WO2014191624A1

WO2014191624A1 - Substrate holder and arrangement for holding substrates

Info

Publication number: WO2014191624A1
Application number: PCT/FI2014/050421
Authority: WO
Inventors: Shuo Li
Original assignee: Beneq Oy
Priority date: 2013-05-29
Filing date: 2014-05-27
Publication date: 2014-12-04

Abstract

The invention relates to a substrate holder and arrangement for supporting one or more planar substrates (2, 8) during processing of the substrate (2, 8) by subjecting the surface (4, 10) of the substrate (2, 8) to successive surface reactions of at least a first precursor and a second precursor, the substantially planar substrate (2, 8) comprising a first side surface (4, 10) and a second side surface (6, 12) and one or more side edges (9, 15) between the first and second side surfaces (4, 10, 6, 12). According to the present invention the substrate holder comprises a groove (26; 32) arranged to receive at least one of the side edges (9, 15) of the substrate (2, 8).

Description

Substrate holder and arrangement for holding substrates

The present invention relates to a substrate holder for holding, and especially to a substrate holder for holding one or more substantially planar substrates during processing of the substrate by subjecting a surface of the substrate to successive surface reactions of at least a first precursor and a second precursor, the substantially planar substrate comprising a first side surface and a second side surface and one or more side edges between the first and second side surfaces, the substrate holder is formed as a groove frame comprising a first side wall and a second side wall arranged to form a groove for receiving at least one of the side edges of the substrate, the first and side walls forming the side walls of the groove frame, as defined in the preamble of independent claim 1 . The present invention also relates to an arrangement for supporting planar substrates during processing of the substrates by subjecting a surface of the substrate to successive surface reactions of at least a first precursor and a second precursor, the arrangement comprising a first substantially planar substrate having a first side surface, second side surface and one or more first side edges between the first and second side surfaces, and a second substantially planar substrate having first side surface, second side surface and one or more second side edges between the first and second side surfaces, and a substrate holder for holding the planar substrate during processing of the substrate, substrate holder is formed as a groove frame comprising a first side wall and a second side wall arranged to form the groove for receiving at least one of the side edges of the substrates, as defined in the preamble of claim 1 1 . Background of the invention

Atomic layer deposition (ALD) is generally known coating method in which surfaces of a substrate is subjected to alternating surface reactions of at least a first and second gaseous precursors. One ALD-cycle is completed when the surfaces of the substrate are subjected once to both or all gaseous precursors. Each time the surface of the substrate is subjected to a precursor, a monolayer of material is formed on surfaces of the substrate. These ALD- surface reactions are normally substantially saturated surface reactions, meaning that the only one monolayer of material is formed on the surfaces of the substrate when the substrate is subjected to a precursor. One basic characteristic of ALD method is the conformality of the surfaces reactions. This means that the ALD growth layers of material grow on all the surfaces which are subjected to the precursors. Thus the coating is formed on all surfaces. In the present context the term atomic layer deposition also covers also atomic layer epitaxy (ALE) and other corresponding coating methods in which the material growth is based on successive substantially self-limiting surface reactions of at least two gaseous precursors.

However, in some applications it is undesirable to form the ALD-coating on all the surfaces of the substrate. For example it may be desirable to coat only one side of many planar or plate like substrates and the other side is left without coating. However, due to the excellent conformality of the ALD-method, the coating tends to grow on all the surface of the substrate and thus also on the side of the surface where it is undesirable.

In prior art the undesirable coating on one side of a planar substrate is solved etching or otherwise removing the coating from the substrate surface in which it is undesirable. However, etching or other removing of coating from a substrate is difficult and time consuming. Furthermore, etching or otherwise removing the coating increases breakage rate of breakable or fragile substrates such as glass or silicon substrates.

Another prior art solution is preventing coating formation on a predetermined portion of the surfaces of a substrate. The coating formation is prevented by placing the substrate against a support surface such that the surface of the substrate on which the coating formation is undesirable is placed against the support surface. The support surface may also be another substrate. In a case of substantially planar or plate-like substrates two substrates may be placed against each other for preventing coating formation on surfaces which are placed against each other. However, using a support surface or placing surface of a substrate against a support surface or a surface of another substrate has the disadvantage that it does not totally prevent coating formation. This problem arises from the fact that there is always a small gap between the surface of the substrate and the support surface or another substrate. The gap may be due to surface roughness or surface profile of the substrate and/or the support surface. The precursor molecules may diffuse into the gap between the surface of the substrate and the support surface or the surface of another substrate. When precursor molecules diffuse to the gap they also form coating on the surfaces defining the gap. The molecules diffuse to a certain diffusion distance into the gap from the edge of the gap forming coating layers and also a diffusion growth end profile on the surface of the substrate on which the coating is undesirable. Therefore, the prior art solutions do not efficiently prevent coating formation on one side of the surface of the substrate.

Brief description of the invention

The object of the present invention is to provide a substrate holder and an arrangement so as to overcome or at least alleviate the prior art disadvantages. The objects of the present invention are achieved with a substrate holder according to the characterizing portion of claim 1 . The objects of the present invention are further achieved with an arrangement according to the characterizing portion of claim 1 1 .

The preferred embodiments of the invention are disclosed in the dependent claims.

