Laser Marking Quality Control: What Preventive Measures Must Be Taken

Semiconductor manufacturing is an intricate process that involves several steps, from growing silicon and doping to laser marking. This last practice is crucial to easily identify wafers, and it allows the making of substrates that serve as the foundation for integrated circuits (ICs), a highly demanded component in today's electronic devices.

For that reason, ensuring the quality of laser marking on wafers is also fundamental. To help you understand the significance of quality control during this step, we’ll explain the methods used and how they guarantee that the marks are consistent, long-lasting, and meet the industry’s specifications.

Understanding Laser Marking in Wafer Manufacturing

Laser marking is a non-contact technique that modifies a wafer’s surface by using a laser beam to leave a noticeable mark. This method, which offers a high-precision and effective substitute for conventional marking techniques, is extensively employed in the semiconductor industry to identify wafers, give them labels, batch information, and ensure the availability of other crucial data.

These markings are essential for traceability and wafer tracking during manufacturing, especially when working with large quantities of semiconductor components.

When wafers are used for IC and Chip fabrication, they’re often processed in multiple stages, including photolithography, etching, deposition, and doping. Due to the wide range of stages and to keep track of the substrates throughout the different processes, unique identifiers like barcodes, QR codes, and serial numbers are engraved onto the wafer's surface using laser marking.

Challenges in Laser Marking on Wafers

As you can see, laser marking is fundamental to providing traceability for substrates throughout the supply chain, helping identify defects, and ensuring that each wafer is properly handled and processed. However, laser marking on wafers presents several challenges that make quality control essential:

• Surface Sensitivity: Wafers are frequently fragile and may have a heat-sensitive surface like a thin oxide coating. Overusing the laser can damage the wafer's surface, resulting in flaws or reduced functionality.
• Small Scale: Wafer markings are usually extremely tiny, sometimes only a few microns. Achieving accuracy is essential because any deviation could lead to poorly placed or unreadable marks.
• High Throughput: Because wafers are processed in batches, the laser marking procedure must be accurate and efficient while preserving consistency. It is essential for quality control that every wafer in a batch has the same marking.
• Environmental Factors: The production environment's temperature, humidity, and contamination levels can all impact the laser marking's quality. All of these factors need to be calibrated correctly for reliable results.

Taking all of these into consideration, semiconductor manufacturers use various quality control techniques to monitor and guarantee the integrity of the laser marking process. Some of the quality control methods employed include:

1. Pre-Mark Inspection and Calibration

It is crucial to ensure the wafer is ready for marking and the equipment is correctly calibrated before starting the laser marking process. During this stage, several control checks are performed, including:

• Laser Calibration: The laser’s power settings need to be ideal for the wafer's material and thickness. Lasers with excessive or insufficient power can produce low-quality marks, such as ones that are too faint or damage the surface.
• Wafer Alignment: The wafer must be aligned properly to ensure the laser marks are placed in the correct locations. There are systems that automatically align a wafer alignment and place it in the ideal position for the laser. Failure to achieve this will lead to future inaccurate marks and identification errors.
• Examining the Wafer Surface: Before the laser marking process begins, the wafer's surface needs to be clear of impurities like dust or oil. Contaminants can interfere with the laser marking process and cause inconsistent marks.

2. Real-Time Monitoring During Marking

After the wafer has been aligned and the laser system has been calibrated, real-time monitoring during the laser marking process is required to ensure the marks are produced as intended. To achieve that, several factors are kept in mind:

1. To guarantee that the energy supplied to the wafer is constant, the laser's power output must be continuously monitored, as any variation could lead to inconsistencies in the depth, clarity, or sharpness of the marking. To do so, automatic power systems adjust the laser’s power as needed.
2. Another element that may affect the quality of the marks is the speed at which the laser marking process is carried out. A laser that moves too fast or too slowly may cause problems like insufficient markings or excessive heat accumulation, so the systems are optimized to maintain a consistent marking speed.
3. Real-time monitoring can guarantee that the laser precisely forms the required pattern for more intricate markings, such as alphanumeric characters or QR codes. Systems that employ cameras or sensors take pictures of the markings while they are being made and confirm that they adhere to the intended design to accomplish this.

3. Post-Mark Inspection

Once the laser marking process is finished, a post-mark inspection is necessary to confirm the marks' quality and ensure the wafer meets the requirements. Oftentimes, the first step is a visual examination using automated optical inspection (AOI) systems.

These devices use high-resolution cameras to take pictures of the wafer surface and detect flaws such as improper alignment, missing marks, or excessive marking depth.

Laser scanners or optical imaging systems are sometimes used to measure the laser marks' clarity, contrast, and accuracy by taking detailed pictures of them. These systems can confirm that the marks satisfy particular optical and dimensional requirements, including size, sharpness, and legibility.

The contrast between the laser mark and the surrounding surface must also be measured to guarantee that the mark is readable and clear. A mark that is too shallow may eventually fade, while one that is too deep may result in unintended damage.

Specialized depth gauges and contrast analyzers are employed to verify these characteristics.

4. Traceability and Data Logging

After every wafer has been appropriately labeled and confirmed to meet quality standards, it is time to record the laser settings, wafer batch number, operator, and inspection results to make the information accessible whenever needed.

Manufacturers can spot patterns, irregularities, or reoccurring problems in the marking process by monitoring the laser marking procedure. Over time, quality can be improved by modifying the procedure using this information.

If flaws are found, manufacturers can identify the underlying cause—such as a calibration error, equipment failure, or environmental influences—by keeping thorough records of the marking procedure to prevent the recurrence of the issue in future batches.

Learn More About Laser Marking

Quality control procedures for laser marking on wafers guarantee the precision, legibility, and longevity of markings—critical for tracking semiconductor wafers during production. As technology develops, automated systems and data-driven feedback loops will improve laser marking accuracy and effectiveness.

While it may seem complex, this is necessary at Wafer World to ensure the best quality of our products. If you want to learn more about how we ensure that, reach out!