Barrier layer, method for forming a barrier layer, and wiring substrate

Abstract

To provide a configuration of a barrier layer which has excellent effect of suppressing metal diffusion from copper wiring and can be selectively formed in desired areas, and a formation method thereof.SOLUTION: This invention relates to a barrier layer formed on a board surface as a base film for metallic wiring such as copper wiring in a wiring board. The barrier layer has a two-layer structure, and consists of a first thin film formed on the board and made of a metal oxide of a metal selected from Al, Zn, Mn, Ti, and Co, and a second thin film formed on the first film and made of Ru. These thin films can be formed under mild film-forming conditions by chemical vapor deposition. The barrier layer can be selectively formed in a desired film-forming area by causing a non-film-forming area to adsorb an inhibitor that inhibits the film formation before forming the thin films that constitute the barrier layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a barrier layer that serves as a base for metal wiring on a wiring substrate for semiconductor devices and the like. Furthermore, this invention relates to a method for forming the barrier layer by chemical vapor deposition (chemical vapor deposition (CVD) method, atomic layer deposition (ALD) method). [Background technology]

[0002] In recent years, copper wiring has become the mainstream for semiconductor device wiring. When applying such copper wiring, it is common practice to set a barrier layer as an underlayer. This is because when copper wiring is formed on a substrate made of insulating material such as Si or SiO2, the copper diffuses into the substrate, making it difficult to maintain the substrate's insulating properties. The application of a barrier layer suppresses the diffusion of copper into the substrate. Generally, copper wiring on semiconductor device wiring substrates is formed by filling openings (trenches and vias) formed in the substrate in a predetermined pattern with copper, and then planarizing them using chemical mechanical polishing (CMP) or the like. In this wiring formation process, a thin-film barrier layer is formed using various thin-film formation processes before the copper is filled into the openings. To date, metal nitrides such as TiN (titanium nitride) and TaN (tantalum nitride) have often been used as the constituent materials for these barrier layers.

[0003] In the field of semiconductor devices, miniaturization and density are constantly being pursued, and miniaturization and miniaturization of wiring structures are also required. This reduction in size (volume) due to the miniaturization of wiring structures increases the wiring resistance, which is the resistance value per unit length of wiring. One way to address this problem of increased wiring resistance is to reduce the thickness of the barrier layer, but if the barrier layer is made too thin, there are concerns that the diffusion suppression effect of copper atoms will be reduced. In other words, there are limits to how much the thickness of the barrier layer can be reduced, so other solutions are required.

[0004] One measure to suppress the increase in wiring resistance due to the reduction in wiring dimensions is the development of low-resistivity barrier layer materials. As mentioned above, even if wiring dimensions are reduced, the barrier layer cannot be simply made thinner. In other words, reducing wiring dimensions increases the proportion of the barrier layer's influence on wiring resistance. Therefore, by making the barrier layer low-resistivity, the increase in overall wiring resistance can be suppressed.

[0005] One possible solution for addressing this issue is the application of ruthenium (Ru) as a constituent material for a barrier layer. Ruthenium is a metal with low resistivity, making it suitable for miniaturization of wiring pitches and promising as a metal material for wiring that can replace copper. Furthermore, a ruthenium thin film can function as a seed layer when electroplating copper onto it, and it also has good adhesion to copper, so it can function as a liner layer as well. Therefore, by using a ruthenium thin film as a barrier layer, the seed layer and liner layer become unnecessary, which allows for an increase in the volume of copper in the wiring and is expected to reduce wiring resistance. Regarding the application of a ruthenium thin film as a barrier layer, Non-Patent Literature 1 discloses a method for forming a ruthenium thin film using atomic layer deposition (ALD) with a predetermined organic ruthenium compound as a precursor. According to this thin film formation process, a suitable barrier layer made of a ruthenium thin film can be formed while precisely controlling the film thickness.

[0006] Another method being considered to suppress the increase in wiring resistance due to the reduction in wiring dimensions is to improve the overall structure of the wiring, including the barrier layer. The barrier layer is set up to suppress the diffusion of copper from the copper wiring into the substrate made of insulating material. Therefore, the barrier layer is not necessary in areas where the copper wiring does not come into contact with the insulating material. For example, multilayer wiring is often used in semiconductor devices. In multilayer wiring, the wiring formed in each layer is interlayer-connected, and holes (vias) for interlayer connection are set in the openings (trenches) that form the wiring pattern. Since the copper wiring of the lower layer is exposed at the bottom of the via, it is not necessary to form a barrier layer in this area. By not forming a barrier layer in these areas and selectively forming a barrier layer only in the necessary areas, the overall film thickness of the barrier layer can be reduced, thereby reducing the wiring resistance of the copper wiring. Examples of attempts to selectively form such a barrier layer include Patent Documents 1 and 2, in which an etching treatment is performed on the via bottom surface after the barrier layer has been formed to selectively form the barrier layer. Patent Document 3 describes a method in which a TiN barrier material is deposited by the ALD method while a block layer is formed on the via bottom surface to form a barrier layer. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Publication No. 8,252,680 [Patent Document 2] U.S. Patent No. 9099535 [Patent Document 3] Japanese Patent Publication No. 2008-78647 [Non-patent literature]

[0008] [Non-Patent Document 1] Chan, R.; Arugagiri, TN; Zhang, Y.; Chyan, O.; Wallance,RM; Kim, MJ; Hurd, TQ Diffusion Studies of Copper on Ruthenium ThinFilm : A Plateable Copper Diffusion Barrier. Electrochemical and Solid-StateLetters 2004, 7 (8), G154 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, although ruthenium has low resistance, its diffusion-inhibiting ability as a barrier layer is not very high. In particular, at high temperatures above 500°C, it cannot suppress the diffusion of copper into the substrate.

[0010] Furthermore, while selective formation of barrier layers, which is an improvement in wiring structure, is useful in itself, efficiently forming such selective barrier layers is difficult. Etching after barrier layer formation, as described in Patent Documents 1 and 2 above, complicates the manufacturing process of wiring boards because it requires microfabrication after barrier layer formation. Moreover, although Patent Document 3 suppresses barrier layer formation in the region by forming a block layer on the via bottom surface, it is necessary to remove the block layer that has been altered during barrier layer formation, and the method for doing so requires complicated additional steps, similar to etching in Patent Documents 1 and 2.