The present invention is based on the idea of preventing material growth on one side surface of a substantially planar substrate. In the present the material growth on one side surface of the substantially planar substrate is prevented or at least considerably reduced by preventing diffusion between the side surfaces of the substrate. . A planar or plate-like or sheet substrate comprises a first side surface, a second side surface and one or more edges between the first and second side surfaces. The substrate holder of the present invention is arranged to receive two superposed substrates and the substrate holder further comprises a groove arranged to receive at least one of the edges of the substrates. This means that the substrate holder is formed such that the side edge of the substrate may be placed inside the groove and the groove is shaped to receive the at least of the side edges inside the groove. The groove further comprises at least one side wall arranged to extend over an edge region of the first side surface of the substantially planar substrate. The side wall of the groove is formed such that it extends over the edge region of the first side surface of the substrate close or in vicinity of the first side surface or the side wall of the groove is placed against the first side surface of the substrate in the edge region such that a diffusion path is formed between the first side surface and the second side surface of the substantially planar substrate. Thus the groove may be arranged to receive at least one of the side edges of the substrate in substantially form-fitting manner such that the diffusion path is formed between the first side surface and the second side surface of the substantially planar substrate. The substrate holder may be provided with a support surface against which the second side surface of the substrate is placed. Alternatively two substrates may be placed to the substrate holder superposed such that the second side surfaces of the substrates are arranged against each other and the coating is provided on the first side surfaces facing opposite directions. The superposed substrates are both arranged to the groove of the substrate holder such the side walls of the groove extend respectively over the edge regions of the first side surfaces of the substrates such that the diffusion path is provided on both substrates. Accordingly substrate holder of the present invention is provided in the form of a groove frame arranged to receive the at least one side edge a first and second superposed substrates such that the first side wall is arranged to extend over an edge region of the first side surface of the first substrate and the second side wall is arranged to extend over an edge region of the first side surface of the second substrate. The present invention also provides a carrier arrangement in which the second side surface of the first substrate is arranged superposed against the second side surface of the second substrate, and that the first and second superposed substrates are arranged into the groove frame such that the first side wall is arranged to extend over an edge region of the first side surface of the first substrate for providing a diffusion path between the first side surface of the first substrate and the first side wall, and the second side wall is arranged to extend over an edge region of the first side surface of the second substrate for providing a diffusion path between the first side surface of the second substrate and the second side wall.

According to the present invention a diffusion path is formed on the edge region of the first side surface of the substantially planar substrate such that diffusion that prevents or reduces material flow from the first side surface to the second side surface. This means that the present invention provides a diffusion path between the first and second side surfaces of the substrate. In the prior art substrate holders and arrangements the diffusion path was formed between the second side surface of the substrate and a support surface against which the second side surface was placed causing precursor material diffuse a predetermined diffusion distance into the gap between the second side surface and the support surface. Therefore material is grown in ALD process on the second side surface along the diffusion distance in the mentioned gap. In the present invention the diffusion path is moved on the first side surface of the substrate or between the first and second side surfaces of the substrate. The precursor materials used in the ALD process diffuse into the diffusion path provided on the first side surface or between the first and second side surfaces of the substrate. The precursor materials can diffuse only a certain diffusion distance into the diffusion path. The present invention provides an extended diffusion path for the precursor materials such that the precursor materials may not diffuse between the second side surface substrate and the support surface as the precursors will react on first side surface, on side edge of the substrate and/or on the side wall of the groove along the diffusion path thus does not reach the second side surface of the substrate. Thus he diffusion distance to the second side surface of the substrate is lengthened which considerably reduces or prevents the diffusion of the precursor molecules to the gap between the support surface and the second side surface of the substrate or between two superposed substrates. This enables coating substantially planar substrates from only one side using ALD method without need to remove coating material from the second side surface of the substrate after the coating process.

Brief description of the figures

In the following the invention will be described in greater detail, in connection with preferred embodiments, with reference to the attached drawings, in which

Figures 1A and 1 B show schematically prior art arrangements for processing substrates by atomic layer deposition;

Figure 2 show schematically one embodiment of the present invention; Figure 3 show schematically a top view of the embodiment of figure 2;

Figure 4 shows schematically another embodiment of the present invention;

Figure 5 shows schematically yet another embodiment of the present invention;

Figure 6 shows schematically an embodiment of the present invention in which two substantially planar substrates are placed against each other; Figure 7 shows detailed characteristics of the embodiment shown in figure 6;

Figure 8 shows schematically an alternative embodiment of the present invention in which two substantially planar substrates are placed against each other; Figure 9 shows schematically yet an alternative embodiment of the present invention in which two substantially planar substrates are placed against each other;

Figures 10A, 10B and 10C show schematically one embodiment of the substrate holder; and Figure 1 1 shows a top view of one embodiment of the present invention. Detailed description of the invention

In the following description, for the purposes of clear explanation, a number of specific details are set forth in order to provide a thorough understanding of the invention. It is apparent to one skilled in the art that embodiments of the invention may, however, be practiced without one or more of these specific details or with some equivalent arrangement. Furthermore, the features of the specific embodiments described below may be combined in any suitable manner.

