Patent Publication Number: US-2010129984-A1

Title: Wafer singulation in high volume manufacturing

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a Continuation-in-part of serial No. (TBD), filed on Oct. 28, 2008, which is currently pending. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a field of semiconductor fabrication and, more specifically, to an apparatus for and method of singulating a wafer in high volume manufacturing. 
     2. Discussion of Related Art 
     Singulating a wafer involves separation of a substrate into individual die. A backside of a wafer to be singulated is first subjected to backgrinding, followed by polishing. Then, a laser beam is used from the backside of the wafer to form a series of modified layers inside the wafer, extending from the active surface of the wafer to the backside of the wafer. Deterioration sites are formed in the modified layers along scribelines that are arranged in a lattice pattern across an active surface of the wafer. Then, the wafer is mounted onto a dicing tape and singulated by expanding the dicing tape to separate the wafer through the deterioration sites. Individual die are picked from the dicing tape. 
     Issues that may arise include rough edges, uneven street width, residual stress, and delamination in low-k dielectric layers on the die. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an apparatus for laser scribing and laser-assisted chemical singulation of a wafer according to an embodiment of the present invention. 
         FIGS. 2-7  show a substrate separated into smaller portions having different sizes and shapes by laser scribing and laser-assisted chemical singulation according to various embodiments of the present invention. 
         FIG. 8  shows processes involved in laser scribing and laser-assisted chemical etching in an embodiment of the present invention. 
         FIG. 9  shows different methods of laser scribing and laser-assisted chemical etching according to various embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     In the following description, numerous details of specific materials, features, dimensions, processes, and sequences are set forth to provide a thorough understanding of the present invention. However, in some instances, one skilled in the art will realize that the invention may be practiced without these particular details. In other instances, one skilled in the art will also realize that certain well-known details have not been described so as to avoid obscuring the present invention. 
     An apparatus  10  (as shown in  FIG. 1 ) for, a method (as shown in  FIGS. 8-9 ) of, and the resultant structures (as shown in  FIGS. 2-7 ) formed by laser scribing and laser-assisted chemical singulation, such as along scribelines or streets of a substrate, and such as in high volume manufacturing (HVM), according to various embodiments of the present invention will be described below. 
     In an embodiment of the present invention as shown in  FIG. 1 , the substrate  300  includes a whole wafer. In an embodiment of the present invention, the substrate  300  includes a  200  mm diameter wafer with a thickness of 670-780 um. In an embodiment of the present invention, the substrate  300  includes a 300 mm diameter wafer with a thickness of 720-830 um. In an embodiment of the present invention, the substrate  300  includes a 450 mm diameter wafer with a thickness of 870-980 um. 
     In an embodiment of the present invention, the substrate  300  includes a device wafer that is bonded to a handle wafer, one of which is thinned from its backside. In an embodiment of the present invention, the substrate  300  includes silicon-on-insulator (SOI). 
     In an embodiment of the present invention, the substrate  300  includes a partial wafer with an irregular size and shape. In an embodiment of the present invention, the substrate  300  includes a quadrant of a wafer, such as of a 450 mm diameter wafer. 
     In an embodiment of the present invention, the substrate  300  includes a wafer that is attached to an interposer, a redistribution layer (to redistribute power and ground contacts), a redistribution layer (to transform off-chip connections from chip scale to board scale), a printed circuit board (PCB), a chip-scale package (CSP), a wafer-level package (WLP), a wafer-level chip-scale package, a 3-D package, or a system-in-package (SiP). 
     In an embodiment of the present invention, the substrate  300  includes an underfill, such as between a flip chip and an organic substrate. 
     In an embodiment of the present invention, the substrate  300  includes a hermetic passivation layer, such as silicon nitride or polyimide. 
     In an embodiment of the present invention, the substrate  300  includes 2 wafers, one of which is thinned and bumped on its backside, that are stacked front-to-front. In an embodiment of the present invention, the substrate  300  includes Cu-to-Cu diffusion bonded interfaces such as formed by thermocompression. 
     In an embodiment of the present invention, the substrate  300  includes 3 or more wafers, all of which are thinned on their backside except for one wafer, that are stacked front-to-back. In an embodiment of the present invention, the substrate  300  includes through-silicon-via (TSV) such as formed by deep reactive ion etch (DRIE). 
     In an embodiment of the present invention, the substrate  300  includes die stacked over wafers. 
     In an embodiment of the present invention, the substrate  300  includes die stacked over die. 
     Many structures, such as die, are formed on the frontside of the substrate  300 . In an embodiment of the present invention, the substrate  300  includes die that measure 0.3-5.0 mm on each side. In an embodiment of the present invention, the substrate  300  includes die that measure 5.0-20.0 mm on each side. In an embodiment of the present invention, the substrate  300  includes die that measure 20.0-40.0 mm on each side. The die are organized into rows and columns delineated by scribelines and streets. 
     Next, thinning, scribing, and dicing of the substrate  300  according to embodiments of the present invention will be described. 
     First, in an embodiment of the present invention, a backside of the substrate  300  is thinned, such as by grinding and polishing, to reduce the thickness that needs to scribed and diced. In an embodiment of the present invention, the backside of the substrate  300  is thinned to 75-125 um. In an embodiment of the present invention, the backside of the substrate  300  is thinned to 25-75 um. In an embodiment of the present invention, the backside of the substrate  300  is thinned to 10-25 um. 
     In an embodiment of the present invention, the substrate  300  is mounted in a holder (not shown) before thinning the backside. 
     Second, in an embodiment of the present invention, 0-2 backside layers, such as a metallic material, are formed on the backside of the substrate  300  after thinning, to provide one or more functions, such as mechanical support, ease of handling (such as clamping), scratch protection, diffusion barrier, thermal conductivity, electrical conductivity, or absorption of light energy. The backside layers may include blanket films or patterned films. Some or all of the layers formed on the backside of the substrate  300  may be partly or entirely removed after singulation. 
     Third, in an embodiment of the present invention, the substrate  300  is mounted in a tape frame (not shown). The tape frame is made of plastic or metal and is rigid, stiff, heat-resistant, and corrosion-resistant. 
     Fourth, in an embodiment of the present invention, the backside of the substrate  300  and the tape frame are attached smoothly to an adhesive side of a tape or film (not shown) without trapping air bubbles. In an embodiment of the present invention, the die attach film (DAF) is a flexible and tough thermoplastic material that has a thermal conductivity of greater than 6.0 W/m-K and can withstand a temperature of 275 degrees Centigrade. In an embodiment of the present invention, the DAF is made of a 3.5-10.0 mils thick polyvinyl chloride (PVC) base film that is coated with a 0.3-1.1 mils thick pressure-sensitive epoxy adhesive and protected with a 0.8-1.0 mils thick release film. 
     Fifth, the die are partially separated (scribed) from their immediate neighboring die by cutting shallow trenches into the frontside of the substrate  300 . In an embodiment of the present invention, laser scribing includes a single wide and shallow trench along the center of the scribelines. In an embodiment of the present invention, laser scribing includes two parallel separated narrow and shallow trenches along the edges of the scribelines. 
     In an embodiment of the present invention,  0 - 2  frontside layers, such as a water-soluble flux. or a temperature-resistant material, are coated on the frontside of the substrate  300  before laser-assisted chemical etch, to provide one or more functions, such as mask for etch, shield from etch debris, or protection from handling damage. The frontside layers may include blanket films or patterned films. Some or all of the layers formed on the frontside of the substrate  300  may be partly or entirely removed during or after wafer singulation. 
     Sixth, according to an embodiment of the present invention, the die are completely separated (diced) from their immediate neighboring die by cutting completely through the substrate  300  from the frontside. In an embodiment of the present invention, wafer dicing includes a single wide and deep trench along the center of the scribelines. 
     In an embodiment of the present invention, wafer dicing removes bulk material, such as Silicon, from the remaining thickness of the substrate  300  by a process of ablation. 
     Wafer dicing is also known as wafer singulation. In an embodiment of the present invention, wafer dicing removes bulk material, such as Silicon, from the remaining thickness of the substrate  300  by a process of laser-assisted chemical etching. 
     In an embodiment of the present invention, laser-assisted chemical singulation with an etch chemical is performed on the frontside of the thinned substrate  300  that has been mounted on the tape frame (not shown) and attached to the die attach film (not shown). 
     In an embodiment of the present invention, the laser-assisted chemical singulation is coatless since the frontside layer is not needed to cover solder bumps protruding from the frontside of the substrate  300 . 
     In an embodiment of the present invention, the laser-assisted chemical singulation is maskless since the frontside layer is not needed to pattern the wafer for scribing or dicing. 