[0011] In the first place, thin films of high-melting-point nitrides such as TiN and TaN, which have conventionally been used as barrier layers, are difficult to form selectively. The deposition of these thin films requires assistance from high-temperature heating or high-temperature plasma. While the application of block layers or mask materials, as described in Patent Document 3 above, is expected to be useful for the selective formation of barrier layers, selective deposition is difficult under the deposition conditions of TiN and other materials because the block layer may be altered or disappear.

[0012] This invention was made against the background described above, and aims to clarify the structure of a barrier layer that can accommodate miniaturized metal wiring, has excellent effect in suppressing metal diffusion from metal wiring, and can be selectively formed in a predetermined region. Furthermore, it provides an efficient method for forming the barrier layer, which also enables selective formation. [Means for solving the problem]

[0013] The inventors considered that a two-layer barrier layer, primarily composed of a ruthenium thin film and supplemented with a metal oxide thin film to complement the diffusion suppression effect, would be suitable as a barrier layer capable of solving the above problems, and conducted diligent research. As a result, they concluded that a thin film of an oxide of one of the following metals is suitable as the metal oxide thin film, leading to the present invention.

[0014] In other words, the present invention relates to a barrier layer formed on the surface of a substrate as an underlayment for metal wiring, comprising a first thin film formed on the substrate, which is made of a metal oxide of one of the following metals: Al, Zn, Mn, Ti, or Co, and a second thin film formed on the first thin film, which is made of Ru.

[0015] As described above, ruthenium is suitable as a barrier layer from the viewpoint of its electrical properties (resistivity), and considering the future trend towards miniaturization of metal wiring, it is a useful material even after accounting for its low diffusion suppression effect on its own. Furthermore, according to the inventors' studies, metal oxide thin films of Al, Zn, Mn, Ti, and Co exhibit an effective diffusion suppression effect when working in cooperation with ruthenium thin films, even if they are extremely thin films of about 1 nm. The diffusion suppression effect due to the addition of these metal oxide thin films is effective even at high temperatures where the effect of the ruthenium thin film is reduced.

[0016] Further, the reason why ruthenium thin films and thin films of metal oxides such as Al and Zn are useful as constituent materials for barrier layers is that these thin films can be formed under relatively mild film formation conditions by applying a film formation process based on a chemical vapor deposition method. Ruthenium thin films and metal oxide thin films such as Al and Zn formed by chemical vapor deposition can be formed by heating at a relatively low temperature, and reactive gases with low aggressiveness can be used. Therefore, these thin films can be selectively formed at regions on a substrate that require a barrier layer. Accordingly, the present invention can accommodate the above-described structural improvements relating to barrier layers, and thus can cope with the miniaturization of metal wiring while providing an improved diffusion suppressing effect. Details of the configuration of the barrier layer according to the present invention and the method for forming this barrier layer based on chemical vapor deposition will be described below.

[0017] A Configuration of the Barrier Layer According to the Present Invention As described above, the barrier layer for metal wiring according to the present invention is a thin film having a two-layer structure including a first thin film made of a predetermined metal oxide thin film and a second thin film made of a ruthenium thin film. Hereinafter, the first thin film and the second thin film will be described.

[0018] A-1 First Thin Film (Metal Oxide Thin Film) The metal oxide thin film, which is the first thin film, is formed on a substrate. The first thin film is formed to improve the inherent function of a barrier layer that suppresses metals (such as copper) from metal wiring such as copper wiring from reaching the substrate. As the metal oxide constituting the first thin film, oxides of metals selected from the group consisting of Al, Zn, Mn, Ti, and Co are used. Even when these thin films of metal oxides are formed in an extremely thin state under the ruthenium thin film, they can effectively suppress the diffusion of copper and the like. In addition, for these metal oxides, several precursors for forming thin films by chemical vapor deposition are known, and oxide thin films can be formed under mild conditions by selecting appropriate reactive gas and reaction conditions.

[0019] It should be noted that the metal oxide constituting the first thin film does not necessarily need to have a stoichiometric composition in part or in whole.

[0020] The thickness of the first thin film is preferably 0.5 nm or more and 3 nm or less. If it is less than 0.5 nm, the diffusion suppression effect of the barrier layer cannot be improved. Further, as the thickness of the metal oxide thin film increases, the effect of the diffusion suppression action also enhances; however, if it exceeds 3 nm, the specific resistance of the barrier layer becomes excessively high, which adversely affects metal wiring. The thickness of the first thin film is more preferably 1 nm or more and 2 nm or less.

[0021] A-2 Second thin film (ruthenium thin film) The ruthenium thin film is formed on the surface of a metal oxide thin film such as a Zn-containing thin film, and is a main component of the barrier layer according to the present invention. The reason why ruthenium is used in the present invention is that it has low specific resistance and favorable electrical characteristics, and thus is suitable as an underlayer for metal wiring. In addition, ruthenium has good adhesion to copper and the like that constitute metal wiring. Therefore, metal wiring can be formed without forming a seed layer or a liner layer on the barrier layer. Accordingly, using a ruthenium thin film as the barrier layer also has the advantage that the thickness (volume) of copper wiring and the like can be secured, and the wiring resistance of metal wiring can be reduced.

[0022] There is no particular limitation on the thickness of the ruthenium thin film. This is because the thickness of the ruthenium thin film does not greatly affect the diffusion suppression effect of the barrier layer. However, to reduce wiring resistance, it is desirable to reduce the proportion of the ruthenium thin film in the total thickness of the wiring. On the other hand, if the thickness of the ruthenium thin film is excessively small, the specific resistance of the barrier layer increases. In consideration of these points, the thickness of the ruthenium thin film is preferably 2 nm or more and 10 nm or less. Since the metal oxide thin film that is the above-described first thin film can be as extremely thin as 0.5 nm or more and 3 nm or less, the total thickness of the barrier layer can be reduced in the present invention, so the present invention is also useful from the viewpoint of reducing wiring resistance by securing the thickness of metal wiring.

