Patent Publication Number: US-6905578-B1

Title: Apparatus and method for multi-target physical-vapor deposition of a multi-layer material structure

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates in general to the field of fabrication of semiconductor integrated circuits and data storage devices, and more particularly to an improved multi-target physical-vapor deposition apparatus and method of use for controlled deposition of a multi-layer material structure onto a substrate in an ultra clean vacuum processing environment. 
     BACKGROUND OF THE INVENTION 
     Several important applications, including spin-valve giant magneto-resistive (GMR) thin-film heads and semiconductor integrated circuits, use multi-layer material stacks to perform various electronic signal processing and data storage functions. For instance, semiconductor integrated circuit (IC) applications often include multi-layer interconnect structures comprised of multiple layers of glue/diffusion barrier, interconnect metal, and anti-reflection coating (ARC) films. For instance, some multi-level interconnect structures in semiconductor ICs employ a multi-layer conductive material stack comprising titanium, titanium nitride, aluminum (doped with copper), and a top titanium nitride ARC layer in each interconnect level. Another application that uses multi-layer material structures is magnetic data storage thin-film head devices. For instance, giant magneto-resistive (GMR) thin-film head and magnetic random access memory (MRAM) spin-valve tunnel junction devices use multi-layer material structures comprising stacks of conductive, magnetic, and/or insulating material layers as thin as 10 to 30 Å. 
     Conventional magnetic data storage devices use thin film heads comprised of inductive and/or magneto-resistive (MR) materials. MR heads enable higher magnetic storage densities compared to the storage densities of devices having inductive heads due to the higher read sensitivity and signal-to-noise ratio of MR senors. The MR heads read the stored information with direct magnetic flux sensing and are, thus, capable of static read-back without dependency on the relative motion (e.g., disk rotation speed) of the magnetic media compared to the head. The MR heads operate based on a resistance change of an MR element (permalloy) in response to the magnetic flux on the media. Both the inductive and MR thin-film heads employ inductive writer elements. 
     Industry transition from inductive heads to MR heads for magnetic data storage systems has allowed rapid technology evolution in terms of maximum storage density (described in Gbits/in 2  and system storage capacities. Industry has increased storage density of magnetic is storage systems at a historical rate of 30% per year and a current annual rate of 60%. Leading edge state-of-the-art rigid disk storage media now have storage densities on the order of 2 to 5 Gbits/in 2  (gigabits per square inch), with industry projecting storage densities approaching 10 Gbits/in 2  by the turn of the century. As the recording densities transition from 2 Gbits/in 2  towards 5 Gbits/in 2 , industry will have to replace the MR head technology with more sensitive devices, such as spin-valve GMR heads. Eventually, to maintain present trends toward improved storage capacities, industry may transition form GMR materials to colossal magneto-resistive (CMR) materials, which could support storage densities approaching 100 Gbits/in 2 . 
     In 1987, the giant magneto-resistive or GMR effect was discovered. GMR materials, usually consisting of at least two ferromagnetic nanostructure entities separated by a nonmagnetic spacer, display a change of resistance upon the application of a magnetic field. GMR materials have a larger relative resistance change and have increased field sensitivity as compared against traditional anisotropic magneto-resistive or MR materials, such as Ni 80 Fe 20  films. The improved relative resistance change and field sensitivity of GMR materials and related magnetic sensing elements allow the production of sensors having greater sensitivity and signal-to-noise ratio than conventional sensors. Thus, for instance, data storage systems using GMR read sensors can store greater amounts of data in smaller disk areas as compared to conventional data storage devices. However, material stacks for fabricating GMR sensors generally use 6 to 8 layers of 4 to 6 different materials, as compared to the MR material stacks, which usually have only 3 layers of materials such as in permalloy layers with Soft Adjacent Layers (SAL). Thus, creating material stacks for GMR read sensors generally required more processing steps, including more complicated equipment and fabrication techniques for high-yield manufacturing of high-performance GMR thin-film heads. 
     In order to meet its goals for improved storage density, industry will likely turn to spin-valve GMR thin-film heads. Spin-valve GMR heads are comprised of multi-layer depositions of 10 to 100 angstrom thick material films having precise thickness and microstructure control as well as extremely cohesive interface control at each interface of a multi-layer spin-valve GMR stack. Each spin-valve GMR stack must have good crystalinity in conjunction with abrupt and smooth material interfaces with minimal interface mixing to ensure proper GMR response and to establish excellent thermal stability. For instance,  FIG. 1  depicts one possible spin-valve GMR configuration. The precision required for spin-valve stack deposition can be understood by comparing the 1.5 nanometer thick layer of cobalt in  FIG. 1  against a typical atomic radius of 0.2 nanometers (corresponding to approximately 7 atomic layers). Essentially, GMR stacks may require controlled deposition of metallic multilayers which comprise ultrathin films as thin as 5 to 10 atomic nanolayers. 
     Another application for GMR materials is magnetic random access memories (“MRAM”), which are monolithic silicon-based nonvolatile memory devices presently based on a hysteretic effect in magneto-resistive or MR materials. MRAM devices are typically used in aerospace and military applications due to their excellent nonvolatile memory bit retention and radiation hardness behavior. Moreover, the MRAM devices can be easily integrated with silicon integrated circuits for embedded memory applications. The implementation of GMR materials, such as spin-dependent tunnel junctions, could improve the electrical performance of MRAM devices to make MRAM devices competitive with semiconductor DRAM and flash EPROM memory devices. However, the performance of MRAM memory depends on precise control of layer thickness values and the microstructures of various thin films in a GMR stack of thin metallic films. Thickness fluctuations and other interface or microstructural variations in thin metallic layers can cause variation in MRAM device performance. Similar difficulties can occur with periodic laminated multi-layer structures, such as laminated flux guide structures of iron, tantalum and silicon di-oxide. 
     The precision-controlled deposition of materials onto a substrate to create the multi-layer structures that can use the GMR effect is a difficult and time consuming process which requires high-performance vacuum deposition equipment, including plasma sputtering, ion-beam and evaporation processes. Although conventional physical-vapor deposition (PVD) technology can create GMR-capable structures, each layer of a structure must be carefully deposited in sequence in a time-consuming sequential series of depositions, a complicated process having a relatively slow throughput. Typically, such conventional PVD technology dynamically rotates a substrate at rapid speeds relative to a target in an attempt to evenly distribute the material being deposited onto the substrate. However, dynamic deposition requires a relatively large process chamber relative to the size of the target and the size of the substrate in order to allow rotation of the substrate. The PVD systems with dynamic rotation also complicate integration of advanced chucks and/or magnetic orientation devices for substrate processing applications. Further, dynamic deposition is inefficient because the target deposits material onto the substrate only when the rotation of the substrate aligns it partially or fully with the target. Material deposited from the target during non-alignment periods is wasted. Also, precise control of layer thickness and interface characteristics cannot be ensured with dynamic deposition, particularly when targets are changed after each dynamic deposition process or substrates are moved is to modules with new targets, thus, allowing impurities to be introduced between deposition layers. Such impurities frequently cause material structures to fail. 
