Machining, Slicing, Dicing, Laser Marking
Silicon wafer Orientation
Crystals are characterized by an orderly array of their atoms. In monocrystalline crystals, this arrangement is the same in any zone of the crystal.
Silicon belongs to the cubic crystal system and has a diamond structure. This is characterized by having each atom symmetrically surrounded by four equally spaced neighbours in a tetrahedral arrangement.
Although Sil’tronix Silicon Technologies provides silicon ingot with the major axis grown in (100) and (111) orientation, we can supply silicon wafer with specific orientation (e.g. (311) or (510)).
Sil’tronix Silicon Technologies uses an X-ray diffraction system to identify the planes in the silicon crystal structure and to check the precise orientation of the crystal for machining to a standard accuracy of 0.5 degrees. We can improve this accuracy to 0.01° if needed. To obtain this very slimp accuracy, Sil’tronix Silicon Technologies uses a special designed bond jig. The orientated material is then precision-transferred to the diamond machining stage.
Sil’tronix Silicon Technologies can also provide wafers with off orientation relative to growing ingot axis (100) or (111). This off orientation can vary from 0.2° (accuracy 0.01°) up to 40° (accuracy 0.5°)
Silicon ingot slicing
The cylindrically ground silicon crystals are mounted on a beam. The ingot is positioned at the ID saw (inner diameter saw) according to the desired orientation. The inner diameter saw has diamond bonded to the inner rim of the blade. The steel saw blade must be tensioned to give it sufficient stability. This tension must be regularly controlled to avoid blade deviation yielding wafers with excessive curvatures, not compatible with customer’s specification
At this stage, we can cut silicon wafer with a mis-cut angle relative to the ingot axis. In fact, thanks to two micrometer screws, we can make disorientation in all the direction of the surface. By this technique, the disorientation can be varied from 0.2° up to 14°.
As the slicing is made wafer by wafer, we can modify the thickness regularly. The thickness of sliced silicon wafers can be varied from 300µm to 20 mm. In fact we can propose to our customer to produce only one wafer with very specific parameters.
For standard thickness (up to 500µm), silicon wafers can be cleaved in small pieces. But this operation causes particles on the wafer and is not convenient for special orientation (like (211)) or for wafers with a mis-cut.
We can propose to dice the wafer in square or rectangular parts with dicing saw. During this operation the wafer is typically mounted on dicing tape, yielding to the minimisation of particles. The area that has been cut away are called die streets which are typically about 75µm wide. The minimum dicing size is 1.5x1.5mm2. There is no maximum dicing size. In fact, by this technique, we can also shape a round wafer into pseudo square (e.g. 6 inches diameter into 156x156 pseudo square)
Dicing is possible for wafer thickness under 1mm. For thicker wafers, we can cut them into small pieces using ID saw. The die streets are larger than the ones obtained by dicing and the minimum dicing size is 5x5 mm2.
Wafer laser Marking
Sil'tronix provides SEMI standard and custom wafer laser marking services. SEMI standard markings include, but are not limited to, M12, M13 and T7 marks commonly found on all silicon wafer substrates. Quality is comparable to major silicon wafer foundry marks.
Wafer Diameters: 2 to 6''
Character height and width: upon request
Font: 0.010” to 1”
Depth: Soft and hard laser marks available.
- Soft Mark: 1-5um in depth
- Hard Mark: 5um to 100um in depth
Mark Location: Front or backside of wafer
Format: Alphanumeric and barcode
Specialty Marks: Company Logo etc.
Sacrificial protective layers such as oxide, nitride, or photoresist are available to protect the wafer surface from debris generated during the laser marking process. Sil'tronix offers post marking wafer cleaning options.