Patent Application
20160087028
The present invention relates to a semiconductor device and to a method for manufacturing same, and more specifically the present invention relates to a semiconductor device having a capacitor comprising a dielectric film having a high dielectric constant.
There is a growing demand for semiconductor devices comprising memory elements which are miniaturized and have a high bit number. A dielectric film having a high dielectric constant is used in a capacitor having this kind of memory element.
The capacitor illustrated in FIG. 2 of Patent Document 1 (JP 2006-135339 A), for example, has a layered structure in which the following are stacked in succession from a lower layer, namely: a storage electrode (15); an AZ structure dielectric film (16) comprising a first dielectric film (16A) that comprises an ALD (atomic layer deposition)-ZrO (zirconium oxide) film, and a second dielectric film (16B) that comprises an ALD-AlO (aluminum oxide) film; and a plate electrode (17) comprising a CVD (chemical vapor deposition)-TiN (titanium nitride) film. It should be noted that the AZ structure denotes a structure comprising an A10 upper layer as A and a ZrO lower layer as Z, from the upper layer toward the lower layer. For example, a TZT structure which will be described later means a combination of TiO as T and ZrO as Z, where ZrO is combined between upper and lower layers of TiO. Furthermore, the numbers in parentheses indicate the reference symbols in the figures of the corresponding prior art and are distinct from the reference symbols in the figures of the present invention; the same also applies to the prior art below.
The abovementioned document indicates that by virtue of the abovementioned structure, a capacitor having a small leakage current can be formed, even when the inevitable heat treatment is carried out after the capacitor has been formed, and a ZA structure, a ZAZ structure or other structures in which said structures are stacked multiple times are also described, in addition to the AZ structure. It is also indicated that the film thickness of AlO is in the range of 0.5 nm-3 nm and the film thickness of ZrO is in the range of 0.5 nm to 10 nm. It is further indicated that the storage electrode constituting a lower electrode and the plate electrode constituting an upper electrode are formed by any materials selected from the group consisting of metals such as W, Ru, Ir and Pt; metallic compounds such as TiN, TaN, WN, RuO and IrO; and impurity-doped polycrystalline silicon. It is also indicated that the dielectric constant of a ZrO film obtained using the abovementioned technology is 20-25 and the dielectric constant of an AlO film is 9.
Furthermore, the capacitor illustrated in FIG. 5I of Patent Document 2 (JP 2012-104719 A) has a structure in which the following are stacked in succession from a lower layer, namely: a lower electrode (23) comprising an ALD-TiN film connected to a contact (12); a dielectric film (30) having a ZAT structure consisting of a first dielectric film (32) comprising ALD-ZrO, a second dielectric film (34) comprising an ALD-AlO film, and a third dielectric film (36) comprising an ALD-TiO film; and an upper electrode (43) comprising an ALD-TiN film. However, said document merely describes the structure and film formation method, and there is no mention of conditions such as film thickness for obtaining a high-performance capacitor.
In addition, Patent Document 3 (JP 2012-80095 A), Patent Document 4 (JP 2012-80094 A) and Patent Document 5 (JP 2012-69871 A) filed by the present inventors propose forming a protective film of titanium oxide between an electrode and a dielectric film comprising zirconium oxide.
As shown in FIG. 13 of Patent Document 3, a capacitor has a TZT structure comprising, from a lower layer: a lower electrode (102) comprising a CVD-TiN (titanium nitride) film; a second protective film (114) comprising an ALD-TiO (titanium oxide) film; a dielectric film (115) comprising an ALD-ZrO film; a first protective film (116) comprising an ALD-TiO film; and an upper electrode (117) comprising a CVD-TiN film. It is indicated that by providing the second protective film (114) comprising a titanium oxide film between the lower electrode (102) and the dielectric film (115), adhesion between the lower electrode (102) and the dielectric film (115) is improved and peeling is unlikely to occur, the crystallinity of the dielectric film (115) comprising a zirconium oxide film is improved, and a higher dielectric constant can be achieved. It is further indicated that by providing the first protective film (116) comprising a titanium oxide film between the dielectric film (115) and the upper electrode (117), the dielectric film (115) is protected from damage (cracking and pin hole formation, and etching and oxygen deficiency) imparted when the upper electrode (117) is formed, the leakage current is reduced, and it is possible to obtain a capacitor having favorable characteristics.
As illustrated in FIG. 10 of Patent Document 4, a capacitor has a TZAZT structure comprising: a lower electrode (102) comprising a CVD-TiN film; a second protective film (108) comprising an ALD-TiO film; a first dielectric film (105) comprising an ALD-ZrO film; a second dielectric film (106) comprising an ALD-AlO film; a third dielectric film (107) comprising an ALD-ZrO film; a first protective film (110) comprising an ALD-TiO film; and an upper electrode (111) comprising a CVD-TiN film. In the abovementioned structure, the first dielectric film (105) and the third dielectric film (107) comprising a ZrO film may have the same thickness or different thicknesses such that the first electrode film (105) has a thickness of 5 nm, for example, and the third dielectric film (107) has a thickness of 1 nm, for example. It is indicated that by adopting a TZAZT structure in which an AlO film is interposed as the second dielectric film (106), it is possible to obtain a capacitor which has an even smaller leakage current than a capacitor having a TZT structure, in addition to the advantages described in Patent Document 3.
As illustrated in FIG. 2 of Patent Document 5, a capacitor has a structure comprising, in succession from a lower layer: a lower electrode (201) comprising a CVD-TiN film; a second protective film (202) having an ALD-TiO film; a first dielectric film (203) comprising an ALD-ZrO film; an Al-doped layer (204) including AlO formed by means of adsorption site blocking-ALD (ASB-ALD); a second dielectric film (205) comprising an ALD-ZrO film; a first protective film (206) comprising an ALD-TiO film; and an upper electrode (207) comprising a CVD-TiN film. The ASB-ALD technique developed by the present inventors makes it possible to reduce the amount of Al per ALD cycle for Al doping, and the heat resistance can be improved while the continuity of crystals in the ZrO films positioned above and below the Al-doped layer can be maintained at an advantageous level. As a result, it is possible to realize a smaller equivalent oxide thickness (EOT: capacitance value per unit surface area expressed as the equivalent thickness of a silicon dioxide (SiO2, dielectric constant: 3.9) film) in comparison with a conventional capacitor. “Cyclopentadienyl tris(dimethylamino)zirconium” and “methylcyclopentadienyl tris(dimethylamino)zirconium” are mentioned as precursors of zirconium (Zr) used in the ASB-ALD, and “methylcyclopentadienyl tris(dimethylamino)titanium” is mentioned as a precursor of titanium (Ti).
Furthermore, Patent Document 6 (JP 2012-248813 A) filed by the present inventors indicates that a TiO film having a rutile crystal structure with a high dielectric constant is obtained under specific conditions, namely conditions such that an amorphous titanium oxide (TiO) film is formed on an amorphous zirconium film by means of ALD using methylcyclopentadienyl tris(dimethylamino)titanium as a titanium starting material, and heat treatment is carried out at a temperature of 300° C. or greater.
