FR2588274A1 - Apparatus and process using a reactor for the vapour-phase chemical deposition of a material on a substrate, with axial symmetry. - Google Patents

Abstract

Reactor and process for forming a deposit using chemical vapour on a substrate 10. The reactor has axial symmetry and the carrier gas for the materials to be deposited on the substrate 10 is directed perpendicularly in relation to the substrate at a substantially uniform rate and in general with an axial symmetry around the substrate; radiation heating chambers 60 arranged above and below the substrate 10 produce a uniform heating by radiation in order to maintain a uniform temperature during the deposition process; the substrate is carried by a support and a rod 80 making it possible to adjust the distance between the substrate and the region where the introduction of the carrier gas for deposit materials is performed; the rod can be turned to improve the uniformity of the gas flow and of the heating in relation to the substrate surface. Application especially to the manufacture of chips, wafers and other similar electronic components.

Description

 The invention generally relates to the chemical deposition of a substance conveyed by a gas on a solid substrate, and more particularly to a reactor with axial symmetry to effect this deposition by chemical vapor.

 It is known, in this particular technical field, to carry out the deposition by chemical vapor of substances or materials, for example by epitaxial deposition using chemical vapor, by directing a jet of gas containing the materials in reaction towards a substrate solid. The gas contains the substance to be deposited on the substrates. The solid substrate must most often be kept at a high temperature in order to maintain the reaction with the surface. The deposition can for example be carried out inside an enclosure which constrains the gas flow to lick one or, preferably, several substrates which have been placed beforehand on a sensitive or receiving support or surface.

 Different problems can arise in the use of reactors for chemical vapor deposition according to the prior art. For example, the deposition reaction which occurs with the substrate extracts the substances to be deposited which are found in the gas stream, which determines a variation in the concentration of reagent in the gas. Since the gas is forced to flow through a wafer or chip-shaped substrate, the variation in concentration can be the cause of a uniformity defect in the deposited layer. This lack of uniformity of the deposited layers can occur on several substrates, or even on only one. In addition, the systems currently in common use have only a limited capacity to ensure a uniform temperature for several substrates or even for a single substrate. In general, a uniform temperature is obtained by associating with the substrate a significant thermal mass.

This large thermal mass and the thermal inertia that it produces can minimize uniformity in the distribution of temperature among the substrates. However, this same large thermal mass limits the rate at which the substrate can be brought to the state of thermal equilibrium, and consequently it can exert a harmful effect on the time necessary to process these substrates. Therefore, a large thermal mass can have a direct impact on productivity.

 In addition, reactors for spite by chemical vapor commonly used for so-called epitaxial deposition can allow self-doping, which is doping of the substance deposited as a result of evaporation from the back of the substrate, for example highly doped. In reactors produced according to the prior art, care was taken to hermetically seal this back side of the substraL awin to prevent self-doping.

 In an attempt to increase the productivity of chemical vapor deposition reactors, the dimensions of these reactors have been increased in order to accommodate more materials forming substrates therein. This dimensional increase resulted in increased contamination of the substrate by particles. The particulate matter in question originates from deposits of undesirable matter on the walls of the reactors, deposits which can detach from the walls and enter the deposition area.

 In these known systems of dep8t by chemical vapor, one can con trict the composition of the gaseous vehicle, the temperature and the autodoping, but one also endeavored to carry out a complementary counter of the dep8t process.

 Research has recently been carried out on the possibility of using a symmetrical gas stream licking each substrate in order to achieve a more satisfactory process of chemical vapor annoyance. By using axially symmetrical flow and appropriate boundary conditions, a more uniform deposit layer can be obtained. The dep8t carried out on a single wafer or chip introduces a certain flexibility into the heating process, which makes it possible to minimize the heating and cooling times. The axially symmetrical gas flow offers the additional advantage of reducing self-doping, that is to say the undesirable doping of the deposition layer by atoms coming from the heavily doped substrate. In addition, the axially symmetrical gas flow makes it possible to use larger substrates, therefore reactors for single wafer or chip. Such single chip reactors tend to reduce contamination by particles from the substrate deposition areas.

 Consequently, it has been found that there is a demand for a chemical vapor deposition reactor which can take advantage of an axially symmetrical flow of the gas and provide uniform heating so that a relatively reduced thermal mass can be associated with the substrate.

 Consequently, one of the aims of the present invention is to provide an improved reactor for spite by chemical vapor.

 Furthermore, the invention aims to provide a reactor for the deposition, by chemical vapor, which is intended for an axially symmetrical substrate.

 On the other hand, the invention aims to provide a starting process by chemical vapor having an axially symmetrical geometry.

