JP2695778B2 - Thin film formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method of forming a thin film used for manufacturing a semiconductor device such as an VLSI device. (Prior art) The thin film forming method is roughly classified into chemical vapor deposition (Chen).
ical Vapor Deposition (CVD) and physical vapor deposition (P
hysical Vapor Deposition (PVD). CVD
The method is a method of forming a thin film on a substrate by using a chemical reaction in a substrate surface or in a gas phase, and is mainly used for forming an insulating film such as a silicon oxide film or a silicon nitride film.
In addition, the PVD method forms a thin film by colliding deposited particles struck into a gas phase by sputtering or the like to form a thin film, and has been mainly used for forming a metal film. On the other hand, in recent VLSI devices, a technique of depositing a thin film in a trench having a high aspect ratio (depth / width) is becoming essential. But,
As shown in FIG. 7A, a conventional plasma CVD method (for example, J, L, Vossen & W, Kerr, Thin Film Processes: A)
When insulator (19) is deposited in deep groove (18) formed in Si substrate (17) using cademic Press, 1978, etc., deposition species deposited in the gas phase are deposited on corner 23. Is large,
The deposited species gradually become difficult to enter the bottom of the groove, so that a cavity 21 is formed and the step coverage characteristics deteriorate. As a method for improving the step covering shape, a technique called a via sputtering method, which is one of the PVD methods, is used (for example, T, Mogami, M, Morim).
oto & H, Okabayashi: Extended Abstracts 16 th Conf.
Solid State Devices & Materiale, Kobe, 1984, P43).
In this method, for example, a silicon oxide film is formed while the substrate surface is physically sputtered with Ar ions, so that the deposition does not occur at the corner 23 in FIG. Occurs. Therefore, it is possible to embed in the groove, but since the deposited species in the gas phase obliquely enter the premises, it is still difficult to embed the groove in the aspect ratio> 1. Further, since a competitive reaction between removal and deposition of the deposited film by physical sputtering is used, the net deposition rate is low and productivity is extremely poor. Furthermore, recently, an ECR bias sputtering method (for example, H, OiKawa, SEMI TECHNOLOGY SYM, 198
6, E3-1) has been proposed, but the problem described above is reduced, but it is not an essential solution. In addition, for example, the pyrolysis method of TEOS (for example, R, D, Rung, Y, Momose &
When a silicon Si oxide film is formed using Y, Nagakubo, IEDM, Tech, Dig, 1982, P237, excellent step coverage characteristics as shown in FIG. 7B are exhibited due to the large surface mobility of the deposited species.
However, when the oxide film embedded in the groove is cleaned by, for example, a diluted HF solution by this method, the removal speed of the oxide film in the central portion 25 is abnormally high as shown in FIG. At present, equalization cannot be realized. It is considered that this is because the strain of the oxide films grown from both sides of the trench wall remains near the center. It is considered that it is extremely difficult to satisfactorily fill a groove having a high aspect ratio even by a method of forming a thin film with a uniform film thickness on a substrate in a conformable manner. (Problems to be Solved by the Invention) In the present invention, when a groove having a high aspect ratio formed in a substrate to be processed such as a semiconductor described above is buried with a thin film, a cavity is formed inside the groove. Another object of the present invention is to provide a method for forming a thin film that solves the conventional problems such as poor step coverage characteristics on a substrate surface. [Structure of the Invention] (Means for Solving the Problems) The present invention provides a method for storing a substrate to be processed having a concave portion formed on a surface thereof in a reaction vessel, and introducing a reaction gas into the reaction vessel. An intermediate product is formed from the reaction gas by generating plasma in the reaction vessel, and the substrate to be processed is cooled and maintained at a temperature equal to or lower than the boiling point of the intermediate product, thereby forming the intermediate on the surface of the substrate to be processed. A method of forming a thin film, wherein a thin film is formed so as to fill the concave portion by forming a liquid layer mainly composed of a product, and the liquid layer is accumulated at the bottom corner of the concave portion and solidified by decomposition. I will provide a. (Operation) (1) According to the present invention, thin films are sequentially formed in a stacked manner from the bottom of a groove having a high aspect ratio, so that it is possible to selectively and ideally completely fill the inside of the groove. (2) After the trench is completely buried, since the deposition is continued as it is, ultra-planarization can be performed simultaneously with the burying. (3) Further, since the above process can be realized at a low temperature,
Ideal for future LSI. (Examples) Hereinafter, details of the present invention will be described with reference to the illustrated examples. FIG. 1 is a schematic diagram showing a thin film forming apparatus according to one embodiment of the present invention. In the figure, reference numeral 1 denotes a grounded vacuum vessel, which is a reaction vessel. A gas inlet 2 is provided in the reaction vessel 1.
