Patent Application
20100032290
The present invention relates to a method for forming a chalcogenide film by means of sputtering, and in more detail, relates to a method for forming, by means of sputtering, a dense chalcogenide film with a stoichiometric composition that is suitably used for a recording layer of a highly integrated memory such as phase change memory capable of nonvolatile operation, and that has no defects such as gaps and cracks therein.
The present invention also relates to a method for manufacturing a recording element including the above method for forming a chalcogenide film, and in particular, to a method for manufacturing a resistance variable type recording element.
The present patent application claims priority based on Japanese Patent Application No. 2007-15059, filed Jan. 25, 2007, the contents of which are incorporated herein by reference.
In recent years, in mobile devices such as mobile telephones and mobile information terminals, there has been an increasing need for handling a large amount of information such as image data. Also in memory elements to be installed in these mobile devices there has been an increasing demand for a high speed, low power consumption, and small nonvolatile memory with a large capacity. In particular, a resistance variable type nonvolatile memory (resistance variable type recording element) which uses a chalcogen compound whose resistance changes depending on its crystal condition, has been drawing attention as a memory that is highly integrated and capable of nonvolatile operation (for example, refer to Patent Document 1).
This resistance variable type nonvolatile memory has a simple structure in which two electrodes sandwich a chalcogenide film that serves as a recording layer, and is capable of stably maintaining the recording state thereof even at room temperature. Therefore it is an excellent memory sufficiently capable of holding memory for more than ten years.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2004-348906
Incidentally, in a conventional resistance variable type nonvolatile memory, if the size of the elements is simply miniaturized in order to achieve high integration, the gap between adjacent elements becomes extremely narrow. Therefore, there has been a problem in that for example if, in order to cause a phase change in a recording layer of a single element, a predetermined electric voltage is applied to electrodes thereabove and therebelow, the heat emitted from the lower electrode may have a negative influence on the adjacent elements.
Consequently, there may be considered a structure where an insulating layer with a low thermal conductivity is formed on a substrate, and a hole with a small diameter is formed in this insulating layer and a chalcogen compound is embedded within this hole, to thereby separate the elements. However, in this structure, it is difficult to densely embed a chalcogen compound in the hole, and it is difficult to obtain a dense chalcogenide film.
Moreover, since the chalcogen compound contains volatile chalcogen elements, a part of the volatile chalcogen elements is volatilized during the film forming process, and the composition of the obtained chalcogenide film is deviated from its stoichiometric composition. Therefore it is difficult to form a chalcogenide film in a state in which its stoichiometric composition is maintained.
The present invention has been achieved in order to solve the above problems, with an object of providing a method for forming a chalcogenide film by means of sputtering, capable of forming a dense chalcogenide film with a stoichiometric composition, having no defects such as gaps and cracks therein.
A further object of the present invention is to provide a method for manufacturing a recording element by applying the above chalcogenide film forming method.
The present inventors earnestly investigated the method of forming a chalcogenide film by means of sputtering, and as a result, discovered that when forming a chalcogenide film within a contact hole in an insulating layer by means of sputtering, in a case where a target having a composition the same as that of the chalcogenide film is used and the diameter of this target is T (m) and the distance between this target and the substrate is L (m), if the ratio L/T of the distance with respect to the diameter of the target is not less than 0.5 and not more than 1.5, it is possible to form a dense chalcogenide film with a stoichiometric composition, having no defects such as gaps and cracks therein. Consequently, the present inventors have completed the present invention.
The present invention provides a method for forming a chalcogenide film within a contact hole formed in an insulating layer on a substrate, the method including: preparing a target having a composition the same as that of the chalcogenide film; setting a ratio L/T of a distance L with respect to a diameter T of the target to a value not less than 0.5 and not more than 1.5, where the diameter of the target is T (m) and the distance between the target and the substrate is L (m); and forming a chalcogenide film within the contact hole by a sputtering process in which a bias electric power is applied to the substrate and a sputtering electric power is applied to the target.
Furthermore, the present invention provides a method for manufacturing a recording element that includes a chalcogenide film, the method including: forming, on a substrate, an insulating layer having a contact hole with an enlarged diameter upper section; forming a first electrode within the contact hole; preparing a target having a composition the same as that of the chalcogenide film; setting a ratio L/T of a distance L with respect to a diameter T of the target to a value not less than 0.5 and not more than 1.5, where the diameter of the target is T (m) and the distance between the target and the substrate is L (m); forming, on the first electrode, a chalcogenide film that serves as a recording layer, by a sputtering process in which a bias electric power is applied to the substrate and a sputtering electric power is applied to the target; and forming a second electrode on the chalcogenide film.
