JP2723148B2 - 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 suitable for forming a semiconductor device having a highly reliable storage capacitor. About. [Prior Art] Conventionally, MOS dynamic random access memory (dynamic operation, random read / write storage device, hereinafter referred to as DRAM)
) Is formed planarly on a silicon substrate, and a silicon oxide (SiO ₂ ) film obtained by directly oxidizing the silicon substrate is mainly used as the insulating film for the capacitor. I was As semiconductor devices become more highly integrated, the area occupied by the elements is increasingly reduced, and it is necessary to reduce the thickness of the insulating film in the storage capacitor section in order to obtain the amount of charge necessary to ensure the normal operation of the device. Occurs. For example, in order to realize a DRAM having a degree of integration of 4 Mbits or more, the thickness of the silicon oxide film must be 10 nm or less, which results in deterioration of withstand voltage, and the storage capacitor portion is easily broken during operation of the semiconductor device. To solve this problem, a laminated storage capacitor has been devised (for example, see Japanese Patent Application Laid-Open No. 56-23771).
No.). According to the present invention, the longitudinal direction of the element is positively used, and the storage capacitor element is formed to extend over another element such as a MOS transistor. With such a configuration, even if the planar area is small, it has a large capacity,
Even if an insulating film having a thickness of nm or more is formed, a necessary capacity can be secured. In this device, an insulating film is formed on a polycrystalline silicon film.Since a silicon oxide film formed by thermally oxidizing the polycrystalline silicon film has poor film quality, the withstand voltage is 2 to 5 MV / cm. This is lower than the withstand voltage of a silicon oxide film formed by thermally oxidizing single crystal Si, which has been a problem when forming a storage capacitor. One of the means for solving this withstand voltage deterioration is to deposit a silicon nitride film on a polycrystalline silicon film by a CVD method, or to slightly oxidize the upper part of the silicon nitride film to form a silicon oxide film / silicon nitride film. A method for forming a two-layer film has been devised. By using these films as the dielectric film for the capacitor, the problem of initial withstand voltage failure can be solved. However, no consideration was given to the reliability of the film, in particular, the destruction characteristics over time. [Problems to be Solved by the Invention] As an insulating film for a storage capacitor element, when a voltage at the time of actual operation is applied, the dielectric breakdown life has a sufficient margin.
However, in the above-mentioned prior art, no consideration has been given to this point. That is, no consideration is given to the time-dependent breakdown characteristics of the insulating film, and there is a problem in reliability. An object of the present invention is to solve the above-described problem of the reliability of the storage capacitor portion and to manufacture a semiconductor device capable of easily manufacturing a highly reliable semiconductor device having a new structure capable of extending the dielectric breakdown life. A method is to provide a semiconductor device. [Means for Solving the Problems] The object is to optimize the thickness of a silicon nitride film when manufacturing a semiconductor device having a multilayer insulating film including a silicon oxide film and a silicon nitride film as constituent elements. Achieved. That is, the present invention reduces the thickness of the silicon nitride film to about 8 nm.
The gist is to set the following. Further, the thickness of the silicon nitride film is desirably about 3 nm or more. [Operation] In general, there is a strong correlation between the dielectric breakdown life of an insulating film and the applied electric field strength, and the larger the electric field dependence of the breakdown life (electric field acceleration coefficient), the longer the breakdown life in a low electric field. The present inventors have studied the dielectric breakdown lifetime of a two-layer structure film of a silicon oxide film and a silicon nitride film, and have found that a change in the thickness of the silicon nitride film greatly changes the lifetime of the entire two-layer film. FIG. 2 shows a two-layer film in which a silicon oxide film is formed on a silicon oxide film / silicon nitride film (silicon nitride film).
