When using photoresist as a mask to etch a metal thin film layer by RIE, how to determine if the etching has been completed?

Dear Ou Zhang :

To determine if the etching of a metal thin film layer using Reactive Ion Etching (RIE) with a photoresist mask has been completed, you can follow these steps:

Visual Inspection: Initially, you can visually inspect the sample under a microscope to see if the metal layer has been completely removed. This can be done by looking for any remaining metal features or changes in surface texture.

Endpoint Detection: RIE systems often have endpoint detection capabilities. Endpoint detection relies on monitoring changes in a specific property, such as optical emission spectroscopy (OES) or mass spectrometry, that occur as the etch process progresses. Once a characteristic signal indicates that the metal layer has been etched through, the process can be stopped.

Time-Based Etching: If endpoint detection is not available or not reliable for your specific process, you can estimate the etch time based on previous experiments or literature values for similar materials. It's important to be cautious with this approach, as over-etching can occur, potentially damaging the underlying layers.

Cross-Sectional Analysis: After etching, you can perform a cross-sectional analysis of the sample. This involves cutting a sample, typically at a specific angle, and examining it under a microscope. This will give you a clear view of the metal layer's thickness and can help confirm if the etching is complete.

SEM/TEM Imaging: Scanning Electron Microscopy (SEM) or Transmission Electron Microscopy (TEM) can be used to inspect the cross-section of the sample to confirm the removal of the metal layer.

Sheet Resistance Measurement: You can also use a four-point probe or other electrical characterization techniques to measure the sheet resistance of the sample. If the metal layer has been completely etched away, the sheet resistance will be that of the underlying substrate.

Ellipsometry: Ellipsometry is an optical technique that can be used to determine the thickness of thin films. By measuring the change in polarization state of light after interacting with the sample, you can infer the remaining thickness of the metal layer.

Contact Angle Measurement: If the metal layer is on a substrate with a different wetting behavior, you can measure the contact angle of a liquid droplet on the surface before and after etching. This can give an indication of the presence or absence of the metal layer.

It's important to note that you may need to use a combination of these techniques for accurate verification. Additionally, always conduct a series of test runs to validate the chosen method for your specific process and materials.

Abdul kaium Mia

This is one of the common problems. It has one solution, your system needs to have highly repeatable such as

1. The PR thickness is almost uniform each time you coat it.

2. The etching rate with specific etching conditions needs to be almost the same.

By knowing the above two conditions and metal film thickness you can easily calculate how much time you need to process.

Thus you can exactly etch as much as you want.

Note: There is not direct way to know it etching is complete or not in RIE

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