In the above method for forming a chalcogenide film and the method for manufacturing a recording element, it is preferable that in a case where a surface area of the substrate is Ss (cm2), a bias electric power thereof is Ps (W), a surface area of the target is St (cm2), and a sputtering electric power thereof is Pt (W), a ratio Ds/Dt of a power density Ds of the substrate with respect to a power density Dt of the target satisfy the following expression (1):
Ds/Dt=(Ps×St)/(Pt×Ss)≦0.1 (1).
Preferably the power density Ds of the substrate and the power density Dt of the target are optimized to thereby densely fill in the contact hole with the chalcogenide film, while maintaining a stoichiometric composition thereof.
Preferably the chalcogenide film includes a chalcogen compound containing at least one element selected from the group consisting of S, Se, and Te.
Preferably the chalcogen compound contains: Te not less than 30% by weight and not more than 60% by weight; Ge not less than 10% by weight and not more than 70% by weight; Sb not less than 10% by weight and not more than 40%; and Se not less than 10% by weight and not more than 70%, and the total content ratio of these Te, Ge, Sb, and Se is not more than 100% by weight.
Preferably the first and second electrodes contain at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ru, Pt, and Ir.
According to the method of the present invention for forming a chalcogenide film by means of sputtering, in a case where the diameter of the target having a composition the same as that of the chalcogenide film is T (m) and the distance between this target and the substrate is L (m), the ratio L/T of the distance L with respect to the diameter T of the target is not less than 0.5 and not more than 1.5. Consequently, it is possible, in a state where the sputtering rate is maintained at an optimum condition, to form, within the contact hole in the insulating layer, a dense chalcogenide film with a stoichiometric composition, having no defects such as gaps and cracks therein.
Moreover, a bias electric power is applied to the substrate and a sputtering electric power is applied to the target. As a result it is possible to form a dense chalcogenide film in a state where the composition of the film containing volatile chalcogen elements maintains its stoichiometric composition.
According to the method of the present invention for manufacturing a recording element that includes the chalcogenide film as a recording layer, in a case where the diameter of the target having a composition the same as that of the chalcogenide film is T (m) and the distance between this target and the substrate is L (m), the ratio L/T of the distance L with respect to the diameter T of the target is not less than 0.5 and not more than 1.5. Consequently, it is possible, in a state where the sputtering rate is maintained at an optimum condition, to form, within the contact hole, a dense chalcogenide film with a stoichiometric composition, having no defects such as gaps and cracks therein.
Moreover, a bias electric power is applied to the substrate and a sputtering electric power is applied to the target. As a result it is possible to form a dense chalcogenide film in a state where the composition of the film containing volatile chalcogen elements maintains its stoichiometric composition.
Therefore, it is possible to provide a recording element in which the recording layer is formed with a dense chalcogenide film with a stoichiometric composition, having no defects such as gaps and cracks thereinside.
1: cooling stage with electrostatic chuck, 2: specimen, 3: target, 4: magnet, 5, 6: power supply, 11: silicon wafer, 12: insulating layer, 13: contact hole, 13a: enlarged diameter section, 14: tungsten, 15: titanium nitride (TiN), 16: lower electrode (first electrode), 17: chalcogenide film, 18: upper electrode (second electrode)
There is described a best mode for carrying out a method for forming a chalcogenide film by means of sputtering of the present invention.
This mode is to give a specific description for a better understanding of the intent of the invention, and should not be construed as limiting the present invention unless otherwise stated.
If the distance between this target 3 and the specimen 2 is L (m) and the diameter of this target 3 is T (m), the ratio L/T of this distance L and the diameter T of the target 3 is adjusted to be not less than 0.5 and not more than 1.5, preferably, not less than 0.7 and not more than 1.3.
For this target 3, a target material consisting of a chalcogen compound, which is a material having a composition the same as that of the chalcogenide film to be formed is suitable, and specific examples of this chalcogen compound include a chalcogen compound containing at least one element selected from a group consisting of S, Se, and Te. More specifically, examples of this include a chalcogen compound containing: Te not less than 30% by weight and not more than 60% by weight; Ge not less than 10% by weight and not more than 70% by weight; Sb not less than 10% by weight and not more than 40%; and Se not less than 10% by weight and not more than 70%, and the total content ratio of these Te, Ge, Sb, and Se is not more than 100% by weight.
Specific examples of this chalcogen compound include Ge2Sb2Te5, GeSb2Te5, and GeSe.
The specimen 2 may have a contact hole for forming the chalcogenide film, and for example, a silicon wafer (substrate) 11 shown in
This silicon wafer 11 is a wafer used in manufacturing a phase change type memory (resistance variable type recording element) with a chalcogenide film serving as a recording layer, in which, on an insulating layer 12 made of silicon oxide formed on a semiconductor circuit or the like (not shown in the drawing) of a silicon substrate, there is formed a contact hole 13 that reaches this semiconductor circuit, and an upper section of this contact hole 13 has an enlarged diameter and serves as an enlarged diameter section 13a. Within the contact hole 13 except for this enlarged diameter section 13a, there is formed a lower electrode (first electrode) 16 of the phase change type memory having a two-layer structure of tungsten (W) 14 and titanium nitride (TiN) 15.
