Substrate holding device, semiconductor manufacturing apparatus and device manufacturing method

A substrate holding device includes a base member capable of removably holding a plate having a contact member to come into contact with a substrate. The base member flatten-corrects the plate by suctioning the plate. The substrate holding device further includes a first attracting mechanism that attracts the substrate onto the plate in a status such that the plate is held on the base member, and a second attraction mechanism that attracts the plate onto the base member.

FIELD OF THE INVENTION

The present invention relates to a substrate holding device for holding a substrate (wafer) and an aligner or a semiconductor device manufacturing method using the substrate holding device.

DESCRIPTION OF THE RELATED ART

With the advance of semiconductor device miniaturization, attachment of foreign materials to the rear surface of a semiconductor substrate such as a wafer, contamination of a wafer chuck, and the like, cause defects of semiconductors and seriously degrade productivity. In a semiconductor fabrication process, to prevent attachment of foreign materials to the rear surface of a semiconductor substrate, on the substrate side, cleaning which is called a back rinse is performed, and on the fabrication apparatus side, the shape, material and the like of the chuck are improved, so as to prevent attachment of foreign materials.

However, as the rear surface of a semiconductor substrate is handled upon transfer, a complete prevention measure has not been found so far.

In a semiconductor substrate process, most of foreign materials attached to the wafer chuck of an aligner are photosensitive material (photoresist) attached to the rear surface of the semiconductor substrate. The photosensitive material attached to the chuck solidifies on the wafer chuck. Further, floating dust in an atmosphere around the apparatus may be accumulated.

A problem occurs in the semiconductor fabrication process especially when the above-described solidified photosensitive material attaches to the chuck. This cannot be removed by a simple cleaning operation.

To remove the solid foreign material attached to the chuck, it is necessary to remove the wafer chuck from the apparatus and scrape the material away with a sharp-edged tool. However, if a knife-edged cutlery, a file or the like is used, the surface of the wafer chuck requiring 0.1 μm order flatness precision may be damaged or the surface precision may be degraded. Accordingly, for wafer chuck cleaning, a special tool is made as a flat plate with a surface precision approximately the same as that of the wafer chuck, having plural grooved sharp edges, and the grooved surface is brought into contact with the chuck to be cleaned, such that the foreign material attached to the chuck surface is scraped away.

FIG. 10shows a conventional wafer chuck (Publication of Japanese Patent No. 2748181).

InFIG. 10, a reference numeral115denotes a wafer chuck: and116, suction grooves to suction-hold almost the entire surface of a wafer. As shown in this figure, generally, a conventional wafer chuck has a thickness of several mm to several tens of mm. This thickness is the minimum thickness necessary to maintain the flatness of the chuck. An extremely thin wafer chuck cannot be made without difficulty.

At present, in the semiconductor fabrication process, a maintenance operator manually removes a substrate holding unit (wafer chuck) from the apparatus and performs cleaning at regular intervals (or at irregular intervals). However, it takes much time for chuck exchange, or the apparatus must be stopped for a predetermined period due to the problem of temperature stability of the apparatus or the like. This problem is one of the factors of degradation of productivity.

Further, as one prevention measure against the problem, means for cleaning the wafer chuck on the apparatus has been proposed (Japanese Patent Laid-Opened No. 7-130637). However, it cannot be considered as the best measure from the viewpoint of preservation of a clean environment in the apparatus.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the above problems of the conventional techniques, and has as its object to provide a semiconductor manufacturing apparatus which enables simple attachment/removal of substrate holding means such as a chuck and cleaning of the substrate holding means and which attains high productivity.

According to the present invention, the foregoing object is attained by providing a substrate holding device comprising: a base member capable of removably holding a plate having a contact member to come into contact with a substrate; a first attraction mechanism that attracts the substrate onto the plate in a status where the plate is held on the base member; and a second attraction mechanism that attracts the plate onto the base member.

Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same name or similar parts throughout the figures thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is a cross-sectional view showing the structure of a substrate holding device (wafer chuck) of a semiconductor manufacturing apparatus according to a first embodiment of the present invention.FIG. 2is an exploded perspective view showing respective parts of the substrate holding device in FIG.1.

