True Non-Contact™ Mode

High-resolution surface imaging of samples without physical contact, minimizing damage during scanning

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What is True Non-Contact™ Mode (NCM)

True Non-Contact™ Mode is a proprietary technology exclusively offered by Park Systems.

True Non-contact mode obtains topography by detecting the attractive van der Waals force between the AFM tip and the sample surface.

In True Non-contact mode, the tip oscillates at a frequency slightly higher than its resonance frequency, where the frequency-amplitude curve has its steepest slope.

As the tip approaches the sample, the attractive force causes a downshift in the effective resonance frequency, leading to a decrease in oscillation amplitude at the driving frequency. The Z-servo maintains this new amplitude, keeping a constant tip-sample interaction while the tip scans in the XY direction.

The major difficulty is in implementing True Non-contact mode is that the tip-sample interaction is not monotonic. If the tip approaches too closely, it enters the repulsive force regime, causing a sharp increase in oscillation amplitude and a mode hop from non-contact to tapping. Even retracting the tip above the original transition point does not immediately recover non-contact mode. This bi-stability makes it challenging to maintain the non-contact mode stably.

To achieve the True Non-contact mode, the tip-sample interaction must be precisely controlled. Developing a fast, low-noise Z-servo system with an amplitude error margin of ±1 nm is the key in achieving stable True Non-contact mode.

Reasons to Use This Mode

A major advantage of True Non-Contact™ Mode, compared to tapping mode, is the prevention of tip wear and sample damage. The results of repetitive scans on a chromium nitride (CrN) tip-checking sample shows that while the tapping mode image became blurry after just a few scans due to tip wear, the True Non-contact mode image remained sharp even after 100 scans.

Sample: CrN tip-checking sample
System: NX10
Scan Size: 1 µm × 1 µm

Applications and Use Cases

True Non-Contact™ Mode can image soft and sticky samples, such as unbaked photoresists, as well as the most delicate and brittle samples, which cannot be imaged with tapping mode AFM.

Sample: Unbaked Photoresist
System: NX-Wafer
Scan Size: 4.75 µm × 4.75 µm

True Non-Contact™ Mode can also image tall features. Sensing attractive forces not only at the tip apex but also along its sides, as the tip approaches vertical features, the Z-servo can quickly retract the tip to climb over the wall.