Procedure to Optimize the Performance of Your Spin Rinse Dryer (SRD)
The following is a typical procedure (recipe) to optimize the performance of your Spin Rinse Dryer (SRD) and to ensure a clean product:
Step #1 Rinse 500 RPM 60 Sec
Step #2 Purge 2000 RPM 10 Sec
Step #3 Dry 1 2000 RPM 60 - 120 Sec
Step #4 Dry 2 600 RPM 120 - 240 Sec
*Note: If the Resistivity Modular is available, you can elect to rinse to resistivity instead of time to ensure a completely rinsed product by selecting auto mode. 1800 RPM is recommended maximum for 200mm Substrates when using your Spin Rinse Dryer.
PROCEDURE FOR SPIN RINSE DRYERS:
The rinse step is the step that allows enough DI water to flow across the substrates surface to remove any particulates or contaminates from previous chemical steps. Generally the time of this step is dictated by the size of the substrate, but normally the rinse step should be set at 60 seconds. If you have the resistivity option, whereby there is resistance probe in the drain area that measures the resistance of the water as it exits the bowl, you should utilize this option during the rinse. By utilizing this option, it gives you the additional benefit of “Rinsing to Resistivity”, of which as the timer expires, the rinse will continue until the Resistivity Set-point is reached, at which time then the recipe will advance to the next step. By utilizing this Resistivity function, it insures that your product is rinsed and ultimately cleaned to a certain cleanliness factor, as determined by the set-point that you program.
Generally, the best DI water will give you approximately 18 meg-ohms of resistance, thus setting the Resistivity Monitor to a set-point somewhere below will yield the best results. Normally the set-point, depending on your quality of DI water, is usually set between 10 – 15 meg-ohms. The other crucial factor within the Rinse Step is how fast I should spin the substrates when they are rinsing. Once again this depends solely on the material composition of your substrates, along with its diameter. Generally speaking, the rule of thumb is to set the Rinse at 500 RPM. It is within this range of revolution that you can actually clock the wafers inside the cassette to provide a complete 360 degree cleaning of the product.
The purge step is the step that allows the water to be blown out of the DI manifold. This is very important, so that there is no residual water left in the manifold to drip out during the Dry Step. Time on this step is based solely on the amount of time required to evacuate all the water from the internal DI line and the Rinse manifold. Generally 5 – 10 seconds is plenty of time to achieve this and it can be double checked by observing the DI line when the purge starts and timing how long it takes. In regards to the speed, there is no real magic behind this number, except you would want to utilize this step to ramp up to the speed of the next step, of which I would set the speed at 2000 RPM and will be explained in the next paragraph.
DRY #1 STEP:
This step is very important, not in just drying, but in improving yield results of your product down the line. It is within this step, that we are using the revolving centrifugal force of the Spin Rinse Dryer to sling as much water off of the substrates as possible, but unfortunately under the forces of gravity there will always be a droplet of water left within the center of the substrate. It is this droplet of water that we must quickly remove to prevent staining or hazing of the center area, due to the droplet drying. The only way to remove this droplet of water is to drop the speed of the revolution in a short enough time span to allow the droplet to run off of the edge of the substrate and fall off. It is here that the amount of time within this step plays the most important part... depending on substrate size, of which you want to minimize this step to get the bulk of the water off of the substrate but not too long to possibly cause problems with the center droplet. Generally this time is between 60 – 120 seconds in length, with 60 seconds for smaller diameter substrates under 125 mm (5”) and 120 seconds for 150-200 mm (6 – 8”) diameter. During this step, it has been found that the best speed to run is anywhere between 1800 – 2000 RPM (1800 for 200mm substrates). It was a misconception in the years past to run the dry speed up to 2800 RPM (the faster the better), however particle studies have shown that any speed over 2000 RPM is detrimental and creates more particulates then less in a Spin Rinse Dryer.
DRY #2 STEP:
This is the “drying” step of the Spin Rinse Dryer. It is within this step, that the bulk of the water is off of the substrate and the center droplet of water has aggressively moved and fallen off of the edge of the substrate. It is within this step that the bowl environment will become warm from the use of bowl heaters and N2 heaters to evaporate any remaining droplets caught within the cassette and on the bowl surface. The time on this step can vary according to personal preferences, but generally no longer than 240 seconds is needed to achieve this state of dryness. In regards to the speed, you need to lower the speed below the speed of Dry #1 Step in order to move the droplet of water from the center of the substrate and as a rule of thumb; we generally set this speed to be 100 RPM over the Rinse speed, thus being at 600 RPM.
To achieve the best performance out of your Spin Rinse Dryer (SRD), the following program should be instituted:
Step #1 Rinse 500 RPM 60 Seconds
Step #2 Purge 2000 RPM 10 Seconds
Step #3 Dry 1 2000 RPM 120 Seconds
Step #4 Dry 2 600 RPM 240 Seconds
ClassOne's Trident Spin Rinse Dryer: Trident Spin Rinse Dryer
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