JP2012234615A5 - - Google Patents

Description

Method and apparatus for aligning laser diodes on a slider

This application claims the benefit of US Provisional Application No. 61 / 330,067, filed 4/30/2010, the entire contents of which are hereby incorporated by reference.

Background Heat assisted magnetic recording (HAMR) generally reduces the coercivity of a medium by locally heating the recording medium, so that the applied write magnetic field is a transient of the medium caused by the heat source. It refers to a concept that allows the magnetization of a medium to be more easily oriented during magnetic dulling. A strictly limited high power laser spot can be used to heat a portion of the recording medium. The heated portion is then exposed to a magnetic field that sets the direction of magnetization of the heated portion. In HAMR, the coercivity of the medium at ambient temperature can be much higher than the coercivity during recording, thereby enabling recorded bit stability with much higher recording density and much smaller bit cells. .

  One strategy for directing light onto a recording medium uses a laser diode mounted on a read / write head (also referred to as a “slider”). The laser diode directs light to a planar waveguide that propagates the light to a small spot close to the air bearing surface of the slider. A near field transducer (NFT) can be included to further collect the light. Near-field transducers are designed to reach localized surface plasmon (LSP) states at specified light wavelengths. In LSP, the high field surrounding the near-field transducer appears due to the collective vibration of electrons in the metal. Part of the field is tunneled into the adjacent media and absorbed, raising the temperature of the media locally for recording.

  A major consideration for thermally assisted magnetic recording (HAMR) is the location of the laser diode used as the optical power source. One current design places the laser diode on top of the slider. Radiation from the laser diode is focused using an external optical element and directed onto the coupling grating on the waveguide. This method requires the development of external optical elements and can be realized by assembling the sliders one by one and using active alignment.

  One possible embodiment integrates a laser diode in the trailing edge of the slider and uses a combination of optical positioning elements such as solid immersion mirrors (SIM) and / or channel waveguides using a waveguide coupler. While guiding the laser to the near-field transducer. Proper alignment between the laser diode and the waveguide is necessary to achieve the desired coupling of light from the laser to the waveguide. In addition, this needs to be accomplished in a cost effective manner.

Overview In one aspect, an apparatus includes: a channel waveguide and a structure including a pocket proximate to the input surface of the channel waveguide; a laser having an output surface and positioned within the pocket; and the walls of the laser and pocket And the stop is positioned at the interface between the laser and the wall of the pocket so that the laser output face and the waveguide input face are separated by a gap. .

  In another aspect, a method includes: providing a structure including a channel waveguide and a pocket proximate to an input surface of the channel waveguide; positioning a laser having an output surface in the pocket; and an output surface of the laser And until the axial stop on at least one of the laser and the wall of the pocket is positioned at the interface between the laser and the wall of the pocket so that the input face of the waveguide is separated by a gap Pushing toward the wall of the pocket; and fixing the relative position of the laser and the channel waveguide.

  In another aspect, a method positions a carrier wafer relative to a head wafer and aligns each of the plurality of laser diodes of the carrier wafer with a corresponding one alignment feature of the plurality of slider portions of the head wafer. Injecting gas between the carrier wafer and the head wafer through an opening in at least one of the carrier wafer and the head wafer to form a preferential surface condition on the solder surface therebetween Performing a reflow operation to bond the laser diode to the corresponding slider portion, the reflow operation further causing a final alignment therebetween in cooperation with alignment features of the slider portion. The

FIG. 2 is a representation of a data storage device in the form of a disk drive that can include a slider in accordance with an embodiment. It is sectional drawing of a part of laser diode and a slider. FIG. 3 is an isometric view of a portion of a laser diode and a slider. It is sectional drawing of a part of laser diode and a slider. It is sectional drawing of a part of laser diode and a slider. It is sectional drawing of a part of laser diode and a slider. FIG. 3 is an isometric view of a portion of a pocket in a slider. It is sectional drawing of a part of pocket in a slider containing a bonding pad. It is sectional drawing of a part of pocket in a slider containing a bonding bump. It is sectional drawing of a part of laser diode and a slider. It is sectional drawing of a part of laser diode and a slider. It is sectional drawing of a part of laser diode and a slider. It is sectional drawing of the 1st wafer containing a some laser diode, and the 2nd wafer containing a some slider. It is sectional drawing of the 1st wafer containing a some laser diode, and the 2nd wafer containing a some slider. It is sectional drawing of the 1st wafer containing a some laser diode, and the 2nd wafer containing a some slider. 1 is a perspective view of a laser diode according to an exemplary embodiment. FIG. 4 is a flowchart illustrating assembly of a laser diode to a slider according to an exemplary embodiment.

