JP3404099B2 - Method for manufacturing capacitor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a capacitor.

[0002]

2. Description of the Related Art A reduction in memory cell area is indispensable for high integration of LSIs. For example, in the case of a dynamic RAM capacitor, storage per unit area is caused by problems such as S / N of read signal and soft error. The amount of charge cannot be reduced in proportion to the cell area. Therefore, thinning of the capacitor insulating film, increasing the dielectric constant, and increasing the capacity by increasing the three-dimensional structure of the capacitor are being studied. However, the thermal oxide film (dielectric constant ε = 3.9) that has been used as a conventional capacitor insulating film has been studied. ) Or the thinning of the nitride film (ε = 7) has already reached the limit in terms of reliability and controllability, and it is necessary to use a material having a higher dielectric constant for higher integration.

The most noticeable material for such a material is tantalum oxide (Ta ₂ O ₅ , ε = 22), which has a high permittivity and a high withstand voltage and has a proven track record as a capacitor. W / Ta _{2 in} Sho 61-36963
O ₅ / Si (Metal-Insulator-Semiconductor = MI
S), Japanese Patent Application Laid-Open No. 62-84544, W / Ta ₂ O ₅ / Si ₃
N ₄ / Si (Metal-Insulator-Nitride-Semiconductor =
MINS), JP 60-152049 A, W / Ta ₂ O ₅ /
W (Metal-Insulator-Metal = MIM) is described.

However, in any case, if the tantalum oxide film is formed and then the upper electrode is formed as it is to form a capacitor, a large leak current will not be applied to the device. The cause of this leakage current is that carbon is mixed into the film from the raw material when the tantalum oxide film is formed by the chemical vapor deposition method using an organic metal raw material, and from the exhaust system when the film is formed by the sputtering method, It is considered that oxygen defects are present in the tantalum oxide film. On the other hand, there is already known a method of improving the breakdown voltage by annealing the formed tantalum oxide film in an oxygen atmosphere or in ozone irradiated with a mercury lamp and then in a dry oxygen atmosphere. It is noted that the withstand voltage of the tantalum oxide capacitor is remarkably improved by annealing in a dry oxygen atmosphere at the above high temperature.
It is described in Japanese Patent No. 963.

[0005]

The withstand voltage of the tantalum oxide capacitor is greatly improved by annealing in the active oxygen atmosphere or the high temperature oxygen atmosphere as described above.
-Type capacitors promote the growth of the silicon dioxide layer generated at the Ta ₂ O ₅ / Si interface, and in MINS-type and MIM-type capacitors, the oxynitride film and the lower electrode are oxidized to reduce the accumulated charge amount. cause.

FIG. 1 shows the withstand voltage and the capacitance of the MIS capacitor, which are defined by the applied voltage at which the leakage current reaches 10 ^-8 A / cm ² with respect to the oxygen annealing temperature. The breakdown voltage improves as the annealing temperature increases, but the capacity decreases. Therefore, in order to obtain a capacitor having a large capacitance, it is necessary to remove the carbon mixed in the tantalum oxide film without oxidizing the interfacial oxide film, the interfacial nitride film or the lower electrode, and perform an annealing method for compensating for oxygen defects.

[0007]

[Problems to be Solved by the Invention] The above problems are caused by the formed tantalum oxide film containing 0.1% of oxygen or oxygen dinitride.
Annealing is performed at a temperature of 600 ° C. or more and 750 ° C. or less in the atmosphere containing the above to remove carbon mixed in the film, and then at a temperature higher than that of the first heat treatment in the range of 700 ° C. or more and 1000 ° C. or less in a non-oxidizing atmosphere. This can be achieved by annealing and crystallizing the film.

[0008]

According to the studies made by the inventors, the carbon mixed in the tantalum oxide film is 200 ° C. to 600 ° C. in the oxygen atmosphere.
Desorb between.