Figures 1A and 1 B schematically show prior art arrangement for holding substrates during processing the substrates by subjecting the surface of the substrate to successive surface reactions of at least first and second precursors according to the principles of atomic layer deposition (ALD). In the following examples substrates are shown as substantially planar, sheet-like or plate-like substrates. However the substrates may have any shape and the present invention is not restricted to any substrate shape. Furthermore the base material of the substrate may be Si, glass or any other material suitable to be processed with ALD. The first planar substrate 2 shown in figures 1 to 1 1 comprises a first side surface 4, a second side surface 6 and a side edge 9 between the first and second side surfaces 4, 6. The side edge 9 comprises an edge surface, a first edge corner 5 between the first side surface 4 and the edge surface, and a second edge corner 1 1 between the second side surface 6 and the edge surface. The second planar substrate 8 shown in figures 1 to 1 1 comprises a first side surface 10, a second side surface 12 and a side edge 15 between the first and second side surfaces 10, 12. The side edge 15 comprises an edge surface 15, a first edge corner 7 between the first side surface 10 and the edge surface, and a second edge corner 13 between the second side surface 12 and the edge surface. Figure 1A shows a planar substrate 2 having a first surface 4 and second surface 6 on opposite sides of the substrate 2. The substrate 2 is supported on a substrate support 20 having a support surface 22. The substrate 2 is arranged on the substrate support 20 such that the second side surface 6 of the substrate 2 is placed against the support surface 22. In this kind of arrangement the support surface 22 covers the second side surface 6 of the substrate 2 and material growth on the second lower side surface 6 of the substrate 2 is undesirable. Therefore, in this kind of arrangement the object is to provide coating only on the first upper side surface 4 of the substrate 2. Thus the substrate support 20 forms a barrier element for preventing or reducing material growth on the second side surface 6 of the substrate 2. However, when even if the second side surface 6 of the substrate 2 and the support surface 22 are substantially planar and straight there remains a tiny gap 14 between the support surface 22 and the second side surface 6 of the substrate 2. In figure 1A the gap 14 is exaggerated for illustrative purposes. Usually the gap 14 is larger than the precursor molecules and thus the precursor molecules 14 may diffuse a certain diffusion distance into the gap 14 from the side edge 9 of the substrate 2. Thus a diffusion material growth is also formed on the second surface 6 of the substrate 2 along the mentioned diffusion distance. Figure 1 B shows another substrate support arrangement in which two substrates 2 and 8 are supported against each other. The first substrate 2 comprises a first side surface 4 and a second side surface 6 on opposite sides of the first substrate 2. The second substrate 8 comprises a first side surface 10 and a second side surface 12 on opposite sides of the second substrate 8. The substrates 2, 8 are arranged against each other, or superposed, such that the second side surface 6 of the first substrate 2 is against the second side surface 12 of the second substrate 8. In this kind of arrangement the second side surfaces 6, 12 of the first and second substrate 2, 8 cover each other and material growth on the second side surfaces 6, 12 of the substrates 2, 8 is undesirable. Therefore, in this kind of arrangement the object is to provide coating only on the first side surfaces 4, 10 of the substrates 2, 8. Thus the substrates 2, 8 form barrier elements for each other for preventing or reducing material growth on the second side surfaces 6, 12. However, even if the second side surfaces 6, 12 of the substrates 2, 8 are substantially planar and straight there remains a tiny gap 16 between the second side surfaces 6, 12 when they are arranged against each other. In figure 1 B the gap 16 is exaggerated for illustrative purposes. Usually the gap 16 is larger than the precursor molecules and thus the precursor molecules 16 may diffuse a certain diffusion distance into the gap 16 from the edges 9, 15 of the substrates 2, 8. Thus a diffusion material growth is also formed on the second side surfaces 6, 12 of the substrates 2, 8 along the mentioned diffusion distance. Figure 2 shows one embodiment of a substrate holder according to the present invention. The substrate 2 is a substantially planar, sheet or plate-like substrate having a first side surface 4, a second side surface 6 and a side edge 9 between the first and second side surfaces 4, 6. The side edge 9 comprises an edge surface, a first edge corner 5 between the first side surface 4 and the edge surface, and a second edge corner 1 1 between the second side surface 6 and the edge surface. The substrate holder comprises a substrate support 20 having a substantially planar support surface 22 and a side wall 24 extending from the support surface 22. The substrate 2 is placed on the support surface 22 such that second side surface 6 of the substrate 2 is against the support surface 22. Thus the support surface 22 is arranged to receive the second side surface 6 of the substrate 2 against the support surface 22. According to the above mentioned a gap 14 is provided between the second side surface 6 and the support surface 22, as described in connection with figure 1A. As may be seen from figure 2, the support surface 22 and the side wall 24 form a groove 26 having a tapering profile towards the bottom 19 of the groove 26. In this embodiment the support surface 22 forms the first side wall of the groove 26 and the side wall 24 forms the second side wall of the groove 26. The substrate 2, or the side edge 9, is arranged into the groove 26 such that the second side wall 24 extends over the first side surface 4 of the substrate 2. Furthermore due to the tapering profile of the groove 26 the first edge corner 5 between the edge surface and the first side surface 4 is arranged or pressed against the inner surface of the groove 26, against the second side wall 24. In other words the groove 26 is arranged to receive the side edge 9 of the substrate 2 such that a first edge corner 5 is received against the second side wall 24 and the second side wall extends over an edge region of the first side surface 4.The second side wall 24 may be attached or secured to support surface 22 mechanically, with an adhesive or any other known means or the second side wall 24 and the support surface 22 may be same material.

As the second side wall 24 extends over and edge region of the first side surface 4 of the substrate 2 a diffusion gap 23 may be formed between the first side surface 4 and the second side wall 24 when the substrate 2 is installed into the substrate holder. The precursor materials may diffuse into the diffusion gap 23 during processing of the substrate with ALD method such that a coating layer is grown on the first side surface 4 also under the second side wall 24. As shown in figure 2, the first edge corner 5 is arranged against the second side wall 24 such that a diffusion barrier is formed between the first and second side surfaces 4, 6 due to the contact between the second side wall 24 and the first edge corner 5. Furthermore, a subsequent diffusion chamber 17 is formed between the bottom 19 of the groove 26 and the side edge 9 or edge surface of the substrate 2. Therefore, the substrate holder of the present invention forms a labyrinth-like diffusion path and considerably lengthens the diffusion distance from the first side surface 4 to the second side surface 6. The diffusion path in this embodiment is provided by the diffusion gap 23, diffusion barrier due to contact between the second side wall 24 and the first edge corner 5, and diffusion chamber 17. This considerably reduces the diffusion of the precursor molecules to the gap 14 between the support surface 22 and the second side surface 6 of the substrate 2. If a precursor molecule is diffused on the second surface 6 of the substrate 2, it first has to diffusion to the diffusion gap 23, then through the diffusion barrier, and through the diffusion chamber 17 and into the gap 14 between the second surface 6 and the support surface 22. Thus molecule has to diffuse through the whole diffusion path and avoid impaction or deposition of the side walls of the diffusion path. Therefore, the diffusion of the precursor molecules into the gap between the second surface 6 and the support surface 22 is effectively prevented or reduced and accordingly also the diffusion growth on the second surface 6 of the substrate 2 is prevented or at least considerably reduced. The second side wall 24 and thus the diffusion gap 23, as shown in figure 2, also have an effect on the diffusion of the precursor molecules. The longer the distance the second side wall 24 extends above the first side surface 4 of the substrate 2 from the edge corner 5 the smaller number of molecules will diffuse towards the edge corner 5 of the substrate 2.

