We’ve all noticed that cloudy film that forms on the inside of our vehicle windshields. A major contributor to this annoying coating is outgassing. Of course, this is not the only situation where outgassing is an issue.
Semiconductors are vital in today’s world and can be found in all the devices that we have become so accustomed to. With features measured in nanometers, semiconductor production requires incredible accuracy. It is critical to remove contaminants from the process chambers and, therefore, the processes are done under vacuum. This presents a challenge when selecting components that must live in a vacuum. The vacuum environment causes materials to outgas which is the release of gasses trapped within the material. These stray molecules are a cause for concern as they can interfere with the semiconductor production processes. Adhesives, rubbers and plastics are common sources of outgassing but even metals and glasses can release gasses from cracks or impurities. However, for most solid materials, the method of manufacture and preparation can reduce the level of outgassing significantly.
Builders of equipment used to produce semiconductors must evaluate each component used in a vacuum chamber to mitigate outgassing as much as possible. To help them achieve this, they work with component vendors who have extensive experience in the industry and offer vacuum compatible products. These vendors can also provide highly customized products that ensure very high performance and quality, as well as addressing concerns with outgassing.
Precision sensors that will operate in high vacuum or UHV (Ultra High Vacuum) environments must be carefully constructed from materials with low vapor pressures in order to avoid outgassing. Also, some innovative methods are often utilized to address the challenges with precision sensors that are needed in a vacuum chamber. An example would be to use a precision photoelectric sensor with separate electronics. The electronics are contained in an amplifier which can be mounted outside of the vacuum chamber and the vacuum compatible sensor, with stainless steel housing, can be threaded into the chamber.
Fortunately, semiconductor equipment builders and their component suppliers are well versed in the challenges associated with outgassing and work together to overcome them. By conquering this, and many other challenges they insure we can continue to enjoy our high-tech gadgets.
As an industry account manager focusing on the semiconductor industry, I’ve come to realize that when it comes to sensors used in semiconductor production equipment, size definitely matters. A semiconductor manufacturing facility, better known as a fab or foundry, can cost thousands of dollars per square foot to construct, not to mention the cost to maintain the facility. Therefore, manufacturers of equipment used to produce semiconductors are under pressure to reduce the footprint of their machines. As the equipment becomes more compact, it becomes more difficult to incorporate optical sensors that are needed for precise object detection.
A self-contained optical sensor that includes the optics along with the required electronics is often much too large. There simply isn’t enough space for mounting in the area where the object is to be detected. An alternative method is to use a remote amplifier containing the electronics with a fiber optic cable leading to the point of detection where the light beam is focused on the target. However, there are some drawbacks to this method that can be difficult to overcome. There are instances where the fiber optic cable is too large and not flexible enough to be routed through the equipment. Also, a tighter beam pattern is often required in semiconductor equipment for precise positioning. To provide a tighter beam pattern with fiber optics, it is necessary to add additional lenses. These lenses increase the size, complexity and cost of the sensor.
The most effective way to overcome the limitations of fiber optic sensors is to use very small sensor heads connected to a remote amplifier by electric cables, as opposed to fiber optic cables. The photoelectric sensor heads are exceptionally small, and because the cables are extremely flexible they can easily accommodate tight bends. Therefore, these micro-optic photoelectric sensors are particularly well suited for use in semiconductor equipment. The extremely small beam angles and sharply defined light spots are ideal for the precise positioning required for producing semiconductors. No supplementary lensing is required.
An excellent example of how this micro-optic sensor technology is utilized in semiconductor equipment is for precision wafer detection needed for automated wafer handling. At the end of a robot arm used for wafer handling there is a very thin end-effector known as a blade. By utilizing a very tightly controlled and focused light spot, the sensor can detect wafers just a few μm thick with extreme precision.
The combination of extremely small optical sensor heads with an external processor unit (amplifier) connected via highly flexible cables is a configuration that is ideal for use in semiconductor production equipment.