Universal Sputterer™ Overview

Click HERE for Detailed Manual...

© 2006
MAT-VAC Technology, Inc.
All Rights Reserved

Last Revision: V1.33 — 13 Oct 07










What Exactly IS Plasma Sputtering?

If you've ever had a flourescent light go bad you've probably noticed that the end of the flourescent tube darkens slowly over time as the tube begins to fail. What is happening in the end of the tube is a sputtering process. The electrode that ignites the plasma (low pressure ionized gas) in the flourescent tube is slowly transferred to the inside of the glass tube each time the tube strikes or arcs. Over time, the entire electrode is eaten away and sputtered onto the glass. When the last of the electrode is consumed, the bulb no longer lights and needs to be replaced. A plasma sputtering system reproduces this effect on a industrial scale with great precision for uniform, thin film coatings.

What is a thin film plasma sputtering system?

The simple answer is that it's a plating machine. But calling it that is gross understatement. Thin film plasma sputtering is a system by which very thin (mono-atomic) layers can be placed on materials that can tolerate vacuum. Plasma can only exist under very rarified conditions and acheiving those pre-conditions is a formidible task.

Click to watch video... The prerequisites for plasma are:
  • Start with high vacuum
  • Add a trace of process gas
  • Apply DC or RF to the targets
Just forming the plasma is only part of the equation. The materials to be sputtered still need to be fed into the system, passed thru the plasma field, and then cycled out of the machine - hopefully without loss of primary vacuum.

There are many components and systems that combine to form an automated thin film batch sputtering system. These include:
  • Rough Vacuum
  • Hi Vacuum
  • Hydraulics (elevator and cover)
  • Pneumatics (valves and other actuators)
  • Process Pneumatics (process gas valves and metering)
  • Fluidics (cooling water)
  • Motion Control
  • Power Switching and management (target selecting, RF autotuning)
  • Machine and Operator Safeties
  • PLC control system w/Manual control/indicator panel
  • Operator GUI
All of these component systems need to be interconnected and structured to operate in an efficient and precise manner to give the most uniform layers possible.

Click to explore the diagram...
Click here for Operator's Manual ...
Click here for "How Do I" ...
Click here for Rack Overview
Click here for Chassis Overview
Click here for Drawings in Name Order
Click here for Drawing Waterfall

Operational Overview:

In the MAT-VAC Technology, Inc. Thin Film Plasma sputtering system operation is very straight forward. The computer contains the process recipes that control the sequence of operations. The materials to be sputtered are placed on a pallet and placed into a Load Lock and the Good To Go (GTG) button is pressed to signal the start of a cycle. The operator (having previously selected the process recipe) then clicks the Cook button on the GUI and the sequence is completely automatic from that point on.

Once the GTG button is pressed the Load Lock is then evacuated and the materials (optionally) are baked to remove any volatiles (normally water).

Once the Load Lock is at an acceptable vacuum level, any previously sputtered pallet is placed on the outfeed tray and the new, unsputtered materies are picked up and placed on the pallet carrier.

Once inside the primary chamber the chamber vacuum is normally brought to the specified hivac level and processing begins.

Sometimes the materials are etched or cleaned at the (optional) etch station. This removes any surface contaminats that the (optional) heat missed.

The production materials are then passed under the plasma field one or more times to transfer the sputter material from the target to the production materials. This can be repeated multiple times with one or more targets of varying composition. Different systems can have different numbers of targets (normally two or three).

Each target also has one or more process gasses associated with it. These gasses both support the plasma field and (optionally) react with the plasma to form compounds on the production materials. Typically oxides and nitrides are produced in this manner. When reactions are not desired, an inert gas (usually Argon) is used to sustain the plasma.

Once all sputtering steps are completed, the production materials are normally cooled and then cycled out.

The details of the process itself are managed by the PLC which runs at a very fast rate (typically 30-60 Hz) as compared to the Windows™ GUI program (4-5 seconds) which is used to monitor and sequence the operations.

Major Component Description:

While the details of each system vary by both basic model and customer requirement, certain items are in common to all systems. Broadly the system divides into two, fully seperable assemblies, the Universal Sputterer™ electronics control rack (which is common to all systems, reguardless of model or option) and the main chassis with process chamber.

The process chamber can take several forms, vertical (9X series), horizontal (6X series), or circular (8X series). Each has different physical structure but all are hivac capable. The most common type of system is the 9X series (horizontal) and these general discussions will be of that series machines unless otherwise noted.