If the minimum processing size dictated by the resolution limit of lithography is F, then a capacitor having an EOT of 0.75 nm or less is required as a capacitor for a DRAM in which F is at the 25 nm level onward. Furthermore, the leakage current (leak current) at 90° C. ensuring reliability must be 10 (fA/cell) or less under an applied voltage of ±1 V. In addition, in terms of an actual device, each memory cell must have a memory retention time (holding time) equal to or greater than a given value which is determined by the refresh interval. In other words, there is a need for a very reliable capacitor which has a small EOT and a small leakage current.
Types of leakage current in an insulating film which may be considered include Schottky current, Pool-Frenkel current and tunneling current, but even assuming that a Schottky barrier has sufficient height and an ideal dielectric film has no defects, tunneling currents such as Fowler-Nordheim tunneling current and direct tunneling current are important.
A tunneling current depends greatly on film thickness and although there is a sharp increase in tunneling current when the film thickness drops below a certain level, experiments have shown that the thickness of the dielectric film as a whole must be a minimum of 5 nm in order to satisfy the abovementioned leakage current specification.
In the method for forming a capacitor described in Patent Document 1, the dielectric constant of zirconium oxide is only 20-25, as also indicated in Patent Document 1. This is believed to be due to the fact that amorphous material having a low dielectric constant and cubic microcrystals having low density and also having a low dielectric constant are predominant in the dielectric film. When amorphous or microcrystalline zirconium oxide is formed into a dielectric film, virtually no problems arise in the dielectric film, such as cracking or pin holes accompanying thermal load when the upper electrode is formed, and therefore it is possible to achieve relatively good leakage current characteristics. It is difficult, however, to obtain a small EOT because of this low dielectric constant.
For example, a dielectric film in which a zirconium oxide film (dielectric constant: 25) and an aluminum oxide film (dielectric constant: 9) are stacked by means of the method in Patent Document 1 may be considered. In this case, setting the thickness of the zirconium oxide film which has a large dielectric constant to be greater than the thickness of the aluminum oxide film makes it possible to achieve a smaller EOT in comparison with the same physical thickness. If the film thickness of aluminum oxide is set at 0.5 nm as the minimum thickness described in Patent Document 1, the EOT of aluminum oxide is around 0.22 nm. If the remaining physical film thickness of 4.5 nm is formed by zirconium oxide having a dielectric constant of 25, the EOT of the zirconium oxide portion is approximately 0.70 nm. This means that the EOT of the stacked dielectric film comprising aluminum oxide and zirconium oxide is 0.92 nm so it is not possible to satisfy the target EOT of 75 nm or less. Even if the film thickness of aluminum oxide were set at zero and a dielectric film (5 nm) comprising a single film of zirconium oxide having a dielectric constant of 25 were produced, the EOT would still be 0.78 nm and the target would not be satisfied.
In Patent Document 2, a layered film in which an ALD-ZrO film, an ALD-AlO film and an ALD-TiO film are stacked in succession is employed as a dielectric film 30 forming part of a capacitor. It could be expected that using a TiO film having a high dielectric constant would make it possible to reduce the EOT of the capacitor. However, Patent Document 2 does not describe any detailed conditions governing the characteristics of the capacitor, such as the thickness and crystallinity of each film, or the heat-treatment temperature etc. It is only the conditions under which the abovementioned films are formed using the semiconductor production apparatus depicted in that invention which are described. The characteristics of the capacitor which is formed are therefore unclear. As is well known, a TiO film forms either a rutile crystal structure or an anatase crystal structure at the crystallization stage. The rutile crystal structure exhibits a very high dielectric constant of 80 or greater, but the anatase crystal structure exhibits a dielectric constant of only around 40. A normal titanium oxide film shifts to a rutile crystal structure via an anatase crystal structure in the crystallization process, and a temperature of 700° C. or greater is required for the shift to the rutile crystal structure. As indicated in Patent Document 6 filed by the present inventors, a TiO film does not readily crystallize to a rutile crystal structure at low temperature unless the TiO film is formed on a material in which at least the base is formed by a predetermined crystal structure. In the capacitor described in Patent Document 2, a TiO film is formed on an AlO film which is a very stable amorphous insulating film, and even if heat treatment is carried out in this state, it is still difficult to produce a TiO film having a rutile crystal structure.
In Patent Document 1 mentioned above, it is necessary to reduce the thickness of the AlO film and the ZrO film and to increase the dielectric constant by crystallizing the ZrO film in order to achieve a small EOT. However, according to experiments carried out by the present inventors, when the thickness of the dielectric in the capacitor described in Patent Document 1 is reduced, the ZrO film does not readily crystallize and it is not possible to reduce the EOT. Furthermore, heat treatment is required at a higher temperature and for a longer time in order to crystallize the ZrO film when it has been thinned, and there are problems in that heat resistance is insufficient and the leakage current increases. As a result of various investigations carried out by the present inventors into measures for avoiding these problems, it was found that it is effective to provide a protective film comprising a TiO film between the dielectric film and the upper electrode and between the lower electrode and the dielectric film, as described in Patent Documents 3-5.
For example, when the technology described in Patent Document 4 or Patent Document 5 is employed, it is possible to impart to a ZrO film a dielectric constant that could not be achieved with the method in Patent Document 1, and also to impart thermal stability. That is to say, investigations carried out by the present inventors showed that it is possible to achieve a dielectric constant of 32-38 when a TiO film having a thickness of 0.4 nm or greater is formed on the lower electrode, a ZrO film is further formed in such a way that the film thickness is 4 nm or greater, and AlO contained therein as an impurity is present at an Al concentration of around 0-10% expressed as Al/(Al+Zr), for example. This results from the fact that the ZrO film is formed after the TiO film has been formed on the lower electrode, whereby the crystallinity of the ZrO film is improved and the density is increased and therefore the proportion of tetragonal crystals having a high dielectric constant is increased, as also described in Patent Document 4. Test calculations similar to those carried out in relation to Patent Document 1 showed that when a zirconium oxide film having a dielectric constant of 38 is used, the EOT is around 0.51 nm if the physical film thickness is 5 nm, which is the required minimum limit for suppressing tunneling current. This satisfies the target EOT of 0.75 nm. Meanwhile, a considerable reduction in leakage current is also confirmed in an evaluation based on a test element group (TEG) formed by a flat capacitor and a small number of three-dimensional capacitors etc.
As described above, in Patent Documents 3, 4 and 5, a second protective film comprising titanium oxide is disposed between a lower electrode and a dielectric, and a first protective film comprising titanium oxide is disposed between a dielectric and an upper electrode. The effect of the second protective film and the first protective film described in Patent Documents 3, 4 and 5 will be summarized below.