     Next, laser scribing and laser-assisted chemical etching of a substrate  300 , such as a wafer, to separate out smaller structures, such as die, having various dimensions and shapes according to embodiments of the present invention will be described. In an embodiment of the present invention, the substrate  300  includes stacked wafers, die stacked on wafers, stacked die, and wafer-level packages. 
     As shown in an embodiment of the present invention in  FIG. 2 , laser scribing and laser-assisted chemical etching are used to separate four adjacent die  11 ,  12 ,  21 ,  22 , such as at an intersection, by removing material between them along the scribelines and street in both the x- and the y-axes. 
     As shown in an embodiment of the present invention in  FIG. 3 , laser scribing and laser-assisted chemical etching are used to singulate die and shape the corners, such as by including notches. 
     As shown in an embodiment of the present invention in  FIG. 4 , laser scribing and laser-assisted chemical etching are used to singulate die and shape the edges, such as to become curved or rounded. 
     As shown in an embodiment of the present invention in  FIG. 5 , laser scribing and laser-assisted chemical etching are used to singulate die with scribelines and street that are irregular, such as having jogs or steps and thus not aligned in a straight line and, such as having different widths in the x-axis and the y-axis. 
     As shown in an embodiment of the present invention in  FIG. 6 , laser scribing and laser-assisted chemical etching are used to singulate die having different sizes and shapes, such as by adjusting the location and width of the scribelines and streets. 
     As shown in an embodiment of the present invention in  FIG. 7 , laser scribing and laser-assisted chemical etching are used to singulate known good die (KGD)  12 ,  22  while bypassing bad die  11 ,  21  by not singulating the bad die (shown as dashed lines). 
     Next, a singulation apparatus  10  according to the present invention that performs laser scribing and laser-assisted chemical etching will be described. In an embodiment of the present invention as shown in  FIG. 1 , a substrate transport mechanism  430  transfers the mounted substrate  300  and tape frame from a cartridge, cassette, or magazine in and out of the singulation apparatus  10 . In an embodiment of the present invention, the singulation apparatus  10  includes two substrate transport mechanisms  430  to improve throughput and tool uptime. 
     In an embodiment of the present invention, the substrate transport mechanism  430  includes a series of interconnected belts or tracks. In an embodiment of the present invention, the belts or tracks move the mounted substrate  300  and tape frame into and out of the enclosure  1000 . Other mounted substrates  300  and tape frames wait or move on other parts of the belts or tracks, such as in one or more queues, to be transferred or processed. 
     In an embodiment of the present invention, the substrate transport mechanism  430  includes a series of interconnected elevators. In an embodiment of the present invention, the elevators raise and lower the mounted substrate  300  and tape frame inside the enclosure  1000 . 
     In an embodiment of the present invention, the substrate transport mechanism  430  includes a series of interconnected robots. In an embodiment of the present invention, the robots load and unload the mounted substrate  300  and tape frame from a chuck  432  inside the singulation apparatus  10 . 
     In an embodiment of the present invention, the singulation apparatus  10  is designed, constructed, and assembled to be modular to accommodate high volume manufacturing (HVM). In an embodiment of the present invention, the singulation apparatus  10  has different configurations depending on various factors, such as operator safety, footprint size, module flexibility, adequate support for thinned substrates without damage (such as warpage or stress), and space for steering and scanning laser beams. 
     In an embodiment of the present invention, the chuck  432  includes a horizontal carousel (platter) or a horizontal susceptor to accommodate high volume manufacturing. In an embodiment of the present invention, the substrate  300  faces downwards in the horizontal carousel (platter) or the horizontal susceptor (so a laser beam points upwards). In an embodiment of the present invention, the substrate  300  faces upwards in the horizontal carousel (platter) or the horizontal susceptor (so a laser beam points downwards). 
     In an embodiment of the present invention, the chuck  432  includes a vertical carousel (platter) or a vertical susceptor to accommodate high volume manufacturing. In an embodiment of the present invention, the substrate  300  faces inwards in the vertical carousel (platter) or the vertical susceptor (so the laser beam points outwards). In an embodiment of the present invention, the substrate  300  faces outwards in the vertical carousel (platter) or the vertical susceptor (so a laser beam points inwards). 
     In an embodiment of the present invention, the horizontal carousel (platter), the vertical carousel (platter), the horizontal susceptor, or the vertical susceptor are designed to hold multiple mounted substrates  300  and tape frames, depending on the size and shape of the substrate  300 . In an embodiment of the present invention, the multiple mounted substrates  300  having different sizes and shapes are processed in the singulation apparatus  10 . 
     In an embodiment of the present invention, the vertical susceptor has a polygonal cross-section. In an embodiment of the present invention, the vertical susceptor includes  5 - 8  vertical faces arranged horizontally around a vertical axis. In an embodiment of the present invention, the vertical susceptor includes 1-4 tiers arranged vertically on each face. 
     In an embodiment of the present invention, the chuck  432  is mounted on a stage  434  in the process chamber  1010  of the singulation apparatus  10 . In an embodiment of the present invention, the stage  434  includes a horizontal or a vertical table. In an embodiment of the present invention, the stage  434  is rigid and isolated from sources of vibration. 
     In an embodiment of the present invention, the stage  434  shifts, raises, lowers, rotates, and tilts the chuck  432  in the process chamber  1010  by using collaborative actuators, with feedback from corresponding sensors, to iteratively locate, position, orient, and align the mounted substrate  300  and frame, to predetermined tolerances, for laser-assisted chemical etch. In an embodiment of the present invention, the stage  434  includes an indexing accuracy of 1.0 um and a rotary accuracy of 4.0 arc-sec. 
     In an embodiment of the present invention, the stage  434  is shifted (translated) with high-speed servo motors and linear encoders connected to HeNe laser interferometers. In an embodiment of the present invention, the stage  434  is raised or lowered with motors and piezoelectric transducers (PZT). In an embodiment of the present invention, the stage  434  is rotated with motors and rotary encoders. In an embodiment of the present invention, the stage  434  is leveled or tilted by motors and actuators. 
     In an embodiment of the present invention, the singulation apparatus  10  includes at least one process chamber  1010  inside the enclosure  1000 . During operation, the process chamber  1010  is sealed off from an environment surrounding the enclosure  1000 . 
     In an embodiment of the present invention, the mounted substrate  300  and frame are held by the chuck  432  in the process chamber  1010  of the singulation apparatus  10 . 
     In an embodiment of the present invention, the chuck  432  includes a clamp to hold the mounted substrate  300  and frame. In an embodiment of the present invention, the chuck  432  includes a vacuum chuck to hold the mounted substrate  300  and frame. In an embodiment of the present invention, the chuck  432  includes an electrostatic chuck to hold the mounted substrate  300  and frame, such as when the process chamber  1010  is under vacuum. 
     In an embodiment of the present invention, an illumination mechanism  110  produces electromagnetic radiation, such as light, from a source in the singulation apparatus  10 . In an embodiment of the present invention, the illumination mechanism  110  expands, filters, homogenizes, shapes, and directs the light, such as in a laser beam  200 , towards the mounted substrate  300  and frame held by the chuck  432  in the process chamber  1010  in the enclosure  1000 . 
     In an embodiment of the present invention, the illumination mechanism  110  is located inside the enclosure  1000 , but outside the process chamber  1010 . The laser beam  200  is transmitted through a window into the process chamber  1010  of the enclosure  1000 . The window is formed from a material that is transparent to the wavelengths of light from the laser beam  200 . 
     In an embodiment of the present invention, cut-off wavelengths for far-ultraviolet (FUV) long pass filters are 155.0 nm for Al 2 O 3 , 134.5 nm for BaF 2 , 131.0 nm for SrF 2 , 122.5 nm for CaF 2 , 112.0 nm for MgF 2 , and 103.5 nm for LiF. In an embodiment of the present invention, transmission curves for alkali halide crystals shift to longer wavelengths as temperature increases. The reverse is also true since the transmission curves for alkali halide crystals shift to shorter wavelengths as the temperature decreases. 
     In an embodiment of the present invention, a focusing mechanism  120  focuses the laser beam  200 , such as in a direction perpendicularly towards the outer surface of the mounted substrate  300  and frame. In an embodiment of the present invention, the focusing mechanism  120  includes a plano-convex lens. In an embodiment of the present invention, the focusing mechanism  120  includes a cylindrical lens. In an embodiment of the present invention, the focusing mechanism  120  includes an f-theta lens. 
