|Plasma Etching and Dry Etching Information||BACK|
Background:Plasma etching or dry etching is one of the most important of all the semiconductor manufacturing process steps. It involves a vacuum process in which plasma is used to selectively remove material from wafers. The material remaining forms the circuit patterns on each chip. Prior to the plasma etching step, the photolithography step has defined which regions are to be removed, and which regions are to remain. The areas where photoresist has hardened (i.e., those which have been exposed to light) cannot be etched away. These areas will remain, forming the active layers of the chip.Types of Plasma Etchers:Reactive Ion Etchers (RIE) use chemically reactive gas plasma to remove material deposited on wafers. A typical RIE (parallel plate) system is made up of an aluminum vacuum chamber where lower electrode is electrically isolated from the rest of the chamber. The plasma is generated by applying a strong RF (radio frequency) electromagnetic field, typically 13.56MHz to the wafer platter (electrode). Above the platter a gas shower which has many small holes encompassing the diameter of the electrode introduces a specified amount of gas or gas mixture depending on the material being etched. This process is typically performed under a vacuum in the range of 10E-5 torr. High density sources such as ICP (inductively coupled plasma) can be used in conjunction with RIE yielding high etch rates. Deep Reactive Ion Etchers (DRIE) employs the same fundamentals as the reactive ion etchers (RIE) and is used to create deep penetration, steep sided holes and trenches. This process is used in the production of MEMS (micro electromechanical systems) and TSVs (through silicon vias) for 3D integration. The Bosch Process is a patented process used in the creation of these vertical structures.Considerations When Selecting a Used or Refurbished Plasma Etcher:
Within the RIE, RIE ICP and DRIE ICP many configurations exist. Below are some of the most common items that should be considered when choosing a plasma etcher.
Cluster Plasma Etcher:
A cluster plasma etcher has multiple etch process chambers fixed about a central transport chamber. This configuration utilizes a load lock which introduces wafers from a cassette into a main transfer chamber which then deals the wafer to various process chambers. When the plasma etching is finished the wafer is loaded into a cassette and exits the load lock. The entire process flow is accomplished without ever breaking vacuum. These are high throughput tools and used from mass production.
Batch Plasma Etcher:
A batch plasma has a single etch process chamber and wafers are typically loaded manually. They are typically used in low volume production and R&D applications. Vacuum is broken each time a specimen is loaded in the process chamber. However, batch tools can be fitted with a load lock alleviating to need to break vacuum which could limit exposure of hazardous gases as well a maintaining base pressure in the process chamber thus improving throughput. One should consider the need of a load lock when choosing a batch process tool.
In all RIE, RIE ICP and DRIE plasma etchers the diameter of the electrode is critical. The diameter of electrode should exceed the area of specimen being etched.
The number of gases is an important consideration when choosing a plasma etcher. Most systems can accommodate six to twelve gas channels per etch chamber. Each gas channel will incorporate a MFC (mass flow controller) which delivers a precise amount of gas. In is important to know what the flow ranges are in the used or refurbished plasma etcher that you are considering. For example if you need a 1000 sccm gas flow and the etcher has 50 sccm MFCs you cannot recalibrate this MFC to the 1000 sccm it is far beyond its range.
It is also a good idea to have extra gas lines installed. Having and extra gas line or two not only gives you room for expanding your process but is also gives you the flexibility to utilize the extra line in case another fails.
Electrodes in a plasma etcher can be heated via fluid or resistance heater. High temperatures in the range of 300C are achieved with resistance heaters.
Selecting the proper vacuum pumping system is important when buying a refurbished or used RIE or DRIE ICP plasma etcher. Considerations such as gas flow, process pressure, and the use of corrosive or reactive gases should be known. Typically a RIE, ICP or DRIE etcher will utilize a turbo pump as well as a mechanical pump. In addition a separate mechanical pump could be used when the etcher is equipped with a load lock. When using corrosive or reactive gases it is important that the vacuum pumps are compatible to operate with those gases. There are certain turbo pumps specifically designed for use with corrosive gases. For the mechanical vacuum pump PFPE (perfluopolyether) oils must be used when processing corrosive and reactive gases such as oxygen. This is critical when processing oxygen as the risk of fire or explosion is high when using hydrocarbon oil.
Plasma etchers and their systems components will require some form of cooling whether it is air cooling or mechanical cooling from a chiller. Below is a link to our chiller considerations document.
To view our complete stock of used RIE, RIE ICP, and other plasma etch tools, visit our Plasma Etcher Tools Category