Method and device for homogenising a gas flow incident on a surface in a vacuum chamber

Abstract

The invention relates to a vacuum evaporation deposition device (30) comprising: - a deposition housing or enclosure; - a deposition support (32); - evaporation means (36) for evaporating a material towards the deposition substrate (32); - reactive gas injection means (41) for injecting a reactive gas into the chamber; - means forming a cover (2) around the deposition substrate, extending from the deposition support, the axis XX' forming an axis of rotational symmetry perpendicular to the surface of the deposition support and centred thereon, the reactive gas injection means (41) comprising a duct provided with a plurality of openings for injecting a reactive gas with an initial momentum distribution that is rotationally symmetrical about the axis XX'.

Description

[0001] DESCRIPTION

[0002] Title: METHOD AND DEVICE FOR HOMOGENIZING A GAS FLOW INCIDENT ON A SURFACE IN A VACUUM ENCLOSURE

[0003] TECHNICAL FIELD AND STATE OF THE PRIOR ART

[0004] The invention relates to the field of methods and devices for deposition of thin layers.

[0005] An application of the invention relates in particular to micro-fabricated circuits with deposition of thin layer films ranging from a few nm to a few 100 nm in the presence of reactive gas.

[0006] The technique of cathode sputtering is known, in which a target of a material to be deposited is used, for example an oxide (resp. a nitride or a hydride). Atoms are removed from this target by bombarding it in a plasma. The deposition is then carried out at high pressure (> pbar), where the free path is millimetric, and where the incidence of the atoms on the substrate is therefore isotropic. These conditions are favorable for controlling in particular the stoichiometry of the deposit, which can be made homogeneous over large surfaces.

[0007] However, this method has the disadvantage of bombarding the deposited surface, and of inducing stresses in the layers, or dislocations in the substrate which may lead to the search for other deposition methods, such as for example evaporation (by electron gun or by Joule effect).

[0008] In the case of evaporative deposition techniques, homogenization of the deposit can be achieved by rotating the deposition stage. In this case, the transverse gradients are partially averaged, but the radial gradients relative to the center of the stage are not eliminated. Furthermore, there are situations where planetary rotation does not provide the solution to homogeneity: when rotation is not possible (for example, in the case of deposition at an angle), or when the deposition time is too short to make a number of rotations of the stage large compared to 1 (for example, if the film to be deposited is too thin and the deposition rate cannot be reduced accordingly). When seeking to evaporate an element in the presence of a reactive gas, the aim is to control both the homogeneity of the gas flow and the flow of the evaporated element.

[0009] The evaporators are designed so that the flow of material (initially in solid form at room temperature) evaporated is homogeneous: to this end, the source is placed far from the deposition plate.

[0010] Regarding the flow of reactive gas, the technical problem cannot be solved in a similar way. Indeed, a gas must be injected into a vacuum chamber. This is done through one or more orifices, causing an expansion of this gas from atmospheric pressure or slightly higher, towards the vacuum of the chamber. Once in the chamber, the molecules do not undergo any collisions with each other and have ballistic trajectories.

[0011] The expansion of gas through an orifice generates a flow of matter having an angular distribution described by the Clausing formula [P. Clausing, Z. Physik 66, 471 (1930)].

[0012] A calculation based on these distributions shows that it is impossible to perfectly focus the flow of molecules leaving an orifice. The majority of molecules exit at an angle away from the axis of the orifice, and populate the vacuum chamber. Consequently, the flow of gas incident on the deposition surface comes largely from molecules that have already encountered a wall of the chamber at least once and is not isotropic. Furthermore, it depends on the geometry of the chamber.

[0013] Each molecule encountering a wall is adsorbed on the surface, remains there for a certain time and is re-emitted with a speed distribution and an angular distribution depending on the temperature of the wall, the chemical species, the nature of the wall.

[0014] A problem that arises is therefore to be able to homogenize a flow of incident gas on a deposition surface, in particular in a vacuum enclosure in ballistic mode, i.e. at pressures lower than, for example, 5.10 -5 mbars. This is particularly the case if one wishes to produce deposits of homogeneous composition (stoichiometry) of alloys between an element (which is in solid form at room temperature) which is evaporated (by electron gun or by Joule effect) with a reactive gas (which is in gaseous form at room temperature and at ambient pressure) which is injected into an enclosure.

[0015] There is also the problem of the homogeneity of a flow of atoms or molecules of a compound, gaseous at ambient temperature and pressure, this flow being incident on a deposition surface placed in a vacuum enclosure in ballistic mode.

[0016] STATEMENT OF THE INVENTION

[0017] An objective of the invention is to be able to carry out a deposit by evaporation, in ballistic mode and in the presence of a reactive gas, this deposit being more homogeneous (in composition) than by known deposition techniques.