     SUMMARY OF THE INVENTION 
     Therefore, a need has arisen for an apparatus and method which can precisely and controllably deposit multi-layer stacks of materials comprising conductive, magnetic, and insulating layers with precision thickness control, excellent uniformity, and coherent ultraclean interfaces. 
     A further need exists for an apparatus and method for depositing multilayer stacks of metallic, magnetic, and/or insulating materials in an efficient manner with an economic fabrication throughput for volume production applications. 
     A further need exists for an apparatus and method for depositing multilayer stacks of metallic, magnetic, and/or insulating materials without introducing impurities or contaminants to the layers and at the material stack interfaces by minimizing the presence of contaminants during a deposition process, and by minimizing the duration of substrate exposure to contamination sources during processing. 
     A further need exists for an apparatus and method that allows real-time monitoring during a multi-step deposition process to directly control multilayer stack film thickness values as well as microstructural and interface/surface properties during the deposition process. 
     In accordance with the present invention, an apparatus and method for depositing multiple layers of thin conductive, insulating, and/or magnetic films is provided that substantially eliminates or reduces disadvantages and problems associated with previously developed deposition systems and processes (such as the prior art plasma sputtering and ion beam deposition systems). Plural targets sequentially deposit material onto a substrate. The targets and substrate are disposed within the same vacuum chamber with ultraclean vacuum base pressure. Each target can comprise a material associated with one layer or several layers of a desired multi-layer structure. The targets can sequentially deposit materials according to a predetermined sequence corresponding to the multi-layer structure, such as a sequence that will create a multi-layer structure for spin-valve GMR thin-film heads or tunneling-junction MRAM devices. A substrate support can align the substrate with the targets in a predetermined sequence. Upon alignment with a target, a power source or process energy source associated with the targets initiates physical-vapor deposition of the material onto the substrate for a duration determined and controlled by a process timer or by a real-time in-situ sensor. 
     More specifically, in one embodiment, the substrate support is sequentially aligned with each of plural targets by an indexing mechanism operating on a substrate chuck assembly. For instance, the targets can be arranged in a circular configuration within a target plane (e.g., vacuum chamber lid) in the vacuum chamber, and an indexing chuck disposed in the vacuum chamber can rotate the substrate-chuck or support mechanism to each target (for instance, to align the central axes of the target and the substrate), the rotation occurring in a substrate plane that is preferably substantially parallel to the target plane. After the substrate aligns with each target, a power source or process energy source (such as DC magnetron, RF magnetron, or RF diode, or a pulsed magnetron energy source) associated with the targets and the substrate can deposit material from each target to the substrate by using preferably static physical-vapor deposition. Via an indexing operation, the indexing chuck can move the substrate to various target positions after a deposition time expires for each respective target, the process or deposition time corresponding to the precise thickness of the layer being deposited and other deposition process parameters. The sequential indexing mechanism cooperates with the targets to align the substrate under each target according to the predetermined order of materials in the multi-layer structure or stack. The indexing mechanism can include a sensing device to ensure proper alignment of the substrate below each respective target (for instance, using a home position sensor on the chuck indexing drive mechanism). 
     In another embodiment of the present invention, plural targets are arranged along the top lid of a physical-vapor deposition (PVD) vacuum chamber to sputter down onto the substrate. A substrate wafer is placed on the substrate support (for instance, a processing chuck) of an indexing chuck to face up at the targets. A substrate can be inserted into the vacuum process chamber through an access valve between the vacuum process chamber and a vacuum handling chamber. The access valve can be closed and the vacuum chamber evacuated with a vacuum pump such as a cryo pump and a water pump to achieve a very low base pressure and to reduce the contaminants present during the physical-vapor deposition sputtering process. The chuck can then align the wafer underneath a first PVD target comprised of a first material. A stepper motor associated with the chuck drive or indexing mechanism can provide precise alignment of the wafer and the target. A DC or RF power source (or alternatively, a pulsed DC or pulsed RF source) can apply either continuous wave or pulsed electrical energy within the vacuum or low-pressure gas medium between the target and the substrate to perform physical-vapor deposition on the substrate using DC magnetron or RF magnetron or RF diode physical-vapor deposition techniques. Upon completion of deposition of the first material by the first target, the chuck indexing drive mechanism can move the indexing chuck to align with a second desired target comprised of a second material according to the predetermined sequence corresponding to the multi-layer structure. The chuck can move the substrate between the first and second or other targets until the desired multi-layer structure has been deposited wherein all layers are deposited in the predetermined sequence, within a single vacuum processing chamber. It is also possible to place another type of processing energy source (e.g., a high-density inductively-coupled plasma or ICP source for soft plasma cleaning applications) in place of any of the process positions (or target positions) within the multi-station indexing-chuck process. 
     In another embodiment of the present invention, a shutter mechanism interposed between a target and the substrate can enhance the processing flexibility and the precision of the physical-vapor deposition process by enabling in-situ precleaning of a target or a substrate. The shutter mechanism comprises an electrically or pneumatically operated shutter, which can be a stainless steel or a titanium metal plate, that is light weight and thin enough to be interposed between the target and the chuck. Power applied to the target can initiate and stabilize a sputtering process (for instance, for initial target cleaning and burn-in), after which the shutter plate can be removed from between the target and the chuck to allow precise control of the sputtering process and deposited film thickness, including the length of time deposition occurs. After a predetermined time corresponding to a desired deposition thickness has elapsed (or when a real-time in-situ thickness sensor determines the process end-point time), the shutter plate can again be reinserted between the target and the substrate to terminate the sputtering process. In one embodiment, the shutter plate cooperates with a rotating shield to reduce contamination during the sputtering process. 
     In another embodiment, electrical chopping can replace the shutter for controlling deposition time intervals. A plasma filament can ignite plasma when the target is aligned with the substrate. The instantaneous ignition of the plasma over the substrate is accomplished through a localized discharge which can provide an evenly distributed sputtered material layer onto the substrate. Power can be distributed to the target in pulses of varying length and intensity to provide time for atoms to diffuse over the deposition surface (pulsed deposition). 
