JP2997743B2 - Insulating film - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a photo-chemical reaction on a surface to be formed at a high speed by a photochemical vapor reaction and a plasma chemical vapor reaction.
Moreover, the present invention relates to a high-quality insulating film. 2. Description of the Related Art Recently, as the integration and scale of LSIs have increased, the area of wiring occupying an IC chip has increased. For this reason, multilayer wiring, miniaturization of patterns and wiring widths are becoming increasingly important. The horizontal dimension of patterns such as wiring and connection holes is miniaturized in accordance with the scaling law, while the vertical dimension such as the thickness of electrode wiring and insulating film is determined by wiring resistance, stray capacitance, withstand voltage, and the like. It is necessary to satisfy the specifications of the element such as migration resistance, and it is not easy to miniaturize the device in the lateral direction. Further, since the wiring and connection hole patterns are formed by highly anisotropic etching for miniaturization, L
The shape of the end face of the pattern of SI becomes sharp. In addition, since the wiring is multi-layered, the
The irregularities on the chip surface become severe. Such unevenness on the surface of the LSI chip causes a reduction in pattern processing accuracy and a reduction in reliability such as disconnection of wiring. As a means for solving such a problem, a technique for flattening an interlayer insulating film is regarded as important. [0005] As a method of manufacturing this interlayer insulating film,
A thermal CVD method is widely known as a conventional thin film forming technique by a chemical vapor reaction (hereinafter referred to as CVD). This thermal CVD
According to the method, thermal energy is applied to a reaction gas for forming a film introduced into a reaction chamber to decompose or activate the gas to form a film. In this case, the energy supply for the reaction is only heat, so the temperature is also high, 500-800 ° C.
Was done in the range. For this reason, it is impossible to fabricate a semiconductor device that is vulnerable to high temperatures, and a technology for forming a film at a low temperature, which is promising as a next-generation LSI device, has been required.
Plasma CVD is also used as a method for forming films 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 ° C., but the high energy state of plasma causes the decomposed and activated reactive species to strike on the surface on which the film is formed, causing damage, thereby forming the film. In addition, it is difficult to obtain good characteristics at the interface between the film and the underlying substrate. Also in this case, it cannot be used for a compound semiconductor such as GaAs as in the case of thermal CVD. On the other hand, recently, there is an optical CVD method as a technique for solving these problems. In this method, a reactive gas is given a light energy to decompose and activate it to form a film on a substrate. It does not need to be heated to a high temperature unlike the thermal CVD method. This is an ideal film forming method without physically damaging the underlying material as in the 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 on a substrate surface having an uneven shape and performing a heat treatment to vitrify, and a method of forming an uneven shape Various methods, such as an etch-back method for performing an etch-back on an insulating film to smooth the shape of the unevenness, have been performed. 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, and the number of steps is increased, the number of manufacturing apparatuses is increased, and the cost is increased. SUMMARY OF THE INVENTION The present invention has been made to solve these conventional problems, and has as its object to form an interlayer insulating film having no sharp steps. According to the present invention, an interlayer insulating film of an LSI or a super LSI is made of a silicon oxide film containing a bond between silicon and nitrogen by being formed using an organic silicon compound. The insulating film, which is formed using an organosilicon compound, is formed using a silicon oxide film containing a bond between silicon and nitrogen. It is an insulating film characterized by the above. This insulating film is accompanied by a photochemical gas phase reaction by an ultraviolet light source, and decomposes or activates a silicide gas and an oxidizing gas to cause a gas phase reaction. Or by performing a photochemical vapor phase reaction, further forming a silicon oxide film to a predetermined thickness by a plasma CVD method, and then performing an etch-back process in the same reaction chamber. Further, if necessary, these steps are repeated to form an insulating film having no sharp unevenness.