     In an embodiment of the present invention, the focusing mechanism  120  has a focal length (F.L.) of 10-25 mm with a depth of focus of ±0.5 mm. In an embodiment of the present invention, the focusing mechanism  120  has a focal length of 25-60 mm with a depth of focus of ±1.0 mm. In an embodiment of the present invention, the focusing mechanism  120  has a focal length of 60-150 mm with a depth of focus of ±3.0 mm. In an embodiment of the present invention, the focusing mechanism  120  has a focal length of 150-375 mm with a depth of focus of ±7.5 mm. 
     In an embodiment of the present invention, a steering mechanism  130  steers the laser beam  200 , such as along an outer surface of the substrate  300 . In an embodiment of the present invention, a galvanometer (galvo) mirror provides y-deflection while another galvanometer (galvo) mirror provides x-deflection. 
     In an embodiment of the present invention, the galvano mirror type scanner has a minimum spatial resolution of 0.6-1.8 nm per step. In an embodiment of the present invention, the galvano mirror type scanner has a minimum spatial resolution of 6-15 um. In an embodiment of the present invention, the galvano mirror type scanner has a minimum spatial resolution of 15-30 um. 
     In an embodiment of the present invention, the focusing mechanism  120  and the steering mechanism  130  are electronically coupled through a closed-loop system to dynamically focus (on the fly) and move the laser beam  200  in real time, such as during laser-assisted chemical etch. 
     In an embodiment of the present invention, the laser beam  200  has a working area of 500×250 mm 2  in the plane of the mounted substrate  300  and frame. In an embodiment of the present invention, the laser beam  200  has a working area of 400×300 mm 2  in the plane of the mounted substrate  300  and frame. In an embodiment of the present invention, the laser beam  200  has a working area of 350×350 mm 2  in the plane of the mounted substrate  300  and frame. 
     In an embodiment of the present invention, an optical scanning mechanism  140  scans the laser beam  200  across an outer surface of the mounted substrate  300  and frame held on the chuck  432  which is mounted on the stage  434  that is stationary. 
     In an embodiment of the present invention, the optical scanning mechanism  140  has a scanning speed of 50-200 mm/sec. In an embodiment of the present invention, the optical scanning mechanism  140  has a scanning speed of 200-600 mm/sec. In an embodiment of the present invention, the optical scanning mechanism  140  has a scanning speed of 600-1,200 mm/sec. 
     In an embodiment of the present invention, the laser beam  200  is operated in a vector scan mode. In an embodiment of the present invention, the laser beam  200  is switched off between scans. In an embodiment of the present invention, the switching includes mechanical, optical, electro-optical, magneto-optical, or acousto-optical switching. 
     In an embodiment of the present invention, the laser beam  200  is operated in a raster scan mode. In an embodiment of the present invention, the laser beam  200  is blanked out as needed (without switching it off) by using a shutter, a deflection plate, or a mirror. 
     In an embodiment of the present invention, a mechanical scanning mechanism  440  scans the stage  434 , on which the chuck  432  is mounted, under a laser beam  200  that is stationary. 
     In an embodiment of the present invention, the mechanical scanning mechanism  440  has a scanning speed of 50-200 mm/sec. In an embodiment of the present invention, the mechanical scanning mechanism  440  has a scanning speed of 200-600 mm/sec. In an embodiment of the present invention, the mechanical scanning mechanism  440  has a scanning speed of 600-1,200 mm/sec. 
     In an embodiment of the present invention, the optical scanning mechanism  140  and the mechanical scanning mechanism  440  are coupled through a close-loop system to scan both the laser beam  200  and the stage  434 , on which the chuck  432  is mounted. In an embodiment of the present invention, the closed-loop system mixes beat frequencies and prevents standing waves. In an embodiment of the present invention, the closed-loop system improves uniformity of the laser-assisted chemical etch. 
     In an embodiment of the present invention, a first computer  100  controls the optical subsystems of the singulation apparatus  10 , such as the illumination mechanism  110 , the focusing mechanism  120 , the steering mechanism  130 , and the optical scanning mechanism  140 . 
     In an embodiment of the present invention, a second computer  400  controls the mechanical subsystems of the singulation apparatus  10 , such as the substrate transport mechanism  430  and the mechanical scanning mechanism  440 . 
     Both computers  100 ,  400  are accessed through a user interface  505  with menu-driven software  500 . 
     In an embodiment of the present invention, a third computer (not shown) communicates with both the first computer  100  and the second computer  400 . 
     In an embodiment of the present invention, the third computer coordinates the singulation apparatus  10  with other singulation apparatus (not shown) to apportion work among them more efficiently, such as to minimize queue time in HVM. 
     In an embodiment of the present invention, the third computer coordinates the singulation apparatus  10  with other equipment (not shown) that are upstream or downstream of the singulation apparatus  10  to improve flow, such as to reduce size of incoming inventory or outgoing inventory in HVM. 
     In an embodiment of the present invention as shown in  FIG. 9 , the laser beam  200  is from a continuous wave (CW) laser. 
     In an embodiment of the present invention, the CW laser beam  200  has a power of 70-500 milliWatt. In an embodiment of the present invention, the laser beam  200  has a power of 0.5-3.0 Watt. In an embodiment of the present invention, the laser beam  200  has a power of 3.0-15.0 Watt. In an embodiment of the present invention, the laser beam  200  has a power of 15.0-60.0 Watt. 
     In an embodiment of the present invention, the laser beam  200  is p-polarized, i.e., the electric field vector of the laser beam  200  oscillates parallel to the plane of the incidence of the laser beam  200 . In an embodiment of the present invention, the laser beam  200  is s-polarized, i.e., the electric field vector of the laser beam  200  oscillates perpendicular to the plane of the incidence of the laser beam  200 . In an embodiment of the present invention, the laser beam  200  is circular polarized. Fresnel refraction depends on polarization. 
     In an embodiment of the present invention, the laser beam  200  is from a lamp-pumped or diode-pumped solid-state (DPSS) laser. The DPSS laser produces excellent beam quality, high repetition rate, and small beam size. 
     In an embodiment of the present invention, the laser beam  200  is from a DPSS laser, such as a CW neodymium-doped yttrium aluminum garnet (Nd 3+ /Y 3 Al 5 O 12  or Nd:YAG) laser. In an embodiment of the present invention, the laser beam  200  has a wavelength of 1,064 nm, 532 nm, 355 nm, or 266 nm. 
     In an embodiment of the present invention, the laser beam  200  is from a DPSS laser, such as a CW neodymium-doped yttrium lithium fluoride (Nd 3+ /YLiF 4  or Nd:YLF) laser. In an embodiment of the present invention, the laser beam  200  has a wavelength of 1,053 nm, 527 nm, 351 nm, or 263 nm. 
     In an embodiment of the present invention, the laser beam  200  is from an argon ion Ar +  CW laser producing illumination having multiple wavelengths, including 514.5 nm, 497.0 nm, 488.0 nm, 476.5 nm, 457.9 nm, 363.8 nm, 351.0 nm, and 334.0 nm. 
     In another embodiment of the present invention as shown in  FIG. 9 , the laser beam  200  is from a pulsed wave (PW) laser. 
     In an embodiment of the present invention, the PW laser beam  200  has a pulse energy of 1-15 mJ. In an embodiment of the present invention, the PW laser beam  200  has a pulse energy of 15-200 mJ. In an embodiment of the present invention, the PW laser beam  200  has a pulse energy of 200-2,200 mJ. 
     In an embodiment of the present invention, the laser beam  200  has a pulse repetition rate of 0.15-2.00 kHz. In an embodiment of the present invention, the laser beam  200  has a pulse repetition rate of 2.0-22.0 kHz. In an embodiment of the present invention, the laser beam  200  has a pulse repetition rate of 22.0-200.0 kHz. In an embodiment of the present invention, the laser beam  200  has a pulse repetition rate of 0.2-1.4 MHz. In an embodiment of the present invention, the laser beam  200  has a pulse repetition rate of 1.4-7.0 MHz. 
     In an embodiment of the present invention as shown in  FIG. 9 , the PW laser is a nanosecond laser. In an embodiment of the present invention, the laser beam  200  has a pulse width of 1-6 ns. In an embodiment of the present invention, the laser beam  200  has a pulse width of 6-24 ns. In an embodiment of the present invention, the laser beam  200  has a pulse width of 24-85 ns. In an embodiment of the present invention, the laser beam  200  has a pulse width of 85-255 ns. 
     In an embodiment of the present invention, a longer pulse width results in a higher laser assisted chemical etch rate. In an embodiment of the present invention, a shorter pulse width results in a lower temperature rise during the laser assisted chemical etch. In an embodiment of the present invention, the pulse width is varied to optimize etch uniformity of the laser-assisted chemical etch. 