The same applies hereinafter. 4) shows the relationship between the electric field acceleration coefficient and the nitride film thickness when a life test is performed. The horizontal axis of the figure indicates the silicon nitride film thickness (nm), and the vertical axis indicates the electric field acceleration coefficient (cm / MV). In the figure, ▽ indicates that the initial thickness of the silicon nitride film was 5 nm, and ○ indicates 1
0 nm, Δ indicates 17 nm, and □ indicates 20 nm, and the silicon nitride film was partially oxidized to form the two-layer film. As is clear from the figure, the thickness of the silicon nitride film before oxidation varies from 5 to 20 nm, but in the two-layer film after oxidation, the thinner the silicon nitride film, the larger the electric field acceleration coefficient, and the lower the electric field acceleration coefficient. It was also confirmed that the fracture life was longer. In other words, the life becomes longer as the silicon nitride film becomes thinner, and the effect becomes remarkable particularly when the thickness is about 8 nm or less. FIG. 4 is a diagram showing the predicted breakdown life of a two-layer film of a silicon oxide film / silicon nitride film having various film thicknesses when 2.5 MV / cm, which is an electric field in actual use, is continuously applied. The horizontal axis of the figure shows the silicon nitride film thickness (nm), and the vertical axis shows the time (second) at which 50% failure occurred when 2.5 MV / cm was continuously applied. When an insulating film is used for a device, the destruction life needs to exceed 10 years plus a margin. The margin is required to be 1.5 digits in consideration of the guaranteed product temperature of 150 ° C., and two digits in consideration of the defect of the insulating film (the difference between 0.01% failure and 50% failure), that is, about 3.5 digits in total. In other words, the destruction life is 1
It takes at least ¹² seconds, and the condition is satisfied in the region where the silicon nitride film thickness is about 8 nm or less from the figure. However, when using such a two-layer film, it is practically difficult to make the silicon nitride film thickness less than about 3 nm. Because, when the nitride film becomes thinner, the oxidation resistance of the silicon nitride film is partially lost, and the oxidation of the polycrystalline silicon film underlying the silicon nitride film progresses, and the film thickness becomes extremely uneven. It is. FIG. 5 shows the results of examining how much the remaining nitride film thickness can be obtained to obtain a film with good uniformity when the initial silicon nitride film thickness is changed and oxidized. The horizontal axis shows the initial silicon nitride film thickness (nm), and the vertical axis shows the silicon nitride film thickness after oxidation (nm). As is apparent from the figure, a silicon nitride film of about 3 nm or more is required. Therefore, by setting the silicon nitride film thickness to about 3 nm or more and 8 nm or less, it is possible to obtain a multilayer insulating film having a long dielectric breakdown life and having a uniform thickness of the silicon nitride film. Example 1 Example 1 Next, a first example of the present invention in the case where an insulated gate field effect diode is manufactured will be described. FIG. 3 (a),
(B) is sectional drawing of the manufacturing process of this insulated gate field effect diode. First, as shown in FIG. 3A, a thick isolation insulating film 2 is formed on an N-type silicon substrate 1. Next, after depositing a polycrystalline silicon film 3 as a lower electrode of the diode by a CVD method, phosphorus diffusion is performed in the polycrystalline silicon film 3 using POCl ₃ as a diffusion source. Next, as shown in FIG. 3 (b), S
A silicon nitride film is deposited to a thickness of about 10 nm using iH ₂ Cl ₂ and NH ₃ as atmosphere gases, and then oxidized by a wet oxidation method to obtain a silicon oxide film (8 nm thick) / silicon nitride film. A two-layer film (thickness: 5 nm) is formed. Further, a polycrystalline silicon film is deposited, and after phosphorus is diffused into the polycrystalline silicon film, the pattern is cut and the upper electrode 6 of the diode is formed to obtain the structure shown in FIG. 3 (b). FIG. 1 shows the dielectric breakdown lifetime-applied electric field characteristic of the field effect diode manufactured in this manner. The horizontal axis indicates the effective electric field strength (MV / cm), and the vertical axis indicates the dielectric breakdown lifetime (second). The figure shows a two-layer film (silicon oxide film (thickness 3 nm) / silicon nitride film (thickness 15 n
The characteristics of m)) are shown for comparison. As is apparent from the figure, the slope of the straight line (ie, the electric field acceleration coefficient) increases by reducing the thickness of the silicon nitride film, and as a result, the actual electric field (2 to 3 MV / c) is obtained.
