Vertical furnace for processing substrates and a liner for use therein

Field

0001The present disclosure generally relates to equipment for processing semiconductor substrates, and more particularly to a vertical furnace and a liner for use therein.

Background

0002Vertical processing furnaces or reactors are commonly used for batch processing semiconductor wafers during several fabrication stages of integrated circuits. Processing steps for which a furnace may be used include oxidation, diffusion, annealing, chemical vapor deposition (CVD) and atomic layer deposition (ALD).

0003A vertical processing furnace may include a thermally resistive heating coil, powered by an electrical power supply. Within the heating coil there may be provided an outer reaction tube which may be bell jar-shaped and an inner reaction tube that may be substantially coaxially disposed within the outer reaction tube. The inner reaction tube may be commonly referred to as a liner. The lower end of the outer reaction tube may be open, while the top end thereof may be closed, typically by a dome-shaped structure. The liner may be provided with a liner opening at both its top and lower end. Alternatively, the top end of the liner may be closed while there is a liner opening at the bottom.

0004The lower ends of both the outer reaction tube and the liner may be supported on a flange, which may define a central opening via which a substrate boat holding a plurality of substrates may enter and exit the reaction chamber that is formed by the interior space of the liner. The substrate boat may be supported on a thermally insulating pedestal, which in turn may be supported on a door plate that may serve to close off the central opening in the flange. The flange may further be provided with a gas feed conduit that connects to a gas injector disposed inside the liner, and a gas exhaust conduit via which a vacuum pump may be connected to a lower end of a gas passage that exists between an outer wall of the liner and an inner wall of the outer reaction tube.

0005In operation, a substrate boat with a plurality of substrates may be introduced into the reaction chamber, which may then be evacuated. Subsequently, a process gas may be fed to the reaction chamber via the gas feed conduit and the gas injector. The process gas may flow into the inner space of the liner while contacting the substrates provided therein. The process gas may exit the open top end of the liner and reach the closed top end of the outer reaction tube; it may reverse its direction and flow downwardly through the gas passage between the inner and outer reaction tubes, so as to be exhausted from the reaction chamber via the gas exhaust conduit by the vacuum pump.

0006An issue may be that the concentration of processing gas and reaction byproducts may change during their way from the gas injector along the substrate boat. This may lead to processing non-uniformity between substrates positioned on different positions in the substrate boat which non-uniformity may be unwanted. Further issues associated with vertical processing furnaces may be contamination of the reaction chamber with small deposit particles. A deposit particle that ends up on a substrate being processed may render an integrated circuits to be manufactured therefrom inoperable.

0007A vertical furnace and a liner for use therein with improved properties may therefore be desirable. <patcit id="pcit0001" dnum="US2018179625A1"><text>US2018/179625A1</text></patcit> discloses a film forming apparatus for performing a film forming process on substrates by heating the substrates while the substrates are held in a shelf shape by a substrate holder in a vertical reaction container.

Summary

0008A vertical furnace for processing a plurality of substrates according to the invention is disclosed in claim 1.

0009A liner constructed to extend in the interior of an outer reaction tube of a vertical furnace for processing a plurality of substrates according to the invention is disclosed in claim 14.

Brief Description of the Drawings

0010While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the invention, the advantages of embodiments of the disclosure may be more readily ascertained from the description of certain examples of the embodiments of the disclosure when read in conjunction with the accompanying drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a schematic cross-sectional side view of an exemplary embodiment of a vertical furnace according to an embodiment;</li><li><figref idref="f0002">Fig. 2</figref> depicts a schematic cross-sectional top view of a liner according to a further embodiment;</li><li><figref idref="f0003">Fig. 3</figref> depicts a schematic cross-sectional side view of the liner of <figref idref="f0002">Fig. 2</figref>;</li><li><figref idref="f0004">Fig. 4</figref> depicts a side view of the liner of <figref idref="f0002">Figs. 2</figref> and <figref idref="f0003">3</figref>; and,</li><li><figref idref="f0005">Fig. 5</figref> schematically illustrates an embodiment of a liner according to a further embodiment.</li></ul>