     In an embodiment of the present invention, the laser beam  200  is from a CO 2  PW laser producing illumination having a wavelength of 10.64 um which corresponds to a frequency of 2.8×10 13  Hz. 
     In an embodiment of the present invention, the laser beam  200  is from an ultraviolet (UV) light laser. 
     In an embodiment of the present invention, the laser beam  200  is from an excimer laser. In an embodiment of the present invention, the laser beam  200  has a wavelength of 351 nm (XeF). In an embodiment of the present invention, the laser beam  200  has a wavelength of 308 nm (XeCl). In an embodiment of the present invention, the laser beam  200  has a wavelength of 248 nm (KrF). In an embodiment of the present invention, the laser beam  200  has a wavelength of 193 nm (ArF). In an embodiment of the present invention, the laser beam  200  has a wavelength of 157 nm (F 2 ). 
     Excimer lasers produce high pulse energy, but at low repetition rates, such as 1-100 pulses per second, with beams having low optical quality. 
     In an embodiment of the present invention as shown in  FIG. 9 , the laser beam  200  is from an ultrafast laser, such as a picosecond laser or a femtosecond laser, to provide temporal confinement. A pulse with a fast rise time (square wave pulse) and a short duration creates less heat during the pulse and permits more of the heat to dissipate between consecutive pulses. 
     In an embodiment of the present invention, the laser beam  200  is from a picosecond laser with a pulse width of 5-35 ( 10   −12 ) picoseconds. In an embodiment of the present invention, the laser beam  200  is from a picosecond laser with a pulse width of 35-175 (10 −12 ) picoseconds. In an embodiment of the present invention, the laser beam  200  is from a picosecond laser with a pulse width of 175-525 (10 −12 ) picoseconds. 
     In an embodiment of the present invention, the laser beam  200  is a femtosecond laser with a pulse width of 5-35 (10 −15 ) femtoseconds. In an embodiment of the present invention, the laser beam  200  is a femtosecond laser with a pulse width of 35-175 (10 −15 ) femtoseconds. In an embodiment of the present invention, the laser beam  200  is a femtosecond laser with a pulse width of 175-525 (10 −15 ) femtoseconds. 
     In an embodiment of the present invention, the laser beam  200  has a shape of an ellipse in cross-section. In an embodiment of the present invention, the laser beam  200  has a ratio of major axis: minor axis of 1:1 (circle). In an embodiment of the present invention, the laser beam  200  has a ratio of major axis:minor axis is (2-3):1. In an embodiment of the present invention, the laser beam  200  has a ratio of major axis: minor axis is (5-10):1. 
     In an embodiment of the present invention, the major axis is oriented across and parallel to a width of the laser-assisted cut along the scribeline or street. In an embodiment of the present invention, the minor axis is oriented across and parallel to a width of the laser-assisted cut along the scribeline or street. 
     In an embodiment of the present invention, the laser beam  200  is scanned parallel to the major axis. In an embodiment of the present invention, the laser beam  200  is scanned parallel to the minor axis. In an embodiment of the present invention, the laser beam  200  is partially scanned parallel to the major axis and partially scanned parallel to the minor axis. 
     In an embodiment of the present invention, the laser beam  200  has a spot size that is adjustable. In an embodiment of the present invention, the spot size is controlled by the focusing mechanism  120 .that adjusts the focal length of the laser beam  200 . In an embodiment of the present invention, the spot size is controlled by the mechanical scanning mechanism  440  that adjusts a height, or separation, of the stage  434 , on which the chuck  432  is mounted. In an embodiment of the present invention, the spot size is adjusted with a cylindrical lens. 
     In an embodiment of the present invention, the laser beam  200  has a single-mode output with an intensity profile that depends on how the light is confined. The modes are quantized so only certain modes are allowed. In an embodiment of the present invention, the boundary conditions imposed on a plane wave propagating through free space, such as the light in the laser beam  200 , results in an intensity profile with a transverse (perpendicular to a direction of propagation) pattern that has cylindrical symmetry. When a radial mode order p=0 (concentric ring of intensity) and an angular mode order, or index, I=0 (angularly distributed lobe), the TEM pI  mode becomes TEM 00  which is the lowest-order, or fundamental, transverse electromagnetic mode. The TEM 00  mode has the same form as a Gaussian beam with a single lobe, and thus a constant phase, across the mode. During propagation, the TEM 00  mode of the laser beam  200  may increase or decrease in overall size, but preserves its general shape. Other higher-order modes have a relatively larger spatial extent than the TEM 00  mode (which is relatively the smallest). 
     In an embodiment of the present invention, the laser beam  200  has a shape of a circle in cross-section. In an embodiment of the present invention, the laser beam  200  has a spot size (diameter) of 45-90 um. In an embodiment of the present invention, the laser beam  200  has a spot size (diameter) of 15-45 um. In an embodiment of the present invention, the laser beam  200  has a spot size (diameter) of 4-15 um. In an embodiment of the present invention, the laser beam  200  has a spot size (diameter) that is limited by diffraction. 
     In an embodiment of the present invention, the laser beam  200  has a fixed spot size on the outer surface of the mounted substrate  300  during operation. In an embodiment of the present invention, the laser beam  200  has a variable spot size on the outer surface of the mounted substrate  300  during operation. 
     In an embodiment of the present invention, the laser beam  200  impinges on the outer surface of the mounted substrate  300  with an incident angle of 87-93 degrees. In an embodiment of the present invention, the laser beam  200  impinges on the outer surface of the mounted substrate  300  with an incident angle of 84-96 degrees. In an embodiment of the present invention, the laser beam  200  impinges on the outer surface of the mounted substrate  300  with an incident angle of 78-102 degrees. 
     In an embodiment of the present invention, multiple laser beams are separated out by beamsplitting apparatus from a laser beam  200  generated by a single source of illumination. 
     In an embodiment of the present invention, multiple laser beams are generated separately from one or more sources of illumination. In an embodiment of the present invention, several transparent windows permit multiple laser beams to enter the process chamber  1010 . 
     In an embodiment of the present invention, the laser-assisted chemical etch includes multiple laser beams  200  that are linked by hardware into one or more gangs which increases throughput when processing parallel rows in a substrate  300 . 
     In an embodiment of the present invention, the laser-assisted chemical etch includes two or more separate laser beams that are multiplexed by software. In an embodiment of the present invention, the separate laser beams have similar properties. In an embodiment of the present invention, the separate laser beams have different properties. 
     In an embodiment of the present invention, a continuous wave laser beam and a pulsed wave laser beam overlap each other spatially to process a substrate  300 . 
     In an embodiment of the present invention, a continuous wave laser beam and a pulsed wave laser beam overlap each other temporally to process a substrate  300 . 
     In an embodiment of the present invention, a continuous wave laser beam and a pulsed wave laser beam do not overlap each other, spatially or temporally, to process a substrate  300 . 
     In an embodiment of the present invention, multiple laser beams interfere destructively, at least in part, to permit a smaller resolution to be achieved. 
     In an embodiment of the present invention as shown in  FIG. 9 , a continuous wave (CW) infrared (IR) wavelength laser beam performs laser scribing  910  with a shallow etch though overlying non-Silicon layers, such as having a thickness of 10-15 um, at or near the surface. In an embodiment of the present invention, a pulse wave (PW) ultraviolet (UV) wavelength laser beam performs laser-assisted chemical etching with a through cut of the remaining thickness of underlying bulk Silicon below the surface in the substrate  300 . 
     In an embodiment of the present invention, the CW IR laser beam is tilted, such as at 60(±20) degrees off-normal, relative to the outer surface of the substrate  300  to avoid a plasma plume which is perpendicular (normal) relative to the outer surface of the substrate  300 . 
     In an embodiment of the present invention, the CW IR laser beam is tilted at a Brewster angle, such as 74 degrees off-normal for a bare Silicon wafer, to minimize loss of laser power due to reflection off the outer surface of the substrate  300 . 
     In an embodiment of the present invention, the PW UV laser beam is normal or overhead, such as at 0(±20) degrees off-normal, relative to the outer surface of the substrate  300 . 
     In an embodiment of the present invention, most, if not all, of the substrate  300  is laser scribed  910  before it is laser-assisted chemically etched  920 . 
     In an embodiment of the present invention, the CW IR laser beam and the PW UV laser beam are connected by hardware and software into a gang, such that the CW IR laser beam leads, such as to perform laser scribing  910 , and the PW UV laser beam follows, such as to perform laser-assisted chemical etching  920 , on the same structure, such as the die, on the substrate  300 . Thus, laser scribing and laser-assisted chemical singulation are performed sequentially with a very small time interval between them. 
