JP2796975B2 - Liquid raw material vaporizer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for vaporizing and supplying a liquid source used in a low pressure chemical vapor deposition (hereinafter, referred to as a low pressure CVD).

(Prior Art) There is a bubbler method as a general method for vaporizing a liquid raw material used in a CVD method.

In this method, a liquid material is placed in an airtight container (bubbler),
In this method, a transport gas (carrier gas) is blown into the liquid, and the raw material vapor generated by bubbling is introduced into a reaction chamber of a CVD apparatus together with the carrier gas.

However, this method has a drawback that the transport amount of the raw material vapor changes due to a change in the level of the liquid raw material in the bubbler.

Further, depending on the bubbling method, there is a disadvantage that the raw material mist is mixed with the raw material vapor and transported.

Further, this method has a disadvantage that the raw material is dewed or fog-ized in the transport pipe due to a decrease in gas temperature due to adiabatic expansion.

When evaporating directly from a raw material container such as a bubbler, the absolute value of the pressure difference in the reaction chamber of the CVD device inside the bubbler is small, so that the flow in one direction is insufficient and the component flowing in the opposite direction, for example, the reaction generated in the reaction chamber It has the disadvantage that the liquid raw material is contaminated by products, oxide dust, droplets and the like.

In addition, as another method of vaporizing a liquid material, a liquid is atomized from a nozzle into a mist in a gas-tight vaporization tank heated to a temperature sufficient to vaporize the liquid material, or atomized using ultrasonic waves. There is a method of using a vaporization tank that is introduced and vaporized, and is introduced into a reaction chamber of a CVD apparatus together with a carrier gas.

This method has the advantage that the evaporation efficiency is good because the raw material liquid is atomized.However, when this method is performed under reduced pressure, particularly when the method is performed at a reduced pressure close to 10 KPa or lower, droplets are not easily generated. Due to the liquefaction or solidification resulting from the adiabatic expansion and the reduced residence time due to the increased gas flow rate, it is difficult to completely remove the droplets in the vaporization vessel.

If the raw material droplets are introduced into the reaction chamber without being vaporized, defects such as loss of uniformity of the formed film and generation of dust such as oxides of raw material components occur.

The present inventors vaporize the raw material liquid used in the reduced pressure CVD method without atomizing it, and introduce only a controlled flow rate gas without introducing mist droplets of the raw material into the reaction chamber of the reduced pressure CVD apparatus. The method of introducing a liquid raw material into a vaporization tank and gently heating it with a heating element such as a heater on the outer periphery of the vaporization tank to vaporize the liquid and its apparatus are described in Japanese Patent Application Nos. 63-110691 and 63-1265.
No. 29 and Japanese Patent Application No. 63-199698.

 The present invention relates to improvements of these inventions.

(Problems to be Solved) When transporting a liquid raw material, it is often the case that the raw material is pressurized with an inert gas such as argon or helium and transported through a transport pipe. In this case, particularly when two or more types of liquid raw materials are mixed, some of these gases and low-boiling raw materials are vaporized in the liquid raw materials in the transport pipe to generate bubbles.

Due to these bubbles, the liquid amount of the liquid raw material changes, and the liquid flow is not constant.

Further, when the raw material liquid containing bubbles is introduced into the vaporization tank from the transport pipe, the bubbles disappear, but at that time, mist droplets of the raw material liquid are generated.

The present invention seeks to provide a vaporizer for eliminating these disadvantages.

(Means for Solving the Problem) According to the present invention, a space for separating a bubble gas and a raw material liquid contained in a liquid raw material is provided in a liquid raw material introduction portion to a vaporization tank, and the bubble gas separated from the raw material liquid in the space is provided. The liquid follows different paths in the vaporization tank, and the raw material liquid is vaporized, then merges again in the vaporization tank and flows out from the gas outlet B.

 The present invention will be described in detail with reference to FIG.

The liquid containing bubbles introduced from the liquid material introduction pipe 3 is separated into a liquid and a gas in the space of the gas-liquid separation section E, and the liquid falls on the spiral along the wall while wetting the uneven inner wall of the vaporization tank. . Heating elements 6-1 and 6 such as heaters around the vaporization tank
The temperature of -2 is raised to heat the wall surface, and the liquid is gently vaporized from the wall surface.

