Backside metal removal die singulation systems and related methods

Implementations of methods of singulating a plurality of die included in a substrate may include forming a groove through a backside metal layer through laser ablating a backside metal layer at a die street of a substrate and singulating a plurality of die included in the substrate through removing substrate material of the substrate in the die street.

BACKGROUND

1. Technical Field

Aspects of this document relate generally to plasma die singulation systems and methods. More specific implementations involve methods of singulating semiconductor die from a substrate.

Semiconductor devices include integrated circuits found in common electrical and electronic devices, such as phones, desktops, tablets, other computing devices, and other electronic devices. The devices are separated through singulating a wafer of semiconducting material into a plurality of semiconductor die. Various layers may be coupled to the front side and/or the backside of the wafer. Upon singulation, the die can be mounted on a package and electrically integrated with the package which may then be used in the electrical or electronic device.

SUMMARY

Implementations of methods of singulating a plurality of die included in a substrate may include forming a groove through a backside metal layer through laser ablating a backside metal layer at a die street of a substrate and singulating a plurality of die included in the substrate through removing substrate material of the substrate in the die street.

Implementations of methods of singulating a plurality of die included in a substrate may include one, all, or any of the following:

The substrate may be less than 50 micrometers thick.

The substrate may be less than 30 micrometers thick.

Removing the substrate material of the substrate in the die street may include removing through one of sawing or lasering.

Removing the substrate material of the substrate in the die street may include removing using plasma etching.

When removing the substrate material of the substrate in the die street through sawing or lasering, the method may include removing damage from a sidewall of the die street through remote plasma healing.

Singulating the plurality of die comprised in the substrate through plasma etching may include removing a portion of the substrate material of the substrate having a width less than a width of the die street.

Implementations of methods of singulating a plurality of die included in a substrate may include forming, on a first side of a substrate, one or more layers, forming a backside metal layer on the second side of the substrate, laser ablating a groove into the backside metal layer to expose at least a portion of the substrate, and singulating a plurality of die comprised in the substrate through plasma etching at the portion of the substrate exposed by the groove. The groove may be located in a die street of the substrate.

Implementations of methods of singulating a plurality of die included in a substrate may include one, all, or any of the following:

Singulating a plurality of die included in the substrate through plasma etching may include plasma etching from the second side of the substrate,

The method may include thinning the second side of the substrate to less than 50 micrometers thick.

The method of singulating a plurality of die in a substrate may include monitoring the laser ablation of the groove using a camera facing the second side of the substrate.

The method of singulating a plurality of die in a substrate may include making near-real-time adjustments to one or more laser parameters based upon data collected through monitoring the laser ablation of the groove using a camera facing the second side of the substrate.

Singulating the plurality of die comprised in the substrate through plasma etching may include removing a portion of the substrate material of the substrate having a width less than a width of the die street.

The backside metal layer may include copper.

Implementations of methods of singulating a plurality of die included in a substrate may include using a laser, grooving through a backside metal layer in a die street coupled to a substrate, actively monitoring a formation of a groove in the backside metal layer, and singulating a plurality of die included in the substrate through removing a substrate material at the grooves in the back metal layer.

Implementations of methods of singulating a plurality of die included in a substrate may include one, all, or any of the following:

Actively monitoring the formation of the groove in the backside metal layer may include monitoring using a camera facing the backside metal layer.

The method of singulating a plurality of die in a substrate may include making near-real-time adjustments to one or more laser parameters based upon data collected through monitoring the formation of the groove using a camera facing the second side of the substrate.

Removing the substrate material at the grooves may include removing through plasma etching.

The method of singulating a plurality of die from a substrate may include removing damage from a sidewall of the die street through remote plasma healing.

The substrate may be thinned to less than 50 micrometers.

DESCRIPTION

Referring toFIG. 1, a cross sectional side view of a portion of a substrate2is illustrated. The term “substrate” refers to a semiconductor substrate as a semiconductor substrate is a common type of substrate, however, “substrate” is not an exclusive term that is used to refer to all semiconductor substrate types. Similarly, the term “substrate,” may refer to a wafer as a wafer is a common type of substrate, however, “substrate” is not an exclusive term that is used to refer to all wafers. The various semiconductor substrate types disclosed in this document that may be utilized in various implementations may be, by non-limiting example, round, rounded, square, rectangular, or any other closed shape. In various implementations, the substrate2may include various substrate materials such as, by non-limiting example, single crystal silicon, silicon dioxide, glass, gallium arsenide, sapphire, ruby, silicon-on-insulator, silicon carbide, polycrystalline or amorphous forms of any of the foregoing, and any other substrate material useful for constructing semiconductor devices. In particular implementations, the substrate may be a silicon-on-insulator substrate.

