HYBRID WAFER DICING APPROACH USING A RECTANGULAR LASER SPOT-BASED LASER SCRIBING PROCESS AND PLASMA ETCH PROCESS

BACKGROUND
1) Field

Embodiments of the present disclosure pertain to the field of semiconductor processing and, in particular, to methods of dicing semiconductor wafers, each wafer having a plurality of integrated circuits thereon.

2) Description of Related Art

In semiconductor wafer processing, integrated circuits are formed on a wafer (also referred to as a substrate) composed of silicon or other semiconductor material. In general, layers of various materials which are either semiconducting, conducting or insulating are utilized to form the integrated circuits. These materials are doped, deposited and etched using various well-known processes to form integrated circuits. Each wafer is processed to form a large number of individual regions containing integrated circuits known as dice.

Following the integrated circuit formation process, the wafer is “diced” to separate the individual die from one another for packaging or for use in an unpackaged form within larger circuits. The two main techniques that are used for wafer dicing are scribing and sawing. With scribing, a diamond tipped scribe is moved across the wafer surface along pre-formed scribe lines. These scribe lines extend along the spaces between the dice. These spaces are commonly referred to as “streets.” The diamond scribe forms shallow scratches in the wafer surface along the streets. Upon the application of pressure, such as with a roller, the wafer separates along the scribe lines. The breaks in the wafer follow the crystal lattice structure of the wafer substrate. Scribing can be used for wafers that are about 10 mils (thousandths of an inch) or less in thickness. For thicker wafers, sawing is presently the preferred method for dicing.

With sawing, a diamond tipped saw rotating at high revolutions per minute contacts the wafer surface and saws the wafer along the streets. The wafer is mounted on a supporting member such as an adhesive film stretched across a film frame and the saw is repeatedly applied to both the vertical and horizontal streets. One problem with either scribing or sawing is that chips and gouges can form along the severed edges of the dice. In addition, cracks can form and propagate from the edges of the dice into the substrate and render the integrated circuit inoperative. Chipping and cracking are particularly a problem with scribing because only one side of a square or rectangular die can be scribed in the <110> direction of the crystalline structure. Consequently, cleaving of the other side of the die results in a jagged separation line. Because of chipping and cracking, additional spacing is required between the dice on the wafer to prevent damage to the integrated circuits, e.g., the chips and cracks are maintained at a distance from the actual integrated circuits. As a result of the spacing requirements, not as many dice can be formed on a standard sized wafer and wafer real estate that could otherwise be used for circuitry is wasted. The use of a saw exacerbates the waste of real estate on a semiconductor wafer. The blade of the saw is approximate 15 microns thick. As such, to insure that cracking and other damage surrounding the cut made by the saw does not harm the integrated circuits, three to five hundred microns often must separate the circuitry of each of the dice. Furthermore, after cutting, each die requires substantial cleaning to remove particles and other contaminants that result from the sawing process.

Plasma dicing has also been used, but may have limitations as well. For example, one limitation hampering implementation of plasma dicing may be cost. A standard lithography operation for patterning resist may render implementation cost prohibitive. Another limitation possibly hampering implementation of plasma dicing is that plasma processing of commonly encountered metals (e.g., copper) in dicing along streets can create production issues or throughput limits.

SUMMARY

Embodiments of the present disclosure include methods of, and apparatuses for, dicing semiconductor wafers.

In an embodiment, a method of dicing a semiconductor wafer having a plurality of integrated circuits involves forming a mask above the semiconductor wafer, the mask composed of a layer covering and protecting the integrated circuits. The mask is then patterned with a rectangular laser spot-based laser scribing process to provide a patterned mask with gaps, exposing regions of the semiconductor wafer between the integrated circuits. The semiconductor wafer is then plasma etched through the gaps in the patterned mask to singulate the integrated circuits.

In another embodiment, a method of dicing a semiconductor wafer including a plurality of integrated circuits involves laser scribing the semiconductor wafer with a rectangular laser spot-based laser scribing process to singulate the integrated circuits.

In another embodiment, a system for dicing a semiconductor wafer having a plurality of integrated circuits includes a factory interface. The system also includes a laser scribe apparatus coupled with the factory interface and having a laser assembly configured to provide a rectangular laser spot-based laser beam. The system also includes a plasma etch chamber coupled with the factory interface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a Flowchart representing operations in a method of dicing a semiconductor wafer including a plurality of integrated circuits, in accordance with an embodiment of the present disclosure.

FIG. 2A illustrates a cross-sectional view of a semiconductor wafer including a plurality of integrated circuits during performing of a method of dicing the semiconductor wafer, corresponding to operation 102 of the Flowchart of FIG. 1, in accordance with an embodiment of the present disclosure.

FIG. 2B illustrates a cross-sectional view of a semiconductor wafer including a plurality of integrated circuits during performing of a method of dicing the semiconductor wafer, corresponding to operation 104 of the Flowchart of FIG. 1, in accordance with an embodiment of the present disclosure.

FIG. 2C illustrates a cross-sectional view of a semiconductor wafer including a plurality of integrated circuits during performing of a method of dicing the semiconductor wafer, corresponding to operation 108 of the Flowchart of FIG. 1, in accordance with an embodiment of the present disclosure.

FIG. 3 illustrates a Gaussian beam scribe line.

FIG. 4A illustrates a square-shaped beam scribe line, in accordance with an embodiment of the present disclosure.

FIG. 4B illustrates a cross-sectional intensity mapping in atomic units for a Gaussian and round beam versus a top-hap and square beam.

FIG. 4C illustrates a schematic of a laser beam apparatus having a beam shaper, in accordance with an embodiment of the present disclosure.

FIG. 4D includes plots of simulation data of a square spot, in accordance with an embodiment of the present disclosure.

FIG. 4E includes plan views of a scribe mask and underlying substrate following laser scribe with a Gaussian beam (upper image), and a square-shaped beam (lower image), in accordance with an embodiment of the present disclosure.

