JPH08213385A - Insulating film forming method - Google Patents

Abstract

PURPOSE: To form an interlayer insulating film free from sharp step-difference, by performing plasma etching wherein a negative bias is applied to a silicon oxide film formed by using organic silicon compound. CONSTITUTION: A silicon oxide coating film 10 is formed on a substrate by an optical CVD method. The pressure in a reaction chamber 1 is adjusted, and high frequency power is applied between a mesh electrode and substrate retainer. TEOS/N2 O is used as reaction gas, and a silicon oxide coating film 11 is formed by a plasma CVD method. After the silicon oxide coating film is thickly formed so as to cover unevenness, reactive gas in a reaction chamber 1 is eliminated, etching gas is introduced, the pressure is adjusted, plasma discharge is generated by applying electric power across the mesh electrode and the substrate retainer, the formed coating film 11 is etched, and the sharp part of an uneven step-difference is eliminated. In this case, the uneven step-difference can be more smoothed by applying a negative bias to the substrate side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a method for forming a high-quality and high-quality insulating film on a surface to be formed under reduced pressure by photochemical vapor phase reaction and plasma chemical vapor phase reaction.

[0002]

2. Description of the Related Art Recently, the wiring area occupied in an IC chip has been increasing with the high integration and large scale of LSI. Therefore, it is becoming more and more important to make the wiring multi-layered and the pattern and wiring width finer.

The lateral dimension of patterns such as wiring and connection holes is miniaturized in accordance with the scaling rule, while the vertical dimension such as the thickness of electrode wiring and insulating film is related to wiring resistance, stray capacitance, withstand voltage, and It is necessary to meet the device specifications such as migration resistance, and it is not easy to miniaturize it in the horizontal direction. Further, the pattern of the wiring and the connection hole is formed by etching with strong anisotropy due to the miniaturization, so L
The end surface shape of the SI pattern becomes sharp.

Further, since the wiring is multi-layered, the LSI is naturally
The unevenness of the chip surface becomes severe. Such unevenness on the surface of the LSI chip leads to a decrease in pattern processing accuracy and a decrease in reliability such as disconnection of wiring. As a means for solving such a problem, a technique for flattening an interlayer insulating film is emphasized.

As a method for producing this interlayer insulating film,
The thermal CVD method is widely known as a conventional thin film forming technology by chemical vapor reaction (hereinafter referred to as CVD). This thermal CVD
According to the method, heat energy is applied to a reaction gas for film formation introduced into the reaction chamber to decompose or activate the gas to form a film. In this case, since the only energy supply for the reaction is heat, its temperature is also high, 500-800 ° C.
It was done in the range of. For this reason, it is impossible to fabricate a semiconductor element that is susceptible to high temperatures, and there has been a demand for a technique for forming a coating film at a low temperature, which is promising for next-generation LSI elements.
In addition, plasma CVD is used as a method to form a film at lower temperatures
The law is known. In this case, high frequency power is applied to the reactive gas introduced into the reaction chamber from the outside to decompose the gas,
It is activated to form a film on a heated substrate. In this case, the heating temperature is in the range of 200 to 400 ℃, but because the plasma, which is in a high-energy state, the reactive species that are decomposed and activated hit the film-forming surface and damage it, so that it is formed. Moreover, it has a drawback that it is difficult to obtain good characteristics at the interface between the coating film and the base substrate. In this case as well, as in the case of thermal CVD, it could not be used for compound semiconductors such as GaAs.

On the other hand, recently, there is an optical CVD method as a technique for solving these problems. This method applies light energy to a reactive gas and decomposes and activates it to form a film on the substrate, which does not require a high temperature as in the thermal CVD method, and the plasma CVD method. It is an ideal film forming method without physically giving damage to the underlying material as described above. As a method of flattening the insulating film formed by the above-described manufacturing method, a method of applying a liquid of an organic silicon compound onto a substrate surface having an uneven shape and subjecting it to vitrification by heat treatment, or having an uneven shape Various methods such as an etch-back method, in which the insulating film is etched back to smooth the uneven shape, are used. Each of these methods for forming a flat interlayer insulating film is divided into a step of forming an insulating film and a step of flattening, resulting in an increase in the number of steps, an increase in the number of manufacturing apparatuses, and a high cost.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve these conventional problems and to form an interlayer insulating film without abrupt steps.

[0008]

The present invention decomposes or activates a silicide gas and an oxidizing gas to cause a gas phase reaction accompanied by a photochemical gas phase reaction by an ultraviolet light source, and causes a gas phase reaction on a substrate to be formed. After forming a silicon oxide film to a predetermined thickness or performing a photochemical vapor phase reaction, a silicon oxide film is further formed to a predetermined thickness by a plasma CVD method and then etched back in the same reaction chamber. It is characterized in that processing is performed.