Referring toFIG. 2, a cross sectional side view of a plurality of layers4coupled to a first side of the substrate ofFIG. 1is illustrated. In various implementations, before singulating a plurality of die from the substrate2, the method of forming a plurality of die may include forming a plurality of die on the substrate. This may include forming a plurality of layers4on a first side6the substrate2. As illustrated byFIG. 2, the plurality of layers4may be patterned, and in various implementations, may be patterned (or otherwise removed) to not be present in a die street8area of the substrate2. The plurality of layers may include, by non-limiting example, one or more metal layers, one or more passivation layers, any other layer, and any combination thereof. In various implementations passivation layers may include, by non-limiting example, silicon nitride, oxides, metal electrical test structures, electrical test pads, silicon dioxide, polyimides, metal pads, residual underbump metallization (UBM), any combination thereof, and any other layer or material capable of facilitating electrical or thermal connection between the one or more semiconductor die and/or protecting the one or more semiconductor die from contaminants. In various implementations, the plurality of die may include power semiconductor devices, such as, by non-limiting example, a MOSFET, an IGBT, or any other power semiconductor device. In other implementations, the plurality of die may include non-power semiconductor devices.

Referring toFIG. 3, a view of the substrate and plurality of layers ofFIG. 2in a flipped orientation is illustrated. The method of forming and singulating a plurality of die includes flipping the substrate and, though not illustrated, in various implementations, the method may include applying a tape to a first side10of the plurality of layers4. Such a tape may be a backgrinding tape in various implementations. Referring toFIG. 4, a view of substrate and plurality of layers ofFIG. 3with the substrate thinned is illustrated. In various implementations, the method of forming and singulating a plurality of die may include thinning the second side12of the substrate2. In various implementations, the substrate2may be thinned to a thickness less than 50 micrometers (μm). In other implementations, the substrate2may be thinned to a thickness less than 30 μm. In still other implementations, the substrate2may be thinned to a thickness less than 100 μm, more than 100 μm, and in other various implementations, the substrate2may not be thinned. In particular implementations, the substrate2may be thinned to a thickness of about 25 μm, and in other particular implementations, the substrate may be thinned to a thickness of about 75 μm. The substrate2may be thinned through backgrinding, etching, or any other thinning technique. In particular implementations, the substrate is thinned using a backgrinding process marketed under the trade name TAIKO by DISCO of Tokyo, Japan to provide an edge ring supporting the thinned substrate.

Referring toFIG. 5, a view of the thinned substrate and plurality of layers ofFIG. 4with a backside metal layer coupled to the second side of the substrate is illustrated. The method of forming a plurality of die and singulating the plurality of die includes forming a backside metal layer14on the second side of the substrate2. In particular implementations, the backside metal layer14may be copper or a copper alloy. In other implementations, the backside metal layer may include any other type of metal, alloy thereof, or combination thereof. In various implementations, the backside metal layer may include an adhesion layer like Ti, TiW, TiN, and/or Al, and any combination thereof followed by a layer of a diffusion barrier such as Ni, NiV, and/or Cu, and any combination thereof followed by an oxide inhibitor (to protect the diffusion barrier from oxidizing) and a solderable metal such as Au, Ag, and/or Sn and any combination thereof. In various implementations, the backside metal layer may be 10 μm thick. In other implementations, the backside metal layer may be more or less thick than 10 μm. In implementations where 10 μm of Cu is used, then a seed metal layer or under bump metal layer (UBM) may be deposited which is used used for electrolytic plating. The seed metal layers typically comprise of an adhesion layer like that previously discussed (Al, Ti, TiW, and/or TiN, or any combination thereof) followed the plated material (Cu or Ni), followed by a diffusion barrier for the diffusion layer such as Au, Sn, and/or Ag or any combination there. The backside metal layer14may be evaporated or sputtered onto the substrate2, however, in other implementations (including implementations having thicker substrates), the backside metal layer14may be plated onto the substrate2or formed on the substrate using another technique. In various implementations, the backside metal layer14may be formed over the entire second side12of the substrate2. In such implementations, the backside metal layer14may strengthen the substrate2. In various implementations, the outer surface16of the backside metal layer may be coated with a film or other layer in order to facilitate removal of any slag resulting from the laser ablation disclosed later herein. This layer may be applied using spray coating, spin coating, or other coating techniques.

