USP_6887801 (1063233), страница 4
Текст из файла (страница 4)
The through holes 36may be placed, at least on the bottom of the holder 30, tocorrespond to a design of channels and/or holes on theprovided along the periphery of the pocket 32 such that theWafer may be inserted With the primary or secondary ?ataligned to pass by the tabs. The Wafer can then be rotated,and pressure may be applied to at least one ?at, alloWing the15through holes 36. Often, once photoresist is applied on theWafer, the Wafer Will be held in place in part by the typicallysticky photoresist after spinning is completed, and so Whentabs to hold the Wafer While the ?ats assure a desiredFor the illustrative embodiment, a receiving primary ?at40 is provided to de?ne a part of the border of the pocket 32.An outer primary ?at 42 is de?ned on an edge of the Waferholder 30 so the outer primary ?at 42 aligns With thethe vacuum force is removed the Wafer stays in place.In other uses, vacuum pressure may be applied to hold aWafer in place and the through holes 36 and/or the channel34 may be plugged to maintain suction.
The step of plugging25holder into a semi-liquid material, or by placing a cap orother device over the back of the holder. A thin plasticadhesive layer (i.e. a specially designed tape) may also beapplied.the structure of many types of Wafers including, forexample, a P-type (111) Si Wafer), a secondary ?at may beprovided as needed for any Wafer design. For example, usingSi terminology to keep discussion simple and short, a WaferFIG. 3 is a cross sectional vieW taken along line 3—3 ofFIG. 2. As illustrated in FIG.
3, the pocket 32 includes achannel 34 as Well as through holes 36. The pocket 32 hasa height 44. The height 44 may be of any desired siZe. In onethe through holes 36 may be performed in a vacuumenvironment by dipping a portion of the back side of theillustrated having only a primary ?at plane (corresponding toholding apparatus having a secondary ?at at an angle of 45degrees to the primary ?at could be used for an n-type (111)Wafer, an angle of 90 degrees for a p-type (100) Wafer, or anangle of 135 degrees for an n-type (100) Wafer. If desired,the ?at may be omitted, for example, for additive or surfaceprocesses or Where speci?c alignment of the crystallineorientation of the underlying Wafer is not needed.rotatable surface of a spinning apparatus.
The loWer portionof the Wafer holder 30 may also include channels or otherdesigns that facilitate passage of vacuum force to thecrystalline alignment.receiving primary ?at 40. AWafer received in the pocket 32can be treated by processing apparatuses designed for alarger Wafer in a Way that accounts for the crystallineorientation of the Wafer.While the Wafer holding apparatus 30 of FIG. 2 isFor example, many conventional spinning apparatusesinclude channels and/or through holes Which apply suctionBy securing a Wafer in a holder such as holder 30, the35present invention may provide added safety in Wafer processing. For example, many Wafers are quite fragile and theuse of a holder may improve durability during processing.Also, given the caustic chemicals often in use, a personWorking in a lab is often required to Wear gloves, making thehandling of a Wafer dif?cult.
The added bulk of the holder30 makes handling easier. Further, in particular With thinned40Wafers, the Wafers themselves tend to be brittle and the useof a holder may prevent accidental breakage during handling. In some embodiments, the use of suction applied tothe back side of a Wafer may also improve surfaceproperties, in particular, reducing curvature caused by dif45ferences in the coef?cient of thermal expansion of layers ofillustrative embodiment, the height 44 is chosen to be equala Wafer.to the thickness of a Wafer that is to be held in the pocket 32.The height 44 may also be chosen to be greater or less thanillustrating various features. The Working embodimentFIG.
4 is a cross sectional vieW of a Working embodimentthe Wafer thickness. In another example, the height 44 isequal to the thickness of a Wafer plus some fraction of thedesired thickness of a photoresist layer to be deposited onthe Wafer.The pocket 32 also has a Width 46 Which may correspondto the siZe of a Wafer to be received by the pocket 32. Theholder 30 may have an overall Width 48 that is chosen toholder 50 Was constructed using aluminum.
