Method and apparatus for manufacturing a semiconductor device

A method of transporting a semiconductor wafer having a ring-shaped stiffening portion can include the steps of pressing the semiconductor wafer from the back surface side to the front surface side thereof on a place different from a place at which the semiconductor wafer is to be held, the step of pressing the semiconductor wafer being conducted before holding the semiconductor wafer having the ring-shaped stiffening portion. The method can include releasing the attachment by suction of the front surface of the semiconductor wafer by supplying a positive pressure onto the chuck table, releasing pressing the semiconductor wafer from the back surface side to the front surface side thereof on the place different from the place at which the semiconductor wafer is to be held and picking up the semiconductor wafer having the ring-shaped stiffening portion from the chuck table while holding the semiconductor wafer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to methods and apparatuses for manufacturing a semiconductor device, and, in particular, to methods and apparatuses for manufacturing thin semiconductor devices such as power semiconductor devices used in power conversion devices.

2. Description of the Related Art

In power semiconductor devices represented by IGBTs (insulated gate bipolar transistors), methods are being developed to reduce the thickness of semiconductor substrates or wafers for producing semiconductor devices to achieve high performance of the devices. In addition, wafers with enlarged diameters are being developed to increase the number of power semiconductor elements that can be formed of a sheet of wafer, thereby reducing the costs of the semiconductor devices.

The reduction in wafer thickness, however, in certain circumstances, may cause a break at the peripheral edge of the wafer resulting in chipping of the wafer. Because thin wafers can show lowered mechanical strength, a problem can also arise that the wafer is liable to generate cracks, breakage, and deflection. These problems are noticeable in wafers with a large diameter, in particular. Thin and large diameter wafers showing large deflection have difficulties in transporting the wafer between manufacturing steps and in positioning the wafer on manufacturing devices.

The manufacturing process of vertical power semiconductor devices typically includes the steps of ion implantation, heat treatment (annealing), metallic film deposition, etc., also on the back surface of the wafer. Hence, the above-mentioned problems can cause difficulty in carrying out these steps on the back surface of the wafer.

In order to solve or minimize such problems, a wafer has been proposed that has a ring-shaped stiffening portion at the periphery of the back surface side of the wafer to reinforce the wafer having a reduced thickness. The wafer having a ring-shaped stiffening portion has the periphery of the back surface side thicker than the central portion of the wafer. Use of the wafer having a ring-shaped stiffening portion substantially reduces warp and deflection of the wafer and enhances strength of the wafer in handling the wafer in the transport step, preventing the wafer from generation of breakage and chipping.

FIGS. 12A through 12Dshow shapes of a wafer having a ring-shaped stiffening portion.FIG. 12Ashows a wafer with an orientation flat110having a ring-shaped stiffening portion111at the periphery of the wafer.

FIG. 12Bshows a wafer with a notch120having a ring-shaped stiffening portion121at the periphery of the wafer.

The inner portion of both the wafers inside the ring-shaped stiffening portion is a region for forming semiconductor device elements.

Japanese Unexamined Patent Application Publication No. 2007-173487 (also referred to herein as “Patent Document 1”), for example, discloses a method for fabricating a wafer having the ring-shaped stiffening portion. The method uses a grinding apparatus provided with a grinding member having a diameter smaller than that of the wafer and grinds the central portion of the wafer thin leaving the peripheral portion of the back surface side of the wafer to form a rib.

FIGS. 13A and 13Bare simplified sectional views showing a grinding step in the process of fabricating a wafer having the ring-shaped stiffening portion.

The following describes a step of fabricating a wafer having the ring-shaped stiffening portion with reference toFIGS. 13A and 13B. The wafer20is first set in a cassette (not depicted) of a grinding apparatus. The wafer20, after positioning by a transport robot or the like, is then transported above a chuck table10and put on the surface of an attachment plate12of the chuck table10. The chuck table10is connected to a vacuum system (not depicted) that supplies a negative pressure through the attachment plate12to attract and hold the wafer20as shown inFIG. 13A. The attachment plate12is made of porous ceramics, for example.

The grinding apparatus is provided with a grinding member133having a diameter smaller than that of the wafer. The grinding member133has a grindstone on the contact surface with the wafer. The grinding member133rotates on its own axis and the axis itself turns around on the wafer to grind the central portion of the wafer.

The grinding apparatus grinds only a central portion of the wafer leaving the peripheral portion with just the thickness as of the original wafer inputted to the grinding apparatus. Thus, a wafer22is fabricated having the central portion ground to a thin desired thickness as shown inFIG. 13B.FIG. 12Cshows a cross-section of a thin fabricated wafer, which has a ring-shaped stiffening portion122(a rib structure) at the periphery of the wafer.

