Photoresist stripping and descum, organic contamination removal for silicon wafer
- Dry ashing of photoresist
- Descum after paternning
- Clean organic contamination on wafer
- Increase surface hydrophilicity for MEMS device
- Improve bonding strength for wire bonding step
Dry photresist stripping or ashing is a rapid chemical etching process for photoresist layer on the silicon wafers. Energetic electrons inside the plasma can breakdown oxygen molecules and generate reactive oxygen atoms. Oxygen radicals can then oxidize the photoresist and generate high vapor pressure by-products CO, CO2 and H2O. Adding small amount of CF4 or SF6 gas can significantly increase the photoresist etching rate because highly reactive fluorine atoms can boost the rate of extracting hydrogen from the photoresist polymer.
Photoresist descum is an additional gentle photoresist etching process after photoreist paternning and development. It is used to remove the residual photoresist scum left on the developed area. Such residual can prevent subsequent dry or wet atching steps and affect the uniformity of the etching rate across the wafer. Descum step can also improve the side wall profile of the photoresist mask and improve the process uniformity.
For MEMS device fabricated on the silicon or quartz wafer, organic contaminations on the wafer surface can increase the water contact angle and make the surface hydrophobic. Oxygen plasma treatment can easily remove the organic contamination and make surface hydrophilic. It's also important to remove the organic contaminant on the bonding pads before wire bonding steps.
In traditional immersion mode plasma etching, sample surface are subject to both chemical reaction with neutral radicals and physical bombardment by energetic ions. For device with thin coatings or highly sensitive to surface charge and high current, immersion mode plasma cleaning may cause irreversible damage to the device. For such device, ion free downstream mode plasma cleaning is recommended.
Tergeo and Tergeo-plus tabletop plasma cleaner
Advantage of Tergeo plasma cleaner over competitors
Better plasma uniformity. PIE Scientific has carried out extensive research to improve the uniformity of the plasma generator. It's extremely difficult to achieve uniform rf electric field with external inductor coil type antenna that is used by some cheap plasma cleaner. If metal rf electrode is placed inside the plasma chamber, then it is intrinsically non symmetric in geometry. Plasma will be stronger close to the high voltage rf electrode, especially at the edge of the electrode. Tergeo plasma cleaner uses two symmetric external electrode design to achieve much better plasma uniformity over other type of plasma cleaner design.
Immersion and ion-free downstream cleaning in one system Tergeo plasma cleaner integrates two plasma sources in one system. Direct plasma source is used for traditional immersion mode plasma cleaning, e.g. samples are immersed in the plasma. In this processing mode, samples are subject to chemical reaction with oxygen or fluorine radicals and physical ion sputtering bombardment. If device has very thin coating, ion sputtering may damage the sensitive coatings. If device is very sensitive to surface charge and high electron current flow, high surface charge or current may cause irreversible damge to the sensitive IC device. In this case, downstream plasma cleaning is recommended. In this mode, plasma is generated in a separate remote plasma source, only neutral oxygen and fluorine radicals can diffuse into the sample chamber and react with photoresist and organic contaminants.
Advanced process control technology. Plasma uniformity and strength can change with chamber pressure. Tergeo plasma cleaner uses advanced MEMS based digital pressure sensor technology for pressure monitoring. In addition, PIE Scientific developed a unique plasma sensor technology that can quantitatively monitor the plasma strength in real time. Quantitative data is the key to achieve repeatable and consistent results from day to day.
Fully automatic operation. In some basic plasma systems, user needs to manually adjust needle valve to introduce gas into the plasma chamber. It's almost impossible to achieve repeatable gas flow rate with manual coarse needle valves without any feedback. Tergeo plasma cleaner uses fully automatic mass flow controller (MFC) to precisely regulate gas flow rate from 0 to 100sccm with accuracy better than 0.2 sccm. Fully automatic operation with multiple recipe support also ensures repeatable performance from day to day because the execution of the cleaning process is controlled by embedded microcomputers.
Oxygen plasma treatment to remove organic contamination on wafer surface and increase surface wettability