In addition to the two primary asseblies (the rack and chassis) there are usually additional components in the form of the mechanical roughing pump, the cryo compressor(s), water chiller and filter, process gas bottles, etc.

A typically system usually requires the following utility services:
  • 208V 100A 3ø Y, 60 Hz
  • 100 PSI Clean, Dry, Shop Air
  • N2 Purge Gas (welding grade)
  • 5 GPM chilled (≈20°C) water (filtered or DI, >100kΩ / cm)
  • Process Gas(ses)
The electric utility is fed into a breaker panel on the rear of the Universal Sputterer™ electronics rack where it is distributed back out to the appropriate items. All of the rest of the utilities, (air, water, gasses, rough vacuum) are connected along the rear of the chassis. The hydraulics are all self contained within the chassis.

The rack connects to the main chassis and chamber thru a series of cables running from the rear of the rack to the Chassis I/O Panel (CIOP) on the rear of the chassis. All signal cables and I/O power are connected in this manner. The rack and the chassis are completely seperable units and can be shipped seperately. All PLC command and control signals in the chassis have one endpoint on the CIOP.

Power for the sputter power supplies, the mechanical and hivac pumps and the hydraulic system are located on the rear of the rack with twist lock NEMA approved connectors.

Located inside the front of the rack, from the bottom up, are the Wintel CPU that runs the Operator GUI program, the PLC with all I/O modules and the manual Diagnostic/Maintenance Panel (DMP). The keyboard/mouse tray and the LCD monitor for the CPU complete the rack.

The major power loads are switch via contactors controlled by the PLC. These loads include:
  • Mech Pump
  • Hydraulic Pump
  • Cryo Pump(s)
  • Heat (optional)
  • Master Power (110VAC and +24 VDC)

Motion Systems:

The chassis has a load lock which is used to transport the pallet into and out of the chamber without compromising the vacuum level inside the chamber. The load lock consists of a small chamber with it's own rough (optionally Hivac) vacuum system and a hydraulic elevator. The hydraulics are needed to hold the chamber sealed against room air pressure when the load lock is open.

The elevator hydraulic motor and control system is also used to raise and lower the cover of the chamber for servicing (9X series only).

The elevator position is sensed by a series of switches located coaxially to the elevator hydraulic cylnder. These switches are augmented by a pressure switch on the hyrdaulic block that is used to monitor the hydraulic pressure. When the elevator is pressing against the seal plate with sufficient pressure, the PLC assumes that the seal will hold against atmosphere. During times that the elevator is sealed and the load lock is exposed to atmosphere the PLC will automatically cycle the hydraulic system to maintain optimum seal pressure even if the hydraulic system exhibits a small amount of blowby or leakback.

Once the Load Lock is evacuated to an appropriate vacuum level, the elevator lowers into the chamber to allow the carrier to drop off the freshly sputtered pallet and to pick up the new work to be sputtered. The timing and sequencing of the elevator and the carrier is a complex ballet of precise motions to allow the pallet transfers to occur.

The carrier motion system is then used to pass the pallet under the various targets and to move the pallet to the (optional) etch platform (normally located at the far end of the chamber).

All of the carrier motions are controlled by a closed loop DC motor/tach control system with position feedback via a precision optical encoder. The encoder allows the motor speed to be ramped as the carrier approaches its designated position preventing pallet spills and giving very precise control over both pallet position and speed. Due to the optical encoder the motion system is much more precise and capable of more elaborate motions than any previous systems. For instance one of the features of the motion system is automatic pallet re-alignment on outfeed. This repositions the pallet to compensate for any sliding that occurred during the process. This helps prevent pallet crashes caused by a mispositioned pallet hitting the seal plate as the elevator moves into the load lock

Certain system may also have an aperature shutter that is used to prevent cross contamination of the targets and/or sputtering on the (optional) etch platform heat lamps. If the shutter system is present the motor controller is much simpler than the carrier motor controller since precise speed control isn't required. A simple AC reversable motor with back to back SSR's (Solid State Relays) are all that is required on the drive side. The postion feedback of the shutter is derived using the same optical position encoder that the carrier uses.

Vacuum Management:

The roughing system consists of a mechanical roughing pump, manifold, valves and connectors. The load lock roughing line is also used to rough the chamber, since the load lock and chamber are connected any time that the elevator is not sealed. The rough manifold, valves and associated plumbing are all made with quick disconnect vacuum fittings to allow easy maintenance without tools. The mechanical pump is normally located externally to the system and is wired to the rack where it can be controlled by the PLC. In most applications the roughing pump is started and allowed to run indefinately. The roughing manifold has a N2 back pressure valve to prevent the pump oil from boiling by maintaining a slight (≈100mT) back pressure when none of the other manifold valves are open. The mech pump is expected to produce a rough vacuum in the under 50mT range.