FIGS. 14A,14B, and14C are sectional views of essential parts in another example of grinding step in the process for fabricating a wafer having the ring-shaped stiffening portion.

The grinding apparatus ofFIGS. 14A,14B, and14C is provided with two grinding members131and132containing abrasive grains of different grain sizes, whereas the grinding apparatus ofFIGS. 13A and 13Bhas a single grinding member133.

In the grinding step ofFIGS. 14A,14B, and14C, a semiconductor wafer20before grinding, which can be an eight inch wafer having a thickness of 725 μm, for example, after positioning by a transport robot (not depicted) or the like, is transported on a chuck table10and held by suction on the surface of an attachment plate12. In the first grinding step, as shown inFIG. 14A, the central portion of the wafer20is ground using a grinding member131that is provided with a grindstone containing abrasive grains having a relatively large average grain size. The grinding step is conducted on the central portion of the wafer20down to a predetermined remaining thickness of 100 to 150 μm, for example, leaving the peripheral portion with a width of 1 to 5 mm, for example. After the central portion is ground to the desired thickness, the second grinding step is conducted, as shown inFIG. 14B, using a grinding member132that is provided with a grindstone containing abrasive grains having a smaller average grain size than that of the grindstone provided on the grinding member131. The second grinding step grinds the back surface of the wafer processed by the first grinding step down to a predetermined thickness of 60 to 120 μm, for example, on the region with an inner circumference diameter smaller than that of the recessed inner circumference formed by the first grinding step. Thus, a wafer23having a ring-shaped stiffening portion is fabricated as shown inFIG. 14C. Here, the second grinding step grinds the wafer to an inner diameter that is smaller than the recessed inner diameter formed in the first grinding step, because positioning accuracy of the grinding machine used in the second grinding step is taken into consideration Thus, the grinding member132used in the second grinding step does not become in contact with the side wall of the ring-shaped stiffening portion that is formed in the first grinding step.

The wafer is ground only on the central portion leaving the peripheral portion of the wafer. Thus, a wafer23as shown inFIG. 14Cis fabricated that is machined to a desired thickness only on the central portion of the wafer, leaving the peripheral portion with the thickness as inputted into the grinding apparatus.FIG. 12Dis a section view of the wafer having a ring-shaped stiffening portion (a rib structure)123at the periphery of the wafer.

The wafer having the ring-shaped stiffening portion formed at the peripheral region of the wafer is transferred to the next step for cleaning and drying. A transport device, not depicted inFIGS. 13A,13B,14A,14B, and14C, picks up the wafer from the attachment plate12of the chuck table10and transported to the predetermined destination.

For transporting a wafer having a ring-shaped-stiffening portion (a rib structure), Japanese Unexamined Patent Application Publication No. 2009-059763 (also referred to herein as “Patent Document 2”), for example, discloses a construction in which the upper surface of the ring-shaped portion is attracted by evacuation suction to transport the wafer.

In the process of grinding by a grinding apparatus to form the ring-shaped stiffening portion at the periphery of the wafer, the process is generally conducted in consecutive steps.

After a grinding step is finished, the wafer having the ring-shaped stiffening portion (a rib structure) is removed from the chuck table and transferred to the next step of cleaning and drying. At the same time, the attachment plate on the chuck table is cleaned with a blush or the like, and the next wafer to be ground is supplied and held by suction on the chuck table.

FIGS. 15A,15B, and15C show conventional apparatus and process for transporting a wafer. A wafer22after completion of the grinding step and having a ring-shaped stiffening portion formed in the step is removed from the chuck table10and transferred to the next step by a transport device80. The transport device80is provided with an attracting member81at the lower end of a support member82and transmits a negative pressure from a vacuum system (not depicted) to the bottom surface of the attracting member81through a supply and exhaust system (not depicted) inside the support member82. The attracting member81attracts the thin central portion of the wafer22by suction as shown inFIG. 15A. The wafer22is removed from the chuck table10by elevating the support member82with the attracting member81attracting the thin region of the wafer22.

While a wafer may be attracted only at the ring-shaped stiffening portion as disclosed in Patent Document 2, enough attraction so as to pick up and transport the wafer requires a flat and enough area of the upper surface of the ring-shaped stiffening portion to be attracted. The large area of the flat upper surface decreases the area of the central portion of the wafer, which is a device-forming region.

Attracting the wafer at the central portion thereof as shown inFIG. 15Aensures an area necessary for attracting the wafer and transportation without failure.

