Introduction to Sputter

[Music] hello I'm nan Jo cursed and this is our in-depth video about sputter deposition of thin films in a vacuum system we use vacuum systems to deposit thin layers of materials such as metals and insulators on to our substrates the thicknesses of these vacuum deposited layers are very thin on the order of five nanometers to 250 nanometers the three most common thin film vacuum deposition techniques are thermal evaporation electron beam evaporation and sputtering and in this video I will introduce you to the process of sputter deposition sputter deposition is usually simply called sputtering sputtering is an entirely different process compared to the other types of thin film deposition we cover in these videos which all use evaporation instead sputtering uses energized atoms that hit the source which are the blue atoms the source material is in the form of a flat plate which we call a target those energetic atoms hit the target and propel source material atoms off of the target and into the vacuum system these are the yellow atoms some of these source atoms hit the target up here and become the thin film the energetic atoms used in sputter deposition are created in a plasma you've probably heard of those three common states of matter liquid solid and gas well plasma is a fourth state of matter but don't let that scare you we use plasmas in our everyday lives one common use of plasma is in fluorescent lights the plasma in a lightbulb is used to generate light in our sputter system we will use an argon plasma which has energetic argon atoms that hit the target and remove source material from that target sputtering is performed in a vacuum system and so after we load the target and we load our substrate we evacuate the chamber using vacuum pumps to about 5 times 10 to the minus 6 Torr we leak a small amount of argon gas into that vacuum chamber argon will be the gas that forms the plasma and argon is used because it's inert it's not reactive and will not result in unwanted chemical reactions during our process when the argon gas is in the chamber we apply a high negative electrical voltage to the target this high voltage is strong enough to strip an electron from the argon atoms close to the target that means that the argon atoms are now ionized and each argon atom has a positive charge these positive argon atoms are attracted to that negatively charged target and they have enough speed to physically knock off individual atoms of the target material this is the sputtering process these sputtered atoms fly off in all directions including toward the substrate that we want to coat and this process continues until the substrate is coated with the desired thickness of material then we turn the voltage off on the target and the sputtering stops sputtering is one thin film vacuum deposition option be sure to take a look at the thermal evaporation and electron beam evaporation videos to learn about two other commonly used thin film vacuum deposition techniques [Music] hello I'm nan Jo cursed at Duke University and I'll be joined in this video by my PhD student Callie Hainan in this video Callie will demonstrate the operation of the sputter deposition system this fabrication tool is located inside a cleanroom so let's get into our cleanroom suit and take a look at the sputter system this is the sputtering system this is the vacuum chamber and positioned behind it out of sight are the mechanical vacuum pump and the high vacuum turbo pump to the right of the vacuum chamber are their electronics which I will discuss in a minute when not in use the vacuum chamber is kept under vacuum at low pressure to keep the inside of the vacuum chamber as clean as possible so the first step to use the spider tool is to vent the chamber this means that a small valve is opened that lifts nitrogen gas into the chamber nitrogen is used because it is clean and free of any moisture we vent the chamber using the touchscreen it takes several minutes for enough nitrogen to fill the chamber and let the chamber pressure equal the room pressure then we can open the door to the vacuum chamber now that venting is complete we can open the vacuum chamber door as with any door on the vacuum chamber there must be some type of seal or gasket that seals the chamber airtight so it can be pumped down to vacuum you can clearly see the door gasket here let's take a look inside the vacuum chamber of the spider tool there are several interesting things to see in the spider system vacuum chamber first we have a port for the turbo pump you can see the turbo pump turbine fins behind the protective screen attached to the turbo pump but hidden from view is the mechanical backing pump that assists the turbo pump next we have a small port used to feed argon gas into the chamber the argon will be ionized to form the plasma the third component is the target located under this movable shutter the target is the material we wish to deposit for example this target is tight Hania note that this system has a three target capacity so we can deposit up to three materials during a single sputtering process the shutter can block spidered material from the sample we can open and shut the shutter to quickly start and stop deposition to achieve precise thicknesses when the shutter is closed nose deposition on the sample occurs when the shutter is open and the plasma is on then deposition occurs the shutter is needed because you cannot quickly turn on or off the plasma