In other words, it is intended to provide a method for forming a silicon oxide insulating film without abrupt irregularities without forming the insulating film on the substrate to be processed. An experimental example will be described below, and a method for forming the oxygen silicon film shown in the present invention will be described. [Embodiment 1] FIG. 2 is 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 an ultraviolet light source chamber (4) in a reaction chamber (1), and the ultraviolet light source chamber (4) is almost equal to the pressure of the reaction chamber (1). It has been adjusted to be. The substrate for film formation (3) is installed in the reaction chamber (1) by a substrate support (2) also serving as a substrate heating heater, with the film formation surface facing downward. In this apparatus, a deposition-up method is employed so that dust such as flakes generated during film formation does not adhere to the substrate. Among the reactive gases, silicide gas and oxide gas are mixed in a pipe, introduced into a reaction chamber from a gas nozzle (7), and mixed near the substrate (3). A direct excitation method in which ultraviolet light emitted from an ultraviolet light source (6) for performing a photochemical vapor phase reaction was applied to a reactive gas through a transmission window (5) was employed. In addition, the reaction was carried out without coating a low vapor pressure oil for preventing a film from being formed on the transmission window (5). In particular, in the case of the present invention, since a silicon oxide film is produced, even if a film is formed on the transmission window, ultraviolet light is sufficiently transmitted therethrough, so there is no particular necessity. Further, a mesh electrode (8) for etching is mounted on the external light transmission window (5). The mesh electrode (8) has a power supply between it and the substrate support (2).
(9) is applied so that high-frequency power can be applied. If necessary, power and bias voltage are applied between the mesh electrode (8) and the substrate support (2) to etch the transmitted light window (5). The substrate to be processed (3) can be etched back in the same reaction chamber. Using this device,
A reaction pressure of 1500 Pa is applied to a substrate having irregularities as shown in (A).
7000Pa, (11-53 Torr) Substrate temperature 200 ° C-400 ° C, input ultraviolet light source power 13.56 MHz, 200W-300W, silicon oxide film by changing the ratio of monosilane and nitrous oxide as reactive gas Was formed. [0013] For photochemical gas phase reaction, because a high proportion oxidizing gas is being its activation, the ratio of N ₂ O with respect to silicon content
A slight excess in the range of 0.005 to 0.05 was added, formed on a single crystal silicon semiconductor substrate, and the film thickness and the refractive index were measured by an ellipsometer. In the reaction between SiH ₄ and N ₂ O, for example, when the 18 nm and 254 nm resonance lines of a low pressure mercury lamp are used as an ultraviolet light source, the photon energy is 6. eV (153 Kcal / mol) 4.9 eV (11
(2.5 Kcal / mol), and if the reactive gas molecules can be absorbed, it is easy to cut off the interatomic bond energy. 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 following process is considered for the photolysis reaction of N ₂ O. N ₂ O + hr (185 nm) → N ₂ + O ( ¹ D) When activated O ( ¹ D) attacks the SiH ₄ molecule, the weak bond Si-H is dissociated and replaced with oxygen radicals to replace Si-O.
A bond is formed. The following reaction can be considered from the refractive index and infrared absorption of the oxygen silicon film when the SiH ₄ / N ₂ O ratio is in the range of 0.005 to 0.05. SiH ₄ + 2N ₂ O → SiO ₂ + 2N ₂ + 2H ₂ Hydrazine and ammonia may be produced, 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 a SiH ₄ / N ₂ O ratio of 0.01, a substrate temperature of 400 ° C., an applied ultraviolet light source power of 13.56 MHz, and a film forming condition of 300 W. As the reaction pressure is increased, the amount of raw material (reaction) gas present in the gas phase per unit time increases, the number of active species contributing to film formation increases, and the film formation rate increases. It is expected that in a region beyond this, the number of times that the active species collides with other molecules increases and does not contribute to the film formation (for example, becomes a secondary product), thereby lowering the film formation rate. That is, it is considered that there is an optimum region in the reaction pressure. FIG. 4 shows the film forming speed when the high frequency power density is varied in the plasma CVD method. The reaction pressure was 0.4 torr, the substrate temperature was 200 ° C., and the nitrous oxide flow rate of the carrier gas for bubbling was 100 SCCM. Within this variable range, it shows a linear increase tendency with respect to the high frequency power density. That is, the supply rate of TEOS is not limited. Since TEOS is not thermally decomposed below 600 ° C and is introduced into the reaction space, it is present in liquid or highly viscous gas state on the substrate surface or in the gas phase. Below, it has good step coverage, but the film quality is-