Alternatively, as shown inFIG. 16A, the wafer after completion of the grinding step having a ring-shaped stiffening portion can be held at the outer peripheral end of the wafer by a holding member92provided at the end of an arm91of a transport device90. The arm91of the transport device90is movable so that the holding member92can approach and leave the ring-shaped stiffening portion of the wafer22. The holding member92moves from a position apart from the ring-shaped stiffening portion and holds the wafer22at the ring-shaped stiffening portion thereof. The arm91is then elevated while holding the ring-shaped stiffening portion of the wafer22with the holding member92to remove the wafer22from the chuck table10. This procedure allows the wafer22to be transferred to the next step without touching the thinned portion of the wafer22.

The process including the grinding step needs to be consecutive. The total time required for the consecutive process should be decreased, the consecutive process on the wafer including: transfer, placing, grinding, picking up, cleaning of the chuck table, and transfer to the next wafer. In the step of picking up the wafer to transfer to the next step, in particular, two problems must be solved simultaneously: to shorten the time for picking up the wafer and to prevent the wafer from any damage.

The chuck table10has the cleaning water dropped on the wafer in the grinding step and the cleaning water used in the cleaning process of the chuck table10remained on the attachment plate12(FIG. 15A) or a combined attachment plate of13and14(FIG. 16B). The attachment plate12(FIG. 15A) or a combined attachment plate of13and14(FIG. 16B) is referred to as the attachment plate12or13and14′ in the following.

If the cleaning water is remained between the wafer22and the attachment plate12or13and14, the wafer22is adhered to the attachment plate12or13and14due to the surface tension of the cleaning water. In the grinding step for forming the ring-shaped stiffening portion, a negative pressure is supplied onto the attachment plate12or13and14from a vacuum system (not depicted) through a supply and exhaust path11. After the grinding step, the negative pressure is released from the attachment plate12or13and14on the chuck table10. However, after the release of the negative pressure, the presence of the cleaning water still inhibits the progress of air leakage through the porous attachment plate12or13and14of the chuck table10and causes the wafer22remaining adhered onto the attachment plate12or13and14. If the wafer22were left on the attachment plate12or13and14for a long period of time for example ten minutes, after the release of the negative pressure, the air leakage through the attachment plate12or13and14would be advanced and the wafer2would become easy to be removed. This means, however, leaves the problem to reduce the time required for picking up the wafer unsolved and lowers the efficiency of the transport operation.

If the wafer22adhered to the attachment plate12or13and14were forced to be separated, the thin wafer22vulnerable to break would cause chipping and cracking. Thus, the problem to pick up the wafer with no damage is left unsolved.

The time duration for picking up the wafer22can be shortened by supplying, after release of the negative pressure, water, air, or a mixture thereof (indicated by the reference symbols70and71inFIGS. 15B,15C and16B) to the attachment plate12or13and14on the chuck table10through the supply and exhaust path11. A positive pressure is given to the surface of the attachment plate12or13and14on the chuck table10by blowing up the water, air, or the mixture thereof (70,71) through the attachment plate. The wafer after releasing adhesion to and separation from the attachment plate on the chuck table10is transferred to the next step by the transport device (80inFIG. 15A,90inFIGS. 16A and 16B).

The blowing up of the water, air, or a mixture thereof70,71shown inFIGS. 15B,15C, andFIG. 16Bcauses deformation in the wafer22. Stress concentration is liable to be developed especially at places damaged by the grindstone in the grinding step and places with varied curvature. Such places are indicated by the symbol223inFIG. 13Band the symbol233inFIG. 14C.

The deformation of the wafer22is very likely to occur at the part B indicated inFIG. 15Cwhere the wafer22is pushed by the attracting member81of the transport device80and at the part B indicated inFIG. 16Bwhere the wafer22varies in thickness thereof.

The wafer22undergoes occurrence of cracks on the ground surface thereof due to such deformation that makes the wafer locally float apart as indicated by the arrow A inFIG. 15CandFIG. 16B. Thus, there is a need in the art for an improved method and apparatus for manufacturing semiconductor devices.

SUMMARY OF THE INVENTION

Embodiments of the invention are directed to these and other needs, and to provide for a method and apparatus for manufacturing a semiconductor device that allows a wafer to be picked up safely and securely after the wafer is attracted on a chuck table and ground on the surface thereof.

In certain embodiments, a front surface of a semiconductor wafer is attracted to an attachment plate of a chuck table and a back surface of the semiconductor wafer is ground in a inside region to a recessed configuration leaving a ring-shaped stiffening portion at a periphery of the wafer. In a procedure of transporting the semiconductor wafer having the ring-shaped stiffening portion from the chuck table, before holding the wafer having the ring-shaped stiffening portion, the semiconductor wafer is pushed at a place different from a place to be held from the back surface side to the front surface side. A positive pressure is supplied to the chuck table to release adhesion of the front surface of the semiconductor wafer. After releasing the pressure against the semiconductor wafer at the different place from the place to be held from the back surface side to the front surface side, the semiconductor wafer having the ring-shaped stiffening portion is picked up from the chuck table while being held.

