Silicon Wet Etching Using Modutek’s Nitrite Etch Bath

Modutek has been designing and manufacturing Silicon Wet Etching components and related equipment for over 30 years. Their more recent Nitrite Etch Bath products, including the “Nb” series, are an upgrade to their “Na” series. The Silicon Nitride Etch Bath has been designed and engineered to provide unparalleled process control. You can also expect flexibility and safety as key components of these systems.

Part of what makes the Nb Series silicon nitride etch bath stand out is its two-tiered diagnostic system. This allows the user of the system to monitor the temperature at the same time as it maintains the acid-to-water ratio through supplemented D.I. water. This new metering system makes the Nb easier to install. It also allows for service in existing process stations or in new ones.

Some of the benefits of the Silicon Wet Etching system include, but are not limited to, the following:

• Controlled Nitride Etching
• Nitride Etch Uniformity
• Remote DI water metering system
• Controls chemicals boiling (no “bumping”)

The silicon nitride etches function in a combination fluid – 85% phosphoric acid (H3PO4) and 15% DI water. These fluids boil at 160°C. Since the water will boil off some of the solution as steam, the NbSeries silicon nitride etch bath includes a refluxor which cools the condenser to cause the steam to condensate back to water which maintains the solution. Please be aware, the condensers are not 100% efficient, which will make it necessary to add water to the solution periodically.

Generally, it is discouraged to add water to acid, but it is required in this case. We have determined some safe ways to do this. For instance, if the acid rapidly agitates or boils, you can add a small amount of water which mixes right away. This poses no safety issues. When the water is added to non-boiling acid, the water sits on top of the acid. More water is added to the top layer of the acid. The water will mix as the heat absorbed by the water makes it boil. The water mixes thoroughly with the acid and the correct reaction occurs.

A basic chemistry rules states, “The temperature of a solution cannot rise above its boiling point, except under special circumstances.” The heater on our system does not have to be controlled the way it is required on other systems. If the heater switch is on, the heater is on. By choosing not to regulate the heater, the heat solution is allowed to boil regardless of the concentration. The system keeps it boiling while water is added to adjust the concentration, which remains at the upper set point.

The Silicon Wet Etching and Nitrite Etch Bath systems also include the following features:

• Etched-foil resistance heater
• PVDF or Teflon reflluxor with safety cover
• Vapor thermocouple
• Uniformity heat transfer
• Ease of installation and repair for new or existing wet station configurations

System Specifications include the following:

• Application: Silicon Nitride Etch
• Operating temperature range: 30 – 180º C
• Chemical usage: H20, H3PO4
• Heat-up rate: 2-3 º C per minute (rate affected by size of system)
• Process temperature control: ± 0.5º C
• Vapor thermocouple for chemical boiling control
• PVDF refluxor with Teflon® cooling coils
• One year warranty

Companies that need additional features may consider any of the following options. Modutek will work with you to design the Silicon Wet Etching system that best meets your company’s needs. Options include, but are not limited to:

• Teflon® gravity drain system
• Auto cover which is pneumatically actuated
• Remote operation timer switches
• Aspirator valve system
• Model C1815a process controller/timer
• RS232 Interface

To learn more about the Silicon Wet Etching products sold by Modutek Corporation, or to learn how our products can be redesigned to work with your Nitride Etch Baths or Quartz Baths and Sub Ambient Systems (BOE), contact us at 866-803-1533.