[0018] The invention firstly relates to a device for deposition by vacuum evaporation, comprising:

[0019] - a storage enclosure or frame;

[0020] - a support or a deposition substrate;

[0021] - gas injection means, for injecting a gas into the enclosure;

[0022] - evaporation means, for evaporating a material towards the deposition substrate;

[0023] - means forming a cover around the deposition substrate.

[0024] The means forming a cover extend from the substrate or the deposition support, an axis XX' forming an axis of symmetry of revolution or rotation of this cover, this axis XX' being perpendicular to the surface of the deposition support and preferably centered thereon. These means forming a cover surround and / or enclose the deposition surface, with the exception of a hole or an opening which is located opposite the source or the evaporation means.

[0025] Preferably, the reactive gas injection means comprise a conduit provided with several orifices which make it possible to inject a gas with a distribution of initial moments having a symmetry of revolution around the axis XX'; these reactive gas injection means are for example in the form of a shower. They are arranged between the evaporation means and the deposition support. The outer wall of the cover may make an angle less than, or greater than or equal to, 90° with the surface of said deposition support.

[0026] The invention therefore proposes an evaporation deposition device which makes it possible to carry out evaporation in ballistic mode, comprising a mechanical cover, around the deposition surface, which determines the flow of incident gas on this surface and which makes it possible to obtain good homogenization of the diffusion of the gas in the direction of the deposition substrate.

[0027] In a device or method according to the invention:

[0028] - the cover has a geometry allowing all points of the deposition surface to see the enclosure and its elements or components under the same solid angle, or under a solid angle that is as homogeneous as possible; for example, the cover has a truncated cone shape, with an axis of symmetry perpendicular to the deposition surface, and a base located on or in the same plane as the deposition surface;

[0029] - and / or the shape of this cache can result from the understanding and modeling of the flow of molecules in ballistic regime in a vacuum enclosure;

[0030] - and / or seen from the deposition surface, this cover preferably has a uniform geometry. It has an orifice to allow the flow of material emitted by a source or evaporation means to pass through;

[0031] - and / or we seek to ensure that each point on the deposition surface sees approximately the same solid angle of the inner surface of the cache. A calculation of the solid angle makes it possible to optimize the geometric parameters of the cache (height, diameter, orientation of the walls) to minimize its variations on the deposition surface. Thus, for a 2-inch deposition surface, we can, for example, obtain a solid angle (and therefore flow) homogeneity better than 0.1%, and approaching 0.05%.

[0032] In a device or method according to the invention, the cache:

[0033] - is for example made of aluminum or stainless steel;

[0034] - and / or has an axis of symmetry perpendicular to the deposition surface and centered on it;

[0035] - and / or has cylindrical or spherical symmetry;

[0036] - and / or is at least partly truncated or even cylindrical in shape; - and / or may have a small side or a base, which has a l ère circular opening, and a large side, opposite the small side, which has a 2 ème circular opening, which may, in certain embodiments, be of a diameter greater than that of the l ère circular opening or, in other embodiments, be of diameter less than that of the l ère circular opening;

[0037] - and / or the cover extends from the deposit support over a length for example between 40mm and 200mm, the upper limit being fixed by the dimensions of the deposit device. An optimum of this length can be sought depending on other parameters such as for example the angle of the cone and / or the opening of the top of the cover;

[0038] - and / or the cover may further comprise a diaphragm, for example made of stainless steel or aluminium, arranged at the entrance to the cover (on the side opposite the deposition support). Such a diaphragm makes it possible to improve the homogenisation effect of the diffusion of the gas towards the deposition substrate.

[0039] A device according to the invention may comprise 2 chambers or a method according to the invention may implement 2 chambers:

[0040] - a first chamber which comprises the means for evaporating a material towards the deposition substrate;

[0041] - a 2 echamber which includes the deposition support, the cover and the means for injecting a gas into the enclosure, the 2 chambers being separated by a wall provided with an orifice to allow a flow of evaporated material to pass towards the deposition support.

[0042] A device according to the invention may further comprise, or a method according to the invention may implement:

[0043] - pumping means to achieve, in the chamber, a pressure of at most 10 -6 mbar or 5 x 10 -7 or 10 -7 mbar before gas injection; for example, these pumping means make it possible to reach, before gas injection, a pressure of the order of, or less than or equal to, 10 -7 mbar or a pressure between on the one hand 10 -8 mbar or 2.10 -8 mbar and on the other hand 8 x 10 -8 mbar or 10 -7 mbar; during gas injection, these means make it possible to maintain a pressure less than or equal to 1.10-5 mbar or 5 x 10' 5 mbar in the storage enclosure or frame;

[0044] - and / or gas supply means, for injecting a gas into the enclosure; this gas is a reactive gas which will react or which reacts with the evaporated material.

