Stealth Dicing Research Articles

Precision Layered Stealth Dicing of SiC Wafers by Ultrafast Lasers.

With the intrinsic material advantages, silicon carbide (SiC) power devices can operate at high voltage, high switching frequency, and high temperature. However, for SiC wafers with high hardness (Mohs hardness of 9.5), the diamond blade dicing suffers from problems such as debris contaminants and unnecessary thermal damage. In this work, a precision layered stealth dicing (PLSD) method by ultrafast lasers is proposed to separate the semi-insulated 4H-SiC wafer with a thickness of 508 μm. The laser power attenuates linearly from 100% to 62% in a gradient of 2% layer by layer from the bottom to the top of the wafer. A cross section with a roughness of about 1 μm was successfully achieved. We have analyzed the effects of laser pulse energy, pulse width, and crystal orientation of the SiC wafer. The anisotropy of the SiC wafer results in various qualities of PLSD cross sections, with the roughness of the crystal plane {10−10} being 20% lower than that of the crystal plane {11−20}.

Stealth dicing of 1-mm-thick glass with aberration-free axial multi-focus beams.

Laser stealth dicing can realize material separation with negligible surface damage, but severe aberrations in thick materials degrade processing quality. This Letter presents a nonlinear point-to-point transformation method combined with spherical aberration compensation to achieve aberration-free axial multi-focus beams. The focus peak intensity increases 7 times at a depth of 0.5 mm after spherical aberration compensation, and reaches 44 times at 3.5 mm. Spherical aberration compensation experiments showed that the width of the heat-affected zone remains almost unchanged at different depths inside the glass, and stealth dicing experiments for 1-mm-thick glass demonstrated that aberration-free 1-focus, 2-foci, and 3-foci stealth dicing can be successfully realized.

Algorithm and Experiment of Silicon Wafer Multifocus Laser Stealth Dicing

Algorithm and Experiment of Silicon Wafer Multifocus Laser Stealth Dicing

High quality full ablation cutting and stealth dicing of silica glass using picosecond laser Bessel beam with burst mode

Glass cutting is widely used in many fields, such as aerospace and integrated electronics. To meet requirements of high-quality glass cutting, methods of full ablation cutting and stealth dicing of silica glass using picosecond laser Bessel beam are studied in this paper. Position synchronized output function of laser source and burst mode (BM) can flexibly adjust drilling spacing and the number of sub-pulses during processing. Through experimental research and theoretical analyses, effect of hole spacing, BM, laser power, and defocusing distance on the roughness of the cross-sections of cutting samples are investigated. The optimal combination of full ablation cutting parameters is obtained with the minimum roughness of the cross-section of 355 nm. To expand the application range of Bessel beam glass cutting, stealth dicing process is developed. Process parameters selection strategy of stealth dicing is obtained. Main parameter that affects the effect of stealth dicing is the defocusing distance. Aforementioned methods may provide simple, efficient, and high-quality full ablation cutting and stealth dicing technologies for glass materials.

Dual Laser Beam Asynchronous Dicing of 4H-SiC Wafer.

SiC wafers, due to their hardness and brittleness, suffer from a low feed rate and a high failure rate during the dicing process. In this study, a novel dual laser beam asynchronous dicing method (DBAD) is proposed to improve the cutting quality of SiC wafers, where a pulsed laser is firstly used to introduce several layers of micro-cracks inside the wafer, along the designed dicing line, then a continuous wave (CW) laser is used to generate thermal stress around cracks, and, finally, the wafer is separated. A finite-element (FE) model was applied to analyze the behavior of CW laser heating and the evolution of the thermal stress field. Through experiments, SiC samples, with a thickness of 200 μm, were cut and analyzed, and the effect of the changing of continuous laser power on the DBAD system was also studied. According to the simulation and experiment results, the effectiveness of the DBAD method is certified. There is no more edge breakage because of the absence of the mechanical breaking process compared with traditional stealth dicing. The novel method can be adapted to the cutting of hard-brittle materials. Specifically for materials thinner than 200 μm, the breaking process in the traditional SiC dicing process can be omitted. It is indicated that the dual laser beam asynchronous dicing method has a great engineering potential for future SiC wafer dicing applications.

