JPH0435695B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for detecting the amount of liquid contained in an inner container of a double-layered container.

[Conventional technology]

In impurity diffusion, which is one of the manufacturing processes for semiconductor devices, a liquid source is sometimes used as a diffusion source. This liquid source storage container generally has a double structure, and the liquid source, such as boron tribromide, is stored in the inner container. The space between the outer container and the inner container is filled with water, and the temperature of the liquid source in the inner container is adjusted via the water by a temperature control means provided around the outer periphery of the outer container. .

The impurity gas produced from the liquid source is sent to the diffusion furnace with its flow rate etc. appropriately controlled, and the amount of liquid in the liquid source gradually decreases according to the amount of impurity gas introduced into the diffusion furnace. Therefore,
To prevent the liquid source from running out completely, the level of the liquid source must be constantly monitored.

[Problem to be solved by the invention]

However, since it is difficult to obtain sufficient reliability if this monitoring work is left to humans, automation of the monitoring work is strongly desired. In other words, there is a need for a device that automatically detects when the liquid level of a liquid source falls below a predetermined level (detection level).

A device as shown in FIG. 4 can be considered as a device for detecting that the liquid level of the liquid source in the inner container has fallen below the detection level. Note that figure a is a side sectional view, and figure b is a top view. In this example, both the outer container 1 and the inner container 2 are made of transparent glass, and a light emitting element 3, a light emitting lens 4, a slit 6, and a light receiving element 5 are provided on the outside of the outer container 1 as shown in the figure. ing. A liquid source 7 is contained in the inner container 2, and the space between the outer container 1 and the inner container 2 is filled with water 8.
The light emitted from the light emitting element 3 illuminates the detection level of the inner container 2 through the projection lens 4, and when the liquid level of the liquid source 7 is lower than the detection level, it is almost completely reflected and reaches the light receiving element 5. (solid line arrow), and if it is high, part of the incident light enters the liquid source 7 (dashed line arrow) and part of the light reaches the light receiving element 5.
This is based on the difference in refractive index between the liquid source 7 and the gas. Due to this effect, when the liquid level of the liquid source 7 becomes below the detection level, the intensity of light incident on the light receiving element 5 increases more than before. That is, from the output of the light receiving element 5, it is possible to detect whether the amount of liquid in the liquid source 7 is above or below the detection level.

However, in order to obtain sufficient detection power, each element must be arranged so that the change in reflected light intensity depending on the presence or absence of the liquid source 7 at the detection level position is maximized. However, since the error in setting the incident angle on the inner container 2 is doubled on the reflection side, the light receiving element 5 must be positioned extremely strictly.
cannot receive reflected light from the inner container 2. Therefore, there was a problem in that the adjustment required a long time.

Furthermore, the relationship between the refractive index n _c of the inner container 2 and the refractive index n _e of the liquid source 7 is generally n _c > n _e (for example,
n _c = 1.5, n _e = approximately 1.3). Therefore, liquid sauce 7
The intensity I ₀ of the light received by the light receiving element 5 when it is filled to a level higher than the detection level and total reflection does not occur,
The relationship between the light intensity _I e received by the light receiving element 5 when total reflection occurs when the liquid source 7 is below the detection level is
I _e > I ₀ , but the ratio I _e /I ₀ can only take a small value of "2" or less. Therefore, even if the positioning is sufficiently adjusted, there is a limit to its detection power.

Furthermore, the inner container 2 is only supported at its upper end in a floating state relative to the outer container 1. Therefore, the horizontal position of the inner container 2 with respect to the outer container 1 is particularly unstable in the lower part where the detection level is located. If the position of the inner container 2 shifts even slightly, the angle of incidence on the surface of the inner container 2 will change, making it impossible for the light receiving element 5 to perform proper detection, resulting in false detection.

An object of the present invention is to solve these problems.

[Means to solve the problem]

In order to solve the above problems, the liquid level detection device of the present invention is provided with light that is disposed outside the side surface of a double-walled container and that passes almost horizontally through the detection level of the inner container. a light emitting means for emitting light that is focused at an appropriate focusing point on the outside of the reflective side of the double-walled container when the liquid level is above the detection level; It includes a light receiving means for receiving light, and a light shielding plate disposed in front of the light receiving means and having an opening in the optical path of the focused light.