Detailed Description

0011As used herein, the term "substrate" may refer to any underlying material or materials that may be used, or upon which, a device, a circuit, or a film may be formed. The term "semiconductor device structure" may refer to any portion of a processed, or partially processed, semiconductor structure that is, includes, or defines at least a portion of an active or passive component of a semiconductor device to be formed on or in a semiconductor substrate. For example, semiconductor device structures may include, active and passive components of integrated circuits, such as, for example, transistors, memory elements, transducers, capacitors, resistors, conductive lines, conductive vias, and conductive contact pads.

0012<figref idref="f0001">Fig. 1</figref> schematically illustrates in a cross-sectional side view an exemplary vertical furnace or reactor 1 according to an embodiment. The furnace 1 is of a double tube type, and may include an outer reaction tube 30 which may be generally bell jar-shaped and a liner 40 which may be openended and function as an inner reaction tube. The outer reaction tube 30 may be surrounded by heating means, such as a thermally resistive heating coil 22 that is powered by an electrical power supply (not shown). The heating means may further be secured to a thermally insulating sleeve (not shown) that surrounds the outer reaction tube 30. Both the reaction tube 30 and the liner 40 may have a generally tubular, for example circular or polygonal, cross-sectional shape. An outer diameter of the liner 40 may be smaller than an inner diameter of the outer reaction tube 30. Accordingly, the liner 40 may be at least partially disposed within the outer reaction tube 30, and extend substantially coaxially therewith around a common central axis L.

0013A gas passage 20 may be defined between an inner wall 32 of the outer reaction tube 30 and an outer wall 41 of the liner 40. In case the reaction tube 30 and the liner 40 have a similar cross-sectional shape, the gas passage 20 may have a substantially uniform width along its axial length. The (average) width of the gas passage may typically be on the order of several centimeters, e.g. in the range of 1-5 centimeters. Both tube 30 and liner 40 may be made of quartz, silicon carbide, silicon or another suitable heat resistant material.

0014In the configuration shown in <figref idref="f0001">Fig. 1</figref>, the liner 40 may delimit a reaction chamber 2 in which a substrate boat 26 is receivable. Both the outer reaction tube 30 and the liner 40 may be supported at their lower end on a flange 8. The flange may be made of stainless steel. The substrate boat 26 may enter and/or exit the reaction chamber 2 via a central furnace opening 10 provided in the flange 8.

0015The substrate boat 26, which may include a plurality, e.g. between 10 and 200, of slots for holding equally many substrates 27 e.g. semiconductor wafers, may be mounted on a pedestal 28, which may be mounted on a seal cap or door plate 12. The pedestal 28 may act as a heat shield for both the door plate 12 and the flange 8, and may reduce heat loss via the lower portion of the furnace 1. In some embodiments, the substrate boat 26 and the pedestal 28 may be rotatable by a motor (not shown).

0016To ensure that the reaction chamber 2 is sealed in a gas-tight manner, several seals such as elastomeric O-rings 14 may be employed in the lower part of the furnace 1, in particular between the outer reaction tube 30 and the flange 8, and between the flange 8 and the door plate 12. Since the reliability of elastomeric O-rings and other seals may diminish when subjected frequently or continuously to high temperatures, the lower part of the vertical furnace 1 may preferably be kept at a lower temperature than that present in the central and upper parts of the reaction chamber 2.

0017The vertical furnace 1 may further include a gas injector 4. The gas injector 4 may be disposed within reaction chamber 2 and include a plurality of gas injection holes 6 provided over the height or axial length of the substrate boat 26. A gas feed conduit 18 may connect to the gas injector 4, possibly via the flange 8, so as to enable the introduction of process gases, e.g. precursor and/or purge gases, into the reaction chamber 2 from the gas injection holes 6.

