Patent Description:
A substrate processing apparatus such as a vertical furnace for processing substrates e.g. semiconductor wafers may include a heating element, placed around a bell jar-shaped process tube. The upper end of the process tube may be closed, for example by a dome-shaped structure, whereas the lower end surface of the process tube may be open.

The lower end may be partially closed by a flange. An interior bounded by the tube and the flange forms a reaction chamber in which wafers to be treated may be processed. The flange may be provided with an inlet opening for inserting a wafer boat carrying wafers into the reaction chamber. The wafer boat may be placed on a door that is vertically moveably arranged and that is configured to close off the inlet opening in the flange.

The flange may support one or more injectors to provide a gas to the reaction chamber. For this purpose the injector may be configured with the internal gas conduction channel. Additionally, a gas exhaust duct may be provided in the flange. This gas exhaust may be connected to a vacuum pump for pumping off gas from the reaction chamber. The gas provided by the injectors in the reaction chamber may be a reaction (process) gas for a deposition reaction on the wafers. This reaction gas may also deposit on other surfaces than the wafers, for example it may deposit in the internal gas conduction channel. Layers created by these deposits may cause clogging and or breakage of the injectors. <CIT> discloses an injector according to the pre-characterizing portion of claim <NUM>. Further prior art is disclosed in the documents <CIT> and <CIT>.

Accordingly an improved injector may be required.

The present disclosure provides an injector according to Claim <NUM>.

The various embodiments of the invention may be applied separate from each other or may be combined. Embodiments of the invention will be further elucidated in the detailed description with reference to some examples shown in the figures.

It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure.

In this application similar or corresponding features are denoted by similar or corresponding reference signs. The description of the various embodiments is not limited to the examples shown in the figures and the reference number used in the detailed description and the claims are not intended to limit what is described to the examples shown in the figures.

<FIG> shows a cross-sectional view of a vertical furnace. The vertical furnace may comprises a process tube <NUM> forming a reaction chamber and a heater H configured to heat the reaction chamber. A liner <NUM> may be provided along the process tube <NUM>, the liner <NUM> may comprise a substantially cylindrical wall delimited by a liner opening at a lower end and a dome shape top closure 2d at the higher end.

A flange <NUM> may be provided to at least partially close the opening of the process tube <NUM>. A vertically movably arranged door <NUM> may be configured to close off a central inlet opening O in the flange <NUM> and may be configured to support a wafer boat B that is configured to hold substrates W. The door <NUM> may be provided with a pedestal R. The pedestal R may be rotated to have the wafer boat B in the reaction chamber rotating.

In the example shown in <FIG>, the liner <NUM> may comprise a substantial cylindrical liner wall having an outer substantial cylindrical surface 2a and an inner substantial cylindrical surface 2b. The flange <NUM> may be configured to at least partially close the tube opening and the liner opening defined more precisely by the lower end surface 2c of the liner <NUM>. The flange <NUM> comprises:.

The substrate processing apparatus may have a vessel for containing silicon precursors and may be operably connected to an elongated injector <NUM> via the gas inlet <NUM>. The injector <NUM> may be constructed and arranged to extend vertically into the reaction chamber I along the substantial cylindrical wall of the liner <NUM> towards a higher second end. The injector may be supported by the flange <NUM> at a lower first end of the injector and may comprising an injector opening to inject gas in the reaction chamber. One or more injectors <NUM> may be used to provide the process gas to the reaction chamber I. One injector <NUM> is shown in <FIG>.

Gas exhaust duct <NUM> for removing gas from the reaction chamber I may be constructed and arranged below the injector opening <NUM>. In this way a down flow F in the reaction chamber of the liner <NUM> may be created. This down flow F may transport contamination of reaction byproducts and particles from the substrate W, the boat B, the liner <NUM> and/or the support flange <NUM> downward to the exhaust duct <NUM> away from the processed substrates W.

