JPH02156564A - Manufacture of semiconductor storage device - Google Patents

Abstract

PURPOSE:To eliminate film thickness irregularity of a base silicon oxide film by a simple processing, and obtain a three-layer insulating film having excellent dielectric strength by forming a base barrier silicon oxide film of a three-layer insulating film structure by using a deposition oxide film without growing a natural oxide film. CONSTITUTION:A polysilicon electrode 12 is formed on a silicon substrate 1, and high concentration impurity is introduced into the electrode. When a barrier silicon oxide film is formed on the electrode 12, a CVD silicon oxide film 2 is deposited by low pressure CVD method, after a natural oxide film is completely eliminated. Hence film thickness difference caused by the difference of face orientation and accelerated oxidation at grain boundary do not generate, thereby forming the CVD silicon oxide film 2 uniformly. A three-layer insulating film formed afterwards by the similar process has excellent dielectric strength.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a highly reliable and high density semiconductor memory device.

BACKGROUND ART As shown in FIG. 2(a), when a capacitive electrode 10 made of impurity-doped polysilicon or a silicon substrate is brought into direct contact with a silicon nitride film 9 and a voltage difference is applied between the two capacitive electrodes 10, a voltage difference is applied between the two capacitive electrodes 10. , the storage capacitance of the MOS dynamic memo is due to the low barrier height of the silicon nitride film 9 against carriers.
The movement of carriers from the capacitor electrode 10 is as shown in 16, and carriers are more likely to be injected, resulting in an increase in leakage current.

In order to suppress this, conventionally a barrier silicon oxide film 11 having a higher barrier height than the silicon nitride film 9 is sandwiched between the capacitor electrode 10 and the silicon nitride film 9 as shown in FIG. 2(b). The method for forming the silicon oxide film 11 includes (i) thermal oxidation of a silicon substrate or polysilicon, and (ii) use of a natural oxide film in the atmosphere when placed in a reduced pressure nitride film deposition furnace. has been used.

In the conventional method, when a silicon oxide film is formed as a capacitor insulating film on a silicon substrate having several planes with different plane orientations, variations occur in the thickness of the silicon oxide film 11. A typical example is a trench-type capacitor shown in FIG. 3(a). In this case, there are planes 6, 7.8 with different plane orientations in the trench dug in the silicon substrate 1, but if a silicon oxide film is formed using the conventional method, this is shown in FIG.
As shown in a), the thickness of the barrier silicon oxide film 13 differs depending on the plane orientation. If silicon nitride film 3 is then deposited and then silicon oxide 114 is formed on its surface layer to form polysilicon electrode 5, good dielectric strength cannot be obtained with this three-layer insulating film.

In addition, when a silicon oxide film is formed as a capacitor insulating film on polysilicon 12 (stack type capacitor) as shown in FIG. 2(b), in addition to the difference in film thickness due to the difference in plane orientation, Accelerated oxidation 15 occurs and barrier silicon oxide film 14
The film thickness variation becomes even larger. Similarly, when a three-layer insulating film is formed, the withstand voltage of the three-layer insulating film deteriorates due to variations in the thickness of the barrier silicon oxide film 14.

Problems to be Solved by the Invention However, according to such a configuration, the barrier silicon oxide film (
There was a problem in that variations in the thickness of the underlying silicon oxide film degraded the dielectric strength of the three-layer insulating film.

The present invention has been tried in view of the above-mentioned problems, and the present invention of a semiconductor memory device in which the barrier silicon oxide film thickness is made uniform and the three-layer insulating film has good dielectric strength voltage solves the above-mentioned problems. Therefore, the structure is such that a base silicon oxide film of a three-layer insulating film is formed using a deposited oxide film without growing a natural oxide film.

According to the present invention, with the above-described structure, the base silicon oxide film is formed by deposition, so there is no variation in film thickness (and the three-layer insulating film can have a good dielectric strength voltage).

Embodiment FIGS. 1(a) and 1(b) are cross-sectional views showing the structures of a trench type capacitor and a stack type capacitor, respectively, according to an embodiment of the present invention. First, the trench type capacitor of the present invention will be explained using FIG. 1(a).

Impurities are introduced at a high concentration into the interior of a trench dug in the silicon substrate 1, and surfaces 6, 7, and 8 having different surface orientations exist in the trench during trench etching.

