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Operating Instructions- Ox-35

Here are operating instructions for the Ox-35 etcher. They come courtesy of superuser Alex Piggott.

 

 

OX-35 Oxford III-V Etcher Instructions

Version: 1.0.4

Last Edit: 2013/02/26 (Alexander Piggott)

General Overview

The OX-35 Oxford etcher is an inductively-coupled plasma (ICP) reactive ion etcher (RIE), designed for etching III-V semiconductors. The OX-35 is currently approved to etch GaAs, InGaAs, InAs, InP, InGaAsP, and GaP only. Please contact Jim McVittie (mcvittie@stanford.edu) for approval to etch other substrates.

There are several important points regarding usage of this etcher:

1.       Only 4” wafers can be etched using this machine. Any smaller chips must be mounted on a carrier wafer for etching. Any carrier wafers that are not etched by the chemistry can be used; Si and SiO2-on-Si wafers are acceptable with most chemistries.

2.       5mm EBR (edge-bead removal) is required on all wafers due to the wafer clamp. The backside of the wafer must also be clean.

3.       Never run the etcher without a wafer in the chamber, especially during cleaning. The plasma will damage the wafer clamp if it is exposed.

4.       Never place a wafer back into the etch chamber after running a process without physically resetting it! The wafer may shift, leading to breakage.

5.       When evacuating the load lock, ensure “Soft Pump” is selected (green check mark) to ensure that the wafer does not shift at the start of pumping.

The measured bias voltage may drift significantly if an oxide carrier wafer is used, but this is not indicative of actual process variations.

Basic Instructions for Etching a Wafer

1.       Log in: system→password. Username = “super user”, password = “ox-35-su”

2.       Vent the loadlock: system→pumping

a.       Press the “Stop” button (stops pumping the loadlock)

b.      Press the “Vent” button (vents loadlock)

3.       Wait for the purge cycle (pre-vent, pump down, and final vent) to complete. The load lock pressure will rise to atmospheric pressure before the machine pumps the load lock back down to base pressure. The cycle should take 1.5 – 2min. You do not have to wait until the vent timer reaches zero, just until the final pump cycle reaches approximately atmospheric pressure (770 torr). The gauge is inaccurate above ~200 torr, and may only reach ~500-600 torr.

4.       Open the load lock and load your wafer.

a.       Wafer flat must face the two screws on the platter

b.      Make sure the wafer is correctly positioned, and firmly pressed against the screws. Even an offset of 1-2mm can cause wafer breakage.

c.       The wafer may shift after being placed in the etch chamber, and returned to the loadlock. Always re-position the wafer after running a recipe.

5.       Evacuate the loadlock: system→pumping

a.       Ensure “Soft Pump” is selected (green check mark)

b.      Press “Stop “ button (stops venting the loadlock)

c.       Press “Evacuate” button (pumps down the loadlock)

6.       When prompted by the system, enter the wafer name.

7.       Load recipe: Process→Recipe

a.       Make sure the system is in “automatic” mode. If it is in manual mode, change it to automatic.

b.      Press “Load”, click “Yes” when asked whether to overwrite, and choose the desired recipe.

c.       You can now edit the steps in the left-hand panel. These settings will only change temporarily unless you manually save the recipe.

8.       Run the recipe: in Process→Recipe, press the “Run” button. The system will automatically load the wafer, run the recipe, and unload the wafer.

9.       Vent the loadlock: system→pumping

a.       Press the “Stop” button (stops pumping the loadlock)

b.      Press the “Vent” button (vents loadlock)

10.   Open the loadlock and retrieve the wafer. NEVER place the wafer back into the etch chamber without physically resetting it! The wafer may shift, leading to breakage.

11.   Evacuate the loadlock: system→pumping

a.       Ensure “Soft Pump” is selected (green check mark)

b.      Press “Stop “ button (stops venting the loadlock)

c.       Press “Evacuate” button (pumps down the loadlock)

12.   Log out: system→password, then press “verify” without entering a username. The program will then enter the “View Only” mode.

 


 

List of Available Gases

The following gases are available for use:

·         BCl3

·         Cl2

·         HBr

·         CH4

·         H2

·         Ar

·         O2

·         N2

·         SF6

 

Standard Recipes (incomplete)

Before etching any wafers, one should run a cleaning recipe, followed by ~15 minutes of seasoning with the intended etch recipe. There should be a 1:1 correspondence between the time spent cleaning, and the time spent running any other recipes. After particularly dirty recipes (e.g. those using methane), even more cleaning is recommended. A blank Si wafer can be used for cleaning, but the same substrate should be used for seasoning as the carrier wafer for the actual etch.

·         OPT - Chamber Clean: standard chamber cleaning recipe

o        O2 (100 sccm), SF6 (100 sccm), 20 mTorr, 70 W RF power, 2000 W ICP power

o        ~10min run is recommended

o        This recipe is extremely effective at etching oxides; use a Si dummy wafer instead when running this recipe.

·         AR - GaAs Etch (High eR) - BCl3/Cl2: GaAs etch recipe

o        BCl3 (5 sccm), Cl2 (5 sccm), Ar (20sccm), 2 mTorr, 30 W RF power, 250 W ICP power

o        Etches 150nm diameter holes at ~130nm per minute

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