A predetermined first and second reactive gas is introduced from the reactor.
The gas in the reaction vessel is exhausted from the gas exhaust port 3. In the reaction vessel 1, a cathode (first electrode) 5 is disposed at a position facing the upper wall 4 of the vacuum vessel acting as an anode (second electrode). A substrate 6 to be processed is placed on the first electrode, and a cooled nitrogen gas 7 flows through the substrate to cool the substrate. Further, a heating means for raising the temperature is provided.
Further, a high frequency power supply 9 is connected to the first electrode via a matching circuit 8. Further, a heater 11 is wound around a region other than the substrate to be processed of the reaction vessel, for example, a wall 10 of the reaction vessel, thereby preventing deposition of a deposited film. Although not shown, another vacuum vessel filled with a vacuum or an inert gas is provided between the reaction vessel 1 and the atmosphere for loading and unloading of the substrate 6 to be processed, and loading and unloading is performed via this vacuum vessel. Means are provided. By using a so-called load lock for the reaction vessel, the reliability of the process is greatly improved. In the figure, reference numeral 16 denotes an insulator. FIG. 2 shows still another embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals. In this embodiment, a thin film is deposited on the substrate 6 to be processed in the same manner as in the previous embodiment, and then the substrate 6 is transported to another reaction vessel 12 via a transporter (not shown) and heated. (Not shown) on a holder 13 provided with a heat treatment. The heat treatment may be performed by irradiating an infrared lamp 14 or the like from above the base 6, for example, in addition to the heating from the base side so as to instantaneously increase the base temperature. Also, the gas inlet during this heat treatment
An inert gas or a first reactive gas can be introduced from 2a. Further, a high frequency power supply 9 is connected via a matching circuit 8 so that plasma can be generated during heating. In the figure, reference numeral 15 denotes a gate valve. The present invention can be applied in various ways. For example, as means for generating plasma, a high-density plasma may be formed by further applying an external magnetic field between the parallel plate electrodes to which the RF power is applied. Other ECR (Electron Scycro)
tron Resonance) discharge, hollow cathode discharge, or
The substrate to be processed may be arranged in a vacuum vessel made of an insulating material such as quartz, and external high-frequency power may be applied to cause discharge. Next, an embodiment of a thin film deposition method according to the present invention using the apparatus shown in FIG. 1 will be described. Here, O ₂ was introduced into the reaction vessel 1 as the first reactive gas, and tetramethylsilane si (cH ₃ ) 4 (TMS) was introduced as the second reactive gas. At this time, a state in which a silicon oxide film is formed on the surface of the Si (silicon) substrate of the substrate 1 to be processed is shown in FIG. The abscissa indicates the substrate temperature, and the ordinate indicates the deposition rate. The cross-sectional view shows the manner in which the shape of the silicon trench (17) formed in the silicon substrate (17) is different depending on the substrate temperature. Plasma was generated by applying RF power of 13.56 MHZ between the first and second electrodes and causing a high-frequency discharge. O ₂ in the reaction vessel
40 cc / min and TMS at 5 cc / min, total pressure 5 × 10 ^-3
Torr. In addition, a magnet was arranged on the second electrode side so that high-density plasma was obtained. From FIG. 3, it was found that the deposition rate showed the maximum value with respect to the change in the substrate temperature. Observation of the buried shape in the silicon trench groove shows that, when the aspect ratio of the trench groove is 1 or more, as shown in FIG. ₂ was deposited on the substrate so that snow was piled up, and so-called conventional plasma CVD was performed. On the other hand, as shown in FIG. 3 (b), as the substrate temperature decreases, preferential deposition decreases at the corner of the groove entrance, and it can be seen that the trench can be completely buried at the substrate temperature of −20 ° C. or less. Was.