FIG. 2 shows the sum of integrated values of X-ray diffraction peaks with respect to the oxygen annealing temperature, and shows the degree of crystallization. As can be seen from this figure, the tantalum oxide layer is 7
Crystallization starts at around 00 ° C., and crystallization progresses as the oxygen annealing temperature increases. Also, in an argon atmosphere at 850 ° C
Even when the annealing was performed at 1, the crystallization was confirmed to be about the same as the oxygen annealing at 800 ° C. However, the withstand voltage of the tantalum oxide capacitor only subjected to argon annealing was low, and it was clarified that crystallization was not the direct cause of the withstand voltage improvement.

FIG. 3 shows the amount of impurity carbon contained in the tantalum oxide layer subjected to various annealings, which was measured by the elastic recoil particle detection method. The higher the oxygen annealing temperature, the smaller the amount of carbon mixed in the film, and it was confirmed that carbon mixed in the film was one of the major causes of the leakage current of the tantalum oxide capacitor. Also, when high-temperature argon annealing is performed after oxygen annealing, the amount of carbon in the film decreases,
It was confirmed that crystallization promotes desorption of impurity carbon in the film and improves the breakdown voltage.

Therefore, first, in an atmosphere containing oxygen or oxygen dinitride in an amount of 0.1% or more, a temperature at which carbon in the film can be removed and which does not oxidize the interfacial oxide film, the nitride film or the lower electrode, That is 600 ° C or higher 750
Annealing is performed at a temperature of ℃ or less, then in an inert gas atmosphere or in an oxygen or dinitride oxygen atmosphere diluted with an inert gas so that the oxygen concentration is 0.1% or less, than in the first heat treatment. If annealing is performed at a high temperature and at a temperature for crystallizing the tantalum oxide film, that is, at a temperature of 700 ° C. or higher (hereinafter referred to as crystallization annealing), a nitride film formed on the interface without growing an oxide film on the interface Alternatively, without mixing the lower electrode metal layer, carbon mixed in the tantalum oxide film can be removed and crystallized to obtain a capacitor insulating film having a large capacity and a good withstand voltage.

[0012]

(Embodiment 1) FIG. 4 is a sectional view of a process of forming a capacitor formed using the concept of the present invention.

As shown in FIG. 4A, the silicon substrate 1
A thermal oxide film 2 was formed on top and the insulating film in that region was removed. Next, a polycrystalline silicon film was formed and processed in the portion where the insulating film was removed to form the lower electrode 3 of the capacitor. Figure 4
As shown in (b), when the polycrystalline silicon film 3 is washed with hydrofluoric acid and then washed with water immediately before the formation of the tantalum oxide film, the surface of the polycrystalline silicon film 3 becomes 1
A native oxide film 4 having a thickness of nm or less was formed. Then, Fig. 4 (c)
Pentaethoxy tantalum on the native oxide film as shown in
Using (Ta (OC ₂ O ₅ ) ₅ ) as a raw material and nitrogen as a carrier gas, a tantalum oxide film 5 was deposited to 10 nm by a chemical vapor deposition method at 420 ° C. in an oxygen atmosphere. The formed tantalum oxide film was first annealed at 700 ° C. for 30 minutes in a dry oxygen atmosphere using a resistance heating furnace, and subsequently, crystallized annealing was performed at 850 ° C. for 10 minutes in an argon atmosphere. FIG. 4D shows a state in which the titanium nitride electrode 6 is formed on the tantalum oxide 5.

The curve (g) in FIG. 5 shows the current-voltage characteristic of the capacitor formed by this method. Further, the curve (e) in the figure is a capacitor not subjected to heat treatment, and the curve (e) is 7
It shows the breakdown voltage of the capacitor which was only oxygen-annealed at 00 ° C. 800 for comparison in a dry oxygen atmosphere
The withstand voltage of a capacitor having a tungsten electrode formed only by annealing at 30 ° C. for 30 minutes is shown in (h). The converted film thickness converted using the relative permittivity of silicon dioxide is (e)
3.1 nm (f) 3.7 nm (g) 3.7 nm (h) 4.2
and the withstand voltage was improved while suppressing the growth of the interfacial oxide film by performing the two-step annealing.