When forming a barrier silicon oxide film on the silicon substrate 1 having the grooves, after completely removing the natural oxide film, a reduced pressure C.
A CVD silicon oxide film 2 is deposited by the VD method. At this time, the conditions for forming the CVD silicon oxide film 2 are that it is inserted into a low-pressure CVD furnace at a low temperature of 300° C. or lower, the pressure is reduced to 10 Torr or lower, and then the temperature is raised to 50 A or lower, for example, 30 A.
A VD silicon oxide film 2 is formed.

If the temperature is below 300°C, the natural oxide film formed on the silicon substrate 1 will be sufficiently thin (the resulting film thickness variations can be ignored. Also, if the temperature is below 10 Torr, the natural oxide film formed on the silicon substrate 1 will remain thin even if the temperature is raised). The film is sufficiently thin (the resulting film thickness variation can be ignored. According to the present invention, the CVD silicon oxide film 2 has a uniform film thickness on any plane having any surface orientation. On top of this, a 6OA silicon nitride film 3 is formed. is deposited by the CVD method, and the surface layer is treated for 30 minutes in a pyro atmosphere at 850°C to form a silicon oxide film 4, with a thickness of about 0.4
When the polysilicon electrode 5 with a thickness of .mu.m is formed, this three-layer insulating film has a good dielectric strength.

Next, the stacked capacitor of the present invention will be explained using FIG. 2(b).

When forming a barrier silicon oxide film on the polysilicon electrode 12 formed on the silicon substrate 1 and doped with impurities at a high concentration, after completely removing the natural oxide film, low pressure CVD is applied.
A CVD silicon oxide film 2 is deposited by the D method, and the deposition conditions are similar to those described above. According to the invention,
The CVD silicon oxide film 2 can be formed uniformly because there is no difference in film thickness due to the difference in plane orientation and no accelerated oxidation occurs at grain boundaries. Thereafter, a three-layer insulating film formed through similar steps has good dielectric strength.

In this embodiment, the deposition conditions for the CVD silicon oxide film 2 are not limited to those described above, and any method may be used as long as the CVD silicon oxide film can be formed without forming a natural oxide film on the silicon substrate 1 or the polysilicon electrode 12. Needless to say.

Effects of the Invention As is clear from the above explanation, the present invention forms a base barrier silicon oxide film for a three-layer insulating film using a deposited oxide film without growing a native oxide film. DRAM with no variation in oxide film thickness
The effective reliability of the storage capacitor insulating film can be improved. This has high practical value industrially.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are cross-sectional views showing the structures of a trench type capacitor and a stacked type capacitor according to an embodiment of the present invention, respectively, and FIGS. 2(a) and (b) are dielectrics forming the capacitor. Band diagrams are shown when a silicon nitride film and a three-layer insulating film are used as the film, respectively, and FIGS. 3(a) and 3(b) are cross-sectional views showing the structures of a conventional trench-type capacitor and a conventional stack-type capacitor, respectively. 1...Silicon substrate, 2...CVD silicon oxide film, 3...Silicon nitride film, 4...
...Silicon oxide film, 5...Polysilicon electrode (upper layer), 6°7.8...Face with different surface orientation, 12...Polysilicon electrode ( Underlayer). Name of agent: Patent attorney Shigetaka Awano and 1 other person l −・ 2−・− 3−・・ 4−・= 5−・− Silicon dead handle CVO silico''/Pulmonary suppuration silicon enriched silicon oxide layer Gorisilicon Den W1 (J:l) ?-Silicon enemy 1t1.Order 10-1 volume of grain

Claims (1)

[Claims] A step of introducing impurities at a high concentration into a semiconductor substrate or polysilicon formed on the semiconductor substrate to form a first electrode of a charge storage capacitor, and a step of forming a natural oxide film grown on the surface of the semiconductor substrate or the polysilicon. a step of depositing a silicon oxide film on the semiconductor substrate or the polysilicon using a CVD method, depositing a silicon nitride film on the silicon oxide film, and oxidizing the upper layer of the silicon nitride film. A method for manufacturing a semiconductor memory device comprising the step of forming a second electrode of a charge storage capacitor on a silicon oxide film.