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Patent US6291290 - Thin film capacitor with an improved top electrode and method of forming the ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA method of making a top electrode for a thin film capacitor with a multi-layer structure that includes a high dielectric oxide layer, a first conductive layer on the high dielectric oxide layer and having a high formability to a reactive ion etching, and a second conductive layer on the first conductive...http://www.google.com/patents/US6291290?utm_source=gb-gplus-sharePatent US6291290 - Thin film capacitor with an improved top electrode and method of forming the sameAdvanced Patent SearchPublication numberUS6291290 B1Publication typeGrantApplication numberUS 09/257,254Publication dateSep 18, 2001Filing dateFeb 25, 1999Priority dateFeb 25, 1998Fee statusPaidAlso published asCN1231973C, CN1236994A, US6380580, US20020030218Publication number09257254, 257254, US 6291290 B1, US 6291290B1, US-B1-6291290, US6291290 B1, US6291290B1InventorsKoji AritaOriginal AssigneeNec CorporationExport CitationBiBTeX, EndNote, RefManPatent Citations (4), Referenced by (10), Classifications (12), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetThin film capacitor with an improved top electrode and method of forming the same
US 6291290 B1Abstract
A method of making a top electrode for a thin film capacitor with a multi-layer structure that includes a high dielectric oxide layer, a first conductive layer on the high dielectric oxide layer and having a high formability to a reactive ion etching, and a second conductive layer on the first conductive layer, the second conductive layer having a high formability to the reactive ion etching. The first conductive layer is deposited with a lower deposition rate than the second conductive layer. An interface between the first conductive layer and the high dielectric oxide layer is such that a density of a leak current across the interface is suppressed at not higher than 1�10−8 A/cm2 upon applying a voltage of 2V across the dielectric oxide layer after the multi-layer structure has been subjected to a heat treatment at 350� C.
What is claimed is: 1. A method of forming a top electrode on a high dielectric oxide layer of a thin film capacitor, said method comprising the steps of:
carrying out a deposition of a conductive material having a formability to a reactive ion etching under a first deposition condition of a first deposition rate to deposit a first conductive layer on said high dielectric oxide layer; and continuing said deposition the same conductive material under a second deposition condition of a second deposition rate which is higher than said first deposition rate to deposit a second conductive layer on said first conductive layer, wherein said first deposition rate is sufficiently low to prevent causing any substantive damage to a top surface of said high dielectric oxide layer and said second deposition rate is sufficiently high to shorten deposition time and to cause damage to said high dielectric oxide layer if said second conductive layer were deposited on the top surface of said high dielectric oxide layer, wherein an interface between said first conductive layer and said high dielectric oxide layer is such that a density of a leak current across said interface is suppressed at not higher than 1�10−8 A/cm2 upon applying a voltage of 2 V across said dielectric oxide layer after said multi-layer structure has been subjected to a heat treatment at 350� C. 2. The method as claimed in claim 1, wherein said first conductive layer is deposited at said first deposition rate by a first sputtering process with applying a target with a first power and then said second conductive layer is deposited at said second deposition rate by a second sputtering process with applying said target with a second power which is higher than said first power.
3. The method as claimed in claim 2, wherein said first power is less than 1.7 W/cm 2, and said second power is more than 1.7 W/cm2.
4. The method as claimed in claim 1, wherein said first and second conductive layers are deposited by a chemical vapor deposition process under a first deposition condition and a second deposition condition.
5. The method as claimed in claim 1, wherein said first and second conductive layers are deposited by an evaporation process under a first deposition condition and a second deposition condition.
6. The method as claimed in claim 1, wherein said conductive material includes at least any one of Ru, RuO2, Ir, IrO2, and combinations or mixtures thereof.
7. The method as claimed in claim 1, wherein said first conductive layer has a thickness of about one-tenth of a thickness of said second conductive layer.
8. A method of forming a top electrode on a high dielectric oxide layer of a thin film capacitor, said method comprising the steps of:
carrying out a first deposition of a first conductive material having a formability to a reactive ion etching under a first deposition condition of a first deposition rate to deposit a first conductive layer on said high dielectric oxide layer; and carrying out a second deposition of a second conductive material having a formability to said reactive ion etching under a second deposition condition of a second deposition rate which is higher than said first deposition rate to deposit a second conductive layer on said first conductive layer, wherein said first deposition rate is sufficiently low to prevent causing any substantive damage to a top surface of said high dielectric oxide layer and said second deposition rate is sufficiently high to shorten deposition time and to cause damage to said high dielectric oxide layer if said second conductive layer were deposited on the top surface of said high dielectric oxide layer, wherein an interface between said first conductive layer and said high dielectric oxide layer is such that a density of a leak current across said interface is suppressed at not higher than 1�10−8 A/cm2 upon applying a voltage of 2 V across said dielectric oxide layer after said multi-layer structure has been subjected to a heat treatment at 350� C. 9. The method as claimed in claim 8, wherein said first conductive layer is deposited at said first deposition rate by a first sputtering process with applying a target with a first power and then said second conductive layer is deposited at said second deposition rate by a second sputtering process with applying said target with a second power which is higher than said first power.