The substrate holding device of the present embodiment is held on a drive mechanism called a wafer stage to sequentially transfer a circuit pattern on a reticle onto a semiconductor substrate (wafer). The wafer stage is capable of positioning in XYZ translation directions and XYZ axial rotation directions by a drive mechanism. Note that other functions than the substrate holding device are omitted.

Numeral1denotes a base member fixed on the wafer stage (not shown). The base member1has a temperature control channel6to maintain a constant temperature of the member, and a temperature control medium is circulated through the channel. Note that in a case where the temperature of the substrate holding base is increased by heat upon exposure or heat from the drive mechanism, a coolant is used. Further, as the temperature control medium, pure water, oil or the like is used.

Numeral2denotes a plate held on the base member1, for directly holding a wafer3. Upon chuck cleaning, only the plate2is removed and is cleaned. This operation will be described in detail later.

The plate2is vacuum-sucked on the base member1by negative pressure in a gap between the base member1and the plate2caused by a plate suction mechanism4. For this purpose, the base member1has a plate suction hole15.

Numeral5denotes a wafer suction mechanism to vacuum-suck the wafer on the plate2. The wafer suction mechanism5is provided on the base member1. Note that as a piping from the wafer suction mechanism5to the wafer, a wafer suction hole14is formed through the base member1and the plate2for holding the wafer3on the plate2by vacuum suction. That is, the plate2is placed on the base member1while the plate is aligned with the base member such that the suction hole provided in the plate2and the suction hole provided in the base member1are aligned with each other.

Even in a status where the wafer is not placed on the plate2, it is preferable that the plate2is sucked to the base member1. For this purpose, in the present embodiment, the plate suction mechanism4and the wafer suction mechanism5function independently of each other.

In the present embodiment, the vacuum suction mechanism is used for holding the wafer3and the plate2, however, the present invention is not limited to the vacuum suction mechanism but any other holding mechanism such as an electrostatic chuck or a mechanical chuck can be used to obtain a similar advantage. In use of the electrostatic chuck to hold the wafer3, the plate2is placed on the base member1while the plate is aligned with the base member such that an electrode provided in the plate2and an electrode provided in the base member1are aligned with each other.

Numeral7denotes wafer contact pins for holding the wafer3on the plate2. Further, numeral2adenotes a ring-shaped contact member provided on a rim of the plate2. The wafer3is supported by the contact member2aand the pins7, and is flat-corrected. Numeral8denotes plate contact pins as contact members for holding the plate2on the base member1. Numeral1adenotes a ring-shaped contact member provided on a rim of the base member1. The plate2is supported by the contact member1aand the pins8.

In the present embodiment, to reduce the footprint and avoid attachment of dust, the pin-shaped projections are used as the respective contact members. Note that the contact members are not limited to the pin-shaped projections but any other members such as ring-shaped projections may be used as long as they attain a similar advantage. Further, even if the projections on the plate are pin-shaped projections, ring-shaped projections may be used on the base member.

FIG. 3Ashows the positional relation between the pins7provided on the plate2and the pins8provided on the base member1.FIG. 3Bshows a positional shift amount d between the central axis of the projection on the plate2(e.g., pin7) and that of the projection on the base member1(e.g., pin8).

It is impossible to form the plate2as a complete solid body. The plate2has a characteristic as an elastic body. Accordingly, when negative pressure occurs between the base member1and the plate2or between the plate2and the wafer3, for example, the plate2is elastically deformed. However, even when the plate2is elastically deformed, the flatness of the surface of the pins7holding the wafer3must be maintained so as to flat-correct the wafer3.

It is desirable that the projections on the base member1(e.g., pins8) be provided under projections of the plate2(e.g., pins7) as shown in FIG.3A.

That is, it is desirable that as the positional relation between the projections on the plate2and those on the base member1, they are coaxially arranged as much as possible. Here “coaxial” does not mean complete coaxial positioning but positioning such that the degradation of flatness caused in the plate2due to the positional shift d is within an allowable range. For example, if the positional shift d is equal to or less than 5 mm, the projections are coaxially positioned, and if the positional shift d is equal to or less than 1 mm, the projections are more preferably coaxially positioned, and further, if the positional shift d is equal to or less than 0.5 mm, the projections are further preferably coaxially positioned. In any case, if the flatness of the plate2is within the allowable range, the projections are in the “coaxial” relation. Further, it may be arranged such that the projections are in the “coaxial” relation if the central axis of the projection on the plate2is within the area of the projection of the base member1.

