Method for manufacturing crystallized laminated structure

Abstract

To provide a manufacturing method for a crystallized laminated structure, the method having excellent manufacturing efficiency.SOLUTION: A manufacturing method for a crystallized laminated structure is provided, including: a laminated structure forming step which is implemented at temperatures below 100°C, including room temperature, and in which a laminated structure 7 is formed on an orientation control layer 4 imparting a crystal axis to an Sb2Te3 layer 5 having a thickness of 2 nm to 10 nm and a GeTe layer 6 upon the crystallization having a thickness of more than 0 nm and not more than 4 nm, the crystal axis being common to both of the layers, wherein in the laminated structure 7, the Sb2Te3 layer 5 and the GeTe layer 6 are laminated, and the GeTe layer 6 includes tiny amount of additive elements (S, Se) at a content of 0.05 at% to 10.0 at%; an Sb2Te3 layer crystallization step of heating and holding the laminated structure 7 to and at a first crystallization temperature of 100°C or more and less than 170°C to crystallize the Sb2Te3 layer 5; and a GeTe layer crystallization step of crystallizing the GeTe layer 6 by heating and holding the laminated structure 7 in which the Sb2Te3 layer 5 is crystallized to and at a second crystallization temperature of 170°C or more and 400°C or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for efficiently producing a crystallized laminated structure in which an Sb2Te3 compound layer and a GeTe compound layer are stacked and crystallized. [Background technology]

[0002] A superlattice phase change memory is known that is capable of memory operation by a superlattice formed by crystallizing a stacked structure of an Sb2Te3 compound layer and a GeTe compound layer (see Patent Documents 1 and 2).

[0003] The laminated structure is generally formed using a vacuum film-forming apparatus. Typically, it is formed using a sputtering apparatus. For example, a compound plate having a composition of Sb2Te3 and a compound plate having a composition of Ge1Te1 are used as targets, and argon gas is used to generate plasma on the targets. Argon ions are collided with the surface of the targets to eject target atoms, and a deposition layer of the scattered target atoms is formed on a substrate placed on a counter electrode opposite the targets. At this time, if the temperature of the substrate is low, the deposited layer will be in an amorphous state, so in order to crystallize the laminated structure, the substrate is first heated to the higher of the inherent crystallization temperatures of the GeTe compound and the SbTe compound, and then sputtering is performed while maintaining this temperature. Typically, the crystallization temperature of the GeTe compound is 230°C, and the crystallization temperature of the SbTe compound is around 70°C. Therefore, an SbTe compound layer and a GeTe compound layer are stacked on the substrate heated to the higher temperature of 230°C, and a superlattice structure in which these compound layers are crystallized is obtained. Therefore, the heating conditions for the substrate are mostly set between 200° C. and 250° C., and it is difficult to obtain a good quality superlattice structure at temperatures other than this range.

[0004] It has also been reported that the laminated structure is prone to interface diffusion (interface mixing) at the interface between the Sb2Te3 compound layer and the GeTe compound layer, making it difficult to obtain a good interface (see Non-Patent Documents 1 and 2). At the interface, a GeSbTe compound layer different from the Sb2Te3 compound layer and the GeTe compound layer is formed, and crystallizes at a specific crystallization temperature. As expected, this crystallization temperature exists between the crystallization temperature of the Ge1Te1 compound and the crystallization temperature of the Sb2Te3 compound, and when the GeSbTe compound layer is formed with a composition of Ge2Sb2Te5, the crystallization temperature appears around 160°C. Furthermore, when the GeSbTe crystal layer is formed, X-ray patterns such as

[0200] and

[0220] that are not seen in the superlattice structure formed by the Sb2Te3 compound layer and the GeTe compound layer appear. Occasionally The peak is identified. The GeSbTe crystal layer is not involved in memory operation, and therefore causes the superlattice phase change memory to lose its function.

[0005] To address these problems, the inventors discovered that by forming the stacked structure by adding a small amount of a second chalcogen element (sulfur or selenium) to the target in addition to Te, the first chalcogen element that is the main component of the GeTe compound layer, a high-quality superlattice structure with suppressed interface diffusion (interface mixing) could be fabricated, thereby providing a functional solution for the superlattice phase-change memory (see Patent Document 3 and Non-Patent Document 3). Adding the chalcogen atoms to the GeTe compound layer suppresses the formation of the GeSbTe crystal layer. However, in actual manufacturing situations, the manufacturing conditions described above, in which the substrate is heated to 200° C. to 250° C. and then the laminated structure is formed, pose a significant burden, and further improvements are desired. That is, under these manufacturing conditions, the following steps are required for each superlattice phase-change memory. First, the substrate is placed in a sputtering device, heated to 200°C to 250°C, and then the constituent layers of the laminated structure are deposited in a crystalline state by sputtering while maintaining the temperature. Next, the heating of the substrate is stopped, and the substrate is allowed to cool to a temperature at which it can be safely removed. Then, the substrate on which the laminated structure has been formed is removed from the sputtering device. Therefore, the heating time required for raising the temperature of the low-temperature substrate to a high temperature of 200°C to 250°C, the waiting time until the temperature stabilizes at the desired heating temperature, and the cooling time required for safe removal, which occur each time an individual superlattice phase-change memory is manufactured, are longer than the time required to form the laminated structure, thereby becoming a manufacturing rate-limiting factor.This increases the manufacturing time when a large number of superlattice phase-change memories are manufactured continuously, hindering efficient manufacturing of the superlattice phase-change memories. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4635236 [Patent Document 2] Patent No. 6238495 [Patent Document 3] International Publication No. 2020 / 012916 [Non-patent literature]

[0007] [Non-Patent Document 1] R. Wang, V. Bragaglia, JE Boschker and R. Calarco, “Intermixing during Epitaxial Growth of van der Waals bonded Normal GeTe / Sb2Te3 Superlattices”, Cryst. Growth Des. 16, 3596-3601 (2016) [Non-patent document 2] A. Lotnyk, I. Hilmi, U. Ross and B. Rauschenbach, “Van Der Waals interfacial bonding and intermixing in GeTe- Sb2Te3- based superlattices”, Nano Res. 11, 1676-1686 (2018). [Non-patent document 3] J. Tominaga and H. Awano, “Intermixing suppression through the interface in GeTe / Sb2Te3 superlattice”, Appl. Phys. Express 13, 075503 (2020). Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to solve the above-mentioned problems in the prior art and to achieve the following object: That is, the present invention aims to provide a method for producing a crystallized layered structure with excellent production efficiency.