The holder 50includes a pocket 52 having a depth 54 of 333 pm. Severalthrough holes 56 are in ?uid communication With severalchannels 58 de?ned in the bottom of the pocket 52. Thepocket 52 has a Width 60 of 3.005 inches (76.33 mm), While55the holder 50 has a Width 62 of 3.937 inches (100Anextra circumferential groove 66 is included in the pocket 52.correspond to a knoWn Wafer siZe, although any appropriateThe groove 66 serves several purposes as noted beloW.siZe may be selected. In one example, the pocket 32 has aWidth 46 corresponding to a 3-inch Wafer, and the holder 30has a Width 48 corresponding to the siZe of a 4-inch Wafer.Other combinations may of course be used With 3, 4, 6, 8 or12 inch Wafers, for example, or any other siZe.The holder 30 may be made of any material including aFor the Working embodiment, the holder 50 Was used toillustrate an improved photoresist layer that is spun With aWafer in the holder 50.
The result of this step is illustratedby FIG. 5, Which is a cross sectional vieW of the Workingembodiment from FIG. 4 With a Wafer inserted in the pocketand photoresist spun on the surface. AWafer 68 is placed inthe pocket 52, and vacuum suction Was applied by the spinapparatus through the through holes 56.
There is a gapbetWeen the edge of the Wafer 68 and the Wall of the pocket52 Which alloWs for easier removal of the Wafer 68 from thepocket 52, but Which also alloWs some photoresist 70 to seepvariety of metals, plastics, ceramics, glass, or crystallinematerials. Some illustrative considerations in choosing thematerial for the holder may include the compatibility of thematerial With selected processes to be performed on a Waferheld in the holder 30, cost of the material, or ability to form65US 6,887,801 B2652.
The method of claim 1 Wherein the spinning step isaround the Wafer 68. Then an amount of photoresist Wasplaced on the Wafer 68, and the Wafer With the holder 50 Wasperformed such that the spinning distributes the photoresistonto both the Wafer and the Wafer receiving apparatus.3. The method of claim 1 Wherein the depth of therecessed portion is selected to ?atten the photoresist pro?lespun to spread the photoresist.
It should be noted again thatthe ?gures are not necessarily to scale.After spinning, a layer of photoresist 70 is deposited overon the Wafer.the surface of the Wafer 68 as Well as the Wafer holder 50.It can be seen that the edge bead of the photoresist 70 isactually over the Wafer holder 50, and not the Wafer 68 itself.Some of the photoresist 70 seeps beneath the Wafer 68 intothe groove 66. The groove 66 helps prevent any of the4. The method of claim 3 Wherein the depth of therecessed portion is substantially equal to the thickness of the10photoresist 70 from reaching the channel 58 and throughhole 56. After a pre-bake of the photoresist 70, and beforeexposure, the edge bead on the photoresist 70 is cleaned offapplied Within the recessed portion.6.
The method of claim 5 further comprising:With acetone, alloWing for effective use of a contact mask forlithography. After eXposure, the Wafer holder 50, Wafer 68and photoresist 70 are subjected to development, during15applying a vacuum force via the channel after the Waferis placed, the vacuum force being applied such that theWafer is held in place in the recessed portion.7. A method of reducing edge bead thickness Whileapplying photoresist to a Wafer comprising:providing a Wafer receiving apparatus for receiving aWafer of a ?rst siZe, the Wafer receiving apparatusincluding a pocket having a depth, Wherein the depth isWhich an amount of alcohol or acetone (depending on Whatis used) seeps into the groove 66, dissolving and removingthe photoresist 70.
When placed on a hot-plate, the alcoholor acetone that seeped into the groove 66 boils andevaporates, eXpanding greatly, and causes the Wafer 68 topop out of the pocket 52, making the step of removing theWafer 68 from the pocket 52 very simple, easy and clean.chosen to correspond to a Wafer of the ?rst siZe;placing a Wafer of the ?rst siZe in the pocket of the WaferFIG. 6 is a graph representing the pro?le of a thickphotoresist layer applied using a Working embodiment of thepresent invention. Again, the dashed lines illustrate acceptable bounds for the photoresist layer.
The acceptable regionWafer.5. The method of claim 1 Wherein the Wafer receivingapparatus further includes a channel coupled to the recessedportion, the channel adapted to alloW a vacuum force to be25receiving apparatus;applying photoresist to the Wafer;spinning the Wafer and the Wafer receiving apparatus80 eXtends over a greater area of the Wafer. The result of theWhile the Wafer is placed in the pocket to create aWorking embodiment is that slightly more than 2 inches ofthe diameter of the three inch Wafer is noW usable, providinga yield of about 44% of the area of the Wafer, nearly doublethat for the three inch Wafer by itself as illustrated in FIG.photoresist layer of a desired thickness; andWherein the Wafer receiving apparatus is siZed to becompatible With machines adapted for use With Wafers1.
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