Development of high sensitivity high vacuum scanning extension resistance microscope (SSRM) equipment
SSRM (Scanning Spreading Resistance Microscope) is a new upgrade to SCM. It uses a biased conductive probe to scan the sample surface or cross-section to measure its electrical performance, and can map the charge carrier density and read out the conductance and resistance of the sample, allowing cross-sectional testing.Diffusion resistance/conductivitydistribution. Compared with C-AFM, it can characterize more electrical characteristic parameters and has a wider measurement range than SMM. It is an indispensable analytical method in the research and development of advanced process platforms. At the same time, according to the latest national experimental standards, the following 4 factors determine the resolution of SSRM:
（a）Needle tip size of conductive probe: The needle tip size of the conductive probe is the most decisive factor. The smaller the needle tip size, the spatial resolutionThe higher.
（b) Sample surface roughness: From a mechanical and electrical perspective, the rougher the sample surface, the greater the change in contact between the probe and the sample.This generates significant noise and affects the measurement data. Therefore, the sample surface roughness pairSCMorSSRMTesting of spatial resolutionThe quantity has a great impact.
（c) Contact force: The greater the contact force, the larger the contact area and the lower the resolution.
（d) Signal contrast at the interface:SSRMIn this case, the greater the signal contrast, the higher the resolution. Therefore, at least one should be selected in the experimentAbove the background noise level10 tests with a signal contrast ratio. If any signal is saturated, the resulting resolution value isIt's very good but it's wrong.
In addition, most SSRM measurements at home and abroad are currently carried out in room temperature atmosphere. Under such conditions, the contact position of the probe with the sample and even the probe with concentrated electric field will inevitably be adhered to water vapor and other impurities in the air, which will cause complex interference to physical and chemical measurements, which will become the main reason for the reduction in resolution and the decrease in image accuracy.
Therefore, in addition to using advanced sample making technology and the following small-size conductive probes, our company also has a self-developed high-vacuum module to develop [high sensitivity and high vacuum SSRM], which greatly eliminates various interference factors that affect spatial resolution, greatly improving the clarity and reliability of measurement results.
Expansion resistor
Apply bias voltage to the sample so that the carriers present directly below the probe flow into the probe, and use a logarithmic amplifier to amplify its current and measure it as the resistance value. At this time, the applied bias voltage is attenuated sharply directly below the probe. Therefore, the carriers that can flow into the probe are limited to the carriers present near the pole of the probe, and are detected as resistance values. This local resistance is called extended resistance.
Diamond coating probe
SSRM mainly uses diamond-coated silicon probes. The needle tip is sharpened to about tens of nm, and the particularly pointed part has sharpness of several nm. SSRM can detect carriers directly under this micro probe, so high resolution measurements can be performed.
Sample delivery requirements
1. Purpose/test content |
2. Sample information |
(1) Number of samples and whether there are samples prepared |
(2) Schematic diagram of the measurement area (TCAD diagram or optical microscope photo, etc.), schematic diagram of the line structure or diffusion layer structure, material and polarity of the semiconductor, required magnification, etc. |
(3) Sample preparation requirements (in which direction to grind, cut, etc.) |
3. Other precautions |
(1) Note the sample delivery time, express order number, etc. |
(2) If there are multiple samples, please specify the test priority |
Test parameters
Sample size requirements | Maximum horizontal direction 5mm×5mm, maximum height 5mm |
Measuring range (Horizontal direction) | 80μm×80μm |
Measuring range (vertical direction) | ～ 1mm |
※To ensure data accuracy, the flatness of the sample surface ~1nm is required. | |
※Generally, the cross-section of the semiconductor device is exposed through mechanical grinding. | |
Depth of detection | Count nm ~ dozens of nm |
※Changes according to the test conditions | |
Detect resistance range | 104～ 1012Oh |
Horizontal direction Spatial resolution | 1nm~Tennms |