[0009] The present inventors have conducted extensive research to solve the above problems and have come to the following findings. The reason why the manufacturing time in the conventional method is long is that the film formation process of the laminated structure, in which each compound layer of the Sb2Te3 compound layer and the GeTe compound layer is heated to the temperature range and formed into a crystalline state while maintaining the temperature stably, and the cooling process of cooling the temperature to room temperature in order to remove the laminated structure, are consecutive processes performed within the same vacuum film formation apparatus, and the manufacturing sequence is such that the formation of the next crystallized laminated structure is not carried out until one crystallized laminated structure has been formed.

[0010] Now, if the manufacturing process of the crystallized laminated structure is separated into two processes, a film formation process in which only film formation is performed at a low temperature below the crystallization temperature, and a crystallization process in which only crystallization is performed at a high temperature above the crystallization temperature, and these processes are performed simultaneously in parallel using separate equipment, the manufacturing time can be significantly shortened. That is, after the first film formation process, the first crystallization process is carried out, but while the first crystallization process is being carried out, the second film formation process is carried out in a separate device, so the manufacturing time can be shortened simply by not having to wait for the completion of the first crystallization process. In addition, by separating the film formation process and the crystallization process, the crystallization process can be performed on a plurality of the laminate structures at once, i.e., the crystallization process becomes a batch process on a plurality of the laminate structures, and the manufacturing time per unit divided by the number of the target laminate structures is significantly shorter than the manufacturing time per unit when the film formation process and the crystallization process are performed consecutively.

[0011] However, when such a separation process is adopted, it is questionable whether a structure equivalent to the crystallized laminated structure manufactured by the conventional method can be obtained, because if not, the superlattice phase change memory finally manufactured will not have the required functions, and the manufacturing process itself will be meaningless. In this regard, the inventors have demonstrated that even when the separation process is adopted, a structure equivalent to the crystallized laminated structure produced by conventional methods can be obtained, and have also succeeded in elucidating the conditions for obtaining such a structure.

[0012] Specifically, (1) when the film formation process is carried out in a non-heated room temperature environment, even if the crystallization process is carried out by heating and holding only the higher of the crystallization temperatures specific to the GeTe compound layer and the crystallization temperature specific to the Sb2Te3 compound layer in accordance with the conventional method, a structure equivalent to the crystallized laminated structure produced by the conventional method cannot be obtained. However, when the crystallization process is carried out by heating and holding in two stages at the respective crystallization temperatures of the GeTe compound layer and the Sb2Te3 compound layer, a structure equivalent to the crystallized laminated structure produced by the conventional method can be obtained. The following findings were obtained: (1) the second chalcogen element added to the GeTe compound layer to suppress diffusion affects the crystallization temperature inherent to the GeTe compound layer, and a temperature range separate from the inherent crystallization temperature exists that is necessary to obtain a structure equivalent to the crystallized stacked structure manufactured by conventional methods; and (2) the GeTe compound layer has different crystallization temperatures in the single layer state and the stacked state, and a temperature range separate from the crystallization temperature inherent to the GeTe compound layer exists that is necessary to obtain a structure equivalent to the crystallized stacked structure manufactured by conventional methods. [Means for solving the problem]

[0013] The present invention is based on the above findings, and the means for solving the above problems are as follows: <1> S A laminated structure is formed on an orientation control layer that provides a common crystal axis to the Sb2Te3 layer and the GeTe layer during crystallization, the Sb2Te3 layer being mainly composed of b2Te3 and having a thickness of 2 nm to 10 nm, and the GeTe layer being mainly composed of GeTe and having a thickness of more than 0 nm but not more than 4 nm, and the GeTe layer contains a trace amount of at least one of S and Se added at a content of 0.05 at % to 10.0 at %. forming the laminated structure on the orientation control layer in an unheated state at room temperature;A method for manufacturing a crystallized laminated structure, comprising: a laminated structure forming step; an Sb2Te3 layer crystallization step of heating and holding the laminated structure at a first crystallization temperature of 100°C or higher but lower than 170°C to crystallize the Sb2Te3 layer; and a GeTe layer crystallization step of heating and holding the laminated structure with the Sb2Te3 layer crystallized at a second crystallization temperature of 170°C or higher but lower than 400°C to crystallize the GeTe layer. <2> The trace element is S. <1> A method for producing the crystallized laminated structure described in claim 1. <3> the laminated structure forming step is a step of forming a laminated structure by using either a GeTe underlayer having a thickness of 3 nm to 10 nm and mainly composed of GeTe or a SbTe3 underlayer having a thickness of 3 nm to 10 nm as an orientation control layer, and when the underlayer is the GeTe underlayer, laminating an Sb2Te3 layer and a GeTe layer in this order on the underlayer, or when the underlayer is the Sb2Te3 underlayer, laminating the GeTe layer and the Sb2Te3 layer in this order on the underlayer. <1> from <2> 2. The method for producing the crystallized laminated structure according to any one of claims 1 to 11. 。 < 4 The Sb2Te3 layer crystallization process and the GeTe layer crystallization process are performed on a plurality of stacked structures. <1> From < 3 1. A method for producing a crystallized laminated structure according to any one of claims 1 to 1. < 5 At least one of the Sb2Te3 layer crystallization step and the GeTe layer crystallization step is carried out in an air atmosphere. <1> From < 4 1. A method for producing a crystallized laminated structure according to any one of claims 1 to 1. < 6 The Sb2Te3 layer crystallization step is carried out as either a step of heating a portion of the laminated structure or a step of heating the entire laminated structure, and the GeTe layer crystallization step is a step of heating the laminated structure including a portion or the entire region of the laminated structure heated in the Sb2Te3 layer crystallization step. <1> From < 5 1. A method for producing a crystallized laminated structure according to any one of claims 1 to 1. < 7The method further includes an epitaxial growth layer forming step of forming an epitaxial growth layer on the stacked structure after the GeTe layer crystallization step. <1> From < 6 1. A method for producing a crystallized laminated structure according to any one of claims 1 to 1. [Effects of the Invention]

[0014] According to the present invention, it is possible to solve the above-mentioned problems in the prior art and to provide a method for producing a crystallized laminated structure with excellent production efficiency. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an explanatory diagram of a crystallized laminated structure manufactured by the present manufacturing method. [Figure 2] 10A and 10B are explanatory diagrams showing modified examples of the crystallized laminated structure; [Figure 3] FIG. 1 is a diagram showing the relationship between the substitution concentration of Te atoms substituted with S atoms in a GeTe layer (Ge(45)Te(55-x)S(x)) and the crystallization temperature. [Figure 4] 1 is a diagram showing the results of X-ray diffraction measurement of the crystalline layered structure according to Reference Example 1. FIG. [Figure 5] FIG. 10 is a diagram showing the results of X-ray diffraction measurements at the stage when the Sb2Te3 layer was crystallized in Example 1. [Figure 6] 1 is a diagram showing the results of X-ray diffraction measurement of the crystallized layered structure according to Example 1. FIG. [Figure 7] 1 is a diagram showing a cross-sectional observation image of the crystallized layered structure according to Example 1, taken with a high-resolution transmission electron microscope. [Figure 8] 10 is a diagram showing a cross-sectional observation image of the crystallized layered structure according to Example 2, taken with a high-resolution transmission electron microscope. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] (Method of manufacturing a crystallized laminated structure) The method for producing a crystallized laminated structure of the present invention includes a laminated structure forming step, an Sb2Te3 layer crystallizing step, and a GeTe layer crystallizing step, and may include other steps as necessary. An example of the method for producing the crystallized layered structure will now be described with reference to the drawings: Figure 1 is an explanatory diagram of the crystallized layered structure produced by this production method.