Detailed Description FIG. 1 is a representation of a data storage device in the form of a disk drive 10 that may include a slider constructed in accordance with an embodiment. The disk drive 10 includes a housing 12 (in this view, the upper portion is removed and the lower portion is visible) that is sized and configured to include the various components of the disk drive. The disk drive 10 includes a spindle motor 14 for rotating with at least one magnetic storage medium 16 within a housing. At least one arm 18 is included in the housing 12, each arm 18 having a first end 20 having a recording head or slider 22, and a second end 24 mounted to pivot on the shaft by a bearing 26. Have An actuator motor 28 is located at the second end 24 of the arm and pivots the arm 18 to position the recording head 22 over the desired track 27 of the disk 16. The actuator motor 28 is not shown in this figure but is regulated by a controller well known in the art.

  For heat-assisted magnetic recording (HAMR), electromagnetic radiation, for example, visible light, infrared light, or ultraviolet light is directed onto the surface of the recording medium to increase the temperature of the localized area of the medium. Facilitates switching of the magnetization of the heated region. Recent designs of HAMR recording heads include a thin film waveguide on the slider to guide light to the recording medium for localized heating of the recording medium. A near-field transducer positioned on the air bearing surface of the recording head can be used to direct electromagnetic radiation to a small spot on the recording medium.

  In a HAMR storage device constructed according to one embodiment, a laser diode chip is positioned on a slider. Precise alignment of the laser diode output and waveguide is achieved by using a laser diode bed (also referred to as a cavity or pocket) with specially designed features such as stops and steps.

  FIG. 2 is a cross-sectional view of an example of a slider used in heat-assisted magnetic recording. The slider 30 includes a substrate 32, a base coat 34 on the substrate, a waveguide 36 on the base coat, and a write pole 38 positioned proximate to the waveguide. The coil 40 includes a conductor that turns the write pole one after another. The laser diode 42 is positioned on the slider to direct light onto the input surface 44 of the waveguide. Light then passes through the waveguide and is used to heat a portion 46 of the storage medium 48 that is positioned proximate to the air bearing surface 50 of the slider. The light may be used with a near-field transducer to further control the thermal effect. It is desirable to align the output face 52 of the laser diode with the input face of the waveguide to achieve high efficiency coupling of light from the laser diode to the waveguide. In addition, physical contact between the output face 52 of the laser diode and the input face of the waveguide will be avoided to prevent damage to the face that may result from such contact.

  In one aspect, a method for alignment of laser diodes and waveguides on a slider for thermally assisted magnetic recording (HAMR). The slider includes geometric features for passive alignment of the laser diode and the channel waveguide when the laser diode is placed on the slider.

  FIG. 3 shows an example of a portion of a slider 60 having a pocket 62 (also referred to as a bed or cavity) having front side stops 64 and 66. The slider includes a planar waveguide portion 68 having an input surface 70 proximate the pocket. The input surface is in the recess 72 in the pocket wall 74 and the stops 64 and 66 are on either side of the recess. The laser diode 76 may be in the form of a laser chip and includes an output surface 78 from which the laser emits electromagnetic radiation, such as visible, infrared or ultraviolet light. The laser diode is positioned in the pocket and can be moved toward the waveguide until it abuts the stops 64 and 66. The stop prevents contact between the laser output surface and the waveguide input surface.

For the apparatus of FIG. 3, alignment is achieved between the laser output face and the waveguide input face by placing a laser diode in the pocket and pushing the laser diode forward to the stop. The input surface on the waveguide side can be formed by a vertical etching process and can be wider than the active output region (ie, output surface) of the laser diode. This design allows for precise control of the distance between the output face of the laser diode and the input face of the waveguide. The distance 80 between the output surface of the laser diode and the input surface of the waveguide is defined by the depth of the recess in the pocket wall. Therefore, the active region of the laser diode is not in mechanical contact with the waveguide and remains undamaged.