First of all, the second protective film has the effect of improving adhesion between the dielectric film and the lower electrode and preventing peeling of the dielectric film which would cause a defect, while also improving the crystallinity of the zirconium oxide dielectric film, thereby increasing the dielectric constant. For example, Patent Document 1 indicates that when zirconium oxide is formed directly on titanium nitride, the dielectric constant of the zirconium oxide film is 20-25. Investigations carried out by the present inventors also confirmed that this could be substantially reproduced. This would suggest that the dielectric film is in an amorphous state or a cubic crystal state with a low dielectric constant, or a mixture of these states. Meanwhile, experiments carried out by the present inventors showed that it is readily possible to achieve a dielectric constant of 32-38 when a second protective film comprising titanium oxide is formed on the lower electrode, after which a dielectric film comprising zirconium oxide as the main component is formed, as described in Patent Document 4 and Patent Document 5.
This would suggest that the second protective film has an effect of promoting crystallization of zirconium oxide and growth of crystal grains thereof.
Table 1 below shows the results of a comparison of peak intensity in X-ray diffraction (XRD) when a second protective film (titanium oxide film on the lower electrode) is present and when it is absent, in regard to a zirconium oxide film having a thickness of 6.6 nm. It should be noted that these results reproduce the results before and after annealing shown in Table 1 of Patent Document 4 (with the rate of change of Sample 1 having been corrected). Sample 1 has a structure in which a zirconium oxide film comprising about 3 at. % AlO and a first protective film comprising TiO having a thickness of 1 nm are formed in succession on a lower electrode comprising a TiN film having a thickness of 10 nm, while sample 2 has a structure in which a TiO film having a thickness of 0.5 nm is formed as a second protective film between the lower electrode and the zirconium oxide film in the structure of Sample 1 (see FIG. 18 of Patent Document 4). As shown in FIG. 16 of Patent Document 4, the diffraction peak intensity is greater immediately after film formation (“as deposition”) in Sample 2 in which the second protective film is present, indicating good crystallinity. Furthermore, as shown in FIG. 17 of Patent Document 4, even after annealing at 450° C. for 6 hours (N2 atmosphere), Sample 2 in which the second protective film is present still demonstrates a large peak. That is to say, it is clear that the presence of the second protective film means that the zirconium oxide film exhibits better crystallinity in comparison with a case in which the second protective film is not present on the lower electrode.
Furthermore, the rate of change in the peak intensity before and after annealing is 2.36 in Sample 1 and 1.15 in Sample 2. The rate of change is smaller when the second protective film is present, so there is less change in crystallinity; in other words, it can be anticipated that the volume shrinkage caused by the thermal load (to be described later) from immediately after film formation until formation of the upper electrode will be reduced. According to Patent Document 4, this can be cited as one reason for which the presence of the second protective film affords greater resistance to the thermal load from formation of the upper electrode and onward.
Meanwhile, the first protective film serves as a stress-alleviating layer and has an effect such that cracks or pin holes are less likely to be formed in the dielectric film, and also has an effect such that even if cracks or pin holes are formed, the surfaces of the cracks or pin holes are less likely to be exposed when the upper electrode is formed, as with the technique of “internal penetration” which is used in glasswork and the like. As a result, it is possible to restrict the penetration of cracks and pin holes into the upper electrode, and it is possible to restrict short-circuit states between the upper electrode and the lower electrode of the capacitor. Furthermore, the presence of the first protective film means that the dielectric film is no longer exposed to a reducing atmosphere or a corrosive atmosphere when the upper electrode is directly formed, and therefore it has the effect of making it possible to avoid problems in terms of oxygen deficiency and problems in terms of the dielectric film itself being etched.
For example, the upper electrode made of titanium nitride is formed by means of known CVD or ALD at a processing temperature of between 350° C. and 450° C. Before the film is formed, a substrate is normally conveyed to a reaction chamber of a film formation apparatus, the temperature is raised to the processing temperature and then held until the substrate temperature is stable. After this, starting material gases are introduced into the reaction chamber in a predetermined sequence and film formation is started. Titanium tetrachloride (TiCl4) and ammonia (NH3) are used as starting material gases, and in this case HCl, Cl2, H2, N2, NH4Cl and the like are produced in the atmosphere as by-products.
Here, a description will be given of a case in which the upper electrode is formed without the first protective film being provided.
However, if the capacitor in Patent Document 4 or Patent Document 5 having the effect of reducing the EOT and reducing leakage current is applied to a gigabit-order product comprising a three-dimensional structure, minority defects in cell units may be observed in evaluation tests under a high-temperature working environment. These minority defects are caused by minute leaks mediated by defects in the dielectric film. If a large leakage current is caused by the defects, it is easily possible to distinguish conforming and nonconforming articles by means of a TEG-based I-V characteristic evaluation, but if the leakage current is very small, it is difficult to distinguish conforming and nonconforming articles using a TEG-based evaluation method in a flat capacitor. Furthermore, even in the case of a three-dimensional structure, averaging occurs with a method in which the leakage current is measured by consolidating several tens of thousands of cells, and observation is still difficult. That is to say, defects accompanying very slight leakage are difficult to distinguish using a flat capacitor and a TEG-based evaluation method, and such defects are observed for the first time as minority defects in cell units under a working environment at a higher temperature than room temperature after application to a product/mounting on a product.
According to investigations carried out by the present inventors, it has been established that it may not be possible to adequately restrict these minority defects even if the method described in Patent Document 4 or Patent Document 5 is employed. In particular, there are times when these defects are manifested as cells having a short memory retention time in evaluation tests in which the device working temperature exceeds 90° C. Cells deemed to be defective in an evaluation test are replaced in the electronic circuit with regular cells which are prepared as a reserve for redundancy. However, the reserve cells are also limited and are also used for replacing defective cells from other modes, so the formation of minority defects ultimately causes a deterioration in the overall yield and there is room for improvement.
In the light of the abovementioned problems, a semiconductor device according to a mode of embodiment of the present invention is characterized in that it comprises a capacitor provided with:
a lower electrode disposed on a semiconductor substrate;
a second protective film which covers at least the surface of the lower electrode;
a dielectric film which covers the surface of the second protective film and has a defect which develops in the film thickness direction from an upper surface opposite the second protective film;
a third protective film having at least a defect-filling film comprising an insulator which fills the defect and is different from the main component of the dielectric film;
a first protective film which covers the dielectric film and the third protective film; and
an upper electrode which covers the first protective film.
By virtue of the semiconductor device according to the present invention, even if a defect such as a crack is already formed in the dielectric film at a stage before the first protective film is formed, the third protective film having a defect-filling film comprising an insulator which fills the defect is provided, and as a result it is possible to avoid minority defects caused by leakage current.
Experimental examples carried out by the present inventors will be described below with the aid of
In order to guard against the abovementioned minority defects, the present inventors carried out various experimental investigations, as a result of which it was found that a zirconium oxide film constituting a dielectric film is already crystallized at the stage immediately after film formation (“as deposition”; referred to below as “as depo.”). The present inventors first of all investigated the film thickness dependency of crystallinity in regard to a zirconium oxide film.
It can be seen from the results in
When crystallization proceeds and crystal grains grow while an amorphous or microcrystalline zirconium oxide film at 4 nm or less grows to a thickness of 5 nm, there is accompanying volume shrinkage, and therefore it is speculated that defects such as cracks and pin holes are already formed in the surface thereof before the first protective film is formed, even though these are not to the extent produced as a result of the thermal load (350° C.-450° C.) when the upper electrode is formed.
