Wafer bonding and detection for high brightness LED cost reduction

The main purpose of high brightness LED lamp, including signal lamp and backlight display. Although the high cost of high brightness LED, but the superiority of LED applications can still be accepted. High brightness LED also has the potential for general lighting. In order to make the high brightness LED can be used to reduce the cost to the room, offices and parking lot, it is necessary to improve the manufacturing of high brightness LED production efficiency to reduce cost to single lumen. Such high brightness LED can replace the incandescent lamp and fluorescent lamp. One of the great advantages of high brightness LED is that its lifetime is measured in decades.

Multi photon high brightness LED emission in all directions, including to under the direction of the substrate. If the substrate has a small band gap than the LED light emitting region, the substrate absorbs about half of the reflected light, which greatly reduces the output of light. If you put a piece of wafer bonding a light emitting diode containing a high reflectivity on the surface of the substrate wafer, wafer substrate and substrate into heat, light will be reflected back through the launch area, which greatly increased the total light output.

Many materials, such as silicon, gallium arsenide, gallium phosphide, gallium nitride, and sapphire, and can be used to produce LED. in compound semiconductor growth photonic layer and transferred to silicon wafer support or similar material, and the back surface of the wafer is exposed. Composite semiconductors are now only 4 inches in size. This limits the size of the LED wafer to wafer with only 2 to 4 inches in diameter. The other problem is that the two bonded crystals have different thermal expansion coefficients and the bonding process is very slow. Because each time only a pair of wafers, which limits the productivity of high brightness LED, the unit cost is also high. These limitations can be overcome by the use of the newly developed SUSS wafer bonding device, which enables simultaneous multi wafer bonding.

On GaN materials of high brightness LED production in two ways: namely, gold gold gold tin eutectic bonding and hot pressing. In the process of Au Au bonding, a layer of 1 to 3 micron thick gold and barrier layer is applied to each wafer. In order to eliminate the influence of surface contamination on the solid diffusion mechanism, several steps of cleaning (UV ozone or chemical wet treatment) should be carried out. The temperature is 250 degrees to400 degrees, the pressure is from to 7MPa, from a few minutes to a few hours. Low temperature time and pressure. If there is not enough time and pressure, there is only a partial bonding between the wafer and the wafer.

Sikkim co melting method is formed intermetallic alloy diffusion through solid and liquid to bond. A wafer is coated with a thin layer of gold, and the other one is coated with a layer of gold of up to 5 microns. Diffusion barrier can be applied if necessary. In order to avoid oxidation of tin at high temperature, wafer bonding is carried out in a gas, such as in a mixture of nitrogen and hydrogen (95%N2,5%H2). This method requires only a low pressure and a slightly higher temperature than the melting point, can be completed within a few minutes.

Device of wafer bonding for synchronous has developed is based on the 8 inch wafer platform to. In order to increase production, 8 inch diameter platform can be accepted at a time of eight inches, four inches, or three 4 inch wafers (Figure 1), and can be simultaneously bonded 3.

This device has a cavity, the cavity is heated and pressurized, and can be inserted into the fixing device. The fixing device is composed of upper and lower plates made of silicon carbide. The upper plate is capable of loading and unloading, and the lower plate is thermally coupled to control the temperature. The flatness of each plate is within 2 microns. The degree of surface meshing between the two plates requires no more than 20 microns in the 200mm range.

Between the first fixing device two wafer will be bonded on the plate, and then through the manual or pneumatic two wafer. A layer of material, such as graphite, may be placed between the wafer and the plate to achieve optimum pressure distribution (Figure two). On board device wafer and the two wafer down closer with fixed position, positioning device is inserted into the cavity of the loader, the plate to move closer to the positioning device, so that the loader can be removed, the inner cavity of the device after sealing, bonding process starts.

The best time LED wafer bonding, the temperature and pressure parameters is to meet the requirements of metal and device is determined by the process, the process was successfully developed and put into production is the key technology to convert quickly and accurately make the wafer surface to combine image appears, with the image that the hole and crack initiation site.

The manual ultrasonic microscope wafer adhesive available laboratory acoustic microscope detection of high brightness LED wafer with the production or use online automatic detection system. Sonoscan supplies these two ultrasound systems with similar resolution. The automatic system takes good bonding wafer through the machine hand, after testing analysis, after drying and then put it back in the wafer box. The image data can be stored in the database, and the image parameters can be used to control the ultrasonic parameters to adjust the image of the sample.

Ultrasonic sensor back and forth on the surface of the wafer scanning, scanning frequency sensor to thousands of times per second to two pulse wave bonding well within wafer, and receives the reflected acoustic echo, each pulse echo becomes a pixel in the image.

Pulse ultrasonic propagation in homogeneous materials is not reflected, but they will come back all or part of the interface reflection. The amplitude of the reflected echo of the interface depends on the acoustic properties of the two interfaces (sound velocity, density). When two high brightness LED crystal tact gold -