JP2656945B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method of manufacturing a semiconductor device, and to provide a method of manufacturing a semiconductor device having a silicon nitride thin film that has no pinholes and retains characteristics of a nitride film as little as possible. A step of depositing a silicon nitride film by a CVD method on a surface of a polycrystalline silicon film, a step of oxidizing at least a part of the surface of the silicon nitride film, and a step of oxidizing at least a surface of the silicon oxide film formed by the oxidation. Converting a part into a silicon oxynitride film by nitriding.

[Industrial applications]

The present invention relates to a method for manufacturing a semiconductor device characterized by forming an insulating thin film used for a capacitor or the like of an integrated circuit.

As the integration and speed of LSIs increase, the thickness of insulating films has been reduced. In particular, it is important to reduce the thickness of the gate oxide film of the MOS FET and the insulating film for the charge storage capacity of the dynamic RAM.

For example, the above-mentioned charge storage capacitance, that is, a capacitor is formed by a dielectric film and electrodes on both sides thereof, and the capacitance value is determined by a current area, a dielectric constant and a thickness of the dielectric film. As the integration progresses, the area becomes smaller, but the capacitance value cannot be so small for information storage, so it is necessary to increase the dielectric constant or reduce the thickness to secure the capacitance value. .

Silicon dioxide (SiO ₂ ) is widely used as an insulating film in integrated circuits, but recently silicon nitride (Si ₃ N ₄ ) has been used as a dielectric film for capacitors of 1 Mbit or more DRAM. Si ₃ N ₄ has a dielectric constant about 50% higher than that of SiO ₂ and is advantageous for high integration. A tantalum oxide film or the like having a higher dielectric constant has not been put to practical use in an integrated circuit yet.

To increase the dielectric constant, it is necessary to select a material,
In this regard, it is not necessary to reduce the thickness of a dielectric film that has been used in the past, and it is a simple method. Of course, if the thickness is reduced, problems such as pinholes appear.
The present invention relates to the formation of this ultra-thin insulating thin film.

[Conventional technology]

SiO ₂ has been mainly used as the material for the insulating film of integrated circuits, but various requirements have emerged with the increase in integration.
The emergence of materials related to SiO ₂ is desired.

Silicon nitride has a dielectric constant of 50 compared to silicon dioxide.
%, It has a dense structure, and has a strong impurity diffusion barrier effect, high-temperature oxidation resistance, and radiation resistance. Methods for introducing Si ₃ N ₄ as a thin film into an LSI manufacturing process include a direct nitridation method of silicon and a deposition method by CVD or sputtering.
The former can form a very thin film uniformly, but has the disadvantage that the reaction temperature is high and the underlying substrate is limited to silicon.
The latter do not have these drawbacks, but in the case of thin films they tend to contain accidental defects.

In the formation of a silicon nitride film by a CVD method, SiH ₄ , SiClH ₃ , SiCl ₂ H ₂ , SiCl ₄ , SiCl ₃ H, or the like is used as a silicon source, and for example, Si ₃ N ₄ is generated by the following reaction.

The more SiCl ₂ H ₂ + NH ₃ → Si ₃ N ₄ + HCl H can be grown at a lower temperature, but the reaction of the above formula is often used for ease of use. By the way, in a film deposited by such a reaction, a pinhole is easily generated in a thin film having a thickness of 10 nm or less (a pinhole is filled by a later deposition in a thick film). There is a problem.

In order to compensate for such a disadvantage of the CVD Si ₃ N ₄ film, it is effective to oxidize the Si ₃ N ₄ film at a high temperature, and this method has been practically used for a memory of 1 Mbit or more. Si ₃ N on silicon substrate
_{The four} films are grown via the SiO ₂ film, and the surface is turned into SiO ₂ by the above oxidation treatment, so that the film has a three-layer structure of SiO ₂ , Si ₃ N ₄ , and SiO ₂ . And even if the Si ₃ N ₄ film has a pinhole, it can be expected that oxygen introduced by the oxidation process fills the pinhole and the pinhole is eliminated.

However, this three-layer structure has difficulty in reducing the film thickness. The thermally oxidized SiO ₂ film on the silicon substrate has a meaning of cleaning the substrate surface, and the substrate surface need not be clean. In high-density memory such as 16M, except for this, the Si ₃ N ₄ film can be formed directly on the silicon substrate and the surface can be oxidized to form a two-layer structure of Si ₃ N ₄ and SiO ₂ It is considered.

[Problems to be solved by the invention]

Oxidation of the surface of the nitride film is effective for removing pinholes, but the surface of the nitride film changes to an oxide film, and the characteristics of the nitride film are lost as the amount of change to the oxide film increases.

It is an object of the present invention to improve such a point and to enable formation of a silicon nitride thin film having no pinholes and without losing characteristics of the nitride film as much as possible.

[Means for solving the problem]

As shown in FIG. 1, in the present invention, a thin film substantially composed of silicon nitride is formed on a substrate by a deposition method,
The thin film is oxidized in an oxidizing atmosphere to form a thin film containing silicon dioxide as a main component on the surface of the thin film. To a layer containing nitride.

[Action]

According to this method, Si ₃ N ₄ layer, SiO ₂ layer, nitrided SiO ₂
An insulating thin film having a three-layer structure is obtained, and the following layer of Si ₃ N ₄ is oxidized to fill even if there is a pinhole, and the oxide layer surface is nitrided. Since it is as thin as possible and the rest is a nitride layer, the characteristics as a nitride film can be maintained as much as possible.

