in this Summary of the Invention or in the Detailed Description. One skilled in the art can recognize that there are numerous modifications, equivalents and alternative constructions that fall within the spirit and scope of the invention as expressed in the claims.  
         [0017]     One embodiment includes a sputtering system that includes a vacuum chamber; a substrate transport system configured to transport a substrate through the vacuum chamber; a cathode for supporting a sputtering target, the cathode at least partially inside the vacuum chamber; and a power supply configured to supply power to the cathode and the power supply configured to output a modulated power signal. Depending upon the implementation, the power supply can be configured to output an amplitude-modulated power signal; a frequency-modulated power signal; a pulse-width power signal; a pulse-position power signal; a pulse-amplitude modulated power signal; or any other type of modulated power or energy signal.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawing wherein:  
         [0019]      FIG. 1  illustrates an exemplary rotatable magnetron for sputtering;  
         [0020]      FIG. 2  illustrates a cross section of an exemplary planar magnetron and target;  
         [0021]      FIG. 3  illustrates a cross section of an exemplary planar magnetron and the corresponding magnetic field lines;  
         [0022]      FIG. 4  illustrates an exemplary race track formed in a planar target;  
         [0023]      FIG. 5  is a block diagram illustrating a nodule formed on a target;  
         [0024]      FIG. 6A  illustrates the arc prevention abilities of a pulsed DC power supply;  
         [0025]      FIG. 6B  illustrates the pulsed DC waveform corresponding to  FIG. 6A ;  
         [0026]      FIG. 7  illustrates the film properties that result from sputtering with steady-state DC voltage;  
         [0027]      FIG. 8A  illustrates three phases of the process for sputtering with a power signal that includes RF superimposed on pulsed DC;  
         [0028]      FIG. 8B  illustrates the pulsed-DC waveform corresponding to  FIG. 8A ;  
         [0029]      FIGS. 9A and 9B  illustrate the film resulting from superimposed RF with and without pulsed DC;  
         [0030]      FIG. 10  illustrates an exemplary chart linking bulk resistance to ion energy;  
         [0031]      FIGS. 11A and 11B  illustrate pulsed-DC measurements at a target and measurements of the resulting ion energy;  
         [0032]      FIG. 12  illustrates a power supply and sputtering system constructed in accordance with the principles of the present invention;  
         [0033]      FIG. 13  illustrates a power supply and sputtering system constructed in accordance with the principles of the present invention;  
         [0034]      FIG. 14  illustrates a power supply constructed in accordance with the principles of the present invention;  
         [0035]      FIG. 15  illustrates a power supply and sputtering system constructed in accordance with the principles of the present invention;  
         [0036]      FIG. 16A  illustrates a frequency-modulated power signal usable with one implementation of the present invention;  
         [0037]      FIG. 16B  illustrates the impact on ion density and ion energy of a frequency modulated power signal;  
         [0038]      FIG. 17A  illustrates an amplitude-modulated power signal usable with one implementation of the present invention;  
         [0039]      FIG. 17B  illustrates the impact on ion density and energy of an amplitude modulated signal  
         [0040]      FIG. 18A  illustrates a pulse-width modulated signal usable with one implementation of the present invention;  
         [0041]      FIG. 18B  illustrates the impact on ion production and energy of a modulated pulse-width signal;  
         [0042]      FIG. 19  illustrates a pulse-position modulated signal usable with one implementation of the present invention;  
         [0043]      FIG. 20  illustrates pulse-amplitude modulation using pulsed DC in accordance with one implementation of the present invention;  
         [0044]      FIG. 21  illustrates pulse-width modulation using pulsed DC in accordance with one implementation of the present invention; and  
         [0045]      FIG. 22  illustrates pulse-position modulation usable with one implementation of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0046]     Referring now to the drawings, where like or similar elements are designated with identical reference numerals throughout the several views, and referring in particular to  FIGS. 6A and 6B , they illustrates the arc prevention capabilities of a sputtering system that includes a pulsed-DC power supply. In this illustration, a pulsed-DC power supply (not shown) is used to provide a pulsed-DC signal to the cathode  90 .  
