As component packing is tighter and circuit geometries trend towards smaller structures, the reduction of submicron particle contamination during the wet bench process steps becomes more important for output quality. When circuit paths are reduced in size, a single submicron particle can block the path and render the final semiconductor component defective. Even when the presence of particles doesn’t cause defects, their influence on semiconductor performance can reduce the quality and lifespan of the final products.
Semiconductor manufacturing facilities and research labs using typical wet bench equipment face challenges when trying to reduce submicron particle contamination to acceptable levels. Innovative solutions such as the use of Megasonic Cleaning and the reduction of wafer handling with a single chamber IPA dryer can help bring down the particle count. When such solutions are integrated directly into the wet bench processing line, throughput and yields can increase. The process may require fewer chemicals and overall facility performance can improve.
How Megasonic Cleaning Reduces Particle Contamination
The use of high-frequency sound waves in cleaning systems is common in many industries but the delicate silicon wafer structures and surfaces require extra-high frequencies to make sure wafers are not damaged. Megasonic cleaners use frequencies of 950 kHz and higher, in the megahertz range, to deliver the soft cleaning action required.
The sound waves from lower frequency systems create microscopic but comparatively large cavitation bubbles in the cleaning bath. The bubbles produce intense scrubbing against the surfaces of the parts to be cleaned, dislodging contaminants and delivering a powerful cleaning action. For the soft surfaces, delicate structures and thin metallic deposits of silicon wafers, such intense cleaning can result in the pitting of surfaces and damage to silicon structures.
In Megasonic cleaning systems, the high-frequency sound waves produce smaller bubbles and more gentle scrubbing. The cleaning action is soft enough to preserve silicon surfaces and structures but strong enough to dislodge contaminating particles. The particles often adhere to the wafer surfaces and are difficult to dislodge with normal rinsing. Megasonic Cleaning breaks the adhesion and creates currents that wash the particles away.
The Megasonic Cleaning action is especially important for submicron particles where the adhesion to the wafer surface inside a boundary layer makes rinsing less effective. The soft scrubbing of tiny bubbles against the wafer dislodges submicron particles effectively and reduces particle contamination.
How the Single Chamber IPA Dryer Reduces Particle Contamination
One of the ways silicon wafers pick up contaminating particles is during the transfer from etching to drying stations. This transfer is especially critical for HF last etching. During the final etching in a wafer fabrication step, the silicon oxide layer is removed through etching with hydrofluoric acid. The wafer is then rinsed and dried before moving on to the next fabrication step. Particles remaining on the wafer surface can interfere with the subsequent fabrication process.
In an innovative development that eliminates this source of particle contamination, a single chamber handles HF last etching and IPA vapor drying. First, hydrofluoric acid is injected into the station chamber to etch the wafer. When etching is complete, the wafer is rinsed with de-ionized water until the acid is neutralized to a safe pH. IPA vapor is then introduced into the station chamber, and after about 15 minutes, the wafers are dry and ready for the next fabrication step. The particle count remains low because the wafers have not been moved throughout the etching and drying process.
Modutek Provides Innovative Semiconductor Manufacturing Equipment for Excellent Results
Modutek works closely with customers to develop innovative wet bench stations that meet their requirements. Attention to customer needs and finding new solutions to common problems allow the company to remain one of the leading wet bench manufacturers.
For Megasonic Cleaning applications, Modutek has partnered with Kaijo Corporation, a world leader in high sound frequency cleaning technology. Modutek’s integration of the Kaijo Megasonic cleaners into the wet bench product line has produced low particle counts that are difficult to obtain with other methods.
Because Modutek designs and builds its own etching and IPA drying stations in house, the company was able to develop its innovative single chamber station and integrate it into its comprehensive wet process product line. In parallel with Megasonic Cleaning, the single chamber station further reduces particle counts, improves yields and reduces costs. On these and other wet process questions, Modutek offers free consultations to ensure customers get the best equipment for their needs.