The vaporized raw material gas is mixed with a carrier gas such as argon or helium introduced from a carrier gas introduction pipe 4, and is then led out from a gas outlet pipe 2 and introduced into a reaction chamber of a CVD apparatus.

It is preferable that the carrier gas introduced from the carrier gas introduction pipe 4 spirally rises in the vaporization tank and enters the gas outlet pipe 2.

On the other hand, the gas that has formed bubbles contained in the liquid material protrudes due to the back pressure in the gas-liquid separation unit E, but contains mist droplets of the liquid material at that time. However, when the gas containing the atomized droplets protrudes, it collides with the wall of the gas-liquid separation unit E, and the atomized droplets are adsorbed on the wall, and only the gas not including the atomized droplets flows out of the gas outlet D and is mixed with the carrier gas. Join.

In this manner, the liquid material and the air bubbles are separated in the gas-liquid separation section E, and follow the different paths, so that the supply of the liquid material to the wet wall is made more continuous, and the vaporization amount of the liquid material is kept more constant. be able to.

In addition, by providing spiral irregularities on the inner wall of the vaporization tank, the liquid raw material introduced from the liquid raw material introduction pipe 3 flows down spirally while wetting the inner wall of the vaporization tank. Is uniformly heated, and since the wetted wall area is large, the raw material liquid is vaporized before reaching the bottom of the vaporization tank, and does not accumulate as a liquid at the bottom of the vaporization tank.
Further, since the vaporization process is performed, the raw material liquid does not cause bumping.

By providing the inner wall of the vaporization tank having such a spiral unevenness, the wet area of the liquid raw material is increased, and a heat transfer area sufficient for gentle evaporation can be obtained.

The material of the vaporization tank according to the present invention is determined by the physical properties of the liquid raw material used. In the case of a corrosive liquid such as tetraethoxysilane, stainless steel is preferable.

Carrier gas is an inert gas such as argon or helium,
Nitrogen or the like is used, but it is preferable to preheat to a certain temperature before entering the vaporization tank.

The spiral groove on the inner wall of the vaporization tank may be a multi-stage groove having an equal height.

(Effects of the Invention) According to the present invention, when the raw material liquid containing bubbles is introduced into the vaporization tank from the liquid raw material introduction pipe and the bubbles disappear, mist droplets of the raw material liquid are generated. , And can be returned to the raw material liquid, and the mist droplet is not transported to the reaction chamber of the CVD apparatus.

In addition, the liquid material and the bubbles contained therein are separated in the gas-liquid separation section, and the vaporization amount of the liquid material, that is, the supply amount of the raw material gas to the reaction chamber of the CVD apparatus, is kept more constant because the liquid material and the bubbles are separated. There is a feature that can be.

Furthermore, by providing spiral irregularities on the inner wall of the vaporization tank, the raw material liquid used in the low-pressure CVD method can be gently vaporized from the inner wall surface of the vaporization tank without being atomized. There is a feature that does not introduce drops.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid raw material vaporizer according to the present invention. In the figure, 1 is a vaporization tank, 2 is a pipe for introducing a mixed gas of a raw material gas and a carrier gas, 3 is a liquid raw material introducing pipe, 4 is a carrier gas introducing pipe, 5 is an inner wall of a vaporizing tank provided with spiral irregularities,
6-1 and 6-2 are heating elements wound around the outer periphery of the vaporization tank, A is a liquid material inlet, B is an outlet for a mixed gas of a material gas and a carrier gas, C is a carrier gas inlet, and D is a liquid material. An outlet E for the bubble gas contained therein is a gas-liquid separation section for separating bubbles and liquid contained in the liquid raw material.

Claims (1)

(57) [Claims] In a closed container provided with a liquid material inlet, a carrier gas inlet and a gas outlet, a space for separating a gaseous gas contained in the liquid material and the material liquid is provided in a liquid material introduction portion into the container. The gas bubbles and the raw material liquid separated in the space follow separate paths in the vaporization tank. After the raw material liquid is vaporized, the raw material liquids merge again inside the vaporization tank and flow out from the gas outlet B. Liquid raw material vaporizer.