10. The methods as claimed in claim 9, wherein said first power is less than 1.7 W/cm2, and said second power is more that 1.7 W/cm2.
11. The method as claimed in claim 8, wherein said first and second conductive layers are deposited by a chemical vapor deposition process under a first deposition condition and a second deposition condition.
12. The method as claimed in claim 8, wherein said first and second conductive layers are deposited by an evaporation process under a first deposition condition and a second deposition condition.
13. The method as claimed in claim 8, wherein said conductive material includes at least any one of Ru, RuO2, Ir, IrO2, and combinations or mixtures thereof.
14. The method as claimed in claim 8, wherein said first conductive layer has a thickness of about one-tenth of a thickness of said second conductive layer.
The present invention relates to a thin film capacitor and a method of forming the same and more particularly to a thin film capacitor with an improved top electrode suitable for advanced semiconductor devices and advanced integrated circuits and a method of forming the same at high throughput and high yield.
The thin film capacitors having the high dieclectric oxide layer sandwiched between top and bottom electrodes have been investigated and reported mostly about improvements in capacitance characteristic and current leakage characteristics both of which are important factors for the thin film capacitors.
A prior art of the thin film capacitor was reported in Japanese Journal of Applied Physics, Vol. 36, No. 9B, pp. 5860-5865. The thin film capacitor has a Pt/(Ba, Sr)TiO3/Pt structure, wherein a (Ba, Sr)TiO3 dielectric layer is deposited by a radio frequency magnetron sputtering method whilst Pt top and bottom electrodes are deposited by a DC sputtering method. There was investigated variations in current leakage of the thin film capacitor over deposition conditions for a second DC sputtering process for the Pt top electrode. It was confirmed that under application of a voltage of −1 V, the leakage of current at a DC power of 0.2 kW is smaller by two or three digits than at DC powers of 0.5 kW and 1.0 kW. The reason why the leakage of current is reduced is that the roughness of an interface of the top electrode with the high dielectric oxide film reduces a Schottky barrier height of the interface between the top electrode and the high dielectric oxide film.
In general, the top electrode as formed receives a heat treatment such as an anneal at a temperature of not less than 350� C. for formation of interconnections extending over the thin film capacitor or a passivation film overlying the thin film capacitor, for which reason if a highly oxidizable metal or highly diffusable metal is used for the top electrode, then a thermal oxidation of the metal may appear whereby the current leakage characteristic is deteriorated.
Similarly to the case of Pt, the use of other materials such as Ru, RuO2, Ir and IrO2 for the top electrode material also causes the same problem with drops in the deposition rate and the adhesiveness of the top electrode even the drop of the sputter power may improve the current leakage characteristics of the thin film capacitor.
Further, Japanese laid-open paten publication No. 8-17806 addresses a method of forming a thin film capacitor having the Pt/(Ba, Sr)TiO3/Pt structure but is silent on the structure of the top electrode and on any influence to the capacitance characteristic by use of Pt for the top electrode.
In the above circumstances, it had been required to develop a novel thin film capacitor with an improved top electrode structure which makes the thin film capacitor free from any problems and disadvantages as described above and a novel method of forming the same.
It is further object of the present invention to provide a novel thin film capacitor with an improved top electrode structure free from the problems with oxidation of an interface of the top electrode with a high dielectric oxide layer due to a heat treatment of not higher than 350� C.
It is a further more object of the present invention to provide a novel thin film capacitor with an improved top electrode structure free from the problems with diffusion of a metal of the top electrode into a high dielectric oxide layer due to a heat treatment of not higher than 350� C.
The first aspect of the present invention provides a multi-layer structure comprising: a high dielectric oxide layer; a first conductive layer on the high dielectric oxide layer, and processing a high formability to a reactive ion etching; and a second conductive layer on the first conductive layer, and the second conductive layer processing a high formability to the reactive ion etching, wherein an interface between the first conductive layer and the high dielectric oxide layer is such that a density of a leak current across the interface is suppressed at not higher that 1�10−8 A/cm2 upon applying a voltage of 2 V across the dielectric oxide layer after the multi-layer structure has been subjected to a heat treatment at 350� C.
The second aspect of the present invention provides a top electrode structure of a thin film capacitor, the structure comprising: a first conductive layer on a high dielectric oxide layer, and processing a high formability to a reactive ion etching; and a second conductive layer on the first conductive layer, and processing a high formability to the reactive ion etching, wherein an interface between the first conductive layer and the high dielectric oxide layer is such that a density of a leak current across the interface is suppressed at not higher that 1�10−8 A/cm2 upon applying a voltage of 2 V across the dielectric oxide layer after the multi-layer structure has been subjected to a heat treatment at 350� C.