Surface observation of the dielectric film after film formation is then attempted using a scanning electron microscope (SEM).
It can be confirmed from the results of
If the titanium oxide film of the first protective film is formed while cracks have been produced in this way, it is speculated that the titanium oxide film will fill the cracks formed in the surface of the zirconium oxide film, as described in Patent Documents 3-5.
Titanium oxide films are known as dielectric films having a high dielectric constant, while at the same time it is also well known that such films are also used as oxide semiconductors. As described in Patent Document 4, titanium oxide of 1 nm or greater behaves as a conductor, and a titanium oxide film still behaves as a semiconductor when the thickness thereof is reduced, so the present inventors believe that the titanium oxide film serving as the first protective film 504 which fills the cracks 506 in the dielectric film forms a minute leak path at the device working temperature which is higher than room temperature, although not to the extent of a short-circuit state which occurs when a titanium nitride conductor penetrates the cracks, and as a result minority defects are produced in cell units. That is to say, crystallization of the zirconium oxide film 503 is promoted by the presence of the titanium oxide film constituting the second protective film 502, and as a result it is believed that this also promotes crack formation.
The semiconductor device according to the present invention is characterized in that it comprises a capacitor provided with: a lower electrode disposed on a semiconductor substrate; a second protective film which covers at least the surface of the lower electrode; a dielectric film which covers the surface of the second protective film and has a defect which develops in the film thickness direction from an upper surface opposite the second protective film; a third protective film having at least a defect-filling film comprising an insulator which fills the defect and is different from the main component of the dielectric film; a first protective film which covers the dielectric film and the third protective film; and an upper electrode which covers the first protective film.
A “dielectric” is generally described in terms of the dielectric constant in the film thickness direction and an “insulator” is generally described in terms of the insulating properties as a material, and the two may indicate the same material. Furthermore, there are also materials which have a high dielectric constant on the one hand while also demonstrating conductor or semiconductor characteristics on the other hand, such as the abovementioned titanium oxide. According to the present invention, the insulator forming the defect-filling film included in the third protective film does not particularly require a high dielectric constant but it does require high insulating properties. On the other hand, the dielectric forming the dielectric film must have a relatively high dielectric constant which is preferably 25 or greater and more preferably 30 or greater. Furthermore, when a plurality of lower electrodes are covered, as with a DRAM (to be described later), the dielectric film preferably has predetermined insulating properties such that short-circuiting does not occur between the lower electrodes. A material different from the main component of the dielectric film (e.g. zirconium oxide) is normally used for the insulator forming the defect-filling film. The insulator forming the defect-filling film is preferably a material having a higher crystallization temperature than the main component of the dielectric film, and more preferably said insulator is an amorphous material which does not crystallize even when the first protective film and the upper electrode are subsequently formed. In the third protective film, the defect-filling film which fills the defect that develops in the film thickness direction has substantially no effect by itself on the dielectric constant of the dielectric film, but it should be noted that a film which is deposited on the surface of the dielectric film when the defect-filling film is formed (referred to below as the “planar protective film”) does have an effect on the dielectric constant in the film thickness direction.
Furthermore, the dielectric film has defects which develop in the film thickness direction from an upper surface opposite the second protective film. These defects are cracks or pin holes etc. which are apparent at the surface of the dielectric film after it has been formed, said defects extending from the upper surface toward the film thickness direction (the direction of the second protective film). This is due to the fact that volume shrinkage accompanying crystallization of the dielectric film during film formation or after film formation is greater on the free upper surface side than on the lower surface side which is fixed by the second protective film. According to the present invention, the crystallinity of the dielectric film has especially good continuity from the upper surface as far as the lower surface, and these defects which occur in multiple locations at the grain boundary also develop and extend from the upper surface up to the lower surface or to the vicinity of the lower surface.
Materials equivalent to those of the first protective film and the second protective film described in Patent Document 4 may be used as the first protective film and the second protective film according to the present invention, but titanium oxide films are preferred.
Exemplary embodiments of the present invention will be described through specific examples below.
According to this exemplary embodiment, a semiconductor device constituting a dynamic random access memory (DRAM) will be described as one example. However, the present invention is not limited to a DRAM and it may equally be applied to semiconductor devices in general in which a capacitor is mounted. The semiconductor device according to this exemplary embodiment will be described below with the aid of
A semiconductor device having capacitors according to this exemplary embodiment will be described first of all with the aid of
The layout of the DRAM memory cell will be described first with the aid of the plan view in
The first active region 702a and the second active region 702b have the same structure and the following description will therefore focus on the first active region 702a. By providing the two gate electrodes 705a, 705b, the first active region 702a is divided into a first capacitance diffusion layer 708a, a bit line diffusion layer 707a, and a second capacitance diffusion layer 708b. A first transistor Tr1 is formed by the capacitance diffusion layer 708a, the first gate electrode 705a and the bit line diffusion layer 707a. Furthermore, a second transistor Tr2 is formed by the second capacitance diffusion layer 708b, the second gate electrode 705b and the bit line diffusion layer 707a. The first capacitor C1 is disposed on the first capacitance diffusion layer 708a and the second capacitor C2 is disposed on the second capacitance diffusion layer 708b. Furthermore, a bit line 709 extending in the X-direction (third direction) is disposed on the bit line diffusion layer 707a which is shared by the first transistor Tr1 and the second transistor Tr2. The second active region 702b has the same structure and comprises a third capacitor C3 on a third capacitance diffusion layer 708c, a fourth capacitor C4 on a fourth capacitance diffusion layer 708d, and a bit line 609 on a bit line diffusion layer 707b.
Reference will now be made to the cross section of
The capacitor configuration will be described next with the aid of
In the configuration of
To describe this from another point of view, the semiconductor device according to this exemplary embodiment comprises: the lower electrode 601 which is disposed on the semiconductor substrate 700; the second protective film 602 which is at least in contact with the lower electrode 601 and covers the upper surface 601S; the dielectric film 603 which is in contact with the second protective film 602, covers the upper surface 602S thereof and has cracks (defects) 610 extending in the film thickness direction; the third protective film 604 comprising an insulator which is different from the main component of the dielectric film 603; the first protective film 605 which is in contact with the third protective film 604 and covers an upper surface 604S thereof; and the upper electrode 606 which is in contact with the first protective film 605 and covers the upper surface 605S thereof, the third protective film 604 comprising the planar protective film 604A which is located on the upper surface 603S of the dielectric film 603, and the defect-filling film 604B which is in contact with one surface (the surface on the lower electrode side) of the planar protective film 604A and projects from the planar protective film 604A in such a way as to fill the cracks 610.