as it can cause the target to heat or cool too quickly it may crack the target material the shutter allows us to slowly increase the spider power and slowly decrease some spider power without unwanted deposition onto the sample attached to the target is an electrical lead used to bias the target with negative voltage this negative voltage is what ionizes the argon gas and then attracts the positively charged argon ions to the target surface which then physically removes or sputters small amounts of the target material the next component is a sample or substrate holder located at the top of the chamber this is where we put our substrate or sample that we will spider deposit a thin film on - here's the thickness monitor which measures the thickness of the material being deposited in real time first we remove the metal plate from the chamber let's load our substrate into the vacuum chamber so we can deposit a thin film of titanium onto it this is the silicon wafer we will use notice the color this is pure silicon today we will deposit a thin film of titanium onto the silicon we place our substrate on the metal plate and hold it down with a small spring then we return the metal plate to the chamber with our sample attached we'll check their desired source material target is in the chamber and note the location one two or three in this case titanium is in position one we set the control knob on the spider system to target number one now let's close the door and pump down the chamber to pump down we select pump on the computer touchscreen the computer controller will turn on the mechanical pump first which will rough pump down the system to a pressure of a few Torr then the computer turns on the high vacuum turbo pump which will pump the chamber to about five times ten to the negative sixth or this is the vacuum level required by this system to do a spider deposition this will take about one and a half hours the system has pumped down to less than five times ten to the negative six Torr so we can now begin the sputtering process first we slow down the turbo pump to forty-five percent of full speed because we will introduce small amounts of argon gas into the chamber we don't want the turbo pump spending at full speed because it will remove the argon gas too quickly remember our GaN is the gas that will ionize and cause the sputtering action okay the turbo pump speed and chamber pressure have stabilized we are nearly ready to begin deposition first let's set up the thickness monitor for the desired material in this case we will deposit titanium the thickness monitor will display the deposited thickness in real time we are now ready to turn on the plasma which is also called stretching the plasma this is done by applying a high voltage to the target and to do this we turn on the power supply that applies the voltage the power applied is set on the controller we must start at low power and slowly raise the power to avoid heating the target too quickly which may crack it the higher the power the faster the source material is sputtered and deposited the typical power ranges from 200 watts to 750 watts for this particular system while the power that we start with is a hundred watts today we will change the power slowly from a hundred watts to five hundred watts and then we will open the shutter to begin depositing the titanium let's get a close-up view of the plasma through this port okay we have struck the plasma can you see the pink purple glow through the viewport that is light being emitted from the plasma the plasma creates the ionized argon atoms that accelerate toward the target as the ionized argon atoms hit the target they knock off titanium atoms this is what we call sputtering once we strike the plasma we slowly ramp the power from a hundred watts to 500 watts when we get to 500 watts we opened the shutter which allows the sputtered titanium atoms from the target to hit our sample mounted at the top of the chamber let's get a close-up view of the shutter opening here we are looking into the chamber at the plasma the shutter is currently closed we are now ready to open it and begin deposition with the shutter now open we are depositing titanium atoms onto our sample located at the top of the chamber we can monitor the thickness using the thickness monitor when we reach our desired thickness we will close the shutter to halt deposition so we are nearing our target thickness of 75 nanometers okay now I will close the shutter to stop deposition and now we can slowly ramp the power back down after ramping down the power we can turn off the power supply and the plasma goes away with the plasma off we turn off the argon gas flow and set the turbo pump speed back to normal which is a hundred percent we are now ready to retrieve our sample to do this we vent the chamber just like at the start of the video with the chamber now vented we can open the door and take out our sample that's it we've deposited a thin film of titanium onto our sample let's compare the wafer before and after titanium deposition the final step is to close the system and start the automated pump down sequence remember that we leave the vacuum chamber under vacuum when not in use to keep it as clean as possible thank you for joining me for this demonstration of spider deposition

Channel: Duke University - SMIF

Views: 35,028

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Id: GgD6G3B-2WU

Length: 13min 25sec (805 seconds)

Published: Thu Jan 23 2020