[0045] According to particular embodiments, the evaporation means comprise at least one electron gun or at least one resistor. These are, for example, coevaporation means.

[0046] The invention also proposes a vacuum deposition method, for example implementing a device according to the invention, in which:

[0047] - a deposition substrate is positioned on the deposition support of a deposition enclosure or frame; this deposition substrate has, for example, a deposition surface with a diameter at least equal to 2 or 3 inches;

[0048] - the enclosure or frame is pumped down to a pressure less than or equal to, for example, 1.10-5 mbar or 5 x 10 -5 mbar or 10 -6 mbar and for example of the order of 10' 7 mbar or at a pressure between on the one hand 10 -8 mbar or 2.10 -8 mbar and on the other hand 8 x 10 -8 mbar or 10 -7 mbar;

[0049] - a reactive gas is injected into the enclosure using the gas injection means and a material is evaporated towards the deposition substrate using the evaporation means, at a pressure less than or equal to 1.10 -5 mbar or 5 x 10 -5 mbar, means forming a cover around the deposition substrate, these means forming a cover extending from the substrate or the deposition support, an axis XX' forming an axis of symmetry of revolution or rotation of this cover, this axis XX' being perpendicular to the surface of the deposition support and preferably centered thereon.

[0050] The cover means surround and / or enclose the deposition surface, except for a hole or opening which is located opposite the source or evaporation means.

[0051] A device or method according to the invention makes it possible to carry out vacuum deposition in ballistic conditions. The reactive gas injected is very much in the majority in the enclosure (there is less than 1% residual gas). The reactive gas injected into the enclosure is for example molecular oxygen (dioxygen) or molecular nitrogen (dinitrogen) or hydrogen or dihydrogen. The evaporation of said material towards the deposition substrate is for example carried out by heating, for example using an electron gun or by Joule effect.

[0052] The evaporated material is a material that is in solid form at room temperature. For example, it is aluminum or chromium or titanium or silicon or a transition metal. The reactive gas is in gaseous form at room temperature and pressure.

[0053] A method according to the invention makes it possible, for example, to produce a deposit of Titanium nitride (TiN) or Niobium nitride (NbN) or Aluminum nitride (AIN), or Titanium oxide (TiO2) or aluminum oxide (granular aluminum -GrAI- or AI2O3), or Silicon hydride (SiH).

[0054] A method according to the invention makes it possible to produce a deposit with a thickness of, for example, between 1 nm and 200 nm.

[0055] In a method according to the invention, the homogeneity of the stoichiometry of the deposit is preferably greater than or equal to 99.8% over a surface of diameter, for example, 2 inches.

[0056] With a device or method according to the invention, a reactive gas is injected which reacts with the evaporated material.

[0057] The gas injection conduit, or means, for injecting a gas into the enclosure, is / are arranged between the evaporation means and the deposition support.

[0058] A compound or a reactive gas used in the context of the present invention (device or method) is in gaseous form at ambient temperature and pressure. An atom or a molecule of this compound or this gas which is deposited on a wall of the enclosure or of the deposition frame, at ambient temperature, remains only for a short time tau (tau "deposition time of the thin film considered in the application) before being re-emitted from the wall towards the enclosure, unless it has undergone during this time a reaction with another atom or molecule present on this wall (for example an oxidation) modifying its chemical nature. The invention (device or method) implements the so-called ballistic regime: this is a gas flow regime in which the free path of the species present is very large compared to the dimensions of the enclosure.This means that the species present experience no or very few collisions with each other when moving within the enclosure.

[0059] The invention implements an evaporation technique, according to which the source of the element to be evaporated is heated, for example with an electron beam or by the Joule effect.

[0060] In this application, the ambient temperature is considered to be 300 K and the ambient pressure to be 1 bar.

[0061] BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Examples of embodiments of the invention will now be described with reference to the accompanying drawings in which:

[0063] - Figure 1A represents an isometric view of a screen according to the invention, comprising a conical cover and a diaphragm;

[0064] - Figure 1B represents a view of a screen according to the invention, on a deposit support and facing a gas distribution conduit;

[0065] - figure 2 schematically represents a screen according to the invention in a situation in a deposition chamber;

[0066] - Figures 3A, 3B and 3C represent different optimization results;

[0067] - Figures 4A, 4B and 4C represent different surface resistance maps for aluminum evaporation in the presence of an oxygen flow on wafers, in 3 distinct configurations: without a cover according to the invention (Figure 4A), with a conical cover according to the invention (Figure 4B), with a conical cover according to the invention equipped with a diaphragm (Figure 4C);

[0068] - Figure 5 represents an oxygen flux distribution on the surface of a wafer, reconstructed from resistance measurements presented in Figures 4A-4C;

[0069] - Figure 6 represents the relative standard deviation of the oxygen distribution in the 3 configurations presented in Figures 4A-4C.