[0017] <Laminated structure formation process> The laminated structure forming step is carried out at a temperature below 100°C, including room temperature, and is a step of forming a laminated structure 7, in which an Sb2Te3 layer 5 and a GeTe layer 6 are laminated and a trace amount of an additive element is contained in the GeTe layer 6, on an orientation control layer 4 that imparts a common crystal axis to the Sb2Te3 layer 5 and the GeTe layer 6 during crystallization.

[0018] The Sb2Te3 layer 5 is formed as a layer containing Sb2Te3 as a main component and having a thickness of 2 nm to 10 nm. When the thickness is 2 nm to 10 nm, a c-axis oriented crystal structure is easily obtained during crystallization, and a crystal structure sharing a crystal axis with the GeTe layer 6 is easily obtained. The method for forming the Sb2Te3 layer 5 is not particularly limited, and examples thereof include known vacuum film formation methods such as sputtering, molecular beam epitaxy, ALD, and CVD. The material for forming the Sb2Te3 layer 5 is not particularly limited, and may be an SbTe compound material (for example, Sb 30 Te 70 As the SbTe compound material, a commercially available product (manufactured by Mitsubishi Materials Corporation) or a material prepared by a known method can be used.

[0019] The GeTe layer 6 is formed as a layer mainly composed of GeTe and having a thickness of more than 0 nm and not more than 4 nm. If the thickness exceeds 4 nm, it may exhibit independent, inherent characteristics, which may affect the characteristics of a superlattice phase-change memory when configured. In this specification, the term "main component" refers to a compound of atoms constituting the basic unit lattice of the layer, and also refers to a compound of atoms of the trace additive element (S, Se) and atoms constituting the basic unit lattice, when the layer contains the trace additive element (S, Se).

[0020] The GeTe layer 6 contains at least one of the trace additive elements S (sulfur) and Se (selenium). These elements are classified as chalcogen elements, like the element Te in the GeTe layer 6, and these atoms constitute the basic unit lattice by substituting for the Te atoms in the GeTe layer 6. The trace additive element is added for the purpose of suppressing the formation of a GeSbTe crystal layer at the interface between the Sb2Te3 layer 5 and the GeTe layer 6 due to substitution of Sb atoms for Ge atoms caused by interfacial diffusion (interfacial mixing). Of the trace additive elements, sulfur (S) is preferred from the viewpoint of effectively suppressing the formation of the GeSbTe crystal layer. The content of the trace additive element in each of the Sb2Te3 layer 5 and the GeTe layer 6 is 0.05 at% to 10.0 at%, and preferably 1.0 at% to 5.0 at%, from the viewpoint of obtaining a superlattice structure in which the formation of the GeSbTe crystal layer is suppressed. If the content of the trace additive element is too high, the phase change characteristics of the superlattice phase change memory are impaired, and if the content is too low, it is difficult to suppress the formation of the GeSbTe crystal layer.

[0021] The method for forming the GeTe layer 6 is not particularly limited, and examples thereof include known vacuum film-forming methods such as sputtering, molecular beam epitaxy, ALD, and CVD. The method for forming the GeTe layer 6 is not particularly limited, and may be a GeTe compound material (Ge 45 Te 55 Compound materials in which the trace additive elements are added to the above-mentioned SiO2, for example, Te(55-x) is replaced with S(x), can be used. Such compound materials can be commercially available (manufactured by Mitsubishi Materials Corporation) or those prepared by known methods.

[0022] The step of forming the laminated structure may involve laminating the Sb2Te3 layer 5 and the GeTe layer 6 one by one, or may involve laminating the Sb2Te3 layer 5 and the GeTe layer 6 alternately and repeatedly to form the laminated structure 7 as shown in FIG. 1. The number of layers when the Sb2Te3 layers 5 and the GeTe layers 6 are alternately and repeatedly stacked is not limited to the example shown in the figure (8 layers each, a total of 16 layers). From the viewpoint of realizing good memory operation in the superlattice phase change memory, the number of stacked layers is preferably about 10 to 50 layers, with each of the Sb2Te3 layer 5 and the GeTe layer 6 counted as one layer.

[0023] The laminated structure 7 is formed on an orientation control layer 4 that provides a common crystal axis to the Sb2Te3 layer 5 and the GeTe layer 6 during crystallization. When the stacked structure 7 is formed on the orientation control layer 4, the Sb2Te3 layer 5 and the GeTe layer 6 during crystallization are given a crystalline orientation in which they grow in an oriented manner sharing the (111) plane direction axis of the GeTe crystals, which have a cubic crystal structure, and the (0001) plane direction axis of the Sb2Te3 crystals, which have a hexagonal crystal structure, and a superlattice structure is given to the stacked structure 7 by the crystal layers of the Sb2Te3 layer 5 and the GeTe layer 6.

[0024] In the example of FIG. 1, the orientation control layer 4 is composed of a GeTe underlayer that contains GeTe as a main component and has a thickness of 3 nm to 10 nm. When the orientation control layer 4 is formed of the GeTe underlayer, an Sb2Te3 layer 5 and a GeTe layer 6 are laminated in this order on the GeTe underlayer. Lamination A structure 7 is formed. The GeTe underlayer can be formed by the same method as the GeTe layer 6, and from the viewpoint of suppressing interfacial diffusion (interfacial mixing) between the GeTe underlayer and the Sb2Te3 layer 5 on the GeTe underlayer, the trace additive element may be added thereto, as in the GeTe layer 6. The GeTe underlayer is crystallized together with the GeTe layer 6 during heating in the GeTe layer crystallization step, which will be described in detail later. The GeTe underlayer can be formed on any basic underlayer. When the GeTe underlayer is formed as a layer that does not contain the trace additive element, the GeTe compound material (Ge 45 Te 55 ) can be used.

