Hard disk media (disks)
Advances in hard disk drive technology are pushing the limits of media production, the platens on which the data is recorded. With ever increasing data densities and the expectation of fewer errors by users, the need for high quality metrology to monitor and characterise the media surface is clear. Taylor Hobson offer products specifically designed to meet these high quality requirements. A one million pixel camera and large field of view enable detailed analysis of the media surface. Automatic characterisation of landing zone laser texturing, edge defects, media surface defects and media roughness are all possible on both glass and aluminium substrates.
Many hard disk drives require a specially textured landing zone to enable the heads to park on the media surface when not being used. This is often created using a laser texturing process which can be monitored using the Talysurf CCI instruments. Automatic characterisation includes: volume, height, density and mean diameter of individual or whole areas of texturing.
Often referred to as odd (outside diameter defects). These are usually caused by problems in the media handling. When the media edge suffers an impact, even if very small, the resulting deformation of the media surface can cause data errors or render the media unusable.
This really describes a whole group of defects causing errors in recorded data because some form of pit or peak is on the media surface. These defects can be caused by delamination, inclusions and contact damage. The Talysurf CCI instrument can characterise these defects, even when they are only a fraction of a micron laterally and sub nanometer in vertically size.
This parameter needs to be monitored as it is one of the key limiting factors on the fly height of the head. Reducing the roughness of the media allows for a reduced fly height giving smaller magnetic spacing which in turn is needed to maintain high data densities on the drive.
Hard disk heads (sliders)
Current advances in hard disk technology, driven by the demand for higher data densities on smaller disk substrates, has meant that much higher tolerances now have to be maintained on the sliders (HDD heads). Controlling the geometry of the sliders to a very high tolerance allows them to fly much closer to the disk surface, reducing the magnetic spacing, which in turn allows for higher data density.
A key limiting factor in the data storage density of a hard disk drive is the flying head height. This is affected significantly by the very small curvature of the Air Bearing Surface (ABS) of the slider side that faces the disk. As a result there is an ever increasing need to control the ABS curvature down to the nanometer level and beyond. By measuring the individual parameters of Crown, Cross Curve (Camber) and Twist the sliders can be modified to bring the overall ABS curvature within tolerance. The ability to correct for dissimilar material errors normally seen in the AlTiC region, the 1 million pixel camera and the large field of view all make the Talysurf CCI 9150 the leading choice for flatness measurement.
Pole Tip Recession
Controlling the pole tip recession region of the slider has, for many years, been one of the most critical metrology applications in the hard disk industry. Year on year these PTR features have been reducing in size and requiring ever higher manufacturing tolerances. For these measurements lateral resolution, number of measurement points, vertical resolution and measurement repeatability are paramount.
The accurate and repeatable measurement of step height is necessary for many hi-tech applications. Taylor Hobson provide a range of instrument designed to meet the very highest requirements for step height measurement. Covering ranges of step height from sub-nanometer to millimetre with repeatability below 0.1 nm.
3D Step Height
Provides the height difference between two planes defined by two areas on a surface. The first area is defined as the reference and the software fits a least squares plane through this area. The second plane is then measured from this. As well as mean step height, maximum height and minimum height, the angle difference is also measured.
2D Step Height
Provides a method of measuring step height for simple geometric shapes such as etched lines or rectangular areas. 2D step height can also be used for measuring thickness where an edge is exposed.
ISO 5436-1 Step Height
When attempting to compare measurements of step height taken on different measurement instruments it is very important to comply to a standard method of measurement. ISO 5436-1 provides an internationally recognised method of measuring step height. The above instruments all support this standard.
MEMS & nanotechnology
Micro Electro-Mechanical Systems are being used today for numerous applications including pressure and acceleration sensors, micro mirror display devices and micro fluidic pumps. MEMS devices extend the fabrication techniques used by the integrated circuit industry to create mechanical elements such as gears, diaphragms and connecting beams. Accurate measurement of all these elements is critical to meet the demand of mass producing low cost high quality MEMS devices.
Accurate measurement of roughness within MEMS devices allows surface interactions to be controlled, whether they are solid to solid interactions as in micro gear systems or solid to liquid as found in micro fluid pumps.
monitoring step height of MEMS devices is an important indicator of performance. Along with lateral dimension information step height gives a good approximation of mass which affects the fundamental oscillating frequency of the individual elements in the device.
lateral dimensions are particularly important when characterising micro gears and fluidic systems. Accurate measurement of volume and surface area as well as critical dimensions such as beam widths all help control the performance of the final device.
Laser etch measurement
Laser etching is one of the predominant methods used for the identification marking of integrated circuits. This is partly due to the fact that laser marking is a tamper proof method of identification. Tamper proof marking has helped greatly reduce IC fraud, the selling of IC is for higher speeds and specifications than they were produced for.
As IC packages have become smaller and thinner the requirement for measuring step height of laser etching has become more important. The target depth of the laser etch is defined by two requirements. Firstly, it must be deep enough to provide tamper proof marking that can be read by IC identification systems and secondly, it must be shallow enough not to damage the circuits on the chip.
The surface finish of the etched mark is an important factor in the easy reading of the final identification, whether by machine or human eye. The rougher the surface, the more light that is scattered and this increases the contrast of the mark to its surrounding surfaces.
Due to the expansion in the use of electro-optical components that are now common place in both telecommunications and display technologies, epitaxy is emerging as a key technique for component production. Epitaxy is the process of depositing very thin layers of semiconductor materials onto the surface of a single crystal substrate. Each crystal layer is known as an epilayer.
Surface texture is a vitally important parameter in specifying the quality of epitaxial semiconductors for both customers and suppliers. With the current drive for ever smaller circuits to be printed on wafers, the tolerances for roughness are becoming tighter. Surface finish for epiwafers is specified in nm, this requires a system with very low noise and high resolution be used to measure them.
IC package measurement
Backend process measurement is important for controlling the final quality of the IC package. Problems in IC packaging can cause connection issues when the device is soldered, detaching of wire bonds or bump on chip contacts and increased stress to be placed on the circuits of the IC. For these reasons it is important to control not just the geometry of the die, but also the flatness of the die seating area, the step height between the attachment points on the die and the package and the roughness of the wire bond attachment areas.
Matching the flatness of the die with that of the die seating area is important to reduce stress placed on the IC during the packaging process and throughout the operation of the device. Controlling the flatness of the overall package is also necessary to ensure correct placement of the IC and good electrical contact being made when soldered.
The surface finish of the die seating area needs to be controlled to ensure good adhesion when the die is attached. Also the roughness of the wire bond attachment areas is important for good electrical conductivity and wire attachment security.
There are many application for step height on the IC package. From the measurement of balls, bumps and leads to the package geometry itself including depth of the die seating area.