Further, it is preferable that the projections on the base member1are arranged under all the projections on the plate2. Note that the projections are not necessarily arranged in this manner. It is preferable that the projections on the base member1are provided under 90% of the projections on the plate2.

Note that in the use of an electrostatic chuck, the above advantage can be similarly obtained even if the projections are not used.

Next, the structure for plate conveyance to automatically attach/remove the plate to/from the base member by the above construction will be described with reference to FIG.4.

Numeral13denotes the wafer stage which is not shown inFIGS. 1 and 2. The wafer stage13is capable of positioning in the XYZ translation directions and the XYZ axial rotation directions by a wafer stage device mechanism22. A bar mirror11as well as the above-described wafer chuck is mounted on the wafer stage13. The bar mirror11is irradiated with a laser beam (interferometer beam)12, thereby the position of the reflection surface of the bar mirror11is measured. That is, the position of the wafer stage13is measured by a laser interferometer (not shown) and the bar mirror11. The result of the measurement is inputted into a controller21. The controller21outputs a drive signal to the wafer stage drive mechanism22based on the input position information of the wafer stage13. The drive mechanism22drives the wafer stage13based on the drive signal.

Numeral9denotes a hand for conveyance used for providing/collecting the wafer3and for providing/collecting the plate2. The hand9grasps a side surface of the wafer3or the plate2by a grasp mechanism10included in the end of the hand9. The grasp mechanism10is controlled based on a signal from the controller21. Further, a Z drive mechanism25drives the hand9in the Z direction. The Z drive mechanism25is controlled based on a signal from the controller21. By using the Z drive mechanism25, the wafer or plate grasped by the hand9can be placed on the base member or the like, or the placed wafer or plate can be removed. In the present embodiment, an edge portion of the wafer3and that of the plate2is grasped. Note that pickup/placement upon conveyance is not limited to the grasp of the side surface. For example, it may be arranged such that the wafer3is lifted in the Z direction from the plate2or the plate2is lifted in the Z direction from the base member1, and the hand holds the bottom surface of the wafer3or the plate2.

Note that a hand drive mechanism23is provided to drive the hand9in the Z or Y direction to, e.g., convey the wafer3and the plate2to the outside of the exposure chamber. The drive mechanism23drives the hand9based on a signal from the controller21.

FIG. 5Ashows a sequence upon attachment of the plate2in the above construction, andFIG. 5Bshows a sequence upon removal of the plate. The controller21controls necessary drive mechanisms and the like based on the sequences.

In an initial status, the plate2and the wafer3are not placed on the base member1. To set the plate2from this initial status, first, a plate to be attached is designated from plural plates (a1). The designation of the plate is made, e.g., by inputting a signal into the controller21or based on stored exposure information. Then, it is checked that the plate2and the wafer3are not placed on the base member (a2and a3). The checking operation is made based on, e.g., signals from pressure sensors provided in the plate suction mechanism4and the wafer suction mechanism5. Thereafter, the designated plate is conveyed from a plate carrier (not shown) (also usable as a wafer carrier) to the status as shown inFIG. 4(a4).

When the plate2has been conveyed to a position above the base member1, the plate2is moved downward and brought into contact with the base member1by the Z drive mechanism25(a5). When the contact between the plate2and the base member1has been checked, the plate suction mechanism4is changed to a sucking status, to suction-hold the plate2and the base member1(a6). The suction between the base member1and the plate2is made by vacuum suction here.

When the suction status has been checked, the hand9changes the grasp mechanism10to a non-suction status (a7), to withdraw the hand9(a8). Thus, the placement of the plate is completed (a9).

Further, when the plate is removed, it is checked that the plate2exists but the wafer3does not exit, and the above operations are made in the reverse order.

