Plasma Etch PE-50 Plasma etcher/cleaner

Introduction: 
Photo of PE-50 system

Figure 1: Front view of PE-50 plasma etcher with door open. The gases are controlled by the manual mass flow controllers (visible at upper right) while the plasma power is controlled by the rotary knob to the left of the touchpad panel.

The system uses Ar and O2 gases and is currently mostly dedicated to O2 plasmas. It can be used for descum, or total removal of photoresist.  Figure 1 shows a front view of the system with the chamber door opened to display the tray where samples are mounted.

Author:

Mario Beaudoin, Rev. 01, November 2016

Process expectation:

AZ4110P photoresist etch rate is roughly 20 nm/min with an O2 plasma at full power and 200 mTorr pressure.

Pre-process check:
The system should be found at atmospheric pressure with the gases open at the wall as shown on figure 2.  The first step is to run a plasma with the chamber empty to make sure that it is operating as expected.  For instance, an oxygen plasma should be white; if it is not white, then the process gas is polluted, probably by nitrogen, and the oxygen line needs to be purged prior to running the process on a real sample.
Choosing menus and setting plasma parameters
Figure 3 shows the touchpad front panel of the PE-50 etcher.  Using the left and right arrows switches between the Setup and Commands menus.  Press the Enter key (big left pointing arrow) to choose the menu you wish to use.
Setup menu
The Setup menu is where the user chooses the plasma parameters.  Set each parameter, followed by the Enter key.  Make sure the Auto-cycle is ON when the end of the Setup menu is reached.  Depressing the UP arrow brings the display back to the main menu.  Following are the values of a typical process:
  • Plasma time: 30s to several minutes
  • Vacuum Set Point: recommend 80 mTorr; this is the lowest vacuum attained during pumpdown
  • Atmospheric Vent: 00:59 min
  • Purge Vent: 45s
  • Gas Stabilize: 59s  (this is roughly the time needed to adjust the plasma pressure by controlling the gas flow)
  • Vacuum Alarm: 3:00min (please notify the ANF management if this happens; probable causes are improperly closed door or failing vacuum pump)
  • Auto-cycle:  Make sure it is ON (Enter key toggles the condition)
  • Hit the UP arrow to get back to the main menu
Commands menu generating plasma

The Commands menu toggles between Plasma, Cycle-ON and Cycle-OFF possibilities.  Only the Plasma needs to be used if the setup chose Auto-cycle.  To begin a process, chose the desired plasma power by turning the black knob at the left of the touchpad clockwise: the Maximum power is 100W.  From the Commands-Plasma menu, hit the Enter key.  The display will show the Vacuum Setpoint (S) and the Attained Vacuum (A).  When the A value reaches the S value, the gases are turned on.  At that point, depress the Left Arrow on the touchpad: the screen will display the chamber pressure.  You now have the Gas Stabilize time, chosen at Setup stage, to purge the lines of residual gas and to set the desired plasma pressure.  Follow this procedure:

  • Open the mass flow controller (MFC) valve until the little black ball hits the top of the display; pressure will be high in the chamber; this step is important to purge both the chamber and the gas line of potential air contamination
  • Close the MFC almost fully.
  • Adjust the MFC flow to control the plasma pressure: pressure should be between 150-300 mTorr for best plasmas (for oxygen, 15 cc/min flow yields roughly 200 mTorr pressure)
  • The plasma will turn on by itself and will be indicated by the red light just above the power knob.
  • An oxygen plasma should be white and and Argon plasma is purplish blue
Removing and terminating the process

The plasma will stop on its own.  If Cycle-ON was properly set at the Setup stage, the system will purge the chamber.  When the cycle has completed, the display will be back to Commands Menu (see Figure 3).  Close the MFC valve, remove your samples and close the door.

photo of incoming gas lines at cleanroom wall

Figure 2: To make sure the gases are on, the black valves need to be parallel to the gas lines

Images of PE-50 control panel

Figure 3: Control panel touchpad. The process parameters are set in the Setup menu while the process is controlled in the Commands menu.