The gas exhaust duct <NUM> for removing gas from the reaction chamber I may be provided below the liner opening of the liner <NUM>. This may be beneficial since a source of contamination of the reaction chamber may be formed by the contact between the liner <NUM> and the flange <NUM>. Again, the down flow F may transport the particles from the liner - flange interface downward to the exhaust away from the processed substrates.

The gas exhaust openings <NUM> may be constructed and arranged between the liner <NUM> and the flange <NUM> for removing gas from the circumferential space between the liner <NUM> and the tube <NUM>. In this way the pressure in the circumferential space and the interior space I may be made equal and in a low pressure vertical furnace may be made lower than the surrounding atmospheric pressure surrounding the tube <NUM>. The vertical furnace may be provided with a pressure control system to remove gas from the reaction chamber.

In this way the liner <NUM> may be made rather thin and of a relatively weak material since it doesn't have to compensate for atmospheric pressure. This creates a larger freedom in choosing the material for the liner <NUM>. The thermal expansion of the material of liner <NUM> may be chosen such that it may be comparable with the material deposited on the substrate in the reaction chamber. The latter having the advantage that the expansion of the liner and the material deposited also on the liner may be the same. The latter minimizes the risk of the deposited material dropping of as a result of temperature changes of the liner <NUM>.

The tube <NUM> may be made rather thick and of a relatively strong compressive strength material since it may have to compensate for atmospheric pressure with respect to the low pressure on the inside of the tube. For example, the low pressure process tube <NUM> can be made of <NUM> to <NUM>, preferably around <NUM> thick Quartz. Quartz has a very low Coefficient of Thermal Expansion (CTE) of <NUM> × <NUM>-<NUM>-<NUM> (see table <NUM>) which makes it more easy to cope with thermal fluctuations in the apparatus. Although the CTE of the deposited materials may be higher (e.g., CTE of Si3N4 = <NUM> × <NUM>-<NUM>-<NUM>, CTE of Si = <NUM> × <NUM>-<NUM>-<NUM>) the differences may be relatively small. When films are deposited onto tube made of quartz, they may adhere even when the tube goes through many large thermal cycles however the risk of contamination may be increasing.

The liner <NUM> may circumvent any deposition on the inside of the tube <NUM> and therefore the risk of deposition on the tube <NUM> dropping off may be alleviated. The tube may therefore be made from Quartz.

A liner <NUM> of silicon carbide (CTE of SiC = <NUM> × <NUM>-<NUM>-<NUM>) may provide an even better match in CTE between deposited film and liner, resulting in a greater cumulative thickness before removal of the deposited film from the liner may be required. Mismatches in CTE result in cracking of the deposited film and flaking off, and correspondingly high particle counts, which is undesirable and may be alleviated by using a SIC liner <NUM>. The same mechanism may work for the injector <NUM> however for injectors <NUM> it may be the case that the injector may be breaking if too much material with different thermal expansion is deposited. It may therefore be advantageously to manufacture the injector <NUM> from silicon carbide or silicon.

Whether a material is suitable for the liner <NUM> and or the injector <NUM> may be dependent on the material that is deposited. It is therefore advantageously to be able to use material with substantially the same thermal expansion for the deposited material as for the liner <NUM> and/or the injector <NUM>. It may therefore be advantageously to be able to use material with a thermal expansion for the liner <NUM> and/or the injector <NUM> relatively higher than that of quartz. For example Silicon Carbide SiC may be used. The silicon carbide liner may be between <NUM> to <NUM>, preferably <NUM> thick since it doesn't have to compensate for atmospheric pressure. Pressure compensation may be done with the tube.

For systems depositing metal and metal compound materials with a CTE between about <NUM> × <NUM>-<NUM>-<NUM> and <NUM> × <NUM>-<NUM>-<NUM>, such as TaN, HfO2 and TaO5, the liner and injector materials preferably may have a CTE between about <NUM> × <NUM>-<NUM>-<NUM> and <NUM> × <NUM>-<NUM>-<NUM>, including, e.g., silicon carbide.

