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/wiki/spaces/BNCWiki/pages/6236192
iLab Name: Fiji200 ALD
iLab Kiosk: BRK Growth Core
FIC: Zhihong Chen
Owner: Jerry Shepard
Location: Cleanroom - G Bay
Maximum Wafer Size: 8"/200 mm
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Overview
| Type | Films Available | Restricted Materials | Available Gases | Wafer Size |
|---|---|---|---|---|
| Thermal / Plasma ALD | Aluminium Oxide Hafnium Oxide Silicon Oxide | BAckside must be clean No outgassing materials in mTorr range No thermally unstable materials | Carrier Gas: Argon Plasma Gases: Argon, Nitrogen, Oxygen, Hydrogen | Small pieces up to full 8 inch wafer. Maximum sample thickness is approximately 6mm. |
General Description
Atomic Layer Deposition (ALD) is a technique that takes advantage of self limiting surface reactions, the nature of the reactions ensures atomic-level thickness control and excellent conformality. Following the standard example, growth of Al2O3 film from water and trimethylaluminum (TMA) precursors will be used here to discuss the principle of ALD film growth. Recipes for other materials use different precursors, but are similar in principle and procedure.
| Principles of Atomic Layer Deposition Film Growth (Aluminum Oxide used for this discussion) | ||
| Thermal Atomic Layer Deposition - The required reaction energy comes from elevated temperatures of the sample and chamber surfaces. | ||
| Processing Steps | Images | |
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| In air, H2O vapor is adsorbed onto most surfaces forming hydroxyl groups with Silicon. (Si - O - H). This is the typical condition of the substrate when placed into the chamber. |
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| The four steps of the ALD Cycle consists of the steps shown to the right. Repeated ALD cycles build self limiting atomic layers at a rate of approximately one angstrom per cycle. | 1. Next, Trimethylaluminum ((CH3)3Al) is introduced into the chamber. Trimethylaluminum reacts with the hydroxyl groups, creating methane as a gaseous reaction byproduct. Al(CH3)3 + :Si-O-H > :Si-O-Al(CH3)2 + CH4 |
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2. Trimethylaluminum continues to react with the adsorbed hydroxyl groups until the surface is passivated. Trimethylaluminum does not react with itself, once all the available hydroxyl groups have been consumed the reaction stops. This self limiting causes the perfect uniformity and conformity of ALD processing. The excess Trimethylaluminum and CH4 byproducts are pumped away. |
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3. The second precursor, H2O, is introduced to the chamber. Water vapor reacts with the CH3 groups on the new surface, forming Al-O bridges and hydroxylating the surface. Methane is produced as a byproduct of this reaction. 2 H2O + :Si-O-Al(CH3)2 > Si-O-Al(OH)2 + 2 CH4 |
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4. H2O continues to react with the CH3 groups until the surface is passivated. Water vapor does not react with OH groups, once all the available OH groups have been consumed the reaction stops. This self limiting causes the perfect uniformity and conformity of ALD processing. The excess water vapor and CH4 byproducts are pumped away. |
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| One complete ALD cycle will produce approximately 1 angstrom (0.1 nm) of film thickness. The ALD cycle can be repeated in this way until the appropriate film thickness is grown. | Two reaction steps in the ALD cycle: Al(CH3)3 + :Si-O-H > :Si-O-Al(CH3)2 + CH4 2 H2O + :Si-O-Al(CH3)2 > Si-O-Al(OH)2 + 2 CH4 | |
| Plasma Assisted Atomic Layer Deposition - Plasma is used to crack precursor molecules and/or add energy for surface reactions. | ||
| Processing Steps | Images | |
| Oxidizing step of the plasma assisted atomic layer deposition cycle. | 3. The plasma assisted ALD cycle proceeds exactly as above until reaching step 3. During this step, O2 plasma or Ozone (O3) is introduced into the chamber. The oxygen radicals react with the CH3 groups on the new surface, forming Al-O bridges and forming a hydroxylated surface. CO, CO2, H2O, and CH4 are produced as byproducts of these reactions. Oxygen Plasma reaction during Al2O3 film growth 4 O(plasma) + :Si-O-Al(CH3)2 > Si-O-Al(OH)2 + CO2 + H20 |
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ALD Temperature Window
