JPS6152231B2 - - Google Patents

Description

[Detailed description of the invention]

Semiconductor device process technology is constantly progressing, and thin film production technology in particular is oriented towards lowering the production temperature. Plasma as a means of lowering the temperature
CVD (chemical vapor deposition) film production technology is already known, but photo-CVD film production technology has recently been attracting attention. The present invention relates to an improvement of a thin film producing reactor for a photo-CVD apparatus. First, the optical CVD method will be explained. In the photo-CVD method, the reaction gas reacts with light energy, and not only can the generation temperature be lowered, but also there is no high-energy particles such as ions and electrons in the plasma CVD method, so there is less damage to the grown film by ions. In addition, since it is easy to make the irradiation intensity of light uniform, it is easy to make the thickness of the grown film uniform, and it is also easy to process large diameter wafers. It is expected to become an important branch of CVD film production technology in the future because of the small number of step depressions that occur in the thin film pattern. The reaction formula of the photoCVD method is expressed by the following formula. hν+Hg uses ultraviolet energy from a mercury lamp as light energy and catalytically generates Hg.
(gas) is used, and 100 to 200°C represents the temperature at which a thin film is formed on a wafer. In any of the above reactions, a low-pressure mercury lamp having the emission spectrum shown in FIG. 1 is currently used as the light source in many cases. FIG. 2 is a schematic structural diagram of a typical example of a conventional photo-CVD reactor. Reference numeral 1 in the figure is a quartz window plate that allows ultraviolet rays to pass through.The upper part forms the light source chamber, and the lower part forms the reaction chamber. 2
is a mercury lamp unit for ultraviolet light, 3 is a reflector, 4 is
is a group of wafers (substrates) placed on the susceptor 5. 6 is an infrared lamp unit, 7 is a thermocouple, 8
is an auxiliary heater, 9 is a gas inlet into the reaction chamber, 10 is
is the exhaust port to the vacuum pump. In this reactor, the substrate 4 is heated by an infrared lamp unit 6 (the auxiliary heater 8 is an auxiliary plate that prevents the substrate from being directly irradiated with infrared light and improves the temperature distribution of the substrate). A reaction gas of a material determined by the thin film formed on the substrate is passed into the reactor from the gas inlet 9, and the energy of ultraviolet light transmitted through the quartz window plate 1 is taken in from the mercury lamp unit 2 to be applied onto the substrate. It produces a thin film at low temperatures. However, a furnace having such a structure has the drawback that a produced film gradually adheres to the entrance window surface (the surface facing the reaction chamber, the bottom surface in the figure) of the quartz plate 1, and the amount of irradiated light decreases. It has been reported that this phenomenon occurs in the case of polysilicon films, and that the formation rate drops dramatically when the formed film exceeds 300 Å, but at present no device has been found that can solve this problem. The present invention was made to solve this problem, and will be described in detail below. FIG. 3 is a schematic structural diagram of a photo-CVD reactor in which the present invention is implemented. Symbols 1, 2, 4, 5, 6 in the diagram
are common to FIG. 1, but the structure and therefore the arrangement of the furnaces are different. In other words, 1 is a window (plate) made of anhydrous quartz, which transmits light energy such as ultraviolet rays into the reaction chamber 12.
Transmits light into the interior with high transmittance. The upper part of the reaction chamber is isolated from the outside air and vacuum-sealed by the quartz window 1 and the O-ring. For the quartz window 1, an anhydrous quartz material with excellent ultraviolet transmittance is used. 2 is wafer 4
A mercury lamp unit supplies ultraviolet light energy near the surface of the wafer, and 4 is a wafer (substrate) on which a thin film is formed by gas phase reaction. 5 is a susceptor that indirectly heats the wafer (mainly silicon);
A carbon material coated with SiC is used. Reference numeral 6 denotes an infrared lamp unit for heating the susceptor 5. A halogen lamp is usually used as the lamp, and a reflector is attached to irradiate the front surface with lamp light. This lamp unit is installed outside the reaction chamber to facilitate lamp replacement, and is also provided with a mechanism for moving it vertically and horizontally. Reference numeral 11 denotes a second quartz window (plate) that transmits infrared light energy to the susceptor 5 in the reaction chamber 12 where a gas phase reaction is carried out, and the lower part of the reaction chamber is isolated from the outside air by this quartz window and the O-ring. ing. Reference numeral 13 denotes a PFA film, which serves to spatially separate the interior of the reaction chamber 12 into the quartz window 1 side and the reaction chamber 12 side so as to prevent reaction products and reaction gas from adhering to the quartz window 1. As will be explained further later, PFA film is heat resistant and has good UV transmittance. 14 is a roll of PFA film, 15 is a film roller for imparting rotational motion to the roll 14, and 16 is an auxiliary roller for smoothly winding and feeding the PFA film 13. 17 is a chamber for the film supply chamber 20a and the film storage chamber 20b, and 18 is a gas purge port, which prevents reaction products and reaction gas from entering the quartz window 1. This section is shown in detail in the purge gas and reaction gas flow chart of FIG. 4, 19a is an upper guide, 19b is a lower guide 22 for reaction gas, 23 is a purge gas, and 24 is an exhaust gas.
Returning to FIG. 3, 20a is a film supply chamber in which an auxiliary roller 16, a film roller 15, and a PFA film roll 14 are stored. A film storage chamber 20b stores an auxiliary roller 16, a film roller 15, and a PFA film roll 14. A water-cooled jacket 21 serves to prevent overheating of the O-ring in the reaction chamber 12, the film, the film supply chamber 20a, and the film storage chamber 20b. Now, the feature of the reactor of the present invention shown in FIG. 3 is that, in order to solve the above-mentioned conventional problems, it has a high usable heat resistance temperature and has a good transmittance of ultraviolet rays. A gas purge chamber (which allows intermediate exhaust including a gas purge port 18) is provided between the reaction chamber 12 and the quartz window 1 via a PFA film to allow gas to enter and exit the quartz window as shown in FIG. Window 1 is configured to prevent reaction products from adhering to the PFA film, and the film with reaction products adhering to it is automatically wound up at any time to ensure that a new film is always replaced. Supplied into the reaction chamber, lamp unit 2
This is because it prevents the amount of incident light from decreasing further. FIG. 5 shows the transmittance characteristics of anhydrous quartz plates with respect to the wavelength of light for quartz plates with thicknesses of 1.5 mm, 10 mm, and 30 mm, and the differences depending on the thickness are small. Figure 6 shows the transmittance characteristics of a PFA film with respect to the wavelength of light, when the film thicknesses are A: 70μ and B: 90μ. PFA film is a fluorine film made of a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene, and is considered to be a thermoplastic version of the conventional PTFE (commonly known as Teflon). In Japan, commercially available products include Toyoflon PFA Film (trade name). This film has the highest mechanical strength among fluorine films at high temperatures, and is chemically stable and is not attacked by almost all chemicals, solvents, and oils. Its properties are shown in the table below. Generally, synthetic resin films such as PFA films have the property of generating heat and solidifying themselves when irradiated with ultraviolet rays, but in the reactor with the structure of the present invention, this property causes a fatal defect.