In figure 1 to 9 the substrates 2, 8 are shown as rectangular planar substrates having four side edges 9. However, it should be noted that the planar substrate may also be circular, triangular, polygonal or any other shape. In one preferred embodiment all the side edges 9 of the substrate 2, 8 or the whole circumference of the substrate 2, 8 is received or arranged into the groove 26 as described above. Figure 3 shows the substrate holder and substrate 2 of figure 2 from above. As may be seen from figure 3, the second side wall 24 is formed to correspond the shape of the rectangular substrate 2 such that all the four side edges 9 of the substrate 2 are received into the groove 26. This enables preventing diffusion growth on the second surface 6 through all the edges of the substrate 2 and from all directions. However, in some embodiments only one or some or part of the edges of the substrate 2 may be arranged into the groove 26.

Figure 4 shows an alternative embodiment of the present invention in which the substrate holder comprises a support surface 25 and a side wall 24. In this embodiment the support surface 25 and the side wall 24 are formed as a one piece element such that the side wall 24 is bend to extend in an angle from the support surface 25 to form the groove 26. Otherwise all the features of the embodiment of figures 2 and 3 apply to the embodiment of figure 4. In figures 2 to 4 the groove 26 is shown as substantially V-shaped or half V-shaped groove and the side wall 24 is substantially straight. However, in an alternative embodiment side wall 24 may also be curved to form a groove 26 with U- or C-shaped or half U- or C-shaped profile with the support surface 25.

In one embodiment the straight side wall 24 extends from the support surface 22, 25 in an angle between 0 and 80 degrees, preferably between 10 and 45 degrees or more preferably between 10 and 35 degrees. The angle affects on the depth of the diffusion chamber 17 between the bottom 19 of the groove 26 and side edge 9 of the substrate 2, as it defines how deep the side edge 9 of the substrate 2 may be inserted into the groove 26. Decreasing the angle increases the depth of the diffusion chamber 17. Increasing the depth of the diffusion chamber 17 increases the diffusion distance and makes the diffusion of precursor molecules between the second surface 6 and the support surface 22, 25 even more unlikely. Furthermore, the angle affects on how close to the first side surface 4 the side wall 24 extends over the first side surface 4. Decreasing the angle provides the side wall 24 closer to the first side surface 4 and thus lowers the diffusion gap 23, and vice versa. Lowering the diffusion gap 23 reduces the diffusion of the precursor molecules into the diffusion gap 23.

In one embodiment the side wall 24 formed from a resilient material, such as plastic, rubber, thin metal sheet or some other suitable material enabling the side wall 24 to resiliently bend or deform when the side edge 9 of the substrate 2 is pressed against the side wall 24. The deformation or bending of the side wall 24 may occur along the side wall 24 or at the bottom 19 of the groove 26 where the side wall 24 is connected to the support surface 22, 25. Alternatively the side wall 24 may be attached resiliently to the substrate support 20, 25 such that the opening angle between the support surface 22, 25 and the side wall 24 is increased when the side edge 9 of the substrate 2 is arranged against the side wall 24. The deformation or bending of the side wall 24 or attachment of the side wall 24 to the support surface 22, 25 provides a biasing force F against the first edge corner 5, as shown in figures 2 and 4. The biasing force F is due to the mentioned resilient deformation or bending as the side wall 24 tends to deform back to the initial form or orientation or position. The biasing force F provides a further sealing effect when the side wall 24 is pressed against the first edge corner 5. Thus a diffusion barrier is provided. In the embodiment of figure 4, the whole substrate holder may be made from resilient material for providing the same biasing force F against the first edge corner 5.