This configuration will be described in further detail. The lower electrode 601 comprises a titanium nitride (TiN) film. The second protective film 602 which is in contact with the lower electrode 601 and is provided in such a way as to cover the upper surface 601S comprises a titanium oxide film. The thickness of the second protective film 602 is preferably in the range of 0.4-2.0 nm and more preferably in the range of 0.5-1.0 nm. As shown in
The dielectric film 603 which is in contact with the second protective film 602 and is disposed in such a way as to cover the upper surface 602S is formed by a zirconium oxide film 603A having at least one impurity-doped layer 603B within the dielectric film 603. The surface density of impurity atoms in one layer of the impurity-doped layer is preferably less than 1.4 E+14 (atoms/cm2), and more preferably no greater than 1.0 E+14 (atoms/cm2). Aluminum (Al) and silicon (Si) etc. may be cited as impurity atoms, but Al is preferred. Furthermore, the concentration of impurity atoms contained in the dielectric film 603 formed by a zirconium oxide (ZrO) film is such that M is between 0.2 and 2%, expressed as M/(Z+M) where Z is the number of zirconium atoms and M is the number of impurity atoms. It should be noted that metal atoms such as Al and Si which form the third protective film are not included in the concentration of impurity atoms. Meanwhile, the concentration of zirconium atoms when the dielectric film and the third protective film are combined is preferably at least 80%, and more preferably at least 90%, in terms of the ratio of the number of atoms expressed as Z/(Z+M′), where M′ is the number of metal atoms excluding zirconium. The abovementioned value of 0.2 to 2% means a state in which impurity molecules such as aluminum oxide (AlO) molecules are scattered within the plane of the zirconium oxide film without the impurity-doped layer 603B forming a continuous film. A case in which Al is introduced as impurity atoms will be described below, where the impurity-doped layer 603B is an Al-doped layer 603B. The zirconium oxide film 603A positioned vertically either side of the Al-doped layer 603B therefore makes contact in regions where the AlO molecules are not scattered, and crystal growth of the zirconium oxide film 603A proceeds simultaneously while spatial continuity is maintained over the whole of the dielectric film 603. That is to say, the Al-doped layer 603B does not inhibit crystal growth of the zirconium oxide film 603A.
On the other hand, the aluminum oxide film in the capacitor having a TZAZT structure illustrated in FIG. 10 of Patent Document 4 mentioned above does inhibit crystal growth of the zirconium oxide film. TZAZT means a structure comprising the following: titanium oxide film (T)/zirconium oxide film (Z)/aluminum oxide film (A)/zirconium oxide film (Z)/titanium oxide film (T). The aluminum oxide film used in Patent Document 4 is an aluminum oxide film in which AlO molecules are present as a continuous film, rather than the Al-doped layer according to this exemplary embodiment in which the AlO molecules are isolated. In the capacitor having a TZAZT structure described in Patent Document 4, the zirconium oxide film positioned vertically either side of the aluminum oxide film is completely separated by the aluminum oxide film, and continuity of crystal growth cannot be maintained. That is to say, the aluminum oxide film used in Document 4 is a factor in the inhibition of crystal growth of the zirconium oxide film. This means that there is a difficulty in achieving a high dielectric constant with a TZAZT structure.
Returning to the description of
The dielectric film 603 having a thickness of 5.0 nm is disposed on the second protective film 602 and therefore the cracks 610 are formed while the dielectric is being formed, as described above.
The third protective film 604 which is disposed in contact with the dielectric film 603 in such a way as to cover the upper surface 603S thereof is formed by an insulating film such as an aluminum oxide film, a silicon dioxide film or a silicon nitride film. The third protective film 604 is provided in such a way as to produce a formed film thickness of at least 0.1 nm on the upper surface 603S of the dielectric film 603. This normally corresponds to two or more cycles of ALD. Furthermore, the thickness of the formed film is preferably at least 0.2 nm and more preferably at least 0.3 nm. In this case the thickness is approximately 0.3 nm. The effect of filling cracks 610 formed in the dielectric film 603 when the third protective film 604 is thinner than 0.1 nm is not adequately demonstrated. On the other hand, the planar protective film 604A affects the dielectric constant in the film thickness direction so if the film thickness is greater it becomes difficult to maintain the capacitance of the capacitor at a permitted value. A film thickness which ensures that capacitance in the permitted range is satisfied is therefore preferred. When aluminum oxide is formed as the third protective film, the thickness of the planar protective film 604A is therefore 1.0 nm or less, preferably 0.6 nm or less and more preferably 0.5 nm or less. It should be noted that the formed film thickness and the planar protective film 604A thickness do not necessarily have to be the same, and it is possible to form a film up to a thickness adequate for correcting defects and then to reduce this to a thickness permitted for the planar protective film 604A. Furthermore, it is not essential for the defect-filling film 604B to completely fill the defects (cracks etc.); provided that it is possible to prevent the formation of a leak path due to the first protective film penetrating into the defects, a state in which the defect-filling film 604B does not completely fill the defects is acceptable. For example, a gap may be left to the extent that the Ti precursor for forming the first protective film cannot penetrate.
As shown in
The first protective film 605 which is disposed in contact with the third protective film 604 in such a way as to cover the upper surface 604S thereof is formed by a titanium oxide film. The thickness of the first protective film 605 is preferably in the range of 0.4-3.0 nm and more preferably in the range of 0.5-1.0 nm. The thickness in this case is 0.6 nm.
The upper electrode 606 which is in contact with the first protective film 605 and is disposed in such a way as to cover the upper surface 605S thereof is formed by a titanium nitride film. The thickness of the upper electrode 606 is preferably 4 nm-10 nm. The thickness in this case is 7 nm.
As mentioned above, the capacitor according to this exemplary embodiment comprises the following elements which are stacked in succession, namely: the lower electrode 601, the second protective film 602, the dielectric film 603, the third protective film 604, the first protective film 605, and the upper electrode 606. On the other hand, in a structure in which the capacitor structure according to this exemplary embodiment is simply vertically inverted, the insulator such as the aluminum oxide film forming the third protective film 604 essentially does not act to promote crystal grain growth or crystallization of the zirconium oxide film forming the dielectric film 603. It is therefore difficult to form a dielectric film 603 having a high dielectric constant. Even if the dielectric film 603 on the aluminum oxide film were forcibly crystallized by means of high-temperature annealing, the titanium oxide film forming the second protective film 602 would penetrate into the cracked portions formed by the high-temperature annealing and therefore the effect of reducing the leakage current would not be demonstrated unless the thickness of the planar protective film 604A were endlessly increased. When the thickness of the planar protective film 604A is increased, however, it is not possible to attain capacitance in the permitted range.
Furthermore, when the upper electrode 606 is disposed on the dielectric film 603 without the third protective film 604 and the first protective film 605 being provided, it can readily be envisaged that a short-circuiting state will be more likely to occur, as shown in
(Method for Manufacturing a Semiconductor Device)
A method for manufacturing a semiconductor device comprising the capacitor according to this exemplary embodiment is characterized in that it makes use of a method in which, before a titanium oxide film constituting the first protective film is formed on the dielectric film, a good quality insulator (aluminum oxide or silicon dioxide) is formed as the third protective film, whereby cracks and pin holes are filled (vapor-phase infiltration afforded by means of ALD), and the defects are repaired, after which the first protective film (titanium oxide) is formed.