[Effect]

When the level of the liquid filled in the inner container is above the detection level, the light from the light emitting means is focused on a predetermined focal point, so most of the light reaches the light receiving means through the opening of the light shielding plate. do. on the other hand,
When the level of the liquid filled in the inner container falls below the detection level, the refractive index in the inner container decreases, so that the light from the light emitting means is not focused at a focal point but diverges. Therefore, only a small amount of light passing through the focal point reaches the light receiving means. That is, the intensity of light reaching the light receiving means changes significantly depending on whether the liquid level is above the detection level or not.

〔Example〕

FIG. 1 is a reference example considered by the inventor prior to the present invention. Figures 2 and 3 are
1A and 1B are a side sectional view and a schematic plan view, respectively, showing one embodiment of the present invention.

First, one embodiment of the present invention will be described with reference to FIGS. 2 and 3. In this embodiment, similar to FIG. 4, the present invention is applied to a double container containing a liquid source of impurity gas to be supplied to a diffusion furnace. The outer container 1 has a cylindrical shape with a bottom and a diameter of 120 mm, and is made of metal, such as stainless steel. At the lower side of the outer container 1,
Glass windows 17 and 18 are provided at positions facing each other. The inside of the outer container 1 has a diameter of 60 mm.
A glass inner container 2 having a cylindrical shape with a bottom is arranged without touching the outer container 1, and the inner container 2
Water 8 is filled between the container 1 and the outer container 1.
The inner container 2 is filled with a liquid source 7, such as boron tribromide, and its upper part is covered with a lid 16. There are two pipes 14 and 15 on the lid 16.
The end of the pipe 14 extends to the vicinity of the bottom surface of the inner container 2, and the end of the pipe 15 is fixed at the top. A carrier gas is fed into the pipe 14, and this gas passes through the liquid source 7 in the form of bubbles, thereby vaporizing the liquid source 7. In this way, the carrier gas containing the vapor of the liquid source 7 is sent to the diffusion furnace via the pipe 15. The upper portion of the inner container 2 is supported by an engaging member (not shown) directly or via the lid 16.

A light emitting element 3 and a light emitting lens 4 are provided on the outside of the window 17, and a light shielding plate 20 having an opening in the center and a light receiving element 5 are provided on the outside of the window 18, and these are arranged in a straight line at the detection level. arranged on a line. The light emitting element 3 is composed of, for example, a light emitting diode or a semiconductor laser.

A temperature control means 12 using a Peltier element is provided around the outer periphery of the outer container 1, and this temperature control means 12 maintains the temperature of the liquid source 7 at a predetermined value based on the output of a temperature sensor 13. works.

Next, the operation of this embodiment will be explained.

First, adjust the position of the light projection lens 4 in advance,
A focal point of light emitted from the light emitting element 3 is determined.
That is, when the liquid source 7 is sufficiently filled in the inner container 2 and the liquid level is above the detection level, light emitted from the light emitting element 3 passes through the opening of the light shielding plate 20 and reaches the light receiving surface of the light receiving element 5. The position of the light projecting lens 4 is adjusted in advance so that the light is focused.
With this adjustment, strong light is incident on the light receiving element 5 when the liquid source is sufficiently filled.

When the carrier gas is sent through the pipe 14 in this state, carrier gas bubbles are generated in the liquid source 7, and a portion of the liquid source 7 is vaporized. The carrier gas containing the vaporized liquid source 7 is pipe 1.
The liquid level in the liquid source 7 gradually falls below the detection level. At this time,
The light beam emitted from the light emitting element 3 diverges as shown by the broken line arrow in FIG. 3, and most of the light is blocked by the light shielding plate 20. All but a very small portion of the light passing through the opening of the light shielding plate 20 is blocked and does not reach the light receiving element 5. This is because the lens action of the double container changes depending on whether or not the liquid source 7 is present in the optical path. The refractive index n of the liquid source 7 is
It has a refractive index of about 1.3, which is almost the same as water 8.
Therefore, if the liquid level of the liquid source 7 is above the detection level, the luminous flux emitted from the light receiving element 3 is
It passes through an optically substantially uniform medium, and this double container acts like a single convex lens due to the shape of the outer container 1. However, when the liquid level of the liquid source 7 falls below the detection level, the refractive index within the inner container 2 decreases to nearly 1.0, and the light emitting element 3
The luminous flux emitted from the 2
The light passes through two concave lenses and diverges as shown by the dashed arrow.