For deposition of material with even a higher CTE, the liner and/or injector materials may be chosen as for example depicted by table <NUM>.

Within the tube <NUM> a purge gas inlet <NUM> may be provided for providing a purge gas P to the circumferential space S between an outer surface of the liner 2b and the process tube <NUM>. The purge gas inlet comprises a purge gas injector <NUM> extending vertically along the outer surface of the cylindrical wall of the liner <NUM> from the flange <NUM> towards the top end of the liner. The purge gas P to the circumferential space S may create a flow in the gas exhaust openings <NUM> and counteract diffusion of process gas from the exhaust tube <NUM> to the circumferential space S as depicted by the arrows.

The flange <NUM> may have an upper surface. The liner <NUM> may be supported by support members <NUM> that may be connected to the outer cylindrical surface of the liner wall 2a and each have a downwardly directed supporting surface. The liner may also be supported directly on the upper surface of the flange <NUM> with it lower surface 2c, while allowing a gas exhaust opening <NUM> between the upper surface and the liner <NUM>.

The supporting surfaces of the support members <NUM> may be positioned radially outwardly from the inner cylindrical surface 2b of the liner <NUM>. In this example, the supporting surfaces of the supporting members <NUM> may be also positioned radially outwardly from the outer cylindrical surface 2a of the liner <NUM> to which they are attached. The downwardly directed supporting surface of the support members <NUM> may be in contact with the upper surface of the flange <NUM> and support the liner <NUM> while allowing a gas exhaust opening <NUM> between the upper surface and the liner <NUM>.

The support flange <NUM> of the closure may include gas exhaust openings <NUM> to remove gas from the reaction chamber of the liner <NUM> and the circular spaces between the liner <NUM> and the low pressure tube <NUM>. At least some of the gas exhaust <NUM> openings may be provided between the upper surface of the flange <NUM> and the liner <NUM>. At least some of the gas exhaust openings may be provided near the liner opening. The gas exhaust openings <NUM> may be in fluid connection with a pump via exhaust duct <NUM> for withdrawing gas from the reaction chamber and the circumferential space between the process tube <NUM> and the liner <NUM>.

<FIG> is a schematic top view of the tube of <FIG>. The figure shows the liner <NUM> with the cylindrical wall defining an inner substantially cylindrical surface 2b and an outer substantially cylindrical surface 2a that form an opening <NUM> for inserting a boat configured to carry substrates.

Also visible are the support members <NUM>. In this example, the liner <NUM> has three support members <NUM> that are equally spaced along the circumference of the outer cylindrical surface 2a of the liner <NUM>. The flange may be provided with positioning projections <NUM> that extend upwards from the upper surface 3a of the flange. The positioning projections <NUM> may engage the support members <NUM> on a tangential end surface thereof. As a result, the positioning projections <NUM> have a centering function for the liner <NUM> relative to the support flange <NUM>.

The liner <NUM> and the notches forming the support members <NUM> may be manufactured from quartz, silicon or silicon carbide. The liner <NUM> delimiting the reaction chamber may have a radially outwardly extending bulge 2e to accommodate the injector <NUM> or a temperature measurement system in the reaction chamber.

<FIG> schematically shows a cross section of an injector <NUM> according to an embodiment for use in the vertical furnace of <FIG> and <FIG>. The injector <NUM> may be configured for arrangement within a reactor of a vertical furnace to inject gas in the reaction chamber I. The injector <NUM> may be configured with an internal gas conduction channel <NUM> to transport gas. The injector <NUM> may be substantial elongated along a first axis and the internal gas conduction channel <NUM> may extend along the first axis.

The injector <NUM> may have a width extending along a second axis X perpendicular to the first axis substantially larger than a depth of the injector extending along a third axis Y perpendicular to the first and second axis. The wall <NUM> of the injector <NUM> may have a varying thickness. The wall <NUM> of the injector <NUM> may have a varying thickness along the second axis X. The varying thickness of the wall <NUM> may vary between <NUM> to <NUM>%. For example with <NUM>% as depicted from <NUM>,<NUM> to <NUM>,<NUM>.