OH groups and C remain in the film, which is not always good. On the other hand, when the substrate temperature is high and the high frequency power density is high, the step coverage is slightly reduced, but the film quality is improved. However, the generation of hillocks on Al increases, which is a problem. From the above, it is considered that there are optimal conditions for the two parameters of the substrate temperature and the high-frequency power density. At a certain reaction pressure, it was found that the substrate temperature was not increased so much that the viscous flow was promoted, and the film quality was stabilized by applying high-frequency power and bias power to the substrate. Here, nitrous oxide used as a carrier gas is also an oxygen supply source of a silicon oxide film to be formed. FIG. 5 shows the film forming speed 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 a factor of 5, the deposition rate increases only by about 15%. That is, it is considered that oxygen necessary for forming the silicon oxide film is sufficiently supplied by the decomposition of TEOS, and oxygen radicals by the decomposition of nitrous oxide do not greatly 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 subjected to plasma and etching using sulfur hexafluoride. Reaction pressure is 0.4t
orr, substrate temperature is 200 ° C., SF ₆ flow rate is 25 SCCM. 0.
It was found that about 500 Å / min was obtained at 56 W / cm ^2, which was sufficient for the etch-back process, and that the isotropic or anisotropic etching shape could be controlled by applying a negative bias power to the substrate. FIG. 7 shows the etching rate when the substrate temperature is varied. Reaction pressure 0.4torr High frequency power density 0.56W
It is considered that there is almost no substrate temperature dependency at a flow rate of 25 SCCM / cm ² and SF ₆ , and it is almost determined by the high-frequency power density. The substrate temperature is one of the important parameters in the etching step when the interlayer insulating film is continuously formed because the process has selectivity. By such a photo-CVD method, a silicon oxide film was formed on a substrate having a concavo-convex shape as shown in FIG. The projection on this substrate had a shape of about 1 μm in height and 0.8 μm in space. First, a silicon oxide film (10) was formed on the substrate by a photo-CVD method, so that the unevenness could be covered uniformly. (FIG. 1 (B)) Thereafter, the pressure in the reaction chamber was adjusted to 10 Pa,
The mesh electrode (8) above the transmitted light window (5) and the substrate support
During (2), a high frequency power of, for example, 13.56 MHz power of 80 W was applied by the power supply (9). The reaction gas is TEOS / N ₂ O, the flow rate of N ₂ O for bubbling is 100 SCCM, and the other conditions are the same as in the photo CVD, and the silicon oxide film (11) is formed by the plasma CVD method.
(FIG. 1 (C)) Although the step coverage of the silicon oxide formation by the plasma CVD method is slightly lower than that of the photo CVD, the film formation rate is 0.5 μm to 2.0 μm.
High speed of 1 μm / min. As shown in FIG. 1 (C), after forming a thick silicon oxide film over the unevenness, the reactive gas in the reaction chamber is evacuated and removed, and then a halide gas such as SF6, which is an etching gas _. CF _3, CF _4, CF ₃ introducing H, etc. into the reaction chamber, and the pressure was adjusted to 10 Pa, the mesh electrode (8) and the substrate support
(2) Electric power was applied during the period to cause plasma discharge, and the formed film (11) was etched to eliminate the sharply raised portions of the uneven steps. (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 steps could be controlled by etching. That is, when a negative bias voltage was applied to the substrate side, the unevenness step could be made smoother. By performing this process, etching was performed at about 0.2 to 0.5 μm to remove sharply abrupt portions of uneven steps as shown in FIG. 1 (D). In this way, an interlayer insulating film having no sharp steps could be manufactured in the same apparatus and the same reaction chamber. In addition, the coating on the inner wall of the reaction chamber and on the transmitted light window (5) could be removed at the same time during the etching process, and there was no need to stop the apparatus for cleaning, which led to an improvement in productivity. In this embodiment, the silicon oxide film is formed by using both the plasma CVD method and the photo CVD method. However, it is apparent that the silicon oxide film may be formed only by the photo CVD method. Example 2 A silicon oxide film was formed on a substrate shown in FIG. 1A by the photo-CVD method under the same conditions as in Example 1 by about 5,000.degree. Was replaced, and the etch-back was performed under the same conditions as in Example 1.