0018The vertical furnace may be used for a LPCVD process. In such a process, a precursor gas, for example tetraethylorthosilicate with the chemical formula Si(OC₂H₅)₄ and the acronym "TEOS" may be used. TEOS may be used as the source material for silicon oxide to be deposited on the substrates with a low pressure chemical vapor deposition process. This process may provide certain advantages in terms of uniformity or density of the silicon oxide layer obtained. Alternatively, a silicon nitride layer may be deposited with an LPCVD process with a different precursor.

0019The concentration of processing gas and reaction byproducts may change after leaving the gas injector 4. If the discharge or exhaust of process gas from the reaction chamber 2 is accomplished via the top opening of the inner reaction tub or liner 40, as described in <patcit id="pcit0002" dnum="US8398773B"><text>U.S. Patent No. 8,398,773</text></patcit>, the concentration of processing gas and reaction byproducts may vary over the substrate boat 26. This may lead to processing non-uniformity between substrates 27 positioned on different positions in the substrate boat 26, which non-uniformity may be unwanted.

0020To minimize processing non-uniformity between substrates positioned on different positions in the substrate boat gas exhaust holes 19 may be provided in the liner 40 to discharge or exhaust gas from the reaction chamber 2. After passing the gas exhaust holes, the gas may turn downwardly through the gas passage 20 between the outer tube 30 and the liner 40, towards the gas exhaust conduit 16 connected to the vacuum pump 24. In <figref idref="f0001">Fig. 1</figref> this gas exhaust path is indicated with reference numeral 21.

0021The configuration of the gas injection holes 6 and the gas exhaust holes 19 makes that process gas introduced into the reaction chamber 2 from the injection holes 6 of the gas injector 4 flows generally over the substrates through the reaction chamber towards the gas exhaust holes 19. The path of the process gas and reaction byproducts in the reaction chamber may thereby be shortened compared to a situation where the process gas is exhausted from the top. This may minimize processing non-uniformity between substrates positioned on different positions in the substrate boat. Further the remaining non-uniformity may be in the horizontal direction over the substrate which may be alleviated by rotation of the substrate boat 26.

0022While being exhausted, reactive gases may form a deposit as they flow through the relatively cold lower portion of the furnace 1, which includes the flange 8 and the gas exhaust conduit 16 (in the embodiment of <figref idref="f0001">Fig. 1</figref> a part of the flange 8). In itself the deposition of by-products adjacent the downstream end of the gas exhaust path 21 does not cause contamination of the reaction chamber 2. Under certain conditions, however, material deposited at the downstream end of the gas exhaust path 21 may be whirled up and be transported back, via the gas passage 20, into the reaction chamber 2 by recirculating gas flows.

0023For instance, when after discharging one substrate boat 26 holding processed substrates 27 from the reaction chamber 2 another substrate boat with a fresh batch of substrates 27 is being loaded into the reaction chamber 2, the reaction chamber 2 may be at atmospheric pressure and the vacuum pump 24 may be temporarily switched off. The introduction of the new, relatively cold substrate boat 26 with the likewise cold unprocessed substrates 27 into the relatively warm reaction chamber 2 may cause significant temperature gradients within the reaction chamber, in particular between the outer reaction tube 30, the liner 40 and the substrate boat 26. These temperature gradients may induce pressure gradients and/or gas density gradients, which may, in turn, drive convective flows over the liner 40. These flows may facilitate particle transport from the downstream end of the exhaust path 21, via the gas passage 20, the gas exhaust holes 19, back into the reactor chamber 2. This way, particles may end up on the substrates 27 of the newly introduced substrate boat 26.

0024To prevent such back flow of deposits, the outer wall 41 of the liner 40 and/or the inner wall 32 of the outer reaction tube 30 may be provided with a flow deflector 50. The flow deflector may protrude from the respective wall into the gas passage 20, in a generally radial direction with respect to the central axis <i>L</i>.

