Applications

Quality control for wafers, TSVs and other devices

Applications in the semiconductor industry range from wafer thickness to device topography and all the 3D features in between. With the high speed and passive optics of the CHRocodile sensors, it is possible to measure in harsh environments, even with the presence of acid or other liquid materials. This enables real time quality control such as defining the stop point during grinding or recipe construction for proper back thinning. Bump heights and TSV depths are other features commonly measured with CHRocodile sensors.

Applications
CHRocodile MI5
Quality assurance measurements in the manufacturing process of semiconductors

Many manufacturing processes are dealing with the removal of layers. For example, during wet etching, solid material is converted into liquid compounds with help of a chemical solution. To check the process optical sensors are used. Sensors are used as well to check rinsing processes that allow contaminants to be removed from the wafer surface.

CHRocodile LR
Encapsulation of chips with dispensing machines (dam and fill procedure)

With procedures called dam and fill, first of all a dam made of a viscous cast compound is set up on the circuit board that completely surrounds the chip. Then a dispensing machine dispenses a material to the inner area of the dam that has a low as possible viscosity. This surrounds the delicate structures and wires completely until the component is completely covered. Precitec chromatic confocal sensors measure the height of these chip cast compound dams without touching them accurately to within a few microns. This ensures that the dam height is sufficient for the subsequent cast of the inner area and the protective paint does not run over unprotected areas. The speed of the measuring procedure enables a 100% check of all components manufactured. As a result, casting components is also suitable for high volume, fully automatic manufacturing.

CHRocodile CLS
Measuring glue beads

In the case of glue beads, they often still rely on a visual inspection. It is important that the glue bead trail is continuous and constant. Several parameters are used as quality criteria that can be determined by optical measuring systems. The glue bead must run in the middle with regard to other structures. Undesirable accumulations of material at the start and end point of the bead can be detected. Even gaps can be detected.

CHRocodile IT TW
Circuit board layer thicknesses

The layer thicknesses of silicon casting compounds or solder resist can be measured. Basically there are two different measuring procedures here, chromatic measuring and interferometric measuring. Silicon casting compound can be measured both chromatically and interferometrically. The layer thickness of coloured solder resist can also be measured with the interferometric measuring method. Here the interferometric method has slight advantages over chromatic measuring because it can tolerate a measuring distance deviation of a few millimeters. A 3D measuring device is required if necessary to adjust the measuring distance so that the measured surface is within the permissible operating range of the measuring head.

CHRocodile CLS
Through Silicon Via (TSV)

Through Silicon Via is a mainly vertical electrical metal connection by a wafer. Here a vertical pile of thinned out individual chips is connected through using small copper structures. After the etching process these protrude a little above the silicon and are known as bumps. The TSV structures before filling – which are holes with a high aspect ratio – and the bumps that occur after filling can themselves be measured with Precitec sensors. The height of the bumps over the silicon structures and the depth of the TSVs are required.

CHRocodile CLS
Chip handling: Chip bonding, OLED & LED chips

Metallic OLED display masks can be measured with the line sensor CHRocodile CLS. Imperfections can be reliably detected here. The sensors are also suitable for the ever more compact LED chip packages for high levels of illumination and small form factors, such as is common for LED background lighting and LC screens. Both cutting profiles and also topographies can be created. When the chips are assembled, Precitec Optronik sensors determine the correct position of chips.

Often individual LED are no longer used but highly integrated chips with a large number of light diodes. When testing these optical chips, contact-free measuring distance sensors are already used to a large extent today. These can measure the height of the LED (Z co-ordinates).

CHRocodile DW
Measuring the thickness of doped wafers

Both high and low doped wafers can be measured to determine the thickness with interferometric measuring systems in the infrared range. Other quality criteria are bowing and warping that are taken into account particularly with very thin wafers. The structures applied in layers can distort wafers. The level of distortion can be determined very accurately with distance sensors.

Product family CHRocodile IT
Non-contact wafer thickness measurement

Simple yet precise distance and thickness measurements of wafers are provided by the sensors from the CHRocodile IT product family. These optical sensors are capable of measuring silicon up to approximately 5mm thick with just one measuring head. The exact determination of thickness all the way into the edge area is achieved with the small spot size of the CHRocodile IT. But the CHRocodile IT family can do even more than silicon wafers: measuring GaAs and sapphire wafers, visually non-transparent films and multi-layered systems. Their robust design enables integration directly into the production process, but they are also capable of performing accurate thickness measurements in the laboratory.

CHRocodile DW
Thickness measurement of doped wafers

As the materials continue to evolve in the semiconductor industry, more sensors are emerging to fill the void where previous versions have failed. Doped wafers are one such example where standard sensors are no longer able to perform up to the required specification. The CHRocodile DW has been designed specifically for this application, using  a wavelength better suited to the transmission of doped materials.

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