This phenomenon is considered to occur by the following mechanism. First, hexamethyldisiloxane (Si (CH ₃ ) ₂ ) ₂ O, which is a reaction product of O radical and TMS, and trimethylsilanol Si
An intermediate product such as (CH ₃ ) ₃ OH liquefies at the temperature shown in FIG. 3, and a liquid layer is formed on the substrate surface. SiO ₂ particles that have further reacted in the gas phase are taken into this liquid layer. Further, it is considered that the oxidation proceeds while O radicals enter and O ions are implanted. On the other hand, the liquid layer can be most stably present at the corner of the bottom of the trench where a large contact area can be obtained with the substrate surface, since the liquid layer is well adapted to the substrate surface.
As a result, when observing the time change of the deposition, the liquid layer is decomposed and solidified from the corner at the bottom of the trench groove, and the deposition of the silicon oxide film formed thereby starts. Accordingly, in this deposition, as shown in FIG. 4, a film is formed in a stacked manner from the bottom of the trench groove, so that the filling into the high aspect ratio groove and the ultra-flattening, which were conventionally impossible, can be performed. It has become possible. Further, since the film can be formed at a low temperature, it is effective for forming an interlayer insulating film in a multilayer wiring process. If N ₂ or NH _{4 is used} instead of introducing O ₂ , a silicon nitride film (Si ₃ N ₄ ) can be formed. In addition, as a second reactive gas, a raw material containing at least one element included in Groups 2 to 6 in the periodic table of the elements is used, and by appropriately changing the substrate temperature, the oxides thereof can be used. It is needless to say that nitrides and nitrides can be easily formed. Further, the gas pressure in the reaction vessel is not limited to the above-mentioned 10 ^-3 Torr, and it goes without saying that the most efficient pressure region is selected according to the discharge method to be used and the reactive gas. Note that when an inert gas such as Ar or He is added to the first reactive gas, the deposited species becomes a metastable active species and has a long life, so that deposition can be performed more efficiently. Alternatively, a single kind of reactive gas may be used to deposit a desired film by a technique such as a thermal decomposition method. During film formation, for example, excimer laser light of 193 nm wavelength or ions,
It has been experimentally confirmed that when the surface is irradiated with electrons or the like, the above-mentioned liquefied layer is activated, the surface migration of the active species in the layer is increased, and the embedding and flattening are performed more completely. In addition, in the formation of the silicon oxide film, for example, when impurities such as POCI ₃ , PCI ₃ , PH ₃ , BCI ₃ , B ₂ H ₆ , and ASH ₄ are added to TMS, an oxide film containing these impurities is formed, This is buried in the trench, and thereafter, impurities can be diffused into the silicon substrate by, for example, instantaneous heating using a heater or a lamp. Conventionally, for example, as shown in FIG. 5, an oxide film containing impurities was formed along the side wall by a thermal CVD method or the like. However, in practice, the impurity concentration in the oxide film formed on the side wall of the silicon trench was changed. Was lower than that of the flat portion, and the desired specific resistance could not be obtained on the side wall. As is apparent from the time course of the deposition shown in FIG. 4, the amount of impurities incorporated in the oxide film of the present invention is extremely uniform. Therefore, after the deposition as shown in FIG. The above problem was solved all at once. The diffusion layer as shown in FIG. 6 is indispensable for obtaining a sufficiently large memory capacity of a large-capacity memory device such as 16M or 64MDRAM in the future. If the above-mentioned heat treatment is performed in-situ after the film is formed, for example, in the treatment chamber of FIG. 1 or FIG.