     In another embodiment, the deposition process can be monitored and controlled on a real-time or post-deposition basis by using associated real-time in-situ and in-line in-vacuo sensors and closed loop controllers. Vacuum-integrated sensors and related controllers can cooperate with the indexing mechanism to provide greatly improved deposition control for a wide range of material thickness values. Sensors can be located within or associated with the vacuum chamber for real-time in-situ measurements, or in a dedicated vacuum metrology module attached to the vacuum chamber for pre-process and post-process in-line measurements. Sensors can monitor substrate, process or equipment state parameters to provide optimal material layer thickness, uniformity, microstructure and/or interface control. For instance, sensors can measure the wafer-state parameters such as the thickness of individual films (e.g., ellipsometry), the sheet resistance of individuals films and stacks, and the composition and thickness of individual films and stacks (e.g., x-ray fluorescence), as well as equipment and process considerations such as plasma source current and voltage, optical emissions for estimating instantaneous deposition rates, vacuum pressure measurements, wafer temperature measurements, as well as magnetic flux uniformity and skew on the chuck surface. These measurements can support closed loop monitoring and control of the equipment and process states to achieve predetermined process state and/or substrate state parameters. 
     The present invention provides important technical advantages by allowing precise production of multi-layer material structures such as spin-valve GMR and MRAM material systems. One important technical advantage is the use of the indexing chuck to allow independent and rapid movement of a substrate among plural targets located in the same vacuum processing environment. Multiple layers of materials can be deposited on a substrate in a single vacuum chamber with ultraclean vacuum base pressure, thus, limiting the contaminants which could otherwise be introduced by changing targets during the deposition process, or by transporting the substrate to multiple vacuum processing chambers. 
     Another technical advantage of the present invention is precise control over film thickness for any of the films in a multi-layer stack which allows deposition of thin layers to fabricate various high-performance device structures including spin-valve GMR, tunneling MRAM, and semiconductor interconnect material systems. The shutter mechanism can provide precise control of stabilized deposition time for each PVD target resulting in improved uniformity for each deposition layer. Moreover, it allows effective in-situ cleaning of the substrate and/or the PVD targets. 
     Another important technical advantage is provided by the electrical chopping process energy source which supports deposition of multiple layers with minimal moving parts. Further, by altering the pulse intensity and frequency, improved diffusion of target atoms can be accomplished over the substrate surface. 
     Another important technical advantage of the present invention is provided by both in-situ and in-vacuo pre- and post-deposition measurements of material layers and process/equipment parameters to allow precision control of process and equipment parameters for achieving precise layer characteristics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein: 
         FIG. 1  depicts one embodiment of a spin-valve material structure for producing GMR material effects; 
         FIG. 2  depicts a side view of a multi-target physical-vapor deposition apparatus and indexing chuck; 
         FIG. 3  depicts a top view of an indexing chuck having plural substrate supports; 
         FIG. 4  depicts a top view of a shuttering mechanism in conjunction with an indexing chuck; 
         FIG. 5  depicts a top view of a shuttering mechanism for plural targets in conjunction with an indexing chuck having plural substrate supports; 
         FIG. 6  depicts a block diagram of a sensor-based control methodology using in-situ measurements during physical-vapor deposition processes; and 
         FIG. 7  depicts a top view of a vacuum metrology module associated with a cluster tool and deposition chamber. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention are illustrated in the figures, like numerals being used to refer to like and corresponding parts of the various drawings. 
     Physical-vapor deposition or PVD is a well-known technique for depositing thin layers of materials onto a substrate for a variety of semiconductor, data storage, optoelectronics, and other applications. Plasma sputtering or plasma PVD is the most widely accepted PVD technique for deposition of various material layers. A power source, such as a DC magnetron or RF magnetron or an RF diode power source, creates power differential between a target assembly comprising the cathode and an anode ring in order to produce a plasma medium between the target and the substrate within a controlled vacuum environment. This electrical power creates a gas discharge plasma and produces ion bombardment on the target surface (e.g., via argon ions), resulting in sputtering of the target material and sputter deposition of the target material onto the substrate. CVC sells physical-vapor deposition tools, such as the CONNEXION® cluster tool, which can support vacuum-integrated physical-vapor deposition of magnetic and non-magnetic as well as electrically conductive and insulating films. The CVC cluster platform can deposit multiple layers of different materials by attaching a physical-vapor deposition module to the cluster platform for each material to be deposited, and then cycling the substrate through each module. However, each process module has a cost associated with it, making the deposition of multiple different material layers expensive using this approach. Also, the process of transferring wafers to and from each module can slow production (due to the wafer handling overhead time) and introduce impurities by repeated exposure of the substrates to the wafer handling vacuum chamber. 
     Referring now to  FIG. 2 , a side view of a multi-target physical-vapor deposition apparatus  10  according to the present invention is depicted to include an indexing chuck mechanism  11  for enabling in-situ deposition of multi-layer material structures, from multiple targets onto a substrate in a single vacuum processing module. Each target essentially forms a process station for depositing material from the target to a substrate to form a layer of the material on the device side of the substrate. Thus, plural process stations are formed within a single vacuum chamber. 
     Multi-target physical-vapor deposition (PVD) apparatus  10  has a vacuum process chamber  12  with plural PVD targets  14  disposed in a target plane along the top chamber lid  15  of vacuum chamber  12 . The combination of a cryo pump  16  and water pump  18  evacuate vacuum chamber  12  and remove impurities such as water in order to establish a very low vacuum base pressure. The cryo pump and water pump can reduce pressure within vacuum chamber  12  to ultraclean base pressure levels typically required for advanced physical-vapor deposition, such as in the 10 −9  Torr base pressure range. This very low base pressure enables ultraclean deposition of pure and controlled multi-layer material stacks by PVD. In an alternative embodiment, a turbo-molecular pump can be used to evacuate the vacuum chamber. 
     Indexing mechanism  11  includes an indexing chuck and clamp assembly  20  disposed in the vacuum process chamber  12  to operationally align a substrate with each target  14  or PVD processing, and a means for moving indexing chuck  20  (e.g., a rotational indexing drive mechanism) to align with each of plural targets  14 . Indexing chuck and clamp assembly  20  can use a mechanical or electrostatic clamp. Indexing chuck assembly  20  is supported by a central shaft  22  and a drive motor  24 , the shaft and motor preferably located along a central axis of vacuum process chamber  12  to rotate co-axial with the central axis of the vacuum process chamber  12 . Motor  24  can vary the target-to-substrate spacing by lifting the indexing chuck  20  towards targets  14  by lowering the indexing chuck  20  away from targets  14  to adjust the deposition distance between any selected target  14  and a substrate. When motor  24  lowers indexing chuck  20  as is depicted in  FIG. 2 , a substrate can be inserted through chamber access valve  26  onto indexing chuck  20 . Motor  24  can then raise the chuck and substrate to engage a clamp (if needed) and control the distance between the substrate and targets  14  to allow optimization of physical-vapor deposition process parameters (e.g., process uniformity, repeatability, etc.). 
