JPS6137780B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device that forms an insulating film between wirings in a semiconductor device having a multilayer wiring structure, and particularly to a method for simplifying the process of forming an insulating film between two wirings. The purpose is to

In semiconductor devices with a multilayer wiring structure, such as Si gate MOSLSI, an SiO ₂ film (hereinafter referred to as CVDSiO ₂ film) formed by vapor phase chemical vapor deposition (CVD) or a phosphorus-containing insulating film is used as an insulating film between wirings. An acid glass film (hereinafter referred to as PSG film) or a laminated film of a CVDSiO ₂ film and a PSG film is used. These CVDSiO ₂ films and PSG films are, for example,
By the reaction of SiH ₄ and O ₂ at 450 °C or
Formed by the reaction of SiH ₄ , O ₂ , and PH ₃ .

In particular, PSG films are used to prevent alkali ions from entering from the outside into the surface of a semiconductor substrate, that is, into the active region where FETs, etc. of semiconductor devices are formed, and to stabilize electrical characteristics such as threshold voltage. It will be done.

Furthermore, when subjected to high-temperature heat treatment, the PSG film flows and smoothly covers the edges of the lower wiring, which have steep side slopes, and can also reduce the difference in height between the concave and convex portions of the substrate surface. Therefore, the Al film formed by vapor deposition on the fluidized PSG film has sufficient thickness even on the side surfaces of the lower wiring, and does not cause breakage even when formed on the upper wiring by photolithography. . In addition, even if the side surface of the lower wiring is steep, the PSG gently covers it.
Since the Al film on the film does not produce any overhang, it forms a positive photoresist film during photolithography.
When irradiating ultraviolet rays, no photoresist remains on the side surface of the lower wiring due to insufficient exposure. Therefore
When etching the Al film, there is almost no etching in the lateral direction, and the Al film on the side surface of the lower wiring can be completely etched using the reactive sputtering method, which can etch faithfully to the photoresist pattern. It is possible to form a fine upper electrode without short circuits.

However, the above formed by CVD method
CVDSiO ₂ films and PSG films have lower film densities than SiO ₂ films formed by thermally oxidizing single-crystalline Si or polycrystalline Si (hereinafter referred to as thermal oxide films), and they also contain particles generated during film formation. Many defects are caused by SiO ₂ particles or powder exfoliated from the reactor. Therefore, when used as an inter-wiring insulating film, short circuits may occur between the upper and lower interconnects, and because the dielectric strength of the film is low, the insulating film may be locally destroyed when voltage is applied. This is a big problem for LSIs that operate at high voltages or for LSIs that operate at high voltages.

Furthermore, as mentioned above, by subjecting the PSG film to high-temperature heat treatment and causing it to flow, the film thickness on the lower wiring edge is reduced, and therefore dielectric breakdown is more likely to occur at this edge where electric fields tend to concentrate even under normal circumstances. Become.

The present invention makes full use of the above-mentioned advantages of the PSG film, such as stabilization of the characteristics of semiconductor devices and flow during high heat treatment, and also has few defects and high dielectric strength, so that even when high voltage is applied, short circuits between wiring and local The present invention relates to a method of manufacturing a semiconductor device having an inter-wiring insulating film that does not cause dielectric breakdown, and is particularly aimed at simplifying the process of forming the inter-wiring insulating film.

Among inter-wiring insulating films, those with few defects are
An insulating film obtained by thermally oxidizing only the surface of the lower wiring made of a semiconductor such as polycrystalline Si is used, but dielectric breakdown is particularly likely to occur at the ends of the lower wiring.
Sometimes, even if only 5V is applied between the upper and lower wirings, local destruction may occur, and as thermal oxidation progresses, the thickness of the lower wiring becomes smaller, so it is necessary to increase the thickness of this insulating film. It has disadvantages such as difficulty in

The inventor of the present invention has found that not only the surface of the semiconductor film is thermally oxidized, but the entire surface of the semiconductor film is converted into a thermal oxide film, which has fewer defects and has a high dielectric strength. We discovered that it is possible to form an inter-wiring insulating film that gently covers the top, so that no electric field concentration occurs when voltage is applied between the electrodes, and therefore no local dielectric breakdown occurs. ).