[0023] Furthermore, the barrier layer according to the present invention is required to comprise both a first thin film (metal oxide thin film) and a second thin film (ruthenium thin film). Therefore, even if there is a region on the substrate consisting only of a ruthenium thin film, that region does not constitute the barrier layer according to the present invention.

[0024] B Wiring board equipped with a barrier layer according to the present invention The two-layer barrier layer structure according to the present invention, as described above, is applied to wiring substrates for various devices such as semiconductor devices and electronic devices. This wiring substrate is a substrate in which a barrier layer and metal wiring are formed on at least a part of the substrate. In the present invention, the above-mentioned barrier layer is formed as the barrier layer, and metal wiring is formed on this barrier layer.

[0025] There are no restrictions on the material, dimensions, and structure of the substrate on which the barrier layer and metal wiring are formed; they are arbitrarily set according to the specifications of the wiring substrate of the device to which they are applied. However, the area on which the metal wiring is formed is made of an insulating material such as Si or SiO2. In addition, for copper wiring substrates formed by the so-called damascene process, substrates with grooves (trenches) and holes (contact holes, vias) corresponding to the wiring pattern are used. Substrates with such trenches and other grooves and holes are also acceptable.

[0026] In a wiring substrate to which the barrier layer according to the present invention is applied, the barrier layer is formed on the substrate surface, and metal wiring is further formed on the barrier layer. In substrates with grooves or holes such as trenches, the inner walls of these are also included in the substrate surface. The barrier layer according to the present invention is formed to suppress the diffusion of metal from the metal wiring into the insulating material portion of the substrate. Therefore, it is preferable that the substrate surface in the portion where the barrier layer is formed in the wiring substrate according to the present invention is made of an insulating material.

[0027] Considering the problems of the present invention, the metal constituting the metal wiring formed on the barrier layer is a metal that can diffuse into and affect the insulating material of the substrate. As a constituent material for metal wiring, in addition to copper, which is currently the mainstream, the application of ruthenium and cobalt is also being considered from the viewpoint of electrical properties such as resistivity. Since there is concern that these metals may also diffuse into the insulating substrate at high temperatures, the present invention is effective.

[0028] C Method for forming a barrier layer according to the present invention The barrier layer according to the present invention consists of a ruthenium thin film and a predetermined metal oxide thin film, and widely known thin-film formation processes can be applied to form each of these thin films. For example, the formation of the ruthenium thin film and the metal oxide thin film is possible even with sputtering (reactive sputtering), which is a film formation process other than chemical vapor deposition. However, in order to cope with the reduction in film thickness due to the miniaturization of metal wiring, it is necessary to deposit a barrier layer with a small film thickness with good coverage. Furthermore, structural low resistance is also necessary through the selective deposition of the barrier layer as described above. For these reasons, the method for forming the barrier layer according to the present invention is preferably by chemical vapor deposition.

[0029] In other words, the method for forming a barrier layer according to the present invention is a method for forming a barrier layer comprising: a first film formation step of forming a first thin film on a substrate by chemical vapor deposition using a metal compound of any of the metals Al, Zn, Mn, Ti, and Co as a precursor; and a second film formation step of forming a second thin film on the first thin film by chemical vapor deposition using a metal compound of Ru as a precursor.

[0030] Chemical vapor deposition (CVD) is a method for producing thin films by introducing vaporized raw material gas and reaction gas, which are precursors made of metal compounds, onto the surface of a substrate, decomposing the metal compound on the substrate, and depositing the metal or metal oxide. Chemical vapor deposition is known to have two main types, depending on the supply of raw material gas and reaction gas: chemical vapor deposition (CVD) and atomic layer deposition (ALD).

[0031] CVD is a film deposition method in which a raw material gas and a reaction gas are introduced onto a substrate simultaneously and reacted until a thin film of the desired thickness is formed. In contrast, ALD is a thin film formation process in which a series of steps constitute one cycle, and this cycle is repeated one or more times to achieve the desired thickness. These steps include introducing a raw material gas onto the substrate and adsorbing the raw material compound onto the substrate surface (raw material adsorption step), exhausting excess raw material gas (raw material gas purging step), introducing a reaction gas and reacting the adsorbed raw material compound with the reaction gas on the substrate surface to form a thin film (reaction step), and further exhausting excess reaction gas (reaction gas purging step).

[0032] Chemical vapor deposition (CVD) can produce thin films with good coverage. Furthermore, metals such as Al and Zn, and ruthenium that constitute the barrier layer according to the present invention can be deposited under relatively low-temperature and mild conditions by appropriately selecting precursors, etc. This enables selective film deposition, which will be described later. Both CVD and ALD methods can be applied to the barrier layer formation method of the present invention. However, when particularly precise control of the film thickness of the barrier layer is required, it is more preferable to apply the ALD method to at least one of the first and second film deposition steps described above. The basic steps of the barrier layer formation method according to the present invention, consisting of a first film deposition step and a second film deposition step, will be described below. Then, a method for selectively forming a barrier layer in a desired region on a substrate based on this barrier layer formation method will be described.

[0033] C-1 Basic method for forming a barrier layer according to the present invention C-1-1 First film formation process (deposition of metal oxide thin film) The first film formation step involves forming an oxide thin film of one of the following metals—Al, Zn, Mn, Ti, or Co—on a substrate by chemical vapor deposition. Examples of metal compounds that serve as precursors for generating the source gas include trimethylaluminum, triethylaluminum, and aluminum chloride for Al; diethylzinc, dimethylzinc, zinc chloride, and zinc acetate for Zn; bis(ethylcyclopentadienyl)manganese(II) and tris(2,2,6,6-tetramethyl-3,5-heptanedionato)manganese(III) for Mn; titanium chloride, tetraisopropyl orthotitanate, and tetrakis(dimethylamide)titanium for Ti; and bis(cyclopentadienyl)cobalt(II), cobalt(II) iodide, and bis(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt(II) for Co. Furthermore, the reaction gas is selected depending on whether it is oxygen, water vapor, hydrogen, ammonia, alcohol, or ozone, and the metal oxide thin film to be formed.