The method for manufacturing a semiconductor device comprising the capacitor according to this exemplary embodiment will be described below with reference to
As shown in
(Method for Manufacturing a Capacitor)
The lower electrode 601 (TiN) is formed by means of known CVD or ALD. For example, said lower electrode 601 may be formed in a temperature range of 350° C. to 600° C. using TiCl4 and NH3 as the reaction gas, for example. The lower electrode 601 is separated into individual lower electrodes 601 by forming a sacrificial interlayer film constituting a mold, then forming a cylinder hole, depositing a TiN film inside the cylinder hole, and removing the TiN film on the sacrificial interlayer film. After this, the sacrificial interlayer film is removed. It should be noted that the upper surface of the second interlayer insulating film 613 comprises a material forming a stopper film when the sacrificial interlayer film is removed.
Next, titanium dioxide (TiO2) is formed as the second protective film 602 on the lower electrode 601. The thickness of the second protective film 602 is preferably in the range between 0.4 and 2.0 nm, and more preferably between 0.5 nm and 1.0 nm. In terms of the formation method, it is possible to use a method in which the lower electrode 601 is heat-treated under an oxidizing atmosphere such as ozone (O3), or a known ALD method, among others.
When ALD is used in order to form the second protective film 602, TiO2 is also formed between adjacent lower electrodes, which is to say on the second interlayer insulating film 713. TiO2 behaves as a semiconductor, and when the TiO2 is thickened, leakage occurs between adjacent lower electrodes so a titanium dioxide film having a certain degree of thickness is preferably formed by thermal oxidation of the surface of the lower electrode 601, after which a titanium dioxide film having a thickness of no greater than 0.20 nm is preferably formed by ALD. As a result, an ALD titanium dioxide film is continuously formed on the lower electrode 601 while a titanium dioxide film formed by means of thermal oxidation serves as a base, but a titanium dioxide film formed by means of thermal oxidation is absent from the second interlayer insulating film 713, so the structure comprising separate islands (602c) is produced.
It should be noted that when the second protective film 602 is formed only by thermal oxidation of the lower electrode 601, it goes without saying that TiO2 is formed only on the lower electrode and therefore there is no problem in terms of leakage current between adjacent cells. However, when TiO2 is formed by means of thermal oxidation, the electrical resistance of the lower electrode rises excessively due to the fact that oxygen diffuses along the grain boundary of TiN, and this may have an adverse effect in terms of the electrode.
Furthermore, when TiO2 is formed by means of thermal oxidation alone, TiO2 is not present on the second interlayer insulating film 713, and therefore a problem arises in terms of adhesion of the dielectric film 603 on the second interlayer insulating film 713 and the dielectric film 603 may peel.
In addition, the thickness of the second protective film 602 is preferably 0.4 nm or greater in order to promote growth of crystal grains and crystallization of the dielectric film 603 comprising zirconium dioxide. The second protective film 602 (TiO2) is therefore more preferably formed by the combined use of thermal oxidation of the lower electrode 601 (TiN) and ALD. The TiO2 which is formed by means of thermal oxidation of the lower electrode (TiN) 601 may be formed before the TiO2 is formed by means of ALD inside the same reaction chamber, in which case the process can be simplified.
According to this exemplary embodiment, in order to form the second protective film 602, the lower electrode 601 is exposed for 30 minutes to an atmosphere comprising O3 at 250° C. in order to oxidize the surface of the lower electrode 601 and TiO2 of 0.4 nm is formed, after which, without further intervention, known ALD is used to additionally form a TiO2 film corresponding to 0.1 nm inside the same reaction chamber (combined thickness: 0.5 nm).
When a film is formed by means of ALD and methylcyclopentadienyl tris(dimethylamino)titanium is used as the Ti precursor, the film formation rate per cycle of ALD film formation is approximately 0.1 nm/cycle, so 1-2 cycles are preferable. 1 cycle is used in this exemplary embodiment.
The Ti precursor is not limited to what has been described above and other Ti precursors may equally be used. In this case, the number of ALD cycles is adjusted in such a way that the target film thickness is achieved in conjunction with the ALD film formation rate.
As a result, second protective films 602a, 602b comprising titanium dioxide and each of around 0.5 nm are formed on the lower electrodes 601a, 601b, and titanium dioxide 602c corresponding to a thickness of 0.1 nm is formed on the upper surface of the second interlayer insulating film 713 which electrically isolates adjacent lower electrodes 601a, 601b.
If TiO2 were at the level of a single molecule, then the thickness of a single-molecule layer of TiO2 would be around 0.3 nm according to calculations, so TiO2 at 0.1 nm does not in fact satisfy a single-molecule layer. Insulation between the adjacent lower electrodes 601a, 601b can therefore be maintained while improving adhesion by interposing the island-like second protective films 602c between the second interlayer insulating film 713 present between the adjacent lower electrodes 601a, 601b and the dielectric film 603 formed thereon. Although the film is not actually continuous in this exemplary embodiment, for the sake of convenience it is still treated as a “film” or “layer” when it is present in such a form.
A dielectric film 603 comprising zirconium dioxide (ZrO2) as the main component is then formed on the second protective film 602. A known ALD method such as that described in Patent Document 3 may be used as the film formation method. In this exemplary embodiment, cyclopentadienyl tris(dimethylamino)zirconium is used as the Zr precursor and the process is carried out at a processing temperature of 250° C. A processing temperature of between 220° C. and 280° C. may be used. A gas comprising O3 may be used as the oxidizing reaction gas, for example.
The thickness of the dielectric film 603 is preferably set at 5.0 nm or greater, including the thickness of the third protective film which will be described later, and more preferably it is set at 5.5 nm or greater. In this exemplary embodiment, the thickness of the dielectric film 603 is 5.0 nm and the third protective film 604 (aluminum oxide) is obtained by three cycles of ALD employing trimethylaluminum (TMA) (corresponding to 0.3 nm), giving a combined thickness of 5.3 nm.
As shown in
Furthermore, the dielectric film 603 may be doped using Al or Si as impurity in order to increase the thermal stability and to adjust the degree of crystallization. In this exemplary embodiment, the Al-doped layer 603B is introduced at four equally divided locations in the film thickness direction of the dielectric film 603 using the ASB-ALD method described in Patent Document 5, as shown in
The impurity concentration may be controlled by the number of times of doping employing ASB-ALD which is carried out while the dielectric film 603 is being formed. In this exemplary embodiment, for example, Al-doping is introduced at equal intervals in the thickness direction of the dielectric film 603 four times with respect to the thickness of the zirconium dioxide film 603A using ASB-ALD. In this process, the concentration of Al expressed as Al/(Al+Zr) taken in terms of the whole of the dielectric film 603 is approximately 2%.
On the other hand, as will be described later, the doping need not necessarily be introduced at equal intervals in the film thickness direction and the concentration may be varied in the thickness direction by varying the intervals in the thickness direction.
According to investigations carried out by the present inventors, crystal growth is less likely to progress with a higher impurity concentration, taken as an average of the impurity contained in the dielectric film 603, and if other conditions are the same, the film thickness at which crystal grains start to grow tends to shift to the thicker side. Furthermore, the XRD peak intensity immediately after film formation tends to be smaller when the impurity concentration is higher, even in the case of zirconium dioxide films having the same film thickness beyond 5 nm.