That is, first, it is checked that the wafer does not exist on the plate but the plate2exists on the base member (b1and b2). The conveyance hand9is moved to hold the plate side surface (b3), and the grasp mechanism10of the conveyance hand9is changed to a grasping status (b4). The plate suction mechanism is released to change the plate into unsucked status (b5), and the hand9is moved upward by the Z drive mechanism25, to separate the plate2from the base member1(b6), into the status as shown in FIG.4. Thereafter, the plate2is conveyed onto the plate carrier (not shown).

Note that the plate2is previously processed so as to have an ultra-flat surface when placed on the base member1. If there is a probability that dust is held between the plate and the base member upon attachment/removal, it is more preferable to provide a function or mechanism to check the flatness after the attachment/removal of the plate.

To correct the wafer-contact surface of the plate2to be ultra flat, it is preferable that the base member1and the plate2respectively have ultra-flat surfaces. Actually, as there is a process limit, it is difficult to attain a complete precision regarding surface distortion. In ultra-flatness processing, precision is obtained by grinding or lapping. In this case, as slight inner stress occurs in the process workpiece, a thin plate as in the present embodiment is distorted. Note that regarding thickness unevenness, such a problem does not occur. Therefore, high-precision thickness control can be made.

In the present embodiment, the base member1has an ultra-flat surface, and the thickness of the plate2is controlled, such that the base member1flatten-corrects the plate2. Accordingly, even if the plate2itself has slight distortion, the wafer-contact surface of the plate2can be corrected to be flat by suctioning the plate2to the base member1. For example, if the surface of both members are vacuum-suctioned to each other in an area of ø300 mm (the area of the suctioned surfaces is about 707 cm2), the suction can be made by a force of 707 kgf at the maximum, and this force can be utilized for correcting the distortion of the plate.

On the other hand, when the surface of the plate2is flatten-corrected by the base member1, the base member1receives a force to distort the base member. However, if the base member is distorted by an amount exceeding the allowable range, the function to correct the flat surface of the wafer is finally degraded.

It is desirable that the rigidity of the base member1is greater than that of the plate2. For example, assuming that the rigidity of the plate2is “1”, the rigidity of the base member1is desirably “2” or greater.

Generally, the focal depth assigned to wafer surface precision in a semiconductor exposure process is 2 μm or less (λ−0.365. NA−0.3, k−1, and if the assignment to the wafer surface precision is 50%, (λNA2)×k×0.5), the limitation of the plate flattening process is 4 μm (e.g., ø150 mm). The relation of rigidity between the plate2and the base member1is the ratio of rigidity required of the base member1in this case (here the surface shape of the base member1is ignored for the sake of simple explanation). Note that the relation between the process precision and the ratio of rigidity (rigidity of plate2/rigidity of base member1) and the flatness of the plate2after flattening-correction is as follows.

Accordingly, as a thin plate (e.g., having a thickness of a wafer) is generated, even if the plate2has distortion, the contact surface of the plate2can be ultra flat by suction-holding the plate to the base member having sufficient rigidity.

Note that even if the focal depth is reduced in the future, the flattening-correction can be made by increasing the rigidity of the base member with respect to the plate rigidity. Further, if the base member has a rigidity higher than that of the plate, the flatness of the flatten-corrected plate2can be increased.

Desirably, assuming that the rigidity of the plate2is “1”, the rigidity of the base member1is “10” or greater. More desirably, assuming that the rigidity of the plate2is “1”, the rigidity of the base member1is “20” or greater.

Note that the plate2is removed from the base member in accordance with a predetermined sequence. As timing of the removal of the plate2from the base member1, {circle around (1)} when contamination of the plate is detected and the contamination level is higher than a predetermined reference level, the plate is removed to be exchanged with another plate; {circle around (2)} when a predetermined period has elapsed since the plate was set on the base member, the plate is removed to be exchanged with another plate; or {circle around (3)} when the substrate holding device is applied to an aligner, the plate is removed in accordance with an exposure history.

Foreign materials attached to the plate2are removed by a cleaner (not shown), and the plate2is reused. Further, it is desirable to provide a device to detect foreign materials attached to the plate to be utilized, and it is further desirable to provide a device to detect smoothness, flaws and the like of the plate.