[0034] The aforementioned metal compounds of Al, Zn, Mn, Ti, and Co can be decomposed at relatively low temperatures, allowing for the deposition of each metal and the formation of oxide thin films. The reaction conditions in the first film formation step are preferably set at a temperature between 100°C and 150°C.

[0035] In the CVD method, the thickness of the metal oxide thin film formed in the first film deposition step is controlled by the reaction time. In the ALD method, it can be controlled by the number of repetitions (cycle count) of the cycle consisting of the aforementioned "raw material adsorption step - raw material gas purging step - reaction step - reaction gas purging step". Furthermore, in the ALD method, the film thickness can also be controlled by the pulse time of raw material gas and reaction gas introduction in the raw material adsorption step and reaction step.

[0036] C-1-2 Second film deposition process (deposition of ruthenium thin film) The second film deposition process also involves forming a thin film (ruthenium thin film) using chemical vapor deposition, and the basic method is the same as the first film deposition process. Furthermore, various ruthenium compounds can be used as precursors for the ruthenium thin film, from the perspective of enabling film deposition at low temperatures.

[0037] Bis(ethylcyclopentadienyl)ruthenium(II), shown in Chemical Formula 1 below, is a suitable precursor for ruthenium thin films. This precursor is a well-known ruthenium compound (organic ruthenium compound) due to its liquid state at room temperature and relatively high vapor pressure, making it suitable for handling and film deposition temperatures.

[0038] (1) Organoruthenium compound A [ka]

[0039] Furthermore, in recent years, organic ruthenium compounds (referred to as organic ruthenium compounds B to E) described in (2) to (4) below have been developed with the aim of further lowering the film deposition temperature and expanding the range of selectable reaction gases.

[0040] (2) Organoruthenium compound B [ka] (In the formula, ligand L1 is a linear or branched hydrocarbon group or cyclic hydrocarbon group having 2 to 13 carbon atoms. Ligand X is one of the following: carbonyl ligand, isocyanide ligand, pyridine ligand, amine ligand, imidazole ligand, pyridazine ligand, pyrimidine ligand, or pyrazine ligand.)

[0041] A specific example of a precursor composed of this organic ruthenium compound B is (η) in formula 3 below. 4 (η)methylene-1,3-propanediyl)tricarbonylruthenium and (η) of formula 4. 4(-2-propyrideni-1-yl,3-propanediyl)tricarbonylruthenium is one example (L1: trimethylenemethane ligand, X: carbonyl ligand). Also, [(η4-methylene-1,3-propanediyl)-ruthenium-dicarbonyl-(2-isocyano-2-methylpropane)] of formula 5 is another example.

[0042] [ka]

[0043] [ka]

[0044] [ka]

[0045] (3) Organic ruthenium compound C [ka] (In the formula, R1 and R2 may be the same or different, and each is either a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.)

[0046] A specific example of a precursor composed of this organoruthenium compound C is dicarbonyl-bis(5-methyl-2,4-hexanediketonato)ruthenium(II) shown in the following formula.

[0047] [ka]

[0048] (4) Organoruthenium compound D [ka] (In the formula, ligand L2 is the ligand represented by either (L2-1) or (L2-2) shown in the following formula, and is a ligand containing one nitrogen atom.)

[0049] [ka] (In the formula, * indicates the position of the atom that bridges the ruthenium atom. R3~R 10 These elements may be identical or different, and each is either a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0050] A specific example of a precursor composed of this organoruthenium compound D is the hexacarbonyl[μ-[(1,2-η)-3-methyl-N-(1-methylpropyl)-1-butene-1-aminato-κC 2 κN 1 :κN 1 Zirthenium (Ru-Ru) is one example.

[0051] [ka]

[0052] (5) Organoruthenium compound E [ka] (Ligands L3 and L4 that coordinate to ruthenium are shown by the following formulas.)

[0053] [ka] (Sulfonation R of ligands L3 and L4) 11 ~R 22 Each of these is independently either a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms.

[0054] Specific examples of precursors composed of this organoruthenium compound E include benzene(methylene-1,3-propanediyl)ruthenium and (methylene-1,3-propanediyl)[1-methyl-4-(1-methylethyl)benzene]ruthenium, as shown in the formula below.

[0055] [ka]

[0056] The above-mentioned organic ruthenium compounds can be used as precursors in both CVD and ALD methods. In chemical vapor deposition, the deposition temperature for ruthenium thin films is preferably between 150°C and 400°C. Below 150°C, the decomposition reaction of the organic ruthenium compound is slow, resulting in a delayed deposition process. On the other hand, above 400°C, uniform deposition becomes difficult, and there are concerns about damage to the substrate. The deposition temperature is the surface temperature of the substrate and is usually controlled by heating the substrate.

[0057] Furthermore, the reaction gas used for ruthenium thin film deposition can be either an oxidizing gas such as oxygen or ozone, or a non-oxidizing gas such as hydrogen, water vapor, ammonia, amine compounds, or hydrazine derivatives. The reaction gas is selected according to the decomposition characteristics of the organic ruthenium compound. For example, the use of an oxidizing gas such as oxygen is preferable for organic ruthenium compound A. On the other hand, both oxidizing and non-oxidizing gases can be used for organic ruthenium compounds B, C, D, and E, and ruthenium thin films can be deposited using either method.

[0058] C-2 Selective Formation of Barrier Layer According to the Present Invention As illustrated above, such as the via bottom surface for interlayer connections in multilayer wiring, there are sometimes areas on the wiring substrate where metal wiring does not come into contact with the insulating material. A barrier layer is not essential in these areas. Similarly, the formation of a barrier layer is not essential in areas on the substrate surface that are not composed of insulating material. Therefore, by designating these areas as non-film-forming regions and selectively forming a barrier layer in areas where the insulating material and metal wiring can come into contact, the overall thickness of the barrier layer can be reduced, thereby lowering the wiring resistance of the metal wiring.

