JP2918835B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device having a high-capacity, high-reliability capacitor. 2. Description of the Related Art As is well known, capacitors having a silicon dioxide film as an insulating film are widely used as capacitors of various semiconductor memories. However, as the integration density of semiconductor integrated circuits has increased, the area of capacitors has also become significantly smaller. When the area of the capacitor is reduced, the capacity is reduced, and the reliability of the semiconductor memory is reduced. Therefore, it has been proposed to use a transition metal oxide having a large dielectric constant, such as Ta ₂ O _5, as a dielectric film of a capacitor to prevent a decrease in capacitance. For example, Japanese Patent Application Laid-Open No. Sho 59-4152 discloses that
After forming a tantalum oxide film on a silicon substrate, heat-treating in a humid oxygen atmosphere to grow a silicon dioxide film at the interface between the tantalum oxide film and the silicon substrate, and then forming a high melting point metal or a high melting point metal silicide. Was formed on the tantalum oxide film to form a capacitor. Further, there is the following known technique as a capacitor forming technique. JP-A-60-58653 discloses that a Ta film is formed directly on a silicon semiconductor substrate, and the T
and the Ta ₂ O ₅ film by oxidizing a film, and (specifically 80 Å) SiO ₂ film at the interface between the silicon semiconductor substrate and the Ta ₂ O ₅ film is described to be formed. This SiO ₂ film depends on the characteristics of the capacitor. JP-A-60-50950 discloses that Si
Substrate is described to oxidize HfN-Si ₃ N ₄ mixture in dry oxygen. Japanese Patent Application Laid-Open No. 57-167669 discloses that a Ta film is formed on a polycrystalline silicon film, the Ta film is made into an amorphous tantalum oxide layer in dry oxygen, and this amorphous tantalum oxide layer is made to crystallize. At the same time, silicon is diffused into crystal grain boundaries generated by crystallization, and the silicon is diffused to fill the crystal grain boundaries with silicon dioxide. In Japanese Patent Application Laid-Open No. 58-154258, a Ta film is formed on a polycrystalline silicon film, this Ta film is used as a tantalum oxide layer, and chlorine is introduced into the tantalum oxide layer. However, according to the study of the present inventor, the capacitor formed by such a method has low long-term reliability, and furthermore, a capacitor between the tantalum oxide film and the silicon substrate. It has been found that the thickness of the silicon dioxide film formed on the substrate becomes large, the capacity is reduced, and the effect of using tantalum oxide as the dielectric film is significantly reduced. That is, the above-described prior art has the effect of reducing the defect density of the tantalum oxide film and improving the breakdown voltage by forming the silicon dioxide film between the silicon substrate and the tantalum oxide film, but has the effect of increasing the unit. The capacity per area is significantly reduced. When the silicon dioxide film thickness is 40 ° or more, the time-dependent dielectric breakdown life when a constant voltage is applied depends on the lifetime in which the silicon dioxide film at the interface is destroyed. Could not get. An object of the present invention is to solve the above-mentioned conventional problems and to provide a method of manufacturing a semiconductor device having a capacitor with a low defect density, a sufficiently high withstand voltage, high long-term reliability, and a large capacitance. . In order to achieve the above object, the present invention provides a method of forming a transition metal oxide film on a capacitor lower electrode and then performing a heat treatment in an oxidizing atmosphere. By supplementing the oxide to the defective portion in the transition metal oxide film, a decrease in breakdown voltage is prevented. When a heat treatment is performed in an oxidizing atmosphere after a transition metal oxide film is formed on the lower electrode, the transition metal oxide film is thicker under the defect portion and the other portions are thinner. Underneath, a thin, underlying oxide film is formed. by this,
The total thickness of the insulating film in the defect portion of the transition metal oxide film is compensated, and the substantial characteristics of the capacitor are determined by the transition metal oxide, and a decrease in breakdown voltage is effectively prevented. Examples As examples conceived by the present inventors,