[0015] Incidentally, the first heat treatment can also obtain the same effect when performing 10 minutes to 3 hours annealing at below 750 ° C. deposition temperature 600 ° C. or higher, oxygen dinitride Kiri囲<br/> gas Alternatively, the same effect can be obtained by annealing in an atmosphere in which oxygen or oxygen dinitride is diluted to 0.1% or more with nitrogen or argon. For the subsequent second heat treatment, annealing is performed at 700 ° C to 1000 ° C for 10 minutes to 30 minutes in a nitrogen or argon atmosphere or in a nitrogen or argon atmosphere containing oxygen or oxygen dinitride at a concentration of less than 0.1%. The same effect was obtained in the case of

(Example 2) FIG. 6 shows a tantalum oxide film after nitriding the silicon oxide layer on the surface by forming a polycrystalline silicon film 3 and using a resistance heating furnace to treat the silicon oxide layer at 800 ° C. for 5 minutes in an ammonia atmosphere. 5 is a cross-sectional view of a capacitor in which a titanium nitride electrode 6 is formed after forming No. 5 in FIG. Also in the capacitor having such a structure, the oxynitride film 7 at the interface may be oxidized by high-temperature oxygen annealing in SSDM, 1992, p5.
21 reported that the crystallization annealing described in Example 1 is effective in suppressing the decrease in capacity due to the oxidation of the interfacial silicon oxynitride layer.

The breakdown voltage of this capacitor is shown in FIG. The curve (i) shows the breakdown voltage of the capacitor which was not heat-treated, (j) was oxygen-annealed at 700 ° C., (k) was oxygen-annealed at 700 ° C. and then argon-annealed at 850 ° C., and (h) was oxygen-annealed at 800 ° C. The converted film thickness is (i) 3.0 nm (j) 3.5 nm (k) 3.5 nm, respectively.
(H) It was 4.2 nm. Nitriding process is over 600 ℃ 1
The same effect can be obtained when the heating is performed at 000 ° C. or lower for 5 minutes or more and 30 minutes or less. Also, for example, SSDM, 1992, p
As described in No. 521, when the temperature rising / falling time is shortened by using lamp heating or the like, a silicon oxynitride layer can be thinned to obtain a capacitor having a large capacity. In this case as well, the crystal described in Example 1 is used. Chemical annealing had a similar effect.

(Embodiment 3) FIG. 8 is a schematic sectional view of a capacitor in which a tungsten layer 8 is formed as a lower electrode on a silicon substrate 1, a tantalum oxide layer 5 is then formed, and a titanium nitride electrode 6 is formed. . In the capacitor having this structure, the tungsten oxide layer 9 grows at the interface between the lower electrode tungsten layer 8 and the tantalum oxide layer 5 due to the high temperature oxygen annealing, which causes a decrease in the capacitance. It had a similar effect. In particular,
When the lower electrode is tungsten and the first heat treatment is performed in an atmosphere containing water and hydrogen, the tungsten oxide 9 existing at the interface between the lower electrode and the tantalum oxide layer is reduced, so that a large-capacity capacitor having good characteristics. was gotten.

Further, even if the second heat treatment is performed after the first heat treatment in an atmosphere containing water and hydrogen, the first heat treatment is performed after the first and second heat treatments. The same effect was obtained even when the heat treatment was performed in the atmosphere. There is no problem even if the lower electrode is a single-layer film made of molybdenum, tungsten, or a nitride or silicide of molybdenum, or a laminated film in which two or more layers including tungsten are laminated.

(Embodiment 4) In the tantalum oxide capacitor having the same structure as that of Embodiment 1, even when the first heat treatment and the second heat treatment are performed in the reverse order, the same effect as that of the first embodiment can be obtained. It was

In the capacitor shown in FIG. 9, a tantalum oxide layer 5 is formed on a silicon substrate 1 which has been washed with hydrofluoric acid, and thereafter,
The titanium nitride upper electrode 6 is formed and then processed.

The curves in FIG. 10 show (o) 6 after forming the tantalum oxide layer 5 for the capacitor having the structure shown in FIG.
Oxygen anneal at 00 ° C. followed by argon anneal at 800 ° C., (n) Argon anneal at 800 ° C. and then oxygen anneal at 600 ° C., (l) No heat treatment for comparison , (M) shows the withstand voltage of a capacitor that was only annealed at 800 ° C. with argon.

