Sputtering Yield Enhancement with Arc Control
By Jeff Sellers, Director of Advanced Technology
In DC magnetron sputtering, arc control is the key to a successful process. Arcing is the primary mechanism for wafer/substrate damage and is the dominant source of particulates. Control arcing and your yield will improve. All sputter systems arc as a natural consequence of the physics of plasma discharge, yet sputtering is an effective, flexible method for quickly depositing high quality films.
Figure 1: The Paschen Curve. A normal sputter process operates in the superglow region.
What is an arc? Referring to the Paschen Curve in Figure 1, a normal sputter process operates in the super-glow region of the curve where an increase in current generates some increase in voltage. You can also see that a slight increase in current density above the super-glow region will push the plasma into the arc region. It is critical to understand that the whole plasma does not have to be pushed to the arc plasma current density, only a single point must exceed the threshold density for an arc to form.
Any disturbance which causes the local current density to increase may precipitate an arc. In the arc region, the plasma impedance collapses due to the regenerative gain, thermal ionization, of the arc discharge. All available energy is then driven into the arc discharge, which generates extreme temperatures and even more thermal ionization, which continues to lower the arc impedance. It is the collapse of plasma energy to a point arc discharge which generates the massive energy densities which cause particulates and wafer damage.
This effect is so pronounced that it actually explodes the surface of the target. Also, if you have observed arcs in a chamber, then you have seen sparks flying through the chamber. Those sparks are white hot particles blown from the target surface by the arc energy. Consider the damage such particles may do to your wafers. (See photo of surface damage to a CD caused by a competitor's arc in Figure 2.)
Figure 2: Surface CD damage caused by arcing with a non-ENI product.
The molten metal splash is approximately 100 microns in width.
The damage shown in Figure 2 was one defect out of hundreds caused by a single arc. Figure 3 is a diagram of the arc that caused this level of damage.
Figure 3: Typical arc waveform, non-ENI product.
The ENI DCG-100 Plasma Generator was designed from the very beginning to effectively control arcs and increase yields in sputtering processes. The keys to successful arc control are first, to minimize the stored energy in the supply's output, thereby reducing arc energy, and second, to rapidly detect the arc and shut off the supply. The DCG 100 uses high frequency FET switchmode power modules to allow the minimum stored energy of any available sputtering supply - approximately 20 times lower than the previous industry standard. The DCG-100 also uses proportional arc control to allow the unit to detect an arc in 10s at any power level. (See Figure 4.)
Figure 4: Typical arc waveform, ENI DCG-100RP2.
The reduction in arc energy dramatically reduces particulates and damage to the substrate and the target surface, resulting in a more stable process with higher yield, improved film quality, and longer target life. For example, one of our customers, a manufacturer of CD-R's (CD-Recordable), went from a 9% to 0% fallout rate due to arc damage after installing the DCG-100 power supply, resulting in a 3% overall yield enhancement - very significant when you make millions of disks a year. Equally notable improvements have occurred with hard disk carbon sputtering resulting in arc damage going to 0% for an overall yield enhancement of 2%.
The value of superior arc control becomes even greater in reactive DC sputtering. In reactive sputtering, a reactive gas mix is introduced into the plasma to deposit a compound on the substrate. A typical process would be a silicon target with an argon/oxygen gas mixture to deposit silicon dioxide on the substrate. Other typical reactive processes include aluminum oxide, titanium nitride, silicon nitride and indium tin oxide.
Due to the random nature of sputtering, some of the reaction products (compounds) will be deposited on the target surface. The compounds are non-conductive, or at least, have high resistivity relative to the target material. As these compounds cover locations on the target, they form micro-capacitors. A simple capacitor is made of two conductors separated by an insulator. In the plasma chamber, the target forms one conductor, the deposited compound is the insulator, and the plasma forms the other conductor.
These capacitances begin to charge up to the plasma potential, but typically experience dielectric break-down due to their small geometry and the high field intensity. When they break down, they flood the local area with charge carriers, causing a large increase in local current density, and push the plasma into arcing. Clearly in a reactive process, this will occur frequently, requiring a third critical component of arc control - arc recovery time. The DCG-100 is between 30 to 100 times quicker than any competitive supply in total time from arc detection back to setpoint.
In some reactive processes, this is still not rapid enough. For these applications, ArcKill™ is the solution. ArcKill™ is a plug-in arc suppression module which allows the DCG-100 to detect and respond to arcs even more quickly. ArcKill™ detects arcs in 200ns, discharges the arc energy, and is back at setpoint in 50 microseconds. (See Figure 5.) This allows an ArcKill-equipped unit to respond to arcs at a very high rate, up to 20,000 arcs/sec. An ArcKill-equipped DCG-100 can run at setpoint even with very high arc rates with no arc damage due to the extremely low arc energy. ArcKill-equipped DCGs are successfully demonstrating their performance in a variety of processes including aluminum oxide, silicon nitride, silicon dioxide, and carbon films.
Figure 5: Typical arc waveform, ENI DCG-100 with ArcKill™.
The DCG also offers a number of other user benefits including 0.1% accuracy and linearity, full safety agency and EMI certification, and a variety of remote control options. The ENI DCG-100 sets a new standard for high performance plasma deposition power supplies and process yields.
Since 1974, MKS ENI has been the technology and market leader in the design and manufacture of RF Plasma Generators for plasma etching, sputtering and deposition. The DCG Series of DC plasma power supplies reflects the advanced expertise which comes only with this experience. For consistently high-performance RF and DC power supplies, rely on ENI.
For More Information:
Learn more about DCG-100 ArcKill™
Learn more about DCG-200 ArcKill™
Need help?
Contact an Applications Specialist by sending an email to MKS ENI Products or call 585-427-8300.
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