The internal gas conduction channel <NUM> of the injector <NUM> may have a substantially oval shaped cross section. The internal gas conduction channel <NUM> may extend along its width in the second axis X substantially larger than it extends along its depth in the third axis Y. The substantially oval shaped cross section may be build up out of a plurality of circles with a fixed radius to accommodate drilling and milling. Rounded corners also avoid the build-up of stress and contamination in the corners. The radius of the circles may be <NUM> to <NUM>, for example a circle having a radius of <NUM>. The horizontal inner cross-section area of the internal gas conduction channel <NUM> inside the injector <NUM> may be between <NUM> and <NUM><NUM>, preferably between <NUM> and <NUM><NUM> and most preferably between <NUM> and <NUM><NUM>.

The substantially oval shaped gas conduction channel <NUM> may be partially pinched off in the middle. Whereby pinched off means that the internal gas conduction channel <NUM> has a smaller depth in the third direction. The middle refers to the middle with respect to the width of the injector <NUM> in the second direction X. Pinching off may be accomplished by the wall <NUM> having the varying thickness. For example, by the <NUM> wall having an increased thickness in the middle of its width which pinches of the gas conduction channel <NUM>.

The substantially oval shaped gas conduction channel <NUM> may be partially pinched off in the middle of the second direction by a bulb <NUM> making the wall <NUM> thicker and extending into and pinching off the gas conduction channel <NUM>. The surface of the bulb <NUM> may be partially following a bulb circle. The bulb circle may have a constant radius with respect to an axis parallel to the first axis. The radius may be between <NUM> to <NUM>, preferably between <NUM> and <NUM> and as depicted it may be <NUM>.

The wall <NUM> of the injector <NUM> may have a varying thickness along the third axis Y. The varying thickness along the third axis Y may be relatively small variation around <NUM>.

The wall <NUM> of the injector <NUM> may have a varying thickness over its circumference along the second and third axis X, Y. The varying thickness of the wall <NUM> may vary between <NUM> to <NUM>%.

The wall <NUM> of the injector <NUM> may have has a varying thickness along a substantial part of the first axis. In this way strength may be added where it is necessary.

The injector <NUM> may have a gas exit opening <NUM>. The gas exit opening <NUM> may have a radius of <NUM> to <NUM>, preferably between <NUM> to <NUM> and most preferably between <NUM> and <NUM>, for example <NUM>.

<FIG> schematically show injectors 17a, b, c according to another embodiment for use in the vertical furnace of <FIG> and <FIG>. The injectors 17a, b, c of <FIG> each may be specially configured to provide process gas at a particular height in the reaction chamber I. The injectors 17a, b, c of <FIG> may therefore be optimized to cooperate together as depicted in <FIG>. Alternatively, each injector <NUM> may be used singularly as depicted in <FIG>. The injectors 17a, b, c may be substantially elongated along a first axis Z.

The injectors 17a, b, c may be configured with an internal gas conduction channel <NUM> to transport process gas. The internal gas conduction channel <NUM> may extend along the first axis Z. The internal gas conduction channel <NUM> of the injector 17a, b, c may have a substantially oval shaped cross section.

The internal gas conduction channel <NUM> may extend along the second axis X between <NUM> to <NUM>, preferably between <NUM> and <NUM>, for example about <NUM>. The internal gas conduction channel <NUM> may extend along the second axis X substantially larger than the channel extends along the third axis Y. The internal gas conduction channel <NUM> may extend along the third axis Y between <NUM> to <NUM>, preferably between <NUM> and <NUM>, for example about <NUM>.

The substantially oval shaped cross section may be build up out of circles with a radius of <NUM> to <NUM>, for example a circle having a radius of <NUM>. This avoids straight corners in the gas conduction channel <NUM> because the corners then will have a minimal roundness of <NUM> to <NUM> for example <NUM>.