In some embodiments, a wafer can be safely and surely picked up and transported smoothly to the predetermined destination preventing the wafer from chipping and cracking.

DETAILED DESCRIPTION

Now, some aspects of embodiments according to the present invention will be described in detail in the following with reference to the accompanying drawings.

A wafer having a ring-shaped stiffening portion at the periphery of the wafer as shown inFIGS. 12A through 12Dcan be formed by a process as shown inFIGS. 13A,13B, andFIGS. 14A,14B, and14C. Descriptions on theFIGS. 12A through 12DandFIGS. 13A,13B, andFIGS. 14A,14B, and14C have been made in the foregoing and are not repeated here.

FIGS. 1A,1B,FIGS. 2A,2B,FIGS. 3A,3B,FIGS. 4A,4B,4C, andFIGS. 5A,5B illustrates the first embodiment according to the present invention. Of the figures,FIGS. 4A,4B, and4C are timing charts showing pressures on some parts in the embodiment.

FIG. 1Ashows a wafer22attached by suction on the surface of an attachment plate12of a chuck table10. The attachment plate12is made of a porous material and has a surface machined to be flat for attaching the wafer22. The chuck table10is connected to a vacuum system (not depicted) through a supply and exhaust path11. A negative pressure (indicated by the symbol60) supplied by the vacuum system is transmitted to the surface of the attachment plate12and attracts the wafer22through vacuum suction.FIG. 1Ashows the wafer22after completion of a grinding step as illustrated inFIGS. 12A through 12D,FIGS. 13A,13B, andFIGS. 14A,14B, and14C.

The following describes a procedure of transferring the wafer22to the next step according to the sequence of the procedure.

FIG. 1Ashows a transport device40that is standing by above the wafer22after completion of the grinding step. The transport device40comprises an attracting mechanism30(indicated inFIG. 2B), which is a pick up device, and a pressing device including a pressing pad43, a pressing pad support arm42, and a pressing pad sliding member41.

The pressing pad43, which is a stiffening portion pressing mechanism, presses the ring-shaped stiffening portion of the wafer22. The pressing pad supporting arm42supports the pressing pad43and is fixed to a pressing pad sliding member41such that the pressing pad43is allowed to be vertically moved independently of the attracting mechanism30.

The pressing pad43is made of an elastic material in this embodiment example. A material for the pressing pad43, although not limited to an elastic material, preferably exhibits such elastic deformability that follows the configuration of the ring-shaped stiffening portion of the wafer22and such rigidity that withstands blowing up of air or the like through the attachment plate12, the blowing up being described afterwards. The favorable materials include foamed resin such as EVA resin and silicone rubber. The pressing pad43has a shape of a ring with a width wider than that of the ring-shaped stiffening portion of the wafer22and projects out toward both the inside and outside so as to cover whole the width of the stiffening portion. The pressing pad43has preferably such a width that projects out toward both inside and outside from the position of the ring-shaped stiffening portion by a dimension larger than 1 mm. The dimension of the pressing pad43covers the ring-shaped stiffening portion without failure irrespective of some positional deviation of the pressing pad43. The inside portion of the pressing pad43covers at least an inside wall of the recessed portion of the wafer22. In addition, in the case the wafer22, like the one illustrated inFIG. 1A, has been ground through two stages as illustrated inFIGS. 14A,14B, and14C, the pressing pad43preferably covers the step part generated in the second grinding step.

An attracting member31shown inFIG. 1Aof the attracting mechanism30indicated inFIG. 2Bis fixed to a support member32(indicated inFIG. 2B) and vertically movable independently of the pressing pad43. The support member32includes an exhausting path (not depicted) communicating with a lower surface of the attracting member31. The exhausting path is connected to a vacuum system (not depicted) and supplies negative pressure to attract and hold the wafer22on the surface of the attracting member31.

In the embodiment example shown inFIG. 1A, the contact surface with the wafer22of the attracting member31of the attracting mechanism30is in a common plane with the contact surface with the wafer22of the pressing pad43. Then, the attracting member31and the pressing pad43are lowered as shown inFIG. 1Buntil the attracting member31comes in contact with the thin portion of the wafer22and the pressing pad43is pushed against the ring-shaped stiffening portion of the wafer22and elastically deformed. The attracting member31and the pressing pad43in the above description are simultaneously lowered. However, another procedure is also possible in which one of the two members is lowered in advance and the other follows.