The third aspect of the present invention provides a method of forming a top electrode on a high dielectric oxide layer of a thin film capacitor. The method comprises the steps of: carrying out a deposition of a conductive material having a formability to a reactive ion etching under a first deposition condition of a first deposition rate to deposit a first conductive layer on the high dielectric oxide layer; and continuing the deposition the same conductive material under a second deposition condition of a second deposition rate which is higher that the first deposition rate to deposit a second conductive layer on the first conductive layer, wherein an interface between the first conductive layer and the high dielectric oxide layer is such that a density of a leak current across the interface is suppressed at not higher than 1�10−8 A/cm2 upon applying a voltage of 2 V across the dielectric oxide layer after the multi-layer structure has been subjected to a heat treatment at 350� C.
The fourth aspect of the present invention provides a method of forming a top electrode on a high dielectric oxide layer of a thin film capacitor. The method comprises the steps of: carrying out a first deposition of a first conductive material having a formability to a reactive ion etching under a first deposition condition of a first deposition rate to deposit a first conductive layer on the high dielectric oxide layer; and carrying out a second deposition of a second conductive material having a formability to the reactive ion etching under a second deposition condition of a second deposition rate which is higher that the first deposition rate to deposit a second conductive layer on the first conductive layer, wherein an interface between the first conductive layer and the high dielectric oxide layer is such that a density of a leak current across the interface is suppressed at not higher than 1�10−8 A/cm2 upon applying a voltage of 2 V across the dielectric oxide layer after the multi-layer structure has been subjected to a heat treatment at 350� C.
FIG. 4 is a fragmentary cross sectional elevation view illustrative of a novel thin film capacitor with an improved top electrode structure in a first embodiment in accordance with the present invention.
FIG. 6 is block diagram illustrative of a structure of a sputtering system as one example of the available sputtering systems for depositing the electrodes of the novel thin film capacitor.
The first aspect of the present invention provides a multi-layer structure comprising: a high dielectric oxide layer; a first conductive layer on the high dielectric oxide layer, and processing a high formability to a reactive ion etching; and a second conductive layer on the first conductive layer, and the second conductive layer processing a high formability to the reactive ion etching, wherein an interface between the first conductive layer and the high dielectric oxide layer is such that a density of a leak current across the interface is suppressed at not higher than 1�10−8 A/cm2 upon applying a voltage of 2 V across the dielectric oxide layer after the multi-layer structure has been subjected to a heat treatment at 350� C.
Second the top electrode structure makes it possible to shorten the time for deposition of the top electrode for improvement in throughput of the thin film capacitor. The first conductive layer is deposited at a sufficiently low deposition rate for prevent the top surface of the high dielectric oxide layer from receiving any substantive damage, whilst the second conductive layer is deposited at a sufficiently high deposition rate for shortening a total time for depositions of the first and second conductive layers.
It is also preferable that the first conductive layer has a thickness of about one-tenth of the thickness of the second conductive layer. It is also preferable that the first conductive layer has a thickness of about one-tenth of a thickness of the second conductive layer. It is not essential for the present invention to limit the thickness of the first conductive layer in contact with the high dielectric oxide layer. It is, however, preferable that the first conductive layer is very thin. The thickness of the first conductive layer is preferably not more that 10 nanometers, and more preferably 5 nanometers. It is also not essential for the present invention to limit the thickness of the second conductive layer separated from the high dielectric oxide layer. It is, however, preferable that the thickness of the second conductive layer is thicker by about ten times that the first conductive layer.
The above above thin film capacitor provides the following advantages.
Fist, the above novel thin film capacitor has the good electric characteristics. The material of the first conductive layer in contact with the high dielectric oxide layer is deposited at a low deposition rate under a low deposition power to prevent reaction on the interface between the first conductive layer and the high dielectric oxide layer or prevent the top surface of the high dielectric oxide layer from receiving any substantive damage.
It is also referable that the first conductive layer and the second conductive layer are made of different conductive materials, each of which includes at least any one selected from the group consisting of Ru, RuO2, Ir, IrO2, and alloys thereof because those materials have high formability to the reactive ion etching. This allows a further substantive scaling down of the thin film capacitor 1 with a high accurate dimension to be defined by the reactive ion etching. This further substantive scaling down of the thin film capacitor 1 allows an increase in density of integration of the semiconductor devices and integrated circuits.
It is also referable that the first conductive layer has a thickness of about one-tenth of a thickness of the second conductive layer. It is also preferable that the first conductive layer has a thickness of about one-tenth of a thickness of the second conductive layer. It is not essential for the present invention to limit the thickness of the first conductive layer in contact with the high dielectric oxide layer. It is, however, preferable that the first conductive layer is very thin. The thickness of the first conductive layer is preferably not more that 10 nanometers, and more preferably 5 nanometers. It is also not essential for the present invention to limit the thickness of the second conductive layer separated from the high dielectric oxide layer. It is, however, preferable that the thickness of the second conductive layer is thicker by about ten times than the first conductive layer.
The third, aspect of the present invention provides a method of forming a top electrode on a high dielectric oxide layer of a thin film capacitor. The method comprises the steps of: carrying out a deposition of a conductive material having a formability to a reactive ion etching under a first deposition condition of a first deposition rate to deposit a first conductive layer on the high dielectric oxide layer; and continuing the deposition the same conductive material under a second deposition condition of a second deposition rate which is higher than the first deposition rate to deposit a second conductive layer on the first conductive layer, wherein an interface between the first conductive layer and the high dielectric oxide layer is such that a density of a leak current across the interface is suppressed at not higher than 1�10−8 A/cm2 upon applying a voltage of 2 V across the dielectric oxide layer after the multi-layer structure has been subjected to a heat treatment at 350� C.