The horizontal inner cross-section area of the internal gas conduction channel <NUM> inside the injector <NUM> may be between <NUM> and <NUM><NUM>, preferably between <NUM> and <NUM><NUM> and most preferably between <NUM> and <NUM><NUM>.

The substantially oval shaped gas conduction channel <NUM> may be partially pinched off in the middle. Whereby pinched off means that the internal gas conduction channel <NUM> is smaller in the third direction Y. The middle refers to the middle with respect to the width of the injectors 17a, b, c in the second direction X. Pinching off may be accomplished by the <NUM> wall having an increased thickness in the middle.

The substantially oval shaped gas conduction channel <NUM> may be partially pinched off in the middle of the second direction by a bulb <NUM> provided to the wall <NUM> and extending into the gas conduction channel <NUM>. The surface of the bulb <NUM> may be partially following a circle. The circle may have a constant radius with respect to an axis parallel to the first axis. The radius may be between <NUM> to <NUM>, preferably between <NUM> and <NUM> and as depicted it may be <NUM>.

The injectors 17a, b, c may have a width extending along a second axis X perpendicular to the first axis substantially larger than a depth of the injector extending along a third axis Y perpendicular to the first and second axis as depicted in <FIG>. The wall <NUM> of the injectors 17a, b, c may have a varying thickness.

The wall <NUM> of the injectors 17a, b, c may have a varying thickness along the third axis Y. The wall <NUM> of the injectors 17a, b, c may have a varying thickness over its circumference along the second and third axis X, Y. The wall <NUM> of the injectors 17a, b, c may have a varying thickness along a substantial part of the first axis X.

The injectors 17a, b may be so called multi hole injectors and have a plurality of gas exit holes <NUM> along their length in the direction of the second end <NUM> opposite to the first end <NUM> as depicted in <FIG> and b. The gas exit opening <NUM> may have a radius of <NUM> to <NUM>, preferably between <NUM> to <NUM> and most preferably between <NUM> and <NUM>, for example <NUM>. The longer injector 17a of the plurality of injectors 17a, b, c may have multiple gas exit holes <NUM> as depicted in <FIG> and may extend within the interior to close to the top closure 2d (<FIG> and <FIG>) of the closed liner <NUM>. The shorter injector 17b of the plurality of injectors 17a, b, c may have multiple gas exit holes <NUM> as depicted in <FIG> and extend to the middle of the boat B.

The size of the gas conduction channel <NUM> may be smaller at the first end <NUM> where the injectors 17a, b, c may connect to the gas inlet <NUM> near the flange <NUM>. Since the temperature is lower near the first end <NUM> less process gas is deposited in the internal channel <NUM> near the first end <NUM>.

The depth of the injectors 17a, b, c in the third direction Y may be decreasing towards the second end <NUM>. The injector which extends within the interior I to close to a top closure 2d of the closed liner <NUM> may have a shape with a dimension in a direction in a radial direction which is decreasing closer to the top closure in <FIG>.

The injectors 17a, b, c of <FIG> each may be specially configured to provide process gas at a particular height in the reaction chamber I. At least one of the injectors 17a, b, c may therefore have a different length.

The longer injectors 17a, c of the plurality of injectors <NUM> as depicted in <FIG> and <FIG> may extend within the interior I to close to the top closure 2d of the closed liner <NUM> as depicted in <FIG> and <FIG>. The longer injector 17c of the plurality of injectors 17a, b, c may have a single gas exit hole <NUM> at the second end <NUM> as depicted in <FIG>. This injector may be called a dump injector 17c which is closed along its elongated length to have only one single process gas exit at its second end <NUM>. <FIG> depicts the cross section of this dump injector which has the same properties as described in relation to <FIG> above except that there is no gas exit hole <NUM> on the side.