Further, if necessary, these steps are repeated to form an insulating film having no sudden uneven steps.
In other words, it provides a method for forming a silicon oxide insulating film without abrupt unevenness without forming it on the substrate to be processed after forming the insulating film. An experimental example will be shown below to show a method for producing the oxygen silicon film shown in the present invention.

[0010]

【Example】

[Embodiment 1] FIG. 2 shows a schematic view of an apparatus for forming a silicon oxide film used in this embodiment. In the drawing, a plurality of ultraviolet light sources (6) are installed in the ultraviolet light source chamber (4) in the reaction chamber (1), and the ultraviolet light source chamber (4) is almost equal to the pressure in the reaction chamber (1). Has been adjusted to The film-forming substrate (3) is installed in the reaction chamber (1) with the film-forming surface facing downward by the substrate support (2) which also serves as a substrate heating heater. This equipment uses a deposition-up method to prevent flakes and other dust generated during film formation from adhering to the substrate.

Among the reactive gases, the silicide gas and the oxide gas are mixed in the pipe, introduced into the reaction chamber through the gas nozzle (7), and mixed near the substrate (3). The direct excitation method was adopted in which the ultraviolet light emitted from the ultraviolet light source (6) which performs the photochemical vapor phase reaction is irradiated to the reactive gas through the transmission window (5). Further, the reaction was carried out without coating low vapor pressure oil for preventing the formation of a film on the transmission window (5). In particular, in the case of the present invention, since a silicon oxide film is formed, even if a coating film is formed on the transmission window, ultraviolet light is sufficiently transmitted, and thus it is not particularly necessary.

Further, a mesh electrode (8) for etching is placed on the outside light transmitting window (5). The mesh electrode (8) is configured such that high frequency power can be applied between the mesh electrode (8) and the substrate support (2) by a power source (9). If necessary, the mesh electrode (8) substrate support ( Transmitted light window (5) with power and bias voltage applied between 2)
And etching back of the substrate (3) to be processed can be performed in the same reaction chamber. Using this device, a reaction pressure of 1500 Pa to 7000 Pa, (11 to 53 Torr), a substrate temperature of 200 ° C to a substrate having irregularities as shown in FIG.
A silicon oxide film was formed by changing the ratio of monosilane and nitrous oxide as reactive gases under the conditions of 400 ° C., input ultraviolet light source power 13.56 MHz, and 200 W to 300 W.

In the case of the photochemical vapor phase reaction, the oxidizing gas has a high ratio of being activated, so that the ratio of N ₂ O to the amount of silicon is set.
It was added in a slight excess in the range of 0.005 to 0.05 and formed on a single crystal silicon semiconductor substrate, and the film thickness and refractive index were measured by an ellipsometer. The reaction between SiH ₄ and N ₂ O is, for example, 6 eV (153 Kcal / mol) 4.9 eV (11 eV) when the resonance lines at 18 nm and 254 nm of a low pressure mercury lamp are used as an ultraviolet light source.
It is 2.5 Kcal / mol) and it is easy to cut the interatomic bond energy if absorption can occur in the reactive gas molecule.

The respective atomic bond energies are shown below. Si─H 74.6 Kcal / mol Si─Si 76 Kcal / mol H─N 86 Kcal / mol H─H 104 Kcal / mol Si─N 105 Kcal / mol O─O 119 Kcal / mol N─O 149 Kcal / mol Si ─O 192 Kcal / mol N ─N 227 Kcal / mol The light absorption edge of SiH ₄ molecule has a peak on the shorter wavelength side than 185 nm, but it is considered that some light absorption is performed.

On the other hand, the photolytic reaction of N ₂ O is considered to be the following process. N ₂ O + hr (185 nm) → N ₂ + O ( ¹ D) When activated O ( ¹ D) attacks SiH ₄ molecule, weak bond Si-H is dissociated and replaced with oxygen radical to replace Si-O.
A bond is formed. The following reactions can be considered from the refractive index and infrared absorption of the oxygen-silicon coating in the range of SiH ₄ / N ₂ O of 0.005 to 0.05. The formation of SiH ₄ + 2N ₂ O → SiO ₂ + 2N ₂ + 2H ₂ hydrazine and ammonia may be considered, but it is difficult to think from the results of this analysis.

FIG. 3 shows the relationship between the reaction pressure and the film formation rate. The gas composition ratio was SiH ₄ / N ₂ O ratio 0.01, the substrate temperature was 400 ° C., the input ultraviolet light source power was 13.56 MHz, and the film formation conditions were 300 W. As the reaction pressure increases, the amount of raw material (reaction) gas present in the gas phase per unit time increases, the number of active species that contribute to film formation increases, and the film formation rate increases. It is also expected that the film formation rate decreases due to the fact that the active species collide with other molecules in a region having a negative polarity and the number of collisions with other molecules increases, and does not contribute to film formation (for example, becomes a secondary product).