[0025] Alternatively, the orientation control layer 4 may be formed of an Sb2Te3 underlayer containing Sb2Te3 as a main component and having a thickness of 3 nm to 10 nm. In this case, as shown in Fig. 2, a GeTe layer 6 and an Sb2Te3 layer 5 are laminated in this order on the orientation control layer 4 serving as the Sb2Te3 underlayer to form a layered structure 7'. Other than this, the layered structure 7 is the same as the layered structure 7. Note that Fig. 2 is an explanatory diagram showing a modified example of the crystallized layered structure. The Sb2Te3 underlayer can be formed by the same method as the Sb2Te3 layer 5, except for the thickness. stratification It is crystallized together with the Sb2Te3 layer 5 during heating in the crystallization step. Furthermore, when the Sb2Te3 underlayer is formed on a known Si (silicon) substrate, a Si layer formed from a Si film, or an electrode layer formed from W (tungsten) or TiN, it is easy to give a common crystal axis to the Sb2Te3 layer 5 and the GeTe layer 6 during crystallization. 1 and 2, reference numeral 2 denotes a substrate, and reference numeral 3 denotes a base layer.

[0026] When the orientation control layer 4 is formed using the GeTe underlayer and the Sb2Te3 underlayer, these underlayers can be formed in the same manner as the Sb2Te3 layer 5 and the GeTe layer 6, as described above, and therefore the manufacturing process is simplified. Furthermore, in the conventional method for manufacturing the laminated structure by thermal deposition, it is known that the Sb2Te3 underlayer is used as an orientation control layer. However, in the present invention, which involves heating at two crystallization temperatures, in addition to the Sb2Te3 underlayer, it is also possible to grow oriented crystal layers of the Sb2Te3 layer 5 and the GeTe layer 6 using the GeTe underlayer as a template, as will be shown in the Examples section below, thereby increasing the freedom of material selection. Furthermore, when the orientation control layer 4 is formed using the GeTe underlayer, a base underlayer 3 formed of any material can be used, in addition to a Si layer formed from a known Si (silicon) substrate or Si film, or an electrode layer formed from W (tungsten) or TiN. This is because each Sb2Te3 layer 5 formed on the GeTe underlayer and crystallized in the Sb2Te3 layer crystallization process (first-stage crystallization process) acts as an orientation film not only for the GeTe layer 6 adjacent above each Sb2Te3 layer 5 but also for the GeTe layer 6 adjacent below each Sb2Te3 layer 5 during the GeTe layer crystallization process (second-stage crystallization process). Therefore, the base underlayer 3 when the orientation control layer 4 is formed using the GeTe underlayer is not particularly limited and can be selected according to the purpose, and may be a heat-resistant plastic film formed from polyimide or the like. In addition, the GeTe underlayer may be formed directly on the substrate 2 (a known heat-resistant substrate) without forming the basic underlayer 3.

[0027] The orientation control layer 4 may be configured as a layer other than the GeTe underlayer and the Sb2Te3 underlayer, and can be appropriately selected from known configurations. Examples of such a configuration include an orientation control layer configuration formed from any of germanium, silicon, tungsten, germanium-silicon, germanium-tungsten, and silicon-tungsten, as disclosed in International Publication No. 2015 / 174240.

[0028] The laminated structure forming step is carried out at a temperature below 100°C including room temperature. Specifically, referring to FIG. 1 again, the laminated structure 7 is formed under the condition that the temperature condition of the orientation control layer 4 (the temperature of the laminated structure 7 is set by the temperature of the substrate 2 through the base underlayer 3 and the orientation control layer 4) is below 100°C. The temperature condition below 100°C is a temperature condition that is distinguished from the first crystallization temperature in the Sb2Te3 crystallization step described in detail later. Actually, in order to reduce the temperature rising time and cooling time when the next film forming process is carried out using the same vacuum film forming apparatus after the first film forming process, it is preferably 50°C or lower. In particular, when the laminated structure 7 is formed on the orientation control layer 4 in a non-heated state at room temperature, there is no time required for the temperature rising and cooling of the orientation control layer 4, and the manufacturing time is significantly shortened. Regarding the temperature condition, although it does not make sense to cool the orientation control layer 4 to a temperature below room temperature to carry out the laminated structure forming step, the lower limit temperature for carrying out the laminated structure forming step is about -50°C. Also, the temperature management in the laminated structure forming step is carried out, for example, by heating the substrate for the base substrate for forming the laminated structure 7 including the orientation control layer 4.

[0029] <Sb2Te3 layer crystallization step> The Sb2Te3 layer crystallization step is a step of heating and holding the laminated structure 7 at the first crystallization temperature to crystallize the Sb2Te3 layer 5. The Sb2Te3 layer crystallization step may be carried out in a vacuum atmosphere or in an air atmosphere. In particular, when carried out in an air atmosphere, the manufacturing process is significantly simplified. Also, the Sb2Te3 layer crystallization step may be a step of heating a part of the laminated structure 7 or a step of heating the whole of the laminated structure 7. As an example of heating a part of the laminated structure 7, after forming the layers of the laminated structure 7 over a large area, an example of heating only the part necessary for fabricating the structure of the superlattice type phase change memory can be cited. The heating means is not particularly limited, and can be appropriately selected from known heating means depending on the embodiment of the Sb2Te3 layer crystallization step. For example, when the heating is performed in a vacuum atmosphere, a vacuum vessel equipped with a heating unit may be used, when the heating is performed in an air atmosphere, a hot plate, a heating furnace, etc. may be used, and when partial heating is performed, partial heating means may be used, such as a nichrome wire heater, a lamp heating device, a laser heating device, etc. In particular, when a focused laser beam or the like is used, the superlattice phase change memory can be fabricated at a desired position. The holding time for heating and holding may be 10 minutes or more, but since a longer holding time reduces production efficiency, the upper limit is about 2 hours.

[0030] The first crystallization temperature is set to a temperature of 100°C or higher and lower than 170°C. The crystallization temperature of the Sb2Te3 layer 5 when it is a single layer, i.e., the intrinsic crystallization temperature of Sb2Te3, is confirmed to be around 78°C. However, heating at temperatures very close to this crystallization temperature takes a long time to achieve uniform crystallization, making it impractical. This is because even if the stacked atoms receive this heating energy and form covalent bonds with neighboring atoms to form crystal nuclei, additional energy is required for crystal growth around these nuclei. In other words, even if atoms form covalent bonds, unless lattice matching can be achieved at the interfaces between the microcrystals during the crystal growth stage (the positions of the atoms are rearranged and bonded at both interfaces), large, uniform crystals cannot be formed, and additional energy is required for this lattice matching. Therefore, the lower limit of the first crystallization temperature is set to 100° C., which is several tens of degrees higher than the intrinsic crystallization temperature of the Sb2Te3 layer 5. In particular, it is preferably 120° C. or higher in order to obtain a good homogeneous film. On the one hand, the upper limit of the first crystallization temperature needs to be a temperature that does not exceed the crystallization temperature of the GeSbTe compound layer in which GeTe and Sb2Te3 are mixed. If this temperature is exceeded, the Sb2Te3 layer 5 and the GeTe layer 6 will crystallize independently of each other, and each layer will crystallize without sharing the crystal axis, so that a good superlattice structure cannot be obtained. Furthermore, GeTe fine crystal grains tend to incorporate Sb2Te3 fine crystal grains, and a GeSbTe crystal layer is likely to occur. Therefore, the upper limit of the first crystallization temperature is less than 170 °C, and in particular, it is preferably 150 °C or lower from the viewpoint of obtaining a good homogeneous film.