FIG. 4F includes plan views of a scribe mask and underlying substrate following laser scribe with a Gaussian beam (upper image), and a square-shaped beam (lower image), and then subsequent plasma etching, in accordance with an embodiment of the present disclosure.

FIG. 5 illustrates the effects of using a laser pulse width in the femtosecond range, picoseconds range, and nanosecond range, in accordance with an embodiment of the present disclosure.

FIG. 6 illustrates a cross-sectional view of a stack of materials that may be used in a street region of a semiconductor wafer or substrate, in accordance with an embodiment of the present disclosure.

FIGS. 7A-7D illustrate cross-sectional views of various operations in a method of dicing a semiconductor wafer, in accordance with an embodiment of the present disclosure.

FIG. 8 illustrates a block diagram of a tool layout for laser and plasma dicing of wafers or substrates, in accordance with an embodiment of the present disclosure.

FIG. 9 illustrates a block diagram of an exemplary computer system, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

Methods of dicing semiconductor wafers, each wafer having a plurality of integrated circuits thereon, are described. In the following description, numerous specific details are set forth, such as rectangular laser spot-based laser scribing approaches and plasma etching conditions and material regimes, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known aspects, such as integrated circuit fabrication, are not described in detail in order to not unnecessarily obscure embodiments of the present disclosure. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.

A hybrid wafer or substrate dicing process involving an initial laser scribe and subsequent plasma etch may be implemented for die singulation. The laser scribe process may be used to cleanly remove a mask layer, organic and inorganic dielectric layers, and device layers. The laser etch process may then be terminated upon exposure of, or partial etch of, the wafer or substrate. The plasma etch portion of the dicing process may then be employed to etch through the bulk of the wafer or substrate, such as through bulk single crystalline silicon, to yield die or chip singulation or dicing. More specifically, one or more embodiments are directed to implementing a rectangular laser spot-based laser scribing process for, e.g., dicing applications.

Rectangular laser spot-based laser beams for wafer dicing using a hybrid laser scribing and plasma etch approach are described. Embodiments described herein may be implemented to reduce stress concentration using a beam shaper during a laser scribing operation of a hybrid laser scribing and plasma etch wafer dicing process. Embodiments described herein may be implemented to reduce stress concentration using a beam shape during laser scribing.

To provide context, a laser scribing portion of a hybrid laser plasma dicing process is very important as the scribed trench profile quality drives the diced die edge quality after a wafer is diced. Embodiments described herein can be implemented to reduces stress concentration in a scribed trench which in turn results in increased quality. A secondary benefit of such an approach is that it can greatly reduce the required pulse repetition rate of the laser which can in turn reduces equipment (hardware) costs.

To provide further context, state-of-the-art laser applications typically use circular spots. When a pulsed laser beam is applied on a wafer to scribe a trench, the scribe trench profile follows the interface between two circular pulses. Sharp corners are observed at these interfaces resulting in stress build up in a protective mask layer used for the plasma process.

In accordance with one or more embodiments of the present disclosure, a method is described that uses square or rectangular laser spots during scribing to reduce stress concentration on scribed trench in silicon wafers. Advantages to implementing one or more embodiments described herein can include the use of square shaped spots to virtually eliminate all sharp corners at the interface between pulses.

In accordance with one or more embodiments of the present disclosure, a scribing laser beam is a rectangular laser spot-based laser beam for improving laser scribing process in hybrid laser dicing. As such, in an aspect of the present disclosure, a combination of a rectangular laser spot-based laser scribing process with a plasma etching process may be used to dice a semiconductor wafer into singulated integrated circuits. FIG. 1 is a Flowchart 100 representing operations in a method of dicing a semiconductor wafer including a plurality of integrated circuits, in accordance with an embodiment of the present disclosure. FIGS. 2A-2C illustrate cross-sectional views of a semiconductor wafer including a plurality of integrated circuits during performing of a method of dicing the semiconductor wafer, corresponding to operations of Flowchart 100, in accordance with an embodiment of the present disclosure.

Referring to operation 102 of Flowchart 100, and corresponding FIG. 2A, a mask 202 is formed above a semiconductor wafer or substrate 204. The mask 202 is composed of a layer covering and protecting integrated circuits 206 formed on the surface of semiconductor wafer 204. The mask 202 also covers intervening streets 207 formed between each of the integrated circuits 206.

In accordance with an embodiment of the present disclosure, forming the mask 202 includes forming a layer such as, but not limited to, a photo-resist layer or an I-line patterning layer. For example, a polymer layer such as a photo-resist layer may be composed of a material otherwise suitable for use in a lithographic process. In one embodiment, the photo-resist layer is composed of a positive photo-resist material such as, but not limited to, a 248 nanometer (nm) resist, a 193 nm resist, a 157 nm resist, an extreme ultra-violet (EUV) resist, or a phenolic resin matrix with a diazonaphthoquinone sensitizer. In another embodiment, the photo-resist layer is composed of a negative photo-resist material such as, but not limited to, poly-cis-isoprene and poly-vinyl-cinnamate.

In another embodiment, forming the mask 202 involves forming a layer deposited in a plasma deposition process. For example, in one such embodiment, the mask 202 is composed of a plasma deposited Teflon or Teflon-like (polymeric CF₂) layer. In a specific embodiment, the polymeric CF₂layer is deposited in a plasma deposition process involving the gas C₄F₈.