Applied about 500 Å. Thereafter, the 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 insulating film without sharp irregularities similar to that of the first embodiment is obtained. A film could be formed. The present embodiment is characterized in that the formation of a film 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 an etching process. It should be added that the uppermost part in the laminated structure of the interlayer insulating film is preferably a photo CVD film. This is because when the second Al film is deposited by sputtering, the uppermost part of the TEOS silicon oxide film may have an adverse effect on the Al film quality due to outgassing (water, H ₂ etc) from the film. . Therefore, the ideal laminated structure of the interlayer insulating film is a 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 withstand voltage of the photo CVD film is 5 MV / cm or more. Although a silicon oxide film is disclosed as an insulating film in the above embodiments, other insulating films, silicon nitride films, PSG, BPSG, and alumina films can be applied. Not only further silane as a reactive gas, and other polysilanes (SinH _{2n + 2),} dimethylsilane, organosilicon compounds such as tetramethylsilane (SiH _r
(CH ₄ ) _4-n ) can be used as needed. As described above, the present invention can be performed at a high speed under conditions clearly different from those used conventionally.
Moreover, it is a method of forming a high quality silicon oxide film,
For the first time, it has become possible to use interlayer insulating films used in VLSIs, etc., with films formed by photo-CVD. According to the method of the present invention, it is possible to form an interlayer insulating film having no sharp unevenness in the same reaction chamber of the same apparatus, thereby reducing the manufacturing cost of the apparatus.
In addition, the etching of the reaction chamber wall and the transmitted light window can be performed at the same time during the etch back process.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a step of producing an interlayer insulating film of the present invention. FIG. 2 shows a schematic diagram of the apparatus used in the present invention. FIG. 3 shows a relationship between a reaction pressure of a silicon oxide film formed by a photo-CVD method and a film formation rate. FIG. 4 shows a relationship between a high-frequency power density of a silicon oxide film and a film forming rate by a plasma CVD method. FIG. 5 shows the relationship between the film formation rate and the flow rate of zinc zinc oxide by the plasma CVD method. FIG. 6 shows a relationship between an etching rate and a high-frequency power density of a silicon oxide film. FIG. 7 shows a relationship between an etching rate and a substrate temperature during plasma etching of a silicon oxide film. [Description of Signs] 1 Reaction chamber 2 Substrate support 3 Film forming substrate 4 Ultraviolet light source chamber 5 Transmitted light window 6 Ultraviolet light source 8 Mesh electrode 9 Power supply 10 Silicon oxide film

   ────────────────────────────────────────────────── ─── Continuation of front page       (56) References JP-A-60-165728 (JP, A)                 JP-A-62-7122 (JP, A)                 Nikkei Microdevices [26] (1987-               8-1) p. 125-133                 Journal of Electr               onic Materials, Vo               l. 13, No. 3, 1984 p. 593-602

Claims (1)

(57) [Claims] A method for forming an interlayer insulating film of an LSI, comprising: forming a silicon oxide film having a uniform thickness on an uneven surface on a surface to be formed having the uneven shape.
A film is formed, and an organic silicon compound and nitrogen oxide are used on the uniform silicon oxide film to form an acid thicker than the uniform silicon oxide film.
After the silicon oxide film is formed by the plasma CVD method,
The unevenness of the thick silicon oxide film suddenly
By removing the steep part, the surface becomes uneven
Insulating film characterized by forming a smooth interlayer insulating film
Forming method. 2. The uniform silicon oxide film is formed by using a photo CVD method.
2. The insulating film according to claim 1, wherein the insulating film is formed.
Forming method. 3. The organic silicon compound is TEOS.
The method for forming an insulating film according to claim 1.