Note that if another plate is used while the removed plate is cleaned, production is continued without suspension during the cleaning.

Further, as the projections of the base member1are to be positioned under the projections of the plate2, the plate2must be aligned with the base member1. Accordingly, similar to a notch18of the wafer or an orientation/flat aligner, an alignment reference mark19such as a notch or orientation/flat aligner is formed in the plate such that alignment is made upon conveyance of the plate as in the case of a wafer. Note that the alignment between the plate2and the base member1is not limited to this method, but any other alignment reference mark may be provided. For example, an alignment mark may be formed on the plate2, or a target for magnetic detection may be provided to detect the relative position of the plate2to the base member, or the plate2may have an edge so as to be measured from the base member1. In this case, it is desirable to provide a sensor to detect the alignment reference mark. Note that the sensor may be provided on the base member1.

Further, it is more desirable that in consideration of a process where local surface precision of the plate influences pattern precision, plates used in exposure are managed by barcode or inscription. Note that management is not only made by barcode or inscription but may be made by any sign for identifying the plate. In this case, it is necessary to provide an identification sensor to identify the sign provided on the plate. Further, it is desirable to provide a storage device for storing a status of use of a plate based on an identification signal from the identification sensor. Then, based on information stored in the storage device, the controller21controls an exposure process and other processes.

Further, as the plate2is brought in direct contact with the wafer, the plate is desirably made of a ceramic (e.g., SiC, SiN) material. Further, the substrate holding base member to hold the plate2is desirably made of ceramic material.

As to a temperature difference between the plate2that has been conveyed from outside of the exposure chamber and the apparatus, a cooling mechanism (cooling channel6) included in the base member1performs temperature control in a short period. Note that to effectively control the temperature of the plate2by the base member1, thermal transfer from the base member1to the plate2can be increased by filling gas in the space suctioning both members to each other. That is, the pressure of the gap between the base member1and the plate2is controlled to an extent to which the plate2can be suctioned, so as not to attain a vacuum state where almost no gas exists in the gap. For this purpose, to control the pressure of the gap between the base member1and the plate2, the plate suction mechanism4desirably has a pressure regulating mechanism (not shown) and a pressure sensor (not shown). The controller21inputs a signal regarding the pressure outputted from the pressure sensor, and controls the pressure regulating mechanism based on the pressure signal. As the pressure regulating mechanism, a throttle or the like can be used. The pressure can be controlled by controlling the opening area of the throttle.

Next, upon placement of the wafer from this status, the wafer is conveyed by a conveyance device (not shown) from the wafer carrier (not shown) in a similar manner to that of the conveyance of the plate2.

The wafer3is conveyed to a position above the plate2, then the wafer is moved downward by the Z drive mechanism25, into contact with the plate2. When the contact has been checked, both members are suction-held by changing the wafer suction mechanism5inFIG. 1to a suctioning status. The wafer and the plate are suction-held by vacuum suction.

When the suction status has been checked, the grasp mechanism10in the hand9is changed to a non-grasping status, and the hand9withdraws, thus plate placement is completed. Further, when the wafer is removed, the above operation is made in the reverse order.

Note that the plate2and the wafer3are conveyed by the same conveyance device, however, they may be conveyed by different conveyance devices depending on the system.

In the present invention, the plate, which may be contaminated due to attachment of photosensitive material or the like upon contact with the wafer, can be replaced with another plate. Accordingly, in comparison with the conventional art, the time to remove the contaminants is not required, and the productivity can be improved.

Further, as the plate on the flat plate can be removed, cleaning to remove the contaminants can be easily made.

Second Embodiment

FIG. 6is a cross-sectional view showing the structure of the substrate holding device (wafer chuck) of the semiconductor manufacturing apparatus according to a second embodiment of the present invention.

The second embodiment uses a plate32corresponding to the wafer diameter.

In a case where wafers having different diameters such as a ø300 mm (12 inch) wafer and a ø200 mm (8 inch) wafer are exposed by a single apparatus, conventionally, a wafer chuck for the ø300 mm wafer must be exchanged with a wafer chuck for the ø200 mm wafer. On the other hand, in the present embodiment, wafers having various diameters can be handled only by changing the plate shape to have a convexity as shown in FIG.6. That is, in the present embodiment, the area of the plate to suction-hold can be changed by appropriately changing the plate.