[0059] The barrier layer according to the present invention has a laminated structure of a metal oxide thin film such as Zn (first thin film) and a ruthenium thin film (second thin film), and these thin films can be deposited at relatively low temperatures by chemical vapor deposition. This allows for the selective formation of a barrier layer in the deposition region of the substrate.

[0060] The specific method involves pre-adsorbing a film-forming inhibitor having a decomposition temperature higher than the film-forming temperature of at least the first thin film into a non-film-forming region, and then performing the first thin-film-forming step and the second film-forming step. In this way, at least the first thin film is not formed on the non-film-forming region, and the two-layer barrier layer of the present invention is not formed there. The two-layer barrier layer of the present invention is selectively formed in the film-forming region. In the present invention, the above-mentioned film-forming inhibitor is referred to as an inhibitor.

[0061] The selective formation of a barrier layer by applying inhibitors as described above is extremely difficult with conventional methods of forming nitride thin films such as TiN and TaN, which are known as barrier layers. Although these nitride thin films can also be deposited by chemical vapor deposition, the deposition conditions require high-energy assistance such as high-temperature heating or plasma irradiation. No compound can withstand such high-energy application without decomposition or alteration. Therefore, even if a compound that acts as an inhibitor is adsorbed in a non-deposited region, similar to the present invention, the inhibitor decomposes during barrier layer formation, making selective deposition in the deposition region extremely difficult.

[0062] The requirements for the compound used as an inhibitor in this invention are, firstly, that its decomposition temperature is at least higher than the deposition temperature of the first thin film (metal oxide thin film). Secondly, it is preferable that the inhibitor is a compound that, after being adsorbed onto a non-film-forming region of the substrate, can inhibit the deposition reaction of metal oxides, etc., on that surface. As a result, the inhibitor suppresses the deposition of at least the first thin film and prevents the formation of a barrier layer in the non-film-forming region. In the above requirements, inhibiting the deposition reaction of metal oxides, etc., means preventing the deposition reaction of metal oxides, etc., by inhibiting the adsorption of the raw material gas (metal compound) onto the substrate surface, etc.

[0063] Furthermore, while the decomposition temperature of the inhibitor compound must be higher than the deposition temperature of the first thin film, it is not essential that it be higher than the deposition temperature of the second thin film. This is because if the decomposition temperature of the inhibitor is at least higher than the deposition temperature of the first thin film, the deposition of the first thin film will be inhibited, and the two-layer barrier layer according to the present invention will not be formed. However, the decomposition temperature of the inhibitor may be higher than the deposition temperature of the second thin film.

[0064] Furthermore, regarding the properties of the inhibitor, a compound that is less likely to adsorb to the insulating material protected by the barrier layer, while being able to adsorb to wiring materials such as copper, is more preferable. An inhibitor compound with such selective adsorption properties can efficiently inhibit film formation in the non-film formation region.

[0065] Based on the above conditions, preferred inhibitor compounds in the present invention include thiol compounds, phosphonic acid compounds, aromatic compounds, and alkyne compounds. Specifically, examples of thiol compounds include dodecanethiol (DDT), ethanethiol, and octadecanethiol, while examples of phosphonic acid compounds include octadecylphosphonic acid. Examples of aromatic compounds include aniline. Examples of alkyne compounds include 4-octyne and 3-hexyne.

[0066] In the basic method for forming a barrier layer according to the present invention described above, which includes first and second film formation steps by chemical vapor deposition, in the barrier layer formation step when applying an inhibitor for selective film formation, first, the inhibitor is adsorbed in the non-film formation region before the first film formation step. Adsorption of the inhibitor is performed by heating and vaporizing the inhibitor and supplying the gas containing the inhibitor to the substrate. At this time, if a compound (such as a thiol compound) that has the property of being difficult to adsorb to insulating materials but adsorbable to wiring materials, as listed above as a preferred inhibitor, is used, the inhibitor can be selectively adsorbed in the non-film formation region without any special operation. Alternatively, as a method for adsorbing an inhibitor that does not have such adsorption properties to the non-film formation region, the inhibitor can be adsorbed indiscriminately onto the entire substrate, and then the inhibitor in the film formation region can be removed by UV lithography or the like.

[0067] When adsorbing inhibitors, it is preferable to maintain a substrate temperature of 25°C to 150°C. Furthermore, it is preferable that the amount of inhibitor adsorbed onto the substrate increases the water droplet contact angle (WCA value) by 30° or more compared to the state before inhibitor adsorption. Since the adsorption characteristics of the inhibitor also differ depending on the material of the non-film-forming region in the substrate, the range of change in the WCA value should be adjusted while controlling the amount of inhibitor supplied and the substrate temperature to achieve a suitable change. After supplying the inhibitor, it is preferable to stop the supply and, if necessary, circulate a purge gas such as an inert gas to purge any excess inhibitor from the reaction system.

[0068] After adsorbing the inhibitor onto the non-film-forming region of the substrate as described above, the thin films are formed in the first and second film-forming steps according to the basic process described above. At this time, since the decomposition temperature of the inhibitor is at least higher than the film-forming temperature of the first film-forming step, the inhibitor remains adsorbed on the non-film-forming region, and therefore the first thin film is not formed in the non-film-forming region. After the second film-forming step, the barrier layer according to the present invention is formed in the film-forming region.

[0069] If the decomposition temperature of the inhibitor is higher than the deposition temperature of the first deposition step but lower than the deposition temperature of the second deposition step, the inhibitor will decompose in the second deposition step. Therefore, the step of decomposing and removing the inhibitor is not necessarily required. However, if the second deposition step is performed without removing the inhibitor, components such as carbon produced by the inhibitor decomposition may contaminate the ruthenium thin film (second thin film). Therefore, in the present invention, it is more preferable to include a removal step after the first deposition step to remove the inhibitor on the non-deposited area, and to perform the second deposition step after the removal step.