In another embodiment, forming the mask 202 involves forming a water-soluble mask layer. In an embodiment, the water-soluble mask layer is readily dissolvable in an aqueous media. For example, in one embodiment, the water-soluble mask layer is composed of a material that is soluble in one or more of an alkaline solution, an acidic solution, or in deionized water. In an embodiment, the water-soluble mask layer maintains its water solubility upon exposure to a heating process, such as heating approximately in the range of 50-160 degrees Celsius. For example, in one embodiment, the water-soluble mask layer is soluble in aqueous solutions following exposure to chamber conditions used in a laser and plasma etch singulation process. In one embodiment, the water-soluble mask layer is composed of a material such as, but not limited to, polyvinyl alcohol, polyacrylic acid, dextran, polymethacrylic acid, polyethylene imine, or polyethylene oxide. In a specific embodiment, the water-soluble mask layer has an etch rate in an aqueous solution approximately in the range of 1-15 microns per minute and, more particularly, approximately 1.3 microns per minute.

In another embodiment, forming the mask 202 involves forming a UV-curable mask layer. In an embodiment, the mask layer has a susceptibility to UV light that reduces an adhesiveness of the UV-curable layer by at least approximately 80%. In one such embodiment, the UV layer is composed of polyvinyl chloride or an acrylic-based material. In an embodiment, the UV-curable layer is composed of a material or stack of materials with an adhesive property that weakens upon exposure to UV light. In an embodiment, the UV-curable adhesive film is sensitive to approximately 365 nm UV light. In one such embodiment, this sensitivity enables use of LED light to perform a cure.

In an embodiment, semiconductor wafer or substrate 204 is composed of a material suitable to withstand a fabrication process and upon which semiconductor processing layers may suitably be disposed. For example, in one embodiment, semiconductor wafer or substrate 204 is composed of a group IV-based material such as, but not limited to, crystalline silicon, germanium or silicon/germanium. In a specific embodiment, providing semiconductor wafer 204 includes providing a monocrystalline silicon substrate. In a particular embodiment, the monocrystalline silicon substrate is doped with impurity atoms. In another embodiment, semiconductor wafer or substrate 204 is composed of a III-V material such as, e.g., a III-V material substrate used in the fabrication of light emitting diodes (LEDs).

In an embodiment, semiconductor wafer or substrate 204 has disposed thereon or therein, as a portion of the integrated circuits 206, an array of semiconductor devices. Examples of such semiconductor devices include, but are not limited to, memory devices or complimentary metal-oxide-semiconductor (CMOS) transistors fabricated in a silicon substrate and encased in a dielectric layer. A plurality of metal interconnects may be formed above the devices or transistors, and in surrounding dielectric layers, and may be used to electrically couple the devices or transistors to form the integrated circuits 206. Materials making up the streets 207 may be similar to or the same as those materials used to form the integrated circuits 206. For example, streets 207 may be composed of layers of dielectric materials, semiconductor materials, and metallization. In one embodiment, one or more of the streets 207 includes test devices similar to the actual devices of the integrated circuits 206.

Referring to operation 104 of Flowchart 100, and corresponding FIG. 2B, the mask 202 is patterned with a rectangular laser spot-based laser scribing process to provide a patterned mask 208 with gaps 210, exposing regions of the semiconductor wafer or substrate 204 between the integrated circuits 206. As such, the laser scribing process is used to remove the material of the streets 207 originally formed between the integrated circuits 206. In accordance with an embodiment of the present disclosure, patterning the mask 202 with the rectangular laser spot-based laser scribing process includes forming trenches 212 partially into the regions of the semiconductor wafer 204 between the integrated circuits 206, as depicted in FIG. 2B. In an embodiment, the laser scribing process is to Scribe through mask and device layer in street to expose the silicon to enable singulation via plasma etch in the next operation. In an embodiment, the laser scribe process is to align and locate for wafer prior to scribe to ensure scribe lines are bisecting the street.

For comparative purposes, as an exemplary case where active focus correction of a laser beam is not implemented, FIG. 3 illustrates a Gaussian beam scribe line.

Referring to FIG. 3, a Gaussian beam scribe line 300 includes a plurality of circular openings 306 in a mask 304 above a substrate 302. The circular openings need to overlap with one another in order to provide a continuous scribe line. Sharp points are observed between overlapping openings. With respect to the Gaussian beam scribe line 300, there can be a delamination tendency of the mask 304 and wafer device layer due to stress concentrations at the sharp corners at the interface of two pulse spots on substrate 302.

In contrast, to FIG. 3, FIG. 4A illustrates a square-shaped beam scribe line, in accordance with an embodiment of the present disclosure.

Referring to FIG. 4A, a square-shaped beam scribe line 400 includes a plurality of rectangular or square openings 406 (square depicted) in a mask 404 above a substrate 402. The rectangular or square openings 406 need not overlap with one another (although they can) and only need be edge-aligned in order to provide a continuous scribe line. With respect to the square-shaped beam scribe line 400, square/rectangular spots can result in a seamless interface between two pulse spots, with no sharp corners or a potential to delaminate.

Additional benefits of square beam shaping can include reduction of pulse overlap which is significant for Gaussian (circular) spots. Use of a square spot can enable use of lower pulse repetition rate (overlap) along a scribe line which can potentially reduce power by as much as 10 times depending on size of the laser spot. Additionally, a narrower Kerf/trench may be achieved due to uniform laser energy distribution within each spot.

As a comparison, FIG. 4B illustrates a cross-sectional intensity mapping in atomic units for a Gaussian and round beam versus a top-hap and square beam.

Referring to FIG. 4B, a Gaussian beam 410 is Gaussian in cross-section (as shown) and is round in a plan view. The spot diameter of the Gaussian beam relative to an ablation threshold is a relatively small portion of the total beam, with other portions of the beam 410 contributing to superfluous energy and heating energy, both of which maybe unwanted. By contrast, a top-hat beam 420 is top-hat in cross-section (as shown) and is square in a plan view, in accordance with an embodiment of the present disclosure. The spot diameter of the top-hat beam relative to the ablation threshold is a relatively large portion of the total beam.

As an exemplary laser assembly, FIG. 4C illustrates a schematic of a laser beam apparatus having a beam shaper, in accordance with an embodiment of the present disclosure.