[0031] <GeTe layer crystallization process> The GeTe layer crystallization process is a process of heating and holding the laminated structure 7 in which the Sb2Te3 layer 5 is crystallized at a second crystallization temperature of 170 °C or higher and 400 °C or lower to crystallize the GeTe layer 6. As the GeTe layer crystallization process, similar to the Sb2Te3 layer crystallization process, it may be carried out in a vacuum atmosphere or in an air atmosphere. In particular, when carried out in an air atmosphere, the manufacturing process is significantly simplified. Also, as the GeTe layer crystallization process, similar to the Sb2Te3 layer crystallization process, it may be a process of heating a part of the laminated structure 7 or a process of heating the entire laminated structure 7. When heating a part of the laminated structure 7, the laminated structure 7 is heated including a part or the whole of the region of the laminated structure 7 heated in the Sb2Te3 layer crystallization process. There is no particular limitation on the heating means, and the matters described for the Sb2Te3 layer crystallization process can be applied. The holding time in the heat holding may also be 10 minutes or more, similar to the Sb2Te3 layer crystallization process. Since the manufacturing efficiency decreases when the holding time is prolonged, the upper limit is about 2 hours.

[0032] The second crystallization temperature is set to a temperature of 170 °C or higher and 400 °C or lower. The present invention is based on the finding that the first crystallization temperature for crystallizing the Sb2Te3 layer 5 and the second crystallization temperature for crystallizing the GeTe layer 6 are in temperature ranges that do not overlap. If these temperatures were the same, the Sb2Te3 layer 5 and the GeTe layer 6 would crystallize independently of each other, and each layer would crystallize without sharing a crystal axis, preventing a good superlattice structure from being obtained. The crystallization temperature of the GeTe layer 6 when it is a single layer without the trace additive elements (S, Se), i.e., the intrinsic crystallization temperature of GeTe, is around 230°C. However, when the GeTe layer 6 is formed as a thin layer with a thickness of more than 0 nm but less than 4 nm, it is unable to form crystal nuclei by itself and crystals grow using the (0001) interface of the crystallized Sb2Te3 layer 5. This eliminates the need for thermal energy to form the crystal nuclei, resulting in a lower crystallization temperature than the intrinsic temperature. Furthermore, during the Sb2Te3 layer crystallization process in the previous step, the volume of the Sb2Te3 layer 5 shrinks as it crystallizes, generating large compressive stress in the amorphous GeTe layer 6 at this stage. This compressive stress also lowers the crystallization temperature of the GeTe layer 6 below the intrinsic crystallization temperature. Furthermore, the contraction of the crystal lattice caused by the addition of the trace additive elements causes lattice mismatch, and the addition of the trace additive elements, even in trace amounts, significantly affects the crystallization temperature. When the Sb2Te3 layer 5 and the GeTe layer 6 share the (111) plane axis of the GeTe crystal and the (0001) plane axis of the Sb2Te3 crystal to form a superlattice structure, the respective lattice constants are 4.172 Å and 4.262 Å, with a mismatch of approximately 2%. As a result, the GeTe in the laminated state of the Sb2Te3 layer 5 and the GeTe layer 6 layer 6 In the case of the alloy without the trace additive elements, the crystallization temperature is confirmed to be around 160°C. On the other hand, as shown in Figure 3, when the GeTe layer 6 contains the trace additive elements (S atoms, Se atoms), the crystallization temperature of the GeTe layer 6 increases with an increase in the content of the trace additive elements. In particular, compared to the GeTe layer 6 in a single layer state, the crystallization temperature of the GeTe layer 6 in a stacked state of the Sb2Te3 layer 5 and the GeTe layer 6 is layer 6 The conductivity of the GeTe layer 6 is significantly increased by adding only a small amount of the additive element.(45) Te (55-x) S (x) 10 is a graph showing the relationship between the substitution concentration of Te atoms with S atoms in GeTe layer 6 and the crystallization temperature. The series indicated by the straight line "1" is for the GeTe layer 6 in a single layer state, and the series indicated by the dashed line "2" is for the GeTe layer 6 in a multilayer state. Therefore, taking into consideration the increase due to the trace additive elements, the lower limit of the second crystallization temperature is set to 170° C. In particular, from the viewpoint of obtaining a good homogeneous film, it is preferably 200° C. or higher. The upper limit of the second crystallization temperature is about 400° C., at which film oxidation does not occur. If the temperature is much higher than 400° C., the X-ray diffraction from the GeSbTe crystal layer may be increased. Occasionally Peaks are observed and a good superlattice structure cannot be obtained. of From the viewpoint of shortening the time, the upper limit of the second crystallization temperature is sufficient even if it is about 300°C. As a result of the above, the crystallized laminated structure 1 is formed by crystallizing the laminated structure 7 . The Sb2Te3 layer crystallization process and the GeTe layer crystallization process are preferably performed on a plurality of stacked structures 7. By adopting such a method, batch processing is performed on a plurality of stacked structures 7, and the manufacturing time can be shortened.

[0033] <Other processes> The other steps are not particularly limited, and examples thereof include a protective layer forming step and an epitaxial growth layer forming step.

[0034] The protective layer forming step is a step of forming a protective layer on the laminated structure 7. The protective layer is not particularly limited, and examples thereof include known protective layers formed during device fabrication. The layer designated by the reference numeral 8 in FIGS. 1 and 2 corresponds to the protective layer.

