How to Calculate Etch Rate

Etch Rate Calculator

Nanometers (nm) Angstroms (Å) Micrometers (µm)

Nanometers (nm) Angstroms (Å) Micrometers (µm)

Seconds (s) Minutes (min)

Results:

function calculateEtchRate() { var initialVal = parseFloat(document.getElementById('initialThickness').value); var initialFactor = parseFloat(document.getElementById('initialUnit').value); var finalVal = parseFloat(document.getElementById('finalThickness').value); var finalFactor = parseFloat(document.getElementById('finalUnit').value); var timeVal = parseFloat(document.getElementById('etchTime').value); var timeFactor = parseFloat(document.getElementById('timeUnit').value); if (isNaN(initialVal) || isNaN(finalVal) || isNaN(timeVal) || timeVal <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // Convert everything to Nanometers (nm) var initialNm = initialVal / initialFactor; var finalNm = finalVal / finalFactor; var deltaThickness = initialNm – finalNm; if (deltaThickness < 0) { alert("Final thickness cannot be greater than initial thickness."); return; } // Convert time to minutes for the standard rate (nm/min) // If input is seconds, timeVal * 0.0166667 = minutes // If input is minutes, timeVal * 1 = minutes var timeInMinutes = (document.getElementById('timeUnit').value == "1") ? timeVal / 60 : timeVal; var rateNmMin = deltaThickness / timeInMinutes; var rateAngstromMin = rateNmMin * 10; var rateUmMin = rateNmMin / 1000; var resultDiv = document.getElementById('etchResult'); var rateOutput = document.getElementById('rateOutput'); var detailsOutput = document.getElementById('detailsOutput'); resultDiv.style.display = "block"; rateOutput.innerHTML = rateNmMin.toFixed(2) + " nm/min"; detailsOutput.innerHTML = "Equivalent to: " + rateAngstromMin.toFixed(2) + " Å/min or " + rateUmMin.toFixed(4) + " µm/min.Total material removed: " + deltaThickness.toFixed(2) + " nm."; }

In microfabrication and semiconductor manufacturing, the etch rate is a critical process parameter. It defines how quickly material is removed from a substrate—typically a silicon wafer—during a chemical or physical etching process. Precise control over the etch rate is essential for achieving the desired device dimensions, ensuring uniformity across the wafer, and maintaining selectivity between different material layers.

How to Calculate Etch Rate

The calculation of etch rate is straightforward and relies on measuring the change in material thickness over a specific period of time. The fundamental formula used in cleanrooms worldwide is:

Etch Rate (R) = (T_initial – T_final) / t

Where:

• T_initial: The thickness of the material before the etching process begins.
• T_final: The thickness of the material remaining after the etching process is completed.
• t: The total duration (time) the material was exposed to the etchant.

Step-by-Step Calculation Example

Imagine you are performing a wet etch on a Silicon Dioxide (SiO₂) layer. To find the etch rate, follow these steps:

1. Measure Initial Thickness: Using an ellipsometer, you measure the starting oxide thickness as 500 nm.
2. Perform Etching: You place the wafer in a Buffered Oxide Etch (BOE) solution for exactly 2 minutes.
3. Measure Final Thickness: After rinsing and drying, you measure the thickness again and find it is now 340 nm.
4. Apply the Formula:
   Change in thickness = 500 nm – 340 nm = 160 nm.
   Etch Rate = 160 nm / 2 minutes = 80 nm/min.

Common Units of Measurement

Depending on the scale of the fabrication process, etch rates may be expressed in several different units:

• Angstroms per minute (Å/min): Used for very slow, precise atomic layer etching (ALE).
• Nanometers per minute (nm/min): The industry standard for most thin-film processes.
• Micrometers per minute (µm/min): Used for bulk micromachining or Deep Reactive Ion Etching (DRIE) where large volumes of silicon are removed.

Factors Influencing Etch Rate

Etch rate is rarely a constant value; it can be affected by several environmental and chemical factors:

• Temperature: In wet etching, higher temperatures generally increase the chemical reaction rate, leading to a faster etch.
• Concentration: The molarity of the etchant solution directly impacts how many reactive species are available to interact with the surface.
• Plasma Power: In dry etching (RIE), increasing the RF power increases ion bombardment and chemical dissociation, usually raising the etch rate.
• Loading Effect: This occurs when a large area of exposed material "consumes" the etchant faster than the system can replenish it, resulting in a localized drop in etch rate.

Why Etch Rate Uniformity Matters

It is not enough to have a high etch rate; the rate must be uniform across the entire surface of the wafer. Etch Uniformity is usually calculated as a percentage, comparing the rates at the center of the wafer versus the edges. High non-uniformity can lead to device failure, as some areas may be "over-etched" (removing necessary material) while others are "under-etched" (leaving unwanted residue).