This lower electrode 16, as with an upper electrode (second electrode) 18 formed on the chalcogenide film described later, may be electrically conductive, and in addition to the above composition, any one of a metal, an alloy metal, a metallic oxide, and a metallic nitride with an electrically conductive property containing at least one type of material selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ru, Pt, and Ir, may preferably be used.
Next, with use of the above sputtering apparatus, the chalcogenide film is formed within the enlarged diameter section 13a of the silicon wafer 11 shown in
In this film formation, in order to form a dense chalcogenide film in a state where the composition of the film containing volatile chalcogen elements maintains its stoichiometric composition, a bias electric power Ps (W) is applied to the specimen 2 with use of the power supply 5 and a sputtering electric power Pt (W) is applied to the target 3 with use of the power supply 6.
In order to optimize these bias electric power Ps (W) and sputtering electric power Pt (W), when the surface area of the specimen 2 is St (cm2), the bias electric power thereof is Ps (W), the surface area of the target 3 is St (cm2), and the sputtering electric power thereof is Pt (W), the ratio Ds/Dt of the power density Ds of the specimen 2 with respect to the power density Dt of the target 3 needs to satisfy the following expression (1):
Ds/Dt=(Ps×St)/(i Pt×Ss)≦0.1 (1).
By optimizing these bias electric power Ps (W) and sputtering electric power Pt (W), volatilization of volatile chalcogen elements is suppressed to a minimum. Therefore the composition of the chalcogenide film to be formed becomes the same as that of the target 3, while the stoichiometric composition of the chalcogenide film is maintained. Moreover, it becomes unlikely to have a gap or the like within the film, and therefore the density of the film is improved.
As a result, as shown in
Next, on this chalcogenide film 17 there is formed an upper electrode (second electrode) 18. This upper electrode 18, as with the lower electrode 16, may be electrically conductive, and for example, may be an electrode having a two-layer structure of tungsten (W) and titanium nitride (TiN), or preferably has a single layer structure or a lamination structure formed with any one of a metal, an alloy metal, a metallic oxide, and a metallic nitride with an electrically conductive property containing at least one type of material selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ru, Pt, and Ir.
Thereby, it is possible to manufacture a phase change type memory 19 with the chalcogenide film 17 serving as a recording layer.
Next, there are described results of an experiment carried out by the present inventors, regarding the method of forming a chalcogenide film by means of sputtering according to the present embodiment.
Referring to
Here, the composition of the chalcogenide film is Ge2Sb2Te5.
Referring to
According to these diagrams, it is understood that in the case where a bias electric power Ps (W) is applied to the specimen 2, a predetermined thickness is ensured for the chalcogenide film formed within the enlarged diameter section 13a, the surface thereof is flattened, and the quality of the film is excellent.
Moreover, it is understood that in the case where a bias electric power Ps (W) is not applied to the specimen 2, while a conically shaped protrusion is formed on the surface of the chalcogenide film formed within the enlarged diameter section 13a, a predetermined thickness is ensured, the surface thereof is flattened, and the quality of the film is excellent.
On the other hand, in the case of the conventional example, the thickness of the chalcogenide film formed within the enlarged diameter section 13a is extremely thin, the electrical characteristic of the film is significantly inconsistent, and the quality of the film is inferior.
As described above, according to the method for forming a chalcogenide film by means of sputtering according to the present embodiment, in the case where the diameter of the target 3 having a composition the same as that of the chalcogenide film is T (m) and the distance between this target 3 and the specimen 2 is L (m), the ratio L/T of the distance L with respect to the diameter T of the target 3 is not less than 0.5 and not more than 1.5. Consequently, it is possible, in a state where the sputtering rate is maintained at an optimum condition, to form, within the enlarged diameter section 13a of the contact hole 13, a dense chalcogenide film 17 with a stoichiometric composition, having no defects such as gaps and cracks therein.
Moreover, since a bias electric power is applied to the specimen 2, it is possible, in a state where the composition of the film containing volatile chalcogen elements maintains its stoichiometric composition, to form a dense chalcogenide film having a flat surface.
Therefore, it is possible to provide a resistance variable type recording element in which a recording layer is formed with a dense chalcogenide film with a stoichiometric composition, having no defects such as gaps and cracks therein.
The present invention may be utilized in forming a dense chalcogenide film with a stoichiometric composition, having no defects such as gaps and cracks therein, and may also be utilized in manufacturing a resistance variable type recording element having such a chalcogenide film that serves as a recording layer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-015059 | Jan 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/051001 | 1/24/2008 | WO | 00 | 7/23/2009 |