         [0047]      FIG. 6B  illustrates a pulsed-DC signal corresponding to  FIG. 6A . Notice that the stable voltage  120  is around negative 100 volts (−100). At periodic intervals, the power supply reverses the voltage for a short period. For example, the power supply can provide a 3 or 4 microsecond positive pulse  125  to the cathode  90 . This positive pulse  125  positively charges the target  95  and the cathode  90 .  FIG. 6A  reflects this charge with the “+” signs on the target  95 . Because the Argon ions  105  are also positively charged, they are repelled by the same positive charge on the target  195 , the other case that also occurs at the same time is that the electrons are drawn toward the cathode from the bulk plasma and recombine with the positive ions to neutralize them thus removing the charge build up. Thus, the reverse pulse  125  expels some fraction of the accumulated ions from the nodule  85 , the ions in the bulk plasma out toward the substrate are more likely to be sent toward the substrate during the reversal (positive voltage) providing ion bombardment to the growing film. The nodule will remain, but the ions on the nodule and the arc potential between the module  85  and target surface are greatly reduced.  
         [0048]     Still referring to  FIG. 6B , after the reverse pulse  125 , the power supply is returned to a normal operating state. That is, the power supply provides forward pulse  130  and then a stable voltage  135  of approximately negative 100 (−100) volts. The frequency and duration of the reverse pulse, the reverse-pulse voltage, and the stable voltage can vary among different target materials and among different quality targets of the same material. Further, these parameters could even vary for the same target over time. Those of skill in the art know how to select the correct parameters for the particular target that they are using.  
         [0049]      FIG. 7  illustrates the film properties resulting from sputtering with steady-state DC voltage. In this system, a steady-state DC voltage (approximately 300 V) is applied to the cathode  90  and target  95 . Ions  145  bombard the target  95 , and sputtered material  140  collects on the substrate  110  as a film  115 .  
         [0050]     This film  115 , however, is not uniform. It contains several gaps that negatively impact conductivity. These gaps indicate that the crystals are not forming properly and that the film will not be high quality.  
         [0051]     Imperfect crystals and gaps can be caused by poor deposition and/or by high energy particles impacting the film. For example, an unnecessarily high cathode voltage can provide too much energy to the sputtered atoms  140 , the reflected neutrals  150  or the generated ions  145 . These high energy particles can impact a growing film  15  and cause disruption. Accordingly, voltage control at the cathode  90  can be useful in producing high quality films.  
         [0052]     Referring now to  FIGS. 8A and 8B , they illustrate three stages of the process for sputtering with super imposed RF and the pulsed-DC waveform (RF not illustrated) corresponding to each stage. In stage  1 , a pulsed-DC voltage with a superimposed RF signal is applied to the cathode and target. The steady-state DC voltage is approximately 100 to 125 V. And the RF waveform is ˜+/−800 VAC to 2200 VAC @ 13.56 MHZ but not limited to this frequency. By using the superimposed RF or any other modulated signal, the cathode voltage can be reduced, and ion/deposition energy can be better controlled. Similarly, the energy of the sputtered material  140  can be better controlled through lower cathode voltages.  
         [0053]     During stage  1 , the target  95  is being bombarded by ions  145  and the target  95  is being sputtered. Notice the high density of sputtered material  140  in stage  1 . The sputtering rate is high, ion density is low, and electron  155  density is high.  
         [0054]     The power supply (not shown) reverses the DC signal applied to the cathode  90  during stage  2 . For example, the power supply pulses the voltage to between positive 50 and 250 volts. During stage  2 , the sputtering rate is low. Notice the lack of sputtered species  140  when compared to stage  1 .  
         [0055]     But the production of ions  145  (including negatively charged desirable oxygen ion) in stage  2  is high when compared to stage  1 . This increased number of ions will be available in stage  3  for bombarding the target. They are also available to gently impact the growing film  115  and pack or settle the sputtered material, thereby closing any film gasp. This process is represented by ions  145  on the film surface.  
         [0056]     Finally, the power supply returns the voltage to a steady state in stage  3 . This stage is similar to stage  1  and produces sputtered material  140  to continue film  115  growth.  
         [0057]     These cycles of sputtering, deposition, ion creation, and compaction create better quality films. Essentially, these cycles sputter a layer for the film, pack that layer, and then sputter another layer. The superimposition of RF with pulsed DC is one way to generate these cycles. Other modulated signals can produce a similar result.  
         [0058]      FIGS. 9A and 9B  illustrate the benefits of utilizing superimposed RF with and without pulsed DC. Good sputtering results can are achieved by applying a combination of RF and pulsed DC to the cathode  90 . An exemplary illustration of this type of film is shown in  FIG. 9B . In this system, the cathode  90  is powered by a pulsed-DC waveform and a superimposed RF signal or another modulated signal. The resulting film  115  is uniform and tightly packed.  
         [0059]      FIG. 9A  illustrates a system that produces a slightly less desirable film  115  than does the system of  9 B. But the system shown in  FIG. 9A  can still produce good films. For this system, the cathode  90  is powered by a steady state DC voltage and a superimposed RF signal. The resulting film may have several gaps between the sputtered atoms.  