Even when the first heat treatment and the second heat treatment were carried out in the reverse order, there was the effect of suppressing the decrease in capacitance and the effect of improving the breakdown voltage to the same extent as in the case of the annealing method described in the first embodiment. . However, it was more effective to improve the breakdown voltage by performing crystallization annealing after performing oxygen annealing. Further, the pressure resistance was insufficient only by argon annealing at 800 ° C.

(Embodiment 5) After the tantalum oxide film is formed, a first heat treatment is performed to remove impurity carbon and repair oxygen defects, and then a tantalum oxide film is formed again to perform the first heat treatment. When the second heat treatment was performed at the end by repeating the above operation more than once, it was possible to obtain a capacitor having a higher withstand voltage.

In FIG. 11, 1 to 10 nm tantalum oxide layers are formed.
The breakdown voltage of the formed capacitor was shown by performing oxygen anneal at 700 ° C. each time, and performing argon anneal at 850 ° C. finally. The finer the film formation, the more the tantalum oxide layer with less impurity carbon and oxygen defects was obtained, and the breakdown voltage was improved.

After forming the tantalum oxide layer, the first heat treatment is followed by the second heat treatment to crystallize the film.
FIG. 12 shows the breakdown voltage of the tantalum oxide capacitor formed by repeating the step of forming the tantalum oxide layer again and performing the first heat treatment and then the second heat treatment one or more times. Similar to the capacitor shown in FIG. 11, the breakdown voltage was improved as the film formation was finely divided, and a more dense and high breakdown voltage capacitor could be obtained as compared with the case of FIG.

(Embodiment 6) FIG. 13 shows a DRAM in which a tantalum oxide capacitor subjected to crystallization annealing is actually applied.
FIG. In the figure, (a) is a crown type structure, and (b) is a fin type structure, which has been devised so as to have a three-dimensional structure and a large effective area in order to secure the capacitance required for a DRAM capacitor of 64 Mbit or later. In the case of such a complicated three-dimensional structure, the CVD method with good coverage is effective. Crystallization annealing is also effective when a tantalum oxide film is used as a gate insulating film of a transistor.

In the above embodiments, titanium nitride was used as the upper electrode, but the same applies to a metal containing at least one element of tungsten, titanium, tantalum and molybdenum or a laminated film of these metals. The effect of is obtained. Similar effects were obtained when the film thickness of tantalum oxide was in the range of 2 nm to 20 nm. Furthermore, although an example using pentaethoxy tantalum as the raw material for forming the tantalum oxide film is shown, other raw materials such as pentamethoxy tantalum, pentabtox tantalum, pentachloro tantalum, pentafluoro tantalum, pentabromo tantalum may be used. The same effect can be obtained by forming by a sputtering method.

[0029]

According to the present invention, a large-capacity, high breakdown voltage, highly reliable capacitor required for a highly integrated LSI can be manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of oxygen annealing temperature dependence of capacitance and withstand voltage of a tantalum oxide capacitor.

FIG. 2 is an explanatory diagram of oxygen annealing temperature dependence of crystallization of a tantalum oxide layer.

FIG. 3 is an explanatory diagram of the effect of reducing the amount of impurity carbon by various heat treatments.

FIG. 4 is a cross-sectional view showing a step of forming a tantalum oxide capacitor.

FIG. 5 is a characteristic diagram of a leakage current density of a tantalum oxide capacitor that has been subjected to crystallization annealing.

FIG. 6 is a cross-sectional view of a capacitor in which a tantalum oxide layer is formed after nitriding a surface oxide film on a first electrode silicon.

FIG. 7 is an annealing condition and leakage current density characteristic diagram of a capacitor in which a tantalum oxide layer is formed after nitriding a surface oxide film on a first electrode silicon.

FIG. 8 is a cross-sectional view of a tantalum oxide capacitor in which the first electrode layer is tungsten.

9 is a sectional view of the evaluated capacitor shown in FIG.