[0070] DETAILED DESCRIPTION OF THE INVENTION Figure 1A schematically represents a cover or screen 2, according to one embodiment of the invention.

[0071] It essentially comprises a truncated cone-shaped side wall, extending, in this example, between a short side or base 21, which has a l ère circular opening 23, and a large side 22, which has a 2 ème circular opening 25 with a diameter greater than that of the circular opening 23. The screen 2 has a symmetry of revolution or rotation around an axis XX'.

[0072] In the configuration shown, it is also provided with a diaphragm 10, which comprises a central circular opening 11 of diameter smaller than the diameter of the opening 25, a part of the latter therefore remaining open. As will be seen below, a cover according to the invention may or may not be provided with such a diaphragm 10. The size of this diaphragm is chosen so as not to block the inlet of evaporated material, and thus not to risk degrading the homogeneity of the material deposit.

[0073] The small side 21 may be provided with a base 12, substantially forming, in this example, a circular crown, in which means 8 are provided for fixing the cover in a deposition chamber of an evaporator.

[0074] The angle a between the outer wall 22e of the cache and a plane which passes through the base 21 is less than 90; this angle can be for example between 80° and 30°; preferably, it is less than 60°. The complementary angle P (180°- a) between the inner wall 22i of the cache and this same plane is greater than or equal to 90°, it is for example between 100° and 150°. In the case where P = 90°, the cache is cylindrical. The example of cache shown in figure 1A is convergent towards the deposition zone, but, alternatively, it can be divergent or cylindrical. For example, in another configuration (not shown) the side located at the base 12 is the large side, which has a l ère circular opening, while the opposite side has a 2 ème circular opening of diameter less than (or even equal to) that of the l ère circular opening; in the case of a diverging cone, the above angles must be taken with the negative sign.

[0075] The angle α of the cache can be optimized so that each point on the surface of a deposition zone (located substantially at the center of the base 21) sees at approximately the same solid angle the inner surfaces 22i of the cache 2 and 10i (which can be seen in FIG. 2) of the diaphragm 10 (see also explanations below, in connection with FIG. 1B). FIG. 1B represents the cache 2, according to an embodiment of the invention, on a support (or plate) 32, around an area in which a “wafer” (or deposition substrate) 33 (for example: a wafer with a diameter of 2 inches or more) can be positioned and on the surface of which a deposition of material(s) can be carried out by evaporation. The axis XX' is perpendicular to the surface of the support 32. The rest of the evaporator deposition enclosure is not shown in figure 1B, except for the gas injection conduit 41 which must combine with the material to be deposited (examples are given above and further on).This conduit is provided with several orifices which allow the gas to be injected, preferably with a distribution of initial moments having a symmetry of revolution or rotation around the axis XX'. The cover has a height h which can also be optimized according to the other geometric parameters of the cover 2 and the diaphragm 10, and constrained by the geometry of the deposition frame.

[0076] It is generally noted that a greater height h produces better homogeneity. Examples of optimization of the dimensions of the cache 2 are presented below, in connection with Figures 3A-3C.

[0077] But the dimensions of the cover (height, angle) must also be chosen according to the volume available in the enclosure.

[0078] Figure 2 shows the cover 2 in position in the deposition enclosure of an evaporator 30. As in Figure 1A, the cover extends from the support 32; it is fixed on or against the latter, around an area in which a “wafer” (or deposition substrate) 33 (for example: a wafer with a diameter of 2 inches or more) can be positioned and on the surface of which a deposition of material(s) must be carried out by evaporation. The axis XX' of the cover is aligned with a central axis of the evaporator.

[0079] A wall 42 separates 2 chambers 38, 40; note that a single chamber could be suitable, the advantage of having 2 chambers being to be able to pump the samples more quickly (smaller volume) and to avoid exposing the sources of materials to the air each time a sample is introduced. A l èrechamber 39 allows a source 34 of a material to be deposited on a wafer to be placed in the deposition chamber. It also includes heating means 36 (for example a resistor or an electron gun). This ère room 39 is separated from a 2 e chamber 40 by a wall 42 in the center of which an orifice 43 is made, allowing, when the heating means 36 are activated, a flow of material 44 to be deposited to be directed from the source 34 towards a deposition wafer 33.

[0080] The support 32 and the screen 2 are located in a 2 ème room 40, separated from the first room by wall 42. It is therefore in this 2 e chamber in which a wafer 33 can be arranged, with a view to carrying out a deposit on its surface.

[0081] The evaporator 30 is connected to pumping means 50 which make it possible to maintain inside the enclosure, or chambers, a pressure less than or equal to 10 -5mbar. For example, we pump at 10 -7 mbar then we can inject gas up to around 4.10 -5 mbar (maximum) or even 10 -5 mbar. These values ​​are not absolute; it all depends on the intended use of the device. As long as the free path is large compared to the size of the enclosure, we are in a ballistic regime, preferred for deposition by evaporation.