FIG. 4Ashows the pressure exerted on the wafer22placed on the attachment plate12of the chuck table10;FIG. 4Bshows the pressure exerted on the wafer22from the attracting member31; andFIG. 4Cshows the pressure exerted on the wafer22by the pressing pad43.

The state illustrated inFIG. 1Bis the one at the time t1inFIGS. 4A,4B, and4C. A negative pressure has been supplied to the surface of the attachment plate12of the chuck table10as shown inFIG. 4A. The attracting member31has been lowered from the position inFIG. 1Aand reached the position of the wafer22but does not yet supply negative pressure for attracting the wafer22as shown inFIG. 4B. The pressing pad43, after reaching the ring-shaped stiffening portion of the wafer22, is further pushed down with elastic deformation of the pressing pad itself until the time t1at which the pressure on the ring-shaped stiffening portion attains a predetermined value.

Then, the procedure advances to the state shown inFIG. 2A. In the state ofFIG. 2A, the supply of negative pressure through the supply and exhaust path11has been stopped, and supply of positive pressure (indicated by the symbol70) starts on the surface of the attachment plate12of the chuck table10from a positive pressure supplying system (not depicted) in order to facilitate removal of the wafer22from the chuck table10. The positive pressure is given by supplying water, air, or a mixture of water and air through the supply and exhaust path11and attains a predetermined value at the time t2.

Since the ring-shaped stiffening portion including the vicinity thereof is pushed toward the attachment plate12of the chuck table10by the pressing pad43, blowing out of water, air, or a mixture of water and air through the attachment plate12is suppressed to prevent the peripheral region from locally floating up like shown inFIG. 15C. Since the local floating up does not occur, no stress concentration takes place at the places of remaining damages generated in the grinding step or the places of varying curvature. Thus, the wafer22does not suffer from any breakage such as cracks upon application of the positive pressure on the surface of the attachment plate12.

The application of positive pressure70is stopped at the time t3after continued application for a predetermined period of time.

Then, the procedure advances to the state shown inFIG. 2B. After stopping the application of positive pressure70, the pressing pad sliding member41alone is elevated at the time t4. The support member32as well as the attracting member31does not move. The pressure exerted by the pressing pad43decreases in the process of elevating the pressing pad sliding member41and eventually becomes null when the pressing pad43departs from the ring-shaped stiffening portion of the wafer22.

Subsequently at the time t5, the attracting member31is supplied with a negative pressure through the exhausting path (not depicted) in the support member32to attract the thin portion of the wafer22.

At this moment of t5, as explained previously with reference toFIG. 2A, adhesion between the wafer22and the attachment plate12has been released by application of positive pressure70in the period from t2to t3. Therefore, after attracting the wafer22by the attracting member31, the wafer22can easily be picked up from the chuck table10by elevating the attracting member31as shown inFIG. 3A. The attracting member31is elevated by elevating the support member32to which the attracting member31is fixed.

Subsequently, the transport device40is moved in the horizontal direction with the attracting member31attracting the wafer22as shown inFIG. 3B.

The embodiment described above allows the adhesion of the wafer22on the chuck table10to be quickly released. The time duration from t2to t3inFIGS. 4A,4B, and4C is about three seconds, for example, whereas it took conventionally about ten minutes for the adhesion to be released naturally (without adding any action for fast release) in order to avoid any damage on the wafer. Thus, substantial reduction of time has been achieved. The wafer is picked up without any damage and transferred to the next step.

FIGS. 5A and 5Bshow essential part of the transport device40, in whichFIG. 5Ais a sectional view andFIG. 5Bis a perspective view. The attracting member31is fixed to the support member32. The support member32includes an exhaust path for supplying negative pressure at the surface of the attracting member31from a vacuum system (not depicted). The pressing pad sliding member41is disposed around the support member32so as to vertically move independently of the support member32. The pressing pad sliding member41is driven vertically by the power from a driving system (not depicted).FIGS. 5A and 5Bshow the state in which the pressing pad sliding member41has been elevated to such a position that the contact plane of the pressing pad43to the wafer22is higher than the attracting surface of the attracting member31. The support member32and the pressing pad sliding member41are constructed coaxially, and the transport device40moves as a monolithic body combining the attracting member31and the pressing pad43in the vertical movement above the wafer22and the chuck table10and in the horizontal movement from a position above the chuck table10to a horizontally different position.