The chemical and physical conditions necessary to obtain self-limiting growth differ for each ALD process. Furthermore, each process is deemed to have a specific temperature window in which ALD behavior is obtained. An idealized temperature window is plotted to the right where the growth per cycle is plotted as a function of temperature. The ideal temperature window represents the temperature range over which the growth per cycle shows weak or no temperature dependence. This is indicated by the horizontal in the plot to the right. Outside the temperature window, chemical and physical processes can disrupt the ALD behavior. Condensation - At low temperatures, some precursors and co-reactants can condense on the surface, leading to an increase in growth per cycle. Low reactivity - The reactivity of the molecules with the surface sites can be too low because of limited thermal energy at low temperatures. This prevents saturation of the reaction and leads to a decrease in growth per cycle. Decomposition - At high temperatures the precursors or co-reactants can decompose, leading to a CVD component and an increase in growth per cycle. Desorption - At high temperatures the film itself or the reactive surface groups involved may desorb or etch. This leads to a decrease in growth per cycle. |
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Specifications
Available Chemistry
| Precursor | Skeletal Formula | Notes |
| H2O (Water) |
| Ultrapure Water (UPW) from the Birck UPW system. Filled directly from faucet to stainless steel cylinder, contamination prevention. Chemical Formula: H2O CAS Number: 7732-18-5 |
| Aluminum Oxide |
| Trimethylaluminum, min. 98% Chemical Formula: (CH3)3Al CAS Number: 75-24-1 Strem #98-4003 |
| O3 (Ozone) |
| See Ozone Delivery System Wiki for details Chemical Formula: O3 CAS Number: 10028-15-6 |
| Hafnium Oxide |
| Tetrakis(dimethylamino)hafnium, 98+% (99.99+%-Hf, <0.2%-Zr) Chemical Formula: Hf(N(CH3)2)4 CAS Number: 19782-68-4 Strem #98-4021 |
| Silicon Oxide |
| Tris(dimethylamino)silane Chemical Formula: ((CH3)2N)3SiH CAS Number: 15112-89-7 Sigma-Aldrich #759562 |
| Gas | Max Flow Rate (sccm) | Notes |
|---|---|---|
| Argon Carrier | 200 | Flows through the manifold, into the process chamber. This gas is used to carry the precursors from the precursor manifold, into the process chamber. |
| Argon Plasma | 1000 | Flows from the plasma generating coil (above the chamber) to the process chamber. If not using plasma, this gas should still be used to prevent precursors from entering the quartz plasma tube. |
| Nitrogen | 200 | Can be used alone, or as a fraction of a plasma gas mixture. |
| Oxygen | 200 | Can be used alone, or as a fraction of a plasma gas mixture. Mass flow controller cannot be powered at the same time the Hydrogen controller is powered. |
| Hydrogen | 200 | Can be used alone, or as a fraction of a plasma gas mixture. Mass flow controller cannot be powered at the same time the Oxygen controller is powered. |
RF Plasma Controls
| RF Source | Max Power (watts) |
|---|---|
| ICP Coil | 300 |
Available Standard Recipes
C:\Cambridge Nanotech\Recipes\
| Recipe Name | Notes |
|---|---|
| IdleSystem | The idle system recipe performs a 10 minute plasma clean of the chamber and sample carrier. It also sets all tool conditions to idle state upon completion. |
C:\Cambridge Nanotech\Recipes\User recipes\Standard Recipes
| Recipe Name | Precursors Used | Notes |
|---|---|---|
| Plasma_SiO2_250C | Organometal: Tris(dimethylamino)silane ((CH3)2N)3SiH | Silicon Oxide recipe using Argon/Oxygen plasma as the oxidizing agent during the ALD cycle. |
Oxidizer: Oxygen Radical O* | ||
Plasma_HfO2_250C Plasma_HfO2_200C Plasma_HfO2_150C Plasma_HfO2_110C | Organometal: Tetrakis(dimethylamino)hafnium Hf(N(CH3)2)4 | A collection of Hafnium Oxide recipes at various temperatures. These all use Argon/Oxygen plasma as the oxidizing agent during the ALD cycle. |
Oxidizer: Oxygen Radical O* | ||
Plasma_Al2O3_250C Plasma_Al2O3_200C Plasma_Al2O3_150C Plasma_Al2O3_110C | Organometal: Trimethylaluminum (CH3)3Al | A collection of Aluminum Oxide recipes at various temperatures. These all use Argon/Oxygen plasma as the oxidizing agent during the ALD cycle. |
Oxidizer: Oxygen Radical O* | ||
Thermal_HfO2_200C Thermal_HFO2_110C | Organometal: Tetrakis(dimethylamino)hafnium Hf(N(CH3)2)4 | A collection of Hafnium Oxide recipes at various temperatures. These use water vapor as the oxidizing agent during the ALD cycle. |
Oxidizer: H2O (Water Vapor) | ||
Thermal_Al2O3_250C Thermal_Al2O3_200C Thermal_Al2O3_150C Thermal_Al2O3_110C | Organometal: Trimethylaluminum (CH3)3Al | A collection of Aluminum Oxide recipes at various temperatures. These use water vapor as the oxidizing agent during the ALD cycle. |
Oxidizer: H2O (Water Vapor) |
C:\Cambridge Nanotech\Recipes\User recipes\High Aspect Ratio Recipes
| Recipe Name | Precursors Used | Notes |
|---|---|---|
| Exposure_Thermal_HfOx_150C | Organometal: Tetrakis(dimethylamino)hafnium Hf(N(CH3)2)4 | Hafnium Oxide recipe using exposure mode of the Fiji ALD. This recipe is intended for high aspect ratio features (10:1). Deep tightly spaced trenches for example. |
Oxidizer: H2O (Water Vapor) |
Sample Requirements and Preparation
Technology Overview
Clean, vacuum compatible non-outgassing materials. Check with Jerry Shepard for compatibility.