[0070] Inhibitors can be removed by heating them to a temperature above their decomposition temperature. Since the decomposition temperature of the inhibitor is at least higher than the film deposition temperature of the first film deposition process, heating to a temperature of 100°C or higher above the film deposition temperature of the first film deposition process is sufficient. Preferably, the upper limit of the heating temperature is 300°C or lower. Furthermore, when decomposing and removing inhibitors, heating the substrate under plasma irradiation can lower the heating temperature and accelerate removal. Preferably, the atmosphere during plasma treatment is hydrogen, oxygen, nitrogen, etc.

[0071] When an inhibitor having a decomposition temperature exceeding the deposition temperature of the second deposition step is used, the inhibitor removal step described above may be performed after the second deposition step. In this case, although the heating temperature tends to be high, removal is possible by using plasma irradiation in combination. [Effects of the Invention]

[0072] As described above, the barrier layer for metal wiring according to the present invention has a two-layer structure composed of a metal oxide thin film of a predetermined metal such as Zn and a ruthenium thin film. The ruthenium thin film alone does not have a particularly high diffusion suppression effect, but in cooperation with the metal oxide thin film it has an extremely effective diffusion suppression effect. The present invention can accommodate thinning of the barrier layer, thereby securing the volume of the metal wiring. Furthermore, since the barrier layer of the present invention has good adhesion to the metal wiring, seed layers and liner layers are not required. As a result, the present invention can effectively solve the problem of increased wiring resistance in metal wiring due to miniaturization. [Brief explanation of the drawing]

[0073] [Figure 1] A flowchart illustrating the process for forming the barrier layer (Ru thin film / ZnO thin film) in this embodiment. [Figure 2] XRD profile of Example 1 (Cu / Ru(4nm) / ZnO(1nm) / Si) after high-temperature heat treatment. [Figure 3] XRD profile of Example 2 (Cu / Ru(4nm) / ZnO(2nm) / Si) after high-temperature heat treatment. [Figure 4] XRD profiles of the comparative example (Cu / Ru(5nm) / Si) after high-temperature heat treatment. [Figure 5] A graph showing the measurement results of resistance values ​​after high-temperature heat treatment for Example 1, Example 2, and the Comparative Example. [Figure 6] A graph showing the measurement results of the interfacial adhesion energy for Example 1 (Cu / Ru(4nm) / ZnO(1nm) / Si) and the comparative example (Cu / Ru(5nm) / Si). [Figure 7] This figure shows the change in WCA value over time when dodecanethiol is adsorbed onto the substrate, as preliminaryly investigated in the second embodiment. [Figure 8] This figure shows the changes in substrate temperature and WCA value when dodecanethiol is adsorbed onto the substrate, as preliminaryly investigated in the second embodiment. [Figure 9] This figure shows the change in the number of ALD cycles and Zn concentration when dodecanethiol is adsorbed onto the substrate, as preliminaryly investigated in the second embodiment. [Figure 10] This figure shows the change in film thickness when a ZnO thin film is deposited on a substrate treated with dodecanethiol, which was preliminaryly investigated in the second embodiment. [Figure 11] This figure shows the correspondence between the number of cycles and the film thickness of the Ru thin film when a barrier layer is selectively formed in the second embodiment.

[0074] First Embodiment The embodiments of the present invention will now be described. In this embodiment, a thin film of Zn oxide (ZnO thin film) was deposited on a substrate as a first thin film, and a ruthenium thin film was deposited on the ZnO thin film to form a barrier layer. Then, copper was deposited on this barrier layer, and the diffusion-suppressing effect of the barrier layer on copper was investigated.

[0075] In this embodiment, a barrier layer was formed by depositing a ZnO thin film and a ruthenium thin film using the ALD method. Figure 1 shows the flow of barrier layer formation in this embodiment. Both the first and second film deposition steps based on the ALD method consist of (i) an adsorption step in which a raw material gas is introduced into the substrate, (ii) a raw material gas purging step in which excess raw material gas is exhausted, (iii) a reaction step in which a reaction gas is introduced to form a thin film, and (iv) a reaction gas purging step in which excess reaction gas is exhausted. In each film deposition step, these steps constitute one cycle and are repeated until the target film thickness is reached.

[0076] [First film deposition process (deposition of ZnO thin film)] In this embodiment, a Si wafer (dimensions 2 cm × 2 cm) was prepared as the substrate, and a first thin film, a ZnO thin film, was deposited on the substrate surface by the ALD method. Diethylzinc (formula shown below) was used as the zinc compound precursor for the ZnO thin film.

[0077] [ka]

[0078] [Second film deposition process (deposition of ruthenium thin film)] Next, as a ruthenium compound that will serve as a precursor for the ruthenium thin film, (η4 -methylene-1,3-propanediyl)tricarbonylruthenium (the above Chemical Formula 3) was used to form a ruthenium thin film.

[0079] The film forming conditions for the first film forming step and the second film forming step in the present embodiment are set as follows.

[0080] First film formation process conditions (i) Raw material gas introduction step · Raw material heating temperature: 10°C · Substrate temperature: 120°C · Introduction time: 1 second (ii) Raw material gas purge step · Purge gas: nitrogen (100 sccm) · Introduction time: 10 seconds (iii) Reaction gas introduction step · Reaction gas: H2O (water vapor) · Introduction time: 1 second (iv) Reaction gas purge step · Purge gas: nitrogen (100 sccm) · Introduction time: 30 seconds

[0081] Second film formation process conditions (i) Raw material gas introduction step · Raw material heating temperature: 10°C · Substrate temperature: 220°C · Carrier gas: nitrogen (50 sccm) · Introduction time: 10 seconds (ii) Raw material gas purge step · Purge gas: nitrogen (100 sccm) · Introduction time: 10 seconds (iii) Reaction gas introduction step · Reaction gas: oxygen (50 sccm) · Introduction time: 10 seconds (iv) Reaction gas purge step · Purge gas: nitrogen (100 sccm) · Introduction time: 10 seconds

[0082] In this embodiment, a barrier layer was created with a ruthenium thin film thickness of 4 nm and ZnO thin films of 1 nm (Example 1) and 2 nm (Example 2), as well as a barrier layer consisting only of a 5 nm ruthenium thin film without a ZnO film (Comparative Example). The thickness of these thin films was controlled by adjusting the number of cycles. Then, copper was deposited on the surface of the barrier layers of Examples 1 and 2 and the Comparative Example by sputtering (thickness 60 nm) to create samples of layered structures for various evaluations.