The case where a silicon substrate and tantalum oxide (Ta ₂ O ₅ ) are used as the lower electrode and the oxide of the transition metal will be described. The thickness of the tantalum oxide film is smaller in the region where the breakdown voltage of the interface between the silicon substrate and the tantalum oxide film is caused than in other regions. According to the present invention, silicon dioxide is selectively grown in the defect region and the total film thickness is increased, so that the withstand voltage is improved, and deterioration of the withstand voltage of the capacitor can be prevented. On the other hand, according to the study by the present inventor, the long-term reliability is lower when the silicon dioxide film thickness is 40 ° or more than when it is 40 ° or less. Therefore, in a region other than the defect region, the silicon dioxide film thickness at the interface between the silicon and the tantalum oxide film is set to 40 ° or less to prevent a decrease in long-term reliability. On the other hand, the silicon dioxide film formed below the defective region has a portion with a thickness of 40 ° or more, but in this case, as will be described later, the breakdown voltage of the region other than the defective portion is more than the withstand voltage. Since the silicon dioxide film grows to have a large breakdown voltage, the long-term reliability is not inferior to other regions. Further, the capacity of the defect region is small because the thickness of silicon dioxide is large, but the area of the defect portion is extremely small as compared with the area of the entire capacitor. The capacity is substantially equal to the capacity of the area other than the defective portion. In a region other than the defect region, the thickness of the silicon dioxide film formed at the interface is 40 ° or less, so that an extremely large capacity can be realized. In order to form a SiO ₂ film thicker than other portions under the tantalum oxide film, it is necessary to form a tantalum oxide film and then perform a heat treatment in a dry oxidizing atmosphere.
If heat treatment is performed in a humid oxidizing atmosphere, a thick SiO ₂ film is formed not only in the lower portion of the defect region but also at the entire interface between the tantalum oxide film and the silicon substrate, and it becomes impossible to obtain a large capacity. I will. It goes without saying that not only a silicon substrate but also a polycrystalline silicon film or a silicide film such as titanium silicide can be used as the lower electrode. Further, even when using titanium nitride or aluminum (the same applies to aluminum alloy), heat treatment is performed in a dry oxidizing atmosphere in the same manner as when silicon is used, so that a tantalum oxide film has a defect region below the defect region.
The object of the present invention can be achieved by forming a titanium oxide film or an aluminum oxide film thicker than other portions. Example 1 FIG. 1 shows that after forming a tantalum oxide film 3 on a silicon substrate 1,
A heat treatment is performed in a dry oxidizing atmosphere at 0 ° C. to form a silicon dioxide film 2 at the interface between the tantalum oxide film 3 and the silicon substrate 1, and a tungsten film 4 is formed on the tantalum oxide film 3 as an upper electrode. FIG. 4 is a cross-sectional view of the capacitor. The thickness of the silicon dioxide film 2 formed at the interface between the silicon substrate 1 and the tantalum oxide film 3 depends on the thickness of the tantalum oxide film 3 and the temperature of the heat treatment in the oxidizing atmosphere. . This relationship will be described below with reference to FIG. In FIG. 3, the horizontal axis represents the thickness of the tantalum oxide film 3 formed on the silicon substrate 1. The vertical axis indicates the thickness of the silicon dioxide film 2 formed at the interface between the tantalum oxide film 3 and the silicon substrate 1 by the heat treatment. When the heat treatment temperature is 800 ° C., when the thickness of the tantalum oxide film 3 is 10 nm or more, almost no silicon dioxide grows on the interface, but as the thickness of the tantalum oxide film 3 becomes thinner than 10 nm, It was found that the silicon dioxide film 2 grew thicker. Similarly, heat treatment temperature is 1,000
When the temperature is set to ° C., the thickness of the SiO ₂ film formed under the tantalum oxide film having a thickness of about 10 nm or more is only about 2 nm or less. The thickness of the SiO ₂ film formed underneath rapidly increases. Therefore, if a heat treatment is performed in a dry oxidizing atmosphere after a tantalum oxide film is formed on a silicon substrate or a lower electrode, as shown in FIG. The lower part is thicker,
Under normal regions (thick portions), thin SiO 2
_Two films 2 are formed. As a result, a reduction in breakdown voltage caused by the local decrease in the thickness of the tantalum oxide film 3 is effectively prevented, and a highly reliable capacitor is formed. FIG. 2 shows a cross-sectional structure of a capacitor formed by forming the upper electrode 4 without performing the above heat treatment after forming the tantalum oxide film. As is apparent from FIG. 2, if the heat treatment is not performed, a thin SiO 2 film having the same film thickness over the entire surface is obtained.