 The invention also aims to provide an apparatus and a method for uniformly heating a substrate having a circular geometry.

 In addition, the invention aims to provide a reactor for dep8t by chemical vapor, which comprises a means suitable for ensuring additional control of the deposition process.

 Finally, the object of the present invention is to provide a reactor for spite by chemical vapor, in which the flow over the substrate of the gas carrying the substance constituting the reagent has an axial symmetry.

 According to the present invention, the various aims set out above, as well as others still, are achieved thanks to an apparatus which comprises a circular reaction chamber for the deposition by chemical vapor of substances on a substrate of substantially circular shape. This circular substrate is supported by a receiver, support or surface, thanks to a rod or column. The gas which conveys the material to be deposited on the substrate is directed towards the surface of the substrate at a practically uniform speed and in a direction perpendicular to this surface, using an apparatus located and controlled at a certain distance from the substrate. This gas is generally channeled so as to flow in an axially symmetrical vein towards the surface of the substrate. A radiation heating device is provided in order to heat the substrate and the apparatus associated with it to a uniform temperature. The uniformity of the temperature provided by the heating device allows the substrate and the associated device to have a relatively low thermal mass. This low thermal mass makes it possible to quickly reach thermal equilibrium for a selected or given temperature of the substrate. The rod or column supporting the substrate can be rotated in order to further increase the uniformity of the temperature and of the result obtained. It is also possible to introduce a complementary gas stream in order to minimize the autodoping of the deposited layer.

These various characteristics of the invention, as well as others still, will emerge clearly on reading the description which follows and refers to the appended drawing, in which
FIGURE 1 is an exploded schematic view of a reactor chamber for chemical vapor deposition according to the present invention;
FIGURE 2 is a schematic cross-sectional view showing the reactor chamber according to the invention for chemical vapor spite;
FIGURE 3 is a schematic cross-sectional view showing a complementary detail of the reactor chamber according to a preferred embodiment, and
FIGURE 4 is a cross-sectional view of the support rod or column which provides additional gas supply to minimize self-doping of the material deposited on the substrate.

 If we refer first to Figure 1, which is an exploded view of the apparatus according to the invention, it can be seen that it essentially comprises the chemical vapor deposition chamber of the reactor. The apparatus containing the reactor chamber in fact comprises two chambers, respectively upper and lower 60, with which are associated several heating elements 50 operating by radiation. These heating elements are essentially constituted by lamps of elongated shape, while the individual chambers can have a square shape in the preferred embodiment. As it appears clearly, it is also possible to adopt other geometric shapes for these chambers. The lamps pass through openings provided for this purpose in the walls of the chambers and are arranged substantially parallel to each other and with respect to the plane of the substrate 10 The upper - and lower chambers are in principle arranged so that the set of lamps in each room is arranged perpendicularly to the lamps in the set of the other room. The substrate 10 and the sensitive support or receiver associated therewith 15 are supported in the reactor by a rod or column 80. The gas 11 which carries the substances to be deposited on the substrate 10 is introduced into the reactor chambers by a device 70.

The latter is generally made of quartz (in order to transmit the heating radiation) and comprises a chamber into which the gas 11 is introduced. The device 70 has a lower surface of range substantially parallel to the surface of the substrate. This bearing surface has a multitude of orifices which make it possible to direct the gas in the form of a substantially uniform vein towards the substrate.

 Referring now to Figure 2, we see in cross section the arrangement of the reactor for chemical vapor deposition. The lamps 50 housed in the two heating chambers 60 ensure uniform heating of the substrate 10 and of the support or receiver 15 associated therewith.

In Figure 2, the lamps are not shown in their perpendicular arrangement in order to show two possible modes of orientation of these heating lamps. In the lower series of heating lamps, parabolic reflectors direct the radiant energy towards the support 15 and the associated substrate 10. In the upper chamber 60 of FIG. 2, the heating lamps 50 situated at the ends of the row are associated with parabolic reflectors. The intermediate lamps are arranged opposite a flat part 52. This flat part and the parabolic reflectors are coated with a material with high reflecting power in order to return the radiation to the substrate-support assembly.

This assembly is in turn supported by a rod or column 80 and, although this is not shown in Figure 2, the base of this rod or column passes through the lower heating chamber 60. The device 70, which delivers the gas containing the material to be deposited on the substrate, has an inlet intended to receive the gas 11 and several orifices 74 whose purpose is to direct this gas uniformly towards the substrate 10.