FIGS. 5A and 5Bshows a pressing pad support plate44. Although the construction can be used in which the pressing pad43is directly supported by the pressing pad support arm42as shown inFIGS. 1A through 3B, another construction can also be employed in which the pressing pad43is fixed to the pressing pad support plate44that is fixed to the pressing pad support arm42as shown inFIGS. 5A and 5B. The pressing pad support plate44has a configuration that does not obstruct vertical movement of the pressing pad43due to the attracting member31and is an annular disk, for example, as shown inFIG. 5B. The use of the pressing pad support plate44for supporting the pressing pad43securely holds the pressing pad43made of an elastic material such as a foamed resin and applies uniform pressure on the wafer22.

FIGS. 6A and 6Bshows a modification in the first embodiment according to the invention.

In the device ofFIG. 6A, the pressing pad43made of an elastic material provided in the transport device40shown inFIG. 1Ais replaced by a pressing member45made of a material less deformable elastically. The pressing member45can be made of an engineering plastic such as polycarbonate, polyamide, etc.

The pressing member45, being made of an elastically less deformable material, does not deform following the shape of the ring-shaped stiffening portion. However, the ring-shaped stiffening portion, being pushed toward the chuck table by the pressing member45, does not locally float up by blowing up of water, air, or a mixture of water and air through the attachment plate12like in a configuration shown inFIG. 15C.

The pressing member45, having certain rigidity by itself, can be readily attached to the pressing pad support arm42.

In the device ofFIG. 6B, the pressing pad43made of an elastic material provided in the transport device40shown inFIG. 1Ais replaced by a hollow pressing tube47. The pressing tube47is a ring-shaped tube made of an elastic material such as rubber containing air or the like in the hollow thereof. Like the pressing pad43shown inFIG. 1B, the pressing tube47elastically deforms upon pressing against the ring-shaped stiffening portion following the shape of the stiffening portion as shown inFIG. 6B.

The pressing tube47is attached, with air or the like filling the hollow thereof, to the pressing pad support arm42. Alternatively, the pressing tube47can be attached to, in place of the pressing pad support arm42, a pressing tube support arm46provided with a supply and exhaust path to the pressing tube47.

The ring-shaped stiffening portion, being pushed toward the chuck table by the pressing tube47, does not locally float up by blowing up of water, air, or a mixture of water and air through the attachment plate12like in a configuration shown inFIG. 15C.

The use of the pressing tube support arm46controls the pressure in the tube, thereby adjusting degree of deformation of the tube following the configuration of the stiffening portion and the pushing force on the stiffening portion.

The second embodiment according to the present invention will be described in the following with reference toFIGS. 7A,7B,FIGS. 8A,8B,FIGS. 9A,9B, andFIGS. 10A,10B, and10C.

FIGS. 7A,7B,FIGS. 8A,8B,FIGS. 9A,9B, andFIGS. 10A,10B, and10C illustrate the second aspect of embodiment according to the present invention. Of these figures,FIGS. 10A,10B, and10C are timing charts showing pressure at some parts in the device of the embodiment.

FIG. 7Ashows a wafer22attached by suction on the surfaces of attachment plates13and14of a chuck table10. The attachment plates13and14are made of a porous material and have a surface machined to be flat for attaching the wafer22. The attachment plate13to attach the outer peripheral portion of the wafer22is made of a relatively high density porous material and has a structure that effectively transmits a negative pressure from a supply and exhaust path11to the attracted surface of the wafer22. Because of the relatively high density porous material, the attachment plate13performs just minimum leakage of atmosphere to the supply and exhaust path11for vacuum suction even though the outer peripheral part of the attachment plate13, the outer peripheral part being not covered with and not in contact with the wafer22, is exposed to the atmosphere.

The attachment plate14to attach by suction the central portion of the wafer22is made of a relatively low density porous material and has a structure that effectively transmits a negative pressure from a supply and exhaust path11to the attracted surface of the wafer22.

The chuck table10is connected to a vacuum system (not depicted) through the supply and exhaust path11. A negative pressure (indicated by the symbol60) supplied by the vacuum system is transmitted to the surface of the attachment plates13and14and attracts the wafer22through vacuum suction.FIG. 7Ashows the wafer22after completion of a grinding step as illustrated inFIGS. 12A through 12D,FIGS. 13A,13B, andFIGS. 14A,14B, and14C.

The following describes a procedure of transferring the wafer22to the next step according to the sequence of the procedure.