For example, the results of a comparison when the concentration of Al expressed as Al/(Al+Zr) was 3%, 4% and 6% with respect to a ZrO2 film having a thickness of 7 nm show that immediately after film formation (“as depo.”), the XRD diffraction peak is clearly smaller when the impurity concentration is higher and it can be understood that the mean particle size of the crystal grains is affected by the impurity concentration.
Furthermore, virtually the same XRD diffraction peak is exhibited at any level after annealing for 6 hours under N2 at 450° C. for the three impurity concentrations mentioned above, and it can be understood that the mean particle size of the crystal grains is substantially uniform. That is to say, it is possible to control the crystallinity of the dielectric film 603 immediately after film formation and control the level of crack/pin hole formation in accordance with the profile and doping concentration of impurity in the dielectric film 603.
The dielectric film 603 is in an amorphous state immediately after film formation and a state in which formation of cracks/pin holes is restricted is produced as a result of the impurity concentration being increased, and a method in which annealing is carried out at a relatively high temperature (e.g. a temperature above 450° C.) could be considered in order to promote crystallization after the first protective film 605 and the upper electrode 606 have been formed, but when this kind of method is actually implemented not only does the dielectric constant failed to increase in the same way as in Patent Document 1, but defects 610 such as cracks are also formed in the dielectric film 603 at that point in time (at the point in time when crystallization is promoted). The surfaces of the cracks 610 which are produced form dangling bonds that form a trap level, and a leak path is formed at the high working temperature of the device (90-110° C.).
The dielectric film 603 is therefore preferably densified to the extent possible before the third protective film 604 is formed and steps are taken to ensure that a thermal load is not applied as far as possible in the subsequent manufacturing steps. To be specific, steps are preferably taken to ensure that the temperature does not exceed 450° C., more preferably to ensure that the temperature does not exceed 420° C., and even more preferably to ensure that the temperature does not exceed 400° C.
Furthermore, when impurity doping is performed using normal ALD or co-adsorption ALD employing a Zr precursor and an Al precursor, as described in Patent Document 5, the surface density of Al adhering in one cycle of ALD employed in Al-doping is excessively high and ZrO2 crystal growth no longer reaches beyond the impurity-doped region. As a result, the dielectric film 603 does not readily crystallize and there is also a reduction in dielectric constant.
However, when doping is carried out using the ASB-ALD method described in Patent Document 5, the surface density of Al adhering in one cycle of ALD employed in Al-doping can be reduced in comparison with a conventional ALD method and this kind of impurity-doped region (doped layer) produces a state in which crystallization of ZrO2 is not inhibited, and crystallization and growth of crystal grains are promoted to the extent that a diffraction peak can already be confirmed by XRD immediately after a film has been formed to around 5 nm (see
If the dielectric film 603 is not sufficiently crystallized after film formation because of the impurity concentration or film formation conditions, heat treatment employing an oxidizing atmosphere may be carried out in order to cause crystallization and growth of crystal grains. This makes it possible to improve the crystallinity of the dielectric film 603 and to densify the dielectric film 603, and cracks may be intentionally formed in a controlled state.
Furthermore, even if the dielectric film 603 crystallizes, heat treatment employing an oxidizing atmosphere may still be performed, as required, with the aim of restoring residual oxygen deficiency in the dielectric film 603 and with the aim of further improving the crystallinity. The heat treatment in an oxidizing atmosphere may be carried out at a temperature of between 250° C. and 450° C., but a temperature of between 350° C. and 420° C. is more preferable. In particular, when O3 is used as an oxidant, the heat treatment is preferably carried out at between 350° C. and 400° C. in order to prevent abnormal oxidation of the dielectric film 603 and of the lower electrodes 601 via the cracks/pin holes present in the dielectric film.
However, annealing in an inert atmosphere such as N2, Ar or He or in an atmosphere comprising a reducing gas such as H2 in particular induces oxygen deficiency in the dielectric film 603 and is therefore undesirable. Oxygen deficiency in the dielectric film 603 forms a trap level, which causes an increase in the leakage current. In addition, heat treatment over a long period of time at a temperature above 500° C. is also undesirable because mutual diffusion starts at the interface of each layer.
Aluminum oxide is then deposited by means of known ALD as the third protective film 604 on the crystallized dielectric film 603. The third protective film 604 is formed using conventional ALD, and ASB-ALD is not employed.
This process is intended to correct defects by filling cracks or pin holes formed in the dielectric film 603 using a high-quality insulating film, and to prevent penetration of the titanium dioxide first protective film 605 (to be described later) into the cracks or pin holes.
The third protective film 604 is preferably thicker from the point of view of filling the cracks or pin holes, but Al2O3 has a dielectric constant of 9.0 and SiO2 has a dielectric constant of 3.9, for example, which are far smaller than the dielectric constant of ZrO2 at 32-38, so increasing the thickness of the film makes it difficult to obtain a small EOT. The film thickness cannot therefore be excessively increased.
When the third protective film 604 is formed by aluminum oxide, the film formation may be carried out using TMA and O3 at a temperature in the range of 220° C. to 400° C., for example. The film formation rate in this case is 0.09 nm per ALD cycle.
Investigations carried out by the present inventors showed that when a film is formed using ALD employing TMA and O3, an adequate effect is demonstrated if 2-5 cycles are carried out, in accordance with the required correction level. This corresponds to 0.18 nm-0.45 nm as the film thickness formed on the upper surface 603S of the dielectric film 603.
Assuming that Al2O3 is at the level of a single molecule, the thickness of a single-molecule layer is approximately 0.35 nm according to calculations, so an approximately single-molecule layer is produced by four cycles.
According to this exemplary embodiment, a film is formed for three cycles (corresponding to 0.27 nm) at 250° C. using TMA and O3 as a reaction gas and employing normal ALD. As a result, the third protective film 604 is formed, comprising the planar protective film 604A which is formed on the surface of the dielectric film 603 and the defect-filling film 604B which is in contact with the planar protective film 604A and projects from the planar protective film 604A in such a way as to fill the cracks 610.
The cracks and pin holes are filled by the third protective film 604 as a result of vapor-phase infiltration, as has already been described, so the time (dosing time) taken for the step of supplying TMA to the ALD reaction chamber in accordance with the ALD sequence is preferably set to be several times longer (e.g. between two times and 10 times longer) than in the case of normal ALD film formation. Specifically, a time of the order of 60 seconds-600 seconds is selected, for example.
Furthermore, the oxidation step employing O3 is also preferably set to be longer than that of the normal ALD sequence in the same way as for the step of supplying TMA in order to fill the deep parts of the cracks or pin holes. It is vital that the oxidation step etc. be suitably modified in order to restrict formation of a new leak path by carbon impurity etc. Specifically, a time of the order of 60 seconds-600 seconds is selected in the same way as for TMA. According to this exemplary embodiment, a dosing time of 120 seconds is used for TMA and a dosing time of 120 seconds is used for O3. The correction of defects by means of vapor-phase infiltration must be carried out after the dielectric film 603 has been formed and before the first protective film 605 is formed, as indicated above. Furthermore, the same also applies when another insulator is used as the third protective film (defect-filling film 604A).
