​A sugar refinery in Thailand is benefiting from optimized batch vacuum crystallization strikes, crystal quality, and yield owning to the Vaisala K-PATENTS® SeedMaster SM-3. The refinery’s advanced process control solution was supplied and commissioned by Contrologic.

The ultimate aim of the automation project was to reduce the use of steam and water during the crystallization batch strikes while simultaneously improving sugar quality by keeping the crystal size distribution (CV) and mean aperture (MA) within tight specifications. This was achieved with a fully automated control strategy based on real-time supersaturation control.

For instance, a comparison of the production yield, energy consumption, and crystal quality before and after implementation revealed that 7 m3 of water was used during a strike before, refinery pan volumes being 85 m3, see image 1 below.

Image 1. Sugar vacuum pan (85 m3).

Before the implementation water was used for eliminating new, unwanted fine crystals. Introducing the process control solution not only removed the need to use water, but also reduced steam consumption by about 25% while increasing yield by about 1%.

Image 2: Syrup feed valves.

Why supersaturation-based control?

Production of good-quality sugar relies on crystal growth, and supersaturation is the driving force for this growth. The speed of crystallization depends on this multivariable function of several parameters. Supersaturation is defined as the ratio of sugar in a solution to the sugar needed to saturate the solution at the same temperature.

Supersaturation has an optimal range where sugar crystals grow evenly and widely, reaching the desired crystal size. Outside this range the crystals will stop growing and may even melt or start to form new crystals spontaneously, creating fines and conglomerates that need to be reprocessed. This is a major problem as it wastes time and energy, increases production costs and water consumption, and decreases the effective yield of produced sugar.

To build supersaturation-based control that would eliminate these challenges, the pan was fitted with a Vaisala K-PATENTS® SeedMaster SM-3 system to provide real-time data for supersaturation calculation. The SeedMaster is specifically designed for sugar crystallization applications. The system consists of a process refractometer and multiparameter monitoring device that provides the parameters necessary for sugar crystallization and enables the implementation of a fully automated control solution.

Why customers choose the Vaisala SeedMaster

Improved product quality and consistency

The quality of the sugar is high, and the quality is consistent from batch to batch. With optimization, the amount of sucrose in the final molasses is reduced while the CV/MA is improved.

Substantial savings from optimizing raw material and steam consumption

Raw material consumption can be reduced, bringing operational savings, but the biggest saving comes from reduced steam consumption. Prior to implementing an automated control strategy using the SeedMaster, the Thai sugar refinery was consuming 39.4 tons of steam per strike; after implementation steam consumption fell to 29.5 tons per strike.   

There is also a cumulative effect, as each step in the sugar production process requires water. Sugar factories generate the steam used for processing and sell the surplus as electricity to the grid. Controlling and optimizing the production process will allow factories to sell more power to the grid.

Less reprocessing of false crystals

When the sugar crystals are of a consistent size it reduces the time and cost associated with reprocessing false crystals.

Fewer labor-intensive tasks

The SeedMaster SM-3 automates supersaturation control, meaning production staff no longer need to spend time on sampling and other manual tasks.

Process control requires the following:

• Concentration control using a digital inline process refractometer
• Absolute pressure control
• Level control
• Microwave density meter

Three control levels for instruments and PID controllers

Would you like to know more?

Accurate process control brings huge advantages to refineries crystalizing sugar. A supersaturation-based control strategy using process refractometers can be used to optimize crystallization, including yield, quality, and energy efficiency.

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Chemical mechanical planarization/polishing (CMP) is a critical, very costly, and challenging nano-polishing process that combines chemical reactions and mechanical abrasion. It is the key enabling step in integrated circuits manufacturing, affecting both yield and productivity.