On the other hand, even if the PSG film has a thickness of 0.5 μm or more, if it is heat-treated in an oxidizing atmosphere such as wet oxygen, oxidizing agents such as oxygen and hydroxyl groups will easily pass through it. Semiconductors such as crystalline Si films have the property of being easily thermally oxidized.

The manufacturing method of the present invention includes a step of forming a thermal oxide film on the surface of a lower wiring made of semiconductor, then sequentially forming a semiconductor film and a PSG film, and performing heat treatment in an oxidizing atmosphere. Utilizing the property of allowing oxygen etc. to easily pass through, the semiconductor film covered with the PSG film is completely converted into a thermal oxide film (semiconductor film thermal oxidation method described above).
It allows the membrane to flow.

As described above, the present invention simplifies the process because the process of thermally oxidizing the semiconductor film covered with the PSG film and the process of making the PSG film flow to flatten the top surface are performed simultaneously.

The present invention will be described in detail below with reference to an embodiment in which the present invention is used in the manufacture of a Si gate MOSLSI, as well as FIG. 1 showing partial cross sections at each manufacturing process.

Boron ions of 10 ¹³ /cm ² were implanted into a P-type Si substrate 1 with a resistivity of 10 Ωcm in order to increase the V _T in the field portion, and then the Si ₃ N _{4 film was selectively oxidized to a thickness of 0.7 μm using the Si 3 N 4} film as a mask. After forming a field oxide film 2, a gate oxide film 3 with a thickness of 0.1 μm, and a gate electrode and lower wiring 4 made of a polycrystalline Si film with a thickness of 0.5 μm doped with phosphorus as an n-type impurity,
Arsenic ions of 4×10 ¹⁵ /cm ² accelerated at a voltage of 150 KV are implanted to form the source and drain 5 (FIG. 1a). By heating in a wet oxygen atmosphere at 800° C., the polycrystalline Si surfaces of the gate electrode and lower wiring 4 are oxidized to form a thermal oxide film 6 with a thickness of 0.1 μm (FIG. 1b). This thermal oxide film 6
serves as a stopper for later thermal oxidation, and because the polycrystalline Si4 is doped with a high concentration of phosphorus, it can be easily oxidized even at temperatures of 800°C during thermal oxidation.
A thermal oxide film 6 of 0.1 μm can be formed.
On the other hand, since the temperature during this thermal oxidation is low, the thermal oxide film 3 on the source and drain 5 regions hardly increases.

Next, by thermal decomposition of SiH ₄ at 600℃, the thickness of 0.1
A polycrystalline Si film 7, which is a semiconductor film of μm thickness, is formed, and by adding PH ₃ during the reaction of SiH ₄ and O ₂ at 450°C, a phosphorus concentration of 8 wt% and a thickness of 0.5 μm is formed.
After forming the PSG film 8 (FIG. 1c), heat treatment is performed for 30 minutes in wet oxygen at 1000°C to flow the PSG film 8 and at the same time, to melt the polycrystalline Si film 7 under the PSG film 8. It is converted into a thermal oxide film 70 (FIG. 1d). During this heat treatment, the gate electrode and lower wiring 4
The thermal oxide film 6 formed on the surface of the source and drain 5 formed on the Si substrate is prevented from being further oxidized because it blocks oxidizing agents such as oxygen.
The area is also not oxidized because the thermal oxide film 3 is formed thereon.

Thereafter, using a photolithography method, a photoresist is used as a mask to form a PSG film 8, a thermal oxide film 70 converted from a polycrystalline Si film, and a thermal oxide film 6 on the surface of the lower wiring 4.
Alternatively, the contact window 9 is opened by etching the thermal oxide film 3 on the surface of the Si substrate with a diluted solution of HF with NH ₄ F or the like. Then, a 1.2 μm thick Al film is formed by vacuum evaporation or the like, and an upper electrode 10 is formed by photolithography (FIG. 1e).

As mentioned above, the PSG film 8 easily passes the oxidizing agent through heat treatment in an oxidizing atmosphere, so the underlying semiconductor film 7 such as a polycrystalline Si film is easily thermally oxidized.
All of it is converted into a thermal oxide film 70, but the surface of the lower wiring 4 is covered with a thermal oxide film 6 before the PSG film 8 is formed.
is formed, the oxidizing agent is blocked and the lower wiring 4 is not thermally oxidized during the heat treatment.
Further, since the thermal oxide film 3 is formed on the surface of the source and drain 5 regions made of the Si substrate, they are not thermally oxidized as well.