〔Example〕

FIG. 2 shows the steps of the method for manufacturing a semiconductor device according to the present invention. 2A, a low-resistance polycrystalline silicon film 12 containing phosphorus (P) at a high concentration is deposited on a silicon substrate 11, and a nitride film 13 is deposited on the polycrystalline silicon film by a CVD method. The polycrystalline silicon film 12 is to be one electrode of a capacitor to be formed, and is usually grown by thermal decomposition of silane (SiH ₄ ) and has a thickness of 0.2 to 1 μm. Nitride film 1
3 is the reaction of SiH ₄ + NH ₃ or SiO ₂ Cl ₂ + NH ₃
It is deposited on the polycrystalline silicon film 12 at a substrate temperature of 0 ° C. 1M
In the case of a bit DRAM, the thickness of the nitride film 13 is about 15 nm,
In the present invention, it may be thinner.

Next, in (b), the state shown in (a) is treated in a humid oxygen atmosphere at 900 ° C. for 30 minutes to form an ultra-thin film 14 of about 2 nm mainly composed of SiO ₂ . In this oxidation step, the nitride film 13 is formed.
Defects (pinholes) disappear and the insulating properties of the film are improved. The oxidation reaction can be represented by the following equation.

Si ₃ N ₄ + 2O ₂ → SiO ₂ + 2NO + N ₂ N The generated N _2, that is, the nitrogen gas, goes out of the nitride film 13 into the atmosphere, but since the NO remains, the thin film 14 is completely (thermally oxidized the silicon substrate directly). It is not a silicon dioxide layer (as it is sometimes), but it can be almost a SiO ₂ layer.

Next, in (c), the state of (b) is treated in NH ₃ at 900 ° C. to nitride the surface of the thin film 14 to form a nitrided oxide film 15. This reaction can be represented by the following equation.

SiO ₂ + NH ₃ → SiOxNy + OH ↑ The oxygen amount x of the product SiOxNy becomes smaller as the processing temperature is higher, but the composition is close to SiON because such a high temperature cannot be used high in the IC manufacturing process. However, its denseness, radiation resistance and current / voltage stress resistance are similar to Si ₃ N ₄ . Also, the dielectric constant is increased by several tens of percent from that of (b) (conventional one).
Since the steps (b) and (c) are based on a direct reaction, the uniformity is good. The uniformity of the film thickness is determined in the step (a).

Oxidation of the nitride film in the step (b) does not easily proceed due to the oxidation resistance of the nitride film. Therefore, the oxidation is performed to a depth of about 20 to 30 °. Also in the nitridation of the oxide film in the step (c), it is not easy to nitride the entire oxide film because the nitride film formed on the surface prevents the progress of nitridation. When not fully nitrided, it has a three-layer structure of a nitrided layer, an oxide layer, and a nitrided layer. However, since the oxide layer is sandwiched by the nitrided layer, there is almost no difference in insulation and the like from the case of the fully nitrided layer. Absent.

Next, in (d), a metal or semiconductor electrode 16 is formed on the nitrided oxide film 15, and a capacitor having the electrodes 12, 16 and the dielectric films 13 to 15 is completed. The maximum electric field strength of this capacitor is 10 MV / cm, which is close to the intrinsic value of Si ₃ N ₄ .

FIG. 3 shows an example in which the present invention is applied to a DRAM memory cell. Reference numerals 11a and 11b denote source / drain diffusion regions, and reference numeral 17 denotes a gate electrode made of poly-insulating silicon, which constitutes the transistor of a one-transistor one-capacitor type memory cell. The capacitor includes a polycrystalline silicon electrode 12, insulating films 13 to 15, and a metal or polycrystalline silicon electrode 16. 18 is a gate insulating film, and 19 is a field oxide film.

In general, a MOS capacitor is used as a capacitor of a DRAM memory cell. However, as the degree of integration increases, a normal two-electrode, one-dielectric capacitor is used.
It is usual that the capacitor is formed by disposing an electrode on 11b via an insulating film. However, this does not increase the degree of integration. Therefore, as shown in FIG. 3, it is considered to form a capacitor over the transistor portion and the field insulating layer. In the present invention, the dielectric film of the capacitor of the memory cell having the structure shown in FIG. 3 can be made thinner and have a higher dielectric constant, and a capacitor having a small area and a required capacity can be formed. In addition, the reliability of the capacitor is high, the life of the memory cell is much longer than the conventional one, and the yield of the device is improved.

In the embodiment, the silicon nitride 13 is grown on polycrystalline silicon, but may be grown directly on a silicon substrate or on a silicon dioxide layer.

〔The invention's effect〕

As described above, in the present invention, since the surface of the nitride film is oxidized and the generated oxide film is subjected to nitriding treatment, even a thin nitride film has no pinholes, and has a high dielectric constant and insulation because it is almost a nitride film. High reliability and radiation resistance as a film are obtained, which is extremely effective.

[Brief description of the drawings]

FIG. 1 is a view for explaining the principle of the present invention, FIG. 2 is a manufacturing process diagram showing an embodiment of the present invention, and FIG. 3 is a sectional view of a memory cell of the embodiment of the present invention. In FIG. 2, 11 is a silicon substrate, 12 is a polycrystalline silicon layer, 13
Is a nitride film, 14 is its oxide layer, 15 is a nitride layer, and 16 is an electrode.

Claims (1)

(57) [Claims] 1. A step of depositing a silicon nitride film on a surface of a polycrystalline silicon film by a CVD method, a step of oxidizing at least a part of the surface of the silicon nitride film, and a step of oxidizing at least a part of the silicon oxide film formed by the oxidation. Converting a part of the surface to a silicon oxynitride film by nitridation.