0025In the vertical furnace 1 of <figref idref="f0001">Fig. 1</figref> both the outer reaction tube 30 and the liner 40 may be provided with the flow deflector 50. The flow deflector may be in the form of an annular baffle 52 that protrudes radially into the gas passage 20. The flow deflectors 50 may be provided at a point about halfway the axial length of the gas passage 20, and sufficiently close to each other to define a narrow Z-shaped gap between themselves and the walls 32, 41 through which gas may pass. The baffles 52 of the flow deflectors 50 may partially or completely encircle or surround the liner 40, such that they necessarily obstruct the flow of gas through the gas passage 20 in the direction of the central axis <i>L</i>, irrespective of the angular position of the gas flow relative to the central axis.

0026In order to warrant an efficient obstruction of a back flow, a flow deflector may preferably protrude sufficiently far e.g. between 1 and 5 cm into the gas passage 20. Precisely what is 'sufficiently far' may depend in particular on the (local) width of the gas passage 20, i.e. on the (local) distance between the inner wall 32 of the outer reaction tube 30 and the outer wall 41 of the liner 40. In general, the flow deflector may preferably protrude radially from the wall on which it is provided over a radial distance of at least 75% of a local width of the gas passage 20.

0027For example, in case the outer reaction tube 30 and the liner 40 define a cylinder jacket-shaped gas passage 20 with a uniform width of 25 millimeters along the central axis <i>L</i>, the flow deflector 50 may preferably extend a radial distance of at least 19 millimeters (i.e. 0.75*25mm) into the gas passage 20. In case the liner 40 is disposed slightly off-axis, e.g. by 5 mm, such that the width of the gas passage 20 varies in the tangential direction between 20 and 30 mm, the distance over which the flow deflector 50 protrudes into the gas passage 20 may vary correspondingly, e.g. between 15 and 23 mm.

0028The liner 40 may be provided with an open tapered top end 54 at the top end of the liner. The open tapered top end 54 may have an opening sufficiently large, for example with a diameter of 310 to 350mm, to allow the top of the substrate boat 26 to pass when the substrate boat 26 moves in the inner space of the liner 40. The open tapered top end 54 may be sufficiently small to prevent exhaust during processing from the open tapered top. It may be preferred that the exhaust may be accomplished through the exhaust hole 19 during processing.

0029The outer reaction tube 30 and liner 40 may normally be manufactured individually, and assembled at a later stage to form the double tube structure of the furnace 1. To enable such assembly, during which the liner 40 is carefully moved into the outer reaction tube 30, at least a few millimeters of clearance between the two components may be desirable. The clearance may preferably be at least 2 millimeters, and more preferably be in the range of 2-8 millimeters. Accordingly, a flow deflector may preferably protrude radially from the wall on which it is provided over a radial distance of no more than a local width of the gas passage 20 minus at least 2 millimeters, or over a radial distance of at least the local width of the gas passage 20 minus 8 mm.

0030As will be illustrated with reference to <figref idref="f0002 f0003 f0004 f0005">Figs. 2 to 5</figref>, a flow deflector 50 may be composed of multiple parts, e.g. baffles, that may be provided at different axial positions, which parts together encircle the inner tube 40. Multiple baffles, which may be provided on the walls 32, 41 of the outer reaction tube 30 and/or liners 40. Several embodiments of such a flow deflector 50 will now be elucidated with reference to <figref idref="f0002 f0003 f0004 f0005">Figs. 2 to 5</figref>. It is noted in advance that in the embodiments depicted in <figref idref="f0002 f0003 f0004 f0005">Figs. 2 to 5</figref>, the baffles 52 of the flow deflector 50 are provided on the outer wall 41 of the liner 40, which liner is shown in isolation. One skilled in the art will appreciate, however, that similar patterns of baffles may alternatively, or in addition, also be provided on the inner wall 32 of the outer reaction tube 30.

