“Dry” (plasma) etching is used for circuit-defining steps, while “wet” etching (using chemical baths) is used mainly to clean wafers. Dry etching is one of the most frequently used processes in semiconductor manufacturing. Before etching begins, a wafer is coated with photoresist or a hard mask (usually oxide or nitride) and exposed to a circuit pattern during photolithography. Etching removes material only from the pattern traces. This sequence of patterning and etching is repeated multiple times during the chip making process.

Etch processes are referred to as conductor etch, dielectric etch, or polysilicon etch to indicate the types of films they are remove from the wafer. For example, dielectric etch is involved when an oxide layer is etched to leave “oxide isolators” separating devices from each other; polysilicon etch is used to create the gate in a transistor; dielectric etch is employed to etch via holes and trenches for metal conductive paths; and metal etch removes aluminum, tungsten, or copper layers to reveal the pattern of circuitry at progressively higher levels of the device structure.

Plasma etching is performed by applying electromagnetic energy [typically radio frequency (RF)] to a gas containing a chemically reactive element, such as fluorine or chlorine. The plasma releases positively charged ions that bombard the wafer to remove (etch) materials and chemically reactive free radicals that react with the etched material to form volatile or nonvolatile byproducts. The electric charge of the ions directs them vertically toward the wafer. This produces the almost vertical etch profiles essential for the miniscule features in today’s densely packed chip designs. Typically, high etch rates (amount of material removed in a given time) are desirable.

Process chemistries differ depending on the types of films to be etched. Those used in dielectric etch applications are typically fluorine-based. Silicon and metal etch use chlorine-based chemistries. A specific etch step may be performed on one or more film layers. When multiple layers are involved and also when the etch process must stop precisely on a particular layer without damaging it, the selectivity of the process becomes important. Selectivity is the ratio of two etch rates: the rate for the layer to be removed and the rate for the layer to be protected (e.g. mask or stop layer). Higher selectivities are usually desirable.

In reactive ion etching (RIE), described above, the objective is to optimize the balance between physical and chemical etching such that physical bombardment (etch rate) is sufficient to remove the requisite material while appropriate chemical reactions occur to form either easily exhausted volatile byproducts or protective deposits on the remainder (selectivity and profile control). Magnetically enhanced RIE can aid processing by increasing ion density without increasing ion energy (which can damage the wafer).

Ideally, the etch rate is the same (uniform) at all points on a wafer. The degree to which it might vary at different points on the wafer is known as non-uniformity (or microloading) and is usually expressed as a percentage. Minimizing non-uniformity and microloading are important objectives in etching.

Source: Applied Materials

Additional Reading

Moving atomic layer etch from lab to fab

ARTICLES



US demand for semiconductor machinery to total $7.4B in 2021

02/16/2018  Growth in demand for wafer processing equipment will account for the majority of value growth.

CSTIC and SEMICON CHINA 2018: Brooks Instrument to present new mass flow controller with self-diagnostics​

02/09/2018  Brooks Instrument will showcase its newly enhanced GF125 mass flow controller (MFC) with high-speed EtherCAT connectivity and embedded self-diagnostics at the China Semiconductor Technology International Conference (CSTIC) in conjunction with SEMICON China 2018 in Shanghai.

Leak check semiconductor process chambers quickly and reliably

02/08/2018  INFICON,a manufacturer of leak test equipment, introduced the UL3000 Fab leak detector for semiconductor manufacturing maintenance teams to easily check the tightness of vacuum chambers for wafer production.

Boston Semi Equipment develops custom automation modules for strip handling equipment

01/31/2018  Boston Semi Equipment (BSE) today announced that it has started shipping units of its new strip load/unload module to a top 10 semiconductor manufacturer.

Turbulent times ahead for trade

01/25/2018  International trade is one of the best tools to spur growth and create high-skill and high-paying jobs. Over 40 million American jobs rely on trade, and this is particularly true in the semiconductor supply chain. Over the past three decades, the semiconductor industry has averaged nearly double-digit growth rates in revenue and, by 2030, the semiconductor supply chain is forecast to reach $1 trillion.

NAURA Akrion Inc. acquired Akrion’s surface preparation business

01/18/2018  Beijing NAURA Microelectronics Equipment Co.,Ltd. and Akrion Systems LLC today jointly announced that the previously announced acquisition by NAURA has been completed.

$55.9B semiconductor equipment forecast: New record with Korea at top

12/12/2017  Today, SEMI, the global industry association representing the electronics manufacturing supply chain, released its Year-end Forecast at the annual SEMICON Japan exposition.

CVD completes purchase of 180,000 sq. ft. facility

12/08/2017  This new facility will be the primary manufacturing center for the Company’s wholly owned subsidiary, CVD Materials Corporation.

Semiconductor industry continues upward trend toward record year

11/30/2017  The semiconductor industry continued its upward trend in the third quarter of 2017, notching 12 percent sequential growth with strength across all application markets, according to IHS Markit.

OEM Group announces post-dice clean solutions for plasma and laser dicing methods

09/28/2017  OEM Group announced today a post-dice clean solution on the proven Cintillio Batch Spray platform following plasma and laser dicing methods.

Understanding the impact of valve flow coefficient (Cv) in fluid systems

09/26/2017  Understanding the impact of valve flow coefficient (Cv) in fluid systems for microelectronics manufacturing.

New deionized water vapor delivery module from Brooks Instrument

09/11/2017  Brooks Instrument will be exhibiting at SEMICON Taiwan 2017 with a new vaporization product, mass flow controllers with high-speed EtherCAT, and a broad range of other mass flow meters, controllers and capacitance manometers for semiconductor manufacturing.