Size Matters When Selecting Sensors for Semiconductor Equipment

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.

1The 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.

2An 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.

3The 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.

 

Technological Alternative to Fiber Optics

Photoelectric applications with space restrictions, small part detection, high temperatures, or aggressive harsh environments may be solved using fiber optic sensors. These sensors allow the electronics to be mounted out of harm’s way while at the same time focusing the light beam on a small target. The sensing tips can be manufactured in a wide variety of housings for unique mounting requirements.

Fiber optic sensors require two components: a remote mounted amplifier, and the fiber optic cable(s). The amplifiers can be basic, with few features, or advanced with many configurable options and digital displays. The fiber optic cables are made of either plastic or glass fibers, each with advantages and application specific solutions.

Many applications, primarily those in the medical Technological Alternative to Fiber Optics 1sciences and semiconductor industries, cannot be solved with fiber optic or miniature photoelectric sensors because they are physically too large to fit in the instruments. Additionally, the cables are typically not flexible enough to be routed through the instruments.  Today, highly flexible and miniature sensors are are being incorporated in other industries due to today’s demands of smaller machines and tools.

MICROmote® sensors are miniaturized photoelectric Technological Alternative to Fiber Optics 2sensors with separate amplifiers that are also available with a variety of functionalities. Their highly flexible, electric sensor cables make them a genuine technical alternative to conventional fiber optics. The photoelectric sensor heads have extraordinarily small dimensions, excellent technical characteristics, and outstanding flexibility for application-specific solutions.

Similar to fiber optic sensors, these micro-optic photoelectric sensors function as either a through-beam or diffuse type sensor with comparable sensing ranges. Unlike fibers, the wired sensing heads are inherently bifurcated type cables so that there is only one connection to the amplifier.

Unlike conventional fiber optic cables,Technological Alternative to Fiber Optics 3 there are no significant coupling losses, minimum bending radius and cyclic bending stresses.  The patented precision elements produce extremely small beam angles with sharply defined light spots unlike standard fiber optics where the beam angle is a function of the fiber geometry.  Additional lenses must be used if the light beam of a fiber optic cable must be focused which adds to the costs.

MICROmote® photoelectric sensors for water detection use a specific wavelength at which water absorbs more light. This significantly simplifies the detection of liquids with high water content using optical sensors. The combination of an ultra-compact design and powerful micro-optics allows for reliable use in capillary tubes where other sensing devices are stretched to their limits.

These sensors can also be used as precision tube Technological Alternative to Fiber Optics 4sensors for detecting bubbles through use of either light refraction or attenuation through the air, or liquid column within the tube. They provide excellent detection for even the smallest air-to-liquid transitions and are reliable for all liquid types, even clear liquids.

In addition, these sensorsTechnological Alternative to Fiber Optics 5 are designed to detect free-floating microbubbles in transparent liquids. Microbubbles refer to little gas bubbles with dimensions smaller than the inside diameter of the tube. Uniform lighting is achieved in the liquid column by using a concentrated arrangement of multiple light beams with very uniform intensity distribution. Gas bubbles that move through this field induce a signal jump in the built-in photoelectric receiver elements

For more information on this technological alternative to fiber optics visit www.balluff.com.