That is, it is considered that the reaction pressure has an optimum region. FIG. 4 shows the film formation rate when the high frequency power density is varied in the plasma CVD method. The reaction pressure is 0.4 torr, the substrate temperature is 200 ° C, and the nitrous oxide flow rate of the bubbling carrier gas is 100 SCCM. Within this variable range, there is a linear increasing tendency with respect to the high frequency power density. That is, the rate of TEOS supply is not limited. TEOS usually does not thermally decompose below 600 ° C, so when it is introduced into the reaction space, it exists on the substrate surface or in the gas phase in a liquid or highly viscous gas state, so that the substrate temperature is low and the high frequency power density is small. Although it has good step coverage underneath, the film quality is
OH groups and C remain in the film and cannot be said to be necessarily good.

On the other hand, under the condition that the substrate temperature is high and the high frequency power density is large, the step coverage is slightly lowered, but the film quality is improved. However, hillocks are often generated on Al, which is a problem. From the above, it is considered that there are optimum conditions for the two parameters of the substrate temperature and the high frequency power density. It was found that at a certain reaction pressure, the substrate temperature was not raised too much, the viscous flow was promoted, and the film quality was stabilized by applying high frequency power and bias power to the substrate. The nitrous oxide used as the carrier gas here is also an oxygen supply source for the silicon oxide film formed.

FIG. 5 shows the film formation rate when the flow rate of nitrous oxide is varied in the plasma CVD method. The reaction pressure is 0.4 torr, the substrate temperature is 200 ° C, and the high frequency power density is 0.35 W / cm ² . Even if the flow rate of nitrous oxide is increased by 5 times, the film formation rate increases only by about 15%. That is, it is considered that the oxygen necessary for forming the silicon oxide film is sufficiently supplied by the decomposition of TEOS, and the oxygen radicals by the decomposition of nitrous oxide do not significantly contribute to the film formation.

FIG. 6 shows the etching rate when the high frequency power density is varied when the silicon oxide film is plasma-etched using sulfur hexafluoride. Reaction pressure is 0.4t
The orr, substrate temperature is 200 ° C, and SF ₆ flow rate is 25 SCCM. 0.
It was found that about 500 Å / min was obtained at 56 W / cm ² , and it could be used for the etch back process sufficiently, and it was possible to control the isotropic or anisotropic etching shape by applying a negative bias power to the substrate.

FIG. 7 shows the etching rate when the substrate temperature is changed. Reaction pressure 0.4 torr High frequency power density 0.56W
At a flow rate of / cm ² and an SF ₆ flow rate of 25 SCCM, there is almost no dependence on the substrate temperature, and it is considered that the high frequency power density determines the temperature. It can be said that the substrate temperature is one of the important parameters because the process has selectivity in the etching process when the interlayer insulating film is continuously formed. By such a photo-CVD method, a silicon oxide film was formed on a substrate having an uneven shape as shown in FIG. The convex portion on this substrate had a shape having a height of about 1 μm and a space of 0.8 μm. Since the silicon oxide film (10) was first formed on this substrate by the photo-CVD method, this uneven shape could be uniformly covered. (Fig. 1 (B))

Thereafter, the pressure inside the reaction chamber was adjusted to 10 Pa,
Between the mesh electrode (8) on the transmitted light window (5) and the substrate support (2) described above, a high frequency power such as 1 is generated by a power source (9).
80W of 3.56MHz power was applied. The reaction gas was TEOS / N ₂ O, the N ₂ O flow rate for bubbling was 100 SCCM, and the other conditions were the same as the photo-CVD, and the silicon oxide film (11) was formed by about 1.5 μm to 2.0 μm by the plasma CVD method ( Figure 1
(C)) Although the step coverage of silicon oxide formation by this plasma CVD method is slightly lower than that of photo CVD,
The film formation rate is as high as 0.5 to 1 μm / min, and it is highly productive.

As shown in FIG. 1C, a silicon oxide film is formed thickly so as to cover the irregularities, and then the reactive gas in the reaction chamber is exhausted and removed. Then, a halide gas such as SF _6, which is an etching gas, is used _. CF _3, CF ₄ , CF ₃ H, etc. are introduced into the reaction chamber, the pressure is adjusted to 10 Pa, and power is applied between the mesh electrode (8) and the substrate support (2) to cause plasma discharge and formation. The coated film (11) was etched to eliminate the abruptly uneven portion. (FIG. 1 (D)) At this time, when a bias voltage was applied between the mesh electrode (8) and the substrate support (2) at the same time, the shape of the uneven step could be controlled by etching. That is, when a negative bias voltage was applied to the substrate side, the uneven step could be made smoother.