Figure 5 shows an alternative embodiment in which the substrate holder comprises a support surface 25 and side wall 27, 29 for forming the groove 26 for receiving the side edge 9 of the substrate 2. In this embodiment the groove 26 is formed with the support surface 25 forming the first side wall of the groove 26, 25 and side wall 27 forming the second side wall of the groove 26. In this embodiment the groove 26 has substantially U- or C-shaped cross section. The second side wall 27 extends substantially parallel with the first side surface 4 of the substrate 2 and over the first side surface 4, such that the diffusion gap 23 is provided between the second side wall 27 and the first side surface 4. The second side wall 27 may be arranged against the first side surface 4 or there may be a small clearance. The side edge 9 of the substrate 2 may be arranged to the groove 26 such that the side edge 9 is against or close to the bottom wall 29. Thus the diffusion gap 23 extends from the first side surface 4 along the side edge 9 to the second side surface 6. Thus a diffusion path is provided from the first side surface 4 to the second side surface 6 or between the first and second side surfaces 4, 6. It should be noted that in figure 5 the groove 26 is substantially rectangular, but the side wall 27, 29 may also be oriented differently to provide tapering or rounded grooves 26. Also a similar U-shaped groove may be provided by bending the substrate holder to form a groove with round bottom. According to the embodiments of figures 2 to 5, the present invention provides an arrangement for supporting planar substrates 2 during processing of the substrates 2 by subjecting a first side surface 4 of the substrate 2 to successive surface reactions of at least a first precursor and a second precursor. The arrangement comprises a substantially planar substrate 2 comprising a first side surface 4, a second side surface 6 and one or more side edges between the first and second side surfaces 4, 6, a substrate support 20 having a support surface 22, 25, and a substrate holder holding the planar substrate 2 during processing of the substrate 2. In the arrangement the substrate 2 is placed to the substrate holder such that the second side surface 6 is against the support surface 22, 25 of the substrate support for processing only the first side surface 4 of the substrate 2. The substrate holder further comprises one or more side walls 24, 27, 29 extending from the substrate support 20, 25 and forming a groove 26 together with the support surface 22, 25. Thus the substrate holder comprises a groove 26 arranged to receive at least one of the side edges 9 of the substrate 2 such that a diffusion path 17, 23 is formed between the first side surface 4 and the second side surface 6 of the substantially planar substrate 2 for preventing precursor flow between the first and second side surfaces 4, 6. The groove 26 may be arranged to receive at least one of the side edges 9 of the substrate 2 in substantially form-fitting manner such that the diffusion path 17, 23 is formed between the first side surface 4 and the second side surface 6 of the substantially planar substrate 2. The second side wall 24, 27, 29 of the groove 26 is arranged to extend over en edge region of the first side surface 4, over the first side surface 4, such that a diffusion gap is formed on the first side surface 4.

Figure 6 shows an alternative embodiment of the present invention in which two planar substrates 2, 8 are arranged superposed on top of each other. The substrates 2, 8 are arranged such that the second side surface 6 of the first substrate 2 is against the second side surface 12 of the second substrate 8. In this arrangement is it desirable that only the first side surfaces 4, 10 of the first and second substrate 2, 8 are processed or coated. The substrates 2, 8 have preferably identical shape such that the side edges 9, 15 of the substrates 2, 8 may be arranged substantially flush with each other, as shown in figure 6. However, the present invention is restricted to identically shaped superposed substrates, but the substrates may have different shapes. In this embodiment the substrate holder comprises a groove 32 which is formed with a first side wall 30 and a second side wall 31 for receiving the side edges 9, 15 of the substrates 2, 8, the first and second side walls 30, 31 forming the side walls of the groove 32. Accordingly the substrate holder forms a frame or cassette having the groove 32 for receiving the side edges 9, 15, or at least part of the side edges 9, 15, of the superposed substrates 2, 8. It should be noted that although all the embodiments in this context show two superposed substrates 2, 8 placed into the groove 32 formed by two side walls 30, 31 , this embodiment may also be used for only one substrate such that a side edge 9, 15 of only one substrate 2, 8 is arranged into the groove 32. The substrate holder of figure 6 may be used for example coating the first and second side surfaces 4, 10 of the substrate 2, 8 with different precursor materials for forming different kind of coatings.

The substrate holder is separate substrate holder and arranged to receive the two superposed substrates 2, 8. This means that the substrate holder is not a part of a reactor or other equipment of an atomic layer deposition apparatus. The substrate holder is thus a totally separate object which may be installed and removed from a reactor chamber, reactor and atomic layer deposition apparatus. The substrate holder may be formed from one or more separate parts such that the two superposed substrate may installed and uninstalled from the substrate holder. Thus the substrate holder is removable substrate holder in which the substrates are loaded into a reaction chamber. Accordingly when the substrates are arranged in the substrate holder the substrates are not touching/connecting the reaction chamber, but instead the substrate holders act as an intermediate part between the reaction chamber and the substrate. Substrates can be removed with their respective substrate holders from the reaction chamber and installed thereto. In other words the substrate holders are separate members in relation to the substrates and in relation to the reaction chamber and atomic layer deposition apparatus.

As shown in figure 6, the groove 32 has a tapering profile towards the bottom 21 of the groove 32, and specifically the first side wall 30 and the second side wall 31 are connected to each other such that they form a substantially V- shaped groove 32. The groove 32 is arranged to receive the at least one edge 9, 5 of the first and second superposed substrates 2, 8 such that first side wall 30 extends over an edge region of the first side surface 4 of the first substrate 2 and the second side wall 31 extends over an edge region the first side surface 10 of the second substrate 8. Thus a diffusion gap 23 is formed between the first side wall 30 and the first side surface 4, and second side wall 31 and the first side wall 10, respectively, as the side walls 30, 31 extend over the first side walls 4, 10. A shown in figure 6, the first side wall 30 is pressed against a first edge corner 5 between an edge surface 9 and the first side surface 4 of the first substrate 2 and the second side wall 31 is pressed against a first edge corner 7 between the edge surface 15 and the first side surface 10 of the second substrate 8. Thus the contact between the side walls 30, 31 and the edge corners 5, 7 provides a diffusion barrier, as described in connection with figures 2 and 4. Accordingly this embodiment forms an arrangement comprising a first substrate 2 having a first side surface 4, second side surface 10 and a first side edge 9, and a second substrate having first side surface 10, second side surface 12 and a second edge 15, the second side surface 6 of the first substrate 2 being arranged against the second side surface 12 of the second substrate 8 such that the first substrate 2 forms the substrate support, or support surface, for the second substrate 8 and the second substrate 8 forms the substrate support, or support surface, for the first substrate 2.