Referring to FIG. 4C, a laser assembly 430 includes a laser source 432 to provide a laser beam 434. The laser beam 434 is directed through a beam shaper 436 and then through a focusing lens 438. The resulting beam has a top-hat plane 440 and provides ablation energy 444 to an object for scribing 442, such as a mask on a wafer. In one embodiment, the laser beam 434 has a wavelength in a range of 510-530 nanometers, an input beam diameter in a range of 8-10 millimeters, a working distance (e.g., distance 444 in FIG. 4C) in a range of 40-55 millimeters, and an output square spot width (side to side, not diagonal) in a range of 6-8 microns. In a particular embodiment, the laser beam 434 has a wavelength of approximately 520 nanometers, an input beam diameter of approximately 9 millimeters, a working distance (e.g., distance 444 in FIG. 4C) of approximately 48 millimeters, and an output square spot width (side to side, not diagonal) of approximately 7 microns. It is to be appreciated that concepts described herein can be applied to scribing other spot sizes and/or wavelengths. The beam shaping optical element would be selected accordingly.

It is to be appreciated that a rectangular laser spot-based laser scribing process can be based on spots having four approximately straight sides, with at least opposing sides having same dimensions. In an embodiment, the rectangular laser spot-based laser scribing process is a square laser spot-based laser scribing process based on spots having four approximately straight sides, with all four sides having a same dimension. As an example, FIG. 4D includes plots of simulation data of a square spot, in accordance with an embodiment of the present disclosure.

Referring to FIG. 4D, spot intensity is shown from a plan view 450 (showing the square shape), a cross-sectional view 460 (showing a top-hat profile in the X-direction), and a cross-sectional view 470 (showing a top-hat profile in the Y-direction). In one or more embodiments described herein, a rectangular laser spot-based laser scribing process is based on a spot shape (square in plan view) and profile (top-hat in cross-section) the same as or substantially the same as is shown in FIG. 4D.

For comparative purposes, FIG. 4E includes plan views 480 of a scribe mask and underlying substrate following laser scribe with a Gaussian beam (upper image), and a square-shaped beam (lower image), in accordance with an embodiment of the present disclosure. FIG. 4F includes plan views 490 of a scribe mask and underlying substrate following laser scribe with a Gaussian beam (upper image), and a square-shaped beam (lower image), and then subsequent plasma etching, in accordance with an embodiment of the present disclosure. Referring to FIGS. 4E and 4F, a square-shaped beam demonstrated narrower and cleaner kerf under comparable process conditions.

With reference again to operation 104 of Flowchart 100 and FIGS. 4A-4F, in accordance with an embodiment of the present disclosure, a rectangular laser spot-based laser scribing process involves using laser spots that are square in plan view and have a top-hat profile in cross-sectional view. In another embodiment, a rectangular laser spot-based laser scribing process involves scribing with a laser beam having a wavelength in a range of 510-530 nanometers, an input beam diameter in a range of 8-10 millimeters, a working distance in a range of 40-55 millimeters, and an output square spot width in a range of 6-8 microns. In an embodiment, a rectangular laser spot-based laser scribing process is an actively-focused laser beam laser scribing process, examples of which are described below. In an embodiment, a rectangular laser spot-based laser scribing process involves using a Gaussian source laser beam. In one such embodiment, the actively-focused laser beam laser scribing process involves using a femto-second source laser beam. In an embodiment, scribing with a rectangular laser spot-based laser scribing process involves scribing with a femto-second a rectangular laser spot-based laser beam. It is to be appreciated that laser wavelength and diameters are not restricted to the above. Similar concepts can be applied with a UV beam laser having wavelengths that are much lower.

In another aspect, actively-focused laser beams for wafer dicing using a hybrid laser scribing and plasma etch approach are described. Embodiments described herein may be implemented to provide active laser beam focus control to compensate for chuck variations in a laser dicing process. Embodiments described herein may be implemented to provide active laser beam focus control to compensate for substrate thickness variations in a laser dicing process. Embodiments may be implemented for active laser beam focus control for laser dicing. In an embodiment, active position control of a lens is used to focus a laser beam in a laser dicing process. In an embodiment, a rectangular laser spot-based laser scribing process is used in conjunction with an actively-focused laser beam laser scribing process.

To provide context, use of a fixed focal position of a laser beam in a laser dicing process can result in scribe profiles that may not be ideal due to variations in the chuck and/or substrate surface due to flatness of chuck surface or levelling offsets that occur due to assembly tolerances in a dicing system. There are no known approaches for actively controlled laser focus during a dicing process.

Advantages to implementing one or more embodiments described herein may include one or more of: (1) increased uniformity of a scribe profile across an entire wafer, (2) lower kerf width, (3) higher wafer yield, and/or (4) increased die density on wafer. In addition, in a case where a wafer is warped, approaches described herein can be used to map warpage on a chuck (and/or substrate) and adjust laser focus to compensate warpage in order to achieve uniform scribe lines across warped wafers and/or a warped support surface.

Embodiments of the present disclosure can be implemented to actively control a focal position of a laser beam used to dice silicon substrates in a laser dicing process. In one embodiment, a topographical map of the silicon substrate chuck is first made by moving the chuck at multiple positions under a fixed high precision laser displacement sensor. The topographical map data is then used to actively control the laser focusing lens position during the scribing. In some cases, wafers are provided with warpage. A warpage map can instead be generated or can also be generated similarly for every wafer prior to scribing to generate clean and uniform scribe lines on warped wafers. Embodiments may include one or more of active laser focus control, chuck level mapping, or warped wafer mapping. It is to be appreciated that since the etching profile followed by the opening shape of laser scribing can be determined by the scribe quality, etching rate and profile uniformity can be improved during plasma dicing process if the scribing process involves active laser focus as described herein.

More generally, a wafer or chuck top surface has some undulation (it is to be appreciated that undulation can be derived from chuck warpage and/or wafer warpage). Based on a chuck and/or wafer surface map, a laser focus lens position is adjusted to ensure that a laser is actively focused on undulated locations of a surface of a wafer.

