Particles

Particle removal is key for maintaining acceptable yields in semiconductor manufacturing. EHD has shown its ability to remove particles from semiconductor wafers.

Below is an example of EHD removal of polystyrene latex spheres (PSLs) from bare silicon. PSLs are an industry standard method for determining the efficiency of particle removal.

PSLs on Silicon before EHD Cleaning

Same area of Silicon after EHD Cleaning

Below are images of a scratch made on a bare silicon wafer. In the first image, silicon debris in the range of 5 microns to less than 50 nanometers is visible. In the second image, the same area of the scratch is shown after EHD cleaning.

Silicon Debris before EHD Cleaning

Same area of Silicon after EHD Cleaning

A unique concept for EHD particle removal is the use of EHD cleaning, in-situ, in vacuum wafer transport systems. One such transport system is manufactured by BlueShift Technologies, whose products can be viewed at www.blueshifttech.com.

Post-CMP

EHD Technology Group is continuing demonstration work to address post-CMP (chemical mechanical planarization) cleaning. As copper interconnect technology advances, smaller via and line geometries make defect removal after CMP more critical. In addition, new low-k dielectric materials create new challenges to wet cleaning methods. EHD’s ability to avoid wetting the wafer being cleaned is of value in this cleaning application.

Wafers with a slurry composed of 50 nanometer silica particles in a KOH solution are exposed to EHD beams for removal analysis in this on-going internal project.

Results will be published on this Web site as they are available.

Strip

Photo resist must be removed after its use in imaging steps. This is known as resist strip.

One extremely difficult resist strip application is removing photo resist from the surface of a wafer after it has been exposed to high intensity ion beams during the implant of impurities into the silicon crystalline structure. This is known as High Dose Implant Strip, or HDIS.

During ion implant, the top surface of the photo resist is severely damaged by the energy of the ion beam. This causes a carbonized crust to form on the resist. This crust is difficult to remove without heated acids and other chemicals.

EHD has demonstrated the ability to break up the crust with physical energy, and then remove the underlying “bulk” resist. Work continues on applying EHD to the critical HDIS process.

Below are images of implanted resist before and after EHD beam cleaning.

Implanted crust & bulk resist before EHD Cleaning

Residual bulk resist after partial EHD Cleaning

Masks

Photolithography masks are used to create patterns, most often in photo resist. Cleaning of the masks themselves is another application where EHD offers benefits.

Advanced masks, such as those for extreme ultraviolet (EUV) exposure, cannot include protective barriers (pellicles) that were included with previous masks. This is due to the unacceptable level of light absorption of the pellicle. EUV mask blanks and patterned masks require stringent particle removal, and are sensitive to chemicals used in cleaning.

During actual use, EUV masks operate in vacuum, making in-situ cleaning with EHD a valuable addition to an exposure system (stepper).

Newer imaging techniques, such as direct imaging templates, are also being investigated for EHD cleaning.

Roadmap

Currently, EHD Technology Group is focusing efforts on successful applications of EHD cleaning in the semiconductor industry.

Other applications have been identified, and will be addressed in the future. Examples include:

Advanced packaging of microelectronics, including 3D packaging, for denser electronic devices such as solid state disks

Disk drive heads and media

Optical components

Medical devices, especially implantables

Aerospace components