It can be assumed that the dielectric breakdown life in m) can have a sufficient margin for 10 years. The dependence of the electric field acceleration coefficient on the thickness of the silicon nitride film was similar to the result shown in FIG. That is, it was confirmed that the two-layer film having the silicon nitride film with a thickness of 5 nm in this example has a large electric field acceleration coefficient and a long breakdown life in a low electric field. Embodiment 2 Next, as another embodiment using the above insulating film, a structure of a highly reliable capacitor which can be formed on an isolation insulating film or an element region will be described. FIG. 6 is a sectional view of a DRAM memory cell having a storage capacitor and a transfer transistor. In the figure, 61 is a P-type silicon substrate, 62 is an isolation insulating film, 63 is a gate insulating film, 64 and 65 are sources and drains composed of a high concentration N-type region, and 66 is a capacitor composed of a polycrystalline silicon film. One electrode, 67 and 68 are a silicon nitride film and a silicon oxide film serving as a dielectric film, 69 is a second electrode made of a polycrystalline silicon film, 70 is an interlayer insulating film, 71 is a bit line made of aluminum wiring, 72 Reference numeral 73 denotes a first word line and a second word line made of a polycrystalline silicon film. In the memory cell having such a configuration, the first electrode 66 of the storage capacitor is a polycrystalline silicon film, and a silicon oxide film 68 / silicon nitride film 67 according to the structure of the present invention is formed on the polycrystalline silicon film. A layer insulating film is formed. The film thickness is a silicon oxide film (8 nm) / silicon nitride film (5 nm) as in the previous example. The performance of such a capacitor shows the same characteristics as the capacitor shown in the previous example,
In particular, a practically sufficient value was obtained for the fracture life. As described above, since the capacitor can be formed on the element region or the element isolation insulating film region, the present invention is extremely effective in manufacturing a highly integrated memory in the future. [Effect of the Invention] As described above, according to the present invention, it is possible to provide a highly reliable silicon oxide film / silicon nitride film having excellent temporal breakdown characteristics. In addition, by using the present invention as a dielectric material of a storage capacitor, a sufficient margin can be provided for a dielectric breakdown life of 10 years in an actually used electric field. Therefore, when the present invention is applied to a semiconductor integrated circuit, the reliability of the device is increased, which is extremely effective in practical use.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1, FIG. 2, FIG. 4, and FIG. 5 are diagrams for explaining the effect of the present invention, It is sectional drawing explaining Example of an Example. 1, 61 silicon substrate 2, 62 element isolation insulating film 3, 6, 66, 69 polycrystalline silicon electrode 4, 67 silicon nitride film 5, 68 silicon oxide film 63 gate Insulating films 64 and 65 Source and drain 70 Interlayer insulating film 71 Bit line 72 First word line 73 Second word line

Continuation of front page    (72) Inventor Masami Ozawa               1-280 Higashi Koigabo, Kokubunji-shi               Central Research Laboratory, Hitachi, Ltd.                (56) References JP-A-59-161861 (JP, A)                 JP-A-60-49662 (JP, A)

Claims (1)

(57) [Claims] Forming one electrode of the storage capacitor element on the main surface of the semiconductor substrate; forming a silicon nitride film on the one electrode by using a CVD method; and oxidizing the surface of the silicon nitride film. Forming a capacitor insulating film having a laminated structure including a silicon oxide film and a silicon nitride film having a remaining film thickness of 3 nm to 8 nm, and forming the other electrode of the storage capacitor element on the capacitor insulating film. A method of manufacturing a semiconductor device. 2. The one electrode is made of a polycrystalline silicon film,
2. The method according to claim 1, wherein the semiconductor device is formed by a method. 3. The above-mentioned silicon nitride film is a low-pressure film using SiH ₂ Cl ₂ and NH _3.
3. The method according to claim 1, wherein the semiconductor device is formed by a CVD method.