[0083] [Confirmation of the diffusion-inhibiting effect of the barrier layer (XRD analysis)] High-temperature heat treatment tests were performed on each sample from Example 1 (Cu / Ru(4nm) / ZnO(1nm) / Si), Example 2 (Cu / Ru(4nm) / ZnO(2nm) / Si), and Comparative Example (Cu / Ru(5nm) / Si) to confirm the effect of the barrier layer in suppressing the diffusion of copper into the substrate (Si). In this evaluation test, each sample was heated in a vacuum at 500°C, 550°C, 650°C, 700°C, and 800°C, and then XRD analysis was performed. If diffusion of copper into the substrate occurs, a peak of copper silicide (Cu3Si) will appear in the XRD spectrum, so it was determined that diffusion of copper into the substrate had occurred when the copper silicide peak appeared. The test results for each sample from Examples 1, 2, and the Comparative Example are shown in Figures 2 to 4.

[0084] As seen from the comparative example (Cu / Ru(5nm) / Si) in Figure 4, the barrier layer composed solely of a ruthenium thin film exhibits a diffusion suppression effect when heated at 500°C. However, the presence of a copper silicide peak at 550°C indicates that the diffusion suppression effect decreased at 550°C. In contrast, referring to Figures 2 and 3, no copper silicide peaks were observed in Example 1 (Cu / Ru(4nm) / ZnO(1nm) / Si) and Example 2 (Cu / Ru(4nm) / ZnO(2nm) / Si) even when heated at 550°C. This confirms that combining a ZnO thin film with a ruthenium thin film improved the copper diffusion suppression effect. Furthermore, the appearance of copper silicide occurred at 650°C in Example 1 (ZnO film thickness 1nm), but at 800°C in Example 2 (ZnO film thickness 2nm). This indicates that the improvement in the diffusion suppression effect of the barrier layer by adding a ZnO thin film to a ruthenium thin film increases with increasing thickness of the ZnO thin film.

[0085] [Confirmation of the diffusion-inhibiting effect of the barrier layer (resistance measurement)] In the high-temperature heat treatment tests described above, the resistivity (sheet resistivity) of the laminated structure after heat treatment was measured at each temperature. Resistivity was measured using the four-probe method. The results of this measurement are shown in Figure 5. As shown in Figure 5, in the comparative example (Cu / Ru(5nm) / Si) where copper diffusion into the substrate occurred at 550°C, an increase in resistance was confirmed above 550°C. On the other hand, in Example 1 (Cu / Ru(4nm) / ZnO(1nm) / Si), no increase in resistance was observed up to 600°C, and in Example 2 (Cu / Ru(4nm) / ZnO(2nm) / Si), no increase in resistance was observed up to 700°C, which was consistent with the XRD results described above. While ruthenium thin films, acting as a barrier layer, effectively suppress copper diffusion at temperatures up to approximately 500°C, their effectiveness diminishes at higher temperatures. Adding a ZnO thin film as a substrate to the ruthenium film enhances its diffusion-suppressing effect as a barrier layer. This effect of the ZnO thin film is effective even at extremely thin thicknesses of 1 nm.

[0086] [Evaluation of barrier layer adhesion] Next, the adhesion of the barrier layer was evaluated for Example 1 (Cu / Ru(4nm) / ZnO(1nm) / Si) and Comparative Example (Cu / Ru(5nm) / Si). The adhesion evaluation was performed using DCB (Double). This method is based on the measurement of interfacial adhesion energy using the Cantilever Beam (DCB) test. In the DCB test, a test specimen was prepared by bonding a Si wafer of the same dimensions as the substrate to the copper layer of each sample using an epoxy adhesive. Tensile loads were then applied to the edges of both the front and back surfaces of the test specimen, and the interfacial adhesion energy was calculated from the relationship between the load and the displacement of the crack opening.

[0087] The results of the adhesion evaluation test described above are shown in Figure 6. From Figure 6, it can be seen that the barrier layer of Example 1, consisting of a ruthenium thin film and a ZnO thin film, showed an extremely high interfacial adhesion energy compared to the barrier layer of the comparative example without a ZnO thin film, confirming that the barrier layer of the present invention also has good adhesion to the substrate.

[0088] Second Embodiment In this embodiment, the feasibility of selective formation of the barrier layer according to the present invention by applying an inhibitor was investigated. Here, a Si wafer (dimensions 4cm × 4cm) having an SiO2 insulating layer (100nm) was prepared as the substrate, and a Cu film was deposited near the center of this substrate by sputtering to form a non-deposited region (2cm × 2cm). Then, dodecanethiol (DDT) was used as the inhibitor, and a barrier layer consisting of a ZnO thin film and a ruthenium thin film was formed in the SiO2 region of the substrate.

[0089] [Preliminary consideration] Prior to forming the barrier layer, a preliminary study was conducted to investigate the adsorption characteristics of the inhibitor to the film-forming region (SiO2 region) and non-film-forming region (Cu region) of the substrate, as well as the feasibility of forming a ZnO thin film.

[0090] First, the relationship between the amount of DDT supplied and the WCA value on the substrate surface was confirmed. DDT, which had been heated to 85°C and gasified, was supplied at predetermined pulse times (Y seconds). After stopping the supply, the substrate was purged with nitrogen gas for 120 seconds after 80 seconds. The DDT supply pulse times Y were 10 seconds, 15 seconds, 30 seconds, 60 seconds, and 90 seconds. After supplying DDT at each pulse time and purging the substrate, the WCA value was measured by collecting the substrate and measuring the water contact angle on the substrate surface.

