Apparatus for fabricating a semiconductor device

A semiconductor fabricating apparatus having a structure, which facilitates a loading and unloading operation of wafers while having a low effect by a high temperature during a heat treatment. The semiconductor fabricating apparatus includes a plurality of ring-shaped holder having brims and recessed portions, the brims for mounting the to-be-processed wafers thereon, thereby performing the required heat treatment. A tweezer plate of a wafer loading-transferring device is inserted onto the recessed portion or taken out therefrom, and the inserted tweezer plate is ascended or descended, so that the wafer can be inserted on the brims or taken out therefrom.

FIELD OF THE INVENTION

The present invention relates to an apparatus for fabricating a semiconductor device; and, more particularly, to an apparatus capable of efficiently performing various heat treatments and facilitating transferring of a wafer onto/from a holder, while preventing slip and generation of impurities and scratches on the wafer.

BACKGROUND OF THE INVENTION

In fabricating semiconductor devices, various heat treatments such as an oxidation treatment, a diffusion process, a chemical vapor deposition (CVD) process or the like are performed. A vertical type heat treatment apparatus having a boat with a plurality of wafers vertically stacked therein is used in performing such heat treatments.

The wafers are first vertically stacked at a predetermined interval inside the boat, and the boat is then loaded into a reaction chamber. Thereafter, the vertically stacked wafers are heat-treated using a heating unit while supplying into the reaction chamber gas chosen depending on the nature of the heat treatment.

Conventionally, a boat used in such vertical type heat treatment apparatus includes, as shown inFIG. 7, a top plate10, a bottom plate11and three supporting bars12, wherein the three supporting bars12are supported by the top and the bottom plates10and11. A plurality of grooves13are formed in each of the three supporting bars12, so that a plurality of wafers4can be vertically stacked and maintained therein. Referring toFIG. 7, only the grooves13formed in top and bottom portions of the supporting bars12are illustrated and grooves in remaining portions thereof are omitted for simplicity.

Further, Japanese Patent Laid-Open Publication No. 1997-251961 discloses two types of wafer loading methods: one employing either inclined or curved grooves into which the wafer is directly inserted and the other employing a ring-shaped (annular) susceptor onto which the wafer is placed. Similarly disclosed in Japanese Patent Laid-Open Publication Nos. 1994-163440 and 1998-50626 are boats using ring-shaped holders.

Direct placing of wafers in the grooves formed in the supporting bars of the boat, as described inFIG. 8, provides minimal surface contact therebetween (three contact points in case ofFIG. 8). Such minimal surface contact generates augmented deformation (due to the weight of the wafer itself) and thermal stresses in the wafers, producing defects, e.g., slip, therein.

Further, if the grooves have sharp edges contacting the heated wafers, such local contacts can easily produce scratches on the wafers softened by heat.

Moreover, the situation can be further aggravated by large surface roughness of the grooves if exist, which further produces scratches thereon. Even in the case where the grooves are provided with inclined or curved edges, such still cannot prevent the slip generation in the wafers, due to its inherent nature of minimized local contacts having small contact areas.

Regarding the prior art holders or susceptors supra, the prior art references lack in their detailed usage and operation, e.g., wafer loading and unloading processes. Therefore, elaborate wafer holders need be devised for their practical implementation in the field of semiconductor fabrication.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to provide an apparatus for fabricating a semiconductor device capable of efficiently performing a heat treatment process at high temperature (at or above 800° C.), without slip generation in wafers and the occurrence of impurities and scratches thereon.

Another object of the present invention is to provide an apparatus for fabricating a semiconductor device capable of expediting and facilitating loading and unloading operation of wafers onto and from a ring-shaped holder.

In accordance with an embodiment of the invention, there is provided an apparatus for fabricating a semiconductor device, including: a substrate processing chamber; and one or more substantially ring shaped holders, each holder including at least one major portion for supporting a circumference of a substrate when the substrate is mounted on the holder, and at least one recessed portion for interconnecting end parts of the major portion, wherein the recessed portion has a height difference with the major portion of the holder and the substrate is processed in the substrate processing chamber while the substrate is mounted on the holder.

In the present invention, a ring-shaped holder for mounting a wafer thereon is inserted and maintained in the grooves formed in the supporting bars of a boat. Thus, such holder provides greater contact area compared to the conventional method of directly loading the wafers into the grooves. Naturally, the adverse effects of using the conventional method of direct loading are effectively eliminated.

