Chapter 4.22
HMDS
(Primeoven and
Sink4 HMDS)
1.0
Title
HMDS (Hexa
Methyl Di Silazane)
2.0
Purpose
Hexamethyldisilazane (HMDS) is widely used in the semiconductor
industry to improve photoresist adhesion to oxides. The HMDS reacts with the
oxide surface in a process known as silylation, forming a strong bond to the
surface. At the same time free bonds are left which readily react with the
photoresist, enhancing the photoresist adhesion.
The process works
not only on silicon dioxide, but other oxides (e.g., Al203) as well.
3.0
Scope
Two methods are
used to prime wafers prior to the application of photoresist. Wafers are coated
with HMDS in the primeoven or in the wet sink. The primeoven is considered the
main process with the HMDS bubbler used as a back-up method, if the primeoven
is not available.
4.0
Applicable Documents
4.1 Hardcopy Y. E. S. primeoven manual in the
office.
4.2 Serial Number: 0024
4.3 Y. E. S. Primeoven LP-5 Model Number: YES/LP
III – M5
5.0
Definitions & Process Terminology
6.0
Safety
Do not allow it
to contact your skin and avoid inhalation. HMDS is flammable and reacts with
strong oxidizers and reducing agents.
7.0
Statistical Process Data
7.1 Refer to problem log.
8.0
Available Processes & Gases
8.1 Hexamethyldisilazane (HMDS)
8.2 Nitrogen
9.0
Equipment Operation
9.1 Primeoven HMDS
9.1.1
Enable primeoven on the wand.
9.1.2
Check to see that the following are correct:
9.1.2.1 The temperature
setting of 100ºC is displayed by red light.
9.1.2.2 The Minarik
controller displays red light on output 01.
9.1.2.3 Small red light is
lit on vacuum gage.
9.1.2.4 Vacuum gage
should read 1000 torr.
9.1.2.5 Check to see if
the thumbwheel is set to 0.
Note: If thumbwheel is not set at 0, turn
thumbwheel to zero.
9.1.3
Open door of primeoven.
9.1.4
Place Teflon® carrier with wafers into oven.
9.1.5
Close door.
9.1.6
Push start button.
Note: System should begin
pump-down to approx. 10 torr.
9.1.7
After three (3 ea) pump/N2-purge cycles to 10 torr, followed by a
pump-down to 1 torr, HMDS is dispensed into chamber.
9.1.8
Exposure to HMDS vapor produces a monolayer coating in one minute.
9.1.9
When the full cycle is completed (length of cycle: approx. 35
min.), an audible alarm will sound. It can be silenced by pushing the red reset
button.
9.1.10
Open the door and remove wafer carriers with red rubber heat
shield.
The optional alternate method for HMDS is the use of the bubbler
through HMDS in the recessed HMDS tank at sink4 in Y1.
9.2
SINK4, SINK5 HMDS
The procedure for using the HMDS at sink4 tank is as follows:
9.2.1
If your wafers were just freshly cleaned, or have been sitting out
in the air for a while, you should dehydrate them by placing them in a Tylan
furnace tube at 750ºC for 5 minutes, or in the convection oven at 120ºC for 15
minutes. If they are coming directly out of the furnace, they may be placed
straight into the HMDS tank as soon as they have cooled.
9.2.2
Place the cassette with your wafers in the HMDS tank in sink 4.
The HMDS bubbler is activated by the HMDS timer mounted on the upper front
panel of the sink. Turn the time switch past 5 initially to activate the time,
and then set your desired time. Prime for 1-3 minutes, taking care to replace
the top cover snugly.
9.2.3
Remove your wafers and spin resist immediately.
10.0
Troubleshooting Guidelines
N/A
11.0
Figures & Schematics
N/A
12.0
Appendices
12.1 Program
Entry
The Minarik WP-6200 series microprocessor-based controller can
drive four outputs and has a decision-making capability based on the status of
up to five user-programmed inputs. (The fifth input is an added special model
for YES.) The system utilizes all four outputs and all five of the inputs. They
are:
output 0 = cycle complete/abort light
output 1 = nitrogen valve
output 2 = vacuum valve
output 3 = HMDS valve
(Inputs are normally open circuits, activating will close
circuit.)
input A = start switch
input B = vacuum gauge, pressure greater than setpoint 1
input C = thumbwheel switch set at 2 or 3
input D = vacuum gauge, pressure greater than setpoint 2
input E = thumbwheel switch set at 1 or 3
The suggested program examines the status of user set interlocks.
These interlocks are the Granville=Phillips vacuum gauge setpoints. In the
steps where the interlocks are examined, we are looking to see if the unit has
reached a sufficient vacuum or pressure. If the interlock is not satisfied, it
means there is a major system leak, a defective pump, or an insufficient vacuum or pressure. If these interlocks are
not satisfied, the process will abort to user pre-programmed subroutines where
the "cycle complete" light flashes rapidly and the system is
back-filled with nitrogen until the reset button is pushed.
Note: The
abort cycles should be allowed to continue until the system has reached
atmospheric pressure, as indicated by the ability to open the door, before
pressing RESET.