FIG. 7Ashows a transport device50that is standing by above the wafer22after completion of the grinding step. The transport device50comprises: a holding member52which is a holding mechanism for holding the ring-shaped stiffening portion of the wafer22at the outermost peripheral portion thereof; a support arm51for supporting the holding member52; a pressing pad54which is a inner region pressing mechanism for pressing the thin portion of the wafer22and vertically moves independently of the holding member52; and a support member53for supporting the pressing pad54. The pressing pad54presses the thin central portion (inner region) of the wafer22. The pressing pad54in this embodiment example is made of an elastic material. A material for the pressing pad54, although not limited to an elastic material, preferably exhibits such elastic deformability that follows the configuration of the ring-shaped stiffening portion of the wafer22and such rigidity that withstands blowing up of air or the like through the attachment plates13and14, the blowing up being described afterwards. The favorable materials include formed resin such as EVA resin and silicone rubber.

The pressing pad54has a shape of a disk covering the thin recessed portion and the inside portion of the ring-shaped stiffening portion. The pressing pad54has a dimension that is a little larger than that of the thin recessed portion and able to cover the inside portion of the ring-shaped stiffening portion. The diameter of the pressing pad54is preferably about 1 mm larger than that of the inner circumferential edge of the ring-shaped stiffening portion. The dimension of the pressing pad54covers the stepped part at the inner circumferential end of the ring-shaped stiffening portion without failure irrespective of some positional deviation of the pressing pad54. The pressing pad54preferably covers the outer side wall of the thin recessed portion (or the inner circumferential side wall of the ring-shaped stiffening portion). However, the pressing pad54that presses at least the thin recessed portion can suppress the local floating up as shown inFIG. 16B.

In addition, in the case the wafer22, like the one illustrated inFIG. 7A, has been ground through two stages as illustrated inFIGS. 14A,14B, and14C, the pressing pad54preferably covers the step part generated in the second grinding step.

The holding member52stands by at the position outer than the outer periphery of the wafer22as shown inFIG. 7Aand is vertically movable independently of the pressing pad54fixed to the support member53. The pressing pad54stands by above the wafer22in the example shown inFIG. 7A.

Then, the holding member52and the pressing pad54are lowered as shown inFIG. 7Buntil the pressing pad54comes in contact with the thin recessed portion of the wafer22and presses the wafer22with elastic deformation of the pressing pad54. The holding member52and the pressing pad54in the above description are simultaneously lowered. However, another procedure is possible as well in which one of the two members is lowered in advance and the other follows.

FIG. 10Ashows the pressure exerted on the wafer22put on the surface of the attachment plate of the chuck table10.FIG. 10Bshows the force exerted by the holding member52to hold the wafer22at the outer peripheral part thereof (which is the ring-shaped stiffening portion).FIG. 10Cshows the pressure exerted on the wafer22by the pressing pad54.

The state illustrated inFIG. 7Bis the one at the time t1inFIGS. 10A,10B, and10C. A negative pressure is supplied to the surface of the attachment plates13and14of the chuck table10as shown inFIG. 10A. The holding member52has been lowered from the position inFIG. 7Aand arrived at the same level as of the wafer22but has not yet moved to the position of holding the wafer22. The pressing pad54, after reaching the thinned recessed portion of the wafer22, is further pushed down with elastic deformation of the pressing pad itself until the time t1at which the pressing pad54presses the thin recessed portion and a part of the ring-shaped stiffening portion with a predetermined pressure.

Then, the procedure advances to the state shown inFIG. 8A. In the state ofFIG. 8A, the holding member52approaches the wafer22from the outside of the wafer and holds the ring-shaped stiffening portion. The holding member52in this example has a construction to hold both the upper and lower surfaces of the ring-shaped stiffening portion as shown inFIG. 8A. Holding the upper surface of the ring-shaped stiffening portion suppresses floating up of the outer peripheral portion of the wafer22due to blowing up of water, air, and the like. Holding the lower surface of the ring-shaped stiffening portion facilitates picking up of the wafer22in a later step.

Then, the supply of the negative pressure through the supply and exhaust path11is stopped, and supply of positive pressure (indicated by the symbol70) starts on the surface of the attachment plates13and14of the chuck table10at the time t2indicated inFIGS. 10A,10B, and10C in order to facilitate removal of the wafer22from the chuck table10. The positive pressure is given by supplying water, air, or a mixture of water and air through the supply and exhaust path11.

In this state, the pressing pad54presses the thin recessed portion, the boundary region between the thin recessed portion and the ring-shaped stiffening portion, and a part of the ring-shaped stiffening portion of the wafer22toward the chuck table10. Therefore, blowing out of water, air, or a mixture of water and air through the attachment plates13and14is suppressed to avoid the local floating up as shown inFIG. 16B. Since the local floating up does not occur, no stress concentration takes place at the places of remaining damages generated in the grinding step or the places of varying curvature. Thus, the wafer22does not suffer from any breakage such as cracks upon application of the positive pressure on the surface of the attachment plates13and14. After applying the positive pressure70for a predetermined period of time, the application of the positive pressure70is stopped at the time t3indicated inFIGS. 10A,10B, and10C.