[0082] For example :

[0083] - the enclosure is pumped to a pressure less than or equal to, for example, 1.10 -5 mbar or 5 x 10 -5 mbar or 10 -6 mbar and for example of the order of 10 -7 mbar or at a pressure between on the one hand 10 -8 mbar or 2.10 -8 mbar and on the other hand 8 x ÎO -8 mbar or 10 -7 mbar;

[0084] - then a reactive gas is injected into the enclosure using the gas injection means and a material is evaporated towards the deposition substrate using the evaporation means, the pressure in the enclosure being kept less than or equal to 1.10 -5 mbar or 5 x 10 -5 mbar.

[0085] The chamber 40 also comprises means 41 for injecting a gas, for example in the form of a circular conduit provided with a plurality of orifices (or "shower"), which makes it possible to homogenize the gas arrival angles. These means 41 are arranged between the evaporator 30 and the deposition support 32. Other means can be used for injecting the gas, for example an arrival from a pipe, but the atoms of the gas then all have the same initial moment, or have a preferred direction, and all come from the same place, which does not promote homogenization of the gas arrival angles. These means make it possible, during an evaporation operation, to inject a flow 46 of gas, for example oxygen, into the chamber 40. These means 41 are supplied for example by an assembly 60 comprising for example a reserve of high pressure gas and a pressure reducer. A flow meter can also be provided to regulate the flow of gas supplied.All these elements can be connected to one or more conduit(s).

[0086] The injected gas is a reactive gas, which will react with the evaporated material. It is in gaseous form at ambient temperature and pressure.

[0087] The gas atoms or molecules have, when there is a very low pressure in the enclosure obtained by the means 50, a mean free path which is very large compared to the dimensions of the enclosure (typically several meters in the pressure ranges used), and they therefore do not undergo any collision with each other. Once emitted into the enclosure, they are therefore adsorbed on the interior walls 40i of the chamber 40. When the cover 2 and the diaphragm 10 are absent, the molecules incident on the wafer come in small part directly from the orifices of the conduit 41, and in major part from the walls of the enclosure and the objects located therein (approximately 90% in the geometry presented in figure 2).

[0088] When the cover 2 and the diaphragm 10 are installed, certain atoms or certain molecules become adsorbed on the inner wall 22i of the cover 2 and on the inner wall 10i of the diaphragm 10. It is essentially these atoms or molecules 48, 52 which come from this inner wall 22i and from the inner wall 10i of the diaphragm 10 which will be sent or diffused towards the surface of the wafer 33 with a view to deposition thereon. However, as explained below, the shape of the cover 2 allows a homogenization of this diffusion.

[0089] The rotational symmetry of the screen 2, whether or not equipped with its diaphragm 10, ensures good homogeneity of diffusion of the atoms of the molecules adsorbed against the inner wall 22i and the inner wall 10i of the diaphragm 10 in the direction of the wafer 33. We seek to ensure that 2 different points of the wafer see the same solid angle of the cache and the diaphragm. These 2 points will not see the same walls in the same way, but then see the same surface integral. We therefore consider the solid angles seen from the wafer: the optimization of the geometric parameters of the cache (angle a, height h, diameter cj) of the diaphragm) can be done by verifying that each point of the wafer sees approximately the same solid angle of the inner wall of the cache.

[0090] Figures 3A-3C show the standard deviation of the relative variations in solid angle of the cache over a 2-inch wafer (the cache geometry being that of Figure 1A), as a function of the angle a and / or the height h, assuming a 3-inch diaphragm. For each value of a, an optimum height can be found to minimize the variations in solid angle and therefore gas flow. We generally see that it is advantageous to increase the height of the cache and to decrease the angle a (which corresponds to a maximization of the cone opening); however, there is a wide range of values ​​a, h for which the relative variations are kept below 0.1%, as shown in Figures 3A-3C. Ultimately, geometric values ​​compatible with the enclosure of the deposition frame are preferably chosen.

[0091] More specifically, Figures 3A-3C are commented below:

[0092] - Figure 3A shows the relative standard deviation of the total solid angle of the cover, seen from a 2-inch deposition surface, in the configuration of an evaporator (Plassys MEB 550S model), as a function of the cover cone angle and the cover height (assuming the geometry presented), for 3 values ​​of the height h (50mm, 70mm, and 100mm). The optimal angle is the one for which the standard deviation is minimal (sign of a uniform solid angle); the geometry is that presented in Figure 1A, comprising a cone and a diaphragm: We then have 4 geometric parameters: h, alpha (a), the diameter of the base 21, and the diameter of the diaphragm 10. We adjust alpha respectively to a fixed h (Figure 3A) and vice versa (Figure 3B), for a diameter of the base and the diaphragm equal to 3 inches (=7.62 cm).