After the correction level has been reached, it is possible to return to the dosing time for normal ALD film formation to form the planar protective film 604A. Furthermore, if a precursor in the film formation space is also oxidized without the source gas being purged, CVD conditions are produced and it is possible to increase the film formation rate in one cycle. That is to say, the defect-filling film 604B and the planar protective film 604A may comprise insulators comprising the same material formed in separate processes.
Investigations carried out by the present inventors show that gas-phase infiltration of the aluminum oxide does not demonstrate an adequate effect with CVD, and ALD must be carried out at least until the correction level is reached.
When the third protective film 604 and the dielectric film 603 are formed at the same temperature, the film formation may take place continuously inside the same reaction chamber so that the process can be simplified. Furthermore, if the temperature at which the third protective film 604 is formed is selected to be greater than the temperature at which the dielectric film 603 is formed, the dielectric film 603 may be exposed to an oxidizing atmosphere before the third protective film 604 is formed, and as a result this can also serve as the heat treatment under an oxidizing atmosphere which is carried out as required after the dielectric film 603 has been formed, and which also makes it possible simplify the process.
The first protective film 605 comprising TiO2 is formed on the third protective film 604 next. The first protective film 605 serves to restrict damage imparted to the dielectric film 603 and the third protective film 604 when the upper electrode 606 is formed. The first protective film 605 may be formed by means of known ALD. The film thickness is preferably between 0.4 nm and 3.0 nm, and more preferably between 0.6 nm and 2.0 nm. In this exemplary embodiment, ALD is used to form the first protective film 605, methylcyclopentadienyl tris(dimethylamino)titanium is used as the Ti precursor, O3 is used as the oxidant, and six cycles of ALD film formation are carried out to produce a film thickness of approximately 0.6 nm.
TiN constituting the upper electrode 606 is formed next using known ALD or CVD employing TiCl4 and NH3 gas. The film thickness is preferably 4 nm-10 nm. The film formation temperature is preferably between 350° C. and 450° C. If the temperature exceeds 450° C., new cracks may be formed in the dielectric film 603 etc., and the surfaces of the cracks produced may form dangling bonds that form a trap level, and a minute leak path may be formed in the high-temperature working environment of the device. Furthermore, if the temperature is lower than 350° C., the concentration of residual chlorine in the TiN film may increase, which may cause a problem in terms of adhesion. After the upper electrode has been formed, the thermal load applied to the capacitor is set at no greater than 450° C., preferably no greater than 420° C., and more preferably no greater than 400° C. In this exemplary embodiment, the upper electrode 606 is formed using ALD at a temperature of 400° C. to produce a film thickness of 7 nm.
After this, a B—SiGe-Poly film is formed to a thickness of 100 nm as the trench-filling upper electrode 607 using diborane, silane and germane as a reaction gas, and tungsten (W) is further formed by means of sputtering as the plate electrode 608. After this, the plate electrode 608 and the trench-filling upper electrode 607 formed in regions other than a memory cell region are removed using a known lithography technique and a known dry etching technique. The EOT of the capacitor formed in this way is 0.74 nm, and the leakage current is approximately 8 fA/cell (8 E-15 A/cell) at 90° C. with an applied voltage of ±1 V.
As is clear from
Furthermore,
In the first exemplary embodiment, the third protective film 604 comprises the planar protective film 604A and the defect-filling film 604B, as shown in
The semiconductor device according to this exemplary embodiment therefore comprises a capacitor provided with: the lower electrode 601 which is disposed on the semiconductor substrate; the second protective film 602 which is at least in contact with the lower electrode 601 and covers the upper surface 601S; the dielectric film 603 which is in contact with the second protective film 602, covers the upper surface 602S thereof and has cracks (defects) 610 extending in the film thickness direction; the third protective film 604 which includes at least the defect-filling film 604B comprising an insulating film which fills the defects 610; the first protective film 605 which covers the dielectric film 603 and the third protective film 604; and the upper electrode 606 which is in contact with the first protective film 605 and covers the upper surface 605S thereof.
According to this exemplary embodiment, the first protective film 605 is provided in a state in which the defects are filled by the defect-filling film 604B. The first protective film 605 is therefore not formed inside the defects 610, and it is possible to restrict an increase in the leakage current under a high temperature in the same way as in the first exemplary embodiment. In addition, the planar protective film 604A which forms part of the third protective film 604 is not present on the upper surface 603S of the dielectric film 603 so it is possible to increase the capacitance of the capacitor by reducing the EOT by around 0.2 nm.
When aluminum oxide is used for the third protective film in the configuration described above, for example, said aluminum oxide is in an amorphous state immediately after formation by means of ALD and it can be more easily removed by etching using chlorine-containing gas plasma than crystalline aluminum oxide. That is to say, the thickness of the planar protective film 604A formed on the upper surface of the dielectric film 603 is less than the thickness of the defect-filling film 604B, which fills the defects, in the thickness direction of the dielectric film 603, so the planar protective film 604A alone can be selectively removed. Furthermore, when silicon dioxide or silicon nitride is used as the third protective film, etching can be easily carried out in a SF6 or HF atmosphere.
The first and second exemplary embodiments employ a configuration for the dielectric film 603 in which impurity-doped layers are provided at equal intervals in the thickness direction of the dielectric film 603 using ASB-ALD. In the third exemplary embodiment, as shown in
In this exemplary embodiment also, the impurity-doped layers 603B are formed by means of ASB-ALD and crystallization of the dielectric film proceeds over the whole of the thickness direction. It is therefore possible to restrict an increase in the leakage current under a high temperature by filling the defects 610 using the defect-filling film 604B while increasing the dielectric constant of the dielectric film 603 in the same way as in the first and second exemplary embodiments. It should be noted that in this exemplary embodiment, the second dielectric film 603b is disposed on the upper electrode 606 side, but this is not limiting and it may equally be disposed on the lower electrode 601 side. Furthermore, it may be offset towards the central portion. The planar protective film 604A may be removed in the same way as in
In the third exemplary embodiment, the second dielectric film 603b comprising the impurity-doped layers 603B formed by ASB-ALD are unevenly distributed in the dielectric film 603, and the impurity-doped layers 603B within the second dielectric film 603b are disposed at equal intervals in the thickness direction within the second dielectric film 603b. In the fourth exemplary embodiment, as shown in
In the first to fourth exemplary embodiments, at least the impurity-doped layers 603B formed by ASB-ALD are contained in the dielectric film 603. In this exemplary embodiment, as shown in
Furthermore, the description above relates to a case in which titanium nitride (TiN) is used for the upper and lower electrodes of the capacitor, but this is not limiting and other metallic materials which can form an MIM capacitance which is useful for a high-capacitance capacitor may be employed, in particular materials exhibiting a greater work function, for example those which have a higher work function than 5.1 eV such as Pt, Ru and RuO2, for example, may be used. TiN which can be formed by CVD that has excellent properties of covering differences in level is preferably used for the cylindrical (crown-type) lower electrode illustrated in the exemplary embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-106832 | May 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/062823 | 5/14/2014 | WO | 00 |