     Indexing chuck assembly  20  rotates (from one angular position to another angular position)as a radial arm in a substrate plane that is substantially parallel to the target plane, the indexing rotation occurring within vacuum process chamber  12  about the central axis with, indexing chuck  20  supported by central shaft  22 . Although  FIG. 2  depicts targets disposed along the top of the vacuum chamber for deposition on a substrate having the device side facing up, in alternative embodiments, the targets could be disposed below the substrate plane to support depostion with the substrate having the device side facing down. Alternatively, the target and substrate planes can be oriented to allow deposition in various vertical and horizontal orientations. Indexing chuck assembly  20  has a balancing arm  28  coupled to central shaft  22  at one end and coupled to substrate support  30  at its other end. Substrate support  30  accepts a substrate through chamber access valve  26 . A clamp  32  secures a substrate by holding the substrate around its periphery against substrate support  30 . A magnet assembly  34  (such as an electromagnet) can be associated with indexing chuck  20 , the magnet assembly  34  providing a magnetic field for in-situ magnetic orientation of the layers during physical-vapor deposition of various material layers. In one alternative embodiment, a heating element can be incorporated with the indexing chuck to provide heating to the substrate during processing. In another alternative embodiment, a cooling device, such as a passage for pumping cooled water, can be incorporated with the indexing chuck to provide cooling to the substrate during processing. 
     Indexing chuck  20  can rotate about the vertical axis of its central shaft to move substrate support  30  from a first target to a second target  14  located on a multi-target lid assembly. A stepper motor  24  can rotate indexing chuck  20  to align the central axis of substrate with the central axis of any of the targets selected for the next process step. Another stepper motor  36  is used to rotate a shutter plate in order to block or expose any target  14  for the purposes of target cleaning, substrate cleaning, or physical-vapor deposition. Stepper motors  24  and  36  can be controlled separately for independent control of the angular positions of the indexing chuck  20  and indexing shutter  38 . In one embodiment, stepper motor  36  is a Parker-Hanifin stepping motor having sixteen user selectable resolutions of up to 50,800 steps per revolution and a rotation speed of 3,000 rpm. A sensing mechanism associated with stepper motor  36  initiates the stepper motor at a zero rotation (e.g., home) position. From the zero rotation (home) position, stepper motor  24  can precisely rotate indexing chuck  20  to align with a predetermined selected target  14 . Stepper motor  24  counts the number of steps which it rotates until it reaches a number of steps associated with the angular position of the predetermined target  14  relative to the zero rotation or home position. This relatively simple design allows precise substrate and target alignment without requiring a real-time feedback loop for the rotation of indexing chuck  20 . The positions of the targets  14  along the lid of vacuum chamber  12  can be computed and associated with an appropriate number of motor steps to allow a control system such as a personal computer associated with stepper motor  24  to align substrate support  30  with various targets sequentially according to a predetermined process sequence. In alternative embodiments, plural indexing chucks can be disposed in the vacuum chamber by plural arms, or by a table supporting all of the chucks. 
     In operation, physical-vapor deposition apparatus  10  accepts a substrate through chamber access valve  26  and secures the substrate against substrate support  30  by engaging clamp  32  against substrate and substrate support  30 . Motor  24  lifts central shaft  22  to press indexing chuck  20  upward against clamp  32  and to adjust the substrate-to-target spacing. Stepper motor  24  then rotates indexing chuck  20  to align substrate support  30  under a first predetermined target  14  (or under another process energy source such as an inductively-coupled plasma or cleaning source). A power source, such as DC (or RF) magnetron power source  40  or RF diode power source  42  can then provide power to target  14  to deposit material from target  14  onto the substrate with sputter down physical-vapor deposition. If desired, the system configuration can be inverted to perform sputter up physical-vapor deposition (by inverting the entire module upside down). The deposition is preferably static deposition, meaning that the substrate does not move relative to the target during deposition of material from the target to the substrate (and that the central axes of the substrate and the target are-preferably aligned). Stepper motor  24  can then rotate indexing chuck  20  to align substrate support  30  with a second target, and thereafter with subsequent targets, according to a predetermined sequence of process steps until the desired is multi-layered material structure has been fabricated. After positioning the indexing chuck  20  and the substrate under each process station (e.g., a PVD target), stepper motor  36  can be used to rotate the shutter plate  38  for in-situ cleaning of the target  14  and/or the substrate. During a material layer deposition, the angular coordinate of the indexing shutter  38  is set such that the target is fully exposed to allow material deposition onto the substrate. 
     Process considerations and the predetermined  25  sequence for depositing a desired multi-layer material structure can be determined by complex control systems or by a simple process and machine control computer associated with physical-vapor deposition apparatus  10 . As an example of how the control system could operate, the time-dependent sequential multi-step operation of indexing mechanism  11  to support the deposition of the multi-layer structure depicted in  FIG. 1  can provide an illustration of the type of process control sequence and equipment needed to deposit a desired material structure. 
     First, five targets corresponding to the five materials of the spin valve GMR structure of  FIG. 1  are coupled to lid  11  at predetermined positions. For instance, any of the PVD targets comprising tantalum (Ta), iron manganese (FeMn), cobalt (Co), copper (Cu), and nickel iron (NiFe) can be mounted onto the-lid  11  in a substantially circular pattern, the circle preferably having an equal-distance radius from each target to the central axis of vacuum chamber  12 . In alternative embodiments, any number of targets can be used, although present structures generally require at least two targets but not more than twelve targets. The circular pattern of the targets allows each target to align with the substrate on substrate support  30  when indexing chuck  20  is rotated about the central axis which is perpendicular to the substrate plane. Each target  14  has an associated power supply to support physical-vapor deposition. Although mounting the targets onto the vacuum chamber lid will support sputter-down physical-vapor deposition, sputter-up or other configurations of deposition processes can be supported in alternate embodiments by disposing the targets in other locations in the vacuum chamber. Further, each target can have its own associated power supply, or alternatively, the targets can share one or more associated DC or RF power supplies. 
     In order to fabricate the multi-layer stack of  FIG. 1 , indexing chuck  20  is rotated by stepper motor  36  to align the substrate with the tantalum target position. A controller, such as a process control computer associated with apparatus  10 , can direct stepper motor  36  to rotate a predetermined number of steps in conjunction with a home sensor to find the angular coordinate corresponding to the position of the tantalum target. The controller can also set equipment state parameters (e.g., DC magnetron power, pressure, and deposition time) to deposit 3.5 nanometers of tantalum on the substrate. For instance, the controller can have up/down actuator and motor assembly  24  lift chuck  20  to achieve a predetermined deposition distance between the substrate and the tantalum target in order to establish the optimal deposition uniformity and material properties. The controller can also operate cryo pump  16  and water pump  18  to evacuate vacuum chamber  12  to a predetermined pressure and to remove contaminants such as water vapor down to very low base pressures (e.g., ≦5×10 −9  Torr). Although stepper motor  24  rotates indexing chuck  20  to position a substrate underneath any one of the plurality of targets  14 , in other embodiments the targets could be moved relative to the indexing chuck by instead moving the targets, the chuck, or by moving both the targets and the chuck. The preferred embodiment of this invention, however, utilizes stationary targets (mounted on the vacuum chamber lid) in conjunction with an indexing chuck assembly. 
