With the increasing development of semiconductor devices, silicon and silicon-based materials still show their superior properties, and it will still be an important material for semiconductor devices and integrated circuits. With the decreasing size of devices, the resistivity, impurity distribution, film thickness and quality control of silicon and silicon-based materials are extremely important. Using spreading resistance profiling (SRP) to test and analyze silicon and silicon-based materials is more intuitive and effective than other testing methods. PAM-XIAMEN can offer silicon wafers with spreading resistance profiling services if necessary.
SRP is also known as spreading resistance analysis (SRA), that is, diffusion resistance distribution is a method for testing electrical parameters such as diffusion resistance, resistivity, carrier concentration distribution, etc. of semiconductor materials with higher resolution, which belongs to an experimental comparison method.
1. Basic Principles of SRP – Spreading Resistance Profiling (Based on Silicon Wafer)
The steps of spreading resistance profile are to measure the spread resistance of a series of point contacts (Rs is the ratio of the potential drop between the conductive metal probe and a reference point on the silicon wafer to the current flowing through the probe), and then use the calibration curve to determine The resistivity of the tested sample near the contact point of the spreading resistance probe is converted into the carrier concentration corresponding to the series of test points.
Schematic of Spreading Resistance Probe Technique Profiling
In order to improve the spatial resolution and at the same time according to the different target measurement depths, the direction of the cross section of the sample can be ground into a series of angles, and the change of resistivity within 5 nm of the resolution depth direction can be measured after grinding the silicon wafer.
Take the silicon epitaxial wafer for example:
|4||Resistivity||0.002 – 0.003||ohm-cm|
|5||Resistivity Radial Variation||<10||%|
|6||Crystal Orientation||<111> 4 +/- 0.5||degree|
|9||Thickness||525 +/- 25||μm|
|15||Surface Appearance||no cratches, haze, edge chips, orange peel, defects, contamination|
|16||Edge Profile||Edge Rounding|
|19||Epi Layer 1||N Phos|
|20||Resistivity||3.8 – 5.2||ohm cm|
|21||Thickness||29.0 – 35.0||um|
|22||Epi Layer 2||N Phos|
|23||Resistivity||0.0014 – 0.0026||ohm cm|
|24||Thickness||36.0 – 44.0|
We test the above specification by SRP test and obtain the resistance and thickness of the epilayers. Please see the diagram attached below:
2. Pros and Cons of Spreading Resistance Profile Measurement
- Excellent spatial resolution;
- Concise and intuitive testing;
- Wide resistivity test range;
- Can be used as a multi-layered profile
- Destructive test
3. Applications of Spreading Resistance Profiling and Analyzing
SRP is more and more widely used in epitaxial wafer and IC pattern wafer testing due to its superior spatial resolution. SRP technology can measure not only the longitudinal resistance change of epitaxial wafer, but also epitaxial layer thickness, transition region and interlayer width.
The resistivity (or concentration) and depth distribution of epitaxial layers such as Si, InP, GaAs, SiC, etc., are tested with the spreading resistance profiling method. Knowing the thickness of the epitaxial layer, the width of the transition region and the resistivity of the substrate and the resistivity of the epitaxial wafer at a certain depth, it is possible to diagnose the quality of the epitaxial wafer.
Please note that SRP measures only the activated partial doping concentration.