Dual-beam stealth laser dicing based on electrically tunable lens

In this paper, we present the development of a high-speed dual-beam stealth laser dicing (D-SLD) method for processing semiconductor wafers based on electrically tunable lenses (ETLs). An SLD system utilizes a laser beam to dice a wafer by inducing interior defects without modifying the surface characteristics of a wafer, thereby presenting significant advantages over conventional dicing methods, e.g., blade dicing or laser ablation. Currently, the throughput of SLD is limited by the serial scanning process; in addition, wafer misalignment and the warpage effects together deteriorate the dicing quality and yield and demand high-cost multi-axis precision stages. To address the issue, we parallelize the dicing process by splitting the laser focus into two foci, where the laser intensity at different depths are automatically adjusted to achieve optimal dicing condition. By combining the height sensor and ETLs, each laser focus, i.e., laser scan lines, can be rapidly controlled axially to compensate the wafer curvature and misalignment errors in real time, leading to substantially improved precision (kerf width < 2 μm) and speed, demonstrated by our experimental results. The new dual-beam laser dicing system presents an effective solution for high-speed wafer dicing as well as other important engineering applications, e.g., fabrication of micro-devices and optical components.

One-Step Femtosecond Laser Stealth Dicing of Quartz.

We report on a one-step method for cutting 250-µm-thick quartz plates using highly focused ultrashort laser pulses with a duration of 200 fs and a wavelength of 1030 nm. We show that the repetition rate, the scan speed, the pulse overlap and the pulse energy directly influence the cutting process and quality. Therefore, a suitable choice of these parameters was necessary to get single-pass stealth dicing with neat and flat cut edges. The mechanism behind the stealth dicing process was ascribed to tensile stresses generated by the relaxation of the compressive stresses originated in the laser beam focal volume during irradiation in the bulk material. Such stresses produced micro-fractures whose controlled propagation along the laser beam path led to cutting of the samples.

Evaluation of Metal/Polymer Adhesion and Highly Reliable Four-Point Bending Test Using Stealth Dicing Method in 3-D Integration

The adhesion between metal and polymer layer was studied using four-point bending tests. It was shown that as the annealing temperature increased, oxidation binding increased, which decreased adhesion and reduced the $G_{c}$ value. A new four-point bending test sample prepared using the stealth dicing method with a 100% success rate was proposed for the first time. With samples prepared with stealth dicing, the region where crack extension occurred was smaller after the stress test. Less crack extension generated less loading on the samples. Owing to the coefficient of thermal expansion (CTE) mismatch after increasing the temperature in a highly accelerated stress test (HAST), a void formed in stealth dicing was made close to the interface between the silicon layer and the polymer layer after the stress test, and less crack extension occurred compared with samples kept at room temperature. The smaller loading force guarantees much more stable measurement with a higher success rate after the stress tests. The stealth dicing method can be applied to other structures, such as redistribution layers (RDLs).

A Novel Dicing tape for WLCSP Using Stealth Dicing Through Dicing tape and Back Side Protection-Film

Abstract Market demand of information terminals for Internet of Things (IoT) is increasing. So market situation requires various semiconductor packages. Wafer Level Chip Size Package (WLCSP) is one of the most important technology among them. We selected stealth dicing (SD) as a manufacturing method for WLCSP because the cutting speed is higher than blade dicing and the yield of semiconductor chip is higher than blade dicing. But, SD process still has some technical issues. In some cases, when the laser is irradiated from circuit side (from surface side of Si wafer), the metal pattern in circuit might prevent the laser focusing. In this case, the laser should be irradiated from backside of Si wafer through dicing tape. We have already developed a transparency suitable dicing tape for the SD process, but the base film material of the dicing tape is poly vinyl chloride (PVC) which is not becoming to conform with some of recent environmental standard. Market situation requires poly olefin (PO) dicing tape because of global environmental consideration. We developed PO dicing tape for SD process through dicing tape by conducting various evaluations. In this study, we report details of the development process of novel PO base film dicing tape with the same performance as PVC base film dicing tape and successfully separated a 12 inch silicon mirror wafer into 1 mm die squares and 12 inch silicon mirror wafer with the back side protection-film into 6 mm die squares.