0031<figref idref="f0002">Fig. 2</figref> depicts a cross-sectional top view of a liner 40 according to an embodiment. The liner 40 may be useable in a vertical furnace such as the one of <figref idref="f0001">figure 1</figref>. The liner 40 may be provided with a bulge 55 which may be radially extending outward with respect to the central axis L of the liner. The bulge 55 may be extending parallel to the central axis L of the liner to accommodate the gas injector 4 in the interior space of the liner 40. The bulge 55 may be extending in the gas passage 20 (see <figref idref="f0001">figure 1</figref>) to accommodate the gas injector 4.

0032The liner 40 may be provided with a gas exhaust hole 19. It may be advantageous to have the gas injector 4 configured opposite the gas exhaust hole 19 with respect to the central axis L of the liner 40. This configuration creates a flow over the full substrate if the process gas is provided to the gas injector 4 and removed from the inner space via the gas exhaust hole 19. The bulge 55 in the liner 40 may therefore be configured opposite the gas exhaust hole 19 with respect to the central axis L.

0033The outer wall 41 of the liner 40 may be provided with a flow deflector in the form of an annular baffle 52 which may protrude radially from the outer surface 41 around the liner 40. In the embodiment as shown in <figref idref="f0002">Figure 2</figref> the baffle 52 may be hardly protruding at the position of the bulge 55 at the outer surface 41 while the embodiment of <figref idref="f0001">figure 1</figref> the baffle 52 is still protruding substantially where the gas injector 4 is located at the liner 40.

0034<figref idref="f0003">Fig. 3</figref> depicts a cross-sectional side view on the liner 40 along the line 59 in <figref idref="f0002">Fig. 2</figref>. Shown is the substrate boat 26 including a plurality of slots for holding a plurality of substrates 27 mounted on a pedestal 28. The pedestal 28 may comprise a heat shield and may be rotatable by a motor (not shown). The outer wall 41 of the liner 40 may be provided with a flow deflector in the form of an annular baffle 52 which may protrude radially from the outer surface 41.

0035The liner 40 may be provided with an open tapered top end 54 at the top end of the liner 40. The open tapered top end 54 may have an opening sufficiently large to allow the substrate boat 26 to pass when the substrate boat 26 moves in the inner space of the liner 40. When the substrate boat is moved into the inner space of the liner, the open tapered top end may be fully open since there is no substrate boat 26 in the opening. The advantage is that any back flow through the gas passage 20 likely will go through the opening at the top and not through the gas exhaust holes 19. The back flow will therefore pass all the flow deflectors 52 and particles in the back flow may be obstructed before reaching the substrates.

0036<figref idref="f0004">Fig. 4</figref> depicts a side view on the liner 40 of <figref idref="f0002">Figs. 2</figref> and <figref idref="f0003">3</figref>. Gas exhaust holes 19 may be provided in the liner 40 to discharge or exhaust gas from the inner space. The outer wall 41 of the liner 40 may be provided with a flow deflector in the form of a plurality of annular baffles 52 which may protrude radially from the outer surface 41.

0037The flow deflectors may comprise a hole flow deflector 56 which may be arranged within 10 mm from the gas exhaust hole 19. The hole flow deflector 56 may be arranged near the lower side of the gas exhaust hole 19. The hole flow deflector 56 may be provided with upstanding ridges 58 directed parallel to the central axis L in a direction of the top end. The gas exhaust hole 19 may be slit shaped. The short side of the slit may be directed in a direction parallel to the central axis L. A particle in the gas flow traveling along the outer wall 41 of the liner 40 in the axial direction L may be obstructed by the flow deflectors, the hole flow deflectors, the ridges and/or the slit shape of the gas exhaust hole to reduce the risk of the particle entering the interior space. Multiple gas exhaust holes 19 in a vertical array may be provided in the liner. The multiple gas exhaust holes 19 in the liner 40 may have an increasing cross-section from bottom to top of the liner. The increasing cross-section may compensate for the increase of distance to the vacuum pump 24 (in <figref idref="f0001">figure 1</figref>) so that for each gas exhaust hole 19 in the array the volume of gas exhausted is substantially equal.

0038The liner 40 may be provided with an open tapered top end 54 at the top end of the liner 40. The open tapered top end 54 may have an opening sufficiently large to allow a substrate boat 26 to pass.