  The relative position between the laser output surface and the waveguide input surface in the lateral direction (ie X direction) is controlled by an etched step in the pocket wall and one or more stops on the laser diode. Can do. This is shown in the embodiment shown in FIG. 4 where a portion of the slider 90 includes a waveguide 92 and a pocket 94. In this example, laser diode 96 includes one or more stops 98 and protruding portions 100. The stop on the laser diode side can be protrusions positioned on both sides of the laser output surface 102. Alternatively, the stop can be part of the side of the laser diode, and the output surface can be recessed on that side. In this structure, the distance between the stop on the laser diode and the output surface can be considered to be defined by a photolithography process. Thus, the geometric distance control is the same as the accuracy of the photolithography process, which can be less than 50 nm.

  A structure for lateral alignment (ie in the Z direction) is shown in FIG. The structure includes one or more etched grooves at the base of the pocket and a mesa structure on the laser chip. In the embodiment of FIG. 5, the laser diode 110 includes a longitudinally extending mesa or protrusion 112 that fits within the groove 114 at the base or bottom of the pocket 116. It may be envisaged to use a mesa to define optical and current confinement for a single mode laser diode. In this configuration, the central portion of the protruding mesa contains an active laser quantum well. The outer region (which is used for mechanical reference) is etched away to the base substrate material of the laser.

  FIG. 6 is a schematic diagram of a portion of a slider 120 constructed in accordance with another embodiment. In the embodiment of FIG. 6, the alignment in the vertical direction (ie, the Y direction) is controlled during the bonding process (where the laser diode 122 is mounted in the slider pocket by the bonding compound 124). The slider includes etched stops 126 and 128 to provide vertical distance control without precise control of the thickness of the bonding compound. One way to obtain a repeatable vertical position of the laser diode chip is to hold it down during the bonding process. Another strategy for holding the laser chip is to use the surface tension of the bonding compound during bonding. This strategy can be thought of as a two-step process. The first step is to place the laser diode chip in the pocket with a coarse tolerance of 2-5 microns. In the second step, it is conceivable to use the surface tension to precisely align the laser diode and the channel waveguide as a result of the reflow process using the bonding compound.

  FIG. 7 shows an example of a portion of a slider 140 having a pocket 142 with stops 144 and 146. The slider includes a planar waveguide portion 148 having an input surface 150 proximate the pocket. The input surface is in the recess 152 in the pocket wall 154 and the stops 144 and 146 are on both sides of the recess. The laser diode 156 may be in the form of a laser chip and includes an output surface 158 from which the laser emits electromagnetic radiation, such as visible light, infrared light, or ultraviolet light. The laser diode is positioned in the pocket and can be moved toward the waveguide until it abuts the stops 144 and 146. The stop prevents contact between the laser output surface and the waveguide input surface.

For the example of FIG. 7, alignment is achieved between the laser output face and the waveguide input face by placing a laser diode in the pocket and pushing the laser diode forward to the stop. The input surface on the waveguide side can be formed by a vertical etching process and can be wider than the active output region (ie, output surface) of the laser diode. This design allows for precise control of the distance between the output face of the laser diode and the input face of the waveguide. More specifically, the distance 160 between the output surface of the laser diode and the input surface of the waveguide is defined by the depth of the recess in the wall portion of the pocket. Therefore, the active region of the laser diode is not in mechanical contact with the waveguide and remains undamaged.

  A plurality of solder bumps 162 are positioned on the bottom 164 of the pocket 142. A laser diode contact pad 164 is also positioned on the bottom of the pocket and may have the shape shown in FIG. The contact pad 166 at the bottom of the pocket serves as a heat sink. The final laser diode chip location depends on the location of the wetting region, the amount of bonding compound (eutectic) material between the bottom of the pocket and the laser diode, and the stop design. The structure of FIG. 7 can be used in a flip chip bonding method. Examples of bonding compounds include solder and epoxy.

  FIGS. 8-12 illustrate how a bonding process can be used to push the laser diode toward the stop. FIG. 8 is a cross-sectional view of a part of the bottom of the pocket in the slider 170. A seed layer 172 is positioned on the bottom of the pocket. A plurality of conductor pads 174 are positioned over the openings in the insulator 174 above the seed layer. The contact pads are formed from a wettable “bump base metal” (UBM) material, such as Au, Cu, Ni, Cr, Ti, TiW, which allows sufficient solder bumps to be formed. Insulating material 176 is positioned between the contact pads. Contact pads may simply be used for positioning or even electrical contacts.