_Two films 2 'are formed. This SiO ₂ film 2 ′ is a natural oxide film of silicon, and when a tantalum oxide film is formed by sputtering in an oxidizing atmosphere, it is also slightly oxidized. Since the thickness of the SiO ₂ film 2 ′ is only about 15 nm, the total thickness of the dielectric film (the tantalum oxide film 3 and the SiO ₂ film) The sum of the film thicknesses of the film 2 ') is insufficient, which causes a breakdown voltage failure. When the heat treatment after the formation of the tantalum oxide film is performed in a humid oxidizing atmosphere, a very thick SiO ₂ film is formed not only below the defect region but also at the entire interface between the tantalum oxide film and the lower electrode. And it becomes impossible to obtain a high capacity. Therefore, after the formation of the tantalum oxide film, a heat treatment is performed in a dry atmosphere to convert the SiO ₂ film 2 having a partially different thickness to the tantalum oxide film 3 as shown in FIG. It must be formed between the lower electrodes 1. As described above, if the tantalum oxide film 3 has a locally thin portion (defect region) and the SiO ₂ film formed at the interface is thin and uniform,
The withstand voltage is reduced in a portion where the thickness of the tantalum oxide film is small, and the reliability is reduced. The present invention is characterized in that an SiO ₂ film having a partially different thickness is formed at the interface between the tantalum oxide film and the lower electrode by a heat treatment in a dry atmosphere. The thickness of the _two films is important for the present invention and will be described below. In FIG. 1, the case where the thickness of the tantalum oxide film 3 formed on the lower electrode is 75 ° will be described. Heat treatment conditions are 800 ° C, 3
The 0 minute condition was chosen. As described above, the thickness of the tantalum oxide film formed on the surface of the silicon substrate, which is the lower electrode, is not uniform, and there is a portion thinner than 75 °. In this case, as shown in FIG.
Under the tantalum oxide film having a thickness of 75 °, a thickness of about 0.5 n
Since the m ₂ SiO ₂ film grows, an SiO ₂ film having a total thickness of about 20 nm is formed together with the SiO ₂ film formed before the heat treatment. According to the present invention, the heat treatment is performed after forming the tantalum oxide film, or as shown in FIG. 4, the effective electric field strength is plotted on the vertical axis and the tantalum oxide film thickness is plotted on the horizontal axis. The effect of the heat treatment will be described. Here, the effective electric field strength is a value obtained by dividing the thickness of the silicon dioxide film equal to the capacitance per unit area of the tantalum oxide / silicon dioxide double-layer film by the voltage applied to the capacitor, and calculated as the silicon dioxide film thickness. Field strength. In FIG. 2, the effective electric field strength is 13 MV in a region where the thickness of the tantalum oxide film 3 is 75 °.
/ Cm, 13 MV in the region where the thickness of the tantalum oxide is less than 75 ° when the heat treatment is not performed.
/ Cm is applied. For example, a region where the thickness of the tantalum oxide film 3 is 20 ° is approximately 19 MV.
/ Cm of effective electric field strength is applied.
When heat treatment is performed in an oxidizing atmosphere at 0 ° C. for 30 minutes, the effective electric field strength is 13 MV / cm in the region where tantalum oxide is formed at 75 ° in a region where tantalum oxide is formed thinner than 75 °. While an intensity is applied, a lower effective electric field intensity is applied. As shown in FIG. 3, in the region where the thickness of the tantalum oxide film is 20 °, a SiO ₂ film having a thickness of about 40 ° is formed by the heat treatment.