Third, the first conductive layer intervening between the second conductive layer and the high dielectric oxide layer prevents peeling of the top electrode from the high dielectric oxide layer for improvement in the yield of the thin film capacitor,
It is also preferable that the first power is less than 1.7 W/cm2, and the second power is more than 1.7 W/cm2. It is not essential for the present invention to limit the power level to be applied to the sputter target, but it is preferable to apply a low power level of, for example, 1.7 W/cm2 to the sputter target for a low rate deposition of the first conductive layer in contact with the high dielectric oxide layer in order to prevent the surface of the high dielectric oxide layer from receipt of any substantive damage. In this case, the thin film capacitor shows the good current leakage characteristics such that the leak current density remains suppressed at not higher than 1�10−8 A/cm2 under applications to the target with the driving voltage in the range of 0 V to 2 V. If, however, the sputter target is applied with a higher power lever than 1.7 W/cm2 for a high rate deposition of the first conductive layer in contact with the high dielectric oxide layer in order to provide the surface of the high dielectric oxide layer from receipt of any substantive damage, then the thin film capacitor shows the undesirable current leakage characteristics such that the leak current density shows a rapid increase from 1�10−8 A/cm2 as the driving voltage to be applied to the target is increased from 1.5 V. Consequently, it is preferable that the power level applied to the sputter target for a low rate deposition of the first conductive layer in contact with the high dielectric oxide layer is suppressed at, for example, not higher than 1.7 W/cm2.
The fourth aspect of the present invention provides a method of forming a top electrode on a high dielectric oxide layer of a thin film capacitor. The method comprises the steps of: carrying out a first deposition of a first conductive material having a formability to a reactive ion etching under a first deposition condition of a first deposition rate to deposit a first conductive layer on the high dielectric oxide layer; and carrying out a second deposition of a second conductive material having a formability to the reactive ion etching under a second deposition condition of a second deposition rate which is higher than the first deposition rate to deposit a second conductive layer on the first conductive layer, wherein an interface between the first conductive layer and the high dielectric oxide layer is such that a density of a leak current across the interface is suppressed at not higher than 1�10−8 A/cm2 upon applying a voltage of 2 V across the dielectric oxide layer after the multi-layer structure has been subjected to a heat treatment at 350� C.
It is also preferable that the first power is less than 1.7 W/cm2, and the second power is more than 1.7 W/cm2. It is not essential for the present invention to limit the power level to be applied to the sputter target, but it is preferable to apply a low power level of, for example, 1.7 W/cm2 to the sputter target for a low rate deposition of the first conductive layer in contact with the high dielectric oxide layer in order to prevent the surface of the high dielectric oxide layer from receipt of any substantive damage. In this case, the thin film capacitor shows the good current leakage characteristics such that the leak current density remains suppressed at not higher than 1�10−8 A/cm 2 under applications to the target with the driving voltage in the range of 0 V to 2 V. If, however, the sputter target is applied with a higher power level than 1.7 W/cm2 for a high rate deposition of the first conductive layer in contact with the high dielectric oxide layer in order to provide the surface of the high dielectric oxide layer from receipt of any substantive damage, then the thin film capacitor shows the undesirable current leakage characteristics such that the leak current density shows a rapid increase from 1�10−8 A/cm2 as the driving voltage to be applied to the target is increased from 1.5 V. Consequently, it is preferable that the power level applied to the sputter target for a low rate deposition of the first conductive layer in contact with the high dielectric oxide layer is suppressed at, for example, not higher than 1.7 W/cm2.
Namely, it is preferable that the first voltage level applied to the target for a low rate deposition of the first conductive layer is set not higher then 1.7 W/cm2, whilst the second voltage level applied to the target for a high rate deposition of the second conductive layer is set higher that 1.7 W/cm2.
It is also preferable that the first conductive layer has a thickness of about one-tenth of the thickness of the second conductive layer. It is not essential for the present invention to limit the thickness of the first conductive layer in contact with the high dielectric oxide layer. It is, however, preferable that the first conductive layer is very thin. The thickness of the first conductive layer is preferably not more than 10 nanometers, and more preferably 5 nanometers. It is also not essential for the present invention to limit the thickness of the second conductive layer separated from the high dielectric oxide layer. It is, however, preferable that the thickness of the second conductive layer is thicker by about ten times than the first conductive layer.
