Meeting the challenge of film frame handling automation
BOB FUNG and JACK YAO, Owens Design, Fremont, CA
Semiconductor and LED manufacturers are interested in automating the film frame handling process as a means to increase throughput and yield in their BEOL processes.
Until recently, the loading and unloading of film frames into process tools in both the semiconductor and LED industries has primarily been a manual operation. Both industries, however, are experiencing an increasing need to automate this process due to the large quantity of dies on wafer and scaling of production throughput.
Film frames are typically used in back-end-of-line (BEOL) operations in the LED and semiconductor industries to contain substrates that will eventually be diced or scribed and then split apart. The frame holds a sticky film that keeps the separated dice or LEDs in a manageable array after they have been separated into individual components. This can be particularly critical in LED manufacturing, where several thousands of LEDs are produced from a 2, 4, or even 6 in. wafer. For the same reason, film frame automation will be even more critical once LED industry migrates into 8 in. wafers.
In semiconductor applications, the film frame can be used to stretch the film to make it easier to pick up individual dice for BEOL test and binning applications, for example. In LED processes, stretching the film frame can be used to separate the individual LEDs after the wafer has been scribed.
Film frames are also particularly useful when processing fragile or thin substrates. In LED manufacturing, for example, the residual LED device wafers are more difficult to handle with standard wafer handling equipment after removal of the base sapphire substrate. Using film frames in such circumstances, will improve production yield by minimized the potential of device damage via improper handling of fragile wafers.
The need for automation
For the semiconductor industry the drive toward film-frame-handling automation is powered by the need to address the timing requirements of BEOL inspection and test applications, where throughput with high yield is critical. The increasing size, weight and value of semiconductor wafers has added ergonomic and risk mitigation concerns that have further fueled the need to automate the process.
The LED industry has been expanding into a wide variety of applications, including aviation and automotive lighting, household appliances, remote controls for electronic systems, television backlighting, traffic systems and even household lighting. As a result, LED manufacturers have found it necessary to increasingly automate their manufacturing processes to enable the greater production volumes required to support this growing demand for their products across an expanding variety of markets.
At the same time, however, both industries are extremely cost sensitive. The semiconductor industry, for example, is driven by the imperative of Moore's Law that has governed number of transistors on integrated circuits doubles approximately every two years, has helped to influence reduction of IC pricing as technology advances. For the LED industry, lowering LED prices has been a key factor in its expansion into many markets and is critical if LEDs are to replace more power-hungry incandescent light bulbs in the home-lighting market.
While LED lighting offers consumers a more environmentally friendly alternative to the incandescent light-bulb, cost-per-watt parity at a minimum will be required to overcome consumer reluctance to adopt a new lighting technology in place of the familiar incandescent light bulb that has been in use for decades. This was amply demonstrated by the recent furor over Congress' attempt to mandate alternatives to the incandescent bulb. For the LED industry, the best route to ensuring widespread adoption of LED lighting in the home is to offer consumers a product that is more environmentally friendly, but which most importantly, costs less and lasts longer.
Challenges to automation
Traditionally, film frame has been handled manually by tool operators. Even today, many film frame applications remain manual. As a result there has been no effort to develop any kind of film frame handling standards in either the semiconductor or LED industries.
Due to this lack of industry-wide backend standards, the semiconductor and LED manufacturers either adopted or developed their own customized solutions that suited their manufacturing needs. In both industries there has been a widespread proliferation of varying film frame form factors, which make it extremely difficult for process tool manufacturers to develop cost effective automation solutions that can meet the needs of a wide range of manufacturers.
While there is discussion within the semiconductor industry of developing film frame handling standards for emerging 450mm processes, this does not address the automation needs of 200 and 300mm manufacturing lines. It also provides no automation relief for the LED industry which is mostly comprised of 50 and 100mm wafers.