[0093] - Figure 3B shows the relative standard deviation of the solid angle of the cover seen from a 2-inch deposition surface, in the configuration of an evaporator (Plassys MEB 550S model), as a function of the height of the cover (assuming the same geometry as that presented above), for 4 typical values ​​of the cone angle: 30°, 40°, 50°, and 70°. The optimal height is the one for which the standard deviation is minimal (a sign of a uniform solid angle); - Figure 3C shows the relative standard deviation of the solid angle of the cover seen from a 2-inch deposition surface, in the configuration of an evaporator (Plassys MEB 550S model), as a function of the height of the cover, and the angle a of the cone of the cover (still in the same geometry as that presented above). Only the values ​​of h and a are represented here for which the relative standard deviation is less than or equal to 0.1%, which translates equivalently to the flow homogeneity.

[0094] Figures 4A - 4C represent different maps of the surface resistance Rc of a 30 nm thick deposit, which results from the evaporation of aluminum in the presence of an oxygen flow (granular aluminum - GrAI) on a wafer 33, in 3 distinct configurations of the evaporator. In these three configurations, the introduction of oxygen into the deposition chamber is done by means of a pipe 41 bent in a circle in a plane parallel to the wafer, pierced with regularly spaced holes, the axes of which are oriented towards the edge of the 2-inch wafer. Note that the holes have a dispersion of diameters of approximately 5% linked to their machining method. This distribution system makes it possible to roughly standardize the density and the initial kinetic moments of the incoming gas. In the first configuration (Figure 4A), the deposition is done without a cover according to the invention. A strong inhomogeneity of the resistance (Rc) is observed, which varies by more than a factor of 2 on the surface of the wafer.

[0095] In the second configuration (Figure 4B), the deposition is made with a truncated cone 2 according to the invention, without a diaphragm. The resistance inhomogeneity is reduced to a factor of 60% on the surface of the wafer.

[0096] In the third configuration (Figure 4C), the deposition is made with a truncated cone-shaped cover 2 according to the invention, provided with a diaphragm 10 for example as shown in Figures 1A and 2A. This time, the inhomogeneity is only 10% on the surface of the wafer.

[0097] The overall homogeneity of resistance is represented on these maps by the min-max scale (on the right in each of these figures) of Rc coded in the gray levels (from 350 to 850 Q in Figure 4A, from 155 to 280 Q in Figure 4B and from 204 to 231 Q in Figure 4C). The information that can be drawn from these figures is therefore the distribution of resistance values: the finer it is, the more homogeneous it is, and the 2D mapping allows us to visualize how the oxygen is distributed. In Figure 4C we see a cylindrical symmetry, as ideally expected. In Figures 4A and 4B, we see a transverse gradient - while the gas distribution is cylindrically symmetric - which shows that there are objects that send oxygen to some places more than to others, or that the distribution sends more gas to one side than the other due to a lack of homogeneity in the size or orientation of the holes.

[0098] The resistance variations observed in these figures come from the dominant inhomogeneity of the gas flow reaching the wafer.

[0099] Three possible contributions to the inhomogeneity of the oxygen deposited on the wafer are identified: the gas distribution system (for example resulting from the irregularity of the orientation and diameter of the holes in the pipe), the deposition enclosure visible to the wafer (for example the pumping holes, a quartz balance, a shutter allowing the deposition to start and stop, the fixing arm of the deposition plate, etc.), or the inhomogeneity of the solid angle of the shutter - when present - seen by the wafer. The influence of each contribution can be determined by comparison: between the first configuration (Figure 4A) and the second configuration (Figure 4B), the implementation of a screen 2 according to the invention makes it possible to hide the lateral inhomogeneities (objects, walls, holes).Between the second configuration (Figure 4B) and the third configuration (Figure 4C), the implementation of a cover 2 according to the invention provided with a diaphragm 10 makes it possible to reduce the impact of the inhomogeneities of the gas injection pipe, and of a large part of the horizontal walls of the enclosure (parallel and facing the wafer). The residual variations in resistance in the third configuration (Figure 4C) are attributed to the inhomogeneity of density and initial kinetic moments of the gas, and to the inhomogeneity of solid angle of the cover seen by the wafer.

[0100] The maps of these 3 figures are validated both experimentally and by simulation. The observed gradients are reproducible from one deposit to another in the same configuration.