  FIG. 9 shows a cross-sectional view of the structure of FIG. 8 with the addition of a plurality of bonding compound (eg, eutectic material) bumps 178 on the contact pads 174.

  FIG. 10 shows a cross-sectional view of the structure of FIG. 9 with the addition of a laser diode 180 having a seed layer 182 on the bottom surface and a plurality of contact pads 184 positioned on the seed layer. Insulating material 186 is positioned between the contact pads. The position of the contact pad on the laser diode is inherently offset with respect to the contact pad in the pocket due to placement tolerances.

  FIG. 11 shows self-alignment due to material reflow (eg, solder reflow), where the laser diode is offset with respect to the desired reference plane in the slider and the surface tension of the eutectic material flowing again causes the force indicated by arrow 188 to produce.

  FIG. 12 shows a cross-sectional view of the structure of FIG. 11 following solidification of the eutectic material. 8-12, it can be seen that the surface tension of the bonding compound can be used to align the contact pads on the laser diode with the contact pads in the pockets. By selecting the relative position of the contact pads on the diode and pocket, surface tension can be used to bring the laser into contact with the stops in FIGS. In addition, the bumps can be intentionally offset to drive the laser to a mechanical stop before reaching self-aligned equilibrium.

  In some embodiments, multiple laser chips can be bonded to multiple sliders simultaneously. Precise alignment of the laser diode output face and the input face of the channel waveguide is achieved by using a laser diode bed with specially designed features such as stops and steps. Immediately following the placement of the laser diode, solder reflow follows with a single tool, so these two process steps described above effectively become one manufacturing step. This method is illustrated in FIGS. 13-15.

  FIG. 13 is a cross-sectional view of a first wafer 200 (also referred to as a head wafer) including a plurality of slider portions 202 and a second wafer 204 (also referred to as a carrier wafer) including a plurality of laser diodes 206. The slider portion includes a bed 208 each having a plurality of solder bumps 210. The carrier wafer includes a plurality of openings 212 that allow the passage of hydrogen radicals from the hydrogen radical source 214. Each of the laser diodes further includes a plurality of solder bumps 216. As shown in FIG. 13, when the two wafers are separated, the hydrogen radicals perform a cleaning function to clean the solder bumps. Hydrogen radicals can be formed using processes such as atmospheric plasma. Alternatively, an active gas (such as formic acid) may be used to form a preferential surface condition on the solder surface.

  FIG. 14 shows the structure of FIG. 13 in which the second wafer is moved toward the first wafer so that the solder bumps in the bed and diode merge. In the step shown in FIG. 14, surface tension is used to direct the laser diode to a stop that defines the final relative position of the laser diode output surface and the waveguide input surface.

  FIG. 15 shows the structure of FIG. 14, where the carrier wafer is moved away from the first wafer, leaving the laser diode attached to the first wafer.

  In one embodiment, an AlTiC head wafer is fabricated with a waveguide element and an etched bed (or pocket) to receive a laser diode. These pockets may include features for passive alignment such as mechanical stops and / or solder bumps. The etched pocket defines the final position of the laser diode chip. The carrier wafer includes holes to allow the flow of chemically active materials such as hydrogen radicals and / or formic acid vapor. The size of the etched pocket should match the placement accuracy of the high speed pick and place tool. The pocket position matches the position of the slider portion on the head wafer. The size of the carrier wafer can be the same as or larger than the head wafer.

  The laser diode can be placed in a pocket on the carrier wafer using a high speed pick and place tool. The laser diode is initially in a pocket on the carrier wafer without mechanical attachment. Possible laser chip movements caused by vibrations or incorrect horizontal orientation are limited by the carrier wafer pocket walls. It is conceivable to reduce the variation in the position of the placement tool by using the pocket wall as a mechanical stop using the free movement of the laser chip.

  The source of chemically active material can have a size that matches the carrier wafer. An example of this chemically active source is a commercial atmospheric plasma tool.

