JPH04286151A - Formation of polycrystalline silicon film - Google Patents

Abstract

PURPOSE:To form a polycrystalline silicon film having a large surface area under a wide forming condition by forming an amorphous silicon layer on a board in vacuum, then ion sputtering the surface in vacuum, then heating it in vacuum, and crystallizing it. CONSTITUTION:An amorphous silicon film 12 formed with an oxide film 11 on a surface of an amorphous insulating film 14 is sputtered with ions 13 in the same vacuum tank immediately before it is heated in vacuum, a spontaneous oxide film on the surface is physically removed, and a clean surface is again formed. A polycrystalline silicon 15 having an extremely fast diffusion speed of silicon atoms on the clean surface, nucleus formation and nucleus grown occurring on the amorphous silicon surface and semispherical crystalline grains on the surface is formed. That is, the steps of forming and heating the amorphous silicon layer in vacuum can be performed in independent steps without limiting to continuous steps.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming polycrystalline silicon used for capacitor electrodes and the like in semiconductor devices.

0002

2. Description of the Related Art In recent years, as DRAMs become more highly integrated, the cell size tends to decrease and the area of the capacitor tends to decrease. Therefore, in order to ensure sufficient capacitance, stacked capacitors and trench capacitors are used, which have a large capacitive area, have α-ray resistance, and have little interference between capacitive parts. However, in a 64Mbit DRAM, the cell area is 2μm.
2 or less, and even if these structures are used, an extremely thin oxide film of 50 angstroms in thickness is required as the capacitor insulating film. Therefore, a method has been proposed in which the current capacitive film thickness is maintained by increasing the area of the capacitive part. Watanabe et al., in Japanese Patent Application No. 2-72462, state that when polycrystalline silicon is formed at a certain temperature range in LPCVD, semicircular spherical grains are densely formed on the surface at the boundary where the amorphous region changes to polysilicon. The results show that the surface area is approximately twice that of polycrystalline silicon grown at other temperatures. Also, Tatsumi is a Tokugan Hei 2
No. 24,915 shows that similar surface hemispherical grains can be obtained by forming amorphous silicon in vacuum and heating the substrate. By applying these polycrystalline silicon to the electrodes of a stacked capacitor, sufficient capacitance and a low leakage current value can be obtained with an oxide film having a thickness of 100 angstroms.

0003

[Problems to be Solved by the Invention] However, according to the method of Watanabe et al., the conditions for the appearance of semicircular spherical grains on the surface are only 10% at a growth temperature of 545°C to 555°C.
℃ range, and when used for production, there was a problem that temperature control for LPCVD was extremely difficult. Also, in Tatsumi's method, after forming the amorphous silicon layer,
In the process before heating the substrate, the substrate cannot be left in the atmosphere, and when used for production, there is a constraint that the formation of the amorphous silicon layer and heating of the substrate must be performed continuously in a vacuum chamber. there were.

An object of the present invention is to provide a method for eliminating such conventional drawbacks and forming a polycrystalline silicon film with a large surface area under a wide range of formation conditions.

[0005]

[Means for Solving the Problems] The method for forming a polycrystalline silicon film of the present invention involves forming an amorphous silicon layer on a substrate in vacuum, then ion sputtering the surface of the layer in vacuum, and then heating it in vacuum. It is characterized by being polycrystalline.

[0006]

[Operation] The principle of the present invention will be explained. When an amorphous silicon film formed on a substrate is left in the atmosphere,
A natural oxide film is formed on the surface of the film due to oxygen in the atmosphere. Further, when removing contaminating impurities on the surface using Branson cleaning solution, an oxide film is similarly formed on the surface. Even if such an amorphous silicon film is heated in a vacuum,
The oxide film on the surface does not evaporate at the crystallization temperature of amorphous silicon. Therefore, silicon atoms on the surface cannot diffuse, and as a result, nucleation and growth on the amorphous silicon surface as shown in Tatsumi's method do not occur, and a hemispherical structure does not appear. In this way, the surface morphology of the polycrystalline silicon film largely depends on the cleanliness of the amorphous silicon surface.

On the other hand, the inventor of the present invention formed an amorphous silicon film on a substrate, then returned the substrate to the atmosphere once again in a vacuum, and performed ion sputtering on the surface of the amorphous silicon film in a vacuum. , tried heating the substrate. As a result, they found that the amorphous silicon film becomes polycrystalline silicon with semicircular grains.