Then, the procedure advances to the state shown inFIG. 8B. After stopping the application of the positive pressure70, the pressing pad54alone is elevated at the time t4indicated inFIGS. 10A,10B, and10C. The holding member52is not moved. The pressure exerted by the pressing pad54decreases in the process of elevating the pressing pad54and ultimately becomes null when the pressing pad54departs from the wafer22.

In this process, the adhesion of the wafer22onto the attachment plates13and14has been released by the application of the positive pressure70on the attachment plates13and14during the period from the time t2to the time t3. The outer peripheral portion (or the ring-shaped stiffening portion) of the wafer22is held by the holding member52. Consequently, in the next step, the wafer can be readily picked up from the chuck table10by elevating the holding member52as shown inFIG. 9A. The holding member52is elevated together with the support member53that fixes the pressing pad54. Accordingly, the pressing pad54does not become in contact with the wafer22.

Subsequently, the transport device50starts to move horizontally with the holding member52holding the outer peripheral portion (or the ring-shaped stiffening portion) of the wafer22as shown inFIG. 9B.

The embodiment described above allows the adhesion of the wafer22onto the chuck table10to be quickly released. The time duration from t2to t3inFIGS. 10A,10B, and10C is about three seconds, for example, whereas it took conventionally about ten seconds for the adhesion to be released naturally (without adding any action for fast release) in order to avoid any damage on the wafer. Thus, substantial reduction of time has been achieved. The wafer is picked up without any damage and transferred to the next step.

Although not shown in the figures, the pressing pad54illustrated inFIG. 7Acan be fixed to a pressing pad support plate that is additionally provided like in the construction illustrated inFIGS. 5A and 5B. The pressing pad support plate has a configuration that does not interfere with vertical movement of the pressing pad54due to the holding member52. The use of the pressing pad support plate for supporting the pressing pad54securely holds the pressing pad54made of an elastic material such as a foamed resin and applies uniform pressure on the wafer22.

FIGS. 11A and 11Bshows a modification in the second embodiment according to the invention.

In the device ofFIG. 11A, the pressing pad54made of an elastic material provided in the transport device50shown inFIG. 7Ais replaced by a pressing member55made of a material less deformable elastically. The pressing member55can be made of an engineering plastic such as polycarbonate, polyamide, etc.

The pressing member55is made in contact solely with the thin recessed portion of the wafer22. This is because the pressing member55, being made of an elastically less deformable material, does not deform following the shape of the ring-shaped stiffening portion. However, the thin recessed portion of the wafer22, being pushed toward the chuck table10by the pressing member55, does not locally float up by blowing up of water, air, or a mixture of water and air through the attachment plate14like in a configuration shown inFIG. 16B.

The pressing member55, having certain rigidity by itself, can be readily attached to the support member53.

In the device ofFIG. 11B, the pressing pad54made of an elastic material provided in the transport device50shown inFIG. 7Ais replaced by a hollow pressing balloon57. The pressing balloon57is a balloon made of an elastic material such as rubber containing air or the like in the balloon. Like the pressing pad54shown inFIG. 7B, the pressing balloon57elastically deforms upon pressing against the ring-shaped stiffening portion following the shape of the stiffening portion as shown inFIG. 11B.

The pressing balloon57is attached, with air or the like filling the interior thereof, to the support member53. Alternatively, the pressing balloon57can be attached to, in place of the pressing member53, a pressing balloon support member56provided with a supply and exhaust path to the pressing balloon57.

The thin recessed portion and the inside of the ring-shaped stiffening portion of the wafer22, being pushed toward the chuck table by the pressing balloon57, does not locally float up due to blowing up of water, air, or a mixture of water and air through the attachment plates13and14like in a configuration shown inFIG. 16B.

The use of the pressing balloon support member56controls the pressure in the balloon, thereby adjusting degree of deformation of the balloon following the configuration of the stiffening portion and the pushing force on the stiffening portion.

Examples of specific embodiments are illustrated in the accompanying drawings. While the invention is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the above description, specific details are set forth in order to provide a thorough understanding of embodiments of the invention. Embodiments of the invention may be practiced without some or all of these specific details. Further, portions of different embodiments and/or drawings can be combined, as would be understood by one of skill in the art.

This application is based on, and claims priority to, Japanese Patent Application No. 2011-054332, filed on Mar. 11, 2011. The disclosure of the priority application, in its entirety, including the drawings, claims, and the specification thereof, is incorporated herein by reference.