         [0060]      FIG. 10  is an exemplary chart demonstrating the link between ion energy (EV) and film quality (bulk resistance). The particular values of this chart may vary according to the target material, but the general curve is illustrative. When ion energy is low (˜1 EV), the film quality could be lower (higher bulk resistance indicates a poorer quality film). And when ion energy is very high (˜1000 EV), the film quality is lower. But when ion energy is moderate, for example, in the 30 to 150 EV range and ion density controlled through the frequency, the film quality is higher. This chart demonstrates that film quality can be controlled by controlling ion energy during the sputtering process. Ions with too little energy do not cause collision cascading in film atoms. That is, ions with too little energy cannot help pack the film atoms together and eliminate gaps, (by the reduction of atomic shadowing). Ions with too much energy destroy forming film crystals and can actually increase the number of gaps and grain boundaries. One way to control ion energy is with power systems that include superimposed RF as described herein or other modulated power supplies.  
         [0061]      FIG. 11A  illustrates the output of a power source that uses pulsed-DC waveforms. The first waveform has a frequency of 350 kHz and a reverse-pulse duration of 1.1 μS. The second waveform has a frequency of 200 kHz and a reverse-pulse duration of 2.3 μS.  FIG. 11B  illustrates the ion energy corresponding to these two DC waveforms. Notice that the ion energy spikes to high levels, which can be destructive to crystals growing on the substrate. Power supplies that limit these spikes can be useful for producing higher quality films.  
         [0062]      FIG. 12  illustrates a power supply  160  and sputtering system  165  constructed in accordance with the principles of the present invention. This system includes a modulated power supply  160  that could include voltage spike suppression or clipping. For example, the power supply  160  could include a pulsed-DC power supply connected (“connected” also means “integrated with”) with an RF plasma power supply. It could also include a DC or AC power supply connected with a RF plasma power supply. And in other embodiments, it could include a pulsed-DC power supply, a DC power supply or an AC power supply connected with a programmable modulated-power source. This modulated power source could output a frequency modulated signal, an amplitude modulated signal, a pulse-width modulated signal, a pulse-position modulated signal, etc. (“Sputtering system” can also mean an integrated power supply and sputtering device.)  
         [0063]      FIG. 13  illustrates another embodiment of a power supply and sputtering system constructed in accordance with the principles of the present invention. This implementation includes an RF plasma supply  170  and an RF match network  175  connected to the sputtering system  165 . It also includes a pulsed-DC power supply  180  and an RF filter  185  connected to the sputtering system  165 . The signals from these two power sources are combined to drive the sputtering system  165 . Those of skill in the art understand how to connect and operate these components so the details are not addressed herein.  
         [0064]      FIG. 14  illustrates a particular power supply constructed in accordance with the principles of the present invention. Note that a “power supply” can include multiple power supplies acting together or a single unit capable of producing the desired waveform. And in this implementation, two distinct power supplies—an RF supply  190  and a pulsed-DC supply  200 —are coupled together to act as a single power source.  
         [0065]     ADVANCED ENERGY&#39;s model RFG3001 (3 KW) RF power supply provides the RF signal. ADVANCED ENERGY is located in Fort Collins, Colo. This power supply can be modified for internal or external arc suppression, and the output from this power supply is fed into a tuner  205  such as an ADVANCED ENERGY XZ90 tuner with DC arc detection and shutdown circuitry.  
         [0066]     The pulsed-DC power supply in this implementation is provided by PINNACLE and is a 20 KW supply with internal arc suppression. The output from this power supply is fed into a high-current RF filter box  210 . This is a standard air or water cooled Tee or Pie filter. And the output from the RF filter box is combined with the output from the tuner and provided to the sputtering system.  
         [0067]      FIG. 15  illustrates a power supply and sputtering system constructed in accordance with the principles of the present invention. This system is similar to the system illustrated in system in  FIG. 13  except that the power supply is an AC power supply  215  rather than a pulsed DC power.  
         [0068]      FIGS. 16-19  illustrate modulated AC power signals that can be used to control ion density and ion energy in a sputtering system—thereby controlling the film properties and quality. These power signals can be used to achieve the previously-described higher-quality films. Additionally, an RF signal can also be superimposed on any of these modulated power signals to further impact film growth.  
         [0069]     Through the variations in amplitude, frequency and pulse width or position, the ratio of ions to sputtered species, sputtering rate and energies of the ions and sputtered species can be controlled. Also important is the ability of some of these modulation methods to control the time for surface mobility on the substrates to occur.  