Extremely high-aspect-ratio ultrafast Bessel beam generation and stealth dicing of multi-millimeter thick glass

We report on the development of an ultrafast beam shaper capable of generating Bessel beams of high cone angle that maintain a high intensity hot spot with subwavelength diameter over a propagation distance in excess of 8 mm. This generates a high intensity focal region with extremely high aspect ratio exceeding 10 000:1. The absence of intermediate focusing in the shaper allows for shaping very high energies, up to Joule levels. We demonstrate a proof of principle application of the Bessel beam shaper for stealth dicing of thick glass, up to 1 cm. We expect that this high energy Bessel beam shaper will have applications in several areas of high intensity laser physics.

Whereabouts of missing atoms in a laser-injected Si: Part 1

ABSTRACTIn a stealth dicing of Si wafers, voids are formed in laser-induced modified volumes (LIMVs). Most of the voids are free from apparent defects such as dislocations and cracks. Needless to say, in what will become a void (pre-void) upon laser injection, Si atoms are present prior to the laser injection. The critical issue is where these missing atoms are after the laser injection. Two obvious possibilities are that (1) they remain inside the Si wafer as interstitials (I’s) or (2) these I’s reach the surface of the wafer to disappear. If (1) is the case, I’s are to coagulate to form dislocation loops of I-type upon post laser-injection annealing. However, it has been shown that this is not the case. In order to see whether (2) is the case, surfaces of a laser-injected Si wafer were studied by a scanning electron microscope in detail. No evidence of I’s having reached the surfaces was obtained.

Characterization and control of laser induced modification inside silicon

Internal modification of silicon is important for wafer stealth dicing. In this paper, the authors report experimental and simulation results of three-dimensional modification inside silicon wafers using laser pulses with 1.55 μm wavelength and 3.5 ns pulse duration. Permanent modification is generated inside silicon by tightly focusing and continuously scanning the laser beam inside samples, without damaging the front and back surface. Cross sections of these modifications are observed after cleaving the samples and are further analyzed after mechanical polishing followed by chemical etching. The shape of the modification is found to depend on the input beam shape, laser power, and scanning speed. With proper conditions, a nearly circular modification is obtained, which has potential application for waveguide writing inside silicon.

The History and Future of Precise Laser Processing by Stealth Dicing

The History and Future of Precise Laser Processing by Stealth Dicing

Laser machining of transparent brittle materials: from machining strategies to applications

Transparent brittle materials such as glass and sapphire are widely concerned and applied in consumer electronics, optoelectronic devices, etc. due to their excellent physical and chemical stability and good transparency. Growing re-search attention has been paid to developing novel methods for high-precision and high-quality machining of transparent brittle materials in the past few decades. Among the various techniques, laser machining has been proved to be an effective and flexible way to process all kinds of transparent brittle materials. In this review, a series of laser machining methods, e.g. laser full cutting, laser scribing, laser stealth dicing, laser filament, laser induced backside dry etching (LIBDE), and laser induced backside wet etching (LIBWE) are summarized. Additionally, applications of these techniques in micromachining, drilling and cutting, and patterning are introduced in detail. Current challenges and future prospects in this field are also discussed.

Fabrication of crack-free device using Stealth Dicing

Fabrication of crack-free device using Stealth Dicing

Controllable laser thermal cleavage of sapphire wafers

Laser processing of substrates for light-emitting diodes (LEDs) offers advantages over other processing techniques and is therefore an active research area in both industrial and academic sectors. The processing of sapphire wafers is problematic because sapphire is a hard and brittle material. Semiconductor laser scribing processing suffers certain disadvantages that have yet to be overcome, thereby necessitating further investigation. In this work, a platform for controllable laser thermal cleavage was constructed. A sapphire LED wafer was modeled using the finite element method to simulate the thermal and stress distributions under different conditions. A guide groove cut by laser ablation before the cleavage process was observed to guide the crack extension and avoid deviation. The surface and cross section of sapphire wafers processed using controllable laser thermal cleavage were characterized by scanning electron microscopy and optical microscopy, and their morphology was compared to that of wafers processed using stealth dicing. The differences in luminous efficiency between substrates prepared using these two processing methods are explained.