Prior to any actual singulation of a plurality of the die, the method of singulating the plurality of die in the substrate may include aligning the substrate. In various implementations, the method may include aligning the substrate from the first side (which may be the front side, or bottom/tape facing side as oriented inFIG. 5) using optics or a camera. In such implementations, the optics or camera may be placed below the substrate and may detect a plurality of alignment features formed on or within the substrate. In various implementations, the alignment features may be formed on or within the die street8of the substrate. In implementations having tape coupled to the first side10of the plurality of layers, the optics or camera may be configured to detect the plurality of alignment features through the tape. In a particular implementation, the substrate may be aligned using an infrared (IR) camera and IR alignment features. In other implementations, the alignment features may be included on an outer surface16of the backside metal layer14. In such implementations, rather than requiring optics or a camera to be below the substrate, the optics or camera may align the substrate from above the substrate (as oriented inFIG. 5). In still other implementations where the substrate includes a ring around the perimeter after thinning the substrate, the method of aligning the substrate may include placing alignment features in the periphery of the substrate and grinding down the perimeter ring. The substrate may then be aligned from the backside, or second side12of the substrate by using the alignment features along the outer edge of the device. Such an alignment method may include using an IR camera.

Referring toFIG. 6, a view of the backside metal layer ofFIG. 5having a groove formed therein is illustrated. Upon aligning the substrate, the method of singulating a plurality of die in the substrate2includes forming a groove18through the backside metal layer14. The groove18is located in/positioned in the die street8. In various implementations, the groove18may be as wide as the die street8or wider than the die street. The groove18may be formed through laser ablating a backside metal layer14at the die street8of the substrate2. As illustrated, in various implementations the groove18extends through the backside metal layer14. In this manner, at least a portion20of the substrate2is exposed. In various implementations, the formation of the groove is stopped at the substrate2. Because laser ablation may form a groove more slowly in the backside metal layer14as compared to the substrate2, care may be required to prevent the laser beam from laser ablating a groove deep into, or through, the substrate2. In order to facilitate the formation of the groove18stopping at the substrate2, in various implementations the method includes actively monitoring the formation of a groove18in the backside metal layer14. In various implementations, a camera facing the backside metal layer14may be used to actively monitor the formation of the groove18. Active monitoring may include monitoring the cleared backside metal and/or measuring the thickness variation of the removed backside metal layer as compared to the original thickness of the backside metal layer.

In such implementations, near-real-time adjustments may be made to one or more laser parameters based upon data collected during the active monitoring to alter the laser characteristics to ensure just the back metal is being ablated. In particular implementations, near-real-time adjustments may include the camera monitoring the formation of the groove one inch behind the laser beam, and, based upon the data collected from the monitoring, immediately making adjustments to the parameters of the laser. In other implementations, near-real-time adjustments may include the camera actively monitoring the formation of the groove less than one inch behind the laser beam or more than one inch behind the laser beam. The parameters of the laser beam which may be adjusted may include, by non-limiting example, laser power, pulse energy, pulse frequency, spot size, focal point, focal depth, and/or speed of movement of the laser beam across the backside metal layer14. In various implementations, especially implementations involving thinned substrates, active monitoring of the formation of the groove18may be critical as the process window for forming the groove may be narrow. This is in part because variations in the thickness of the tape upon which the thinned substrate is mounted may be 5 microns or more across the tape, meaning that for a back metal layer of 10 microns thickness, the laser beam will see 50% variation in apparent thickness of the back metal layer at a particular focal depth just because of tape thickness variation. Through such active monitoring and near-real-time adjustments, any tilt in the substrate or chuck and any variations in the thickness of the tape may be compensated for by adjusting the parameters of the laser. In this manner, the backside metal layer14may have a groove18formed entirely through the thickness without the groove being formed into (or substantially into) the substrate2.

Referring toFIG. 7, a view of the substrate ofFIG. 6singulated into a plurality of die is illustrated. The method of singulating a plurality of die22in a substrate2includes singulating the plurality of die in the substrate through removing substrate material of the substrate2at the grooves18in the die street8. As illustrated byFIG. 7, the plurality of die are singulated from the backside of the substrate. Because of this, there is no need to flip the substrate over in order to singulate the substrate from the front side. The ability to singulate the die from the backside may reduce damage to the substrate, and especially a thinned substrate, as it requires the substrate to be handled less, increasing the yield of the process correspondingly. Further, in implementations where the plurality of die are singulated from the backside through laser ablation (as disclosed later herein), because it is singulated from the backside and not the front side, redeposition of the back metal layer may be reduced as residual backmetal may more easily flow away from the sidewalls of the die.