In other words, during the heat treatment process performed at varying temperatures throughout the process, the wafer experiences deformations due to, e.g., temperature variations during wafer temperature ramping up and down processes and a high heat treatment temperature; and in the conventional method of loading, such phenomenon is the primary cause of the adverse effects. However, the ring-shape holder of the present invention, which offers greater contact area with the wafer, provides a greater uniform support for the wafer, thereby effectively reducing or eliminating the generation of slip in the wafer, regardless of the deformations or thermal contractions/expansion thereof.

Moreover, the ring-shape holder absorbing heat from a heater reduces temperature gradient on a surface of the wafer, thereby enhancing uniformity in temperature. In particular, it is preferable to have the outer diameter of the ring-shape holder greater than that of the wafer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a first preferred embodiment of the present invention will be described with reference to the accompanying drawings ofFIGS. 1 to 3D.

FIG. 3Ashows a plan view of a holder1in accordance with the first preferred embodiment of the present invention;FIG. 3Bdescribes a front view of the holder1ofFIG. 3A;FIG. 3Cillustrates an enlarged view of a portion “D” shown inFIG. 3B; andFIG. 3Dpresents a partial cross sectional view of the holder taken along the line A—A shown inFIG. 3A.

As shown inFIG. 3A, the holder1for mounting a wafer or substrate4thereon and formed in a shape of ring includes brims (thicker portions)2and recessed portions (thinner portions)3having upper surfaces lower than those of the brims2. The holder1has a generally flat bottom surface. The ring-shaped holder1, as shown inFIG. 1A, is inserted into grooves formed in the boat supporting bars5provided in a boat to be supported thereby. A wafer4to be processed is disposed on the brims2. Each of the recessed portions3has a width larger than that of an inserting portion of a tweezer plate6(as shown inFIGS. 4A to 5) and a depth deep enough for the tweezer plate6to be lowered and extracted from the holder1after placing the wafer thereon, so that the wafer4can be loaded on and unloaded from the brims2by using the tweezer plate6.

In other words, in case of placing a wafer onto the holder1, the tweezer plate6having an unprocessed wafer placed thereon is transferred in the direction of the arrow shown inFIG. 1A. Specifically, the unprocessed wafer is transferred over the brims2, while the inserting portion of the tweezer plate6passes through the recessed portions3until the wafer4is concentrically aligned with the holder1. Then, the tweezer plate6having the unprocessed wafer4placed thereon is lowered while maintaining its alignment with respect to the holder1. Consequently, the wafer4is mounted on the brims2of the holder1and the tweezer plate6is lowered further as to be disengaged from the wafer. The disengaged tweezer plate6is then transferred in the reverse direction of the arrow mentioned above until the tweezer plate6is completely disengaged from the holder.

In a similar manner, a wafer4placed on the brims2of the holder1can be retrieved by first transferring the tweezer plate6in the direction of the arrow until it is completely aligned with the wafer4, at which time it is raised. Consequently, the tweezer plate6engages in a contact with the wafer4and further raises the wafer above the brims, at which time the tweezer plate6is transferred in the reverse direction of the arrow, through the recessed portions3.

Therefore, such configuration of the ring-shaped holder1, having the brims2for loading the wafer4thereon and the recessed portion3enabling the tweezer plate6to pass therethrough, facilitates and expedites loading, and unloading operation of the wafer4.

FIGS. 2A and 2Bdescribe exemplary enlarged partial views of an end portion14provided inFIG. 1B(FIG. 1Bis a schematic cross sectional view taken along the line a–a′ inFIG. 1A). As shown inFIGS. 2A and 2B, respective top contact surfaces of the brims2are tapered or curved toward the center of the wafer4. Such configuration can effectively prevent a point or line contacts between the bottom of the wafer4and an edge portion of the holder1having a sharp angle. Therefore, the occurrence of scratches on bottom of the wafer4can be dramatically reduced.

Moreover, by reducing surface roughness of the holder1, micro protrusions thereon are reduced and formation of scratches on the surface of the wafer4can be further prevented, reducing the generation of slip caused by the scratches on the wafer4. A better result is expected from the holder1having a smaller surface roughness, but with about ⅕ to 1/10 of a conventional surface roughness, i.e., Ra (centerline mean roughness) of about 0.5 to 0.1 μm, satisfactory results can be achieved.

Further, the holder1and the supporting bars5shown inFIG. 6are made of SiC, and are arranged so that the holder1can be inserted or removed into or from grooves formed in the supporting bars5of the boat15. The holder1and the supporting bars5, however, can also be formed of single crystalline silicon or polycrystalline silicon. The simple single structure of the ring-shaped holder1of the present invention including the brims2and the recessed portions3as described inFIGS. 1A and 1B, can be readily manufactured using SiC, single crystalline silicon, or polycrystalline silicon.