FIG. 10 is a leakage current density characteristic diagram of a tantalum oxide capacitor annealed in the reverse order.

FIG. 11 is a leakage current density characteristic diagram of a capacitor.

FIG. 12 is a leakage current density characteristic diagram of a tantalum oxide capacitor.

FIG. 13 is a cross-sectional view of a DRAM capacitor part to which a tantalum oxide film is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Element isolation film, 3 ... High concentration phosphorus dope polycrystalline silicon, 4 ... Interface silicon oxide layer, 5 ... Tantalum oxide layer, 6 ... Titanium nitride electrode , 7 ... Oxynitride film, 8
... tungsten layer, 9 ... tungsten oxide layer, 10 ... half
Conductor area, 11 ... Word line, 12 ... Bit line, 13 ... Bottom
Partial electrode, 14 ... Tantalum oxide layer, 15 ... Upper electrode.

Front page continuation (72) Inventor Shinpei Iijima 1-280, Higashi Koikekubo, Kokubunji, Tokyo, Hitachi Central Research Laboratory (72) Inventor Natsuki Yokoyama 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi Ltd. Central Research Laboratory (72) Inventor, Yo Oji 1-280, Higashi Koigokubo, Kokubunji, Tokyo, Central Research Laboratory, Hitachi, Ltd. (72) Teruaki Kisu, 5-20 Kamisuihonmachi, Kodaira-shi, Tokyo Hitachi Ultra L.S.I.・ Engineering Co., Ltd. (72) Inventor Yuichi Matsui 1-280, Higashi Koigokubo, Kokubunji, Tokyo Metropolitan Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-63-312664 (JP, A) JP-A-5 -114698 (JP, A) JP 5-243524 (JP, A) JP 57-167669 (JP, A) JP 4-328862 (JP, A) JP 2-283022 (JP, A) ) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 27/04 H 01L 21/822 H01L 27/108 H01L 21/8242 H01L 21/316

Claims (7)

(57) [Claims] 1. A tantalum oxide layer is formed on a first electrode extending on a first insulating film formed on a silicon substrate, and then carbon contained in the tantalum oxide layer is desorbed.
For the first heat treatment in an oxygen or oxygen dinitride atmosphere,
Or, in an atmosphere diluted with argon or nitrogen with oxygen or oxygen dinitride concentration of 0.1% or more, 600 ° C or more 75
It is performed at a temperature of 0 ° C. or lower and before the first heat treatment at a higher temperature .
Serial and in an inert atmosphere of argon or nitrogen at a temperature tantalum oxide layer can be crystallized or argon or
Or after performing a second heat treatment in an oxygen atmosphere diluted with nitrogen to 0.1% or less to crystallize the tantalum oxide layer,
A method of manufacturing a capacitor, comprising forming a second electrode on the tantalum oxide layer. 2. The method for manufacturing a capacitor according to claim 1, wherein at least one of the first and second heat treatments uses lamp heating to shorten the temperature raising / lowering time or the temperature raising / lowering time and the annealing time. 3. The method for manufacturing a capacitor according to claim 1, wherein the first electrode is a silicon layer. 4. The method of manufacturing a capacitor according to claim 3 , wherein the tantalum oxide layer is formed after nitriding the surface of the silicon layer. 5. The capacitor according to claim 1, wherein the first electrode is a single-layer film made of one of tungsten, molybdenum, nitrides thereof, or a silicide thereof or a laminated film in which two or more layers are laminated. Manufacturing method. 6. The method according to claim 1 , wherein the first heat treatment is performed in an atmosphere containing water and hydrogen, or after the first heat treatment or after performing the second heat treatment after the first heat treatment. A method for manufacturing a capacitor, wherein heat treatment is performed in an atmosphere containing hydrogen. 7. The method according to claim 1, wherein a series of steps of performing the first heat treatment after forming the tantalum oxide layer is repeated a plurality of times, or after performing the first heat treatment after forming the tantalum oxide layer , A method for manufacturing a capacitor, wherein a series of steps of performing a second heat treatment is repeated a plurality of times.