Effective electric field intensity applied since growth is about 8 MV / cm
It's just Therefore, the withstand voltage is effectively improved in a portion where the tantalum oxide film is locally formed to be thin. On the other hand, the results shown in FIG. 5 were obtained for the long-term reliability of a capacitor in which the dielectric film was a two-layer film of a tantalum oxide film and a silicon dioxide film. This result was obtained by applying a constant electric field to the capacitor and measuring the average life until the capacitor was destroyed. As is clear from FIG. 5, when the thickness of the silicon dioxide film formed at the interface between the tantalum oxide film and the silicon substrate is 50 ° or more, the capacitor is easily broken, but the thickness is 40%.
平均 The life expectancy will be much longer if: Therefore, in a capacitor using a two-layer film of a tantalum oxide film and a silicon dioxide film as a dielectric film, very good results can be obtained if the thickness of the silicon dioxide film is set to 40 ° or less. FIG. 6 shows that an effective electric field strength of 13 MV / cm was applied to a capacitor having a dielectric of a 75 ° -thick tantalum oxide film and a two-layer film of a silicon dioxide film formed at the interface between the silicon substrate and the tantalum oxide. In this case, the life until the insulation is damaged is increased by setting the thickness of the silicon dioxide film to 20 °.
The results obtained by changing the measurement in the range of Å60 ° are shown. As is clear from FIG. 6, it is understood that when the silicon dioxide film thickness is 40 ° or less, the life is sharply increased. The reason is because the silicon dioxide film thickness is thin, the electron conduction mechanism is eliminated becomes broken break less susceptible to silicon dioxide damage becomes as including more direct tunneling component. Similar results were obtained when the thickness of the tantalum oxide film was other than 75 °. Therefore, the thickness of the silicon dioxide film formed under the portion other than the defect region of the tantalum oxide film is 40 °.
It is preferable to set the following. As shown in FIG. 4, in a region where the thickness of the tantalum oxide film 3 is less than 40 °, the thickness of the silicon dioxide film 2 formed at the interface between the tantalum oxide film 3 and the silicon substrate 1 is 40 ° or more. Become. However, as shown in FIG. 4, the effective electric field intensity applied to this region becomes smaller than 9.5 MV / cm. In this case, as shown in FIG. 5, the lifetime is 10 ⁵ seconds or more, which is not inferior to the lifetime of the region where the tantalum oxide is formed to a thickness of 75 °. Therefore, even if a silicon dioxide film having a thickness of 40 ° or more is formed under the defect region of the tantalum oxide film, there is no possibility that the withstand voltage and the average life will be reduced. Not only tantalum oxide, but T
Similar effects were observed for oxides of i, Hf, Nb or Zr. <Embodiment 2> This embodiment is an example of a semiconductor device having a highly reliable capacitor which can be formed on an isolation insulating film or an element region by using the lower electrode of the capacitor as a polycrystalline silicon film. It is. FIG. 7 is a sectional view of a memory cell having a storage capacitor and a transfer transistor. In FIG. 7, symbol 5 is a P-type silicon substrate, 6 is a gate insulating film, 7
Is a field insulating film, 8 and 9 are n ⁺ regions serving as a source and a drain, and 10 is a first electrode (lower electrode) of a capacitor.