Heavy metal contamination such as carbon or nickel can be completely avoided and a high quality film deposited. Incidentally, in the reactive gas, for example, by mixing the gas containing H ₂ and a halogen element, is reduced a methyl group in the TMS, more stable CH ₄ and CH ₃ for such CI is formed is removed In addition, the concentration of carbon impurities in the film is reduced, and higher quality is achieved.
Further, for example, H ₂ , N _2, etc. and AI (CH ₃ ) ₃ , Ti (C
Organometallic compounds such as _{2 H 5) 2, W (} CO) 6, Cr (CO)
It has been confirmed that when a carbonyl metal or a metal halide such as No. ₆ is used, the metal can be embedded in a high aspect ratio space such as a contact hole. In addition to the above-mentioned thin film formation, for example, GeH ₄ , SiH ₄ , SiCI ₄ , GeC
By using a gas containing at least Si, such as I _4, it is possible to deposition of Si and Ge. AS (CH ₃ ) ₃ , ASH ₃ , Ga (C
If H ₃ ) ₃ or GaH ₃ is used, it is possible to deposit a group III-V compound such as GaAs, and if a reactive gas containing In and P is used, a group II-VI compound such as InP can be deposited. . Further, by using a reactive gas containing at least carbon and hydrogen, it becomes possible to deposit various polymer organic films. For example, introducing methacrylsan methyl (MMA)
By lowering the substrate temperature to −30 ° C. or less and performing deposition, PMMA used for an electron beam resist can be formed. [Effects of the Invention] As described in detail above, according to the present invention, it is possible to completely bury high-aspect-ratio fine grooves at a low temperature without generating cavities. This is extremely effective for forming an interlayer insulating film of wiring. Further, since a uniform plasma can be used for the substrate to be processed, the present invention can form a highly uniform film particularly on a large-diameter wafer, and at the same time, can obtain a high deposition rate.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 4 and 6 are views for explaining an embodiment of the present invention, and FIGS. 5 and 7 are views for explaining a conventional example. 17: substrate (such as Si), 18: deposited film, 19: cavity, 20: deposited film containing impurity for forming diffusion layer, 21: diffusion layer.

   ────────────────────────────────────────────────── ─── Continuation of front page    (56) References JP-A-61-218134 (JP, A)                 JP-A-57-172741 (JP, A)                 JP-A-57-178317 (JP, A)                 JP-A-61-247035 (JP, A)                 JP-A-59-168643 (JP, A)                 JP-A-63-207121 (JP, A)

Claims (1)

(57) [Claims] An intermediate product is formed from the reaction gas by housing a substrate to be processed having a concave portion formed on the surface thereof, introducing a reaction gas into the reaction container, and generating plasma in the reaction container. Then, the substrate to be processed is cooled and maintained at a temperature equal to or lower than the boiling point of the intermediate product, whereby a liquid layer mainly composed of the intermediate product is formed on the surface of the substrate to be processed, and the liquid layer is formed in the concave portion. Characterized in that the thin film is deposited so as to fill the concave portion by flowing into the substrate and decomposing and solidifying from the bottom surface of the concave portion. 2. 2. The thin film forming method according to claim 1, wherein the reaction gas contains oxygen and an organic silane-based gas, and the temperature below the boiling point is -20 [deg.] C. or less. 3. The substrate to be processed is a silicon substrate, the thin film is a silicon oxide film, and a gas containing an element serving as an n-type impurity or a p-type impurity in the silicon substrate is added to the reaction gas. 2. The method for forming a thin film according to claim 1, wherein: