Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
  • H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
  • H01L21/6838—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping with gripping and holding devices using a vacuum; Bernoulli devices

Definitions

• the invention relates to a device and a method for holding objects, in particular semiconductor wafers.
• the semiconductor wafers are repeatedly subjected to deposition processes in which the wafers are coated on both sides. Since the build-up of several different layers on the back of the wafer is undesirable and can lead to impairments of other processes, back-side etching steps are carried out in the course of the entire production process. This is usually done by coating the entire surface of the front, and then removing the corresponding layer on the back of the wafer, either wet or dry, using the CDE method (chemical downstream etch method, microwave plasma or RF plasma). Then the coating on the front of the wafer has to be stripped again.
• CDE method chemical downstream etch method, microwave plasma or RF plasma
• the wafer wafers which are already largely structured, are also used the structured top quickly turned downwards on a rotating air cushion, while a wet chemical etching solution flows from above onto the back of the pane.
• the rapid rotation of the wafer has the consequence that the chemicals are thrown outwards over the edge of the rear of the wafer and thus cannot attack the structured front of the wafer.
• the front of the window is no longer protected by coating the front of the window as before, but by means of a neutral gas.
• the sealing of the front of the pane in a vacuum against the reactive process gas is achieved via an orifice 50 (see FIG. 6) with a fine, defined adjustable gap (gap) 52 near the pane edge 53, which without touching the pane front 55 via an indirect Stop 58 is adjusted.
• the neutral gas that flows through this gap 52 is let into the space between the aperture 50 and the front of the pane, with a slight overpressure to the outside into the reaction space and thereby prevents the reactants from penetrating to the front of the pane.
• the disk lies on at least 3 tips during the etching.
• German Offenlegungsschrift 195 02 777 AI has the disadvantage that the layer to be removed on the rear side of the pane at the points 56 where the silicon wafer lies on cannot be removed at the same speed as in the other places, since that Etching gas cannot reach the support points directly. A longer overetch (> 50%) is required to free the support from the layer to be etched. This is not a problem as long as the stop layer, which lies under the layer to be removed, is thick enough (e.g. 50 n for 6 "wafers) and the selectivity of the etching gas is sufficient.
• stop layers which usually consist of silicon oxide
• the stop layers are only 8 nm thick, a sufficiently long overetching time is no longer possible even with good selectivity of the etching gas in order to clear the locations at the contact points.
• the silicon wafer can bend due to the overpressure on its top, which leads to a gap widening at some edge points, through which etching gas can penetrate to the top of the wafer.
• a device for holding and protecting objects which has a base, walls arranged on the base and defining an outer region and an inner region, at least one feed to the outer region, at least one feed to the inner region and means has in order to generate an overpressure in relation to an ambient pressure in the outer region (via the feed).
• a method for holding and protecting an object in which an overpressure is generated over an outer area of the surface of the object with a protective gas relative to the ambient pressure and a negative pressure is generated over an inner area of the surface of the object with respect to the ambient pressure , whereby part of the protective gas is passed over the edge of the surface of the object.
• a vacuum it is not necessary for a vacuum to be generated over the inner region of the surface of the object.
• the inner region of the surface of the object can be subjected to a lower overpressure than the outer region of the surface of the object or with ambient pressure.
• a negative pressure can also be set in this case over the inner region of the surface of the object.
• the excess pressure generated in the outer region of the device above the outer region of the surface of the object protects this surface from aggressive gases, while the negative pressure generated in the inner region of the device above the inner region of the surface of the object or a lateral holder holds the object against the Device holds.
• the possibly already structured front side of the semiconductor wafer is protected from the aggressive etching gases.
• a lacquering of the front side of the semiconductor wafer is no longer necessary, as a result of which some process steps in conventional processes such as protective lacquering, 0 2 plasma lacquer removal and a wet chemical post-cleaning of the front side of the semiconductor wafer can be avoided. This leads to increased throughput and considerable savings in the chemicals and costs required.
• means are preferably provided in order to generate a negative pressure in relation to an ambient pressure in the inner region (via the feed).
• the base is preferably designed as a flat cover plate.
• the base is disc-shaped.
• the base and the walls are in one piece, preferably made of aluminum.
• the outer area of the device completely surrounds the inner area of the device.
• spacers preferably punctiform spacers, in particular sapphire balls, are evenly distributed over the circumference (eg 6 pieces) at the distal end of the outer wall. These spacers not only prevent the sensitive sections on the front of a semiconductor wafer from coming into flat contact with the device for holding, but also prevent the semiconductor wafer from moving laterally relative to the device due to frictional forces. It is further preferred if projections are provided on the outer wall, which can serve as indirect stops for a wafer transport mechanism within an etching chamber.
• the outer area is divided into several sectors, each of which has a feed for building up excess pressure. This can prevent the object from tipping over, since each sector now keeps the object at a distance.
