JPS6028136B2 - Furnace tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a furnace core tube suitable for impurity deposition onto semiconductor wafers.

Conventionally, when p-type impurities are deposited on a semiconductor wafer and then diffused into a silicon wafer using boron nitride (BN), for example, boron, which is a p-type impurity source, is deposited on a boat. By placing a nitride wafer (with a slightly oxidized surface) and a silicon wafer face-to-face, inserting the boat into the quartz tube in this state, and then heating the quartz tube from the outside, A boron oxide (chord 03) atmosphere is created in the quartz tube, which deposits boron oxide on the silicon wafer and creates a thin diffusion layer with a high impurity concentration on the silicon wafer surface. A known method is to re-diffuse boron impurities into a silicon wafer in a clean atmosphere.

During this deposition process, an inert gas (N2) is fed from one end of the quartz tube to prevent the surface of the silicon wafer from being oxidized.

By the way, in the heating device used in this method, the quartz tube is in an open state when heated, and inert gas is fed from one end, so the temperature distribution in the longitudinal direction inside the quartz tube is The silicon wafers arranged on the boat have different amounts of impurities introduced depending on the position where they are placed, causing variations in the resistivity of the silicon wafer surface.

As a method to solve this problem, a heating device having means for reducing the pressure or vacuum inside the quartz tube is used, and the semiconductor wafer and the impurity source (BN
) have been proposed by the applicant of the present application in a closed tube method in which the tubes are placed facing each other and heated so that gas containing impurities uniformly reaches the surface of the semiconductor wafer. However, in such a closed tube method, in order to obtain a high impurity concentration region, a high temperature heat treatment of about 100,030 degrees Celsius is performed at the time of deposition, so that silicon atoms are locally evaporated particularly from the silicon wafer surface, and the silicon wafer surface becomes rough.

Furthermore, due to the evaporation of the silicon atoms, the surface of the boron nitride turns black and gray, making it unusable for the next deposition. Furthermore, after deposition, foreign substances other than poronic acid particles adhere to the silicon wafer surface, causing stains that are difficult to remove by etching. It has also been revealed that the yield of semiconductor devices manufactured through this process is reduced.

Therefore, it has been desired to form a protective film on the silicon wafer surface in order to prevent the surface from becoming rough and dirty. Therefore, an object of the present invention is to provide a furnace core tube that is suitable for forming such a protective film and that allows extremely easy loading and unloading of objects to be heated, such as semiconductor wafers.

To achieve the above object, the present invention is a cylindrical furnace core tube, which is provided with a cap at one end for taking in and out the object to be heated, and a tapered exhaust port at the other end. is provided, and a gas inlet is provided on the side of the furnace core tube in the vicinity of the entrance.

Hereinafter, a detailed explanation will be given using examples. FIG. 1 shows the heating apparatus of the present invention in which objects to be heated such as a semiconductor wafer and an impurity source are inserted into a quartz tube;
Figures a to d show the structure of a semiconductor wafer during the impurity diffusion process used in the heating device.

First, in FIG. 1, this heating device includes a diffusion furnace 1 including a heater and a furnace core tube 2 made of quartz glass or silicon.
One end of the furnace core tube 2 is provided with a removable cap 3 and an opening 7 into which it can be attached. A part of the cap 3 is provided with a hole 5 through which a pull-out rod 4 for moving the boat, which will be described later, is passed through. A narrow exhaust port 6 is formed at the other end of the furnace core tube 2 to reduce pressure and create a vacuum inside the furnace core tube 2, and is connected to a vacuum pump (not shown). Furthermore, a gas inlet 8 is formed in the side of the furnace core tube 2 near the entrance portion 7 on the opposite side from the exhaust port 6 of the furnace core tube 2 . Further, the hole 5 is designed so that outside air does not enter even if the inside of the furnace core tube 2 is reduced in pressure and evacuated. in this way,
In particular, the structure of the furnace core tube 2 is such that the gas inlet is not attached to the cap 3 itself, but is provided independently.

Therefore, the cap 3 can have an extremely simple structure. Therefore, the cap 3 can be easily removed, and workability is extremely improved. Moreover, as is clear from FIG. 1, the exhaust port 6 has a narrower diameter at the other end of the furnace core tube 2.
It is located at the center of the furnace core tube 2. Therefore, the pressure inside the furnace core tube 2 can be reduced uniformly and quickly. Further, according to the present invention, foreign matter such as reactants attached to the wall of the furnace core tube (especially likely to accumulate near the exhaust port) is not thrown up when the workpiece is taken in and out, so the workpiece (specifically, semiconductors) is not thrown up. The foreign matter will not adhere to the wafer surface and cause problems. Additionally, since the exhaust port is formed by forming the furnace core tube into a tapered structure, foreign matter collects at the curved portion of the furnace core tube near the exhaust port, thereby reducing the amount of foreign matter that enters the exhaust port. Therefore, it can be expected to have the effect of reducing the causes of failure in the exhaust system. Such a furnace core tube of the present invention is extremely suitable for heat treatment of semiconductor wafers under reduced pressure.

The boat 9 placed in the furnace core tube 2 is an elongated support made of quartz glass and silicon, and on this boat 9 are placed a silicon wafer 10 and boron nitride (a source of diffused impurities). BN) A plurality of wafers 11 are appropriately arranged. Next, a method for depositing and diffusing boron impurities on a silicon wafer using the above heating device will be described below.