     Next, various processes to perform laser scribe of the substrate  300 , such as in the singulation apparatus  10 , will be described. 
     In an embodiment of the present invention as shown in  FIG. 9 , laser scribing  910  removes surface layers, such as metal and oxide, with a thickness of 10-15 um, from the substrate  300  by a process of ablation. In an embodiment of the present invention, laser scribing removes test element groups (TEG) and metal pads that are located in the scribelines between adjacent die. In an embodiment of the present invention, laser scribing is performed on the thinned substrate  300  that has been mounted on the tape frame and attached to the die attach film. 
     In general, energy of a photon increases as wavelength of light decreases. In particular, photon energy is 3.5 electron Volts (eV) for a wavelength of 355 nm, such as produced by a Nd:YAG laser. In particular, photon energy is 4.7 electron Volts (eV) for a wavelength of 266 nm such as produced by a Nd:YAG laser. In particular, photon energy is 5.0 electron Volts (eV) for a wavelength of 248 nm, such as produced by a KrF laser. In particular, photon energy is 7.9 electron Volts (eV) for a wavelength of 157 nm, such as produced by a F 2  laser. 
     A band gap of a material refers to an energy difference between a top of a valence band and a bottom of a conduction band. Electrons that gain energy by absorbing phonons (heat) or photons (light) can become excited enough to jump across the band gap and become carriers for electrical conduction. 
     A material with a small band gap, such as less than 3.0 eV, is considered to be a semiconductor. In an embodiment of the present invention, Germanium is an elemental semiconductor with a band gap, E g , of 0.67 eV at a temperature of 300 K. In an embodiment of the present invention, Silicon is an elemental semiconductor with a band gap, E g , of 1.12 eV at a temperature of 300 K. In an embodiment of the present invention, Gallium Arsenide is a III-V compound semiconductor with a band gap, E g , of 1.43 eV at a temperature of 300 K. In an embodiment of the present invention, Silicon Carbide is a semiconductor with a band gap, E g , of 2.86 eV at a temperature of 300 K. In an embodiment of the present invention, Silicon Germanium (SiGe) is a semiconductor with a band gap of 0.35-0.65 eV upon application of a uniaxial (applied in the channel direction) compressive stress. 
     A material with a large band gap, such as greater than 3.0 eV, is considered to be an electrical insulator. In an embodiment of the present invention, Silicon Nitride is an insulator with a band gap, E g , of 5.0 eV at a temperature of 300 K. In an embodiment of the present invention, Diamond is a form of Carbon insulator with a band gap, E g , of 5.5 eV at a temperature of 300 K. In an embodiment of the present invention, Silicon Dioxide is a form of insulator with a band gap, E g , of 9.0 eV at a temperature of 300 K. 
     A material with a band gap that is smaller than a photon energy of a laser is opaque (low ablation threshold) and is ablated by the laser when enough incident energy is absorbed by the lattice to induce heating, melting, and evaporation of the material. However, a material with a band gap that is larger than the photo energy is transparent (high ablation threshold) and is not ablated by the laser since most of the incident energy is transmitted rather than absorbed. 
     In an embodiment of the present invention, the laser scribing is performed with a laser beam  200  with a wavelength of 355 nm (ultraviolet), a pulse width of 10-120 nsec, a pulse energy of 30-125 uJ, a repetition rate of 30-150 kHz, consecutive pass overlapping of 65-85%, and a stage scanning speed of 25-200 mm/sec. 
     As shown in block  910  in an embodiment of the present invention in  FIG. 9 , laser scribing with nanosecond pulses of light, such as with a short ultraviolet wavelength of less than 400 nm, achieves ablation of materials through a physical process that thermally heats, melts, and evaporates the materials. However, the large temperature rise enlarges the heat affected zone (HAZ), increases stress, increases micro-cracking, increases delamination, increases deposition of debris on the surface, and increases deposition of recast material in the cut (trench). In an embodiment of the present invention, laser scribing with nanosecond pulses is limited to a substrate  300  with a thickness of greater than 50 um since die strength is significantly reduced. 
     In an embodiment of the present invention, the laser scribing is performed with a laser beam  200  with a wavelength of 1,064 nm (infrared), a pulse width of 1-15 psec, a pulse energy of 10-40 uJ, a repetition rate of 30-150 kHz, consecutive pass overlapping of 65-85%, and a stage scanning speed of 1-15 mm/sec. 
     As shown in block  910  in an embodiment of the present invention in  FIG. 9 , laser scribing with picosecond or femtosecond pulses of light, such as with a long infrared wavelength of 700-1,500 nm, achieves ablation of materials through an intense optical field that excites and breaks atomic bonds in the materials. Electrons in the conduction band (or in defect states below the conduction band) are excited to the vacuum level, thus ablating the material. Picosecond or femtosecond pulses result in a lower temperature rise and allow laser scribing of a substrate  300  that has been thinned to even below 50 um since die strength is mostly preserved. 
     Next, various processes to perform laser-assisted chemical etch of the substrate  300 , such as in the singulation apparatus  10 , will be described. 
     A gas feed line  451  with a pump transports the etch chemical  452  to the process chamber  1010  in the singulation apparatus  10 . 
     In an embodiment of the present invention, the etch chemical  452  is diluted with one or more types of carrier gas. In an embodiment of the present invention, the carrier gas is an inert gas, such as Helium (He), Argon (Ar), or Xenon (Xe). 
     In an embodiment of the present invention, Helium maximizes ionization potential of a gaseous mixture, suppresses plasma formation by a high-powered focused laser beam, minimizes attenuation of laser energy by interaction of the plasma with the laser beam, maximizes transmission of the laser beam through the gaseous mixture, and reduces localized thermal damage to the substrate  300 . 
     In an embodiment of the present invention, the carrier gas is N 2 . In an embodiment of the present invention, the carrier gas is H 2 . 
     In an embodiment of the present invention, the inert gas diluent, such as Argon, alters the thermodynamics of the reaction of the etch chemical  452 . In an embodiment of the present invention, the inert gas diluent, such as Argon, alters the kinetics of the reaction of the etch chemical  452 . In an embodiment of the present invention, the laser assisted chemical cut with inert gas diluent results in a cut in the substrate  300  that is wider, less uniform, and more rounded in cross-section. 
     During operation, a mass flow controller adjusts a flow rate of the etch chemical  452  and the carrier gas into the process chamber  1010 . 
     In an embodiment of the present invention, one or more nozzles dispense the etch chemical  452  and the carrier gas in continuous streams towards the mounted substrate  300  and frame held by the chuck  432 . 
     In an embodiment of the present invention, one or more nozzles dispense the etch chemical  452  and the carrier gas in discontinuous pulses towards the mounted substrate  300  and frame held by the chuck  432 . 
     In an embodiment of the present invention, one or more nozzles dispense volatile byproducts (not shown) of the reaction towards the mounted substrate  300  and frame held by the chuck  432  to slow down the etch process. In an embodiment of the present invention, the volatile byproducts of the reaction are produced in situ to achieve self-contained efficiency. In an embodiment of the present invention, the volatile byproducts of the reaction are produced ex situ to achieve decoupled flexibility. 
     In an embodiment of the present invention, one or more nozzles dispense volatile byproducts (not shown) of the reaction towards the mounted substrate  300  and frame held by the chuck  432  to reverse the etch process. 
     The etch chemical  452  is, directly or indirectly, induced by the laser beam  200  to etch the wafer  300 . In an embodiment of the present invention, the etch is diffusion-limited or mass transfer-limited. In an embodiment of the present invention, the etch is reaction-limited. The reaction steps may be non-steady state (transient) or steady state. The reaction steps may be irreversible or reversible. The reaction steps may be serial or parallel. The reaction steps may compete with each other. 
     The laser-assisted chemical etch requires interaction of an etch chemical  452  and a laser beam  200  in the process chamber  1010 . In an embodiment of the present invention, the interaction of the etch chemical  452  and the laser beam  200  in the process chamber  1010  is direct, such as in a line-of-sight in-situ photolytic process. In an embodiment of the present invention, the interaction of the etch chemical  452  and the laser beam  200  in the process chamber  1010  is indirect, such as in a downstream ex-situ thermolytic process. 
     In an embodiment of the present invention, the interaction of the etch chemical  452  and the laser beam  200  in the process chamber  1010  is alternately direct and indirect. In an embodiment of the present invention, the interaction of the etch chemical  452  and the laser beam  200  in the process chamber  1010  is sequentially direct and indirect. In an embodiment of the present invention, the interaction of the etch chemical  452  and the laser beam  200  in the process chamber  1010  is concurrently direct and indirect. 