The vacuum, gas, and throttle valves, as well as the (optional) etch platform actuator are all electro/pneumatic actuation. This means that the electrical control single from the PLC is first applied to a pressure manifold with air lines running to the actual operating valve. This allows the internal wiring of the chassis to be greatly simplified as all of the valve controls are run to a single point and only non-conductive air lines need to be run to the actual valve/actuator body.

Located under (9X/8X) or behind (6X) the chamber is the hivac cryo pump. This pump is a capture type operating at a very low temperature (typically under 10°K) that condenses and freezes out any stray molecules of gas and provides operating pressures in the 10-6 to 10-7 Torr range. The pump consists of the cold head and the external compressor.

The cryo pump is connected to the chamber by a large aperature gate valve and regulated by an inline throttle valve. This allows the pump rate to be reduced during sputtering operations so as not to consume all of the process gasses.

Like all 'capture' type pumps, the cryo's will reach a saturation level and need to be regenerated (purged) before they can continue pumping efficiently. The PLC and GUI provide completely automated (unattended) cryo pump regeneration.

If the system has been ordered with a hivac load lock option, the Load Lock will have it's own cryo pump system, essentially identical to the one in the chamber with the single exception of no throttle valve is needed for the Load Lock.

Each cryo pump cold head has it's own dedicated temperature and pressure gauges as well as valves to control the N2 purge gas and the regen (rough) lines. Optical sensors are used on the gate valves to give positive position indication to the PLC.

The chamber and load lock pressure setpoints are determined by a Granville-Phillips 303 type Vacuum Process Controller. This provides medium and high vac setpoints for both the Load Lock and chamber. Typically the medium vacuum is 50mT or better as determined by the convectron gauges and the hivac level is 5.0 x 10-6T as measured by the ion gauge portion of the 303.

Process Gas(ses):

The process gas system consists of an MKS250 gas controller and a MKS247 four channel readout to control the (up to four) gas channel Mass Flow Controllers. The chamber pressure feedback to the gas system is via an MKS Baratron gauge. Typical control range is under 50mT. Each gas channel is equipped with a PLC controlled electro-pneumatic stop valve and is plumbed to an inlet port on the chassis rear apron. The gas outlet from the MFC's are routed to the chamber depending on the specific customer requirements. General chamber flow or target gas rings are available as well as custom solutions.

Power:

The final ingredient for the production of plasma is power. The systems can be equipped with either DC or RF power supplies depending on the nature of the targets. Generally metal targets can use DC power while non-metalics require RF. The etch platform can only use RF. Both type of powersupplys can be used should the customer so desire.

Each power supply has command and control monitoring from the PLC as well as cooling water and safety interlock signals. Power from the sputtering power supply is routed to the appropriate target by a bank of contactors (DC) or a series of vacuum high voltage relays (RF). Additionally the RF power supply output has a autotune/load network that optimizes the RF power coupling as the impediences in the chamber vary. This ensures maximum coupling of the RF power into the plasma field under all but the most adverse conditions. The outputs from the RF power supply are monitiored by the PLC and the operator GUI and emergency shutdown conditions are monitored and enforced if the RF coupling factor (VSRW) becomes too low.

The autotune feature has a 'learn' button that causes the PLC to memorize the current load and tune settings for the specified target. The next time that the target is selected the PLC will preset the load and tune outputs to these settings. Once the plasma is lit, the autotune circuit will maintain optimum VSWR automatically.

The targets (and the optional etch platform) are all plumbed with cooling water on a separate flow circuit from the DC/RF power supply cooling circuit. Each cooling circuit has it's own flow sensor wired into the safety circuit and PLC. The water used in the system needs to be filtered and/or deionized. In order to prevent leakage between targets the resistance of the water must be over 100kΩ per cc (preferably over 1MΩ per cc).

Safety:

The safety interlock signals are a completely independent circuit from the PLC or CPU. These operate instantly independent of the state of the rest of the system. The safety inputs are provided to the PLC so it can determine if the system is safe to operate.

There are three primary inputs to the safety relay (K1), Chamber Vacuum, water Flow, Safety Cover. When any of these are not met, the safety relay (K1) drops out instantly disabling both the DC and RF power supplies and alerting the PLC.