Sample preparation
Cutting and Embedding: Firstly, carefully cut a sample of appropriate size from a substrate material with a silicon nitride insulation layer (such as silicon wafers, circuit boards, etc.), typically measuring a few millimeters square. If the sample size is too small or the shape is irregular, in order to facilitate subsequent operations, it can be embedded in suitable embedding materials such as epoxy resin to ensure that the sample is fixed and easy to handle and polish.
Grinding and polishing: Use sandpaper of different particle sizes to grind the surface of the sample in order from coarse to fine (such as transitioning from 200 mesh to 2000 mesh) to remove scratches and damage layers generated during the cutting process, making the sample surface as smooth as possible. Afterwards, a polishing cloth combined with a polishing agent is used for polishing treatment to further improve the surface smoothness and provide good surface conditions for SEM observation.
SEM observation and analysis
Choose the appropriate observation mode:
Secondary Electron Imaging (SEI) mode: This mode is highly sensitive to the morphology of the sample surface, and can clearly present the microscopic undulations, particle distribution, and the presence of defects such as cracks and pores on the surface of the silicon nitride insulating layer. For example, by observation, it can be found that the surface roughness of the insulation layer formed by silazane under different process conditions (such as different curing temperatures, different deposition rates, etc.) varies, and the uniformity of its phase structure can be preliminarily judged.
Back scattered electron imaging (BEI) mode: mainly based on the different scattering abilities of electrons by different elements in the sample for imaging. Elements with higher atomic numbers have stronger backscattered electron signals. This mode can be used to distinguish different phases that may be contained in the silazane insulation layer. For example, when inorganic fillers (such as aluminum oxide, boron nitride, etc.) are added to the insulation layer, the BEI mode can see that the filler phase and the silazane matrix phase show different gray contrast, so as to greatly determine the distribution of different phases and phase interface and other information.
Adjust the appropriate acceleration voltage and working distance: Generally speaking, the acceleration voltage is selected between 5-20 kV according to the specific situation of the sample. For samples such as silicon nitride insulation layers that are relatively thin and not particularly complex in composition, lower acceleration voltages (such as 5-10 kV) may be more suitable, which can help reduce the penetration and damage of electron beams to the samples and obtain clearer and more accurate surface information. The working distance is usually adjusted within a range of a few millimeters to over ten millimeters, in order to find the working distance value that can make the image focus clear and the resolution optimal, to ensure the accuracy and reliability of the observed phase structure details.
Image analysis and phase structure inference: By observing SEM images of different regions, analyze the texture, particle morphology, and distribution characteristics of the silicon nitride insulation layer surface. For example, if a regular arrangement of granular structures is seen on the surface and similar distribution patterns are observed in different regions, it may imply the existence of a certain crystalline phase or uniformly dispersed second phase; If there are obvious regional boundaries with significant differences in morphology, grayscale, etc. on both sides of the boundary, it may indicate the existence of different phases, and further analysis of the size, shape, and relationships between phases can be conducted to make preliminary inferences about the phase structure.