In the case of the pre-HMDS vacuum cycle, if there is insufficient
vacuum, it will be useless to continue, since there will not be enough of a
vacuum to vaporize HMDS. The setpoints control the decision making process of
whether to continue the process or not. The proper setpoints are in the control
of the process engineer. Suggestions are 100-Torr for setpoint #1, and 10-Torr
for setpoint #2.
12.2 Re-Install
Program
Recheck the system in the following manner:
Insert key and turn to horizontal
position.
Confirm that the system is ready for
operation:
►
oil in the pump
►
pump exhaust connected and on
►
pump on
►
vacuum line connected
►
nitrogen lines connected
►
sufficient nitrogen pressure
►
cabinet exhaust on
►
system power on
►
HMDS in flask
►
temperature controller setpoints selected and stable
►
vacuum gauge setpoints selected
12.2.1
If the display of the microprocessor is off, press the green ON
button. The display should read RESET. If not, push the RESET (RST)
button.
12.2.2
Press the yellow program (PGM) button. You are now in the
program entry mode. This is possible only if the microprocessor was previously
in the reset mode. The display should now read the first step 01 and a
function, some data and the outputs to be activated.
12.2.3
Press the grey function (FUNC) button with up indicator once.
You will see the function display change. Continue pressing and the display
will march through all seven of the available functions. By pressing the FUNC
with down indicator you can reverse the direction.
12.2.4
Set the function display to M 99:59. This means that you
are programming in minutes and seconds. Using the DATA yellow buttons
set the time to 02:00 (02 mins, 00 secs).
12.2.5
Push the orange OUTPUT button #2 (O2). This
instructs the microprocessor to open the vacuum valve. (Step #1 is not
programmed as 2 minutes of output 2 in the actual process.) The OUTPUT
buttons both write and erase. If you push an OUTPUT button when the LED
indicator above is on, it will turn the LED off (erase the output ON
command).
12.2.6
Push the STEP button with the up indicator once. The
display now reads step 02. If you pushed the STEP button too many
times you can go backwards using STEP with the down indicator. Push
either grey FUNC button until you get to the IF _> _ statement
(> = GOTO). Using the yellow DATA buttons set the display to
read IF B> 30. This means on input B (insufficient vacuum) go to step
30 (abort cycle). (An input for the micro is a switch closure to ground). If
the vacuum gauge reads a pressure above the setpoint, the gauge's relay closes.
If the vacuum gauge reads below the setpoint (higher vacuum) the relay contacts
are open and no input signal is present.
12.2.7
Using these instructions as a guideline, complete program entry as
follows:
|
Program |
Priming Cycle |
Inputs
Activated |
|
0 1 2 3 4+ |
1 minute 10 seconds 1 minute Place vacuum in
flask Not used |
None E only C only E and C |
12.3 Process
Programs
|
STEP |
FUNC |
DATA |
OUTPUT |
COMMENTS |
|
01 |
IF A> |
03 |
|
Does not permit programming of Micro, |
|
02 |
GOTO |
01 |
|
Because it is in a constant RUN mode
when the key-lock is closed…Once START is pressed (input A), the
process goes to Step 03. |
|
03 |
IF C> |
05 |
|
Checking for Program 3 to replace vacuum
in flask… (Inputs C and E must be closed.) |
|
04 |
GOTO |
06 |
|
|
|
05 |
IF E> |
65 |
|
If so, go to 65 … Program 3 |
|
06 |
L = |
0003 |
|
3 loops of 7/9 |
|
07 |
M |
03:30 |
O2 |
3-1/2 min vacuum |
|
08 |
IF B> |
30 |
|
Low vacuum alert/abort, go to 30 |
|
09 |
M |
03:00 |
O1 |
3 min of HOT nitrogen back-fill |
|
10 |
IF B> |
12 |
|
If sufficient nitrogen back-fill pressure, go to 12 |
|
11 |
GOTO |
35 |
|
Low N2 pressure alarm/abort, go to 35 |
|
12 |
L> |
07 |
|
Loop back to 07 |
|
13 |
M |
04:00 |
O2 |
4 min vacuum pump down |
|
14 |
IF D> |
40 |
|
High vacuum alarm/abort (not reaching 10 Torr) |
|
15 |
IF C> |
60 |
|
Input C only, go to 60 … Program 2 |
|
16 |
IF E> |
55 |
|
Input E only, go to 55 … Program 1 |
|
17 |
L = |
0060 |
|
60 loops of … Program 0 |
|
18 |
S |
0100 |
O3 |
… 1 second of priming |
|
19 |
IF D> |
45 |
O3 |
Priming cycle alarm/abort (pressure exceeds 10 Torr) |
|
20 |
L> |
18 |
O3 |
Loop back to 18 |
|
21 |
M |
01:30 |
O2 |
1-1/2 min vacuum (final steps: To remove
HMDS vapors and backfill |
|
22 |
M |
01:30 |
O1 |
1 min nitrogen |
|
23 |
M |
02:30 |
O2 |
2-1/2 min vacuum |
|
24 |
M |
04:00 |
O1 |
4 min nitrogen |
|
25 |
M |
10:00 |
O0 |
10 min complete light/sound alert …PROCESS DONE |
|
26 |
GOTO |
00 |
|
RESET |
|
27 |
GOTO |
00 |
|