First, the boat 9 on which the silicon wafer 10 and the boron nitride wafer 11 whose surface has been slightly oxidized is placed in the vicinity of the open □ end 7 of the furnace core tube 2, and the open end 7
is sealed with a cap 3, and the inside of the furnace core tube 2 is reduced in pressure and evacuated through the exhaust port 6 using a vacuum pump.

Next, the boat 9 is moved to the soaking section in the furnace core tube 2 by the pull-out rod 4, and the surface of the silicon wafer 10 is coated with boron nitride and boron oxide (B203) on the surface of the wafer 11 at a low temperature of 1000 pm or less. is deposited to form a first poron silicate glass film 12 (see FIG. 2a).

In this case, silicon atoms are not evaporated from the silicon wafer 10 because the deposition is in low-temperature dung air. Next, from the gas inlet 8, a certain amount of oxygen or oxygen, argon, nitrogen,
A mixed gas with an inert gas such as helium is poured to form a thin (about 1000 A) thermal oxide film (Si02) 13 on the surface of the silicon wafer 10 [see 2b]. Note that the oxide film 13 is similar to the first poron silicate glass film 1.
2 may be formed by vapor phase growth. The thickness of this oxide film 13 is selected so that poron atoms can pass therethrough during deposition at high temperatures, which will be described later. Thereafter, the supply of oxygen or mixed gas is stopped, and the inside of the furnace core tube 2 is heated to a high temperature (1100
(approximately qo) - Under reduced pressure, boron nitride wafer 11 is applied to the surface of the oxide film 13 of the silicon wafer 10.
By depositing boron oxide (B03) on the surface, the second
While forming a poron silicate glass film 14 of
Due to the boron impurities in the first poron silicate glass film 12 and the boron impurities in the second poron silicate glass film 14 that diffuse through the oxide film 13, a shallow p-type high concentration diffusion layer of boron impurities is formed in the surface layer of the silicon wafer 10. 15 [see Figure 2c].

Next, the inside of the furnace core tube 2 is returned to normal pressure, the boat 9 is pulled to the entrance end 7 of the furnace core tube 2 using the pull-out rod 4, the cap 3 is removed, and the boat 9 is taken out.

Then, only the silicon wafer 10 is extracted, and the first and second poron silicate glass films and oxide film on the wafer surface are removed by etching. This silicon wafer 10
is placed in a diffusion furnace with an oxidizing atmosphere, and the boron impurities in the p-type high concentration diffusion layer 15 formed on the surface layer of the silicon wafer 10 are re-diffused to form a desired p-type semiconductor region 16. See Figure 2 d]. At this time, the thermal oxide film 1
7 is formed on the surface of the silicon wafer 10.

In all of the above methods, the deposition process is performed continuously in the same furnace tube, but the deposition process at low temperature and reduced pressure and the deposition process at high temperature and reduced pressure may be performed in separate furnace bodies.

In addition, during the deposition process at low temperature and reduced pressure and at high temperature and reduced pressure, if a certain amount of oxygen or a mixed gas of oxygen and an inert gas is supplied, the surface of the boron nitride wafer can be coated particularly during high temperature deposition. Boron oxide (B2
03) is generated, suppressing the reduction of boron oxide on the surface of the boron nitride wafer, and preventing substances other than boron oxide from evaporating from the boron nitride wafer itself. It is also possible to apply the ampoule diffusion method in which silicon wafers and boron nitride wafers are sealed in advance in a quartz tube, placed in a furnace core tube, and deposited and diffused under reduced pressure. Although the above method has been described with respect to silicon wafers, it can also be applied to impurity diffusion methods into semiconductor wafers such as germanium.

In addition to boron nitride, metal nitrides such as phosphorus, indium, and aluminum, and metal oxides thereof can also be used as impurity sources. As explained above, if the impurity diffusion method into a semiconductor wafer using the heating device of the present invention is used, the glass film and oxide film containing oxidized impurities can be first removed from the surface of the semiconductor wafer in a low-temperature atmosphere where the semiconductor atoms do not evaporate. These films act as protective films and can prevent the base semiconductor atoms from evaporating at high temperatures and under reduced pressure. In addition, since impurity atoms are deposited on the semiconductor wafer surface from both the oxidized impurity glass film in contact with the semiconductor wafer, the oxidized impurity glass film on the oxide film, and the oxidized impurity glass film on the oxide film, the oxidation Even with a film, a highly concentrated diffusion layer can be formed with high precision. Furthermore, since there is an oxide film on the semiconductor wafer during deposition at high temperature and under reduced pressure, there are effects such as preventing foreign matter from directly adhering to the surface of the semiconductor wafer from the outside.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a heating device of the present invention, and FIGS. 2 a to 2 d are partial cross-sectional views of a semiconductor wafer in a process from impurity deposition to diffusion using the heating device of the present invention. 1... Diffusion furnace, 2... Furnace core tube, 3... Cap, 4... Pull-out rod, 5... Hole for passing the draw-out rod, 6... Exhaust port, 7... Opening, 8...Gas inlet, 9...Boat, 10...Silicon wafer, 11...Boron nitride wafer, 12
...First poron silicate glass film, 13... Thin oxide film, 14... Second poron silicate glass film, 15...
... p-type high concentration diffusion layer, 16 ... p-type semiconductor region, 17 ... thermal oxide film. Figure 1 Figure 2

Claims (1)

[Claims] 1 A cylindrical furnace core tube, one end of which is provided with an opening for taking in and out the heated object to which a cap can be attached, the other end of which is provided with a tapered exhaust port, and a A furnace core tube characterized in that a gas inlet is provided on the side of the furnace core tube.