Megasonic Quick Dump Process Recommendations

PROCESS DESCRIPTION: ACCUMEG MEGASONIC QUICK DUMP SYSTEM

The purpose of the Accumeg quick dump process is to remove, or keep suspended, any trace ionic species and/or particulate contaminants carried over from prior process steps that are held in the fluid boundary layer surrounding the wafers. The QDR rinse sequence is also critical for cleaning the QDR process vessel walls and cassette.
While there are many processes which benefit from megasonic quick dump enhancement, two representative processes are shown in the table below. Process A is typical of quick-dump rinse that follows a prior cool process (under 100o C), while Process B similarly describes a quick-dump rinse that follows a prior hot process (over 100o C). The following table presents the general requirements for these two typical processes. Following the Table of General Process Requirements, is a more detailed recommended process sequence for both A and B is given. Table of General Process Requirements:


A

Time/Temp/Flow

Set points for Rinsing immediately following an under-100oC prior process

[Examples: Post SC1 (NH4OH+H2O2+DI H2O) or SC2 (HCL+H2O2+DI water) Cleans]
 
  1.   Start with a fresh, ambient DI-water cascade overflow of approximately 30 seconds, turn the megasonic energy on, then insert wafer load. All following rinse cycles should be with cold DI water. Do a minimum of four dump, fill and spray cycles, ending in wafer-load withdrawal during an overflow with bottom fill only. 
  2.   DI-water fill rate must be adequate to fill the process vessel within 40-60 seconds with a combination of top spray and bottom fill. The top spray should be approximately 30% of the total DI-water flow.
 
B Time/Temp/Flow

Set points for Rinsing immediately following an   over-100oC prior process

[Examples: Post Hot Piranha (H2SO4+H2O2+DI water) or Hot Phosphoric (H3PO4) applications]
  1.   Start with a fresh, hot DI-water cascade overflow of approximately 30 seconds, turn the megasonic energy on, then insert wafer load. Do a minimum of 5 to 8 dump, fill and spray cycles, ending in wafer-load withdrawal during an overflow with bottom fill only. (The exact number of cycles depends upon the severity of carried-over contamination).
  2.   The DI-water temperature during the first two (2) rinse/dump cycles should be 65-70oC DI water. The subsequent cycles can be with ambient DI water.
  3.   DI-water fill rate must be adequate to fill the process vessel within 40 to 60 seconds with a combination of top spray and bottom fill DI water. The top spray should be approximately 30% of the total DI-water flow.
 
C  Megasonic Power Requirements
  1.   Megasonic power should only be applied when the transducer is completely covered by DI water to a depth of at least 6 mm. Failure to observe this procedure could result in the damage of the transducer voiding the warranty.
  2.   The amount of megasonic power required depends upon a number of factors such as degree of contamination, wafer surface condition and water temperature. However, a middle initiating point around which to determine the best power set point is usually in the 1½ to 2 watts per cm2 of the transducer area.

 

A and B Processes: Recommended Flow Description

  1.   Both processes commence by dumping the process vessel contents held over from last step of the prior batch (Step 15);
  2.    The Megasonic Quick Dump process vessel is filled using top spray and bottom fill manifolds and is permitted to overflow for thirty (30) seconds;
  3.    The top spray is turned off and the megasonic power is turned on;
  4.    The wafer load is inserted;
  5.    With the megasonic power on, the wafer load is held in the overflowing quick dump rinse process vessel for approximately five (5) seconds;
  6.    DI-water top spray is turned on; (Note: the DI bottom fill remains on)
  7.    The process vessel quick dump is activated;
  8.    Megasonic is turned off; (Note: DI water remains on)
  9.    Quick Dump closes after approximately four (4) seconds;
  10.   Once the water-fill level is approximately 6 mm above the transducer, the megasonic power is turned on;
  11.   With the megasonic power on, the process vessel continues to be filled by both the top spray and bottom fill;
  12.   Once filled, the process vessel is allowed to overflow for approximately 5 seconds and then again dumps;
  13.   The above megasonic-rinse sequence (Steps 8 through 12) is repeated for the minimum number of cycles recommended for the particular A or B process (See Recommended Process Parameters in preceding chart);
  14.   In the last cycle, the process vessel does not dump but remains in overflow mode with the megasonic power and DI bottom fill on, and the DI top spray off, while the wafer load is removed from the QDR and proceeds to its next process step;
  15.   Once the wafer load has been removed from the ACCUMEG Quick Dump Rinser, the megasonic power and DI-water fills are turned off (except for a trickle purge of approximately 4-6 L/hr which is required to remain on at all times). The system remains in this standby condition, ready for the beginning of the next cycle.


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