     In an embodiment of the present invention, photolysis of molecules to produce reactive radicals may result from exciting multiple photons in a ground electronic state. In an embodiment of the present invention, photolysis of molecules to produce reactive radicals may result from exciting a single photon in an excited electronic state. 
     In an embodiment of the present invention, the dissociation of gaseous molecules may be induced by multiple photons in the infrared spectral region. In an embodiment of the present invention, the dissociation of gaseous molecules may be induced by a single photon in the ultraviolet and visible spectral region. 
     In various embodiments of the present invention, the etch chemical  452  includes BrCl, BrF, Cl 2 , ClF 3 , NF 3 , OF 2 , SF 6 , or XeF 2 . In an embodiment of the present invention, the etch chemical  452  includes a halocarbon, such as CF 2 HCl. In an embodiment of the present invention, the etch chemical  452  includes an organometallic compound. 
     In an embodiment of the present invention, the etch chemical  452  includes Cl 2 . Gaseous Cl 2  dissociates when exposed to light of sufficient intensity in the ultraviolet region (200-400 nm) or the shorter part of the visible region (400-500 nm) with a peak at about 330 nm. The gaseous Cl 2  does not dissociate when exposed to light in the longer part of the visible region (500-700 nm) or the infrared region (700 nm-1 mm). 
     In an embodiment of the present invention, irradiation of the gaseous Cl 2  with a Nd:YLF PW laser beam  200  having a wavelength of 351 nm results in dissociation into Cl radicals. In an embodiment of the present invention, the laser beam  200  produces pulses with a pulse width of 100 ns and a repetition rate of 8 kHz. 
     As shown in block  920  in an embodiment of the present invention in  FIG. 9 , laser-assisted chemical etch is performed with ultraviolet (UV) light and Chlorine (Cl 2 ). 
     In an embodiment of the present invention, when the wafer  300  is exposed to both the etch chemical  452  and light of 220-400 nm wavelength in a laser beam  200  with a fluence that is less than 100 mJ/cm 2 , (regime 1) the wafer  300  will be etched at a rate that is almost linearly dependent on the fluence of the laser beam  200 . In regime 1, the laser-assisted chemical etch includes discrete steps, such as diffusion of the etch chemical  452  in the process chamber  1010  to (or near) the wafer  300 , (chemical) adsorption (chemisorption) of (some of) the etch chemical  452  to the wafer  300 , absorption of energy from the laser beam  200  by the etch chemical  452  on (or near) the wafer  300 , photolytic dissociation (or decomposition) of the etch chemical  452  on (or near) the wafer  300  to form radicals, transfer of photoelectrons to the radicals to produce ions, diffusion of the ions (and some of the radicals) about 8-10 nm into the wafer  300 , breakage of the Si—Si bonds in the lattice of the wafer  300  by the ions (and some of the radicals), reaction of the ions (and some of the radicals) with the silicon in the wafer  300 , formation of volatile (and non-volatile) byproducts on (or near) the wafer  300 , desorption of the volatile byproducts from the wafer  300 , and diffusion of the volatile byproducts away from the wafer  300 . 
     As shown in block  920  in an embodiment of the present invention in  FIG. 9 , laser-assisted chemical etch is performed with infrared (IR) light and Chlorine (Cl 2 ). 
     In an embodiment of the present invention, when the wafer  300  is exposed to both the etch chemical  452  and light of 400-1,400 nm wavelength in a laser beam  200  with a fluence that is greater than 440 mJ/cm 2 , (regime 3) the wafer  300  is etched at a rate that is highly non-linearly dependent on the fluence of the laser beam  200 . In regime 3, the laser-assisted chemical etch includes discrete steps, such as diffusion of the etch chemical  452  in the process chamber  1010  to (or near) the wafer  300 , (chemical) adsorption (chemisorption) of (some of) the etch chemical  452  to the wafer  300 , absorption of energy from the laser beam  200  by the wafer  300 , heating up of the wafer  300 , thermolytic dissociation (or decomposition) of the etch chemical  452  on (or near) the wafer  300  to form radicals, transfer of photoelectrons to the radicals to produce ions, diffusion of the ions (and some of the radicals) about 8-10 nm into the wafer  300 , excitation of the lattice of the wafer  300 , breakage of the Si-Si bonds in the lattice of the wafer  300  by the ions (and some of the radicals), reaction of the ions (and some of the radicals) with the silicon in the wafer  300 , formation of volatile (and non-volatile) byproducts on (or near) the wafer  300 , desorption of the volatile byproducts from the wafer  300 , and diffusion of the volatile byproducts away from the wafer  300 . 
     In an embodiment of the present invention, when the wafer  300  is exposed to both the etch chemical  452  and light of 400-500 nm wavelength in a laser beam  200  with a fluence that is 100-440 mJ/cm 2 , (regime 2) the wafer  300  is etched at a rate that is moderately non-linearly dependent on the fluence of the laser beam  200 . In regime 2, the laser assisted chemical etch includes a combination of photolytic and thermolytic dissociation (or decomposition), such as on (or near) the wafer  300  to form radicals. 
     As shown in block  920  in an embodiment of the present invention in  FIG. 9 , laser-assisted chemical etch is performed with infrared (IR) light and Sulfur Hexafluoride (SF 6 ). 
     In an embodiment of the present invention, the etch chemical  452  includes SF 6 . In an embodiment of the present invention, the SF 6  molecules are relatively inert to Silicon in the substrate  300 . The SF 6  molecules do not chemisorb on the Silicon at room temperature. Only one monolayer of the SF 6  molecules will physisorb on the Silicon at 20 Torr. In an embodiment of the present invention, the SF 6  molecules have a vibrational relaxation time of less than 0.25 us at 2 Torr. 
     In an embodiment of the present invention, irradiation of the gaseous SF 6  with PW IR (10.64 um) CO2 laser beam results in multiphoton absorption and dissociation of SF 6  into SF 4  and atomic F. In an embodiment of the present invention, the laser beam  200  produces pulses with an intensity of 3.0-5.0 J/cm 2  and a shape having a half-width of 150 ns in a main pulse and 2 us in the tail. 
     In an embodiment of the present invention, irradiation of the gaseous SF 6  with a Nd:YAG CW laser beam  200  having a wavelength of 1,064 nm results in dissociation into F radicals. 
     In an embodiment of the present invention, solid Silicon in the substrate  300  scavenges SF 4  to produce SiF 4 . In an embodiment of the present invention, the same amount of SiF 4  is produced for each pulse (intensity) of the laser beam  200  so the yield of SiF 4  per pulse (intensity) is linear up to SF 6  pressure of about 1.5 Torr. 
     The dissociation of SF 6  decreases exponentially (and then saturates) with increasing SF 6  pressure greater than 1.5 Torr due to collisional deactivation of the excited SF 6  molecules. In an embodiment of the present invention, SF 6  molecules have a mean free path for molecular collision that decreases as gas pressure increases, such as &lt;100 um at 2 Torr, &lt;10 um at 20 Torr, and &lt;2 um at 100 Torr. 
     In an embodiment of the present invention, atomic F reacts with Silicon in the substrate  300  even at room temperature. In an embodiment of the present invention, atomic F has a mean free path for molecular collision of about 3,000 um at 2 Torr. 
     In an embodiment of the present invention, gaseous H 2  can be added to scavenge atomic F and produce HF does not etch Silicon (but will etch SiO 2  to produce SiF 4  and water). As a result, the gaseous H 2  prevents diffusion of F to Silicon in the substrate  300  and almost completely suppresses the heterogeneous processes that produce SiF 4 . 
     In an embodiment of the present invention, H 2 O (water) is adsorbed on the substrate  300  (and the walls of the process chamber  1010 ) to scavenge the atomic F and produce HF, which etches SiO 2 , but does not etch Silicon. The SF 4  is very reactive and is hydrolyzed by the H 2 O (water) to produce SO 2  and HF. 
     In an embodiment of the present invention, a capacitive manometer adjusts a global pressure in the process chamber  1010  to 7-40 Torr during operation. In an embodiment of the present invention, a capacitive manometer adjusts a global pressure in the process chamber  1010  to 40-200 Torr during operation. In an embodiment of the present invention, a capacitive manometer adjusts the global pressure in the process chamber  1010  to 200-750 Torr during operation. 
     In an embodiment of the present invention, the process chamber  1010  is pressurized. In an embodiment of the present invention, a capacitive manometer adjusts a global pressure in the process chamber  1010  to 750-1,000 Torr during operation. 
