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Thin film removal is a form of laser ablation and is the process of removing a very thin layer of material from a substrate. This process is used in a variety of different application areas, the most common being in the electronics and semiconductors industries.
Our redENERGY G4 Pulsed Fiber Lasers are ideal for thin film removal as their subtle control of pulse characteristics and high repetition rates allow for sufficient pulse overlap at high processing speeds. This application insight looks at thin film removal, scribing of molybdenum films and ITO removal and the advantages of using a Pulsed Fiber Laser for this application.
The thin film material itself can be naturally occurring such as oxide from titanium (Figure 1) or it can be something that has been applied to a material such as Indium Tin Oxide (ITO) on a glass substrate (in solar cell production).
Removing a thin film from a substrate creates a circuit that can be used in solar cells, liquid crystal displays, plasma displays, and touch sensitive panels.
In thin film removal there are a variety of substrates and thin film materials used including glass, ceramics, plastics, silicon or metals.
Figure 1. Thin Oxide Film Removal from Titanium
One of the most common thin film removal technologies has been the lithography process. It uses multi-step processes, using masks to create the pattern for removal, and chemicals to remove the thin film through chemical etching. However there are many issues with this process such as; high investment cost, time-consuming/multi step process, inflexibility, and environmental problems.
Another common method of thin film removal is mechanical scribing. This uses a stylus and wire brushes for large areas. This method is not as precise and also the wire brushes are prone to wear.
Fiber Laser Technology is a proven process capable of performing an ablation using a high intensity :aser beam to vaporise the thin film directly from the surface substrate. This leaves the patterning necessary for the proper circuit configuration.
Very high frequencies of up to 1 MHz are used in thin film removal, which produces precise material removal. This means that the damage of the base material, be it glass, plastics, or silicon, is minimised when processed by a Fiber Laser.
Fiber Lasers also offer accurate and precise scribing of the thin film allowing complex and intricate patterns to be scribed.
Figure 2. Thin Film Removal of Molybdenum from Glass Substrate. 20W; 125kHz WF2 4m/s scan speed 40µm scribe width
Thin layers of Molybdenum can be applied to glass substrate and used in photovoltaic cells. The scribing of this thin layer to create a photovoltaic circuit is known as a P1 scribe in CIGS type cells. Figure 2 illustrates the result of this process.
Careful control of the pulse energy is crucial in order to; completely remove the film, produce minimal burr to the patterned edge, lack of cracking/delamination of the Mo film and no damage to the glass substrate.
Indium Tin Oxide (ITO) is another thin film that can be scribed by Fiber Lasers to make solar cells but is also used in flat screen TVs and touch sensitive screens. ITO is an example of a Transmissive Conducting Oxide (TCO) of which there are several types commonly used.
In ITO removal the frequency of the Laser has an effect on the quality of the edge produced (Figure 3). Generally, increasing the frequency gives a better edge quality with less scalloping associated with the pulse overlaps.
The results generated are highly material dependant and so application trials are advised to identify the optimum processing parameters – our Apps Labs can help you with these trials if required, simply contact your sales representative for more details.
Figure 3. Thin Film Removal of ITO. 20W; 125kHz WF2 1m/s scan speed 80mm f-theta lens 40µm scribe width.
Many of these materials only require low pulse energies to remove the layer without damaging the substrate and can benefit from a Pulsed Fiber Laser, with their ability to operate pulse frequencies of up to 1MHz.
Trials with our redENERGY G4 Pulsed Fiber Laser have shown that using high pulse frequencies result in significant improvements in scribe quality.
Using low pulse energy short pulses gives enhanced control of the heat input into the process and helps reduce debris and minimises thermal damage.
There are also the other benefits of Fiber Lasers including ease of use, low maintenance and low total cost of ownership.
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