If only the plate32is changed in correspondence with the wafer diameter that is changed, automatic exchange by the conveyance mechanism as shown inFIG. 4can be realized, thus working time can be greatly reduced.

That is, the type of wafer to be held is specified from an exposure condition inputted into the controller21or stored in the memory (not shown) of the controller21. Then the controller21designates a plate to be sucked on the base member1based on the specified wafer type. The identification of the plate at this time may be made by using an identification sign such as a barcode provided on the plate. Note that attachment/removal of the plate thereafter is made in the same manner as that described in the first embodiment.

Although the vacuum suction is used as an attraction mechanism of the base member1and the plate2(34) in the above first and second embodiments, other mechanisms such as electrostatic attraction, magnetic attraction and mechanical fixing may be used.

Third Embodiment

Next, an embodiment of a scanning aligner where the substrate holding device of the first or second embodiment is mounted on a wafer stage will be described with reference to FIG.7.

A mirror platen96is supported by a floor or base91via a damper98. Further, the mirror platen96supports a reticle stage platen94and supports a projection optical system97positioned between a reticle stage95and a wafer stage93.

The wafer stage93is supported on a stage platen92supported by the floor or base91, for carrying and positioning the wafer. Further, the reticle stage95, supported on the reticle stage plate94supported by the mirror platen96, is movable while carrying a reticle having a circuit pattern. Exposure light to expose the reticle mounted on the reticle stage95is emitted from an illumination optical system99.

Note that the wafer stage93is scanned in synchronization with the reticle stage95. While the reticle stage95and the wafer stage93are scanned, the positions of these stages are continuously detected respectively by interferometers, and fed back to driving units of the reticle stage95and the wafer stage93. This attains accurate synchronization between the scan start positions of these stages and high-precision control on scanning speed in a constant-speed scan area. While these stages are scanned with respect to the projection optical system97, the reticle pattern is exposed and thus the circuit pattern is transferred onto the wafer.

Fourth Embodiment

Next, an embodiment of the semiconductor device manufacturing method utilizing the above aligner will be described.FIG. 8shows a flow of a fabrication of a semiconductor device (e.g., a semiconductor chip such as an IC or an LSI or a liquid crystal panel, a CCD or the like). At step S1(circuit design), a circuit design of the semiconductor device is made. At step S2(mask fabrication), a mask where the designed circuit pattern is formed is fabricated. At step S3(wafer fabrication), a wafer is fabricated by using material such as silicon. At step S4(wafer process) called a preprocess, the mask and the wafer are used for forming an actual circuit on the wafer by lithography. At step S5(fabrication) called a post process, the wafer fabricated at step S4is used for forming a semiconductor chip. The step S5includes an assembly process (dicing and bonding), a packaging process (chip encapsulation) and the like. At step S6(inspection), inspections such as an operation test and an endurance test are performed on the semiconductor device fabricated at step5. Through these processes, the semiconductor device is completed and shipped (step S7).

FIG. 9shows the wafer process in detail. At step S11(oxidation), the surface of the wafer is oxidized. At step S12(CVD), an insulating film is formed on the surface of the wafer. At step S13(electrode formation), an electrode is formed by vapor-deposition on the wafer. At step S14(ion implantation), ions are implanted into the wafer. At step S15(resist processing), a photoresist is applied to the wafer. At step S16(exposure), the circuit pattern on the mask is expose-printed on the wafer by the above aligner. At step S17(development), the exposed wafer is developed. At step S18(etching), the portions other than the developed resist image are removed. At step S19(resist stripping), the unnecessary resist after the etching was removed. These steps are repeated until a multiple circuit pattern is formed on the wafer. By using the fabrication method of the present embodiment, the conventionally low-efficient device fabrication process can be improved.

According to the substrate holding device of the present invention, as the plate can be removed and cleaned, time to remove contaminants is not required. Thus, the productivity can be improved. Further, as the plate on the flat plate can be removed, cleaning to remove the contaminants can be easily performed.

The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to appraise the public of the scope of the present invention, the following claims are made.