     During operation, a local pressure in a vicinity, such as within 10-20 um, of a location that the laser beam  200  impinges on the etch chemical  452  and the mounted substrate  300  and frame is different from the global pressure in the process chamber  1010 . In an embodiment of the present invention, the local pressure in the vicinity, such as within 10-20 um, of the location that the laser beam  200  impinges on the etch chemical  452  and the mounted substrate  300  and frame is higher than the global pressure in the process chamber  1010 . In an embodiment of the present invention, the local pressure in the process chamber  1010  is 30-250 Torr higher than the global pressure during operation. 
     In an embodiment of the present invention, a global temperature in the process chamber  1010  is 25 (ambient) to 75 degrees Centigrade. 
     In an embodiment of the present invention, the process chamber  1010  is heated or cooled during operation by circulating a coolant through a heat exchanger  433  and inside the walls (not shown) of the process chamber  1010  to control a temperature of the process chamber  1010 . In an embodiment of the present invention, the process chamber  1010  includes walls covered with carbon. 
     In an embodiment of the present invention, the chuck  432  is heated or cooled during operation by circulating a coolant through the heat exchanger  433  and inside the chuck  432  to control a temperature of the chuck  432 . In an embodiment of the present invention, the coolant includes water with additives. 
     In an embodiment of the present invention, the inert gas diluent is preheated so as to locally heat the substrate  300  and thus modify the etch process. In an embodiment of the present invention, the inert gas diluent is precooled so as to locally cool the substrate  300  and thus modify the etch process. 
     The band gap, E g , of Silicon is 1.1 eV at a temperature of 300 K. The band gap of Silicon decreases as the temperature increases. For photon energies larger than the band-gap energy, the excitation mechanism at the surface of the Silicon is dominated by generation of electron-hole pairs. 
     Depending on optical absorption coefficient and thermal conductivity of the wafer  300 , a local temperature of the wafer  300  in a vicinity of a location that the laser beam  200  impinges on the wafer  300  during operation may be different from the global temperature in the process chamber  1010 . 
     When in a solid phase, silicon is a semiconductor and absorption of incident electromagnetic radiation, such as light, depends strongly on wavelength. In an embodiment of the present invention, absorption of energy from the light by silicon exceeds 50% for wavelengths of about 400-1,400 nm, with a peak absorption of energy from the light of about 68% (and a penetration depth by the light of about 100 um) at a wavelength of about 1,000 nm. However, when in a liquid (molten) phase, silicon behaves like a metal and absorption of incident electromagnetic radiation, such as light, depends only very slightly on wavelength. 
     Silicon has a melting point of 1,685 K and a boiling point of 3,173 K. Thermal conductivity of silicon increases significantly after it melts. In an embodiment of the present invention, thermal conductivity of silicon is 150 W/(m-K) in the solid phase and 450 W/(m-K) in the liquid phase. 
     In an embodiment of the present invention, the laser beam  200  has a fluence of 3.0-9.0 J/cm 2 . Consequently, the local temperature of the outer surface of the wafer  300 , such as in a heat-affected zone (HAZ) of within 10-20 um of the location that the laser beam  200  impinges on the wafer  300 , is higher than the global temperature in the process chamber  1010 . 
     In an embodiment of the present invention, the laser-assisted chemical etch of silicon in the wafer  300  occurs at a local temperature of 75-200 degrees Centigrade. In an embodiment of the present invention, the laser-assisted chemical etch of silicon in the wafer  300  occurs at a local temperature of 200-400 degrees Centigrade. In an embodiment of the present invention, the laser-assisted chemical etch of silicon in the wafer  300  occurs at a local temperature of 400-600 degrees Centigrade. 
     If the local temperature of the wafer  300  in the vicinity of the laser beam  200  is high enough, non-volatile byproducts on (or near) the wafer  300  are removed by laser ablation or evaporation. 
     In an embodiment of the present invention, the non-volatile byproducts include Copper halides, such as CuBr 2 , CuCl 2 , or CuF 2 , or Copper Oxides, such as CuO, depending on the type of etch chemical  452  that is dispensed in the process chamber  1010 . 
     In an embodiment of the present invention, a gas exhaust line  459  with a valve, filter, and a rotary pump transports an excess of the etch chemical  452  out of the process chamber  1010 . 
     In an embodiment of the present invention, the volatile byproducts include Silicon halides, such as SiBr 4 , SiCl 4 , or SiF 4 , depending on the type of etch chemical  452  that is dispensed in the process chamber  1010 . 
     In an embodiment of the present invention, a gas exhaust line  459  with a valve, filter, and a rotary pump transports the volatile byproducts out of the process chamber  1010 . 
     In an embodiment of the present invention, a showerhead dispenses a purge gas  458  towards the mounted substrate  300  and frame held by the chuck  432  in the process chamber  1010  to quench the reaction. In an embodiment of the present invention, the purge gas is an inert gas, such as Argon. In an embodiment of the present invention, the purge gas and the diluent gas include the same type of gas, such as Helium. 
     In an embodiment of the present invention, the laser-assisted chemical (volumetric) removal rate for silicon in the wafer  300  is 1.2×10 5  um 3 /sec. In regime 1, the laser-assisted chemical (volumetric) removal rate scales strongly with laser beam  200  power. In regime 3, the laser-assisted chemical (volumetric) removal rate scales weakly with etch chemical  452  gas pressure. 
     In an embodiment of the present invention, the laser-assisted chemical (vertical) etch rate for silicon is 2-15 nm/sec in the scribeline or street. In an embodiment of the present invention, the laser-assisted chemical etch rate for silicon is 15-75 nm/sec in the scribeline or street. In an embodiment of the present invention, the laser-assisted chemical etch rate for silicon is 75-225 nm/sec in the scribeline or street. 
     In an embodiment of the present invention, the laser-assisted chemical (vertical) etch rate for silicon is 0.01-0.15 nm/pulse in the scribeline or street. In an embodiment of the present invention, the laser-assisted chemical etch rate for silicon is 0.15-1.50 nm/pulse in the scribeline or street. In an embodiment of the present invention, the laser-assisted chemical etch rate for silicon is 1.50-7.50 nm/pulse in the scribeline or street. 
     In an embodiment of the present invention, the robots in the substrate transport mechanism  430  are articulated to provide random access to various processing chambers  1010 ,  1020 . 
     In an embodiment of the present invention, the singulation apparatus  10  includes multiple process chambers  1010 ,  1020  arranged in a horizontal plane. In an embodiment of the present invention, the multiple process chambers  1010 ,  1020  are arranged from left to right. In an embodiment of the present invention, the multiple process chambers  1010 ,  1020  are arranged from front to back. In an embodiment of the present invention, the multiple process chambers  1010 ,  1020  are arranged radially in a horizontal plane. 
     In an embodiment of the present invention, the singulation apparatus  10  includes multiple process chambers  1010 ,  1020  arranged in a vertical plane. In an embodiment of the present invention, the multiple process chambers  1010 ,  1020  are stacked vertically in one or more towers. In an embodiment of the present invention, the multiple process chambers  1010 ,  1020  are arranged radially in a vertical plane. 
     In an embodiment of the present invention, the multiple mounted substrates  300  and tape frames are processed at different times in the same process chamber  1010 . In an embodiment of the present invention, the multiple mounted substrates  300  and tape frames are processed at the same time in different process chambers  1010 ,  1020 . 
     In an embodiment of the present invention, the multiple process chambers  1010 ,  1020  run the same process in parallel to increase feed rates or throughput for a product. 
     In an embodiment of the present invention, the multiple process chambers  1010 ,  1020  offer a choice of different processes in parallel for different products. 
     In an embodiment of the present invention, the multiple process chambers  1010 ,  1020  run different processes in series, such as in sequential processing of a product. 
     In an embodiment of the present invention, the laser-assisted chemical etch includes two or more types of etches that are performed sequentially. In an embodiment of the present invention, the two or more sequential etches are performed in situ in one process chamber  1010 . In an embodiment of the present invention, the two or more sequential etches are performed in separate process chambers  1010 ,  1020 . 
     In an embodiment of the present invention, the different processes include (a) a laser scribe process, such as with small energy pulses at a high repetition rate, to remove surface layers, such as metal and oxide, of the substrate  300  with a thickness of about  10  um, followed by (b) a laser dice process, such as with large energy pulses, to etch underlying layers, such as bulk silicon in the substrate  300 . 
     In an embodiment of the present invention, the different processes include (a) a first process to etch a cut or trench through the substrate  300 , and (b) a second process to modify a slope, such as an undercut, of the sidewalls of the cut or trench. 