• the distance which is automatically and self-adjusted, is only influenced by the set inert gas flow and the net force (which can be set via the pressure difference).
• the means for generating an overpressure in the outer region have a gas reservoir, which is preferably connected directly to the feeds to the outer region.
• the feeds are dimensioned such that, during use of the device, the pressure drop along a feed is greater than the pressure difference between the overpressure m in the outer region and the ambient pressure.
• the gas flow which is proportional to this pressure difference, remains constant; ie the gas reservoir acts as a source with a constant gas flow for any number of sectors.
• the pressure drop along a feed is preferably more than 2 times, in particular more than 10 times, greater than the pressure difference between the excess pressure in the outer region and the ambient pressure.
• lateral spacers are provided on the outer wall or on the projections.
• nitrogen, oxygen, a noble gas or mixtures thereof are used as the protective gas.
• the process gas used for the etching can also be used if it is not excited.
• FIG. 1 is a schematic sectional view of an embodiment of the device according to the invention.
• FIG. 2 shows a schematic sectional view of a further embodiment of the device according to the invention
• FIG. 3 shows a schematic top view of a further embodiment of the device according to the invention.
• Fig. 6 is a schematic representation of a method for backside etching according to the prior art.
• the device 10 according to the invention has a disk-shaped cover plate 11 (base), from which two annular walls 12 and 13 extend. These walls 12 and 13 define an annular outer region 14 and a circular inner region 15.
• the inner wall 13 is approximately twice as thick as the outer wall 12.
• Two openings (feeds) 16 and 17 are provided in the cover plate 11. The opening 16 extends from the top of the cover plate 11 to the annular outer region 14 and the opening 17 extends from the top of the cover plate 11 to the circular inner region 15
• Protrusions 18 are provided on the outside of the wall 12 and serve as indirect stops.
• the silicon wafer 20 is arranged parallel to the cover plate 11 at the distal end of the walls 12 and 13. As a result, an outer gap 21 is formed between the outer wall 12 and the front of the silicon wafer 20 and an inner gap 23 between the inner wall 13 and the front of the silicon wafer.
• the inner gap 23 is approximately twice as high as the outer gap 21.
• sapphire balls (not shown), which extend uniformly over the circumference and extend into the outer gap 21 and are provided at the distal end of the outer wall 126 touch the surface of the silicon wafer 20 selectively.
• FIG. 1 shows a transport mechanism 30 through which the silicon wafer 20 can be guided to the device 10 according to the invention.
• the reactive particles of the etching gas excited by a plasma will reach the back of the silicon wafer 20 from below. They can then be sucked off together with the etched products through an opening m in the etching chamber wall (not shown).
• a non-caustic neutral gas For example, nitrogen, oxygen, argon, but also the non-excited etching gas itself, for example CF 4 or NF 3 , can be used
• the gas inlet system 44 (see FIG. 4) for the protective gas thus forms the means for generating an overpressure in the outer region 14 via the feed 16 in relation to the ambient pressure in the etching chamber.
• the inner wall 13 separates this outer area 14 from the inner area 15 above the silicon wafer 20, so that a significantly lower pressure can be set here.
• the vacuum pump 45 used for protective gas thus forms the means for generating a negative pressure in relation to an ambient pressure in the inner region 15 via the feed 17.
• the inner wall 13 Silicon wafer excluded by the inner wall 13. However, since the inner wall 13 is wider than the outer wall 12, the outflow of protective gas to the pumped inner region 15 is limited. If the outer wall is 2 mm wide, the inner wall 13 is spaced about 3 mm, set back 0.1 mm and 4 mm wide. With a set outer gap 21 of 0.1 mm on the outer wall 12, the inner wall 13 would then have an inner gap 22 of 0.2 mm and approximately the same amount of protective gas would flow through both gaps.
• the overpressure required for sealing then generates only a correspondingly small force on the small annular surface on the front side of the silicon wafer 20 below the outer region 14 in relation to the total surface of the silicon wafer 20.
• this would only be about 100 g downward load.
• the disc weight of about 54 g.
• a working pressure p 1 of 400 mTorr in the etching chamber would already be sufficient to compensate for this force, provided the inner area 15 of the device 10 is evacuated.
• a normal working pressure in the chamber of 800 mTorr would push the silicon wafer 20 upwards with about 150 g.
• the silicon wafer will touch the outer wall 12 at one point, but a larger outer gap 21 will appear opposite.
• the bulk of the protective gas will then escape there; ie the silicon wafer 20 becomes slightly oblique in contact or flutter.
• This can be prevented by dividing the outer area 14 into several sectors of the same size (for example 6), each separately receiving an equally large flow of protective gas. This keeps each sector at a distance, the disc can no longer tilt and hit one side at the top.
• the distance which is automatically and self-adjusted, is only influenced by the set inert gas flow and the (adjustable) net force upwards. Since the disc is now completely non-contact, it will swim away to the side if there is no side limitation whatsoever.
