Xactix XeF2

Dry Etching
Etch/Dep room
Sun, 01/01/2006
Coral Name: 
Vapor phase isotropic silicon etch for structure release.



This tool is meant to isotropically etch silicon using a gas phase. The gas is produced by a solid source of XeF2

XeF2 vapor phase etching exhibits nearly infinite selectivity of silicon to photo-resist, silicon dioxide, silicon nitride and aluminum. Being a vapor phase etchant, XeF2 avoids many of the problems typically associated with wet processes. K. Pister discusses the use of xenon difluoride, as an etchant for MEMS applications, in part in US patent number 5,726,480.




Login in

The e1 Series is set up so that individual users are required to log in to the system. When starting the e1 Series the prompt below will be displayed. The general username/pwd to use is engineer/recipe

Main menu

Upon a successful login, the main menu will be displayed as shown below which also indicates the software version number.  When the main menu is displayed, the chamber is under vacuum and ready for use. A schematic for the machine is shown on the right. Red dots denote closed valves, while green dots represent open valves. Pressure gauges for the main chamber and the expansion chamber are at the bottom right. The three options available on the main menu consist of performing an etch, loading/unloading a sample, and accessing the maintenance menu.




To load/unload a sample:

  1. Press “Load/Unload sample” on LCD screen.  The system will go through prompts to ensure a correct decision: Are you sure? Press YES if you’re sure, NO if you’re not. This prompt is provided since the load/unload process can be time consuming and is inconvenient if accidentally started. The system begins chamber purges and flushing cycles to evacuate the chamber, shown below.
  2. If the chamber ventilation shroud covering the chamber is not pulled fully forward (see Figure 30), a request to close the shroud will be displayed before venting the chamber.  Move the shroud forward and acknowledge the prompt.
  4. When the chamber is vented, the dialog box below will appear and you can open the chamber lid. The lid will rest open on the stop behind chamber.
  5. If desired, load a sample.  If the sample holder and pins have not been placed inside of the chamber, and you wish to do so, please do so now.
  6. Close the lid.
  7. Press  “Done” on LCD screen as shown below, the system will go through a purging cycle prior to chamber pump-down.  As a side note, the Examine button only pumps the chamber down, without purges, so that the system can be quickly vented to load the sample.  This is very useful when examining a sample away from the system to prevent moisture from accumulating in the chamber.  However, it is always necessary to press Done before etching the sample.
  8. During the pumping cycle, a “click” sound will be heard that indicates that the ventilation shroud
    can be moved. 

Viewing the Log

The log may be viewed by clicking on the “View Log” button on the Main Menu. The log file is a database that is queried by beginning date and ending date. The “Today”: button will automatically set the dates to the current month, day, and year. The lot number, username, recipe, note’s keyword(s), and/or etching mode used can further specify your search.  Wildcard characters (*,?) may be used to fully specify the search criteria.



If the boxes are left blank, clicking the search button will reveal all history info, displayed in a tabular



Other Main Menu items

At the bottom left side of the main menu are buttons for changing the user’s password and logging out.

The log shows all of the operations that have been recently performed. The log can also be useful for

accessing the exact start and end times of a run. The “change password” button allows a user to

change their password by entering their username and previous password. The log-out button is used

to exit the system. A prompt will appear once the button has been pressed inquiring if the user wishes

to log out. Once the log out has been completed the system returns to the login screen.


Recipe Manager

The recipe manager may be used to copy other users’ recipes, located in their personal directory to the
current user’s personal directory. This option is limited to users with configurable etch access. The
current user’s personal recipes are displayed in the left box (in this case admin). The personal directory
for other users is found in the right box. The pull down bar at the top right can be used to select from
the personal recipes of various users. To copy a recipe into the current user’s directory, select the
desired recipe and click on the left arrow icon between the two directory windows.
A recipe may also be copied from the user’s personal directory to the global directory (if the user has
global write access). This is done by highlighting a recipe in the user’s directory, selecting Global
Recipes in the right window and then using the right arrow to copy it to the Global Directory. 

Performing an Etch

In order to perform an etch, the “perform etch” button in the main menu must be selected. The Xetch will prompt you to enter the lot number of the sample being etched. Press done once number is entered. The “perform etch” screen is shown below with lot number, “EXAMPLE” in this case; the screen pictured is for the normal etch mode.
It is important to note that in the “perform etch” screen, some options may not be available to certain users depending on the privileges which were given during the creation of their account.
The e1 Series software may be run in one of three operating modes that can be used during an etch.
Only one operating mode (Normal) is included with the system.
• The normal mode, (included at delivery) utilizes a pulsed etch with a set xenon difluoride
pressure and etch time.