         [0070]      FIG. 16A  illustrates a frequency-modulated power signal. Frequency modulation (FM) is the encoding of information in either analog or digital form into a carrier wave by variation of its instantaneous frequency in accordance with an input signal. The left-most wave forms in  FIG. 16  illustrate an arbitrary signal and its impact on frequency.  
         [0071]      FIG. 16B  illustrates the impact on ion density and ion energy of a frequency modulated power signal. Due to a high pulsing frequency, high concentrations of ions are created. During the lower frequency regions, the sputtering rate is high, and during the higher frequency regions, the sputtering rate is low. The ratio of sputtered species to ions varies between the two differing sections. As the sputtering rate is decreased the ion concentration is increased and vice versa. This variation gives unique dynamics for improved film growth.  
         [0072]      FIG. 17A  illustrates an amplitude-modulated power signal. Amplitude modulation is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. That is the traditional explanation, but in the case of plasma sources, the voltage, current, and power level can be modulated by what ever percentage desired.  
         [0073]      FIG. 17B  illustrates the impact on ion density and energy caused by an amplitude modulated signal. The amplitude modulation varies the sputtering rate allowing new types of processes, and film growth.  
         [0074]      FIG. 18A  illustrates a pulse-width modulated signal. Pulse-width modulation is a way to represent data over a communications channel. With pulse-width modulation, the value of a sample of data is represented by the length of a pulse.  
         [0075]      FIG. 18B  illustrates the impact on ion production and energy of a modulated pulse-width signal. Due to a high pulsing frequency high concentrations of ions are created. During the large pulse width regions, the sputtering rate is high, and during the short pulse width regions, the sputtering rate is low. The ratio of sputtered species to ions varies between the two differing sections.  
         [0076]      FIG. 19  illustrates a pulse-position modulated signal. Pulse-position modulation is a form of signal modulation in which the message information is encoded in the temporal spacing between a sequence of signal pulses. As with the other modulated signals, the encoded information varies ion density and energy.  
         [0077]      FIGS. 20-22  illustrate modulated DC power signals that can be used to control ion density and ion energy in a sputtering system—thereby controlling the film properties and quality. The existing DC and composite DC sputtering processes are limited in some respects in their ability to effectively control film properties. DC and composite DC processes can and do exhibit power limitations as well as the inability to finely control the sputtering process energies. The use of pulsed DC power supplies to sputtering cathodes has benefited many film deposition processes and film properties, especially in conductive transparent films, by better controlling the sputtering energies. This control is achieved due to the fact that these power supplies inherently extinguish and re-ignite the plasma at user defined frequencies and intensities. At the beginning of each power pulse or plasma ignition from either of these systems, there is a broader distribution of electron energies producing ions and therefore, a greater percentage of the sputtered species and ions are generated. In DC and composite DC processes, because there is only an initial plasma ignition, the distribution stabilizes out to a lower average value of electron energy.  
         [0078]     With this in mind, it can be said that for pulsed power there are many beginnings and plasma ignitions to increase the average electron/ion energies to a much higher value thus giving this benefit to the process. By controlling the pulse duration and duty cycle you can control the electron/ion energies and the relative number of generated specific sputtered species and ions. Using pulsed power can give the operator effective control over more of the sputtered thin film properties.  
         [0079]     Beyond the typical pulsed DC power supplies—with their user defined frequencies and settings for forward and reversal timing—is a new area of output power to the sputtering cathodes and in general plasma sources. The new methods and systems provide power that has been modulated in one or more methods. For the most part, the modulation methods that work for AC power supplies also work for DC power supplies. Accordingly, these DC-system illustrations are similar to the previous AC illustrations.  
         [0080]      FIG. 20  illustrates pulse-amplitude modulation using pulsed DC.  
         [0081]      FIG. 21  illustrates pulse-width modulation using pulsed DC. With pulse-width modulation, the value of a sample of data is represented by the length of a pulse.  
         [0082]      FIG. 22  illustrates pulse-position modulation, which is a form of signal modulation in which the message information is encoded in the temporal spacing between a sequence of signal pulses.  
         [0083]     Just as with the AC examples, through the variations in amplitude, frequency and pulse width or position, the ratio of ions to sputtered species, sputtering rate and energies of the ions and sputtered species can be controlled. Also important is the ability of some of these modulation methods to control the time for surface mobility on the substrates to occur.  
         [0084]     In summary, embodiments of the present invention enable higher yields and higher quality thin films, and different films than possible with standard DC, AC, RF sputtering processes and most likely target materials. This is achieved, in one embodiment, through the ability to control sputtering energies, ion densities, rate and energies to promote improved film growth. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention as expressed in the claims.