Analyze post-CMP cleaning and residue removal with QSense

Contamination control and surface cleanliness is key for successful silicone processing. Here we show how QSense technology can be used to analyze contaminant adsorption and desorption at various conditions, and to assess and compare the efficiency of post CMP cleaners

Analyze molecule-surface interactions in real-time

QSense technology is based on Quartz crystal microbalance with dissipation monitoring, QCM-D, which is a surface sensitive real-time technology for analysis of molecule-surface interactions and layer properties at the nanoscale. Monitoring changes in resonance frequency, f, and dissipation, D, of a quartz crystal, surface interactions and layer properties can be charac­terized and quantified in terms of mass, thickness, and viscoelastic properties.

The information provided by QSense QCM-D allows for analysis of, for example, molecular adsorption/desorption, surface etching, and cleaning processes.

In the context of cleaning analysis, the method is suitable to:

• investigate the removal of residues by post CMP cleaners
• quantify removal rates
• quantify the amount removed from, or remaining at, the surface after the wash step
• compare the efficiency of different cleaning agents
• identify the optimal concentration of the cleaning agent

The technology is also used in more fundamental work. For example, in a study¹ by Wu et al., QSense QCM-D was used to investigate the fundamentals of contaminant adsorption and desorption to gain insights that would help develop chemistries and processes suitable for the 10 nm technology node and beyond.

The model system used in this study was benzotriazole (BTA), a copper corrosion inhibitor used in barrier CMP slurries and post-CMP cleaning formulations, adsorbed on Copper. Then, tetramethylammonium hydroxide (TMAH) and acetohydroxamic acid (AHA) -based solutions were used to analyze the BTA removal.

What does QSense analysis look like? Analyzing layer build-up and removal

As already mentioned, the cleaning efficiency is analyzed by looking at the mass loss from the sensor surface, i.e., the mass removal rate and total amount removed. To run such an analysis, the key steps in the measurement is to first add the chemical or component, which is later to be removed by the cleaning agent, to the surface. Fig. 1. Next, the surface adhering layer is exposed to the cleaning agent of interest and the mass removal is monitored.

Analyzing layer build-up and removal - a schematic example

In this example, we would like to analyze and compare the removal efficiency of slurry additive using two different cleaning agents. We would like to compare the removal rates and the total amount removed. We run two experiments using the same surface chemistry and solvent conditions in the two cases, Fig 1.

• The measurements start by exposing the two surfaces to a solvent to establish a reference baseline
• Next, the surfaces are exposed to the slurry additive, which adsorbs to the two surfaces. The QSense analysis allows us to monitor the additive uptake at the surface. When the adsorption has reached saturation, there is a rinse step to remove additive remaining in the bulk.
• Next, we expose the two surfaces to the two different cleaning agents to be compared. The QSense measurement allows us to monitor the removal process - we can follow in real-time how the cleaning agents interact with the additive layers at the surface and how they are being removed.
• The removal rate and total removed amount can then be compared between the two measurements to reveal which of the two cleaning agents is most efficient. In this schematic example, Fig. 1, the cleaning agent used in A) would be both faster and more efficient than the cleaning agent used in B) as shown by the slope of the curves and the net mass loss.
  
  

Figure 1. Schematic illustration (not to scale) of how post CMP cleaning and residue removal can be analyzed and compared using QSense QCM-D.

Concluding remarks

QSense technology provides time-resolved information on surface-molecule interactions which can be used to analyze and compare the efficiency of post-CMP cleaning approaches, and to explore how to best remove post-CMP residue.

Download the overview to learn more about QSense analysis in CMP