Etch Menu Features

On the right side of the “perform etch” screen a valve schematic of the e1 Series is shown so that the user can monitor the machine operation. In addition to this, at the bottom of the right side of the screen are two counters. The first counter displays how much time has transpired during the etch portion of the cycle. The second counter shows the number of cycles completed. 
At the very bottom of the screen; “START ETCH”, this is used to begin the etching process; “STOP”, this is used to end the etch prematurely; “CHANGE CYCLES” button which at any time during an etch can be used to add cycles to the etch in-progress. Once selected, the “Change # of Cycles” menu on next page, is prompted. The top row of arrows will add cycles in this order, (right to left); ones, tens, hundreds, and thousands; the lower row of arrows, having the same values, will remove cycles. All the user has to do is click on the designated arrow for the desired number of cycles needed to be added to the etch in-progress. For an example, an extra 125 cycles have been added to the etch by clicking the right most arrow (ones) five times, the next right most arrow (tens) twice, and the 2nd from left most arrow (hundreds) once.  

NOTE: The “CHANGE CYCLES” button will only appear on the etch screen, if the etch parameter “Soft Stop” is set to “TRUE”, and only once etching has been started.

If “Soft Stop” is made “TRUE” in the “Etch Parameters” menu, the Xetch will allow the current cycle to finish before ending the entire etch. If the “STOP” button is pressed twice, the Xetch will prompt the above menu. Choosing “Yes, Hard Stop” will end the etch cycle
immediately and return the user to the main menu. If “No, Keep Waiting” is chosen only the current cycle will be completed before returning the user to the main menu. 

At the bottom of the screen there is a figure labeled ETA. This feature displays the expected completion time. The ETA is continuously updated during the process run.
Once the desired recipe settings have been chosen then etching can be initiated. By pressing the “Start Etch” button at the bottom left, the set values are stored and used to complete the desired etching sequence. At this point all of the controls will be disabled except for the stop button. 

At the bottom left side of the main menu are buttons for viewing the e1 Series Log, changing the user’s password, and logging out.
The log shows all of the operations that have been recently performed. The log can also be useful for accessing etch information, such as the exact start and end times of a run.
The change password button allows a user to change their password by entering their username and previous password.
The log out button is used to exit the system. A prompt will appear once the button has been pressed inquiring if the user wishes to log out. Once the log out has been completed the system returns to the login screen.


Performing an Etch in the Normal Mode

 Normal Mode Etching Variables

Number of cycles

Since the e1 Series is primarily a pulsed xenon difluoride etching system, the duration of etching is controlled by the number of cycles. A cycle consists of the xenon difluoride sublimating to the set pressure in the expansion chamber, etching for a set amount of time and evacuation of the main chamber and expansion chamber. 
Etch Time
When the valve between the main chamber and expansion chamber is opened the pressure equilibrates and the etching process begins. The etch time is the time between the opening of the valve between the expansion chamber and the process chamber and the opening of the valve between the process chamber and the pump. 
XeF2 Pressure
In order to introduce the proper amount of xenon difluoride into the main chamber a set pressure charge of xenon difluoride must be delivered to the expansion chamber. Because xenon difluoride has a vapor pressure of ~4T at room temperature the upper limit for the XeF2 pressure is approximately 4T. Due to the slightly elevated temperature inside of the etcher cabinet, you may be able to get considerably higher XeF2 pressures, however.
N2 Pressure
Nitrogen can be added into a recipe to improve selectivity. The pressure obtained in the expansion chamber likewise controls the amount of nitrogen introduced into the process chamber. The above variables can be set either by moving the white slider on the scroll bar or by tapping or depressing on the arrows at the top and bottom of the scroll bar to increment each value or by direct entry through the keyboard. Additionally, a range button is included for the number of cycles, etch time and nitrogen pressure so that the user can input higher values than the default range allows. The “perform etch screen” is shown below in normal mode. 


 Process tips


Material Effect
Acrylic     Does not etch 
Aluminum  Does not etch
 Gallium  Does not etch
Molybdenum  Etches
 Nickel  Does not etch
Nitride Does not etch 
 Packaging metal  Discolors
Poly-Si Etches 
 Photoresist  Does not etch. May be difficult to strip after long etches
 Platinum  Does not etch
 Silicon  Etches
 Silicon Carbide Does not etch
 Silicon Germanium  Etches
Titanium  Etches
 Tungsten  Etches very rapidly