Atmospheric Plasma – OntosTT

Atmospheric Plasma. How does it work?

ONTOS utilizes an internal glow-discharge plasma which creates a high density stream of reactive gas radicals. As the gas flows down out of the internal plasma zone, the high-energy species (ions and hot electrons) recombine in a few microseconds, and the gas cools rapidly. But the chemically active radicals created by the plasma are still present in the downstream gas flow. It is this stream of neutral but highly reactive radicals that react with the surface of your substrate to modify the surface, chemically.

Because all of the high-energy charged plasma particles have recombined by the time the gas stream exits the aperture, the reactions on the surface are accomplished without any bombardment. This means that your substrate will NOT be subjected to sputtering damage or electric field discharge – this is very important for sensitive surfaces!

ONTOS Atmospheric Plasma does not require a process chamber or controlled ambient. Typically, the gas aperture is spaced only a millimeter or two above your substrate. The gas flow exiting the aperture displaces the atmosphere in the space between the plasma head and the substrate. This creates an exclusion zone filled only with the downstream gas, and allows the chemical surface reactions to proceed without interference from room air.

For a comparison of ONTOS Atmospheric Plasma to vacuum plasma systems and competing atmospheric plasma systems ⇒ Download PDF.

Do you have a surface problem ?

Process engineers know that native oxides and organic contamination on surfaces can disrupt subsequent processes such as solder bonding, wire bonding, thin film deposition, hybrid assembly, etc. Traditional methods of surface preparation, such as wet etching, fluxing, or vacuum plasma treatment, all have their drawbacks.

Atmospheric Plasma System for Surface Preparation

ONTOS provides the process engineer with a new alternative – a rapid atmospheric process which reduces native oxidation and organic contamination.

Passivation of the surface against re-oxidation can also be performed – this process creates a few monolayers of modified surface that resist reaction and diffusion of oxygen – and yet is thin enough that it does not interfere with subsequent processes.

ONTOS provides a simple, effective, clean surface modification method which does not require the throughput- robbing vacuum chamber associated with traditional plasma systems. Additionally, ONTOS performs this surface modification without ion bombardment and without the cross-contamination issues often associated with conventional plasma systems.

ONTOS is capable of handling both reducing or oxidizing chemistries.

• With reducing chemistry, it removes both native oxides and residual organics, and it is capable of passivating treated surfaces against re-oxidation. These attributes make ONTOS the ideal surface preparation for semiconductor interconnect bonding.
• With oxidizing chemistry, oxygen radicals are introduced to the substrate surface to remove organics, or grow a controlled thin oxide layer on semiconductors.

ONTOS performs these surface modification processes with only activated benign gasses (no halogens, no flammables, no toxics) in a low-energy atmospheric environment, making the system OSHA and EPA-friendly.

Clean and Green

ONTOS patents and patents pending processes and equipment provide these benefits without the use of acids, toxics, fumes, vacuum chambers, pumps, liquids, or hazards. ONTOS utilizes commonly available semiconductor-grade gasses and an atmospheric plasma source to provide local chemistry right at the surface of your part, with zero hazardous by-products or waste.

SYSTEM DESCRIPTION/SPECIFICATIONS:

• Uniquely‐designed atmospheric plasma source with 25, 40 or 100 mm‐wide process zone. The glow discharge‐type plasma is entirely contained inside the source.
• Computer‐controlled X‐Y‐Z stage. In the standard version, the vacuum chuck accommodates die or wafer from 2 to 200 mm (300mm with the 300mm version). The system can handle substrate thicknesses up to 20 mm.
• 300 W RF generator (600W when Plasma-Head 100mm is installed) has a wide‐range auto‐tune network, system computer control and monitoring of forward and reflected power. Safety interrupts.
• 4 Mass Flow controllers provide precise digital control of gas to the plasma source.
• ESD‐safe, interlocked enclosure; Exhaust for process gases (no scrubber required).
• Fully Automatic system supplied with its control laptop. Software developed in LabVIEW™. Menu‐driven interface with user configurable recipe libraries.