[0035] The epitaxial growth layer forming step is a step of forming an epitaxial growth layer on the stacked structure 7 after the GeTe layer crystallization step. In the method for producing the crystallized layered structure of the present invention, crystalline layers of the Sb2Te3 layer 5 and the GeTe layer 6 are formed with large crystal grains. Therefore, when the epitaxially grown layer is formed on the stacked structure 7, the epitaxially grown layer is likely to have large crystal grains. The structure of the epitaxially grown layer is not particularly limited, and may be a layer made of Sb2Te3 or GeTe, or may be a layer made of any other material. When the epitaxially grown layer is a layer made of Sb2Te3 or GeTe, it may be formed by thermal film formation in the conventional method to remove stacking faults in the stacked structure 7. In this case, the epitaxially grown layer formation step is performed consecutively after the GeTe layer crystallization step, thereby eliminating the temperature rise time required for substrate heating in thermal film formation. [Example]

[0036] (crystallization temperature of monolayer) A preliminary measurement was carried out to confirm the crystallization temperatures of the GeTe layer and the Sb2Te3 layer. First, as a target for forming the GeTe layer, Ge 45 Te 55 Ge in which some of the Te in the material is replaced by S 45 Te 52 S3 (containing 3 at%) target and Ge 45 Te 45 S 10 A target containing 10 at% S was prepared. In addition, a target with an adjusted composition, Sb, was prepared as the target for forming the Sb2Te3 layer. 30 Te 70 Target prepared. Next, sputtering was carried out at room temperature using a sputtering device (ULVAC, QAM) with these three targets. Ledo Amorphous single-layer Ge was deposited on a SiN thin film formed in a sample preparation unit dedicated to the ultrafast differential scanning calorimetry (Flash DSC) manufactured by 45 Te 52 S3 layer, Ge 45 Te45 S 10 The Sb2Te3 layer and the Sb2Te3 layer were each formed to a thickness of 50 nm under the conditions of a pressure of 0.5 Pa and an RF power of 20 W. Next, these Ge 45 Te 52 S3 layer, Ge 45 Te 45 S 10 The crystallization temperatures of the Sb2Te3 layer and the Sb2Te3 layer were measured using the differential thermal analyzer, with the temperature rise rate of the differential thermal analyzer set to 10°C / sec. The crystallization temperature measurement results for the single layer state are shown in Table 1 below.

[0037] [Table 1]

[0038] As shown in Table 1 above, it is confirmed that the crystallization temperature of the GeTe layer increases as the S content increases.

[0039] (Crystallization temperature of laminated structure: Samples A to C) A preliminary measurement was carried out to confirm the crystallization temperature in the stacked state of the GeTe layer and the Sb2Te3 layer. First, the Ge 45 Te 52 S3 target and the Sb 30 Te 70 The target was set in the sputtering device, and the Ge target was deposited to a thickness of 0.8 nm on the SiN thin film of the sample preparation unit at room temperature. 45 Te 52 The S3 layer and the Sb2Te3 layer having a thickness of 4.0 nm were alternately formed in this order eight times to obtain a stacked structure of Sample A having a total of 16 compound layers. The thickness was adjusted by adjusting the time and power of the sputtering. The sputtering was performed under a vacuum of 2×10 -4The sputtering was performed under the conditions of a 0.05 Pa pressure, an argon gas pressure of 0.5 Pa, and an RF power of 20 W applied to each target. The sputtering time, depending on the composition, was 15 to 25 seconds per 1 nm of thickness. This sputtering time was determined by measuring the thickness per time using a step gauge after film formation for a predetermined time using a Si substrate.

[0040] Next, the Ge 45 Te 52 Instead of the S3 target, the Ge 45 Te 45 S 10 The Ge was formed on the SiN thin film of the sample preparation unit in the same manner as in the method for forming the laminated structure of sample A, except that a target was used. 45 Te 45 S 10 A stacked structure of Sample B was obtained in which a total of 16 layers, including the Sb2Te3 layer and the Sb2Te3 layer, were formed.

[0041] Next, we investigated the S-doped Ge 45 Te 55 A target (Mitsubishi Materials Corporation, 2 inches) was prepared. 45 Te 52 Instead of the S3 target, the Ge 45 Te 55 The stacked structure of Sample C was obtained in the same manner as in Sample A, except that a target was used, in which a total of 16 layers of GeTe layers and Sb2Te3 layers were formed on the SiN thin film of the sample preparation unit.

[0042] For each of the laminated structures of Samples A to C, the above-mentioned indications were carried out in the same manner as in the case of the single layer. difference The crystallization temperature was measured using a thermal analyzer. The measurement results of the crystallization temperature in the laminated state are shown in Table 2 below.

[0043] [Table 2]

[0044] As shown in Table 2 above, in each of the laminate structures of Samples A and B, the first crystallization temperature was confirmed to be 72°C, and the second crystallization temperatures were confirmed to be 218°C and 232°C. On the other hand, in the laminated structure of Sample C, a crystallization temperature was also confirmed near 160° C. That is, the first crystallization temperature was confirmed near 72° C., and then the second crystallization temperature was confirmed in the temperature range of 162° C. or higher. This is believed to be because Sb atoms are replaced with Ge atoms due to interface diffusion (interface mixing), and the GeSbTe crystal layer is formed at the interface between the GeTe layer and the Sb2Te3 layer. From the above results, it is confirmed that each of the stacked structures of Samples A and B containing the trace additive elements has two crystallization temperatures corresponding to the GeTe layer and the Sb2Te3 layer, and that these layers are crystallized with a sufficient temperature difference between the two crystallization temperatures.

[0045] (Reference example 1) Next, a crystallized laminated structure according to Reference Example 1 was manufactured in accordance with the prior art (see Patent Document 3 (International Publication No. 2020 / 012916) and the like). Specifically, it was manufactured by the following manufacturing method.

[0046] First, a 200 μm sapphire substrate (manufactured by Shinkosha) was placed in the sputtering device, and the vacuum back pressure was adjusted to 1.0×10 -4 Sputtering was performed using a silicon material (B-doped Si, manufactured by Mitsubishi Materials Corporation) as a target under conditions of a deposition gas pressure of 0.5 Pa and Ar, a temperature of 25°C, and an RF power of 100 W, to form an amorphous silicon layer with a thickness of 50 nm on the sapphire substrate as an underlayer.

[0047] Next, while maintaining the vacuum back pressure, sputtering was performed using the Sb2Te3 target under the conditions of an argon gas pressure of 0.5 Pa, a temperature of 25°C, and an RF power of 20 W to form the Sb2Te3 underlayer on the amorphous silicon layer to a thickness of 4.0 nm. After formation, the sapphire substrate was heated at 210°C to crystallize the Sb2Te3 underlayer.

[0048] Next, the vacuum back pressure and the Ar deposition gas pressure were maintained, the substrate heating temperature was kept at 210° C., and the RF power was set to 20 W. 45 Te 52 Sputtering was carried out using an S3 target to form the GeTe layer containing 3 at % S atoms on the Sb2Te3 underlayer to a thickness of 0.8 nm, and the layer was crystallized. Next, under the same film-forming conditions as those for the Sb2Te3 underlayer, the Sb2Te3 layer was formed on the GeTe layer to a thickness of 4.0 nm and crystallized. Next, the GeTe layers and the Sb2Te3 layers were alternately and repeatedly stacked under the same conditions as the first layer, to form the crystallized stacked structure in which 16 layers in total were stacked, with 8 layers of the crystallized Sb2Te3 layers and 8 layers of the crystallized GeTe layers alternately stacked.