The apparatus 90 (not shown in detail) serves to extract the gas from the deposition chamber so as to ensure the axial symmetry of the gas flow. This device 90 can have several openings and its main role consists in blocking the flow of gas. The apparatus 90 also constitutes a source of thermal dispersion in order to guarantee the uniformity of the temperature in said substrate-support assembly.

 Referring now to Figure 3, there is shown a more detailed arrangement of the reactor chamber. The chambers 60 are provided with lamps 50 electrically and mechanically connected to the rest of the apparatus by a coupling device 51. These lamps 50 can be associated with reflective elements, as shown in FIG. 2. The device 70 comprises a first plate 72 and a second plate 71. The plane of this second plate 71 is substantially parallel to that of the substrate 10 and this plate 71 has several orifices intended to direct the gas 11 towards the substrate. This substrate 10 is supported by a rod 80. The gas is forced to flow along a path formed by several baffles 91, in order to maintain the axial symmetry of the gas flow. The substrate and the upper part of the rod are essentially enclosed between the plate 71, the plate 75 and the external surfaces 76 in order to restrict the gas flow. The gas can also title extracted from the enclosure through several orifices. The case 8 is connected to the heating chambers 60 and comprises an additional device, not shown, for connecting the upper and lower parts of the components of the reactor and supporting the device forming the inner enclosure.

 If one examines Figure 4, one sees there a method allowing to pocket the doping of the layer of dep8t. The axially symmetrical flow of the gas 11 circulates towards the outside, towards the edges of the substrate 10.

This substrate 10 is supported above the support 15 by means of studs 16. This support 15 is in turn supported above the column 80 by spacers 81 and by the vertical wall of this column 80. The gas 13 flows through a passage formed in the column 80, then through an opening 83 provided in the support 15, to end in the interval which separates this support from the substrate. This outward radial flow, together with the outward radial flow of the carrier gas 11, distances the unwanted atoms from the doping of the substrate with respect to the part of the substrate which receives the deposit.

Operation
The structure of the chemical vapor deposition reactor is designed to take advantage of the advantageous effects which result from an axially symmetrical flow of carrier gas over a substrate. This type of gas flow, also called stagnation point flow, has the following advantages: radial uniformity of the concentration of the materials deposited in the vicinity of the substrate, radial uniformity of the gas temperature isotherms above the surface of the substrate, and radial uniformity of chemical reaction rates in the gas and on the surface of the substrate.

 The device 70 which, in the preferred embodiment, may consist of plates of materials having openings in the plate closest to the substrate, constitutes a convenient technical means for introducing the gas jet with axial symmetry into the chamber. In the preferred embodiment, these openings are located at the vertices of equilateral angles. A means, such as baffles 91, is provided to prevent the process of extracting the carrier gas from appreciably disturbing the axial flow of the gas. The device 70 will preferably be made of a material capable of transmitting a large fraction of the radiation to the support-substrate assembly.

 The heating chambers are arranged in a similar manner in order to maintain the axial symmetry of the deposit in formation and to maintain a uniform temperature above the substrate. The multiple lamps 50 are arranged inside the heating chambers. On the walls 53 of these chambers as well as on the reflection zones 52 and the parabolic reflectors 51, a material with high reflecting power has been deposited in order to increase the thermal efficiency as well as the area of the heat sources situated opposite the substrate to treat. If we refer for example to Figure 2, we see that the edge of the substrate is not exposed to radiation like the rest of the substrate, due to the absence of heating sources in the direction of the devices 90. compensate for this colder environment, the outermost heating lamps can be of higher wattage, which increases the radiant heating in this area. By changing the position of the heating elements and allowing the orientation of the end lamps, or by extending the heating chamber well beyond the location of the substrate, one can also compensate for the increase in heat loss in the extreme zone of the substrate. The dimensions of the heating chamber can be coated with a material with relatively high reflecting power, which produces the same effect as the adoption of complementary sources of heat, relative to the substrate, thanks to the reflected radiation. Heating lamps can be a function of that of the lamps which are in the opposite room, in order to further reduce the structure resulting from the use of discrete sources of heat. The rod or column which supports the substrate can also be rotated to further reduce the remaining thermal structure.

 Figure 4 shows a particular embodiment of the present invention in which a gas flow 13 can be used to reduce self-doping. The gas streams 11 and 13 have the effect of distancing the doping materials (which evaporate from the underside of the substrate) from the surface of the substrate which receives the materials forming the desired spite. The support column 80 will preferably be composed of a transparent material for a wide range of the thermal radiation spectrum.

 The thinning or elimination of the sensitive or receptive support on which the substrate is placed can also reduce the mass which must be heated to reach thermal equilibrium. By reducing this thermal mass, it is possible to process a larger quantity of substrate in a given time and thus obtain a better production yield.

