Chapter 5.35

Nanox

Atmospheric Furnace for Growing Carbon Nanotubes

(nanox)

1.0         Title

Nanox atmospheric furnace for growing carbon nanotubes and wet oxidation (in Room 432b)

2.0         Purpose

This document describes the operation of the nanox atmospheric 3-zone furnace, which is capable to accept centimeter size chips. This furnace is designed for the growth of carbon nanotubes in sub-atmospheric conditions.  Nanox is also capable of performing wet oxidation on III-V semiconductors.

3.0         Scope

This chapter covers the general furnace operation for nanox, which includes process recipe loading, wafer loading/unloading, process status monitor, and user level problem diagnosis.

4.0         Applicable Documents

Revision History

4.1       EUROTHERM temperature controller/programmer TYPE818 manual (copy in office).

4.2       EUROTHERM MODEL808 digital temperature controllers installation and operation manual (copy in office)

4.3       EUROTHERM MODEL842 process monitor/indicator operation and installation manual (copy in office)

5.0         Definitions & Process Terminology

5.1         Carbon nanotube growth: A high temperature process that achieves the growth of carbon nanotube on solid phase catalyst.

5.2         Annealing: A high temperature process that keeps chips in an inert atmosphere.  Nanox may be used to anneal centimeter sized chips at high temperatures (up to 1100oC) for samples that do not require a clean environment.

5.3         Wet Oxidation: Oxidation using nitrogen bubbled through water.

6.0         Safety

Follow general safety guidelines in the lab as well as the specific safety rules, listed below:

6.1         Electric Shock Hazard: Nanox furnace operates on high voltage. Do not open or touch the high power electrical parts in the furnace cabinet.

6.2         Burn Hazard: The furnace can reach temperatures up to 1100ºC. Components like pulling rods, boats, and chips coming out of the furnace are very hot. Proceed with caution. Avoid touching any furnace quartz ware to prevent burning your hands, as well as contaminating the furnace. No flammable chemical, especially organic solvents are allowed at the load station, when the tube is open.

6.3         Chemical Hazard: Do not process toxic, potentially explosive material (confined environment at elevated temperatures, may cause explosion). Consult with process staff, if you are not sure about your process/material safety.


7.0         Statistical/Processes Data

7.1         Problem and comment section, under the equipment menu of the wand.

7.2         Enable message for users.

8.0         Available Processes, Gases, Process Notes

8.1         The available gases are: Methane (CH4), Ethylene (C2H4), Hydrogen (H2), Argon (Ar), methanol (CH3OH), and nitrogen (N2).

9.0            Equipment Operation

9.1         Enable System

Enable nanox in Wand.

9.2         Set Up Process Conditions

It can take up to an hour to have a stabilized process condition depending on how far the required process condition is from the current setting and the individual process requirements

9.2.1          Check Master Power

Make sure the breaker labeled MAIN is at on position. (master power is always left on)

9.2.2          Set Gas Flow Rates

Set the gas flow rates for the growth recipe.  For each channel on the MKS 651c meter, push each setpoint switch to ‘set’.  The set point can be adjusted by turning the set screws appropriate to each channel.

9.2.3          Set Pressure

As of now, there is no feedback control for the pressure inside the chamber.  The pressure may be set by adjusting manually the valve on the pump assembly.

9.2.4          Set Furnace Temperature

9.2.4.1    Constant temperature setting: It is used to stabilize the system or for a single temperature process. In most situations when the secondary display (see Figure 3) indicates SP (= setpoint), set point may be adjusted using the up or down bottom. Short presses step the setpoint by single units. Long presses accelerate the display for large changes. When the secondary display does not indicate SP, it is most likely that (1) manual is selected and lower display is forced to indicate the output power. Press Auto/manual bottom to switch to Auto setting. Or (2) Adaptive tune is engaged. Disengage the setting by depressing both the up and down bottoms together for 3 seconds.