[0049] Finally, a tungsten (W) layer was formed as a protective layer to a thickness of 20 nm on the Sb2Te3 layer that constituted the uppermost layer of the crystallized layered structure using the sputtering apparatus.

[0050] Next, the crystallized layered structure according to Reference Example 1 thus produced was subjected to X-ray diffraction. Occasionally X-ray diffraction was performed using a horizontal sample multipurpose X-ray diffraction device (Rigaku Corporation). Occasionally The measurement results are shown in Figure 4. As shown in FIG. 4, in the crystallized layered structure of Reference Example 1, peaks of (006), (009), (0015), and (0018) can be confirmed, which confirm the formation of a superlattice structure by the layered structure of the crystallized GeTe layer and the Sb2Te3 layer. This confirms that the crystallized layered structure of Reference Example 1 has the superlattice structure in which the GeTe layer and the Sb2Te3 layer are grown on a common crystal axis, as has been reported previously.

[0051] Example 1 Next, the stacked structure formed by film formation at room temperature without heating the sapphire substrate at 210°C was heated and held at two crystallization temperatures after film formation to produce the crystallized stacked structure according to Example 1. Specifically, it was produced by the following manufacturing method.

[0052] First, using the sputtering apparatus, the amorphous silicon layer was formed on the sapphire substrate in the same manner as in Reference Example 1 to a thickness of 50 nm. Next, the Ge was deposited on the amorphous silicon layer under the same sputtering conditions as those used to form the stacked structures of Samples A to C at room temperature. 45 Te 52 The GeTe underlayer (containing 3 at % of S atoms) was formed to a thickness of 3.2 nm using an S3 target.

[0053] Next, the Sb was deposited on the GeTe underlayer under the same sputtering conditions as those for forming the stacked structures of Samples A to C at room temperature. 30 Te 70 The Sb2Te3 layer was formed with a thickness of 4.0 nm using the target. Next, the Ge was deposited on the Sb2Te3 layer under the same sputtering conditions as those used to form the stacked structures of Samples A to C at room temperature. 45 Te 52 The GeTe layer (containing 3 at % of S atoms) was formed to a thickness of 0.8 nm using an S3 target. Next, the Sb2Te3 layers and the GeTe layers were alternately and repeatedly stacked under the same conditions as the first layer, to form the stacked structure in which 8 Sb2Te3 layers and 8 GeTe layers were alternately stacked for a total of 16 layers (the stacked structure formation process). Furthermore, while maintaining the temperature at room temperature, a tungsten (W) layer was formed as the protective layer to a thickness of 20 nm on the GeTe layer that constituted the uppermost layer of the laminated structure using the sputtering apparatus.

[0054] Next, the sapphire substrate on which the laminated structure was formed was removed from the sputtering device, and then set in a vacuum chamber (an infrared lamp annealing device manufactured by ULVAC, Inc.) and heated to a vacuum of 1×10 -4 The Sb2Te3 layer was crystallized by heating and holding under the conditions of Pa, a heating temperature of 140°C, and a holding time of 0.5 hours (the Sb2Te3 layer crystallization step).

[0055] The sapphire substrate on which the Sb2Te3 layer has been crystallized is temporarily removed from the vacuum chamber, and the X-ray Occasionally X-rays by the device Occasionally The measurement results are shown in Figure 5. As shown in FIG. 5, crystal peaks corresponding to the (009) and (0018) planes of Sb2Te3 can be confirmed, which confirms the formation of the crystallized Sb2Te3 layer.

[0056] The sapphire substrate on which the laminated structure was formed was again set in the vacuum chamber, and this time, the vacuum was reduced to 1×10 -4 The GeTe layer was crystallized by heating and holding under the conditions of Pa, a heating temperature of 230° C., and a holding time of 0.5 hours (the GeTe layer crystallization step). In this manner, the crystallized layered structure according to Example 1 was manufactured.

[0057] Subsequently, the crystallized laminated structure according to Example 1 after cooling was subjected to the X-ray diffraction. Occasionally X-rays by the device Occasionally The measurement results are shown in Figure 6. As shown in FIG. 6, in addition to the crystal peaks corresponding to the (009) and (0018) planes of Sb2Te3, crystal peaks corresponding to the (006) and (0015) planes of GeTe can be confirmed, which confirms the formation of the crystallized GeTe layer. In addition, the X-ray diffraction pattern of the crystallized laminated structure according to Example 1 shown in FIG. Occasionally The measurement results are shown in FIG. 4, which is an X-ray diffraction pattern of the crystalline layered structure according to Reference Example 1. OccasionallyThe results are very similar to those of the measurements, and in both cases, the peaks of (006), (009), (0015), and (0018) are confirmed, but no other peaks are confirmed. This shows that the crystallized layered structure of Example 1 can form the superlattice structure in which the GeTe layer and the Sb2Te3 layer are crystal-grown along a common crystal axis, just like the crystallized layered structure of Reference Example 1 using the conventional method.

[0058] FIG. 7 shows a cross-sectional image of the crystallized layered structure according to Example 1 observed by a high-resolution transmission electron microscope (scanning transmission electron microscope, manufactured by JEOL Ltd.). As shown in FIG. 7, in the crystallized layered structure according to Example 1, the superlattice structure having uniform crystal orientation in which the atomic arrangements of the GeTe layer and the Sb2Te3 layer are aligned is obtained.

[0059] Example 2 The vacuum chamber was used to achieve a vacuum of 1×10 -4 Instead of heating and holding under the conditions of 1 Pa, a heating temperature of 140°C, and a holding time of 0.5 hours, a hot plate (Yamato Scientific Co., Ltd., hot plate) was used to heat and hold under the conditions of an air atmosphere, a heating temperature of 140°C, and a holding time of 0.5 hours (the Sb2Te3 layer crystallization step), and a vacuum of 1×10 using the vacuum container. -4 The crystallized laminated structure of Example 2 was manufactured in the same manner as Example 1, except that instead of performing heating and holding under the conditions of Pa, heating temperature 230°C, and holding time 0.5 hours, heating and holding was performed using the hot plate under the conditions of air atmosphere, heating temperature 230°C, and holding time 0.5 hours (the GeTe layer crystallization process).

[0060] Subsequently, the crystallized laminated structure according to Example 2 after cooling was subjected to the X-ray diffraction. Occasionally X-rays by the device Occasionally Measurements were taken. Surprisingly, almost the same measurement results as those shown in FIG. 6 were obtained, and it was found that the crystallized layered structure according to Example 2, which was crystallized under an air atmosphere, was also able to form the superlattice structure in which the GeTe layer and the Sb2Te3 layer were grown on a common crystal axis.