[Table] Therefore, we conducted an ultraviolet irradiation test on PFA film. As a result of a test at room temperature, the temperature of the film was below 40°C, and no solidification was observed, demonstrating that it is sufficiently durable for practical use. Next, a partial structure of the reactor of the present invention will be further explained with reference to FIG. In order to minimize the adhesion of reaction products to the lower surface of the quartz window 1, PFA film guides 19a and 19b are used between the reaction chamber 12 and the quartz window 1 except for the path of incidence of ultraviolet rays.
(the shaded area in Figure 4). Furthermore, in order to prevent the reaction gas from going around the quartz window 1, the flange on the quartz window 1 side has a
Individual grooves are provided, and the reaction gas is prevented from flowing into the quartz window 1 by performing gas purge 18 from the inner circumferential side of the grooves and exhaust gas 24 from the outer circumferential side. There is. Moreover, if the pressure on the quartz window 1 side is made even slightly higher than the pressure in the reaction chamber 12, the reaction gas purge effect of this gas purge method will be further enhanced, so the probability that the reaction gas will reach the quartz window 1 is extremely small. Therefore, adhesion of reaction products to the surface of the quartz window 1 hardly occurs. Also, during CVD film formation, reaction products adhere to the PFA film, reducing the amount of ultraviolet irradiation and slowing down the formation rate. When the film is wound onto the roll 14 in the film storage chamber 20b at the right end in FIG. 3 and a new film is supplied from the roll in the film supply chamber 20a, the amount of ultraviolet ray irradiation is restored and the generation speed is increased. By repeating this operation, the desired film thickness (usually 5000
It is possible to obtain a CVD film with a thickness of 10,000 Å to 10,000 Å. Needless to say, a structure that facilitates film replacement is desirable. Therefore, the PFA film guide (shaded area in Figure 4) has a structure that allows it to be separated into upper and lower guides 19a and 19b.To replace the film, the flange to which the upper guide 19a is fixed and the upper flange of each roll chamber 17 are separated. It is now easy to do once you open it. Further, since the roll chamber 17 is intermediately exhausted between the reaction chamber 12 and the reaction chamber 12, there is almost no inflow of reaction gas. Therefore, there is no problem of contamination due to reaction gas. On the other hand, since this roll chamber has a drive unit, there is a slight risk of generating a small amount of fine powder, but since intermediate exhaust is performed by the exhaust 24, this fine powder hardly ever enters the reaction chamber 12. Finally, we will explain the cooling of PFA film. As shown in the table above, PFA film is
The limit temperature for use is 260°C on the high temperature side, and it is desirable to keep it as low as possible. Therefore, the side surfaces of the reaction chamber and the lower surface of the lower guide 19b are water-cooled. For example, PFA film has a thickness of 25, 50,
5 types: 75, 100, 125 (each μm), width 500, 1000
Two types (each mm) and one with a film length of 50 m are commercially available. The unit price per square meter of PFA film with a thickness of 125 μm is currently around 5,600 yen. According to an estimate, if a 6,000 Å thick polysilicon film is formed on a 4-inch wafer, the film cost per wafer will be 1,020 yen, but PFA film can be washed. Note that the film 13 is not limited to a PFA film, and it goes without saying that any PFA-equivalent film with high heat resistance and high ultraviolet transmittance can be used. As explained in detail above, the optical CVD of the present invention
In the device reactor, when ultraviolet rays are applied from above through a quartz window to a substrate on which a thin film is to be formed on the surface, reaction products in the reaction chamber adhere to the quartz window, reducing the light energy entering the reaction chamber. In order to prevent this, a PFA film is placed directly under the quartz window and above the reaction chamber.
This invention has a remarkable effect on increasing the production rate of thin films and improving the quality of thin films, and whereas conventional methods required considerable effort to remove reaction products that adhere to quartz windows, the present invention can Since it only needs to be updated, it requires almost no effort (automatic winding may be possible in the future), is economical, and has great practical effects.

