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While traditional Ion Beam Sputtering (IBS) systems provide good process control, there are drawbacks for certain applications. Denton’s patented Biased Target Sputtering (BTS) can overcome many of the well-known process issues of IBS. In BTS, the low-energy ions generated are below the sputter threshold, and a negative voltage is applied to the target to ensure sputtering from the target only. This unique approach makes BTS a better choice for applications requiring densest, most defect-free films.
Overview of Biased Target Sputtering
In a standard IBS configuration, the ion source produces a fairly mono-energetic ion beam that is tightly focused in the center of the target. This leads to poor target utilization.
The well-known issues of a standard IBS configuration are:
- High-energy ions can sputter from the target – as well as other system components and shields
- Particulate contamination from system components and shields can lead to lower film quality
- Using large targets to minimize contamination can be costly
- Long source-to-target distance leads to a large footprint
BTS addresses all of these issues. In BTS, low-energy ions below the sputter threshold are generated, and a negative voltage is applied to the target to enable sputtering from the target only. This process offers solutions to the drawbacks of IBS:
- Low-energy ions below the sputter threshold cannot cause contamination
- High-energy ions can only sputter the target
- Enables use of smaller targets, reducing cost of ownership
- Potentially shorter source-to-target distance
Biased Target Sputtering offers excellent control of thin film interfaces, provides independent control over ion currents and energies, and operates at a low pressure. This eliminates contamination and scatter from beam overspill, prevents surface damage, enables tight stress control, and creates dense, defect-free films.
BTS improves cost of ownership with increased target usage that allows a reduction in overall target size. The system design makes it possible to achieve excellent uniformity. Denton’s BTS module also offers pulsed sputtering and co-sputtering of two target materials simultaneously.
General Benefits of Biased Target Sputtering
Biased Target Sputtering offers excellent control of thin film interfaces, provides independent control over ion currents and energies, and operates at a low pressure. BTS eliminates contamination and scatter from beam overspill, enables tight stress control, and creates dense, defect-free films.
The benefits of BTS include:
- Higher yield, with lower contamination and particle generation
- Improved film quality
- Lower cost of ownership (COO) due to improved target utilization and uniform erosion
- Tight control over thin film interfaces with graduated energy processes.
- Potentially smaller footprint
There are many applications where Biased Target Sputtering offers superior and more cost-effective performance over other thin film deposition technologies.
1. AR and HR Coatings for Edge-Emitting Lasers and VCSELs
Biased Target Sputtering provides superior performance in applying anti-reflection (AR) or highly reflective (HR) coatings on edge-emitting lasers (EELs), vertical-cavity surface-emitting lasers (VCSELs), and other optical devices. Because of its low operating pressure and low ion energy, BTS is an ideal solution for laser facet coatings. The ultralow contamination offered by BTS leads to higher performance in lasers, and fewer defects enables a higher laser damage threshold.
The graduated energy process supported by BTS can also reduce the stress on the resulting thin film. Reduced stress in thin films is crucial for optical coatings, where wavefront aberrations must be minimized.
2. High-Quality VOx IR Absorbers for Microbolometers
To meet application demands for next-generation microbolometers, developers need a thin film process that can produce coatings with an improved thermal response while maintaining deposition rates suitable for manufacturing. These components are used to convert thermal radiation into an electrical signal. BTS enables tighter ion energy control for improved thermal response, as well as good target utilization without overspray.
Important factors for the performance of microbolometer arrays are the resistivity, thermal coefficient of resistivity (TCR), and signal noise. TCR is a measure of each pixel’s ability to convert IR radiation into an electrical signal via a change in resistance as they are heated.
There are a number of stable VOx compounds, including VO2, V2O3, and V2O5. The more unstable VO1.8 is most commonly used for microbolometers. All these different VOx compounds have different characteristics, so the ability to control stoichiometry is critical to the manufacturing process of next-generation high TCR focal plane arrays.
The tighter ion energy control of BTS reliably produces VOx phases with higher TCR when compared with a traditional IBS configuration (3 to 5.5 -%/K for BTS vs 2 to 3 for IBS). The difference in resistivity is even greater (103 to 105 compared to 10-1 to 101).
3. EUV Lithography (Extreme UV) Mask Blanks
Biased Target Sputtering is particularly valuable in the creation of extreme ultraviolet (EUV) mask blanks in EUV lithography.
Because of its short wavelengths (between 5 and 50 nm, about 100 times shorter than visible light wavelengths), extreme ultraviolet light is used in the etching of fine-featured patterns and nano-machining in semiconductor manufacturing. As feature sizes get smaller and smaller, EUV’s very short wavelengths help to meet process demands for etching patterns.
However, EUV lithography is a very complex process that requires the use of high-precision optics and coatings. The EUV mask blanks used to block the light during the etch process must be defect-free, or the irregularities will be printed on the wafers, reproducing the defects across hundreds or thousands of semiconductor chips.
The use of low-energy ions in BTS eliminates the particulate-derived defects seen in processes using high-energy ions, which can sputter from the target, the shields, and other system components. Using BTS to create EUV mask blanks results in the extremely thin, dense, and defect-free films needed for this demanding application.
Learn More about Biased Target Sputtering and Denton’s Infinity IBD with BTS
Denton’s Infinity Ion Beam Deposition system with the Biased Target Sputtering (BTS) module offers independent control over ion currents and energies and operates at a low pressure to provide excellent control of thin film interfaces.
The system increases target utilization, lowers contamination and particle generation, and provides uniform erosion. The system provides a lower cost of ownership compared to other IBD platforms.
If you are interested in learning more about Denton’s Infinity Ion Beam Deposition system, contact us today!