Analysis of Residual Stress around Semi-Circular Surface Notches due to Excessive Pressure

Residual stresses due to excessive internal pressure applied to an array of semi-circular surface notches is analyzed by body force method. The treated problem corresponds to a simple model of the Stealth Dicing (SD) which is expected as an alternative splitting technology applicable to brittle materials. In SD, laser beam of specific wave length is focused and scanned inside of the material to produce a SD-process zone which includes an array of microvoids. Each microvoid is thought to be received an excessive internal pressure due to thermal expansion and then material is split along a plane which contains an array of microvoids. After the mechanical splitting process, there expected to present a considerable residual stresses in the vicinity of an array of microvoids exposed at the splitting surface. In the present study, by analyzing the elastic-plastic stress fields near the array of surface microvoids, the mechanical characteristics of the SD induces surface is discussed.

Stealth dicing of sapphire wafers with near infra-red femtosecond pulses

The quality of the reflecting faces after dicing is critical for the fabrication of efficient and stable laser diodes emitting in the green–violet region. However, high-quality faces can be difficult to achieve for devices grown on a sapphire substrate as this material is difficult to cleave cleanly. We have therefore investigated a technology known as “stealth dicing”. The technology uses a pulsed laser to damage a plane of material inside of the wafer due to multi-photon absorption instead of cutting through the wafer surface. If the damage is induced in a line of stress points, the sample can then be cleaved easily along the damaged plane to leave a high-quality surface. The use of this technique also reduces thermal damage and debris.

Steepest ant sense algorithm for parameter optimisation of multi-response processes based on taguchi design

Due to the continuous refinements in engineering operations, process parameters need to be optimised in order to improve the production quality. In this study we present a novel method based on the hybridisation of an ant colony system search mechanism with a steepest ascent method to achieve such a parameter optimisation. The proposed algorithm has been implemented and run on two real time industrial applications. Experimental results showed that the optimised parameters for a stealth laser dicing process provided by the new method were able to increase the production quality by improving production precision, which is measured in terms of average deviation from the expected result and relative variance. The novel method we propose was able to identify improved settings for a stealth laser dicing process with five parameters, resulting in a greatly reduced rate of product failures. Additionally six parameters were optimised for another industrial application, namely a grease filling system with twin towers, using only 23 experiments, leading to an increase in the tool life (objective of the optimisation) from the previous average of 9236 U produced to 13,883 U. The new method performed better than conventional response surface methods, showing therefore to be promising for other similar industrial applications.

Multi-Strata Stealth Dicing Before Grinding for Singulation-Defects Elimination and Die Strength Enhancement: Experiment and Simulation

We report on defects characterization and reduction as well as die strength enhancement using stealth dicing (SD) on high-backside reflectance (82%) 2-D NAND memory wafers. This is performed using three-strata subsurface infrared (1.342 μm) nanosecond pulsed laser die singulation with a partial-SD before grinding integration approach. In this paper, a combination of simulation, characterization, and optimization of the multi-strata SD process has led to the elimination of mechanical and absorptive laser singulation related defects such as frontside and backside surface ablation, and topside, backside, and edge chipping. At the same time, the kerf width and kerf straightness are robust against the effects of test element structures located along the dicing streets. There is a consistent coverage of high-quality SD kerf production with near-zero kerf loss across the 300 mm wafer. Multi-strata SD-unique defects such as interference effects and inter-strata cleavage plane {111} damage have been addressed. SD-related integrated defects including Si dust residue post-backgrinding and die attach film-related defects post-die separation have also been resolved. We illustrate the performance of this approach by demonstrating defect-free eight die stacks of 25 μm thick memory dies.