FIG. 1 is a fragmentary across sectional elevation view illustrative of a novel thin film capacitor with an improved top electrode in accordance with the foregoing present inventions. A novel thin film capacitor 1 has the following structure. A bottom electrode layer 102 is provided on a semiconductor substrate 101. A high dielectric oxide layer 103 is provided on the bottom electrode layer 102. A top electrode 105 is provided on a high dielectric oxide layer 103. The top electrode 105 further comprises a conductive layer 104 made of a single conductive material which shows a formability to a reactive ion etching. The conductive layer 104 further comprises a first part 104 a which has been deposited at a first deposition rate and a second part 104 b which has been deposited on the first part 104 a at a second deposition rate which is higher than the first deposition rate. The first part 104 a and the second part 104 b are made of the same conductive material but are deposited at different deposition rates from each other so that the second deposition rate of the second part 104 b is higher than the first deposition rate of the first part 104 a. After the above thin film capacitor 1 having the top electrode layer 104 is subjected to a heat treatment at 350� C., the above thin film capacitor 1 shows a good leak current density characteristic such that the leak current density remains suppressed yet not higher than 1�10−8 A/cm2 under application of a driving voltage in the range of 0 V to 2 V.
The conductive layer 104 may be deposited by any one of a sputtering method, a chemical vapor deposition method and an evaporation method, provided that the second deposition rate of the second part 104 b is higher than the first deposition rate of the first part 104 a. When the sputtering method is applied to deposit the top electrode 105, the first part 104 a is deposited by applying a target with a first power and then the second part 104 b is deposited by applying the same target with a second power which is higher than the first power so that the second deposition rate of the second part 104 b is higher than the first deposition rate of the first part 104 a. It is not essential for the present invention to limit the power level to be applied to the sputter target, but it is preferable to apply a low power level of, for example, 1.7 W/cm2 to the sputter target for a low rate deposition of the first part 104 a in contact with the high dielectric oxide layer 103 in order to prevent the surface of the high dielectric oxide layer 103 from receipt of any substantive damage. In this case, the thin film capacitor shows the good current leakage characteristics such that the leak current density remains suppressed at not higher than 1�10−8 A/cm2 under applications to the target with the driving voltage in the range of 0 V to 2 V. If, however, the sputter target is applied with a higher power level than 1.7 W/cm2 for a high rate deposition of the first part 104 a in contact with the high dielectric oxide layer 103 in order to provide the surface of the high dielectric oxide layer 103 from receipt of any substantive damage, then the thin film capacitor shows the undesirable current leakage characteristics such that the leak current density shows a rapid increase from 1�10−8 A/cm2 as a driving voltage to be applied to the target is increased from 1.5 V. Consequently, it is preferable that the power level applied to the sputter target for a low rate deposition of the first part 104 a in contact with the high dielectric oxide layer 103 is suppressed at, for example, not higher than 1.7 W/cm2.
It is also preferable that a first thickness of the first part 104 a is much thinner than a second thickness of the second part 104 b. For example, the first thickness of the first part 104 a is about one tenth of the second thickness of the second part 104 b. The above novel thin film capacitor 1 with the improved top electrode 105 may be fabricated as follows. The bottom electrode 102 is deposited on the semiconductor substrate 101. The high dielectric oxide layer 103 is deposited on the bottom electrode 102. The top electrode 105 is then deposited on the high dielectric oxide layer 103, wherein the first part 104 a is deposited on the high dielectric oxide layer 103 at a lower deposition rate before the second part 104 b is deposited on the first part 104 a at a higher deposition rate. The first part 104 a and the second part 104 b are made of the same material such as Ru or Ir which has a high formability to the reactive ion etching. However, the first part 104 a in contact with the high dielectric oxide layer 103 is deposited at a low deposition rate by applying the sputter target with the low power level of not higher than 1.7 W/cm2, whilst the second part 104 b separated from the high dielectric oxide layer 103 is deposited at a high deposition rate by applying the sputter target with the high power level of higher than 1.7 W/cm2.
It is also not essential for the present invention to limit the thickness of the second part 104 b separated from the high dielectric oxide layer 103. It is, however, preferable that the thickness of the second part 104 b is thicker by about ten times than the first part 104 a. The top electrode 105 further comprises a conductive layer 104 made of a single conductive material which shows a formability to a reactive ion etching. The conductive layer 104 further comprises a first part 104 a which has been deposited at a first deposition rate and a second part 104 b which has been deposited on the first part 104 a at a second deposition rate which is higher than the first deposition rate. The first part 104 a and the second part 104 b are made of the same conductive material but are deposited at different deposition rates from each other so that the second deposition rate of the second part 104 b is higher than the first deposition rate of the first part 104 a. After the above thin film capacitor 1 having the top electrode layer 104 is subjected to a heat treatment at 350� C., the above thin film capacitor 1 shows a good leak current density characteristic such that the leak current density remains suppressed at not higher than 1�10−8 A/cm2 under application of a driving voltage in the range of 0 V to 2 V.
It is preferable that the conductive layer 104 includes at least any one of Ru, RuO2, Ir, IrO2, and alloys thereof because of those materials have high formability to the reactive ion etching. This allows a further substantive scaling down of the thin film capacitor 1 with a high accurate dimension to be defined by the reactive ion etching. This further substantive scaling down of the thin film capacitor 1 allows an increase in density of integration of the semiconductor devices and integrated circuits.