Polycrystalline silicon film, 4 is a tungsten electrode, 12
Is an interlayer insulating film, and 11 is an aluminum wiring. 13 and 14 are a first word line and a second word line, respectively, made of polycrystalline silicon. Here, the aluminum wiring 11 is a bit line. In the memory cell as described above, the first electrode of the storage capacitor is a polycrystalline silicon film 10, and a dielectric made of a two-layer film of a tantalum oxide film 3 and a silicon dioxide film 2 is formed on the polycrystalline silicon film 10. A film is formed. As shown in FIG. 7, the silicon dioxide film 2 under the locally thinned region of the tantalum oxide film 3 is formed thicker than other portions. In regions other than the region where tantalum oxide is locally thin,
The thickness of the silicon dioxide film 2 under the tantalum oxide film 3 is 4
0 ° or less. The performance of the capacitor formed by forming the tungsten film 4 as the upper electrode showed the same characteristics as the capacitor formed on the silicon substrate shown in the first embodiment. As shown in FIG. 7, in the capacitor according to the present embodiment, the capacitor can be formed on the element region (transfer transistor) or the element isolation insulating film region (thick SiO ₂ film 7). Extremely effective in manufacturing. In addition to tantalum oxide, Ti, Hf,
Similar effects were observed when using an oxide of Nb or Zr. <Embodiment 3> As shown in FIG. 8, an upper electrode 4 made of a tantalum oxide film 3 and a tungsten film is formed on a silicon substrate 5 having a steep step on the surface by a well-known sputtering method. Form a capacitor. By doing so, the thickness of the oxidized portion formed on the side surface of the step in the tantalum oxide film 3 is smaller than the film thickness of the portion formed on the horizontal portion, and a breakdown voltage failure is likely to occur. However, when the Ta ₂ O ₅ film is formed on the step, and then annealed in a dry oxidizing atmosphere at 900 ° C., the thickness of the Ta ₂ O ₅ film 3 is reduced as shown in FIG. In the thin side portion, since the SiO ₂ film is formed thicker than the flat portion at the interface between the Ta ₂ O ₅ film 3 and the silicon substrate 5, the withstand voltage of the side portion does not deteriorate, and is larger than the withstand voltage of the capacitor shown in FIG. Withstand pressure is obtained. On the other hand, Ta formed on the flat part
_{Since the} SiO ₂ film formed at the interface between the ₂ O ₅ film 3 and the Si substrate 5 is extremely thin, the capacitance of the plane portion is almost the same as that of the capacitor shown in FIG. Therefore, according to the present invention, even realm where there is a step of the silicon substrate, a high-capacity, highly reliable, and it is possible to form a sufficient pressure of the capacitor. [0040] In <Example 4> above embodiment, as the lower electrode of the capacitor, but the silicon substrate is used or a polycrystalline silicon film, in this embodiment, as the lower electrode, with titanium emissions (TiN) film nitride . In FIG. 10, reference numeral 1 denotes a silicon substrate, 15 denotes a TiN film as a first electrode of a capacitor, 16 denotes a titanium oxide film, 3 denotes a tantalum oxide film, and 4 denotes a capacitor. A tungsten film as a second electrode is shown. In this embodiment, first, Ti
An N film 15 is formed on the silicon film 1 to a thickness of 500 ° by a well-known reactive sputtering method using an N ₂ -Ar mixed gas using Ti as a target. After forming the tantalum oxide film 3 with a thickness of 100 ° on the TiN film 15 by reactive sputtering in an Ar—O ₂ mixed gas using tantalum as a target, heat treatment was performed in a high-temperature dry oxidizing atmosphere at 600 ° C. . By this heat treatment, a titanium oxide film 16 grows at the interface between the tantalum oxide film 3 and the TiN film 15 as the first electrode. A second (upper) electrode 4 made of a tungsten film was formed on the tantalum oxide film 3 to form a capacitor. As shown in FIG. 10, in a region where the thickness of the tantalum oxide film 3 is small, the thickness of the titanium oxide film 16 below this region is larger than in other portions. Therefore, this portion does not cause deterioration of the breakdown voltage. If oxidation is not performed, a thick titanium oxide film is not formed in this portion, which causes deterioration in breakdown voltage. FIG. 11 shows a histogram comparing the breakdown voltage when the oxidation treatment is performed after forming the tantalum oxide film and when the oxidation treatment is not performed. It can be seen that the oxidation treatment significantly improved the breakdown voltage. The dielectric constant of titanium oxide is
Since it is larger than SiO ₂ , even if a titanium oxide film is used as a part of the dielectric film of the capacitor, the decrease in capacitance can be ignored, which is also extremely advantageous. Note that T
When using iN, a preferable heat treatment temperature range is 500.