After this treatment, etching was carried out to a depth of about 0.2 to 0.5 .mu.m to remove the abrupt portions of the uneven steps as shown in FIG. In this way, an interlayer insulating film without abrupt steps could be produced in the same device and reaction chamber. In addition, the coating on the reaction chamber inner wall and the transmitted light window (5) could be removed at the same time during the etching process, and it was not necessary to stop the device for cleaning, which led to improved productivity. Further, although the plasma CVD method and the photo-CVD method are used in combination in the production of the silicon oxide film in the present embodiment, it is obvious that the photo-CVD method alone may be employed.

[Embodiment 2] Under the same conditions as in Embodiment 1, a silicon oxide film is formed on the substrate shown in FIG. And replace the etchback under the same conditions as in Example 1.
About 500Å was applied. After that, a reactive gas is further replaced, and a silicon oxide film is formed again by the photo-CVD method under the same conditions. Such a cycle is repeated a plurality of times, and the interlayer insulation without sharp irregularities and steps as in Example 1 is performed. A film could be formed.

In the present embodiment, the film formation by photo CVD and the plasma etching are alternately performed, so that the reaction chamber contaminated by the film formation can be simultaneously cleaned by the etching process. In addition, it should be added that it is desirable that the uppermost part of the laminated structure of the interlayer insulating film is a photo CVD film. This is because when the second layer Al film is sputter-deposited, the TEOS silicon oxide film at the uppermost portion may adversely affect the Al film quality due to the gas released from the film (moisture, H ₂ etc.). . Therefore, the ideal layered structure of interlayer insulating film is photo CVD film / plasma CVD
Film / Photo CVD film.

The withstand voltage, which is important as an interlayer insulating film, can be sufficiently provided by the first-layer photo CVD film. For reference, the breakdown voltage of the photo CVD film is 5 MV / cm or more. Although the silicon oxide film is disclosed as the insulating film in the above embodiments, other insulating films, silicon nitride films, PSG, BPSG, and alumina films can be applied. Furthermore, not only silane but also other polysilanes (SinH _{2n + 2} ), dimethylsilane, tetramethylsilane, and other organosilicon compounds (SiH _r
It is also possible to use (CH ₄ ) _4-n ) if necessary.

[0028]

As described above, according to the present invention, at a high speed under a condition which is clearly different from the condition used conventionally,
Moreover, it is a method of forming a high-quality silicon oxide film,
For the first time, it became possible to use a film formed by the optical CVD method for the interlayer insulating film used in VLSI and the like.

According to the method of the present invention, an interlayer insulating film having no abrupt unevenness can be formed in the same reaction chamber of the same device, and the device cost and the manufacturing cost can be reduced.
In addition, it has the feature that the inner wall of the reaction chamber and the transmitted light window can be etched at the same time during the etch back process.

[Brief description of drawings]

FIG. 1 shows a process of producing an interlayer insulating film of the present invention.

FIG. 2 shows a schematic diagram of an apparatus used in the present invention.

FIG. 3 shows the relationship between the deposition pressure and the reaction pressure of the silicon oxide film formed by the photo-CVD method.

FIG. 4 shows the relationship between the deposition rate and the high frequency power density of a silicon oxide film formed by the plasma CVD method.

FIG. 5 shows the relationship between the deposition rate and the flow rate of nitrogen-zinc oxide formed by plasma CVD.

FIG. 6 shows the relationship between the etching rate and the high frequency power density of a silicon oxide film.

FIG. 7 shows the relationship between the substrate temperature and the etching rate during plasma etching of a silicon oxide film.

[Explanation of symbols]

 1 Reaction Chamber 2 Substrate Support 3 Coating Substrate 4 Ultraviolet Light Source Chamber 5 Transmitted Light Window 6 Ultraviolet Light Source 8 Mesh Electrode 9 Power Supply 10 Silicon Oxide Coating

Claims (4)

[Claims] 1. A method for forming an insulating film, which comprises subjecting a silicon oxide film formed using an organosilicon compound to plasma etching with a negative bias applied. 2. The method for forming an insulating film according to claim 1, wherein the gas used for plasma etching is a halide gas. 3. An insulating film forming method according to claim 1, wherein isotropic etching or anisotropic etching is performed by applying a negative bias. 4. A method for forming an insulating film, which comprises cleaning the reaction chamber at the same time as etching back a silicon oxide film formed by using an organic silicon compound by plasma etching with a negative bias applied.