FIG. 2 is a fragmentary across sectional elevation view illustrative of another novel thin film capacitor with an improved top electrode in accordance with the foregoing present inventions. A novel thin film capacitor 1 has the following structure. A bottom electrode layer 102 is provided on a semiconductor substrate 101. A high dielectric oxide layer 103 is provided on the bottom electrode layer 102. A top electrode 105 is provided on the high dielectric oxide layer 103. The top electrode 105 further comprises a first conductive layer 107 made of a first conductive material which shows a formability to a reactive ion etching and a second conductive layer 108 made of a second conductive material which shows a formability to the reactive ion etching. The first conductive layer 107 is formed on the high dielectric oxide layer 103 and the second conductive layer 108 is formed on the first conductive layer 107. The first conductive layer 107 is deposited at a first deposition rate and the second conductive layer 108 is deposited at a second deposition rate which is higher than the first deposition rate. The first conductive layer 107 and the second conductive layer 108 are made of different conductive materials from each other and are deposited at different deposition rates wherein the deposition rate of the second conductive layer 108 is higher than the deposition rate of the first conductive layer 107. After the above thin film capacitor 2 having the top electrode layer 105 comprising the first conductive layer 107 and the second conductive layer 108 is subjected to a heat treatment at 350� C., the above thin film capacitor 1 shows a good leak current density characteristic such that the leak current density remains suppressed at not higher than 1�10−8 A/cm2 under application of a driving voltage in the range of 0 V to 2 V.
It is preferable that the first conductive layer 107 includes at least any one of Ru, RuO2, Ir, IrO2, and alloys thereof and the second conductive layer 108 also includes at least other one of Ru, RuO2, Ir, IrO2, and alloys thereof because those materials have high formability to the reactive ion etching. This allows a further substantive scaling down of the thin film capacitor 1 with a high accurate dimension to be defined by the reactive ion etching. This further substantive scaling down of the thin film capacitor 2 allows an increase in density of integration of the semiconductor devices and integrated circuits.
When the sputtering method is applied to deposit the top electrode 105, the first conductive layer 107 is deposited by applying a target with a first power and then the second conductive layer 108 is deposited by applying the same target with a second power which is higher than the first power so that the second deposition rat of the second conductive layer 108 is higher than the first deposition rate of the first conductive layer 107.
It is not essential for the present invention to limit the power level to be applied to the sputter target, but it is preferable to apply a low power level of, for example, 1.7 W/cm2 to the sputter target for a low rate deposition of the first conductive layer 107 in contact with the high dielectric oxide layer 103 in order to prevent the surface of the high dielectric oxide layer 103 from receipt of any substantive damage. In this case, the thin film capacitor shows the good current leakage characteristics such that the leak current density remains suppressed at not higher than 1�10−8 A/cm2 under applications to the target with the driving voltage in the range of 0 V to 2 V. If, however, the sputter target is applied with a higher power level than 1.7 W/cm2 for a high rate deposition of the first conductive layer 107 in contact with the high dielectric oxide layer 103 in order to provide the surface of the high dielectric oxide layer 103 from receipt of any substantive damage, then the thin film capacitor shows the undesirable current leakage characteristics such that the leak current density shows a rapid increase from 1�10−8 A/cmas the driving voltage to be applied to the target is increased from 1.5 V. Consequently, it is preferable that the power level applied to the sputter target for a low rate deposition of the first conductive layer 107 in contact with the high dielectric oxide layer 103 is suppressed at, for example, not higher than 1.7 W/cm2.
It is also referable that a first thickness of the first conductive layer 107 is much thinner than a second thickness of the second conductive layer 108. For example, the first thickness of the first conductive layer 107 is about one tenth of the second thickness of the second conductive layer 108.
The above novel thin film capacitor 2 with the improved top electrode 105 may be fabricated as follows. The bottom electrode 102 is deposited on the semiconductor substrate 101. The high dielectric oxide layer 103 is deposited on the bottom electrode 102. The top electrode 105 is then deposited on the high dielectric oxide layer 103, wherein the first conductive layer 107 is deposited on the high dielectric oxide layer 103 at a lower deposition rate before the second conductive layer 108 is deposited on the first conductive layer 107 at a higher deposition rate. The first conductive layer 107 is made of Ru which has a high formability to the reactive ion etching and the second conductive layer 108 is made of Ir which also has a high formability to the reactive ion etching. Further, the first conductive layer 107 in contact with the high dielectric oxide layer 103 is deposited at a low deposition rate by applying the sputter target with the low power level of not higher than 1.7 W/cm2, whilst the second conductive layer 108 separated from the high dielectric oxide layer 103 is deposited at a high deposition rate by applying the sputter target with the high power level of higher than 1.7 W/cm2.