８００800 ° C. Not only TiN but also NbN or Ta
After forming a tantalum oxide film using N as a lower electrode and then performing a heat treatment at 500 to 800 ° C. in a dry oxidizing atmosphere, the withstand voltage and long-term stability of the capacitor can be significantly improved. Using Al or an Al alloy (such as an Al-Si alloy) as a lower electrode,
Even at 500 ° C., good results could be obtained. In addition, for example, tantalum Cie Risaido, tungsten
Nshi Risaido, such as molybdenum silicide, titanium silicide, various silicides can be used as the lower electrode of the capacitor. The range of the heat treatment temperature in this case is almost the same as when a single crystal silicon substrate or a polycrystalline silicon film is used. Good results can be obtained by performing the heat treatment in the range of 600 to 1,000 ° C. As the upper electrode (second electrode), Al or Al-Si
Alloy, polycrystalline silicon, W, Mo, W-silicide, T
It goes without saying that many materials used for electrodes and wirings, such as a-silicide, Mo-silicide, and Ti-silicide, can be used. The atmosphere in which the heat treatment is performed preferably has a water vapor content of about 1,000 ppm or less. If the water vapor content in the atmosphere is large, as described above,
Although a thick oxide film is formed under the portion other than the defective portion, a preferable result can be obtained if the water vapor content is 1,000 ppm or less. As is apparent from the above description, according to the present invention, the capacity of the capacitor can be significantly increased without lowering the breakdown voltage or the long-term life.
It is extremely useful for improving the integration density of a semiconductor integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view illustrating a configuration of the present invention. FIG. 2 SiO ₂ generated when heat treatment is not performed
Sectional drawing which shows the structure of a film | membrane. FIG. 3 is a diagram for explaining an effect of the present invention. FIG. 4 is a diagram for explaining an effect of the present invention. FIG. 5 is a diagram for explaining the effect of the present invention. FIG. 6 is a diagram for explaining the effect of the present invention. FIG. 7 is a sectional view showing an embodiment of the present invention. FIG. 8 is a diagram for explaining another embodiment of the present invention. FIG. 9 is a diagram for explaining another embodiment of the present invention. FIG. 10 is a sectional view and a histogram for explaining still another embodiment of the present invention. FIG. 11 is a sectional view and a histogram for explaining still another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... silicon substrate 2 ... silicon dioxide 3 ... tantalum oxide 4 ... tungsten 5 ... p-type silicon 6 ... gate insulating film 7 ... field insulating film 8 ... source 9 ... drain 10 ... polycrystalline silicon 11 ... aluminum ( Bit line) 12 interlayer insulating film 13 polycrystalline silicon (word line) 14 polycrystalline silicon (word line)

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Noriyuki Sakuma               1-280 Higashi Koikebo, Kokubunji-shi, Tokyo                 Central Research Laboratory, Hitachi, Ltd. (72) Inventor Kiichiro Mukai               1-280 Higashi Koikebo, Kokubunji-shi, Tokyo                 Central Research Laboratory, Hitachi, Ltd.                (56) References JP-A-60-37766 (JP, A)                 JP-A-60-58653 (JP, A)                 JP-A-57-167669 (JP, A)

Claims (1)

(57) [Claims] What is claimed is: 1. A method for manufacturing a semiconductor device, comprising: forming a capacitor insulating film that forms a dielectric film from a transition metal oxide on a capacitor lower electrode, comprising: forming a capacitor lower electrode on a predetermined surface region of a semiconductor substrate; Depositing a metal oxide on a predetermined surface including a step of the capacitor lower electrode to form a capacitor insulating film; and forming a corner above the step between the capacitor lower electrode and the deposited transition metal oxide. Performing a heat treatment in an oxidizing atmosphere to form an oxide of a substance contained in the capacitor lower electrode, which is thinner in the periphery and thicker in the periphery of the lower corner ; A method of manufacturing a semiconductor device. 2. 2. The method according to claim 1, wherein the capacitor lower electrode is made of polycrystalline silicon. 3. 2. The method according to claim 1, wherein the capacitor lower electrode is made of a metal, a metal nitride, or a metal silicide. 4. 4. The method according to claim 3, wherein the capacitor lower electrode is made of metal silicide. 5. The capacitor lower electrode is made of Al, Al alloy, Ti
4. The method according to claim 3, wherein the semiconductor device is made of one of N, NbN, TaN, tantalum silicide, tungsten silicide, molybdenum silicide, and titanium silicide.