 The substrate can advantageously be moved vertically in both directions relative to the plate through which the carrier gas is introduced. This flexibility provided in the position of the substrate makes it possible to better control the conditions under which the deposition takes place.

 Another source of uniformity defects lies in the radiation field to which the support-substrate combination is subjected, due to the absorption and temperature characteristics of the device 70, of the rod or column and of any other structural member than it is necessary to interpose between the radiation sources and the support-substrate assembly.

Account must be taken of the disturbances which occur in the radiation field as a result of the presence of elements such as the thermal influence exerted by structural members under the effect of absorption and emission of radiation. .

 The foregoing description should not be considered as limiting the scope of the invention, since it relates only to the preferred embodiment thereof. Modifications and variations may come to mind of those skilled in the art without however departing from the basic principles of the invention.

Claims (19)

 1. A reactor for the deposition by chemical vapor on a substrate comprising the actual substrate (10) of circular shape, this reactor being characterized in that it comprises a heating means (60) making it possible to uniformly heat the said substrate (10), and a gas flow means (70) which forms an axially symmetrical gas flow perpendicular to said substrate.  2. A reactor for the deposition by chemical vapor according to Claim 1, characterized in that it comprises a sensitive support (15) for supporting said substrate (10), this support making it possible to control the distance between the flow means gas (70) and said substrate (10).  3. A reactor for chemical vapor deposition according to Claim 1, characterized in that it comprises a support means (15) intended to receive the substrate (10) and makes it possible to rotate the latter.  4. A reactor for the deposition by chemical vapor according to claim 1, characterized in that the gas flow means (70) comprises devices (73, 74) making it possible to introduce the gas at a uniform speed and in a direction perpendicular to a surface of said substrate (10).  5. The reactor for chemical vapor deposition according to Claim 1, characterized in that the heating means (60) comprises first and second chambers, at least one of which comprises several heating lamps (50).  6. The reactor for the deposition by chemical vapor according to claim 5, characterized in that said chambers (60) comprise on at least part of their inner walls a coating of material with high reflecting power (51, 52).  7. The reactor for chemical vapor deposition according to claim 1, characterized in that said axially symmetrical gas flow makes it possible to obtain a gas flow configuration with a stagnation point.  8. The reactor for chemical vapor deposition according to Claim 1, characterized in that it comprises a chamber (76) provided with several orifices having substantially an axial symmetry and which is situated at a uniform distance from the substrate ( 10), said heating means comprising several heating lamps (50) which give the substrate a substantially uniform temperature, and at least one opening disposed symmetrically around the periphery of said circular substrate.  9. The reactor for deposition by chemical razor according to Claim 8, characterized in that said chamber is made of a material which can be traversed by the heating radiation.  10. The reactor for spite by chemical vapor according to claim 8, characterized in that it comprises an opening (83) located below said substrate (10) to introduce a second gas flow towards said substrate (10) .  11. The reactor for dep8t by chemical vapor according to claim 8, characterized in that said heating lamps (50) are arranged above and / or below said substrate (10).  12. The reactor for spite by chemical vapor according to claim 8, characterized in that said substrate (10) is supported by a suitable support or receptor (15).  13. The reactor for spite by chemical vapor according to claim 8, characterized in that said chamber (76) and said opening or said openings are designed so as to produce a gas flow said to point of stagnation.  14. The reactor for the chemical vapor deposition according to claim 8, characterized in that it comprises a first heating chamber disposed on a first base of the substrate (10) as well as a second chamber disposed on a second side of said substrate, these first and second heating chambers comprising several heating lamps (50), while the heating lamps of the first chamber are arranged perpendicularly to the heating lamps of the second chamber.  15. The reactor for spite by chemical vapor according to Claim 8, characterized in that it comprises means making it possible to rotate said substrate (10).  16. A process for the chemical vapor deposition using the reactor according to Claim 1, characterized in that it comprises the following phases  a) a uniform substrate (10) is produced;  b) this substrate (10) is heated uniformly to a predetermined temperature, and  c) a gas is circulated around said substrate, the gas flow having an axial symmetry, this gas containing materials capable of forming a deposit on said substrate.  17. A process for the chemical vapor deposition according to Claim 16, characterized in that the substrate is rotated.  18. Process for the chemical vapor deposition according to Claim 16, characterized in that a second gas flow is introduced which circulates around a second surface of said substrate in order to minimize the self-doping effect.  19. Process for the chemical vapor deposition according to Claim 16, characterized in that the phase which consists in producing said gas flow produces a gas flow at a stagnation point with respect to said substrate.