[0061] FIG. 8 shows a cross-sectional image of the crystallized layered structure according to Example 2 observed by the high-resolution transmission electron microscope. As shown in FIG. 8, in the crystalline layered structure according to Example 2, similar to the crystalline layered structure according to Example 1 (see FIG. 7), the superlattice structure having uniform crystal orientation in which the atomic arrangements of the GeTe layer and the Sb2Te3 layer are aligned is obtained. For this reason, the Sb2Te3 layer crystallization step and the GeTe layer crystallization step can be performed in an air atmosphere instead of in a vacuum atmosphere.

[0062] (Comparative Example 1) The crystallized laminated structure of Comparative Example 1 was manufactured in the same manner as in Example 1, except that the heating temperature in the Sb2Te3 layer crystallization process was changed from 140°C to 80°C and the heating temperature in the GeTe layer crystallization process was changed from 230°C to 220°C.

[0063] The crystallized laminated structure according to Comparative Example 1 was subjected to the X-ray diffraction Occasionally X-rays by the device Occasionally When the measurement was carried out, the peaks of (006), (009), (0015), and (0018) appeared, which confirmed the formation of the superlattice structure, but the height of each peak was about half that of each of the crystallized stacked structures of Examples 1 and 2. The heating temperature in the GeTe layer crystallization step was almost the same as in Example 1. From this result, it is inferred that the low heating temperature in the Sb2Te3 layer crystallization step prevented the Sb2Te3 layer from being sufficiently crystallized, and that the GeTe layer was crystallized on the Sb2Te3 layer in this state, resulting in the formation of the superlattice structure in a state where the crystal grains of both Sb2Te3 and GeTe were small.

[0064] (Comparative Example 2) The crystallized laminated structure of Comparative Example 2 was manufactured in the same manner as in Example 1, except that the heating temperature in the Sb2Te3 layer crystallization process was changed from 140°C to 180°C and the heating temperature in the GeTe layer crystallization process was changed from 230°C to 220°C.

[0065] The crystallized laminated structure according to Comparative Example 2 was subjected to the X-ray diffraction Occasionally X-rays by the device Occasionally When the measurement was carried out, the (006) and (009) peaks appeared, but the (220) peak seen in the GeSbTe crystal layer was also confirmed, confirming that the GeSbTe crystal layer not involved in the memory operation of the superlattice phase-change memory was formed in part. Since the heating temperature in the GeTe layer crystallization step was almost the same as in Example 1, it is inferred from this result that the high heating temperature in the SbTe layer crystallization step caused the SbTe layer and the GeTe layer to crystallize independently, and that these layers were crystallized without sharing a crystal axis. It is also inferred that as the crystallization of SbTe crystal grains and GeTe progresses at high temperatures, GeTe microcrystal grains incorporate SbTe microcrystal grains, forming the GeSbTe crystal layer.

[0066] (Comparative Example 3) A crystallized laminated structure according to Comparative Example 3 was manufactured in the same manner as in Example 1, except that the heating temperature in the GeTe layer crystallization step was changed from 230°C to 450°C.

[0067] The crystallized laminated structure according to Comparative Example 3 was subjected to the X-ray diffraction Occasionally X-rays by the device Occasionally When the measurement was carried out, a (009) peak appeared, but the (200) and (220) peaks observed in the GeSbTe crystal layer became larger, confirming that the GeSbTe crystal layer, which is not involved in the memory operation of the superlattice phase-change memory, had been formed in a large area. From this result, it is inferred that the crystallization of the GeTe was accelerated by high-temperature heating beyond its limit, at a rate exceeding the crystal growth rate that could utilize the orientation template of the Sb2Te3 layer, and that as a result, the GeTe layer incorporated Sb2Te3 into a part of it, destroying its orientation and causing crystal growth. [Explanation of symbols]

[0068] 1. Crystallized laminated structure 2 boards 3 Foundation layer 4 Orientation control layer 5 Sb2Te3 layer 6 GeTe layers 7. Laminated structure 8 Protective layer

Claims

1. Sb ２ Te ３ Sb ２ Te ３ A layer structure in which a GeTe layer having a thickness of more than 0 nm and 4 nm or less and a GeTe layer mainly composed of GeTe and containing at least one trace additive element of S and Se in a content of 0.05 at % to 10.0 at % is formed by crystallizing the Sb ２ Te ３ a step of forming the layered structure on an orientation control layer that imparts a common crystal axis to the GeTe layer and the GeTe layer, the step of forming the layered structure on the orientation control layer in an unheated state at room temperature; The laminated structure is heated and held at a first crystallization temperature of 100° C. or higher and lower than 170° C., and the Sb ２ Te ３ Sb crystallizes the layer ２ Te ３ a layer crystallization step; The Sb ２ Te ３ a GeTe layer crystallization step of heating and holding the stacked structure in which the layers have been crystallized at a second crystallization temperature of 170° C. or higher and 400° C. or lower to crystallize the GeTe layer; A method for producing a crystallized laminated structure, comprising:

2. 2. The method for producing a crystallized layered structure according to claim 1, wherein the trace additive element is S.

3. The laminated structure forming step includes forming a GeTe underlayer having a thickness of 3 nm to 10 nm and an Sb ２ Te ３ Sb ２ Te ３ When one of the underlayers is a GeTe underlayer, an Sb underlayer is formed on the underlayer. ２ Te ３ A layer and a GeTe layer are laminated in this order, and the underlayer is ２ Te ３ When the underlayer is formed, the GeTe layer and the Sb ２ Te ３ 3. The method for producing a crystallized laminated structure according to claim 1, wherein the layer is laminated in this order to form a laminated structure.

4. The method for producing a crystallized laminated structure according to claim 1, wherein the Sb 2 Te 3 layer crystallization step and the GeTe layer crystallization step are carried out on a plurality of laminated structures.

5. The method for producing a crystallized laminated structure according to claim 1, wherein at least one of the Sb 2 Te 3 layer crystallization step and the GeTe layer crystallization step is carried out in an air atmosphere.

6. A method for manufacturing a crystallized laminated structure described in any of claims 1 to 5, wherein the Sb 2 Te 3 layer crystallization process is carried out as either a process of heating a portion of the laminated structure or a process of heating the entire laminated structure, and the GeTe layer crystallization process is a process of heating the laminated structure including a portion or the entire region of the laminated structure heated in the Sb 2 Te 3 layer crystallization process.

7. A method for manufacturing a crystallized laminated structure described in any one of claims 1 to 6, further comprising an epitaxial growth layer formation step of forming an epitaxial growth layer on the laminated structure after the GeTe layer crystallization step.

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