New possibility in SIMS, AES, ESCA and XPS depth profiling. Applying this low energy ion gun at low angle, eliminates mixing effect in layers.

General

It is known that high-energy ion bombardment by Ar⁺ ions (usually at 5-10 keV) causes damage to the thinned specimen. For the semiconductor crystals (Si, GaAs) this damage is mostly of the form of an amorphized layer on both surfaces of the sample. By decreasing the ion beam energy and its incident angle this damage decreases. The ultra-high-vacuum version of the low-energy ion gun operates at very low ion energies (50-2000 eV) in an extremely clean environment. It was developed for depth profiling in analytical system such as SIMS, UPS, AES, ESCA and XPS.

The main results obtained using the ultra-high-vacuum ion gun are as follows:

• the depth resolution is independent of the thickness of the layer removed
• its value is better than 2 nm

Features

• wide use in standard sample preparation and in analytical depth profiling,
• extremely low ion energies,
• high milling rate,
• reduced surface damage for HRTEM examinations and
• full control of ion source parameters

1. Sample preparation and depth profiling

The low-energy ion gun is a perfect tool for both sample preparation and depth profiling. The low-energy ion beam produced ensures minimal surface damage during the sample preparation and guaranties removal of only surface atomic layers when used for analytical depth profiling. The low energy of the ion beam prevents amorphization on the sample surface and artificial rearrangement or ion beam induced diffusion of atoms in the treated zone.

2. Operating modes

The low-energy ion gun can be operated with 50-2000 V accelerating voltage and 7-80 µA beam current. The low ion energy ensures minimum sample damage. High thinning rates can be achieved during the sample preparation by large-angle, high-energy bombardment, while the low-energy and low-angle ion beam is perfect for surface cleaning and endpolishing. The standard low-energy ion gun operates with Ar⁺ ions, but has been successfully tested with Xe and CF4 gases.

3. High thinning rates

The low ion energy used at milling does not necessarily mean low thinning rates. The high beam current and the geometrical structure of the ion source permit for considerably high thinning rates (up to 28 µm/h on Si-specimens at 30° incident angle and 2000 eV ion energy). Thinning and polishing is achieved rapidly, without destroying the original structure of the sample. Focusing of the ion beam is also available to provide even more efficient depth profiling.

Table 1. Characteristic values of the milling rate on Si at 30°

4. Reduced surface damage

The exclusive capability of the low-energy ion gun to produce damage-free samples at low-energy ion bombardment provides a unique opportunity to study the real nanostructures in synthesized and natural materials in all fields of technical sciences and materials research.

State-of-the-art research on semiconductor-oxide interfaces of multilayered semiconductors, GaAs samples, Si wafers and HSLA steel foils clearly demonstrates the power and efficiency of the low-energy ion gun in the field of HRTEM sample preparation.

5. Full control of ion source parameters

All ion source parameters, including accelerating voltage and ion current can be automatically controlled form a computer (optional feature), but conventional, manual adjustment is also available.

Download in PDF format