(ALD) Atomic layer deposition is an outward controlled thin film deposition process that allows precise film thickness control, homogeneity on large-area substrates, and conformality on 3D (nano)structures. When designing an ALD process, the following stages are taken:
- Precursor and co-reactant selection are essential considerations.
Before establishing an ALD process, selecting an appropriate mix of precursor and co-reactant from which to work is necessary. The most important thing to reminisce is that the precursor and co-reactant molecules should have the proper components to produce a substance with the required composition. In addition, they must be reactive towards the surface groups that have formed during the previous subcycle. This must result in the formation of reactive surface groups following the dosing of the compound. Furthermore, the substance’s volatility, thermal stability, and reactivity must be suitably high.
- Chemical structure
It is essential to check if the developed material has the desired elements soon after deposition of the first ALD film Rutherford backscattering spectroscopy (RBS) and X-ray photoelectron spectroscopy (XPS) are two standard methods for investigating the chemical composition, albeit XPS is usually more readily available. If the material should be conductive, a simple four-point probe conductivity measurement can determine if the substance is high purity. A quick examination of the refractive index can also reveal whether the desired material is obtained. If the deposited material differs significantly from what was expected, the proceeding may be a waste of time. However, optimizing the deposition temperature, dosage, and purge periods can lead to material composition improvement in many circumstances. It is critical to understand that chemical composition and stoichiometry determine the final material qualities.
- Control of the thickness
It is important to note that ALD deposits the same amount of material in each cycle, allowing precise control over the final thickness. To prove this, each process’s thickness or material increase must be established, referred to as the growth per cycle in the industry (GPC). Defining the GPC can be done both in situ and ex-situ by depositing different samples with varying cycles and monitoring the material increase during deposition. Usually, the film thickness is measured (e.g., by spectroscopic ellipsometry), although other methods of checking for linear growth include counting the number of deposited atoms (e.g., by Rutherford backscattering spectroscopy) or measuring the mass of deposited particles (e.g., by spectroscopic ellipsometry) (e.g., by a quartz-crystal microbalance).
- Saturation of the market
The growth per cycle (GPC) must be measured as a function of dosing and purge times to demonstrate self-limiting growth, which is one of the essential properties of ALD. To achieve optimal performance in an AB-type (i.e., two-step) process, adjusting the precursor dose and purge times, the co-reactant exposure and purge times, and the co-reactant exposure and purge times is necessary. This is accomplished by selecting three of the four periods with a somewhat significant duration and maintaining those constants while changing the fourth time. As a result, it is essential to perform this procedure for each step, with the first step being the confirmation of saturation of the precursor dosage period. It will then be possible to check the saturation of the other dosing times and depending on the findings. It may be compulsory to repeat the procedure with slightly different dosing and purging times.
For all your ALD precursors needs, contact Optima Chem today. We provide several ALD precursor manufacturing services.
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