The top electrode 105 further comprises a first conductive layer 107 made of a first conductive material which shows a formability to a reactive ion etching and a second conductive layer 108 made of a second conductive material which shows a formability to the reactive ion etching. The first conductive layer 107 is formed on the high dielectric oxide layer 103 and the second conductive layer 108 is formed on the first conductive layer 107. The first conductive layer 107 is deposited at a first deposition rate and the second conductive layer 108 is deposited at a second deposition rate which is higher than the first deposition rate. The first conductive layer 107 and the second conductive layer 108 are made of different conductive materials from each other and are deposited at different deposition rates wherein the deposition rate of the second conductive layer 108 is higher than the deposition rate of the first conductive layer 107. After the above thin film capacitor 2 having the top electrode layer 105 comprising the first conductive layer 107 and the second conductive layer 108 is subjected to a heat treatment at 350� C., the above thin film capacitor 1 shows a good leak current density characteristic such that the leak current density remains suppressed at not higher than 1�10−8 A/cm2 under application of a driving voltage in the range of 0 V to 2 V.
It is preferable that the first conductive layer 107 includes at least any one of Ru, RuO2, Ir, IrO2, and alloys thereof and the second conductive layer 108 also includes at least other one of Ru, RuO2, Ir, IrO2, and alloys thereof because those materials have high formability to the reactive ion etching. This allows a further substantive scaling down of the thin film capacitor 1 with a high accurate dimension to be defined by the reactive ion etching. This further substantive scaling down of the thin film capacitor 2 allows an increase in density of integration of the semiconductor devises and integrated circuits.
An n-type silicon substrate 11 having a resistivity of 0.1 Ωcm was prepared. A bottom electrode 12 of RuO2 having a thickness of 200 nanometers was deposited on the silicon substrate 11 by a first DC sputtering method. An electron cyclotron resonance chemical vapor deposition method was carried out by use of Ba(DPM)2, Ti(i-OC3H7) and oxygen gases under conditions of a substrate temperature of 500� C., a gas pressure of 7 mTorr, and a plasma excitation microwave power of 500 W, thereby depositing a (Ba, Sr)TiO3 high dielectric oxide layer 13 with a thickness of 30 nanometers on the bottom electrode 12.
It was confirmed that the first deposition condition for depositing the first part 14 a contributes to suppress the peeling of the top electrode 15 from the (Ba, Sr)TiO3 high dielectric oxide layer 13. This results in improvement in reliability of the thin film capacitor.
The adhesiveness was evaluated by varying the thickness of the first part 104 a in the range of 5-20 nanometers. It was also confirmed that the adhesiveness is improved as the thickness of the first part 14 a is made thin. The thickness of the first part 14 a is not more than 10 nanometers, and preferably about 5 nanometers.
FIG. 5 is a diagram illustrative of variations in density of leak current of the novel thin film capacitor with the improved top electrode structure and the conventional thin film capacitor. It was shown that the leak current characteristics of the novel thin film capacitor are remarkably improved as compared to the leak current characteristics of the conventional thin film capacitor.
As the driving voltage applied to the thin film capacitor is over 1.5 V, the conventional thin film capacitor shows the undesirable current leakage characteristics such that the leak current density shows a rapid increase from 1�10−8 A/cm2.
FIG. 5 apparently shows that when the prior art was applied, then the current leakage characteristics of the conventional thin film capacitor are not good, for example, a leak current density of not less than 1�10−6 A/cm2 upon zero driving voltage application to the thin film capacitor. Upon increase in the driving voltage to the thin film capacitor, the thin film capacitor shows a simple increase in the leak current density. In contrast to the conventional thin film capacitor, the novel thin film capacitor with the improved double-layered top electrode shows good current leakage characteristics, for example, a low leak current density of not less than 1�10−8 A/cm2 upon zero driving voltage application to the thin film capacitor. Upon increase in the driving voltage from 0 V to about 2 V, the above low leak current density almost remains unchanged. For example, under the application of the driving voltage of 2 V to the novel thin film capacitor, the leak current density remains not less than 1�10−8 A/cm2. Namely, the novel thin film capacitor shows the stable and good leak characteristics.
The adhesiveness of the Pt first conductive layer 14 to the (Ba, Sr)TiO3 high dielectric oxide layer 13 was evaluated by varying the thickness of the Pt first conductive layer 14 in the range of 5-20 nanometers. It was confirmed that as the thickness of the Pt first conductive layer 14 is reduced, the adhesiveness of the Pt first conductive layer 14 to the (Ba, Sr)TiO3 high dielectric oxide layer 13 is improved. For example, a preferable thickness range of the Pt first conductive layer 14 is not thicker than 10 nanometers. In contrast, the thin film capacitor shows the good current leakage characteristics such that the leak current density remains suppressed at not higher than 1�10−8 A/cm2 under applications to the target with the driving voltage in the range of 0 V to 3 V.