In accordance with one or more embodiments of the present disclosure, a femtosecond-based laser is used as a source for a rectangular laser spot-based laser scribing process. For example, in an embodiment, a laser with a wavelength in the visible spectrum plus the ultra-violet (UV) and infra-red (IR) ranges (totaling a broadband optical spectrum) is used to provide a femtosecond-based laser pulse, which has a pulse width on the order of the femtosecond (10⁻¹⁵seconds). In one embodiment, ablation is not, or is essentially not, wavelength dependent and is thus suitable for complex films such as films of the mask 202, the streets 207 and, possibly, a portion of the semiconductor wafer or substrate 204.

FIG. 5 illustrates the effects of using a laser pulse width in the femtosecond range, picosecond range, and nanosecond range, in accordance with an embodiment of the present disclosure. Referring to FIG. 5, by using a laser beam in the femtosecond range, heat damage issues are mitigated or eliminated (e.g., minimal to no damage 502C with femtosecond processing of a via 500C) versus longer pulse widths (e.g., significant damage 502A with nanosecond processing of a via 500A). The elimination or mitigation of damage during formation of via 500C may be due to a lack of low energy recoupling (as is seen for picosecond-based laser ablation of 500B/502B) or thermal equilibrium (as is seen for nanosecond-based laser ablation), as depicted in FIG. 5.

Laser parameters selection, such as beam profile, may be critical to developing a successful laser scribing and dicing process that minimizes chipping, microcracks and delamination in order to achieve clean laser scribe cuts. The cleaner the laser scribe cut, the smoother an etch process that may be performed for ultimate die singulation. In semiconductor device wafers, many functional layers of different material types (e.g., conductors, insulators, semiconductors) and thicknesses are typically disposed thereon. Such materials may include, but are not limited to, organic materials such as polymers, metals, or inorganic dielectrics such as silicon dioxide and silicon nitride.

A street between individual integrated circuits disposed on a wafer or substrate may include the similar or same layers as the integrated circuits themselves. For example, FIG. 6 illustrates a cross-sectional view of a stack of materials that may be used in a street region of a semiconductor wafer or substrate, in accordance with an embodiment of the present disclosure.

Referring to FIG. 6, a street region 600 includes the top portion 602 of a silicon substrate, a first silicon dioxide layer 604, a first etch stop layer 606, a first low K dielectric layer 608 (e.g., having a dielectric constant of less than the dielectric constant of 4.0 for silicon dioxide), a second etch stop layer 610, a second low K dielectric layer 612, a third etch stop layer 614, an undoped silica glass (USG) layer 616, a second silicon dioxide layer 618, and a layer of photo-resist 620, with relative thicknesses depicted. Copper metallization 622 is disposed between the first and third etch stop layers 606 and 614 and through the second etch stop layer 610. In a specific embodiment, the first, second and third etch stop layers 606, 610 and 614 are composed of silicon nitride, while low K dielectric layers 608 and 612 are composed of a carbon-doped silicon oxide material.

Under conventional laser irradiation (such as nanosecond-based irradiation), the materials of street 600 behave quite differently in terms of optical absorption and ablation mechanisms. For example, dielectrics layers such as silicon dioxide, is essentially transparent to all commercially available laser wavelengths under normal conditions. By contrast, metals, organics (e.g., low K materials) and silicon can couple photons very easily, particularly in response to nanosecond-based irradiation. In an embodiment, a rectangular laser spot-based laser scribing process is used to pattern a layer of silicon dioxide, a layer of low K material, and a layer of copper by ablating the layer of silicon dioxide prior to ablating the layer of low K material and the layer of copper.

In case that the rectangular laser spot-based laser beam is a femtosecond-based laser beam, in an embodiment, suitable femtosecond-based laser processes are characterized by a high peak intensity (irradiance) that usually leads to nonlinear interactions in various materials. In one such embodiment, the femtosecond laser sources have a pulse width approximately in the range of 10 femtoseconds to 500 femtoseconds, although preferably in the range of 100 femtoseconds to 400 femtoseconds. In one embodiment, the femtosecond laser sources have a wavelength approximately in the range of 1570 nanometers to 200 nanometers, although preferably in the range of 540 nanometers to 250 nanometers. In one embodiment, the laser and corresponding optical system provide a focal spot at the work surface approximately in the range of 3 microns to 15 microns, though preferably approximately in the range of 5 microns to 10 microns or between 10-15 microns.

In an embodiment, the laser source has a pulse repetition rate approximately in the range of 200 kHz to 10 MHz, although preferably approximately in the range of 500 kHz to 5 MHz. In an embodiment, the laser source delivers pulse energy at the work surface approximately in the range of 0.5 uJ to 100 uJ, although preferably approximately in the range of 1 uJ to 5 uJ. In an embodiment, the laser scribing process runs along a work piece surface at a speed approximately in the range of 500 mm/sec to 5 m/sec, although preferably approximately in the range of 600 mm/sec to 2 m/sec.

The scribing process may be run in single pass only, or in multiple passes, but, in an embodiment, preferably 1-2 passes. In one embodiment, the scribing depth in the work piece is approximately in the range of 5 microns to 50 microns deep, preferably approximately in the range of 10 microns to 20 microns deep. In an embodiment, the kerf width of the laser beam generated is approximately in the range of 2 microns to 15 microns, although in silicon wafer scribing/dicing preferably approximately in the range of 6 microns to 10 microns, measured at the device/silicon interface.

Laser parameters may be selected with benefits and advantages such as providing sufficiently high laser intensity to achieve ionization of inorganic dielectrics (e.g., silicon dioxide) and to minimize delamination and chipping caused by underlayer damage prior to direct ablation of inorganic dielectrics. Also, parameters may be selected to provide meaningful process throughput for industrial applications with precisely controlled ablation width (e.g., kerf width) and depth. In an embodiment, a rectangular laser spot-based laser scribing process is suitable to provide such advantages.