This situation is exacerbated by the cost-sensitivity of the BEOL processes that use film frame handlers in both the LED and semiconductor markets. While manufacturers in both industries are eager to increase throughput in their BEOL process to enhance volume production and yield, they are reluctant to do so if automation significantly increases their manufacturing costs. At the same time, process tool OEMs struggle to deliver automation solutions that will deliver an acceptable return on investment (ROI) due to the need to highly customize each system design In addition to the lack of industry standards and added hardware cost, attempts to automate film frame handling also face technical challenges relating to the management and alignment of film frames in and out of cassettes.
Traditionally, most equipment companies have leveraged the use of "off the shelf" robots as a key component in wafer automation. Unfortunately, using a typical robot and robotic end-effector to remove a film frame from a cassette via an insert, lift and pull motion path is frequently not feasible due to the limited slot pitch of the cassette.
Alternatively, removing film frames from cassettes by dragging the frames out by their leading edges could be a problem in some applications due to particle generation. Obviously, an automation solution that increases throughput, but decreases yields is not going to be seen as an optimal solution.
A final technical challenge involves proper alignment of the film frame relative to the target substrate. Proper alignment is often complicated by the fact that the substrate's mechanical features used for alignment are not accessible due to the supporting structure of the film frame. Misaligning the substrate or wafer prior to dicing or scribing would be disastrous in terms of lost product.
Meeting the automation challenges
What is needed, then, is an automation solution that can address these technical automation challenges, while offering a cost-effective solution that can be easily customizable to meet differing film frame configurations.
|FIGURE 1. Film frame handler configured for side-by-side cassettes.|
Such a system, such as that shown in FIGURE 1, would require easily customizable mechanisms and grippers to remove film frames from cassettes with tight slot pitches. These specialized film frame grippers need to grip the front edge of the film frame to extract it from the cassette. Since this approach does run the risk of particle contamination, the front edge of the film frame must be gripped in such a way that the frame can be slightly lifted vertically so that there is no rubbing between the frame and the cassette when the frame is extracted from or replaced into the cassette.
|FIGURE 2. Film frame being removed from cassette and placed under an alignment camera.|
The issue of aligning the substrate with the film frame can be resolved using a combination of mechanical and vision technology to ensure fame and substrate alignment. Coarse alignment can be easily achieved by biasing two edges of the frame against two reference planes (FIGURE 2). Once this is done, fine alignment can be achieved with a vision system that is able to locate known features on the substrate. Using this information, the film frame handling system can accurately make position corrections as needed.
|FIGURE 3. A modular design allows vertical stacking, prealignment and multiple handoff locations.|
Most importantly, the film frame handling system requires cassette loadports that can be easily and cost-effectively tailored to meet the requirements for each unique frame and individual application (FIGURE 3). This requires that the overall architecture of the automation be very flexible and adaptable. However, the automation approach must be optimized in terms of functional flexibility and cost.
Film frames are used to handle wafers to be separated into individual devices in BEOL inspection, test and packaging applications in the semiconductor and LED industries. Handling film frames has traditionally been a manual process, which has led to a lack of industry-wide standards and a proliferation of varying film factors. Today, both semiconductor and LED manufacturers are interested in automating the film frame handling process as a means to increase throughput and yield in their BEOL processes. Since these manufacturing processes are extremely cost sensitive, the lack of standards has created a challenge in developing effective automation solutions. This cost and risk challenge has been exacerbated by various technical challenges involving removal of film frames from cassettes, substrate alignment and particle contamination . Fortunately, these technical challenges, as well as the development of customizable cost-effective solutions are possible.
BOB FUNG is Vice President of Engineering for Owens Design. He has a 30 year career in the disk drive, semiconductor and PV equipment development. JACK YAO is Director of Business Development at Owens Design. Prior to joining Owens Design, Jack spent twelve years in the semiconductor equipment industry working for Aviza Technology, ASML, Silicon Valley Group and Watkins Johnson. www.owensdesign.com.
Solid State Technology | Volume 56 | Issue 3 | May 2013