[0101] These maps show: - a very pronounced asymmetry in the case where no cache according to the invention is used (figure 4A); It is clear that the observed distributions reflect the asymmetry inside the evaporator, such an asymmetry being due to the different elements (already mentioned above) arranged inside it;

[0102] - a better distribution with nevertheless a residual transverse gradient, in the case where a cache according to the invention is used, but without a diaphragm (this is the case in figure 4B);

[0103] - excellent homogeneity of the deposit obtained (figure 4C), with symmetry of revolution in the case where screen 2 is used in combination with a diaphragm 10.

[0104] To precisely characterize the homogeneity of the gas flow, one can exploit the dependence of the surface resistance of films, for example of GrAI, deposited as a function of the gas flow during deposition.

[0105] To characterize this dependence, we first deposit a large number n (n>50) of films made under identical conditions (same thickness, for example 30nm, same evaporation rate, for example 1nm / s, same gas supply configuration, without cover 2), but at different gas flows, controlled by a mass flow meter. We only use the resistance value measured at the center of the plate, to avoid homogeneity problems. This statistic makes it possible to define an average curve, representing the average surface resistance of the film as a function of the oxygen flow. Thus, by bijection when measuring a surface resistance it is possible to assign it a flow value, called effective gas flow. This makes it possible to quantify and compare the homogeneity of the gas flow, on deposits possibly made under different conditions and having different resistance values.To convince ourselves and validate the method, we can measure that the effective flux distribution reconstructed in this way from a resistance map on a 2-inch wafer has the same relative standard deviation regardless of the average flux, in the same shower configuration (a sign of the same relative inhomogeneity of gas flow). Figure 5 represents the effective flux distribution for each of the deposits presented in Figures 4A-4C (distribution 5a, respectively 5b, 5c, corresponding to the case of Figure 4A, respectively 4B, 4C).

[0106] Figure 6 represents the relative standard deviation of the flux distribution in the 3 configurations described above for Figures 4A-4C.

[0107] From these figures, we understand that the gas distribution on the surface of a wafer becomes more refined as the caches are installed.

[0108] In Figures 5 and 6, it can be observed that the effective flux distribution (representing the homogeneity of the gas in the deposited film) is refined when the cover and then the diaphragm are introduced, and that this refinement of the distribution is not an artifact due to the change in the absolute flux value.

[0109] In Figure 6 we quantify the relative gas inhomogeneity over 2 inches: it is > 0.8% without cover (which translates into a factor > 2 of resistance variation for GrAI around 500 ohms of surface resistance) and falls to less than 0.2% with the tested version of the cover (which translates into less than 2% of resistance variation for GrAI around 200 ohms of surface resistance).

[0110] The cache version used in this experiment is non-optimal from the solid angle point of view: its height h=60mm, and its angle ct=51° predict a solid angle inhomogeneity of 0.8%, and for this height the optimal angle is 40° allowing to achieve an inhomogeneity of 0.04%, i.e. an additional reduction of a factor of 20.

[0111] This optimization relies on the solid angle of the cache as seen by the wafer but neglects variations in gas density adsorbed by the walls of the cache; for example, one can expect the inner surface of the diaphragm to be less populated with molecules than the inner surface of the cone which sees part of the enclosure directly; or one can expect the edges of the aperture 11 of the diaphragm to be more populated than the corners at the junction with the cone. The density of adsorbed molecules can therefore weight the calculation of the integral of the solid angle, but relies on unknowns depending on the precise parameters of the enclosure and the gas distribution. This solid angle optimization therefore gives a first approach to cache design, to be refined by experience.

[0112] The invention makes it possible to control a gas flow (reactive gas) incident on a deposition surface in a vacuum chamber. In particular, it makes it possible to control the geometry of the emitting surfaces of the chamber having a non-zero solid angle seen by the deposition surface. The invention can, for example, be applied to the formation of oxides of elements deposited in the presence of oxygen: Aluminum to produce granular aluminum, or alumina AI2O3; Chromium to produce CrzOs; Titanium to produce TiO?; and in general transition metals to produce magnetic thin films.

[0113] It also applies to the formation of hydrides, or nitrides, or elements deposited in the presence of nitrogen, or dihydrogen: for example Titanium or Niobium in the presence of nitrogen to produce TiN or NbN; for example Silicon in the presence of dihydrogen to produce Si H.

[0114] The invention makes it possible to homogenize gas flows injected into a vacuum enclosure in ballistic or molecular mode (where the free path of the molecules is greater than the dimensions of the enclosure), typically in pressure ranges less than or equal to 10 -4 mbar or 10 -5 mbar.

[0115] The invention makes it possible to obtain deposits of homogeneous materials (in stoichiometry) on surfaces which may be, for example, of diameter greater than 2 inches, in the presence of reactive gas and, for example, by evaporation by electron gun or by Joule effect.