Furthermore, when the inside of the inner container 2 changes from liquid to gas, the reflectance at the inner surface of the inner container 2 increases,
The amount of light that passes through this area is significantly reduced. Therefore,
The light passing through the aperture of the light-shielding plate 20 is almost completely lost due to divergence due to the lens action and attenuation of the amount of light due to the mirror effect, and the amount of light that reaches the light-receiving element 5 is extremely small.

It should be noted that there was a concern that when the liquid level of the liquid source 7 was above the detection level, the carrier gas bubbles coming out from the tip of the pipe 14 would act on the light, causing the luminous flux to diffuse and cause false detection. Experiments revealed that bubbles have little effect on the diffusion of light flux.

By the way, in the reference example shown in FIG. 1, a lens 10 and a light shielding plate 11 are provided in place of the light shielding plate 20 with openings in the above embodiment, and when the liquid source 7 is at a detection level or higher, light from the light emitting element 5 is When the light is focused, the light is blocked, and when the light becomes below the detection level and diverges, the diverging light is focused on the light receiving element 5 using the lens 10. Although this device is also capable of detecting the amount of liquid, the problem remains that in order to increase the detection power, a fairly large lens 10 is required, resulting in an expensive device. Therefore, the device of the above-mentioned embodiment was considered, which has sufficient detection power and can be configured at a much lower cost than this reference example.

In the above embodiment, the outer container 1 is made of metal, but if it is made of a transparent material such as glass, the windows 17 and 18 are unnecessary.

Further, in the above embodiment, the number of detection levels is one, but by setting a plurality of detection levels and detecting the presence or absence of liquid at each level, it is possible to continuously know changes in the amount of liquid.

In the embodiments described above, the present invention is applied to a double-layered container for storing a liquid source for impurity diffusion in a semiconductor device, but it can also be applied to a double-layered container for storing other liquids.

〔Effect of the invention〕

As explained above, according to the liquid level detection device of the present invention, the light emitting means and the light receiving means are provided so as to be sandwiched between the double-layered container, and the light shielding plate is further provided with an opening that transmits the light focused at the focusing point. With a simple configuration in which it is provided in front of the light receiving means, the intensity of light reaching the light receiving means can be significantly changed depending on whether the liquid level is above the detection level or below. Therefore, by monitoring the output of the light receiving means, it is possible to automatically detect that the liquid level has fallen below the detection level. Moreover, since it monitors changes in the intensity of light passing through the inner container, unlike reflective types, even if the position of the inner container shifts slightly from side to side, it will hardly affect the amount of light received by the light receiving means. ,
It is easy to adjust the position of each element, and moreover, stable detection accuracy can be obtained over a long period of time.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a reference example considered prior to the present invention, Fig. 2 is a side sectional view showing an embodiment of the present invention, Fig. 3 is a schematic plan view thereof, and Fig. 4 is a diagram showing a prior art. FIG. 1...Outer container, 2...Inner container, 3...Light emitting element,
4... Lens for projecting light, 5... Light receiving element, 10... Lens for focusing light, 20... Light shielding plate.

Claims (1)

[Scope of Claims] 1. A liquid level detection device for detecting whether the level of liquid filled in an inner container of a double-layered container is below a detection level, comprising: The light passes approximately horizontally through the detection level of the inner container, and when the liquid level of the liquid filled in the inner container is above the detection level, the light is appropriately focused on the outside of the opposite side of the double-walled container. a light-emitting means for emitting light converging to a point; a light-receiving means disposed near the convergence point and receiving the convergent light from the light-emitting means; and an aperture disposed in front of the light-receiving means in the optical path of the convergent light. A liquid amount detection device comprising: a light shielding plate having a light shielding plate;