9.2.4.2    Watch the substrate temperature at SUBSTRATE TEMP indicator. Note that the substrate temperature may have an offset to the set point. You should refer to the substrate temperature (boat temperature) as your process temperature.

9.2.4.3    Programmable temperature process: The EUROTHERM TYPE818 temperature controller/programmer is able to program desired temperature profiles with standard ramping parameters. Actually programming your set points or ramping profile is a set of operations initiated by pressing the mode key and going into program mode. The manual is located below oxidation furnace table. Refer to it to set the required heating profile. Do a test run before heating your sample.

9.3         Nanotube Growth

9.3.1          After the temperature has stabilized, pull out the glass paddle in the tube and load the samples.  Promptly insert the paddle back into the furnace.

9.3.2          Turn on the vacuum to pump down the furnace.  You may need to push on the furnace door to achieve the vacuum.  The base pressure of the pump is about 2.1 torr.

9.3.3          Wait for the temperature to stabilize again.  You may flow argon during the stabilization.

9.3.4          When the temperature has stabilized, turn on the process gases (Methane, Ethylene , Hydrogren, and/or Methanol) and time your run.  Make sure that the pressure does not exceed 100 torr – there is a safety interlock that disables all gas flow when the pressure exceeds this pressure.

9.3.5          Upon the end of your growth process, turn off the process gases first and wait until the base pressure is reached.  Stop the EUROTHERM program and cut off the power to the furnace.  You may turn on Ar or open the lid of the furnace to cool down faster.  If your process temperature is very high (>850oC), you need to wait for the furnace to cool down to a lower temperature (about 700oC) before opening the lid.

9.4         Wet Oxidation

9.4.1          For Wet Oxidation Only

Make sure DI water is enough for the stabilizing time AND the process time. Refill the bubbler when necessary. Do not fill the bubbler over 80% to avoid overflow

9.4.2          Select N2 Flow Path

Caution! Remove the cap of bubbler before turning on the N2 gas to avoid initial force. Put the cap back after 5 seconds) Toggle N2 supply up to flow N2 through bubbler for wet oxidation process, and toggle down to bypass bubbler for anneal process.

9.4.3          Adjust N2 Flow Rate

in N2 flow control unit, only Ch1 and Ch 3 are used. Use Ch1 for all the settings when process requires N2 to flow through the bubbler. Use Ch3 for all the settings when process requires N2 to bypass the bubbler.

9.4.3.1    Toggle on power of the N2 flow control unit (see Figure 1)

9.4.3.2    Toggle on required channel (Ch2 when N2 flow through the bubbler, Ch2 when N2 bypass the bubbler).  The LED of the corresponding channel will be lit.

9.4.3.3    Rotate the channel display to the desired channel.  N2 flow rate is shown in unit of 10 sccm.

9.4.3.4    In corresponding channel section, adjust N2 flow on SET PT screw using a small flathead screwdriver.

9.4.4          Set Bubbler Temperature (for wet oxidation only)

Water temperature is indicated in bubbler temperature controller.  The water temperature set point can be viewed by pressing * button.  The set point can be changed by pressing both * and p buttons with up or down arrows.

9.5         Unload Sample

You may unload once the temperature is below 350oC to ensure that the precious nanotubes are not destroyed in air.  To unload, turn off the argon flow first.  After the base pressure is reached, you may turn off the vacuum, and vent the chamber until atmospheric pressure is reached.  The furnace door can now be opened and the samples retrieved.  The vent valve is located at the back of the pump assembly.

9.6         Return to Standby Setup

Please close the lid of the oven and insert the paddle back into the furnace.  Leave the chamber vented, and make sure that the vacuum and all gase flows are off before leaving.

10.0        Troubleshooting Guidelines

11.0        Figures & Schematics

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 1 - Nanox Oxidation Furnace Front Control Panel  (wet oxidation)

 

Figure 2 – Nanox controls for Nanotube growth

 

Figure 3 - Details of Master Temperature Controller