The single gas exit hole <NUM> at the second end <NUM> of the dump injector may have the same properties as described in relation to <FIG> above. The single gas exit hole <NUM> of the dump injector may be between <NUM> and <NUM><NUM>, preferably between <NUM> and <NUM><NUM> and most preferably between <NUM> and <NUM><NUM>. The injectors 17a, b, c of <FIG> may therefore be optimized to cooperate together as depicted in <FIG>.

<FIG> depicts how the injectors 17a, b, c of <FIG> may be arranged in a tube <NUM>. The injector 17a, b may be the multihole injectors (see <FIG>) provided with a series of exit openings <NUM> extending in the elongated direction along the injector 17a, b to transport gas out of the conduction channel into the reaction chamber I. The shorter injector 17b and/or the longer injector 17a of the plurality of injectors 17a, b, c may have multiple gas exit holes <NUM>. The exit openings <NUM> may be substantially round. The series of exit openings <NUM> may be aligned along a line over the surface of the multihole injectors 17a, b.

The exit openings <NUM> may be configured such that gas is injected in at least two different directions substantially perpendicular to the elongated direction of the multi hole injector so as to improve mixing of the process gas in the reaction chamber I. The series of openings <NUM> may therefore be aligned along at least two lines over the surface of the injector <NUM>. Whereas a first line with openings may be shown in <FIG> a similar second line with openings <NUM> may be configured on the other side of the injector <NUM> as depicted in <FIG>. The series of openings <NUM> along a first line may be configured such that gas is injected in a first direction and the series of openings <NUM> along a second line may be configured such that gas is injected in a second direction. The first and second direction may be under an angle between <NUM> to <NUM> degrees with each other.

Exit openings <NUM> may be provided pair-wise at the same height as depicted in <FIG>. Alternatively, the exit openings <NUM> may be provided pair-wise at unequal height to improve the strength of the injector <NUM>. The two exit openings may inject the gas in two directions, for example under an angle of about <NUM> degrees, to improve the radial uniformity.

The distance between the openings <NUM> of the series of openings may be constant when going from the first end <NUM> to the second end <NUM> of the multihole injector <NUM> in <FIG> and b. Advantageously each exit opening <NUM> may have a substantial equal flow of process gas through the exit opening <NUM>.

The distance between the exit openings <NUM> of the series of exit openings may also be designed such that it decreases when going from the first end <NUM> to the second end <NUM> of the multihole injector <NUM>. The later may be beneficial to compensate for pressure loss when the processing gas is transported from the first end <NUM> to the second end <NUM>.

The area of the exit openings for multihole injectors may be between <NUM> to <NUM><NUM>, preferably between <NUM> to <NUM><NUM>, more preferably between <NUM> and <NUM><NUM>. Larger openings may have the advantage that it takes longer for the openings to clog because of deposited layers within the openings. The number of exit openings <NUM> may be between <NUM> and <NUM>, preferably <NUM> and <NUM>, and more preferably <NUM> and <NUM>.

The longer injector 17c of the plurality of injectors 17a, b, c may have a single gas exit hole at the second end as depicted in <FIG>. This injector 17c may be called a dump injector 17c which is closed along its elongated length to have only one single process gas exit at its second end near the top closure 2d of the liner. The single gas exit hole at the second end of the dump injector may have the same properties as described in relation to <FIG> above.

The exit opening <NUM> of the gas injector <NUM> may be configured to reduce clogging of the opening. The exit opening may have a concave shape from the inside to the outside. The concave shape with the surface area of the opening on a surface on the inside of the injector larger than the surface area of the exit opening <NUM> on the outside of the injector may reduce clogging. The larger area on the inside allows more deposition at the inner side where the pressure and therefore the deposition is larger. On the outside the pressure is reduced and therefore the deposition is also slower and a smaller area may collect the same deposition as a larger diameter on the inside.