0039<figref idref="f0005">Fig. 5</figref> schematically illustrates an embodiments of a liner 40 according to an embodiment. The embodiment features a flow deflector 50 comprising a plurality of identical baffles 52 that protrude radially from, and extend substantially tangentially along, the outer wall 41 of the liner 40 at different axial positions. Each of the baffles 52 may extend tangentially along the outer wall 41 of the liner 40 through an angle <i>α</i> of approximately 40 degrees relative to the central axis L. It is contemplated, however, that in other embodiments the angle <i>α</i> of at least some of the baffles 52 may be smaller or larger than 40 degrees, e.g. be in the range of 30-90 degrees.

0040Furthermore, the baffles 52 may extend substantially perpendicular to the outer wall 41. The baffles 52 may be disposed at a discrete number of spaced apart axial positions, spread across the height of the liner 40. For example, six baffles may be equidistantly spaced apart across the height of the liner 40 as depicted in <figref idref="f0005">Fig. 5</figref>. Consequently, when the liner 40 is incorporated in a vertical furnace 1 similar to that shown in <figref idref="f0001">Fig. 1</figref>, the flow deflector 50 will be approximately uniformly distributed over the length of the gas passage 20, at least such that it extends in all of three equally long axially extending portions of the gas passage 20 that together cover the total length thereof (e.g. in the depicted orientation: a bottom portion, a middle portion and a top portion of the gas passage 20).

0041Each of the axial positions in the embodiment of <figref idref="f0005">Fig. 5</figref> may feature a number of tangentially spaced apart baffles 52. As depicted a series of six equidistantly tangentially spaced apart baffles 52 may be provided. The series of baffles 52 at different axial positions have been rotationally offset relative to each other, and may partially overlap which each other, in such a way that, seen in the axial direction L, the flow deflector 50 - i.e. all the baffles 52 considered in conjunction - encircle the liner 40 at least completely. In fact, they may be considered to encircle the liner more than once.

0042Due to the fact that the flow deflector 50 is configured such that it encircles the liner 40 more than once, a gas flow traveling along the outer wall 41 of the liner 40 in the axial direction L may be obstructed several times by different baffles 52 of the flow deflector 50. Furthermore, because the flow deflector 50 is approximately uniformly distributed over the axial length of the liner 40, there is no particular axially extending portion of the outer wall 41 that is devoid of baffles 52 and that may for that reason facilitate the development of relatively strong back flows. Instead, the flow deflector 50 may be considered as somewhat of a maze made up of flow breaking/deflecting baffles 52 that scatter developing, axially directed flows that might be capable of transporting deposit.

0043Gas exhaust holes 19 may be provided in the liner 40 to discharge or exhaust gas from the reaction chamber. The flow deflectors may comprise a hole flow deflector 56 which may be arranged within 10 mm from the gas exhaust hole 19 in the liner 40. The hole flow deflector may be arranged towards the lower side with respect to the gas exhaust hole 19. The gas exhaust hole may be slit shaped and the short side of the slit may be directed in a direction parallel to the central axis L. Multiple gas exhaust holes in a vertical array may be provided in the liner. The multiple gas exhaust holes 19 in the liner 40 may have an increasing cross-section from bottom to top along the liner.

0044According to an embodiment the flow deflector may include a number of baffles that extend helically along the outer wall of the liner around the central axis L. From the perspective of back flow prevention, it may be tempting to construct and employ a flow deflector with a relatively large number of baffles. However, a larger number of baffles may mean an increase in flow resistance along the exhaust path, which in turn may increase the demands placed on the vacuum pump of a thermal processing furnace. Numerical simulations have shown that the increase in flow resistance caused by the presence of a modest number of helically extending baffles may be relatively small and practically of no concern to most applications.

0045Although illustrative embodiments of the present invention have been described above, in part with reference to the accompanying drawings, it is to be understood that the invention is not limited to these embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.