It is to be appreciated that the dicing or singulation process could be stopped after the above described laser scribing in a case that the laser scribing is used to pattern the mask as well as to scribe fully through the wafer or substrate in order to singulate the dies. Accordingly, further singulation processing would not be required in such a case. However, the following embodiments may be considered in cases where laser scribing alone is not implemented for total singulation.

Referring now to optional operation 106 of Flowchart 100, an intermediate post mask-opening cleaning operation is performed. In an embodiment, the post mask-opening cleaning operation is a plasma-based cleaning process. In a first example, as described below, the plasma-based cleaning process is reactive to the regions of the substrate 204 exposed by the gaps 210. In the case of a reactive plasma-based cleaning process, the cleaning process itself may form or extend trenches 212 in the substrate 204 since the reactive plasma-based cleaning operation is at least somewhat of an etchant for the substrate 204. In a second, different, example, as is also described below, the plasma-based cleaning process is non-reactive to the regions of the substrate 204 exposed by the gaps 210.

In accordance with a first embodiment, the plasma-based cleaning process is reactive to exposed regions of the substrate 204 in that the exposed regions are partially etched during the cleaning process. In one such embodiment, Ar or another non-reactive gas (or the mix) is combined with SF₆for a highly-biased plasma treatment for cleaning of scribed openings. The plasma treatment using mixed gases Ar+SF₆under high-bias power is performed for bombarding mask-opened regions to achieve cleaning of the mask-opened regions. In the reactive breakthrough process, both physical bombardment from Ar and SF₆along with chemical etching due to SF₆and F-ions contribute to cleaning of mask-opened regions. The approach may be suitable for photoresist or plasma-deposited Teflon masks 202, where breakthrough treatment leads to fairly uniform mask thickness reduction and a gentle Si etch. Such a breakthrough etch process, however, may not be best suited for water soluble mask materials.

In accordance with a second embodiment, the plasma-based cleaning process is non-reactive to exposed regions of the substrate 204 in that the exposed regions are not or only negligible etched during the cleaning process. In one such embodiment, only non-reactive gas plasma cleaning is used. For example, Ar or another non-reactive gas (or the mix) is used to perform a highly-biased plasma treatment both for mask condensation and cleaning of scribed openings. The approach may be suitable for water-soluble masks or for thinner plasma-deposited Teflon 202. In another such embodiment, separate mask condensation and scribed trench cleaning operations are used, e.g., an Ar or non-reactive gas (or the mix) highly-biased plasma treatment for mask condensation is first performed, and then an Ar+SF₆plasma cleaning of a laser scribed trench is performed. This embodiment may be suitable for cases where Ar-cleaning is not sufficient for trench cleaning due to too thick of a mask material. Cleaning efficiency is improved for thinner masks, but mask etch rate is much lower, with almost no consumption in a subsequent deep silicon etch process. In yet another such embodiment, three-operation cleaning is performed: (a) Ar or non-reactive gas (or the mix) highly-biased plasma treatment for mask condensation, (b) Ar+SF₆highly-biased plasma cleaning of laser scribed trenches, and (c) Ar or non-reactive gas (or the mix) highly-biased plasma treatment for mask condensation. In accordance with another embodiment of the present disclosure, a plasma cleaning operation involves first use of a reactive plasma cleaning treatment, such as described above in the first aspect of operation 106. The reactive plasma cleaning treatment is then followed by a non-reactive plasma cleaning treatment such as described in association with the second aspect of operation 106.

Referring to operation 108 of Flowchart 100, and corresponding FIG. 2C, the semiconductor wafer 204 is etched through the gaps 210 in the patterned mask 208 to singulate the integrated circuits 206. In accordance with an embodiment of the present disclosure, etching the semiconductor wafer 204 includes ultimately etching entirely through semiconductor wafer 204, as depicted in FIG. 2C, by etching the trenches 212 initially formed with the rectangular laser spot-based laser scribing process.

In an embodiment, patterning the mask with the laser scribing process involves forming trenches in the regions of the semiconductor wafer between the integrated circuits, and plasma etching the semiconductor wafer involves extending the trenches to form corresponding trench extensions. In one such embodiment, each of the trenches has a width, and each of the corresponding trench extensions has the width.

In accordance with an embodiment of the present disclosure, the resulting roughness of mask opening from laser scribing can impact die sidewall quality resulting from the subsequent formation of a plasma etched trench. Lithographically opened masks often have smooth profiles, leading to smooth corresponding sidewalls of a plasma etched trench. By contrast, a conventional laser opened mask can have a very rough profile along a scribing direction if improper laser process parameters are selected (such as spot overlap, leading to rough sidewall of plasma etched trench horizontally). Although the surface roughness can be smoothened by additional plasma processes, there is a cost and throughput hit to remedying such issues. Accordingly, embodiments described herein may be advantageous in providing a smoother scribing process and/or more reliable trench formation process from the laser scribing portion of the singulation process.

