Thickness Measurement Method of Ultrasonic Scanning Microscope
How Ultrasonic Scanning Microscopes Work
The block diagram of the ultrasonic scanning microscope system is shown. The ultrasonic transmitter receiver generates ultrasonic pulses of a specific frequency (5 MHz to 2 GHz), and reaches the sample through the coupling medium (such as deionized water, alcohol, etc.). Since the transmission of ultrasonic energy requires the medium to be continuous, discontinuous interfaces such as pores, impurities, delaminations, cracks, etc. will interfere with the propagation of ultrasonic signals or cause reflections of ultrasonic signals. When the ultrasonic signal passes through the sample, due to the difference in acoustic impedance of different materials, reflected waves will appear at the interface with defects or poor bonding. The reflected echo signal received by the ultrasonic transducer is transmitted to the A/D data acquisition card through the ultrasonic transmitter receiver, and the echo signal is processed and displayed on the screen in the form of a waveform. The internal image of the device corresponding to the waveform can also be displayed on the operation interface. The three-axis motion system carries the ultrasonic transducer to scan the device under test at high speed, and finally obtains a high-resolution ultrasonic image of the corresponding interface.
Principle of Ultrasonic Thickness Measurement
The frequency of ultrasonic waves is high, the directivity is good, and the speed of sound in a homogeneous medium is the same. When the ultrasonic pulse generated by the ultrasonic transducer reaches the measured object through the coupling agent, part of the ultrasonic signal penetrates the measured object, and the other part of the ultrasonic signal is reflected by the bottom surface of the object. The ultrasonic transducer receives the echo reflected by the bottom surface of the measured layer, accurately calculates the round-trip time of the ultrasonic wave, and calculates the thickness value according to formula 1. From the ultrasonic transmission speed of conventional materials in Table 1, some commonly used speed data can be found.
Ultrasonic thickness measurement method
The schematic diagram of the ultrasonic waveform shows the corresponding relationship between the ultrasonic wave and its passage through the device. From it, the key to the thickness measurement method is to find the waveform of the thickness layer of interest, set the front surface gate of the device, and set the data gate in the thickness layer of interest. In the Ultrasonic Scanning Microscope Smartscan software, the key is how to determine the thickness of the device and the layer of interest.