In various implementations, the plurality of die22may be singulated through removing the substrate material of the substrate2in the die street8through plasma etching from the second side6of the substrate2at the portion20of the substrate exposed by the groove18. In various implementations, a plasma etch process marketed under the tradename BOSCH® by Robert Bosch GmbH, of Stuttgart, Germany (the “Bosch process”), may be used to singulate the substrate2into a plurality of die22. In other implementations, other plasma etch processes may be used to singulate the plurality of die22from the substrate2. In various implementations, though not illustrated herein, singulating the plurality of die included in the substrate through plasma etching may include removing a portion of the substrate material of the substrate having a width less than a width of the die street. In such implementations, the width of the removed portion from plasma etching is less than the width of the die street as plasma die singulation is capable (with the use of photolithography or other masking techniques) of creating a die street narrower than the die street created through laser ablation. In other implementations, and as illustrated byFIG. 7, the width of the removed portion of the substrate may be the same as the width of the die street8by singulating the plurality of die22through removing through plasma etch all of the substrate material of the substrate2in the die street8.

Referring toFIGS. 8-11, a method for singulating a plurality of die similar to the method illustrated byFIGS. 5-7is illustrated. Referring specifically toFIG. 8, a view of a backside metal layer coupled to a substrate is illustrated. The substrate28may be the same as or similar to any substrate disclosed herein, the plurality of layers32coupled to the substrate may be the same as or similar to any type of plurality of layers disclosed herein, and the backside metal layer30may include any type of backside metal layer disclosed herein. Likewise, the backside metal layer30, the plurality of layers32, and the substrate28may be formed using the same or a similar method as any method disclosed herein. The method of singulating a plurality of die may also include aligning the substrate using any alignment technique disclosed herein. Referring toFIG. 9, a view of the backmetal layer ofFIG. 8having a groove formed therein is illustrated. The method of singulating a plurality of die includes forming a groove34in the backside metal layer30using the same or a similar method as the methods for forming grooves disclosed herein. As illustrated byFIG. 9, the sidewalls36of the groove34may be rough as a result of the laser ablation.

Referring toFIG. 10, a view of the substrate ofFIG. 9singulated into a plurality of die is illustrated. The method of singulating a plurality of die38in a substrate28includes singulating the plurality of die in the substrate through removing substrate material of the substrate28at the grooves34in the die street40. As illustrated byFIG. 10, the plurality of die are singulated from the second side42, or backside, of the substrate28. Because of this, there is no need to flip the substrate28over in order to singulate the substrate from the front side. As previously discussed, the ability to singulate the plurality of die38from the backside of the substrate28may reduce damage to the substrate, and especially a thinned substrate, as it requires the substrate28to be handled less. In various implementations, the plurality of die38may be singulated through removing the substrate material of the substrate28in the die street40through sawing or lasering at the exposed portion42of the substrate28exposed by the groove34. In particular implementations, the method of singulating the plurality of die may include forming the groove34through laser ablation and singulating the plurality of die38through laser ablation. The two-step laser ablation process may prevent re-deposition of the backside metal layer30into the substrate28as the backside metal layer30in the die street40will be cleared away prior to the singulation of the plurality of die38.

As illustrated byFIG. 10, when singulating the plurality of die38using a laser beam or a saw blade, the sidewalls44of each die results in the production of damage, chips, and/or cracks in the sidewalls44of the die street40and layers adjacent to the die street. The presence of the cracks and chips has the potential to compromise the reliability of the resulting semiconductor package (and reduce the die strength) if/when the cracks and chips propagate into the device portion of the semiconductor die. Since the saw process involves the rubbing of the rotating blade against the substrate surface, and the laser process involves melting and ablating the material under the focus of a laser beam on the substrate surface, the damage, chipping, and cracking can only be influenced through saw or laser processing variables (such as, by non-limiting example, substrate feed speed, blade kerf width, cut depth, multiple saw cuts, blade materials, laser power, focal depth, pulse energy, pulse repetition rate, etc.) but not eliminated entirely.

Referring toFIG. 11, a view of the plurality of die ofFIG. 10having smoothed sidewalls is illustrated. In implementations where the plurality of die38are singulated through lasering or sawing, the method of singulating the plurality of die may include removing damage from a sidewall44of the die street40through remote plasma healing. In such implementations, an isotropic or substantially isotropic plasma etch may be applied to the sidewalls44of the die street40. The plasma may penetrate/facilitate reaction with the materials of the cracks and/or chips of the sidewalls44formed when the plurality of die38were singulated from the substrate28. As the plasma encounters the cracks and/or chips, the damaged portion(s) of the substrate28may etch away and result in smoothed, or healed, sidewalls44of the die street, as illustrated byFIG. 11.

In places where the description above refers to particular implementations of backside metal removal die singulation systems and related methods and implementing components, sub-components, methods and sub-methods, it should be readily apparent that a number of modifications may be made without departing from the spirit thereof and that these implementations, implementing components, sub-components, methods and sub-methods may be applied to other backside metal removal die singulation systems and related methods.