In an embodiment, etching the semiconductor wafer 204 includes using a plasma etching process. In one embodiment, a through-silicon via type etch process is used. For example, in a specific embodiment, the etch rate of the material of semiconductor wafer 204 is greater than 25 microns per minute. An ultra-high-density plasma source may be used for the plasma etching portion of the die singulation process. An example of a process chamber suitable to perform such a plasma etch process is the Applied Centura® Silvia™ Etch system available from Applied Materials of Sunnyvale, CA, USA. The Applied Centura® Silvia™ Etch system combines the capacitive and inductive RF coupling, which gives much more independent control of the ion density and ion energy than was possible with the capacitive coupling only, even with the improvements provided by magnetic enhancement. This combination enables effective decoupling of the ion density from ion energy, so as to achieve relatively high density plasmas without the high, potentially damaging, DC bias levels, even at very low pressures. This results in an exceptionally wide process window. However, any plasma etch chamber capable of etching silicon may be used. In an exemplary embodiment, a deep silicon etch is used to etch a single crystalline silicon substrate or wafer 204 at an etch rate greater than approximately 40% of conventional silicon etch rates while maintaining essentially precise profile control and virtually scallop-free sidewalls. In a specific embodiment, a through-silicon via type etch process is used. The etch process is based on a plasma generated from a reactive gas, which generally a fluorine-based gas such as SF₆, C₄F₈, CHF₃, XeF₂, or any other reactant gas capable of etching silicon at a relatively fast etch rate. In an embodiment, the mask layer 208 is removed after the singulation process, as depicted in FIG. 2C. In another embodiment, the plasma etching operation described in association with FIG. 2C employs a conventional Bosch-type dep/etch/dep process to etch through the substrate 204. Generally, a Bosch-type process consists of three sub-operations: deposition, a directional bombardment etch, and isotropic chemical etch which is run through many iterations (cycles) until silicon is etched through.

Accordingly, referring again to Flowchart 100 and FIGS. 2A-2C, wafer dicing may be preformed by initial ablation using a rectangular laser spot-based laser scribing process to ablate through a mask layer, through wafer streets (including metallization), and partially into a silicon substrate. Die singulation may then be completed by subsequent through-silicon deep plasma etching. A specific example of a materials stack for dicing is described below in association with FIGS. 7A-7D, in accordance with an embodiment of the present disclosure.

Referring to FIG. 7A, a materials stack for hybrid laser ablation and plasma etch dicing includes a mask layer 702, a device layer 704, and a substrate 706. The mask layer, device layer, and substrate are disposed above a die attach film 708 which is affixed to a backing tape 710. In an embodiment, the mask layer 702 is a water soluble layer such as the water soluble layers described above in association with mask 202. The device layer 704 includes an inorganic dielectric layer (such as silicon dioxide) disposed above one or more metal layers (such as copper layers) and one or more low K dielectric layers (such as carbon-doped oxide layers). The device layer 704 also includes streets arranged between integrated circuits, the streets including the same or similar layers to the integrated circuits. The substrate 706 is a bulk single-crystalline silicon substrate.

In an embodiment, the bulk single-crystalline silicon substrate 706 is thinned from the backside prior to being affixed to the die attach film 708. The thinning may be performed by a backside grind process. In one embodiment, the bulk single-crystalline silicon substrate 706 is thinned to a thickness approximately in the range of 50-100 microns. It is important to note that, in an embodiment, the thinning is performed prior to a laser ablation and plasma etch dicing process. In an embodiment, the photo-resist layer 702 has a thickness of approximately 5 microns and the device layer 704 has a thickness approximately in the range of 2-3 microns. In an embodiment, the die attach film 708 (or any suitable substitute capable of bonding a thinned or thin wafer or substrate to the backing tape 710) has a thickness of approximately 20 microns.

Referring to FIG. 7B, the mask 702, the device layer 704 and a portion of the substrate 706 are patterned with a rectangular laser spot-based laser scribing process 712 to form trenches 714 in the substrate 706. Referring to FIG. 7C, a through-silicon deep plasma etch process 716 is used to extend the trench 714 down to the die attach film 708, exposing the top portion of the die attach film 708 and singulating the silicon substrate 706. The device layer 704 is protected by the mask layer 702 during the through-silicon deep plasma etch process 716.

Referring to FIG. 7D, the singulation process may further include patterning the die attach film 708, exposing the top portion of the backing tape 710 and singulating the die attach film 708. In an embodiment, the die attach film is singulated by a laser process or by an etch process. Further embodiments may include subsequently removing the singulated portions of substrate 706 (e.g., as individual integrated circuits) from the backing tape 710. In one embodiment, the singulated die attach film 708 is retained on the back sides of the singulated portions of substrate 706. Other embodiments may include removing the mask layer 702 from the device layer 704. In an alternative embodiment, in the case that substrate 706 is thinner than approximately 50 microns, the rectangular laser spot-based laser scribing process 712 is used to completely singulate substrate 706 without the use of an additional plasma process.

A single process tool may be configured to perform many or all of the operations in a rectangular laser spot-based laser beam ablation and plasma etch singulation process. For example, FIG. 8 illustrates a block diagram of a tool layout for laser and plasma dicing of wafers or substrates, in accordance with an embodiment of the present disclosure.

Referring to FIG. 8, a process tool 800 includes a factory interface 802 (FI) having a plurality of load locks 804 coupled therewith. A cluster tool 806 is coupled with the factory interface 802. The cluster tool 806 includes one or more plasma etch chambers, such as plasma etch chamber 808. A laser scribe apparatus 810 is also coupled to the factory interface 802. The overall footprint of the process tool 800 may be, in one embodiment, approximately 3500 millimeters (3.5 meters) by approximately 3800 millimeters (3.8 meters), as depicted in FIG. 8.

In an embodiment, the laser scribe apparatus 810 houses a laser assembly configured to provide a rectangular laser spot-based laser beam. In one such embodiment, the laser assembly is configured to provide the rectangular laser spot-based laser beam with laser spots that are square in plan view and have a top-hat profile in cross-sectional view. In another such embodiment, the laser assembly is configured to provide the rectangular laser spot-based laser beam having a wavelength in a range of 510-530 nanometers, an input beam diameter in a range of 8-10 millimeters, a working distance in a range of 40-55 millimeters, and an output square spot width in a range of 6-8 microns. In an embodiment, the laser scribe apparatus 810 is configured to pre-map a topography of a semiconductor wafer or a topography of a chuck for supporting a semiconductor wafer, or both, e.g., for an actively-focused laser beam laser scribing process. In an embodiment, the laser assembly includes a Gaussian source laser beam. In an embodiment, the laser assembly includes a femto-second source laser beam.