Set appropriate number of cycles to grow the film thickness desired. Most recipes generate approximately 1 angstrom per cycle of film thickness. There is an 50 nm administrative limit on the film thickness allowed in one growth. If you need to grow films thicker than this, you will need special permission from the engineer and Professor Zhihong Chen.
1 nm = 10 angstrom, or 10 ALD cycles will produce approximately 1 nm of film. (500 ALD cycle limit)
Sample Requirements and Preparation
Small silicon samples, on the order of 5 x 5 mm and smaller, can be lost in the chamber during pumping. These samples cannot be retrieved. A good solution to this problem is presented in the image below. Two glass slides are placed such that they are perpendicular to the loading tool arm. The sample is placed between these two slides to shield the sample from gas flows created by initial pumping and stabilize its position on the chuck.
| Note |
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New glass slides are not clean! You must clean them using the standard TAI solvent cleaning process before placing them on the chuck or inside the ALD chamber. |
Standard Operating Procedure
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Questions & Troubleshooting
How do I know if my growth proceeded as expected?
The Fiji does not provide direct feedback that ALD growth has taken place. The best indication we can get from the Fiji itself is tool performance throughout the recipe. This is easily checked by reviewing the pressure peaks associated with your growth process. Upon close examination, you will find two sets of peaks, one from the precursor material, and one from the oxidizing material. These pulses alternate on the pressure graph so that one pulse will be precursor (precursor is the very first pulse in standard recipes), followed by oxidizing agent, followed again by precursor and so on for the number of cycles defined in the recipe. In a successful growth, all precursor pulses should be roughly equivalent in peak height and all oxidizer pulses should be roughly equivalent in peak height. Comparing an oxidizer to precursor pulse will only indicate differences/similarities in vapor pressure for the two materials. Also worth noting, the first couple pulses of either precursor or oxidizer may be higher than the remaining process as they have had more time to vaporize while idle. Since ALD is a self limiting process, this should have little to no effect on your growth.
| Instructions | Graphics |
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We have recently developed a tool and placed it on the desktop of the Fiji computer. You will find a spreadsheet called "Growth Check.xlsm". |
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Open this spreadsheet, and press the |
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An Open file dialog will launch for you to select the pressure log data from your growth process. This should open up in the appropriate folder by default. You will see data logs from all recipes run on the system in the form of .txt files. Find the file associated with your growth, select, and press Open. File names are formatted as: Year_Month_Day_Hour_Minute_Second_Recipe_Name.txt Hour field is in 24 hour format example: File name "2019_08_21-15-38-21_Thermal_Al2O3_250C.txt" means: The recipe named "Thermal_Al2O3_250.txt" was ran, starting at 3:38:21 pm on August 21, 2019. |
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| Spreadsheet macro will run behind the scene and end with a dialog box stating "Process Complete", press OK. |
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| You should now see a chart with data from the fifth cycle and last cycle of your process. Each frame should contain two pulses as shown in the example data. If peaks are missing or significantly different between the frames, your growth likely experienced a problem and should be investigated. |
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Process Library
References
Per E-mail on 5/8/2018 from Adam Bertuch
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