[0008] This is based on the following principle. That is, as shown in FIG. 1(a), an amorphous insulating film 1
Immediately before heating the amorphous silicon film 12 on which the oxide film 11 is formed on the surface in the vacuum chamber, sputtering is performed with ions 13 in the same vacuum chamber to physically remove the natural oxide film on the surface. It is based on creating a clean surface again. The diffusion rate of silicon atoms on a clean surface is extremely fast, and nucleation and growth occur on the amorphous silicon surface, resulting in polycrystalline silicon 15 with semicircular spherical crystal grains on the surface as shown in Figure 1(b).
is formed.

[0009]

[Example] Examples of the present invention will be explained in detail. Here, an MBE apparatus equipped with a 40 cc electron gun was used to form an amorphous silicon layer and heat the substrate. The sample wafer was heated to a thickness of 20 mm by thermal oxidation on the surface.
4 inch n with 0.00 angstrom oxide film
A type silicon (001) substrate was used. 7 angstroms/s from electron gun silicon evaporator at room temperature substrate temperature
2000 angstrom thick amorphous silicon layer was formed on the oxide film. After taking the substrate out into the atmosphere and leaving it for 15 hours, it was placed in the vacuum chamber again and the surface was irradiated with argon ions for 20 seconds using an ion gun with an accelerating voltage of 3 kV, and then heated for 10 minutes at 650°C in the same vacuum chamber. Then, the amorphous silicon layer was made polycrystalline.

[0010] Whether or not the above sample was crystallized was determined by in-situ observation using high-speed reflection electron diffraction. The formed samples were evaluated by cross-sectional transmission electron microscopy.

[0011] As a result of cross-sectional transmission electron microscopy observation of the above sample, the sample surface exhibited a hemispherical uneven structure, confirming the effect of the present invention.

Further, an oxide film having a thickness of 100 angstroms was formed on the polycrystalline silicon thus formed, a capacitor was manufactured, and its capacitance was measured. Figure 2 shows the relationship between the heating temperature and capacitance after amorphous silicon is deposited, when it is formed according to the present invention, when it is exposed to the atmosphere before heating and then heated in a vacuum without according to the present invention, and when it is formed in Tatsumi. This is a comparison with the case formed according to the method. In the polycrystalline silicon film formed according to the present invention, heating of the substrate can be performed over a wide range of heating temperatures.
Approximately twice the capacity was obtained as with Tatsumi's method. This means that the cleanliness of the amorphous silicon surface, which was not exposed to the atmosphere until after polycrystallization, was preserved in the sample polycrystallized according to the present invention. . On the other hand, in the case of a sample that was once exposed to the atmosphere and not according to the present invention, the capacitance did not increase even if the substrate was heated, and the capacitance remained almost the same as that immediately after the formation of amorphous silicon. This confirmed that the present invention is extremely effective for increasing the capacitance of an amorphous silicon film once left in the atmosphere.

[0013]Although the present invention is directed to silicon wafers, the method of the present invention is applicable to silicon wafers (SOS) where silicon exists only on the surface.
e) Substrates and more generally SOI (Silicon)
Of course, it can also be used for on insulator (on insulator) boards and the like. Furthermore, in this example, an amorphous silicon layer was formed using an electron gun type silicon vapor deposition device within an MBE device, but similar effects were confirmed with amorphous silicon layers formed by gas source MBE, LPCVD, and sputtering. . Furthermore, this time we have described the case of a natural oxide film as the oxide film on the surface of the amorphous silicon layer, but similar effects were also confirmed with thermal oxide films, Branson oxide films, and oxide films produced by plasma oxygen.

[0014]

As described above in detail, according to the present invention, semicircular spherical irregularities can be formed on the surface of an amorphous silicon film once left in the atmosphere. That is, it becomes possible to perform the formation and heating of the amorphous silicon layer in vacuum as independent steps without depending on specific temperature conditions and without limiting them to continuous steps. Thereby, a storage electrode of a capacitor with a large capacity can be manufactured under a wide range of manufacturing conditions.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the concept of the present invention.

FIG. 2 is a diagram comparing the relationship between heating temperature after amorphous silicon deposition and capacitance under various formation conditions.

[Explanation of symbols]

11 Oxide film 12 Amorphous silicon film 13 Ion 14 Amorphous insulation film 15 Polycrystalline silicon

Claims (1)

[Claims] 1. A polycrystalline silicon film characterized in that after an amorphous silicon layer is formed on a substrate in vacuum, the surface thereof is subjected to ion sputtering in vacuum, and then heated in vacuum to polycrystallize it. Formation method.