  The process of assembling the laser diode and slider includes the steps shown in the flowchart of FIG. 17, as shown in FIGS. Initially, the carrier wafer is positioned 230 near the head wafer, for example, with a few millimeter spacing (see FIG. 13). A source of chemically active material is positioned near the carrier wafer to provide a flow of chemically active material through holes in the carrier wafer (232). The chemically active source is turned on (234) and the wafer is heated above the solder melting point. Some time is taken for solder reflow and precleaning of the solder surface (236) to remove the oxide from the solder surface. The gap between the wafers should be selected so that the cleaning material can access the solder on both wafers simultaneously.

  The wafers are then contacted (238) so that the solder on both wafers is in contact with each other (see also FIG. 14). The cleaning process continues until just prior to bonding until the small gap restricts access to the solder. In the case of passive alignment with a mechanical stop, additional movement may be applied (240) to push the laser diode chip into contact with the stop on the head wafer and switch the heater off. (242). During the solder solidification, the laser is continuously pushed toward the stop (244). After solidification, the carrier wafer is released (250) (see also FIG. 15). When using solder bumps for self-alignment, the laser is allowed to float (246) and the heater is switched off (248). The laser should be floating during solder solidification.

  The bond pad outline and layout have a great effect on the self-alignment characteristics of the laser diode. First, the size, shape and amount of the solder array directly affects the alignment characteristics. A nominal layout is shown in FIG. 16 and shows an example of a self-aligned bond pad layout for an edge emitting laser diode 220 with a central heat sink connection 222 and an outer alignment pad 224. The pad layout includes a combination of solder self-aligned bumps and elongated heat sink connections to provide solder self-alignment, electrical contacts, and thermal cooling by the slider / head structure.

  While several embodiments have been described, it will be apparent to those skilled in the art that various modifications can be made to the described embodiments without departing from the scope of the claims. The implementations described above and other implementations are within the scope of the following claims.

  36 channel waveguide, 44 input face, 62 pocket, 52 output face, 42 laser, 74 wall of pocket, 64, 66 stop, 72 gap.

US Pat. No. 7,358,109

Claims (15)

A structure including a channel waveguide and a pocket proximate to an input surface of the channel waveguide;
A laser having an output surface and positioned in the pocket;
A stop on the laser and at least one of the wall of the pocket,
A device wherein the stop is positioned at the interface between the laser and the wall of the pocket so that the output face of the laser and the input face of the waveguide are separated by a gap.   The apparatus of claim 1, wherein the stop is proximate to a recess in the pocket wall. The stops close to the output face of the laser apparatus according to claim 1 or 2. A first plurality of pads on the laser;
A second plurality of pads in the pocket;
The apparatus of any one of claims 1 to 3 , further comprising a bonding material positioned between individual pads of the first and second plurality of pads.   The apparatus of claim 4, wherein the relative alignment between the plurality of pads is offset with respect to a desired reference plane. Further comprising a heat sink that is positioned between the laser and the bottom of the pocket, according to any one of claims 1-5. A groove in the bottom of the pocket;
Further comprising a mesa extending into the groove from the laser apparatus according to any one of claims 1-6. Further comprising an additional stop between the edges of the pocket and the laser apparatus according to any one of claims 1-7. Providing a structure including a channel waveguide and a pocket proximate to an input surface of the channel waveguide;
Positioning a laser having an output surface in the pocket;
An axial stop on at least one of the laser and the wall of the pocket is positioned at the interface between the laser and the wall of the pocket so that the output surface of the laser and the input surface of the waveguide are separated by a gap. Pushing the laser toward the wall of the pocket until
Fixing the relative position of the laser and the channel waveguide.   The method of claim 9, wherein the stop is proximate to a recess in the pocket wall. Press proceeds step the laser toward the wall of the pocket, press against the wall portion of the laser using a surface tension, comprising the step of the output face of the laser is aligned with the input face of the channel waveguide, according to claim 9 or 10. The method according to 10 .   The method of claim 11, wherein an intentional laser offset is used to cause lateral alignment prior to contact with the stop.   The method of claim 11, wherein the relative alignment between the laser pad and the substrate pad is offset such that contact between the laser and the stop in the axial direction is reached prior to full alignment. .   The method of claim 11, wherein the solder reflow height is lower than the vertical stop height so that the solder is tensioned and pulls the laser against the vertical stop. The method according to any one of claims 9 to 14 , further comprising injecting at least one of hydrogen radicals and a surface activation gas into the gap between the pocket and the laser.