Reducing the pressure with the injector may result in a reduction of the reaction rate within the injector <NUM> because the reaction rate typically increases with increasing pressure. An additional advantage of a low pressure inside the injector is that gas volume through the injector expands at low pressure and for a constant flow of source gas the residence time of the source gas inside the injector reduces correspondingly. Because of the combination of both, the decomposition of the source gases may be reduced and thereby deposition within the injector may be reduced as well.

The process gas that may be injected via the injector <NUM> in the reaction chamber I to deposit layers on the wafers W in the wafer boat B may also deposit on the internal gas conduction channel or on the outer surface of the injector <NUM>. This deposition may cause tensile or compressive stress in the injector <NUM>. This stress may cause the injector <NUM> to break which causes down time of the vertical furnace and/or damage to the wafers W. Less deposition within the injector therefore may prolong the lifetime of the injector <NUM> and make the vertical furnace more economical.

Temperature changes of the injector <NUM> may even increase these stresses. To alleviate the stress the injector may be made from a material which may have the coefficient of thermal expansion of the material deposited with the process gas. For example, the gas injector may be made from silicon nitride if silicon nitride is deposited, from silicon if silicon is deposited or from silicon oxide when silicon oxide is deposited by the process gas. The thermal expansion of the deposited layer within the injector may therefore better match the thermal expansion of the injector, decreasing the chance that the gas injector may break during changes of temperature.

Silicon carbide may also be a suitable material for the injector <NUM>. Silicon carbide has a thermal expansion which may match many deposited materials.

A disadvantage of a low pressure inside the injector is that the conduction of the injector decreases significantly. This would lead to a poor distribution of the flow of source gas over the opening pattern over the length of the injector: the majority of source gas will flow out of the holes near the inlet end of the injector.

To facilitate the flow of process gas inside the injector, along the length direction of the injector, the injector may be provided with an internal gas conduction channel with a large inner cross section. In order to be able to accommodate the injector according to the invention inside the reaction chamber, the tangential size of the injector <NUM> may be larger than the radial size and the liner <NUM> may be provided with an outwardly extending bulge to accommodate the injector.

In an embodiment the two source gases, providing the two constituting elements of the binary film, are mixed in the gas supply system prior to entering the injector. This is the easiest way to ensure a homogeneous composition of the injected gas over the length of the boat. However, this is not essential. Alternatively, the two different source gases can be injected via separate injectors and mixed after injection in the reaction chamber.

The use of two injector branches allows some tuning possibilities. When gas of substantially the same composition is supplied to both parts of the injector, via separate source gas supply, the flows supplied to the different injector branches can be chosen different to fine-tune the uniformity in deposition rate over the boat. It is also possible to supply gas of different composition to the two lines of the injector to fine-tune the composition of the binary film over the boat. However, the best results may be achieved when the composition of the injected gas was the same for both injector lines.

Since the injector <NUM> may be supported at its first end <NUM> by the flange <NUM> the injector <NUM> may wiggle a little bit at its second end <NUM> because it is a very long and thin structure as depicted in <FIG>. It is therefore desirable or necessary to design the liner <NUM>, injector <NUM> and the wafer boat B so that there is enough space between the three.

An outer side wall of the injector <NUM> may be tapered towards the second end <NUM> of the injector over at least <NUM>%, preferably <NUM>%, more preferably <NUM>%, and even more preferable over <NUM>% of its length. By having the injector <NUM> tapered at the second end <NUM> it may occupy less space in the small space between the liner <NUM> and the wafer boat in the reaction chamber I near its second end <NUM> where the tolerances are the tightest. The tolerances at which the injector <NUM> with its tapered second end <NUM> may be positioned in the small space may therefore be a bit more relaxed.

The injector extending within the interior to close to a top closure of the closed liner may therefore have a shape with a dimension in a direction in a radial direction which is decreasing closer to the top closure. Also in vertical furnaces where no liner <NUM> is used an injector <NUM> with a tapered shape at its second end <NUM> may be useful in relaxing the tolerances of positioning the injector in between the tube and the boat.