[0116] The invention makes it possible in particular to produce oxides, nitrides or hydrides by evaporation by electron gun or by Joule effect in the presence of a flow of molecular oxygen or molecular nitrogen or hydrogen. The deposited materials will then have a homogeneous composition over large surfaces (for example with a diameter greater than or equal to 2 or 3 inches), which is of interest for certain applications, for example for transition metal oxides in the field of magnetic sensors, or in the field of quantum technologies (for example granular aluminum, or for example titanium nitride, or for example niobium nitride, or for example silicon hydride).

Claims

CLAIMS 1. Device (30) for deposition by vacuum evaporation, in ballistic mode, comprising: - a storage enclosure or frame; - a deposit support (32); - evaporation means (36) for evaporating a material towards the deposition substrate (32); - gas injection means (41), for injecting a reactive gas into the enclosure; - means forming a cover (2) around the deposition substrate, extending from the deposition support, an axis (XX') forming an axis of symmetry of revolution of this cover, this axis being perpendicular to the surface of the deposition support and centered therein, the gas injection means (41) comprising a conduit provided with several orifices which make it possible to inject a reactive gas with a distribution of initial moments having a symmetry of revolution around the axis XX'.

2. Device according to claim 1, in which the outer wall of the cover makes an angle less than, or greater than or equal to, 90° with the surface of said deposit support (32).

3. Device according to claim 1 or 2, in which the cover is made of aluminum or stainless steel.

4. Device according to one of claims 1 to 3, in which the cover is at least partly frustoconical in shape.

5. Device according to one of claims 1 to 4, the cover comprising a small side or base (21), which has a l ère circular opening (23), and a large side (22), which has a 2 ème circular opening (25) of diameter greater than that of the l ère circular opening (23).

6. Device according to one of claims 1 to 5, further comprising a diaphragm (10) arranged at the entrance to the cover (2).

7. Device according to claim 6, in which the diaphragm is made of stainless steel or aluminum.

8. Device according to one of claims 1 to 7, comprising 2 chambers (38, 40), a first chamber (38) which comprises the means (36) for evaporating a material towards the deposition substrate (32), a 2 e chamber (40) which comprises the deposition support (32), the cover (2) and the means (41) for injecting a gas into the enclosure, the 2 chambers being separated by a wall (42) provided with an orifice (43) to allow a flow (44) of evaporated material to pass through.

9. Device according to one of claims 1 to 8, further comprising pumping means (50) to achieve, in the chamber, a pressure of at most, or less than or equal to, 5.10 -5 mbar.

10. Device according to claim 9, the pumping means (50) making it possible to achieve: - before injection of gases, a pressure of the order of, or less than or equal to, 10 -7 mbar or a pressure between on the one hand 10 -8 mbar or 2.10 -8mbar and on the other hand 8 x 10 -8 mbar or 10 -7 mbar ; - during evaporation, a pressure less than or equal to 1.10 -5 mbar or 5 x 10 -5 mbar in the storage enclosure or frame.

11. Device according to one of claims 1 to 10, further comprising gas supply means (60), for supplying the means (41) for injecting a gas into the enclosure.

12. Device according to one of claims 1 to 11, the means (36) for evaporating a material towards the deposition substrate (32) comprising means for heating the material to be evaporated, for example an electron gun or at least one resistor (36).

13. Device according to one of claims 1 to 12, the gas injection means (41) being arranged between the evaporation means and the deposition support.

14. Vacuum deposition method using a device according to one of claims 1 to 13, in which: - a deposition substrate (33) is positioned on the support (32); - the enclosure is pumped to a pressure less than or equal to 10 -6 mbar; - a gas is injected into the enclosure using the gas injection means (41); - a material is evaporated towards the deposition substrate using the evaporation means (36), the pressure in the deposition enclosure or frame being less than or equal to 5xl0 -5 mbar.

15. The method of claim 14, wherein the gas injected into the enclosure is molecular oxygen (dioxygen) or molecular nitrogen (dinitrogen) or hydrogen or dihydrogen.

16. Method according to claim 14 or 15, in which said material is evaporated towards the deposition substrate by heating, for example using an electron gun or by Joule effect.

17. Method according to one of claims 14 to 16, in which the evaporated material is aluminum or chromium or titanium or silicon or a transition metal.

18. Method according to one of claims 14 to 17, in which a deposit of titanium nitride (TiN) or niobium nitride (NbN) or aluminum nitride (AIN), or titanium oxide (TiO2) or aluminum oxide (granular aluminum -GrAI- or AI2O3), or silicon hydride (SiH) is carried out.

19. Method according to one of claims 14 to 18, in which the deposition substrate (33) has a deposition surface with a diameter at least equal to 5.08 or 7.62 cm.

20. Method according to one of claims 14 to 19, in which a deposit with a thickness of between 1 nm and 200 nm is produced.

21. Method according to one of claims 14 to 20, in which the evaporation is carried out in ballistic mode.

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