1. Field of the Invention
The present invention relates to an apparatus for heat processing a substrate, and in particular to an apparatus such as a lamp annealing apparatus and a CVD apparatus by which a substrate is annealed, oxidized or nitrided, or a film is formed on a substrate with active gas or inert gas introduced into a furnace.
2. Description of the Related Art
A certain type of apparatus for heat processing a substrate has a heat processing furnace having a flat or horizontally spread form. One substrate is placed in the furnace. Active gas or inert gas is introduced into the heat processing furnace for performing various kinds of heat processing on the substrate, and specifically for annealing, oxidizing or nitriding the substrate, or forming a film on the surface.
In the apparatus for heat processing the substrate of the aforementioned type, it is necessary to ensure high uniformity of quality of processed substrates and high reproducibility of the heat processing. For this purpose, it is desired that the gas introduced into the heat processing furnace forms a uniform flow without a turbulence or spiral flow at a region accommodating the substrate in the furnace.
In the heat processing of the substrate under a normal or high pressure, it is necessary to replace gases in the heat processing furnace within a short time in order to improve throughput. For this purpose, it is desired that the gas introduced into the heat processing furnace at a high velocity forms a uniform flow without a turbulence.
The active or inert gas is supplied into the heat processing furnace through a piping in which a gas control unit formed of, e.g., a mass-flow controller and a valve is arranged. In general, the piping has an inner diameter from about 1/3 to about 1/4 inch. An area of a section, which is perpendicular to the direction of the gas flow, in the inner space of the heat processing furnace is considerable larger than that of a passage in the piping. Therefore, in order to form the aforementioned uniform flow of the gas introduced into the heat processing furnace, it is necessary to flow the gas into the heat processing furnace by a pressure which is uniform over the whole surface perpendicular to the direction of the gas flow.
For this purpose, the conventional heat processing furnace is provided at its one end with a gas introduction unit. An example of such a gas introduction unit is shown in FIGS. 1 and 2.
FIG. 1 shows a laterally sectional view showing a heat processing furnace of the apparatus for heat processing a substrate in the prior art. The apparatus for heat processing the substrate includes a heat processing furnace 50 of a flat box-like form which is open at one end and accommodates one substrate 10, and a gas introduction unit 52 arranged at the other end of heat processing furnace 50.
Gas introduction unit 52 includes a gas introduction pipe 54, which is connected to a gas supply source (not shown) via a piping and protrudes into heat processing furnace 50, and a gas nozzle pipe 56 disposed at an end of gas introduction pipe 54 in heat processing furnace 50.
Gas nozzle pipe 56 is in communication with gas introduction pipe 54. Gas nozzle pipe 56 fixed to gas introduction pipe 54 is perpendicular to the direction of the length of the gas introduction pipe 54 and parallel to the direction of the width of heat processing furnace 50. Gas nozzle pipe 56 has, at its surface opposed to substrate 10, a plurality of gas nozzle holes 58 which are distributed over the entire length thereof.
In the conventional apparatus shown in FIG. 1, gas is introduced from the gas supply source via gas introduction pipe 54 into gas nozzle pipe 56. The diameter, number and positions of gas nozzle holes 58 are determined appropriately so that the gas introduced into gas nozzle pipe 56 is distributed over the entire width of the heat processing furnace 50 (i.e., entire length of the gas nozzle pipe 56), and is supplied uniformly into the heat processing furnace 50 from a plurality of gas nozzle holes 58.
FIG. 2 shows another example of the apparatus for heat processing the substrate in the prior art. This apparatus for heat processing the substrate includes a hollow heat processing furnace 60 of a flat box-like form which is open at one end and accommodates one substrate 10, and a gas introduction unit 62 provided at the other end of the heat processing furnace 60.
Gas introduction unit 62 includes two parallel partition plates 64 and 68, which partition the inner space of heat processing furnace 60 at the other end into a first gas introduction chamber 74 and a second gas introduction chamber 76, and a gas introduction pipe 72 arranged at the other end of heat processing furnace 60. Gas introduction pipe 72 is in communication with first gas introduction chamber 74 and is connected to the gas supply source (not shown) via a piping.