The injector <NUM> may comprise multiple branches, for example two branches, each provided with a separate gas feed conduit connection. One branch may inject process gas into the lower part of the reaction chamber and the other branch injects process gas into the upper part of the reaction chamber. The branches may be connected by connecting parts. However, it is not essential for the invention that the injector comprises two or more injector branches. The branches may be partially tapered at their second end.

The injector <NUM> may be manufactured from ceramics. The ceramics may be selected from siliconcarbide (SiC), siliconoxide (SiOx), silicon, or aluminumoxide (AlOx). The injectors may be manufactured in a process in which first the injector is formed and secondly the injector is baked to harden the ceramics.

Preceramic polymers may be used as precursors which may form the ceramic product through pyrolysis at temperatures in the range <NUM>-<NUM>. Precursor materials to obtain silicon carbide in such a manner may include polycarbosilanes, poly(methylsilyne) and polysilazanes. Silicon carbide materials obtained through the pyrolysis of preceramic polymers may be known as polymer derived ceramics or PDCs.

Pyrolysis of preceramic polymers is most often conducted under an inert atmosphere at relatively low temperatures. The pyrolysis method is advantageous because the polymer can be formed into various shapes prior to pyrolysis into the ceramic siliconcarbide. Prior to pyrolysis the material is much softer and therefore easier to be shaped in a form.

The injector <NUM> may comprise a bottom portion connected to a top portion wherein the top portion may be slightly tapered and ends at the second end <NUM>. The bottom portion may be between <NUM> and <NUM> long starting from the first end <NUM> and may be substantially straight.

The bottom portion may be provided with a connection pipe <NUM> (see <FIG>). The connection pipe <NUM> may be fitted in a hole in the flange <NUM> (in <FIG>) to position and hold the injector <NUM>. Such a construction on the first end <NUM> of the injector may be advantageously if the injector is heated because it allows for expansion of the injector <NUM>. A disadvantage may be that it allows for some wiggling of the injector <NUM> especially at the second end <NUM>.

By having the second end <NUM> tapered the tolerance for wiggling of the injector <NUM> may be increased. The top portion may have a cross sectional area at the second end <NUM> that is <NUM> to <NUM>%, preferably <NUM> to <NUM>%, and most preferably <NUM> to <NUM>% smaller than the cross sectional area at the first end. The top portion may have a wall thickness at the second end that is <NUM> to <NUM>%, preferably <NUM> to <NUM>% and most preferably <NUM> to <NUM>% than the wall thickness at the first end <NUM>.

The injector <NUM> may have a cross sectional area at the second end that is <NUM> to <NUM>%, preferably <NUM> to <NUM>%, and most preferably <NUM> to <NUM>% smaller than the cross sectional area at the first end. The injector may have a wall thickness at the second end <NUM> that is <NUM> to <NUM>%, preferably <NUM> to <NUM>% and most preferably <NUM> to <NUM>% smaller than the wall thickness at the first end <NUM>.

Claim 1:
An injector (<NUM>) configured for arrangement within a reaction chamber (I) of a substrate processing apparatus to inject gas in the reaction chamber (I), the injector (<NUM>) being substantially elongated along a first axis (Z) and configured with an internal gas conduction channel extending along the first axis (Z) and provided with at least one gas entrance opening and at least one gas exit opening, whereby the injector (<NUM>) has a width extending along a second axis (X) perpendicular to the first axis (Z) substantially larger than a depth of the injector extending along a third axis (Y) perpendicular to the first (Z) and second axis (X), wherein the wall (<NUM>) of the injector has a varying thickness and wherein the internal gas conduction channel (<NUM>) has a substantially oval shaped cross section whereby the internal gas conduction channel (<NUM>) extends along the second axis (X) substantially larger than the internal gas conduction channel extends along the third axis (Y), wherein the substantially oval shaped cross section is partially pinched off in the middle of the second direction by the wall (<NUM>) having an increased thickness.