     After the tantalum target and substrate are aligned, the controller can initiate physical-vapor deposition of Ta by applying power (e.g., DC electrical power) from the power source to the tantalum target for a predetermined deposition time and at a predetermined power level. The controller can cease deposition by eliminating the power applied to the target once the thickness of the tantalum has reached the desired 3.5 nanometers. If necessary, a target pre-clean can be performed prior to PVD of Ta by first closing the shutter and applying the electrical power to Ta target and then performing deposition of Ta by opening the shutter. 
     In one embodiment, the controller can vary the power over time, for instance by pulsing (e.g., pulsed DC power), to allow the material to diffuse over the substrate. For instance, the controller can provide power with electrical chopping by switching the power source on and off. As an example, while 400 watts of power (average electrical power) could deposit a two nanometer thick film in a single one second pulse, the same material layer thickness may also be deposited using 10 sequential cycles of 10% duty-cycle pulses, each having a 400 watt (peak power) 100 millisecond pulse followed by 900 milliseconds of no power. Electrical chopping can combine the advantages associated with precision controlled low film growth rates, such as improved surface diffusion of sputtered material (and improved material layer microstructure control), with the desirable properties of a high power deposition environment, such as improved plasma density and enhanced plasma stability. In essence, electrical chopping mimics the effects of dynamic deposition by changing the plasma directed at the substrate over time. Filaments or other electron sources proximate the target can aid the initiation of deposition and stabilization of plasma by providing an electric charge (e.g., electrons) to the plasma associated with the target. Other energy sources such as optical sources may be used instead of electron sources to accomplish the same result. 
     Once the tantalum layer deposition is complete, stepper motor  24  can rotate indexing chuck  20  to align the substrate with the position of the nickel iron (NiFe) target. The controller can again adjust the equipment state parameters (e.g., DC magnetron power, substrate temperature, pressure, etc.) and apply power to deposit a 4 nanometer thick layer of nickel iron (e.g., Ni 80%, Fe 20%) onto the substrate. Again, if desired, a sputter pre-clean process can be performed on the NiFe target (by first closing the indexing shutter) in order to clean the target prior to the PVD process. Stepper motor  24  can continue to rotate indexing chuck  20  to align with each subsequent target according to the sequence of the multi-layer structure. Note that the tantalum and cobalt targets will each make two deposits according to the predetermined sequence (see FIG.  1 ), meaning that indexing chuck  20  will have to align the substrate with each of these targets twice during the multi-step spin-valve GMR process sequence. Alternatively, two targets each of tantalum and cobalt could be used. Once the multi-layer structure is complete, the substrate can be removed from vacuum chamber  12  through access valve  26  and replaced with a new substrate that will be processed for deposition of a similar multi-layer spin-valve GMR structure (or any other multi-layer material structure). 
     Referring now to  FIG. 3 , one embodiment of an indexing chuck  20  is depicted having plural substrate supports  30 . Each substrate support  30  can securely hold one substrate as described above (or a substrate carrier comprising a plurality of substrates). The use of plural substrate supports in the same vacuum chamber can enhance processing throughput by allowing simultaneous processing of multiple substrates and deposition of plural multi-layer structures in the same vacuum environment. The deposition on plural substrates can be accomplished by sequentially depositing individual layers or complete structures on a first and then a second substrate. Alternatively, simultaneous deposition of the same material from plural targets or of different materials from plural targets to each substrate can be accomplished. In a PVD chamber with N target positions, we may use indexing chuck designs with either a single chuck arm or multiple (2−N) chuck arms. 
     For instance, one relatively simple multi-layer laminated structure used in thin-film head devices can be used to illustrate the operation of physical-vapor deposition apparatus  10  equipped with plural substrate supports (i.e., a plurality of chuck arms). Multiple layers of silicon dioxide (SiO 2 ) and iron tantalum nitride (FeTaN) alloy deposited on a substrate in an alternating sequence can form a laminated magnetic multi-layer structure suitable as low-loss magnetic flux guides and inductive cores. First and second target positions a comprised of silicon dioxide, as well as third and fourth target positions comprised of an iron tantalum nitride alloy can be disposed in a circular configuration on the lid of the vacuum chamber. The configuration can correspond to the position of each substrate support so that an indexing chuck  20  with two substrate support arms (spaced apart by 180°) will align both substrates either with the first and second targets simultaneously or with the third and fourth targets simultaneously. For instance, the targets can each be arranged in 90 degree increments (assuming four target positions), while the substrate support chuck arms can be arranged at 180° from one another (assuming two arms). 
     A personal computer associated with physical-vapor deposition apparatus  10  can provide instructions to stepper motor  24  to rotate indexing chuck  20  from the first or second target to the third or fourth target according to the predetermined sequence, with a power source depositing the silicon dioxide or iron tantalum nitride alloy when substrate supports  30  align with the appropriate targets. The indexing chuck can repeatedly align the substrate supports to allow the deposition of many (e.g., fifty or more) layers of each material. In this way, physical-vapor deposition apparatus  10  can advantageously deposit plural materials from plural targets in a single vacuum chamber module, thus increasing throughput and decreasing the likelihood of introducing impurities to the deposited structure. 
     In alternative embodiments, the number and composition of targets can be altered to allow “continuous flow” or “assembly-line” processing of substrates. For example, a multi-layer structure having layers in a sequence of T 1 , T 2 , T 3  and T 4  can be deposited on each of four substrates by using an indexing chuck with four substrate holders (four chuck arms spaced apart by 90° from one another). Four targets T 1 , T 2 , T 3  and T 4 , and the four substrate holders (four chuck arms) can be arranged in matching circular configurations, each of the targets and each of the holders divided into 90 degree intervals. A first substrate S 1  on a first support can be aligned with target T 1  for deposition of the first layer in the sequence. The indexing chuck can then be rotated to align S 1  with T 2 , and another substrate, S 2 , can be added on the second substrate support arm aligned with T 1  for simultaneous deposition of T 2  onto S 1  and T 1  onto S 2 . The process repeats to allow simultaneous deposition of T 3  onto S 1 , T 2  onto S 2 , and T 1  onto a new substrate S 3  supported on the third support (third chuck arm). The next repetition completes the deposition of the predetermined sequence on S 1  by simultaneously depositing T 4  onto S 1 , T 3  onto S 2 , T 2  onto S 3 , and T 1  onto a new substrate S 4  supported on the fourth support. S 1  can then be removed and replaced with a new substrate to allow continued (continuous flow) production of the desired multi-layer structure as described above. 