Facilities required:

• Power: 110‐220VAC single‐phase, 15A.
• Gases: 4 channels of gas supply by ¼” stainless or Teflon tubing; Swagelok compression fittings. (All gases are non‐toxic, non‐flammable.)
• Exhaust: 1-3 cfm.
• Lab vacuum: 20‐25” Hg for stage vacuum.

Surface Preparation for Bonding:

• SnAg, SAC, Cu, Ni, Ag, In, Au – reflow or TC bonding.
• Au-to-Au (demonstrated as low as 100°C).
• Cu-to-Cu (demonstrated as low as 250°C).
• SiO2–to–SiO2 (demonstrated at Room Temp.)

Photoresist residue removal:

• Removes all traces of post-development PR residue.
• Replaces Oxygen RIE or UV-Ozone– reduce oxides on exposed metals instead of growing them!
• Activates photoresist surface for excellent wetting during aqueous processes.

Photomask cleaning

• Removes organic contamination without damaging sensitive mask materials. (EUVL-safe!)
• Enables extreme wetting for aqueous cleaning processes – spot-free.

Native oxide removal from semiconductor surfaces:

• Epi preparation.
• Remove uncontrolled air oxidation and organics.
• Capable of dangling bond passivation with Nitrogen, Oxygen, or Hydrogen.
• Zero bombardment damage.

Organic contamination removal prior to adhesive bonding:

• Very effective at removing organics, including Silicones.
• Activates surfaces for better wicking and adhesion.

Pre-plating surface preparation

• De-scums photoresist or laser-etched pattern.
• Reduces oxides from plating base.
• Activates resist surface, sidewalls, and plating base for optimum wetting.
• Even in very small geometries.

Surface Preparation for Interconnect Bonding

ONTOS Atmospheric Plasma was developed to eliminate hydrocarbon contamination and reduce surface oxides to promote metal-to-metal bonding. The initial development was carried out on Indium to Indium compression bonding at room temperature or for reflow bonding .

The system is also capable of passivating the exposed metal surfaces against re-oxidation. This passivation is performed at the atomic level on the surface and therefore can be left in place during subsequent bonding without affecting interconnect adhesion or conduction. Consistent bonding is enabled at reduced temperatures and bond forces, compared to other surface preparation techniques.

• For applications such as 3D integration, flip chip, and other die interconnection processes, a variety of metals is used to form an electrical and mechanical bond between the two components. Native oxides and organic contamination, however, quickly form on most common bond materials, hindering the integrity of the joint and adversely affecting long-term reliability.
• This surface preparation approach has been applied to Sn, Ag, Cu, Au, Sn, In, Ni, and other metals with excellent results.

Surface activation for direct bonding.

• SiO2–to–SiO2 (demonstrated at Room Temperature)
• Au-to-Au (demonstrated as low as 100°C).
• Cu-to-Cu (demonstrated as low as 250°C).

Semiconductor and Metal Surface Activation

With oxidizing chemistry, ONTOS can passivate sensitive semiconductor surfaces without damaging them, and can prepare ultra-clean, ultra-activated surfaces for direct bonding: die-to-die, die-to-wafer, or wafer-to-wafer.

ONTOS Atmospheric Plasma also produces highly activated surfaces for improved wetting, wicking, and adhesion. Activation has been demonstrated on Sn, Ag, Cu, Au, In, Ni, Al, Ti, Si, SiO2, Si3N4, Al2O3, photoresist, and FR composites.

The contact angle photos below for Tin-Silver are typical for all of the materials we have tried to date:

With reducing chemistry, comparable surface activation can be achieved while avoiding the oxidation of metal surfaces. This can be extremely useful in preparing photoresist-patterned wafers for subsequent aqueous processes such as plating, etching, anodic oxidation, etc.