In an embodiment, the laser is suitable for performing a laser ablation portion of a hybrid laser and etch singulation process, such as the laser ablation processes described above. In one embodiment, a moveable stage is also included in laser scribe apparatus 810, the moveable stage configured for moving a wafer or substrate (or a carrier thereof) relative to the laser. In a specific embodiment, the laser is also moveable. The overall footprint of the laser scribe apparatus 810 may be, in one embodiment, approximately 2240 millimeters by approximately 1270 millimeters, as depicted in FIG. 8.

In an embodiment, the one or more plasma etch chambers 808 is configured for etching a wafer or substrate through the gaps in a patterned mask to singulate a plurality of integrated circuits. In one such embodiment, the one or more plasma etch chambers 808 is configured to perform a deep silicon etch process. In a specific embodiment, the one or more plasma etch chambers 808 is an Applied Centura® Silvia™ Etch system, available from Applied Materials of Sunnyvale, CA, USA. The etch chamber may be specifically designed for a deep silicon etch used to create singulate integrated circuits housed on or in single crystalline silicon substrates or wafers. In an embodiment, a high-density plasma source is included in the plasma etch chamber 808 to facilitate high silicon etch rates. In an embodiment, more than one etch chamber is included in the cluster tool 806 portion of process tool 800 to enable high manufacturing throughput of the singulation or dicing process.

The factory interface 802 may be a suitable atmospheric port to interface between an outside manufacturing facility with laser scribe apparatus 810 and cluster tool 806. The factory interface 802 may include robots with arms or blades for transferring wafers (or carriers thereof) from storage units (such as front opening unified pods) into either cluster tool 806 or laser scribe apparatus 810, or both.

Cluster tool 806 may include other chambers suitable for performing functions in a method of singulation. For example, in one embodiment, in place of an additional etch chamber, a deposition chamber 812 is included. The deposition chamber 812 may be configured for mask deposition on or above a device layer of a wafer or substrate prior to laser scribing of the wafer or substrate. In one such embodiment, the deposition chamber 812 is suitable for depositing a photo-resist layer. In another embodiment, in place of an additional etch chamber, a wet/dry station 814 is included. The wet/dry station may be suitable for cleaning residues and fragments, or for removing a mask, subsequent to a laser scribe and plasma etch singulation process of a substrate or wafer. In yet another embodiment, in place of an additional deep silicon etch chamber, a plasma etch chamber is included and is configured for performing a plasma-based cleaning process. In an embodiment, a metrology station is also included as a component of process tool 800.

Embodiments of the present disclosure may be provided as a computer program product, or software, that may include a machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to embodiments of the present disclosure. In one embodiment, the computer system is coupled with process tool 800 described in association with FIG. 8. A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., a computer) readable storage medium (e.g., read only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media, optical storage media, flash memory devices, etc.), a machine (e.g., computer) readable transmission medium (electrical, optical, acoustical or other form of propagated signals (e.g., infrared signals, digital signals, etc.)), etc.

FIG. 9 illustrates a diagrammatic representation of a machine in the exemplary form of a computer system 900 within which a set of instructions, for causing the machine to perform any one or more of the methodologies described herein, may be executed. In alternative embodiments, the machine may be connected (e.g., networked) to other machines in a Local Area Network (LAN), an intranet, an extranet, or the Internet. The machine may operate in the capacity of a server or a client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine may be a personal computer (PC), a tablet PC, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a web appliance, a server, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines (e.g., computers) that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies described herein.

The exemplary computer system 900 includes a processor 902, a main memory 904 (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory 906 (e.g., flash memory, static random access memory (SRAM), MRAM, etc.), and a secondary memory 918 (e.g., a data storage device), which communicate with each other via a bus 930.

Processor 902 represents one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. More particularly, the processor 902 may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, processor implementing other instruction sets, or processors implementing a combination of instruction sets. Processor 902 may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. Processor 902 is configured to execute the processing logic 926 for performing the operations described herein.

The computer system 900 may further include a network interface device 908. The computer system 900 also may include a video display unit 910 (e.g., a liquid crystal display (LCD), a light emitting diode display (LED), or a cathode ray tube (CRT)), an alphanumeric input device 912 (e.g., a keyboard), a cursor control device 914 (e.g., a mouse), and a signal generation device 916 (e.g., a speaker).

The secondary memory 918 may include a machine-accessible storage medium (or more specifically a computer-readable storage medium) 932 on which is stored one or more sets of instructions (e.g., software 922) embodying any one or more of the methodologies or functions described herein. The software 922 may also reside, completely or at least partially, within the main memory 904 and/or within the processor 902 during execution thereof by the computer system 900, the main memory 904 and the processor 902 also constituting machine-readable storage media. The software 922 may further be transmitted or received over a network 920 via the network interface device 908.

While the machine-accessible storage medium 932 is shown in an exemplary embodiment to be a single medium, the term “machine-readable storage medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “machine-readable storage medium” shall also be taken to include any medium that is capable of storing or encoding a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present disclosure. The term “machine-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, and optical and magnetic media.

In accordance with an embodiment of the present disclosure, a machine-accessible storage medium has instructions stored thereon which cause a data processing system to perform a method of dicing a semiconductor wafer having a plurality of integrated circuits. The method includes forming a mask above the semiconductor wafer, the mask composed of a layer covering and protecting the integrated circuits. The mask is then patterned with a rectangular laser spot-based laser scribing process to provide a patterned mask with gaps, exposing regions of the semiconductor wafer between the integrated circuits. The semiconductor wafer is then plasma etched through the gaps in the patterned mask to singulate the integrated circuits.

Thus, hybrid wafer dicing approaches using a rectangular laser spot-based laser beam and plasma etch process have been disclosed.

HYBRID WAFER DICING APPROACH USING A RECTANGULAR LASER SPOT-BASED LASER SCRIBING PROCESS AND PLASMA ETCH PROCESS

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