     Referring now to  FIG. 4 , a shuttering mechanism is depicted which can enhance cleanliness of the target materials, control of film thickness and the quality of interface cohesion between deposited films. Shutter assembly  44  is disposed in vacuum chamber  12  to interpose between indexing chuck  20  and the targets  14 . Shutter assembly  38  has a rotating shutter plate  46  coupled to a shutter indexing rotation stripper motor  36 , the shutter rotating in a shutter plane that is between and substantially parallel to the substrate plane and the target plane. Shield  46  has a hole or circular opening  50  which can allow physical-vapor deposition of a material from a selected target to a substrate  52  while blocking the access to the remaining targets. Shield hole  50  has a diameter which is somewhat larger than the diameter of an associated target (or its diameter may be larger than the diameter or diagonal dimension of the substrate and smaller than the target diameter). The shutter assembly has two primary purposes. One purpose is sputter cleaning of any of the targets by closing the shutter at the selected target location prior to opening the target and performing the PVD process. The second purpose is to align the shutter opening with any selected target to perform depositions while blocking the non-selected targets. 
     In operation, shield  46  is interposed between the target plane and the substrate plane with shield hole  50  aligned with substrate support  30  and the selected target during the deposition process. Shield  48  rotates with indexing chuck  20  to maintain a path for deposition of material from targets  14  to substrate  52  (except during target sputter clean when the shutter opening is not aligned with the selected target). When substrate  52 , shield hole  50 , and a selected target  14  are axially aligned, shutter assembly  38  can then rotate to block shield hole  50 , thus preventing deposition of material onto substrate  52 . Shutter assembly  38  can be rotated between this target-to-substrate blocking configuration and a target-to-substrate open view deposition configuration in which shutter opening  50  is aligned axially between the target and the substrate to allow deposition of material from the target to the substrate. An electric or pneumatic actuator (e.g., stepper motor  36 ) is associated with shutter assembly  38  for rapidly moving shutter plate  46  between the blocking (no deposition and/or target sputter cleaning mode) and deposition configurations. In one embodiment, shutter plate  46  is comprised of a thin titanium or stainless steel sheet (if necessary, reinforced with radial ribs) which is insulated from direct electrical contact with the target or the substrate (the shutter plate  46  is preferably grounded) so as to allow deposition from the target to the substrate (with the shutter opening aligned with the selected target and the substrate) as well as to allow cleaning of the target (by applying power to the target) and cleaning of the substrate (by applying power to the indexing chuck assembly  20 . The light weight of this stainless steel or titanium sheet enhances rapid actuation between the blocking and deposition configurations (typical target-to-target shutter indexing time is less than 5 seconds). 
     Shutter assembly  38  improves the control of the deposition of a material from a target to substrate  52 . For instance, power can be applied to the target to stabilize the plasma and initiate physical-vapor deposition to shutter  46  (in conjunction with target cleaning) while shutter  46  is in a blocking configuration for the selected target. This advantageously pre-cleans the target by depositing the external layer of material from the target to shutter  46 , and also allows stabilization of the deposition process by first stabilizing the plasma. Shutter  46  can then be rapidly actuated or indexed to,a deposition configuration (shutter opening  50  axially aligned with the target and the substrate) which allows the material from the target to be deposited onto substrate  52 . After a predetermined deposition time, shutter  46  can be actuated back (by index rotation) to a blocking configuration to terminate deposition of material onto substrate  52 , and then electrical power (either RF or DC power in pulsed or continuous mode) can be cut off from the target. In one alternative embodiment, shutter  46  can provide dynamic-mode mechanical chopping by opening and closing shutter  46  to control the duty cycle of the pulsed deposition process described above as an alternative to electrical chopping. Similar to electrical chopping, mechanical chopping (using the rotating shutters) mimics the effect of dynamic physical-vapor deposition without actually rotating the substrate relative to the target during deposition of the material from the target. A pulsed deposition (either wing pulsed DC/RF electrical power or by mechanical chopping wing shutter rotation) process can be used to obtain precision controlled reduced deposition rates for controlled deposition of very thin films. In another embodiment, shutter  46  can preclean a substrate rather than a target by applying an electrical bias (RP or DC) to the substrate chuck while closing the shutter. 
     Shutter  46  advantageously provides a capability for precise control over the deposition time associated with each target, thus eliminating the transient plasma start-up and stabilization effects. Further, the physical-vapor deposition plasma and related process can stabilize while shutter  46  is in a blocking configuration, thus allowing a stable plasma and sputtering flux from the target to develop before shutter  46  is actuated to its deposition configuration (i.e., shutter hole aligned with target and substrate). In addition, the stabilization of the PVD plasma and deposition process provide in conjunction with precision control of the active process time precise and abrupt interfaces between material layers. Thus, shutter mechanism  38  can be used to enable or support deposition of material structures for applications such as spin-value GMR and magnet RAM (MRAM) devices. 
     Referring now to  FIG. 5 , another embodiment of an alternative shutter assembly  54  is depicted. Shutter assembly  54  can support simultaneous or concurrent depositions from plural (e.g., two or more) targets associated with plural shield holes  60  in shield  58  (example shown in  FIG. 5  shows two shield holes in conjunction with a 2-arm indexing chuck and up to four targets). For instance, shutter assembly  54  can support the simultaneous or concurrent depositions of a multi-layer structure comprised of iron tantalum nitride (FeTan) and silicon dioxide (SiO 2 ) onto two separate substrates as is described above. Shutter assembly  54  simply rotates with the indexing drive mechanism and alternates between a blocking position and deposition position to precisely control depositions from the two different targets in order to fabricate a laminated FeTan/SiO 2  structure. 
     One significant advantage of the multi-target physical-vapor deposition apparatus  10  of this invention depicted herein over existing or prior art dynamic physical-vapor deposition systems is that the static multi-target indexing deposition used by the present invention allows the use of various in-situ sensors in the vacuum chamber to monitor the substrate or process states and to control the substrate and physical-vapor deposition process parameters. Referring now to  FIG. 6 , one embodiment of a monitoring and control system  100  is depicted. Monitoring and control system  100  relies upon in-situ sensors that can be located in or proximate the actual deposition vacuum chamber for real time, in-situ measurements of deposition parameters (including the substrate state, process state, and/or equipment state parameters), or in-vacuu sensors that can be located in a dedicated vacuum metrology module attached to a central wafer handler for in-vacuu pre/post-deposition measurements and run-by-run process control. The following table lists various useful in-situ process and equipment state sensors which can measure equipment or process or substrate state parameters directly in the vacuum chamber or through chamber viewports in support of monitoring and control system  100 . 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Sensor/Supplier 
                 Primary Application 
                 Secondary Application 
               
