JPH0372078A - Method and device for forming thin film - Google Patents

Abstract

PURPOSE:To form thin films suitable for mass production with excellent reproducibility and controllability by maintaining a bubbler container always in a stationary state and supplying a specified volume of gaseous raw materials to a CVD reaction chamber while preventing the change in the flow rate of the gaseous raw materials with time. CONSTITUTION:A specified volume of the TEOS (tetraethoxyorthosilicate) liquid is injected into the bubbler vessel 2, then gaseous Na for transportation controlled in flow rate is passed to start bubbling. A valve 15 is closed and an evaporating gas is introduced toward a branch pipe 21 at this time. A variable valve 26 is so controlled that a pressure gage 34 in the upper part of the vessel 2 attains a prescribed pressure and the liquid TEOS corresponding to the flow rate of the evaporated gaseous TEOS from the vessel 2 is continuously supplied 13 to recover 25 approximately the same volume of the liquid TEOS. On the other hand, gaseous O2 contg. O3 and the evaporated gaseous TEOS in the stationary state in the vessel 2 are supplied to the CVD reaction chamber 16 evacuated to a high vacuum. The valve 15 is closed and the valve 20 is opened again to end the film formation.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a method and apparatus for vaporizing a liquid raw material using a bubbler method and supplying the vaporized raw material to a CVD reaction chamber to form a thin film on a substrate surface. Regarding.

(Prior Art) Conventionally, with the increase in the density of LSIs, the patterns of semiconductor elements have become finer and three-dimensional. In manufacturing such semiconductor devices, it is important to form a thin film with good flatness on a pattern with large steps and undulations, and to flatten the steps and undulations. Various methods are currently being considered as to what process should be used to planarize silicon dioxide 5i02 as an interlayer insulating film.
A CVD method using tetra ethoxy ortho silicate (hereinafter abbreviated as TEOS) as a raw material is a technology that is considered to be very promising in the future. Among these methods, there are plasma CVD method, thermal CVD method, and CVD method using ozone 03, but since the film can be formed at a lower temperature (~400°C), it does not deteriorate the characteristics of the underlying Al thin film, and there are no steps. Ozone 03 and T
The CVD method using EOS is superior to other methods. Conventionally, film formation has been carried out in the pressure range from 100 Torr to atmospheric pressure, and the film forming rate has been up to 300 Torr.
About 0λ/min was obtained.

By the way, as a gas supply mechanism used in such a CVD apparatus, a bubbler system is generally used because TEOS is a substance that is a liquid at room temperature and has a low vapor pressure (~2 Torr at room temperature). In this method, as shown in Fig. 4, a bubbler container 2 containing a liquid raw material 1 is kept at a predetermined temperature, and an inert gas (such as Ar or N2) for transporting vaporized gas is inserted into a dip tube 3 inserted below the liquid surface. etc.) to generate air bubbles from the tip of the dip tube 3 (bubbling) to promote vaporization of the liquid raw material (TEOS).

(Problems to be Solved by the Invention) The bubbler method is simple and widely used not only in TEOS but especially in CVD using a liquid with a low vapor pressure as a raw material, but it has the following drawbacks.

First, as a procedure for film formation, the bubbler container 2 is heated to a constant temperature in a constant temperature bath, the valve 15 between the bubbler container 2 and the CVD reaction chamber is opened, and bubbling is started. The raw material gas flow rate after opening the valve 15 shows a temporal change as shown in FIG.

That is, from the opening of the valve 15, the raw material gas flow rate shows an overshoot-like peak and then settles down, but gradually decreases with time. This gradual decrease in the flow rate of the raw material over time depends on the amount of raw material in the bubbler container, and the larger the amount of raw material, the smaller the amount of decrease, showing a temporal change as shown in a.

However, as the amount of raw material decreases, the degree of decrease increases, and the raw material gas flow rate itself decreases as a whole, showing a temporal change as shown in b.

The reason why such a phenomenon occurs is considered as follows.

When a liquid vaporizes, the liquid is cooled by the heat of vaporization. The degree of cooling increases inversely with the amount of liquid. Although the entire bubbler container 2 is kept in a constant temperature bath,
If the vaporization rate of the liquid is high, thermal resistance between the constant temperature bath and the liquid in the bubbler container will cause a temperature difference between the two. In other words, this is because the system that controls the liquid temperature to a constant level does not have good followability to changes in liquid temperature. To prevent this, the control system may be configured to increase follow-up performance, but it is quite difficult to completely suppress the change over time due to a decrease in the amount of liquid.

Since the bubbler method has drawbacks in reproducibility and controllability as described above, it is difficult to maintain constant conditions for forming thin films. For this reason, the shape shown in Figure 4 is the actual CV for mass production.
It cannot be used for D equipment.

On the other hand, there is also a gas supply device exclusively for TEO3 that is of a different type. This heats the TEOS to a fairly high temperature, causing the TEOS to
The idea is to supply vaporized gas using the vapor pressure of O3 itself, and to control the flow rate using a mass flow controller. However, because the vapor pressure of TEOS is low, it is difficult to obtain a large flow rate of vaporized gas, and the pressure range used (100To
Due to the restriction that it cannot be operated at (atmospheric pressure), this gas supply device cannot actually be used in the CVD method using 03-TEOS, which has excellent step coverage.