Partition plates 64 and 68 are provided with a plurality of gas nozzle holes 66 and a plurality of gas nozzle holes 70, respectively. A plurality of gas nozzle holes 66 and a plurality of gas nozzle holes 70, which are formed in partition plates 64 and 68, respectively, are positioned alternately to each other in the direction of the length of partition plates 64 and 68. The first gas introduction chamber 74, second gas introduction chamber 76 and the inner space of heat processing furnace 60 are communicated with each other via gas nozzle holes 66 and 70.
In the conventional apparatus for heat processing the substrate, gas is introduced from the gas supply source via gas introduction pipe 72 into first gas introduction chamber 74. The introduced gas first impinges upon the partition plate 64 to be dispersed widthwise of the heat processing furnace 60, so that the gas is introduced uniformly into the second gas introduction chamber 76 via a plurality of gas nozzle holes 66.
The gas introduced into second gas introduction chamber 76 impinges upon partition plate 68 to be dispersed widthwise of the heat processing furnace 60, so that the gas flows uniformly into the heat processing furnace 60 through a plurality of gas nozzle holes 70.
The following problem exists in the apparatuses for heat processing the substrate having the gas introduction units shown in FIGS. 1 and 2. In these apparatuses, it is necessary to determine appropriately the diameter, number and positions of the gas nozzle holes in accordance with an intended flow rate of the gas flowing through the heat processing furnace in order to form the uniform gas flow without a turbulence at the region in the heat processing furnace accommodating the substrate. However, if the flow rate of the gas supplied into the heat processing furnace is changed in conjunction with kinds of desired processing, the flow velocity and pressure of the gas in the gas nozzle pipe or gas introduction chamber change from those corresponding to the intended flow rate described above. Therefore, the gas supply rate of a certain gas nozzle hole differs from that of another gas nozzle hole.
As described above, the gas introduction unit arranged in the conventional apparatus for heat processing the substrate enables the uniform gas flow only if the gas flow rate varies within an extremely restricted range, but cannot achieve the uniform gas flow if the gas flow rate varies over a wide rage. Consequently, the processing may be performed with the gas flow rate different from the intended flow rate described above, in which case an irregular gas flow is caused, and thus uniform heat processing cannot be effected on the substrate. For example, in the processing for oxidizing the surface of the substrate, an oxide film having a uniform thickness cannot be formed on the surface of the substrate.
The conventional apparatus also has the following disadvantage. In a certain apparatus which effects the heat processing on the substrate under the normal pressure, the gas used therein is changed from one kind to another during a series of processes. The gas remaining in the heat processing furnace must be replaced with another kind of gas to be subsequently used every time such change is to be done. If a long time is consumed in this replacement, a long time is required for completing a series of processes, resulting in a low throughput.
In the apparatus for heat processing the substrate described above, increase of the flow rate of gas may be performed as direct measures for reducing the time required for the replacement of gas in order to improve the throughput. However, in the conventional apparatus for heat processing the substrate, if the flow rate of gas is increased, uniform flow velocity of gas cannot be obtained at a plane perpendicular to the flow direction of gas and the gas flow is disturbed. Since increase of the flow rate of gas and the resultant disturbance in the gas flow cause a turbulence, the flow velocity of gas cannot be sufficiently increased in practice. The time required for replacement of gas can be reduced only to a limited value, so that the throughput cannot be improved.
The conventional apparatus also has the following disadvantage. In FIGS. 1 and 2, the gas nozzle holes of the gas introduction unit emit the gas in the direction parallel to the surface of the substrate. In this case, velocity gradient locally occurs in the gas flow as well as the periphery thereof immediately after the gas passes through the holes. Therefore, if a distance between the gas nozzle hole and the substrate is short and the number of gas nozzle holes is small, stripes consisting of thick and thin portions of gas are formed on the substrate surface. As a result, portions of the substrate surface which are exposed to the thick gas and thin gas are processed under different conditions, so that uniform heat processing cannot be performed.
The following disadvantage additionally exists in the conventional apparatus. In the conventional apparatus shown in FIG. 1, the gas nozzle pipe of the gas introduction unit is projected from the wall at the other end of the heat processing furnace toward the center of the heat processing furnace. In the apparatus shown in FIG. 2, the inner space at the other end of the heat processing furnace is partitioned by the partition plates to form the gas introduction chamber of the gas introduction unit. In either case, provision of the gas introduction unit increases the length of the heat processing furnace, resulting in increase of the entire length of the apparatus. This is also the disadvantage of the conventional apparatus.