Conductivity Control System (CCS)

CONDUCTIVITY CONTROL SYSTEM (CCS) OVERVIEW

The Chemwest Conductivity Control System (CCS) has been designed to continuously adjust the amount of CO₂ injected into an ultrapure water (UPW) stream to achieve the targeted conductivity. Changes in the UPW flow rate are not a problem for the CCS. Closed-loop control based upon conductivity is used to ensure the conductivity is maintained even as the flow rate changes rapidly.

The system uses membrane contactor technology to provide bubble-free injection of the CO₂. An all fluoropolymer flow path is used to maintain the purity of the DI water and prevent the introduction of particles or contaminates.

The CCS operates in a wide range of UPW flow rates and conductivity levels providing the flexibility to meet an array of application requirements.

APPLICATIONS

Wet Etch Clean (WEC) critical rinses
Extreme Ultraviolet Lithography (EUV) mask cleaning
Photolithography reticle cleaning
Photolithography spin-rinse process
Post Chemical Mechanical Planarization (CMP) rinse process
Photoresist residual removal

PROCESS BENEFITS

IMPROVED YIELDS

PRE IMPROVEMENT

The use of low conductivity UPW during the wafer rinsing process prevents the dissipation of wafer surface changes that may be present on the incoming wafer or generated during the rinse process. Particle attraction and adhesion to the wafer surface can result in yield limiting defects. Adding CO₂ to UPW during the rinse process will help to reduce the surface charge and may allow for the release of these defect causing particles¹ from the wafer surface.

ESD DEFECT REDUCTION

Static buildup on the wafer surface during the wafer rinse process can occur if low conductivity UPW is used. Catastrophic wafer defects due to electrostatic discharge (ESD) have been reported as a result of this static buildup during spin rinse processing.² Increasing the conductivity of the UPW rinse water through the use of CO₂ injection can significantly reduce this type of defect.

CORROSION CONTROL

Corrosion of metal lines (Cu, Al) can occur during the UPW rinse process that follows resist/polymer removal with amine based chemistries. This is due to the creation of hydroxyl ions when the water interacts with the hydroxyl amines. The addition of CO₂ into the UPW rinse water neutralizes the hydroxyl ions preventing this metal corrosion from occurring.³

¹ Harumoto, M. et al., "Post-Develop Blob Defect Reduction", SPIE Advanced Lithography 2009, Conference Proceedings Paper. http://spie.org/x648.xml?product_id=813605
² Halladay, J. et al., "Elimination of ESD Defects Using DICO2", SEMATECH Surface Preparation and Cleaning Conference, March 31-April 2, 2008 http://qcepttech.com/documents/0210HalladaySpansion.pdf
³ Gu, M. et al., "An Improved Wet Cleaning Method for 90nm Node- Semiconductor processing Technology", Future Fab Intl., Issue 18, Jan. 12, 2005 http://www.future-fab.com/documents.asp?d_iD=3028

FEATURES AND BENEFITS

Features	Benefits
Automatic Conductivity Control	High performance, high precision closed loop conductivity control ensures optimum process stability and maximizes process window
Direct Injection Gasification Method	Delivers a stable conductivity CO₂ / UPW mixture with low gas consumption and simple system design and control with no bubble generation
Programmable Maintenance	Automatic maintenance of membrane contactor ensures optimum gas transfer efficiency and minimum downtime
Visual Human/Machine Interface software	Visual touchscreen software allows simple setup and programming of process conditions
Embedded Communication	Analog and digital output to customer tool and remote control by customer tool through industry standard connectors and protocols. Provides connections via Customer Ethernet for data logging / monitoring functions
Safety Alarms, Sensors	Process parameter alarms and system leak sensors ensure process and machine safety
Membrane Technology	Unique membrane reduces gas usage and ensures low Cost of Ownership

SPECIFICATIONS

System flow range	1-60 L/min ⁽¹⁾
Conductivity range	0.5 – 40 µS/cm² ⁽²⁾
Transient stability	± 5% of setpoint
Steady State Stability	± 2% of setpoint	(Dependent upon incoming UPW flow stability)
UPW requirements	Pressure Range	0.21 – 0.48 MPa (30-60 PSIG)
	Max Temperature	40°C
CO₂ requirements	Pressure Range	0.2 – 0.7 MPa (30-100 PSIG)
	Minimum Purity	Grade 4
N₂ requirements	Pressure Range	0.15 – 0.7 MPa (20-100 PSIG)
	Minimum Purity	Grade 2
CDA requirements	Pressure Range	0.5 – 1.5 MPa (75-215 PSIG)
Electrical requirements	120 vac, 60 hz, 1 ph	FLA 5.1A, Max. 10A
Box Dimensions (Maximum; No Ftgs)	Standard System	Height-57", Width-24", Depth-12"

¹ Higher flow rate systems can be developed. Systems rated for >40L/min will be larger in dimension.
² Conductivity range is dependent upon UPW flow range and temperature. Each system is shipped tuned for target conductivity setpoint and flow range. Please consult Chemwest for your specific requirements.
³ System requires a minimum of 200mm (8") above and 200mm (8") below the unit to allow facility connections.