• FIG. 2 therefore shows a schematic sectional view of a further embodiment of the device according to the invention.
• the elements that have already been shown in FIG. 1 are identified by the reference symbols used in FIG. 1.
• spacers 25 are provided on the projection 18 in the embodiment according to FIG.
• the sapphire balls in the outer columns are dispensed with in this embodiment.
• the outer region 14 of the device is divided circumferentially into six chambers (not shown), each of the six chambers having its own opening 16 (see FIG. 4) in the cover plate 11.
• the chambers make it possible to generate almost the same overpressure over the entire circumference of the device 10, even if the silicon wafer 20, now floating completely freely, moves relative to the device. Too much lateral movement of the
• spacers 25 are provided, which limit this lateral movement.
• FIG. 3 shows a schematic sectional view of a further embodiment of the device according to the invention. Like the device shown in Fig. 2 is also in this device the outer region 14 is divided into a plurality of sectors (chambers, not shown), each of which has its own feed 42.
• a gas reservoir 40 is created in a cavity of the device 10 and is supplied with the protective gas via a feed 41 in such a way that a constant excess pressure is maintained in relation to the ambient pressure.
• feeds 42 eg bores, tubes; length 50 mm, cross section 1 mm 2
• the feeds 42 are selected in a geometry so that they deliberately oppose the gas flow with a high resistance. In order to obtain a sufficiently high gas flow for the individual sector, the pressure in the gas reservoir p 4 must be set accordingly high.
• FIG. 4 shows a schematic sectional view of a further embodiment of the device according to the invention.
• the elements that have already been shown in FIG. 1 are identified by the reference symbols used in FIG. 1.
• the holding pins 31 which are connected to the outer wall 12 by means of springs 32.
• the holding pins 31 are brought into contact with the edge of the silicon wafer 20 by a movement mechanism 35.
• the holding pins 31 engage with the edge of the silicon wafer 20 and thus exert an additional holding force on the silicon wafer 20.
• a pressure p 3 can be set in the inner region 15 of the device, which alone is not would be sufficient to carry the silicon wafer 20.
• the holding pins 31 can prevent the silicon wafer 20 from touching the outer wall 12 if the pressure p 3 is chosen too low. Accordingly, the pressure p 3 in the inner region 15 can be set so that bending of the silicon wafer 20 is prevented.
• 5a to 5c show a schematic representation of the process by which the silicon wafer 20 is gripped with a device 10 according to the invention.
• the silicon wafer 20 is brought into the etching chamber by a wafer handling system (not shown) and placed on the transport mechanism 30.
• the silicon wafer is carried by at least three pins (Fig. 5a).
• the transport mechanism 30 now lifts the silicon wafer 20 in the direction of the device 10 until a part of the transport mechanism 30 comes into contact with the projections 18 (FIG. 5b).
• protective gas is already let into the outer area 14 of the device 10 and protective gas is pumped out of the inner area 15 of the device 10.
• the movement mechanism 35 brings the holding pins 31 into engagement with the edge of the silicon wafer 20, as a result of which the silicon wafer 20 is held by the device 10 (FIG. 5c).
• the pins of the transport mechanism 30 can now be moved back, so that the back of the silicon wafer is now completely free. This results in the situation shown in FIG. 4.
• the devices according to the invention thus make it possible to etch the back of a silicon wafer without coating the front.
• the back of the pane is not touched during the etching, long overetching is no longer necessary. This means that processes with very high changes, for example in the case of extremely thin stop layers.
• the device according to the invention can also be used for processes other than the backside etching.
• the device according to the invention can also be used in vacuum transport systems in which one wants to avoid touching the front and rear of the window.
• the exemplary embodiments described in FIG. 2 or 3 were well suited for this, since in this case these devices did not contain any moving parts.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Manufacturing & Machinery (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Power Engineering (AREA)
• Container, Conveyance, Adherence, Positioning, Of Wafer (AREA)
• Drying Of Semiconductors (AREA)
• Casings For Electric Apparatus (AREA)
• Buffer Packaging (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 1997
  • 1997-01-28 DE DE19703059A patent/DE19703059A1/de not_active Ceased
• 1998
  • 1998-01-20 TW TW087100728A patent/TW348157B/zh active
  • 1998-01-28 EP EP98909293A patent/EP0904598A1/de not_active Ceased
  • 1998-01-28 KR KR1019980706854A patent/KR20000064544A/ko not_active Application Discontinuation
  • 1998-01-28 CN CN199898800069A patent/CN1216157A/zh active Pending
  • 1998-01-28 WO PCT/DE1998/000250 patent/WO1998033205A1/de not_active Application Discontinuation
  • 1998-01-28 JP JP10531492A patent/JP2000508837A/ja not_active Ceased

Non-Patent Citations (1)

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