               
                   
               
             
            
               
                 B-H looper with 
                 H cc , H ch , H k , α 80  and B/ 
                 Use pickup coil as 
               
               
                 Helmholtz and pickup 
                 thickness of individual 
                 eddy current sensor to 
               
               
                 coils. Coils can be 
                 films. 
                 measure sheet resist- 
               
               
                 installed inside 
                 Low field B-H loop of 
                 ance. 
               
               
                 chamber to probe an 
                 spin valve GMR: 
                 Use Helmholtz coils to 
               
               
                 effective diameter of 
                 coercivities, coupling 
                 apply field on sub- 
               
               
                 3″. Chuck should have 
                 field, moments, etc. 
                 strate for MR and 
               
               
                 fixture to pick up, 
                   
                 Kerr-MO measure- 
               
               
                 rotate and put down 
                   
                 ments. 
               
               
                 wafer. 
               
               
                 Four point probe 
                 Sheet resistance of 
                 MR ratio of ferro- 
               
               
                 sensor. Probe head 
                 individual electrically 
                 magnetic films. 
               
               
                 can be mounted over 
                 conductive films and 
                 GMR ratio of spin 
               
               
                 wafer center and may 
                 stacks. 
                 valves. 
               
               
                 extend/retract away 
               
               
                 from wafer surface. 
               
               
                 Spectral ellipsometer 
                 Film thickness of 
                 Exploit Kerr-MO 
               
               
                 that can be installed 
                 individual films and 
                 effect by performing 
               
               
                 on optical ports to 
                 stacks. 
                 ellipsometry with 
               
               
                 measure a spot on the 
                   
                 applied external field. 
               
               
                 wafer. 
               
               
                 XRF sensor installed 
                 Composition and thick- 
               
               
                 on optical ports (with 
                 ness of individual films 
               
               
                 special windows). 
                 and stacks. 
               
               
                   
               
            
           
         
       
     
     The following table lists sensors which can be implemented in a metrology module associated with the physical-vapor deposition apparatus  10 . 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Sensor/Supplier 
                 Primary Application 
                 Secondary Application 
               
               
                   
               
             
            
               
                 Spectral ellipsometer 
                 Film thickness for 
                 Reflectance 
               
               
                 installed on optical 
                 individual films and 
                 (specular/non- 
               
               
                 ports to measure a 
                 stacks (as well as 
                 specular) measurement 
               
               
                 spot at the center of 
                 thickness uniformity 
                 of surface roughness. 
               
               
                 the wafer. 
                 profiles). 
                 Exploit Kerr-MO 
               
               
                   
                   
                 effect by performing 
               
               
                   
                   
                 ellipsometry with 
               
               
                   
                   
                 applied external 
               
               
                   
                   
                 field. 
               
               
                 I-V Probe 
                 Plasma source current 
                 Plasma diagnostics 
               
               
                   
                 and voltage 
               
               
                 Optical emission 
                 Estimation of 
                 Small signal power 
               
               
                 sensor in conjunction 
                 instantaneous 
                 perturbation to 
               
               
                 with current/voltage 
                 deposition rate 
                 estimate system gain 
               
               
                 probes. 
                 through indirect 
                 (detect drifts) and 
               
               
                   
                 measurement of plasma 
                 alter sputtering 
               
               
                   
                 density. 
                 power to maintain 
               
               
                   
                   
                 deposition rate. 
               