     In an embodiment of the present invention, the laser beam  200  makes one pass to produce the cut when the laser beam  200  has a top hat cross sectional profile. In an embodiment of the present invention, the laser beam  200  is operated at a constant velocity and does not pause until the direction needs to be changed, such as at the end of a row. In an embodiment of the present invention, the laser beam  200  is operated as a collinear series of interrupted strokes in which a pause occurs after each stroke. In an embodiment of the present invention, the stroke may be selected to be equivalent to a length of a side of a die, such as 20-30 mm. 
     In an embodiment of the present invention, the laser beam  200  has a Gaussian cross sectional profile with a higher intensity near its center. Then, multiple passes are made to smooth out the non-uniformity in the profile of the laser beam  200 . The multiple scan lines are separated by a step size that is small enough to result in a large overlap, such as 65-85%. 
     In an embodiment of the present invention, the laser beam  200  makes 2-12 passes to produce the cut. In an embodiment of the present invention, the laser beam  200  makes 12-50 passes to produce the cut. In an embodiment of the present invention, the laser beam  300  makes 50-100 passes to produce the cut. 
     In an embodiment of the present invention, the dicing speed is 50-200 mm/sec. In an embodiment of the present invention, the dicing speed is 200-600 mm/sec. In an embodiment of the present invention, the dicing speed is 600-1,200 mm/sec. 
     In an embodiment of the present invention, the laser-assisted chemical cut includes a sidewall slope which has two regions. An upper ¾ of the sidewall slope is steep and vertical while a lower ¼ of the sidewall slope is shallow with rounded lower corners near a flat bottom. 
     In an embodiment of the present invention, the laser-assisted chemical cut has a truncated v-shaped profile with sloped sidewalls, sharp bottom corners, and a flat bottom surface (trench floor). 
     In an embodiment of the present invention, the laser-assisted chemical cut has a u-shaped profile with vertical sidewalls, rounded bottom corners, and a flat bottom surface (trench floor). 
     In an embodiment of the present invention, the laser-assisted chemical cut has a re-entrant (undercut) profile with an upper lip or overhang, curved sidewalls, rounded bottom corners, and a flat bottom surface (trench floor). 
     In an embodiment of the present invention, the different processes include (a) a first process to etch through the substrate  300 , and (b) a second process to smooth the surface of the sidewalls of the cut or trench. 
     In an embodiment of the present invention, the different processes include (a) a first process to etch through the substrate  300 , and (b) a second process to reduce stress in the substrate  300  near the cut or trench due to the etch. 
     Otherwise, accumulated stress may relax and cause damage to the substrate  300 . In an embodiment of the present invention the damage is manifested macroscopically as micro-cracking in the substrate  300  or delamination of layers of the substrate  300 . In an embodiment of the present invention the damage is manifested microscopically as dislocations within the crystalline lattice of the substrate  300 . 
     In an embodiment of the present invention, the stress is reduced by annealing the substrate  300  in a localized region around the cut or trench, such as with a flash anneal or spike anneal. In an embodiment of the present invention, the stress is reduced by heating the substrate  300  along the edges and sidewalls of the cut or trench, such as with a laser. In an embodiment of the present invention, the stress is reduced by removing the damaged area, such as with a wet etch or dry etch. 
     In an embodiment of the present invention, the different processes include (a) a first process to etch through the substrate, and (b) a second process to remove contamination, such as redeposited material, or recast, from the laser. 
     In an embodiment of the present invention, the substrate  300  is cleaned by bombarding with ions, such as Argon. 
     In an embodiment of the present invention, the substrate  300  is cleaned with a plasma. 
     In an embodiment of the present invention, a fast deep etch to make a rough cut in a central trench is followed by slow etches along both sides of the central trench to smooth the surface of the sidewalls of the cut or trench. 
     In an embodiment of the present invention, a shallow etch in two parallel narrow trenches along both edges of the scribeline, such as to prevent lateral defect propagation as a crack-stop or to limit lateral heat spreading by conduction, is followed by a deep central etch to connect the two parallel narrow trenches. 
     In an embodiment of the present invention, a wide shallow central etch is followed by a narrow deep central etch. 
     In an embodiment of the present invention, a narrow deep central etch is followed by a wide shallow central etch. 
     In an embodiment of the present invention, if a die shift or a die rotation is present in the die in a row, every die in the row is aligned separately and cut through a center of the street in that row. 
     In an embodiment of the present invention, the laser-assisted chemical etch is performed in two orthogonal orientations. A wafer is first cut into rows in process chamber  1010 . Then, the rows are cut into chips in a separate process chamber  1020 . 
     In an embodiment of the present invention, etching in one orientation only in each process chamber allows a faster feedfrate. 
     In an embodiment of the present invention, alternating between etching in a forward direction and etching in a reverse direction in adjacent rows also allows a faster feedrate. In an embodiment of the present invention, bi-directional laser assisted chemical etch is used to cut rows only. 
     In an embodiment of the present invention, the trench floor of the laser-assisted chemical cut has a roughness of 15.2 nm root mean square (RMS). In an embodiment of the present invention, the trench floor has a roughness of 20 nm RMS. 
     In an embodiment of the present invention, a depth of the laser-assisted chemical cut is 45-60 um. In an embodiment of the present invention, a depth of the laser-assisted chemical cut is 30-45 um. In an embodiment of the present invention, a depth of the laser-assisted chemical cut is 15-30 um. In an embodiment of the present invention, a depth of the laser-assisted chemical cut is 6-15 um. 
     In an embodiment of the present invention, a width of the laser-assisted chemical cut is 90-120 um. In an embodiment of the present invention, a width of the laser-assisted chemical cut is 60-90 um. In an embodiment of the present invention, a width of the laser-assisted chemical cut is 40-60 um. In an embodiment of the present invention, a width of the laser-assisted chemical cut is 20-40 um. The cut is positioned in the scribelines or street that separate adjacent die on the wafer  300 . 
     In an embodiment of the present invention, an aspect ratio of depth to width of the laser-assisted chemical cut is (0.07-0.25):1.00. In an embodiment of the present invention, an aspect ratio of depth to width of the laser-assisted chemical cut is (0.25-0.75):1.00. In an embodiment of the present invention, an aspect ratio of depth to width of the laser-assisted chemical cut is (0.75-2.50):1.00. In an embodiment of the present invention, an aspect ratio of depth to width of the laser-assisted chemical cut is (3.00-5.00):1.00. 
     In an embodiment of the present invention, a sidewall slope of the laser-assisted chemical cut is 60-70 degrees. In an embodiment of the present invention, a sidewall slope of the laser-assisted chemical cut is 70-80 degrees. In an embodiment of the present invention, a sidewall slope of the laser-assisted chemical cut is 80-90 degrees. In an embodiment of the present invention, a sidewall slope of the laser-assisted chemical cut is 90-100 degrees (re-entrant profile). 
     Invasiveness refers to thermally-induced or chemically-induced changes in a region of the wafer  300  near the laser-assisted chemical cut. The invasiveness may be physically observable and/or electrically detectable. Invasiveness cannot be avoided, but should be limited to a small horizontal and vertical proximity from the laser-assisted chemical cut. An invasiveness-free zone does not include any defect, damage, or non-homogeneity associated with the laser-assisted chemical etch. 
     In an embodiment of the present invention, invasiveness to an underlying device is limited to a vertical proximity of 5-10 um. In an embodiment of the present invention, invasiveness to an underlying device is limited to a vertical proximity of 10-15 um. In an embodiment of the present invention, invasiveness to an underlying device is limited to a vertical proximity of 15-20 um. 
     In an embodiment of the present invention, the laser-assisted chemical etch produces a cut that is straighter (laterally), steeper (vertically), smoother, has less damage, or has less induced stress. In an embodiment of the present invention, the laser-assisted chemical etch produces a cut with less die chipping, micro-cracking, or delamination of interlevel dielectric (ILD) passivation, especially for low dielectric constant (k) or ultra-low k material. In an embodiment of the present invention, the laser-assisted chemical etch produces a cut with greater die edge fracture strength. 
     After singulation, the substrate  300  may go through other processes, such as cleaning, inspection, storage, die separation, and pick-and-place. Die inspection includes 100% visual inspection at 100× magnification with a microscope. Olympus makes inspection equipment. Viking makes die separation equipment. Apollo and Viking make pick-and-place equipment. 
     Many embodiments and numerous details have been set forth above in order to provide a thorough understanding of the present invention. One skilled in the art will appreciate that many of the features in one embodiment are equally applicable to other embodiments. One skilled in the art will also appreciate the ability to make various equivalent substitutions for those specific materials, processes, dimensions, concentrations, etc. described herein. It is to be understood that the detailed description of the present invention should be taken as illustrative and not limiting, wherein the scope of the present invention should be determined by the claims that follow.