Available sputtering systems for depositing the electrodes of the novel thin film capacitor are not limited to a specific one. FIG. 6 is a block diagram illustrative of a structure of a sputtering system as one example of the available sputtering systems for depositing the electrodes of the novel thin film capacitor. The sputtering system 20 has a vacuum changer 2 which accommodates a substrate holder 3 on which substrates 4 are mounted for forming a novel thin film capacitor. The vacuum chamber 2 also accommodates a high frequency electrode plate 5 with a sputter target 6 which faces to the substrate 4 on the substrate holder 3 and is distanced from the substrates 4 on the substrate holder 3. It is of course possible to provide the high frequency electrode plate 5 with plural different sputter targets 6. It is alternatively possible to provide a plurality of the high frequency electrode plate 5 so that different targets 6 are provided on the plural high frequency electrode plates 5. A shutter 7 may optionally be provided between the substrate holder 3 and the high frequency electrode plate 5. An inert gas supplier 21 is further provided for supplying an inert gas into the vacuum chamber 2. A vacuum pump 22 is also provided for causing a vacuum of the vacuum chamber 2. A high frequency power supply 10 and a power controller 9 are provided for supplying a high frequency power through the power controller 9 to the high frequency electrode plate 5 under control of the power, whereby the power controller 9 controls the power to be applied to the target 6 on the high frequency electrode plate 5. Since the deposition rate depends on a voltage corresponding to the power to be applied to the target 6, then the power controller 9 controls the deposition rate. A control unit 8 is further provided which is connected to both the vacuum pump 22 and the power controller 9 for controlling the deposition time of sputtering process and a degree of the vacuum in the vacuum chamber 2.
In place of (Ba, Sr)TiO3, materials represented by a chemical formula ABO3 are available for the high dielectric oxide layer, wherein A may comprise at least any one selected from the group consisting of Ba, Sr, Pb, Ca, La, Li and K, and B may comprise at least any one selected from the group consisting of Ti, Zr, Ta, Nb, Mg, Fe, Zn and W. For example, there are available SrTiO3, (Sr, Ca)TiO3, (Ba, Sr, Ca)TiO3, PbTiO3, Pb(Zr, Ti)O3, (Pb, La)(Zr, Ti)O3, Pb(Mg, Nb)O3, Pb(Mg, W)O3, Pb(Zn, Nb)O3LiTaO3, LiNbO3, KTaO3, KTaO3, KTaO3, and KNbO3. Further, there are available materials represented by the chemical formula (Bi2O2)(Am−1BmO3m+1) (m=1, 2, 3, 4, 5), wherein A may comprise at least any one selected from the group consisting of Ba, Sr, Pb, Ca, K and Bi, and B may comprise at least any one selected from the group consisting of Nb, Ta, Ti, and W. For example, Ba4Ti3O12, SrBa2Ta2O9, and SrBa2Nb2O9 are also available. In addition, Ta2O5 is further available which has a chemical composition different from those of the above chemical formula.
A second embodiment according to the resent invention will be described in detail with reference to FIG. 4 which is a fragmentary cross sectional elevation view illustrative of a novel thin film capacitor with an improved top electrode structure in a first embodiment in accordance with the present invention.
The adhesiveness was evaluated by varying the thickness of the first conductive layer 17 in the range of 5-20 nanometers. It was also confirmed that the adhesiveness is improved as the thickness of the first conductive layer 17 is made thin. The thickness of the first conductive layer 17 is not more than 10 nanometers, and preferably about 5 nanometers.
When the prior art was applied, then the current leakage characteristics of the conventional thin film capacitor are not good, for example, a leak current density of not less than 1�10−6 A/cm2 upon zero driving voltage application to the thin film capacitor. Upon increase in the driving voltage to the thin film capacitor, the thin film capacitor shows a simple increase in the leak current density. In contrast to the conventional thin film capacitor, the novel thin film capacitor with the improved double-layered top electrode shows good current leakage characteristics, for example, a low leak current density of not less than 1�10−8 A/cm2 upon zero driving voltage application to the thin film capacitor. Upon increase in the driving voltage from 0 V to about 2 V, the above low leak current density almost remains unchanged. For example, under the application of the driving voltage of 2 V to the novel thin film capacitor, the leak current density remains not less than 1�10−8 A/cm2. Namely, the novel thin film capacitor shows the stable and good leak characteristics.
The adhesiveness of the Ru first conductive layer 17 to the (Ba, Sr)TiO3 high dielectric oxide layer 13 was evaluated by varying the thickness of the Ru first conductive layer 17 in the range of 5-20 nanometers. It was confirmed that as the thickness of the Ru first conductive layer 17 is reduced, the adhesiveness of the Ru first conductive layer 17 to the (Ba, Sr)TiO3 high dielectric oxide layer 13 is improved. For example, a preferable thickness range of the Ru first conductive layer 17 is not thicker than 10 nanometers. In contrast, the thin film capacitor shows the good current leakage characteristics such that the leak current density remains suppressed at not higher then 1�10−8 A/cm2 under applications to the target with the driving voltage in the range of 0 V to 3 V.
The following descriptions will focus on possible modification to the above present invention. In this embodiment, the bottom electrode is made of RuO2. Nothwithstanding, conductive materials are available for the bottom electrode, which are capable of keeping conductivity in an oxygen atmosphere during the process for formation of the high dielectric oxide layer on the bottom electrode. For example, there are available for the bottom electrode material Ru, Ir, Re, Os, Rh, and oxides thereof as well as at least any one selected from the group of silicide compounds in addition at least any one selected from the group of Pt, Au, Ag, Pd, Ni, Co and alloys thereof.
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