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To: Kirk © who wrote (52107)	4/5/1998 10:34:00 AM
From: fred douglas liebling	Read Replies (1) \| Respond to of 186894

Hate to be trite here but for tax reasons can anyone tell me the date of Intel's last stock-split? thanks

To: Kirk © who wrote (52107)	4/5/1998 11:43:00 AM
From: Maxwell	Read Replies (1) \| Respond to of 186894

Kirk: Semiconductor processing technology has progressed at exponential rate within the last five years. At 0.25um you can't even see the spacing between 2 metal lines with less than 50X in magnification. <<Are back-end process so much "dirtier" because they involve adding and removing material (metal and passivation) which is just harder to clean as opposed to diffusions and oxidations which are fairly clean by nature?>> You are correct. The best cleaning solvent in removing defects are still the RCA processes (developed by RCA) which involved ammonia/peroxide and sulfuric/HF solutions. These cleaning process are used in the front end. They cannot be used in the backend because they corrode the metals. Thus organic cleaning solvents are used in the backend to strip the resists and cleaning metals. These solvents don't do as good as a job as the RCA and acid mixes and can add in defects. Furthermore etching metals and oxide (for contacts) are very dirty. As you etch, these materials (oxide and metal) have to go somewhere and most are pumped out in the chamber and the rest get deposited in the chamber walls and the shower heads. The more you etch the dirtier your system gets. Eventually the redeposited residues fall back on your wafers and cause defects. The same way goes for depositing thin films. Eventually the system has to be taken down to clean before it can be put back in production. <<I always wondered why we had to pay so much more for "just" an extra layer of metal on a complicated bicmos wafer. From your hint, it seems that we are paying for the extra yield loss.>> The reason is that to make a more powerful chip designers must add more transistors. To make the chip die size smaller with more transistors engineers must increase the number of metal layers. This will make the chip runs faster because shrinking the chip decreases the RC delay and improve the switching speed of the transistor. In the competitive semiconductor industry everyone must follow this path or else your technology be obsolete. Maxwell