CMP in a nutshell

Polishing is done with a slurry that includes an oxidizing agent, typically hydrogen peroxide (H₂O₂). During manufacturing, a wafer is pressed against a polishing pad while both wafer and pad are rotated counterclockwise at slightly different velocities. As slurry is dispensed on the center of the pad, the combination of mechanical and chemical actions gradually removes material from the wafer surface, leading to a surface that is locally and globally planar. 

CMP slurries are mixed or diluted at the plant before use. Oxide polishing slurries are commonly purchased in concentrated form and diluted with water on-site to minimize shipping and labor costs. Some multicomponent polishing slurries may only be blended immediately prior to their use because of their short post-mix lifespan. The correct blend is essential as it is directly linked to chemical reaction rates and the wafer polishing rate; any defects in the blend have a negative impact on manufacturability and reliability. Although the slurry control at the point of manufacture (POM) is tight, subsequent processes – including transportation, handling, and filtration – can affect the chemical properties, and therefore continuous slurry monitoring is required until point of use (POU) to ensure high yield. Effective, rapid, reliable, precise, and cost-effective metrology tools and methodologies are required, so many fabrication plants choose to use refractometers.

How refractive index helps to improve production quality

Refractive index (RI) – a continuous, in-line, non-slurry-consuming measurement – helps fabrication plants identify slurry composition faults quickly as it conveys real-time information about the process, reducing the number of wafers at risk.

CMP slurry carries nanoparticles to solids content levels of 1–30% depending on the slurry type, making it challenging to analyze. However, once calibrated to a specific slurry’s temperature/RI characteristics, RI measurements can successfully determine the concentration of hydrogen peroxide in tungsten slurry to within ±0.03% by weight even in these difficult conditions.

Moreover, unlike conductivity probe tests, RI measurements can monitor H₂O₂ slurry density, an indicator of settling and degradation of the slurry over time. Therefore, the RI is used not only to qualify the final product but also to monitor batch-to-batch variations in the incoming raw slurry and to validate the blend-addition steps.

An attractive feature of some slurry delivery systems has been the ability to use an automated chemical-spiking function in the day tank.

Vaisala K-PATENTS® Semicon Refractometer benefits

The Vaisala K‑PATENTS Semicon Refractometer is specifically designed for semiconductor manufacturing environments. It has a small footprint and the construction is metal-free, making it ideal for measuring chemicals without corroding the process.

The Vaisala K‑PATENTS Semicon Refractometer is the superior choice for CMP operations because:

• Measurement is fully digital, and drift is impossible
• The integrated temperature measurement component ensures highly accurate RI measurement
• It offers direct density measurement
• The robust design tolerates process vibrations with no measurement errors
• Built-in diagnostics give an instant overview of process conditions
• Of the availability of different high-quality flow cells, that are designed to reduce and even eliminate fouling.

References

Diversified Fluid Solutions has been using the Vaisala K-PATENTS Semicon Refractometer successfully for years in its CMP operations and has found the device extremely reliable and accurate. “As advanced process nodes bring increasing numbers of CMP steps, we must ensure that the slurries delivered to the polishing tools maintain consistent chemical and mechanical characteristics,” explains Karl Urquhart, Director of R&D, Chemical Technology, Diversified Fluid Solutions. “Inline RI monitoring can evaluate the chemical composition of incoming material, qualify blend addition steps, and validate a uniform CMP slurry blend in a single real-time, non-slurry-consuming measurement.”

The first H₂O₂ measurement installation for CMP slurry was installed at a large semiconductor fabrication plant in 2013, replacing auto-titration. The measurement device has remained stable ever since, with no instrument maintenance required beyond routine flushing of the slurry blender.

In general, after installing a Vaisala K-PATENTS Semicon Refractometer the wafer throughput at fabrication plants increases by approximately 20%. In addition, CMP slurries are strictly controlled and enable improved uniformity of the planarization process.

Would you like to know more?

RI measurement is a simple, cost-effective, and accurate technique that provides real-time information on slurry composition, making a refractometer the metrology instrument of choice for many fabrication plants.

Contact us for more information.