               
                 RGA 
                 Confirmation of 
                 Implementation of 
               
               
                   
                 partial pressures pre 
                 pump/purge/burn-in to 
               
               
                   
                 and post processing. 
                 stay within partial 
               
               
                   
                   
                 pressures limits. 
               
               
                 Acoustic thermometer 
                 Wafer temperature 
                 Correct for drifts in 
               
               
                 embedded in chuck. 
                 (including temperature 
                 wafer temperature 
               
               
                   
                 uniformity) 
                 from run to run. 
               
               
                 Magnetic flux/skew 
                 Magnetic flux and skew 
                 Equipment diagnostics 
               
               
                 sensor embedded in 
                 on chuck surface to 
               
               
                 chuck. 
                 detect buildup of 
               
               
                   
                 ferromagnetic and AFM 
               
               
                   
                 layers on wafer clamp 
               
               
                   
                 and increase in 
               
               
                   
                 magnetron stray field 
               
               
                   
                 as target erodes. 
               
               
                 Atomic absorption 
                 Flux of atomic species 
                 Estimate deposition 
               
               
                 sensor installed on 
                 in plasma. 
                 rate based on model 
               
               
                 optical port. 
                   
                 that includes effect 
               
               
                   
                   
                 of pressure and 
               
               
                   
                   
                 target to substrate 
               
               
                   
                   
                 spacing. 
               
               
                   
               
            
           
         
       
     
     Any one or a combination of the sensors in Table 1 or Table 2 can provide input to a control loop for the purpose of equipment/process/wafer state parameter control for optimizing a deposition process. The sensors and associated control for each sensor can be classified as related to a wafer state, which involves the properties of deposited films; a process state, which involves the plasma density, ion flux, ionization ratio and other process parameters; and equipment state, which varies the process state by changing equipment-related parameters such as vacuum chamber pressure, power settings, and substrate-to-target spacing. 
     Referring now to  FIG. 7  a top view of a cluster tool  134  and a vacuum metrology module  136  are depicted in association with physical vapor deposition apparatus  10  to support monitoring of process parameters with monitoring sensors as described in the above table. An optical port  130  can accept a sensor, such as a signal associated with a spectral ellipsometer, so that measurements can be made by a sensor associated with a second optical port  132 . Vacuum metrology module  136  can hold sensors to obtain in-vacu post process sensor readings. An associated control system  138  can accept sensor measurements to provided model-based process end-point detection or other control as described herein. 
     Monitoring and control device  100  depicted in  FIG. 6  can enhance physical-vapor deposition process control to provide high-quality multi-layer structures such as spin valve GMR material stacks. Monitoring and control device  100  can operate using one or more processors, such as personal computers, associated with vacuum chamber  12 . Equipment state  102 , process state  104 , and wafer state  106  depict the parameters associated with physical-vapor deposition. Physical-vapor deposition is initiated with an initial process recipe  108  which can be altered by feedback signals to create updated tuned process recipe  110 . The updated process recipe  110  establishes an equipment state  102  by providing equipment state settings such as vacuum chamber pressure settings, electrical power settings, substrate cooling or heating, and substrate-to-target spacing settings. Real-time equipment sensors  112  sense the equipment settings and provide the sensed equipment settings to real-time equipment controller  114 . Real-time equipment control loop  114  incorporates the output of the real time equipment sensors  112  to provide corrections for the equipment state needed to ensure that the equipment state achieves the parameters set forth in the updated process recipe  110 . 
     Equipment state  102  can influence the process state  104 , such as the plasma density, ion flux, and ionization ratio produced by associated equipment settings. Real-time process sensors  116  monitor the process state and provide measurements of the process state to real-time process control loop  118 . Real-time process control loop  118  can provide corrective action to equipment state  102 , thus altering the equipment state to achieve a predetermined process state when the process state produced by equipment settings according to the process recipe varies from expected performance. 
     Process state  104  results in an output depicted as wafer state  106  such as the quality or thickness of a film deposited on a substrate. Real-time wafer sensors  120  can measure film thickness through an in-situ spectral ellipsometry thickness monitor having access to the wafer through a port located along the vacuum chamber walls, and can provide film thickness measurements to alter equipment state  102  to correct deviations from expected thickness results. Wafer state  106  can also be measured by post-process in-situ wafer sensors  122 . Post-process wafer measurements can be passed to run-by-run loop  124  which provides early warning and product variation control aspects. The early warning aspect monitors deposition results to detect failures that can be caused by sudden changes in the process, such as flaking or arcing, but that cannot be corrected by real-time control. The early warning aspect can notify an operator of a failure to meet specifications to cancel further processing of the failed wafer. This early warning can provide significant savings by scrapping failed wafers before continued expensive processing is accomplished. The product variation control aspect of the run-by-run loop  124  monitors slow process changes or drifts that can result from target wear, deposition on chamber walls and wafer chucks and other wafer equipment aging effects. Process changes can also be introduced by factors other than the physical-vapor deposition apparatus itself, such as variations in targets and substrates. Thus, product variation control aspect can identify lot-to-lot or run-to-run variations, and can inform an operator of these variations. The product variation control provides an update to the process recipe  110  based on quantitative models for the relationship between physical properties, microstructure, process conditions, and equipment state to optimize process recipes. 
     Intelligent diagnosis loop  126  can accept process measurements and wafer measurements to provide equipment diagnosis by analyzing anomalous process conditions not otherwise serious enough to trigger hardware fault. Intelligent diagnosis loop  126  monitors trends in process conditions to provide a prognosis of the equipment state which can predict faults and future failures. Intelligent diagnosis loop  126  output can allow optimal scheduling of equipment maintenance to increase uptime, and accordingly to provide better throughput. 
     Monitoring and control device  100  can provide a number of advantages for processing of wafers on an industrial scale. First, the early warning, drift recognition and real-time control can reduce the number of scrapped wafers. Second, fault detection will allow preventive maintenance based on actual equipment state rather than a set time schedule, and slow degradation of equipment can be compensated to optimize process parameters with direct feedback. Third, feedback control based on real-time measurements can provide dramatic improvement of process control to enable reliable processing of multi-layer structures for performing advanced GMR effects. Finally, the wafer, process, and equipment state sensors will enable rapid development of process models to improve existing processes based on measured production results. 
     Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.