[0091] Figure 7 shows the measurement results of the WCA value in each region of the substrate after supplying DDT under the above conditions. From Figure 7, the WCA value in the SiO2 region of the substrate has hardly changed. From this, it can be seen that DDT is not adsorbed on SiO2. On the other hand, in the Cu region, the WCA value increases with increasing time (supply amount) between pulse times of 0 seconds and 15 seconds, and there is almost no change in the WCA value after 15 seconds. From this, it can be seen that in the Cu region of the substrate, the amount of adsorbed DDT increases with the supply amount, but the amount of adsorbed DDT saturates after a predetermined time (15 seconds in this embodiment).

[0092] Next, while fixing the DDT supply pulse time to 15 seconds, we observed the change in the WCA value when the substrate temperature was varied. The results of this test are shown in Figure 8. From Figure 8, it can be seen that there was no change in the WCA value in the SiO2 region of the substrate, indicating that adsorption does not occur even when the substrate is heated. In the Cu region, the WCA value increased with increasing substrate temperature up to around 120°C, indicating an increase in adsorption. The WCA value decreased above 180°C, which is presumed to be due to the decomposition of DDT. From these two test results, it was confirmed that DDT adsorbs to Cu but not to SiO2, and that it is possible to control and optimize the amount of DDT adsorbed to Cu.

[0093] Therefore, in the above test, the preferred conditions for the DDT adsorption process in this embodiment were set to a pulse time of 15 seconds and a substrate temperature of 120°C. After adsorbing DDT onto the substrate under these conditions, a ZnO thin film was formed, and the feasibility of forming the ZnO thin film in each region was confirmed. The film formation conditions for the ZnO thin film were the same as in the first embodiment, and film formation was performed by changing the number of ALD cycles.

[0094] After depositing a ZnO thin film at each cycle count, the Zn concentration on the surface of each region of the substrate was analyzed by XPS. The results are shown in Figure 9. In the SiO2 region of the substrate, a constant Zn concentration was measured from cycle 40 onwards, while in the Cu region, Zn was not detected even as the number of cycles increased. This indicates that the ZnO thin film was formed only in the SiO2 region of the substrate.

[0095] Figure 10 shows the change in film thickness with the number of cycles for a ZnO thin film formed in the SiO2 region of the substrate. Figure 10 also shows the results when a ZnO thin film was similarly deposited on a substrate (SiO2) that had no prior exposure history to an inhibitor (dodecanethiol). From Figure 10, it can be seen that even in a substrate where DDT is partially adsorbed in this embodiment, the film thickness in the SiO2 region increases with increasing cycle count, and there is no difference in film deposition efficiency. In other words, the adsorption treatment with DDT does not affect the region where the barrier layer is formed.

[0096] [Confirmation of the possibility of selective formation of a barrier layer] Based on the results of the preliminary studies described above, it was confirmed that selective formation of the barrier layer is possible in this embodiment. The same substrate as in the preliminary studies was prepared, and DDT was adsorbed in an adsorption process (pulse time 15 seconds, substrate temperature 120°C). A ZnO film was deposited on top of it, and the substrate after the ZnO film deposition process was heated and plasma treated to decompose and remove the DDT. DDT removal was performed by heating the substrate to 150°C and exposing it to hydrogen plasma (hydrogen flow rate 30 sccm, RF output 100W) for 5 minutes.

[0097] Deposition of a ruthenium thin film on a ZnO thin film is performed using a precursor (η 4 (-methylene-1,3-propanediyl)tricarbonylruthenium (as shown in Formula 3 above) was used, and the same conditions as in the first embodiment were applied.

[0098] Figure 11 is a graph showing the thickness of the ruthenium thin film when the number of cycles for ruthenium thin film deposition is set from 50 to 200 cycles. As shown in Figure 11, the thickness of the ruthenium thin film increases linearly with increasing cycle count. As shown in the preliminary study above, due to the action of the inhibitor DDT, the ZnO thin film is deposited only in the SiO2 region of the substrate, and therefore, in this embodiment, a two-layer barrier layer is formed only in that SiO2 region. Accordingly, it has been confirmed that the barrier layer according to the present invention can be selectively formed in the deposition region (insulating material) by applying an inhibitor. [Industrial applicability]

[0099] As described above, the two-layer barrier layer according to the present invention can exhibit an effective diffusion suppression effect while also supporting selective film formation. The barrier layer of the present invention can contribute to suppressing the increase in wiring resistance while accommodating the miniaturization and finer pitch of metal wiring on wiring substrates. The present invention is suitable for application to wiring in various semiconductor devices, and in particular, can accommodate the miniaturization of wiring in ultra-miniature semiconductor devices.

Claims

1. In a barrier layer formed on the substrate surface as an underlayment for metal wiring, A first thin film made of a Zn metal oxide is formed on the substrate, A barrier layer comprising a second thin film made of Ru, formed on the first thin film.

2. The barrier layer according to claim 1, wherein the thickness of the first thin film is 0.5 nm or more and 3 nm or less.

3. In a wiring substrate in which a barrier layer and metal wiring are formed on at least a portion of the substrate, A wiring substrate having the barrier layer described in claim 1 or claim 2 formed as the barrier layer, and the metal wiring formed on the barrier layer.

4. The wiring board according to claim 3, wherein the surface of the portion of the substrate where the barrier layer is formed is made of an insulating material.

5. A method for forming a barrier layer according to claim 1 or claim 2, A first film formation step involves forming a first thin film on a substrate by chemical vapor deposition using a Zn metal compound as a precursor, A method for forming a barrier layer, comprising a second film formation step of forming a second thin film on the first thin film by chemical vapor deposition using a metal compound of Ru as a precursor.

6. The substrate has a film-forming region where a barrier layer is formed and a non-film-forming region where a barrier layer is not formed. The process includes adsorbing an inhibitor that inhibits the formation of a first thin film onto the surface of the non-film-forming region of the substrate, The method for forming a barrier layer according to claim 5, wherein after adsorbing the inhibitor, the barrier layer is selectively formed in the film-forming region by performing a first film-forming step and a second film-forming step.

7. A method for forming a barrier layer according to claim 6, comprising a removal step of removing inhibitors on a non-film-forming region after the first film-forming step, and a second film-forming step performed after the removal step.

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