Lam Research Rainbow 4420 plasma etch system

Where the Rainbow 4420 fits

The Lam Research Rainbow 4420 belongs to the 4400 series of single-wafer plasma etchers, which Lam built in several variants for different films; the 4420 is the polysilicon and silicon member. It etches one wafer at a time between parallel-plate electrodes with a recipe-controlled gap, fed automatically from cassettes through entrance and exit load locks. Fabs used it for gate poly and silicon etch on 150 and 200 mm lines for years, and used Rainbow 4420 etchers still run in pilot lines, MEMS foundries and power-device fabs.

For a pilot line, the attraction is repeatability: the same recipe on every wafer, cassette in and cassette out. The tool is less suited to labs that process pieces or change chemistries often. In that case an Oxford Plasmalab 80 Plus or ICP tool fits better.

Inspection points specific to the 4420

Thirty-year-old production etchers fail in known places, and we check each:

• Electrode assembly: wear and erosion of the upper and lower electrodes, the gap drive and the ceramic and quartz parts around them.
• RF generator and match: power delivery, reflected power and tuning range.
• Wafer transport: belts, arms, sensors and load lock doors, which cause most mis-handles.
• Vacuum: chamber and load lock base pressures, leak-up rates and pump condition.
• Gas delivery: mass flow controllers, valves and corrosion on chlorine lines.
• Electronics: controller boards, storage media and the stored recipes.

Where the tool runs at the seller's site, we watch it cycle a cassette and record any faults.

Refurbishment and decontamination

Because the 4420 usually ran chlorine-based chemistry, any work on it starts with purging and decontamination of the chamber and gas lines. Refurbishment then covers electrode parts, seals and consumables, transport adjustment, pump service and RF checks. A certified unit runs a test etch with rate and uniformity data in the report.

Keeping a legacy etcher running

Spare parts for the 4400 series come from used and refurbished stock; we are independent of Lam Research. Before you buy, we list the parts that are hard to find and suggest which spares to hold. Older controller hardware and storage media are a real risk, and we back them up on the first visit. Our post on keeping legacy tools running covers the approach in more detail.

Upgrades worth considering are dry pumps for corrosive processes, optical emission endpoint detection and replacement of failing control electronics where compatible parts exist.

Facilities

• Three-phase power, depending on configuration
• Process cooling water
• Clean dry air for pneumatics and nitrogen for purge and venting
• Process gas supply, with toxic or corrosive gas cabinets and detection for chlorine-based gases
• Exhaust with suitable abatement
• Floor space for the tool and its pumps, often in a sub-fab or service chase

Buying advice

Confirm wafer size, the chemistries the unit ran and whether all handler parts are present. Ask for the recipe set and any service logs. If you plan to etch a different film from the one the unit ran, check that its electrodes and gas panel suit the new process, because the 4400 variants were built for specific films and converting one means sourcing parts. Plan your toxic gas safety systems before the tool arrives, and see the etch category for other platforms.