Laser Stealth Dicing

A process for laser stealth dicing involves the use of a laser source 380 to focus a beam of infrared light. The laser beam is then focused to a depth within the substrate 210, typically to the bottom of the part 326, and on a second main surface 214, typically opposite the first main surface 212. The distance L between the two surfaces may be the original value, or reduced to make the process more efficient.

Infrared (IR) light

IR lasers can be used to make perforations on semiconductor wafers. These perforations are located below the surface of the wafer and do not affect the front or back surfaces. This stealth dicing technique is used to cut small semiconductor devices that are not too sensitive to external impact. This process does not cause chipping, and is capable of creating sharp edges.To perform stealth dicing, a single-crystalline semiconductor wafer is placed in an IR-laser-diamond pattern. This pattern can be customized by changing the focus depth and laser power. The first SD pass aims to form the polysilicon stress regions on the semiconductor wafer. The process conditions are listed in Table 3. In the first SD pass, an IR beam 506 is split into two 1.1-Watt beams that are focused to depths of 28 microns and 38 microns, respectively. Each beam is measured from the non-device side of the semiconductor wafer 502.The first step in stealth dicing is to place the semiconductor wafer on a tabletop. In a stealth dicing tool, a metal layer covers the scribe street. Once the device side of the semiconductor wafer faces the laser, the beam of the stealth laser is focused on the other side of the device. The laser beam then scans the scribe streets of the semiconductor wafer, ablating the metal layer.

Optical system

An optical system for laser stealth dicing can produce single-pass, clean-cut slices with no external tensile stress or chemical agent. The laser process parameters include repetition rate, pulse overlap, and energy. These parameters influence cutting efficiency. Optical microscopy and optical profilometry can be used to measure the cut edge quality and flatness of the final cuts. These results support a more efficient laser process.Optical systems for laser stealth dicing have many advantages over conventional dicing techniques. For example, they can reduce the overall cost of dicing, and can be used on ultrathin semiconductor wafers, specialty wafers, and MEMS. This technique is more environmental friendly than conventional dicing methods, since the process is dry and therefore gentle on the environment. This process reduces water consumption by up to 622 tons per year.

Process steps

A single pass stealth dicing procedure requires ultrashort pulsed Bessel beams, which are able to produce an overall acceptable level of cut edges. The laser's wavelength, f, is chosen to produce the highest energy per pulse, with the repetition rate determined by the number of pulses per second. Both parameters play a critical role in the laser-induced dicing of quartz plates. The latter determines the amount of heat and energy released by the laser in a given volume of material.Stealth dicing is an innovative wafer fabrication technique. The method produces a row of perforations in the SD layer without affecting the front and back surfaces. The resulting row of perforations is a highly precise and accurate representation of the underlying layer, preventing the chip from breaking during assembly. This process is more effective in reducing the costs and increasing production yields because it does not generate excessive heat or debris.

Damage to wafer

One of the common challenges of semiconductor manufacturing is how to minimize the impact on a wafer during dicing. This can be done in two ways. First, laser ablation can be used to cut a wafer without causing any damage, but stealth dicing can be more effective for reducing the impact on the die by producing sharp edges. Second, stealth dicing does not require water for cleaning and processing. And third, stealth dicing reduces the street width and yield, making it ideal for long shaped dies.A x100 microscope was used to view the wafer. A 25 mJ pulse energy was applied to a sample at a depth of 330-270 mm. It was exposed to the laser in increments of 50 mm over a period of 100 ms, and the duration was based on the shutter speed to prevent beam blocking. During each half-second interval, 100 pulses were delivered to the sample.