During the heat treatment in an oxidizing atmosphere, the semiconductor film 7 is doped with phosphorus contained in the PSG film 8 formed thereon, resulting in a higher thermal oxidation rate than a semiconductor film without additives. The semiconductor film 7 is made by adding impurities such as phosphorus by mixing an impurity gas such as PH ₃ into the SiH ₄ described above during the formation of the semiconductor film 7, or by a thermal diffusion method after the film formation. When formed, the thermal oxidation rate can be further increased, and a thick thermal oxide film 70 can be formed even with a short heat treatment. Furthermore, by increasing the pressure in the reaction vessel to, for example, 7 atmospheres when performing heat treatment, the above-mentioned oxidation rate can be further increased, and the same effect can be obtained even with low-temperature heat treatment.

As in the above embodiment, when a contact window is opened by etching the PSG film, thermal oxide film, etc. with a diluted HF solution using a photoresist as a mask after heat treatment in an oxidizing atmosphere (see Fig. 1e). ) PSG film 8
Since the etching speed of the PSG film is higher than that of the thermal oxide film 70, 6 below, the thermal oxide film 70, 6 or the thermal oxide film 3 below it is etched after the PSG film is etched. Then, the PSG film 8 is largely etched in the lateral direction, and as a result, the opened contact window 9 becomes significantly larger than the opening diameter of the photoresist. To avoid this, as shown in Figure 2, a
After forming the PSG film 8 in the steps shown in ~c, a region larger than the contact window including the contact window portion is formed.
After the PSG film is removed by photolithography to form an opening 90 (FIG. 2a), the heat treatment described above is performed. Thereafter, a contact window 9 is opened in the opening 90 using photolithography (FIG. 2b), but when this contact window 9 is opened, the PSG film 8 has already been removed, and the etching speed is almost the same. Since only the thermal oxide films 70, 6 or the thermal oxide film 3 are etched, they are not etched to a large extent in the lateral direction, and therefore the opened contact windows 9 do not become too large, making it possible to open minute contact windows. can.

In the method for manufacturing a semiconductor device of the present invention described above, the process of oxidizing the semiconductor film covered with the PSG film and the process of fluidizing the PSG film are performed simultaneously, so the manufacturing process is greatly simplified. There is. Furthermore, the insulating film consists of three layers: the first insulating film formed by the manufacturing method of the present invention, the thermal oxide film converted from the semiconductor film, and the fluidized PSG film.
As mentioned above, since there is a thermal oxide film with a high dielectric strength, it has sufficient characteristics as an inter-wiring insulating film, with few defects that cause short circuits between wires and a high dielectric strength. Also, because the surface is a fluidized PSG film,
As described above, fine upper wiring can be easily formed. Furthermore, PSG films on semiconductor films tend to flow during heat treatment, and in particular, PSG films on semiconductor films to which phosphorus has been added do not have a drop in phosphorus concentration due to diffusion of phosphorus into the semiconductor film during heat treatment. It flows easily and can produce greater effects.

[Brief explanation of the drawing]

FIGS. 1a to 1e are partial cross-sectional views at each step of a method for manufacturing a semiconductor device according to an embodiment of the present invention,
FIGS. 2a and 2b are partial cross-sectional views of each step of the manufacturing method in which a part of the same process is improved. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate (P-type Si substrate), 4... Lower wiring, 6... First thermal oxide film, 7... Second semiconductor film (polycrystalline Si film), 8... Phosphorsilicate glass film ( PSG film), 70... second thermal oxide film.

Claims (1)

[Claims] 1. A step of heat-treating a semiconductor substrate on which a lower wiring made of a first semiconductor film is formed in an oxidizing atmosphere to form a first thermal oxide film on the surface of the lower wiring; A step of forming a second semiconductor film, a step of forming a phosphosilicate glass film, and a heat treatment in an oxidizing atmosphere to flow the phosphosilicate glass film and convert the second semiconductor film into a second semiconductor film. 1. A method for manufacturing a semiconductor device, comprising a step of converting into a thermal oxide film. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the second semiconductor film is a semiconductor film doped with phosphorus.