SMM ： Scanning Microwave Microscopy
Features
Similar to an AFM, the sample surface is scanned by a platinum probe and the surface roughness recorded. The SMM adds microwave irradiation from the same probe and the reflected waves are detected. The signal is proportional to the carrier concentration which can then be quantitatively determined. The instruments are additional features of an atomic force microscopy (AFM) system.
- Measurement of carrier concentrations between 1014 and 1021cm-3is possible for Si device.
- Simultaneous AFM image acquisition possible.
- Various semiconductors such as Si, SiC, GaN, InP, GaAs, etc. can be measured. Standard known samples are necessary for quantitative measurements, though.
Application Examples
The carrier concentration and its distribution can be visualized, and diffusion layers of various semiconductor devices can be identified. Applications include:
- Discrete components such as bipolar transistors, diodes, double-diffused metal oxide semiconductor (DMOS) devices, insulated gate bipolar transistors (IGBTs).
- Each layer and 2D electron gas in thin films of light-emitting devices such as light-emitting diodes (LEDs) and laser diodes (LDs).
- Identification of elements in large-scale integrated circuits (LSIs).
- Observation of device defects originating from ion implantation and leaks.
Principle of operation
The electric charge carrier distribution is determined by microwave reflection. Microwaves emitted from the probe irradiate the sample and the carriers therein reflect the waves. The intensity of the reflected wave depends on the carrier density so scanning the probe and simultaneously recording the signal yields the spatial distribution correlated with carrier concentration. The microwave intensity at the sample surface strongly depends on the probe distance so the sample region subject to microwave reflection is limited to an area just below the probe. The size of this area can be regarded as the spatial resolution of the SMM, and it is about 10 nm in regions with high carrier concentrations and an order of magnitude lower in regions with low carrier concentration (see Figure 2).
Data examples
SMM carrier concentration map in a Si planar field-stop IGBT.
The uncalibrated SMM signal can be used for qualitative evaluation. Since the relation between the carrier concentration and microwave reflectance is assumed to be linear, it can be converted into a semi-quantitative carrier concentration distribution image if the carrier concentrations of at least two points in the image data can be given as known information. However, this assumes that the source material of the carriers is the same at the two concentrations.
Data format of deliverables
- PNG file (ASCII data file upon request).
Specifications
Items for enquiries
- Purpose and scope of the analysis
- Sample information:
● Number of samples, availability of preliminary samples.
● Measurement location (CAD drawing or optical micrograph) , cross-sectional shape, Schematic of sample wiring and diffusion layer structure, type of material (semiconductor), doping polarity, estimated carrier concentration, desired field of view for measurement, etc.
● Handling instructions.
- Details on delivery
● Preferred due date for preliminary analysis report.
● Due date for delivery of final report.
- Additional relevant information
Caution
- Samples will not be returned.
- Semi-quantitative carrier concentration results are only indicative.
［SMM］走査型マイクロ波顕微鏡法の分析事例はこちらからご覧ください。