[Brief explanation of the drawing]

FIG. 1 is an example of the emission spectrum of a low-pressure mercury lamp, FIG. 2 is a typical structural schematic diagram of a reactor in a conventional optical CVD device, and FIG. 3 is a schematic structural diagram of a reactor in an optical CVD device according to the present invention. FIG. 4 is a detailed view of a portion of FIG. 3, showing the flow of purge gas and reaction gas. FIG. 5 is a light transmission characteristic diagram of an anhydrous quartz plate, and FIG. 6 is a light transmission characteristic diagram of a PFA film. 1... Quartz window (plate), 2... Ultraviolet lamp unit, 3... Reflection plate, 4... Substrate (wafer), 5
...Susceptor, 6...Infrared lamp unit, 7
... Thermocouple, 8 ... Auxiliary heater, 9 ... Gas inlet, 10 ... Vacuum pump inlet, 11 ... Second quartz window (plate), 12 ... Reaction chamber, 13 ... PFA film, 14 ... ...Film roll, 15...Film roller, 16...Auxiliary roller, 17...Film chamber (including film chambers 20a, 20b), 18...Gas purge port, 19...Guide, 20a...Film supply chamber, 20b...Film storage chamber, 21...Water cooling jacket, 22...
Reaction gas flow, 23...Reaction gas input, 24...Exhaust.

Claims (1)

[Claims] 1. A reaction chamber that is sealed by upper and lower transparent quartz window plates and side walls and contains a susceptor and a group of substrates (wafers) lined up on it, and a light source that irradiates ultraviolet rays into the reaction chamber through the upper quartz window plate. unit, a heat source unit that heats the substrate group through the lower quartz window plate and the susceptor, and a heat source unit that is located directly below the upper quartz window and can be moved in one direction within the reaction chamber, and after being moved, it is rolled up outside the reaction chamber. A film with high heat resistance and good UV transmittance, a film roller device for winding and winding the film, and a reaction gas installed in the middle of upper and lower guides along the film at the entrance and exit of the film into the reaction chamber. 1. A thin film production reactor for a photo-CVD apparatus, characterized in that it is equipped with an introduction groove and a purge gas discharge groove to produce a uniform thin film on a substrate surface by photo-CVD.