The groove 32 shown in figure 6 is substantially V-shaped as the first and second side walls 30, 31 are straight. Figure 7 shows the side walls 30, 31 and the substrates 2, 8 in the groove 32 in greater detail. In one embodiment the at least one of the first and second side walls 30, 31 is formed from a resilient material, or the first and second side walls 30, 31 are connected resiliently to each other such that the substrate holder may deform or bend when the side edges 9, 15 of the substrates 2, 8 are arranged into the groove 32 and against the side walls 30, 31 . The dotted line in figure 7 show the initial shape or position of the side walls 30, 31 when the substrates 2, 8 are not inside the groove 32. In the initial shape or position of the side walls 30, 31 the opening angle a of the V-shaped groove 32 between the edge supports may be, between 10 to 80 degrees, preferably, between 10 to 50 degrees and more preferably between 10 to 35 degrees. In figure 7 the first and second side walls 30, 31 are a distance Di apart from each other at the tip of the side walls 30, 31 . When the substrates 2, 8 are arranged into the groove 32 such that the first edge corner 5 of the first substrates 2 is pressed against the first side wall 30 and the first edge corner 7 of the second substrates 8 is pressed against the second side wall 31 , the side walls 30, 31 or the groove 32 deform resiliently or in relation to each other such that opening angle is increased to value β, as shown in figure 7. At the same time the distance Di between the tips of the edge supports increases value Ad to D₂. Accordingly the position of the side walls 30, 31 when the side edges 9, 15 of the substrates 2, 8 are in the groove 32 against the side walls 30, 31 is shown with solid line in figure 7. The resilient deformation of the groove 32 exerts a biasing force F against the first edge corners 5, 7 of the substrates 2, 8 due to the tendency of the side walls 30, 31 to return to the initial position shown with the dotted line. This biasing force F provides additional sealing effect as the side walls 30, 31 are pressed against the substrates 2, 8. Thus a diffusion barrier is provided between the substrates 2, 8 and the substrate holder. As shown in figures 6 and 7 a diffusion chamber 17 is formed between the bottom 21 of the groove 32 and the side edges 9, 15 of the substrates 2, 8. The diffusion chamber 17 increases the diffusion distance from the first side surface 4, 10 to the second side surface 6, 12. The angle α, β of the V-shaped groove 32 affects the depth of the diffusion chamber 17 between the bottom 21 of the groove 32 and side edges 9, 15 of the substrates 2, 8, as it defines how deep the side edges 9, 15 of the substrates 2, 8 may be inserted. Decreasing the angle α, β increases the depth of the diffusion chamber 17. Increasing the depth of the diffusion chamber 17 increases the diffusion distance and makes the diffusion of precursor molecules between the second surfaces 6, 12 of the substrates 2, 8 even more unlikely. Furthermore, the angle α, β affects on how close to the first side surface 4, 10 the side walls 30, 31 extend over the first side surface 4, 10. Decreasing the angle α, β provides the side walls 30, 31 closer to the first side surface 4, 10 and thus lowers the diffusion gap 23, and vice versa. Lowering the diffusion gap 23 reduces the diffusion of the precursor molecules into the diffusion gap 23. According to the above mentioned the substrate holder of figures 6 and 7 and the substrates 2, 8 together form arrangement in which a diffusion path is formed to extends between the first side surfaces 4, 10 and the second side surfaces 6, 12. The diffusion path is provided between the substrates 2, 8 and the substrate holder such that diffusion of precursor molecules is prevented or at least considerably reduced. The diffusion path comprises the diffusion gap 23 provided between the side walls 30, 31 and the first side surfaces 4, 10, diffusion barrier formed by the contact between the side walls 30, 31 and the first edge corners 5, 7, and the diffusion chamber 17. Thus the diffusion path provides a lengthened diffusion distance from the first side surfaces 4, 6 to the second side surfaces 6, 12. In an alternative embodiment the side walls 30, 31 may be formed and connected to each in another manner for forming substantially U- or C-shaped groove 32, as shown in figures 8, 9. In the embodiment of figure 8 the groove 32 is formed as substantially U- or C-shaped groove, having a first side wall 35, second side wall 37 and curved bottom wall 36 connecting the side walls 35, 37. The first and second side wall 35, 37 are arranged to extend over the first side surfaces 4, 10, and specifically edge regions, of the first side surfaces 4, 1 , of the substrates 2, 8. The side walls 35, 37 extend substantially parallel with the first side surfaces 4, 10 of the substrates 2, 8 and over the first side surfaces 4, 10, such that the diffusion gap 23 is provided between the side walls 35, 37 and the first side surfaces 4, 10, respectively. The side walls 35, 37 may be arranged against the first side surfaces 4, 10 or there may be a small clearance. The side edges 9, 15 of the substrates 2, 8 may be arranged into the groove 32 such that the side edges 9, 15, or the first edge corners 5, 7, are against or close to the bottom wall 36, thus forming a diffusion barrier as discussed above. In this embodiment the biasing force F may be smaller than in V-shaped grooves or it may be difficult to achieve. The diffusion gap 23 extends along the first side surfaces 4, 10 to the side edges 9, 15. A diffusion chamber 17 is formed between the bottom wall 36 and the side edges 9, 15 of the substrates 2, 8. Therefore, a diffusion path is provided from the first side surface 4, 10 to the second side surface 6, 12. The diffusion path comprises the diffusion gap 23, the diffusion barrier and the diffusion chamber 17. Figure 9 shows yet an alternative embodiment in which two substrates 2, 8 are arranged superposed as described above. In this embodiment the groove 32 of the substrate holder is formed as a U-shaped groove having substantially rectangular form. The groove 32 comprises first and second side walls 38, 40 and a bottom wall 39 between them. The groove 32 s arranged to receive the side edges 9, 15 into the groove 32 such that the side walls 38, 40 extend over the first side surfaces 4, 10 or edge regions thereof such that the diffusion gap 23 is formed between the first side surfaces 4, 10 and the side walls 38, 40. The side walls 38, 40 may be arranged to extend parallel to the first side surfaces 4, 10 and they may be arranged against the first side surfaces 4, 10 or a clearance may be provided between the side walls 38, 40 ad the first side surfaces 4, 10. In an alternative embodiment the side walls 38, 4 may extend in an angle in relation to the first side surfaces 4, 10. The side edges 9, 15 may be arranged against the bottom wall 39 or a small clearance may be provided between the bottom wall 39 and the side edges 9, 15. Thus a second diffusion gap or diffusion chamber 17 is provided between the bottom wall 39 and the side edges 9, 15. Accordingly a diffusion path is formed from the first side surfaces 4, 10 to the second side surfaces 6, 12. The diffusion path comprises the diffusion gap 23 and the second diffusion gap or diffusion chamber 17.

In a preferred embodiment the substrate holder is formed as a perimeter, frame or ring such that all the side edges 9, 15 or the whole side edge 9, 15 of a substrate 2, 8 may be received into the groove 26, 32. Thus the side walls 24, 30, 31 , 35, 37, 38, 40 may be arranged over the first side surfaces 4, 10 or edge regions thereof for forming the diffusion path. Figures 10A, 10B and 10C show one embodiment in which the substrate holder or the side walls form a perimeter with the groove for receiving all the side edges of a square shaped substrate 2, 8. In one embodiment the substrate holder may be provided from three separate parts, as shown in figures 10A, 10B and 10C. The first part 34 is L-shaped and the substrate 2, 8 is first inserter into this first part 34 or groove thereof. Then a second linear part 36 is arranged in the direction of arrow A and last the third part 38 is arranged in the direction of arrow B to complete the circumferential substrate holder and groove. The second and third part 36 and 38 may also be combined to form another L-shaped part. This way all the side edges of the substrates 2, 8 may be arranged into the groove and the diffusion growth on the second side surfaces 6, 12 may be prevented or minimized from all directions.

As shown in figures 2 to 9 that the side walls of the groove are arranged to extend a predetermined distance over the first surface 4, 10 of the substrate 2, 8. The diffusion of precursor molecules may also be affected by altering the length of the side walls of the groove, as shown in figure 1 1 . The length of the side walls may be chosen different on different directions relative to the precursor flow direction G. The length of the side walls may be smallest in the first part 41 having groove opening in the flow direction G and largest in the fourth part 44 having groove opening in the opposite to the flow direction G. The length of side walls of the second and third part 42, 43 opening along the flow direction may be preferably between the length of the side walls of the first and fourth part 41 , 44. It should be however noted, that the length may be chosen also differently. It is apparent to a person skilled in the art that as technology advanced, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.

Claims

1 . A substrate holder for holding one or more substantially planar substrates (2, 8) during processing of the substrate (2, 8) by subjecting a surface (4, 10) of the substrate (2, 8) to successive surface reactions of at least a first precursor and a second precursor, the substantially planar substrate (2, 8) comprising a first side surface (4, 10) and a second side surface (6, 12) and one or more side edges (9, 15) between the first and second side surfaces (4, 10, 6, 12), the substrate holder is formed as a groove frame (32) comprising a first side wall (30; 35; 38) and a second side wall (31 ; 37; 40) arranged to form a groove (32) for receiving at least one of the side edges (9, 15) of the substrate (2, 8), the first and side walls (30, 31 ; 36, 37; 38, 40) forming the side walls of the groove frame (32), characterized in that the groove frame (32) is arranged to receive the at least one side edge (9, 15) of a first and second superposed substrates (2, 8) such that the first side wall (30; 35; 38) is arranged to extend over an edge region of the first side surface (4) of the first substrate (2) and the second side wall (31 ; 37; 40) is arranged to extend over an edge region of the first side surface (10) of the second substrate (8).

2. A substrate holder according claim 1 , characterized in that:

- the groove (26; 32) has at least partly tapering profile towards the bottom (19; 21 ; 29; 36; 39) of the groove (26; 32); or

- the first side wall (22; 30) and the second side wall (24; 31 ) are connected to each other such that they form a substantially V-shaped groove (26; 32); or - the first side wall (25; 35; 38) and the second side wall (27; 37; 40) are connected to each other such that they form substantially U- or C-shaped groove (32).

3. A substrate holder according to claim 2, characterized in that the substantially V-shaped or tapering groove (26; 32) provides an opening angle (a):

- between 0 and 80 degrees;

- between 10 and 45 degrees; or

- between 10 and 35 degrees.

4. A substrate holder according to claim 2 or 3, characterized in that the substantially V-shaped or tapering groove (26; 32) the is arranged to receive the side edge (9, 15) of the substrate (2) such that an edge corner (5, 7) between the side edge (9, 15) and the first surface (4, 10) of the substrate (2, 8) is received against the side wall (24; 30, 31 ; 35, 37).

5. A substrate holder according to claim 2, characterized in that the substantially U- or C-shaped groove (32) comprises the first and second side walls

(25, 27; 35, 37; 38, 40) and a bottom wall (29; 36; 39).

6. A substrate holder according to claim 5, characterized in that the substantially U- or C-shaped groove (32) is arranged to receive the side edge (9, 15) of the substrate (2) against the bottom wall (29; 36; 39) of the groove (32).

7. A substrate holder according to any one of claims 1 to 6, characterized in that the side walls (24; 27; 30, 31 ; 35, 37; 38, 40) are formed from resilient material such that the substrate holder or groove (26; 32) may deform for providing a biasing force (F) to the side edge (9, 15) or edge corner (5, 7) of the substrate (2, 8) when the side edge (9, 15) of the substrate (2, 8) is received in the groove (26; 32).