Since SiC, single crystalline silicon, and polycrystalline silicon have high thermal resistance and chemical resistance, and retain its shape and form even at a temperature ranging from about 1200 to 1300° C., they are preferred as a material of the holder1, supporting bars5and the boat15. Though their lack of weldability makes them less desirable in fabricating complex shapes and designs, the simple structure of the ring-shaped holder1used in the preferred embodiment allows the holder1to be formed of SiC, single crystalline silicon, or polycrystalline silicon, facilitating the insertion of a plurality of holders1into the grooves formed in the supporting bars5and maintaining the holders1therein, as shown inFIG. 6. In comparison, of the materials mentioned above, SiC has better thermal resistance and chemical resistance than those of the others, and is substantially more stable against oxidation. Thus, SiC is preferred for use as the material of the holder1and the supporting bars5over the others.

There has been proposed a conventional holder for mounting a wafer thereon, which is divided into two, where one of the divided sections of the holder is welded onto the supporting bars and the other attached to the welded section after a wafer is placed thereon. However, since SiC has a very high melting point, it is difficult to precisely welded one of the sections of the holder at predetermined positions on the supporting bars. Therefore, SiC is not suitable material of the holder in such prior art scheme.

Alternative to welding may be employed in the above prior art holder, such as inserting the holder directly into the grooves. However, such method forces the holder divided into two to be easily disengaged therefrom. Moreover, such method precludes the holder from being symmetrically loaded into the grooves. In contrast, the brims2and the recessed portions3of the ring-shaped holder1in accordance with the preferred embodiment are formed as a single unit, enabling the holder to be stably maintained in the grooves formed in the supporting bars5.

In contrast to the conventional art, the wafer4of the present invention is placed on the long arc-shaped brims2. Therefore, area of contact between the holder1and the wafer4becomes much larger, and the thermal and deformation (due to the weight of the wafer itself) stresses are effectively distributed in the wafers, thereby greatly reducing the generation of slip.

Further, the ring-shaped holder1of the present invention includes the recessed portions3functioning as a passageway for the tweezer plate6, thereby facilitating transfer of the wafer4onto and from the holder1as mentioned above.

In accordance with the preferred embodiment, a ring-shaped holder1having a size defined in the following is employed as a holder1, although other holders having various shapes and sizes can be used. That is, as shown inFIG. 3A, the outer and inner diameters r1and r2of the holder1are 308 mm and 280 mm, respectively. The two brims2are symmetrically disposed with respect to a vertical axis of the ring-shaped holder1. More rigorously, the inventive holder1has a plane symmetry with regard to a plane passing through the center line A—A while normally bisecting the holder1. An angle made by each of the brims2forming an angle with respect to the center point thereof is 126° (the horizontal axis bisects the angle, forming an angle α at 63°). Formed on the circumferential portions of the ring-shaped holder1are straightened portions, each having a length W3of 55.3 mm, that are in contact with the supporting bars5(4 such bars as inFIG. 1). Accordingly, the distance I between the straight portions disposed at two opposite sides of the holder1is 303 mm, which is smaller than the outer diameter r1.

As shown inFIG. 3B, the distance r3between bottom portions of the straightened portions is 294 mm. The straightened portions of the ring-shaped holder1guarantees firm placement of the holder1into the supporting bars5of the boat. The holders1are engaged with the supporting bars5, by means of inserting the holder1into the grooves13of the supporting bars5, accordingly, the outer portions of the brims2are formed to be thin as shown inFIG. 2. Further, the inner diameter of the recessed portions3is 280 mm identical to that of the brims2.

As shown inFIG. 3B, the thickness t1and t2of the brims2and the recessed portion3are 8 mm and 2 mm, respectively, yielding depth of the recessed portion3of about 6 mm. Further, as shown inFIG. 3C, the thickness t3of the recessed portion3adjoining the brims2is 3 mm.

A width W1of the recessed portion3having the thicknesses t2and t3is 127 mm. A width W2of a portion having the thickness t2of 2 mm is 120 mm, which functions as a passageway for the tweezer plate6. Since the width and the thickness of the inserting portion of the tweezer plate6are at most about 105 mm and 2 mm, respectively, the tweezer plate6having such dimensions can be freely passed through the recessed portion3having a depth of 6 mm (with the thickness of 2 mm). Accordingly, placing the wafer4onto the brims2or retrieving therefrom is facilitated by the use of the tweezer plate6.

