Project

# Title Team Members TA Documents Sponsor
9 Dieagnosis
 Josh Hartman
Megan Zeng
The Minh Pham
 Yushi Zhou design_document1.pdf
proposal2.pdf
# Automated Optical Wafer Inspection System

Team Members:

- Megan Zeng (meganlz2)
- Josh Hartman (joshh3)

# Problem

In ECE 444, wafers are inspected under a microscope after fabrication steps to make sure the process was completed correctly. Since a wafer can contain dozens of dies and hundreds of devices, it is not practical to inspect every device after every fabrication step. Instead, only a small number of locations are usually inspected, and the rest of the wafer is assumed to be similar.

This can make it difficult to determine why a device fails after fabrication. For example, a problem with photoresist removal, etching, or deposition may affect a region of the wafer without being noticed during manual inspection. If the problem is only discovered during electrical testing, it can be difficult to determine which fabrication step caused it.

An automated inspection system could scan a much larger portion of the wafer after each fabrication step and identify regions that differ from the expected surface condition. This would provide additional information about where a fabrication problem may have occurred without requiring manual inspection of the entire wafer.

# Solution

We propose an automated optical wafer inspection system that uses a laser and photodiode to measure the optical response of different locations on a wafer. A low-power laser will illuminate the wafer, and a photodiode will measure reflected or scattered light from the surface. The measured signal will be compared against a baseline from an "ideal" wafer. Differences in the measured signal can indicate changes in the surface caused by fabrication anomalies.

The wafer will be mounted on an X-Y stage that moves it through a grid of measurement locations. The laser and photodiode will remain fixed while the wafer moves underneath them. A microcontroller will control the stage, collect measurements from the photodiode, and record the measurement location. The measurements will then be sent to a computer, where they will be compared against the baseline and displayed on a map of the wafer.

The system will be enclosed to reduce the effects of ambient light and keep the optical components in fixed positions. One intended application is inspecting a wafer after photoresist removal to identify regions where resist may remain before the wafer proceeds to a thermal processing step. Removing PR before a furnace step is important because PR can both severely contaminate the furnace and ruin sections of the wafer. Other surface anomalies may also be detectable depending on the optical response of the wafer at different stages of fabrication.

# Solution Components

## Subsystem 1: Optical Sensing

The optical sensing subsystem will illuminate the wafer and measure the reflected or scattered light. A low-power laser will be used so that the system can provide a consistent optical measurement at a small, localized point. Lenses may be used to control the size and focus of the laser spot on the wafer, depending on the results of initial testing.

The subsystem will contain:

- Laser: 650nm 5mW laser, specific part will be chosen based on cost and availability
- Photodiode: Vishay BPW34
- Transimpedance amplifier: Texas Instruments OPA380
- Filtering: RC low-pass filter
- Optical components: Lens and mounts for the laser and photodiode

The photodiode will produce a current based on the amount of incident light. The transimpedance amplifier will convert this current into a voltage that can be measured by the microcontroller. Filtering will be used to reduce noise in the measurement.

The exact optical geometry and lens configuration will be selected during development based on the measured signal strength and repeatability.

## Subsystem 2: Wafer Motion and Positioning

The motion subsystem will move the wafer through a predefined scan pattern and allow each optical measurement to be associated with a location on the wafer.

The subsystem will contain:

- Stepper motors: NEMA 17 stepper motors
- Motor drivers: Texas Instruments DRV8825
- Position sensors: Mechanical limit switches
- Stage: Custom X-Y motorized stage
- Wafer holder: Custom holder for a 4-inch wafer

The stage will be brought to a known origin using the limit switches before a scan begins. The microcontroller will then move the wafer to each measurement location based on the number of commanded motor steps. The system will pause briefly after each movement before taking a measurement so that vibrations from the motor do not significantly affect the optical measurement.

## Subsystem 3: Data Acquisition and Control

The data acquisition and control subsystem will control the scan, collect the photodiode measurements, and communicate with the computer.

The subsystem will contain:

- Microcontroller: STM32G474RET3
- ADC: Integrated in the MCU
- Motor control: Digital step/direction outputs for the DRV8825 drivers
- Limit switch inputs: Inputs for bringing stage to origin
- Communication: USB or UART connection to a host computer
- Custom PCB: Contains the microcontroller, optical sensing circuitry, motor interfaces, and power regulation

The microcontroller will control the motors and take one or more photodiode measurements at each scan location. Each measurement will be stored along with the corresponding X-Y position and then transmitted to the host computer.

## Subsystem 4: Data Processing and Wafer Mapping

The data processing subsystem will process the collected measurements and produce a map of the wafer.

The subsystem will contain:

- Host computer
- Python data processing software
- Python-based wafer mapping and visualization

A baseline scan will be used to determine the expected optical response for an ideal wafer condition. Measurements with a significant difference from the baseline will be marked as anomalies. The software will associate these measurements with their positions on the wafer and display the results as a two-dimensional map.

## Subsystem 5: Enclosure

The subsystem will hold the wafer, stage, laser, and photodiode in fixed positions while limiting ambient light reaching the photodiode.

The subsystem will contain:

- Enclosure: Custom machined housing
- Mounts: Mounts for the laser and photodiode. Possibly integrated into the enclosure

The enclosure will provide an environment for optical measurements and reduce noise caused by ambient lighting.

# Criterion For Success

1. Wafer positioning: The system will automatically move a 4-inch wafer through a predefined scan grid and return to a known home position.

2. Measurement repeatability: Consecutive measurements taken at the same wafer location under identical conditions will not have large swings (within 10% of each other).

3. Optical anomaly detection: The system will distinguish between two wafer surface conditions with a measurable difference in optical response.

4. Spatial mapping: The system will record the X-Y location of every optical measurement and generate a two-dimensional map covering the scanned region of the wafer.

5. Ambient-light rejection: With the enclosure installed, changes in ambient lighting will cause insignificant change (less than 5%) in the photodiode measurement.

Smart Frisbee

Ryan Moser, Blake Yerkes, James Younce

Smart Frisbee

Featured Project

The idea of this project would be to improve upon the 395 project ‘Smart Frisbee’ done by a group that included James Younce. The improvements would be to create a wristband with low power / short range RF capabilities that would be able to transmit a user ID to the frisbee, allowing the frisbee to know what player is holding it. Furthermore, the PCB from the 395 course would be used as a point of reference, but significantly redesigned in order to introduce the transceiver, a high accuracy GPS module, and any other parts that could be modified to decrease power consumption. The frisbee’s current sensors are a GPS module, and an MPU 6050, which houses an accelerometer and gyroscope.

The software of the system on the frisbee would be redesigned and optimized to record various statistics as well as improve gameplay tracking features for teams and individual players. These statistics could be player specific events such as the number of throws, number of catches, longest throw, fastest throw, most goals, etc.

The new hardware would improve the frisbee’s ability to properly moderate gameplay and improve “housekeeping”, such as ensuring that an interception by the other team in the end zone would not be counted as a score. Further improvements would be seen on the software side, as the frisbee in it’s current iteration will score as long as the frisbee was thrown over the endzone, and the only way to eliminate false goals is to press a button within a 10 second window after the goal.