8. A substrate holder according to any one of claims 1 to 7, characterized in that the first and second side walls (22, 24; 25, 27, 29; 30, 31 ; 35, 37; 38, 40) are connected resiliently to each other such that the substrate holder may deform for providing a biasing force (F) to the to the side edge (9) or edge corner (5) of the substrate (2) when the side edge (9) of the substrate (2) is received in the groove (26).

9. A substrate holder according to claim 1 to 8, characterized in that the groove (32) is arranged to receive the at least one side edge (9, 15) a first and second superposed substrates (2, 8) such that the first side wall (30; 35; 38) is pressed against a first edge corner (5) between the side edge (9) and the first side surface (4) of the first substrate (2) and such that the side wall (31 ; 37; 40) is pressed against a second edge corner (7) between the side edge (15) and the first side surface (10) of the second substrate (8).

10. A substrate holder according to any one of claims 1 to 9, characterized in that the groove (26; 32) is arranged to form a perimeter or ring for receiving all side edges (9, 15) or the whole side edge (9, 15) of the substrate (2, 8).

1 1 . An arrangement for supporting planar substrates (2, 8) during processing of the substrates (2, 8) by subjecting a surface (4, 10) of the substrate (2, 8) to successive surface reactions of at least a first precursor and a second precursor, the arrangement comprising:

- a first substantially planar substrate (2) having a first side surface (4), second side surface (10) and one or more first side edges (9) between the first and second side surfaces (4, 10), and a second substantially planar substrate (8) having first side surface (10), second side surface (12) and one or more second side edges (15) between the first and second side surfaces (10, 12); and

- a substrate holder for holding the planar substrate (2, 8) during processing of the substrate (2, 8), substrate holder is formed as a groove frame (32) comprising a first side wall (30; 35; 38) and a second side wall (31 ; 37; 40) arranged to form the groove (32) for receiving at least one of the side edges (9, 15) of the substrates (2, 8), characterized in that the second side surface (6) of the first substrate (2) is arranged superposed against the second side surface (12) of the second substrate (8), and that the first and second superposed substrates (2, 8) are arranged into the groove frame (32) such that the first side wall (30; 35; 38) is arranged to extend over an edge region of the first side surface (4) of the first substrate (2) for providing a diffusion path (23) between the first side surface (4) of the first substrate (2) and the first side wall (30; 35; 38), and the second side wall (31 ; 37; 40) is arranged to extend over an edge region of the first side surface (10) of the second substrate (8) for providing a diffusion path (23) between the first side surface (10) of the second substrate (8) and the second side wall (31 ; 37; 40).

12. An arrangement according to the claim 1 1 , characterized in that the in the groove (26; 32) is arranged to receive at least one of the side edges (9, 15) of the substrates (2, 8) in substantially form-fitting manner such that the diffusion path (17, 26; 17, 18; 23, 32) is formed between the first side surface (4, 10) and the second side surface (6, 12) of the substantially planar substrates (2, 8).

13. An arrangement according to claim 1 1 , characterized in that the first and second superposed substrates (2, 8) are arranged into the groove frame (32) such that the first side wall (30; 35; 38) is pressed against a first edge corner (5) between the side edge (9) and the first side surface (4) of the first substrate (2) and such that the second side wall (31 ; 37; 40) is pressed against a second edge corner (7) between the side edge (15) and the first side surface (10) of the second substrate (8).

14. An arrangement according to any one of claims 1 1 to 13, characterized in that:

15. An arrangement according to claim 14, characterized in that the substantially V-shaped or tapering groove (26; 32) provides an opening angle (a):

- between 0 and 80 degrees;

- between 10 and 45 degrees; or

- between 10 and 35 degrees.

16. An arrangement according to claim 14 or 15, characterized in that the substrate (2, 8) is arranged into the substantially V-shaped or tapering groove (26; 32) such that an edge corner (5, 7) between the side edge (9, 15) and the first surface (4, 10) of the substrate (2, 8) is received against the side wall (24; 30, 31 ; 35, 37).

17. An arrangement according to claim 14, characterized in that the substantially U- or C-shaped groove (32) comprises the first and second side walls (25, 27; 35, 37; 38, 40) and a bottom wall (29; 36; 39), and that the substrate (2, 8) is arranged into the groove (26; 32) such that the side edge (9, 15) of the substrate (2, 8) or an edge corner (5, 7) between the side edge (9, 15) and the first side surface 4, 10) of the substrate (2, 8) is against the bottom wall (29; 36; 39) of the groove (32).

18. An arrangement according to any one of claims 1 1 to 17, characterized in that the side walls (24; 27; 30, 31 ; 35, 37; 38, 40) are formed from resilient material such that the substrate holder or groove (26; 32) may deform for providing a biasing force (F) to the side edge (9, 15) of the substrate (2, 8) or an edge corner (5, 7) between the side edge (9, 15) and the first side surface 4, 10) of the substrate (2, 8) when the side edge (9, 15) of the substrate (2, 8) is received in the groove (26; 32).

19. An arrangement according to any one of claims 1 1 to 18, characterized in that the first and second side walls (22, 24; 25, 27, 29; 30, 31 ; 35, 37; 38, 40) are connected resiliently to each other such that the substrate holder may deform for providing a biasing force (F) to the to the side edge (9) or an edge corner (5, 7) between the side edge (9, 15) and the first side surface 4, 10) of the substrate (2, 8) when the side edge (9) of the substrate (2) is received in the groove (26).

20. An arrangement according to any one of claims 1 1 to 19, characterized in the that the that the groove (26, 32) is formed as a perimeter or ring for receiving all edges (5, 7, 9, 1 1 , 13, 15) or the whole edge (5, 7, 9, 1 1 , 13, 15) of the substrate (2, 8).