Such holder1is made of SiC, and an additional SiC layer having a thickness of about 60 μm is deposited thereon by a CVD (chemical vapor deposition) method. Further, each portion of the ring-shaped holder1has a tolerance of surface flatness of about ±0.05 μm. Adjoining portions between the brims2of the holder1and the wafer4are designed so as to have the curved or inclined surface as shown inFIGS. 2A and 2B.

In accordance with a second preferred embodiment, as illustrated inFIG. 3E, only a single recessed portion3′ and one brim2′ are formed in the holder1′, in which case an end portion8″ including guiding grips8at the tip of the tweezer plate6shown inFIG. 5should be removed therefrom in order to enable the wafer4to properly mounted on the single continuous brim2′.

Subsequently, such a mounting operation of the wafer on the holder1and the subsequent heat treatment process are described usingFIGS. 4A,4B and9. First, as shown inFIG. 4A, each of a plurality of wafers4disposed in a cassette7are mounted on respective tweezer plates6of a wafer transferring device9, and are then taken out from the cassette7. Next, as shown inFIG. 4B, by first rotating the wafer transferring device9, so that the wafers4face the ring-shaped holders1disposed in the boat15, the rotated wafer transferring device9can now transfer the plurality of wafers4to above each of the ring-shaped holders1placed in the boat15. Thereafter, the tweezer plates6are lowered, and places the wafers4on the brims2or2′ of the holder1, respectively. Upon completion of placing the wafers4on the holders1, the tweezer plates6are retracted, covering the same path as the original incoming path, thereby exiting and disengaging from the boat15. By repeating such process, a desired number of wafers4are transferred from one or more cassettes7to the ring-shaped holder1disposed in the boat15and then a heat treatment process can be performed thereon.

After the wafers4are taken out from the cassettes7and are transferred into the boat15by the wafer transferring device9, as shown inFIG. 9, the wafer containing boat15is loaded into a gas reaction chamber or substrate processing chamber19and the predetermined heat treatment is initiated. The reaction chamber19is arranged in a heat diffusing tube17for providing uniform temperature distribution in the reaction chamber19, and heaters16are disposed outside the heat diffusing tube17, to provide appropriate heating to the wafers4loaded in the reaction chamber19. The reaction chamber19maintaining a predetermined gas atmosphere during the heat treatment process, has a gas supply inlet18for introducing gas thereinto.

After finishing the heat treatment, the boat15is taken out from the reaction chamber19, and the wafers4are discharged from the holders1, which are provided for subsequent processing. Needless to say, in transferring the wafers4from the holders1back into the cassette7, the above mentioned sequence of loading may be carried out in a reverse order.

An exemplary tweezer plate6provided with the wafer transferring device9is described inFIG. 5. The tweezer plate6, in accordance with the first preferred embodiment of the invention to be used for the holder1shown inFIG. 3A, has placement grips8and8′ for placing a wafer4therebetween. The placement grips8and8′ are configured to be higher than portions on which the wafer4is placed, and the wafer4is placed on a lower portion between the placement grips8and8′. Further, as shown inFIG. 5, rims of the placement grip8′ is in an arc shape, thereby facilitating the placement of the wafer4on the lower portion between the placement grips8and8′ to ensure the loading on a predetermined position on the tweezer plate6.

FIG. 6describes an exemplary boat15in accordance with the present invention. A multiplicity of ring-shaped holders1or1′ are stacked on a multiplicity of grooves formed in the boat supporting bars5. As described above, each of the wafers is placed on each of the holders1or1′. Further, inFIG. 6, reference numerals10and11indicate the top and bottom plates for fixing the supporting bars5therebetween.

By using the ring-shaped holder in accordance with the present invention, the heat treatment can be carried out at about 800° C. with respect to the silicon wafers having a diameter of 30 cm without any hindrance.

In accordance with the present invention, a desired heat treatment is performed, while placing a wafer on arc-shaped brim(s) of a holder. Thus, when compared with a wafer that is directly supported on the grooves formed in the supporting bars, the thermal stress generated during the heat treatment process and the deformation due to the weight of the wafer itself are reduced, resulting in reduction of the generation of slip, and also the occurrence of the impurities and scratches due to the contact between the wafer and the holder is also reduced, thereby improving the throughput of product wafers.

The ring-shaped holder having one or two brims onto which the wafer is placed further includes one or two recessed portions where the tweezer plate of the wafer transferring device can be passed through, thereby facilitating the loading/unloading operation of the wafer.

Moreover, the simple configuration of the single bodied ring-shaped holder having the brim(s) and the recessed portion(s), can be readily manufactured using SiC having the high thermal resistance and chemical resistance, thereby allowing the holder to be easily and firmly inserted into grooves of the boat supporting bars and stably maintained therein.