Currently, the 03-T bubbler method, which can provide a large flow rate even at atmospheric pressure, is inferior in reproducibility and controllability.
It is widely used in the EOS CVD method.

(Means for Solving the Problems) This invention solves the problems of reproducibility and controllability in the bubbler method, and provides a method and apparatus for producing thin films that have excellent reproducibility and controllability and are suitable for mass production. purpose.

That is, the thin film forming method of the present invention is a method for forming a thin film on a substrate surface by guiding raw material gas to a CVD reaction chamber using a bubbler method, by keeping the raw material contained in a bubbler container constant at all times. CV of raw material gas
It is in a state where it can be supplied to the D reaction chamber, and when forming a thin film, the raw material gas is guided to the CVD reaction chamber, while when forming a non-thin film,
The present invention is characterized in that the source gas is guided to a place other than the CVD reaction chamber.

Further, the thin film forming apparatus of the present invention is a thin film forming apparatus comprising a bubbler type gas supply mechanism and a CVD reaction chamber, wherein the gas supply mechanism controls a bubbler container and the amount of raw material inside the bubbler container. and a pipe connecting the bubbler container and the CVD reaction chamber, and the pipe is provided with a branch pipe, and a valve is provided in each of the pipe and the branch pipe. It is said that

In the thin film forming apparatus, the branch pipe may be connected to a recovery device for the source gas sent from the bubbler container.

(Function) According to the thin film forming method of the present invention, the bubbler container is always maintained in a steady state, so even if the flow path of the raw material gas is switched, the flow rate of the raw material gas to the CVD reaction chamber does not change over time. A constant amount of raw material gas is supplied without any problems.

Further, according to the thin film forming apparatus of the present invention, it is possible to flow the raw material gas from the bubbler container to either the CVD reaction chamber or the branch pipe. Therefore, the bubbler container can be maintained in a steady state, and as a result, a constant amount of source gas can be supplied to the CVD reaction chamber when necessary.

According to a thin film device in which a branch pipe is connected to a recovery device, it is possible to recover the raw material gas that flows from the bubbler container to the branch pipe when producing a non-thin film.

(Example) Fig. 1 shows an example of the present invention, in which 1 is a TEO3 liquid as a raw material, 2 is a bubbler container, 3 is a dip tube for bubbling, and transport gas Ar is supplied from a cylinder 4. It can be introduced into the TEO3 liquid 1 in the bubbler container 2 from the tip of the dip tube 3 via the mass flow controller 5. There is TEOS in bubbler container 2.
A liquid level sensor 6 is installed, and an external level indicator 7 can detect the TEO3 liquid level.

Further, a temperature sensor 8 and a heater 9 are installed in the bubbler container 2 to keep the temperature of the TEO8 liquid constant. 10 is a TEO5 storage tank, and a pressure of about +1 kg/c+ff is constantly applied to the upper space inside the tank by an Ar gas cylinder 11 and a pressure regulator 11a. Due to this pressure, the TEO3 liquid 1 is transported to the liquid mass flow controller 13 through the tube 7'12 inserted into the storage tank, and the TEO3 liquid 1 is transported to the liquid mass flow controller 13 through the tube 7'12 inserted into the storage tank.
3 to the bubbler container 2. This liquid mass flow controller 13 operates in response to a signal 14 from the level indicator 7 of the bubbler container 2.
It is configured so that TEO9MI in the bubbler container 2 is always constant. Bubbler container 2 is connected to CVD reaction chamber 16 via valve 15 . During film formation (thin film creation), the TEOS gas vaporized in the bubbler container 2 and the Ar gas for transportation are introduced into the CVD reaction chamber 16, and the substrate supported by the heater 51 is introduced through the gas diffusion plate 50. 52 so that it can be sprayed. The CVD reaction chamber 16 contains ozone 03 with a concentration of about 8vo 1% from an ozone generator (not shown) as another reaction gas.
The two gases are also introduced through a ring-shaped pipe 55 having a large number of holes. The reacted gas and transport Ar gas in the CVD reaction chamber 16 are exhausted through a variable valve 17 and a stop valve 18 by a single rotary pump. On the other hand, when not forming a film (when creating a non-thin film), vaporized TEOS gas and Ar
The gas passes through a valve 20 and is introduced into a branch pipe 21 branched from the upper part of the bubbler container 2.
This allows it to be led to a heat exchanger 22 for EO5 recovery. This heat exchanger has approximately -
Refrigerant at 30° C. is introduced and discharged in the direction of arrows 23 and 24. The TEOS gas condenses in this heat exchanger 22, and the liquefied TEOS can be recovered in a TEO5 recovery tank 25 connected to the lower part of the heat exchanger. A gas for transportation that does not liquefy in the heat exchanger 22 passes through the variable valve 26 and stop valve 27 to the rotary pump 2.
8 and can be exhausted. The TEO3 recovery tank is equipped with a liquid level sensor 29 and an indicator 30, and when the level reaches the level above the - window, the recovered TE01 can be transferred to the storage tank by opening the valve 31. ing. A liquid level sensor 32 and a display 33 are also installed in the TEO8 storage tank 10, so that it is possible to detect whether or not it is necessary to fill the TEO5 raw material.

Next, using the thin film forming apparatus of the above embodiment, 5i0
2. The procedure for creating a thin film will be explained.

First, after injecting a certain amount of TEO3 liquid into the bubbler container 2, the temperature of the TE01 liquid is set to 65°C. and,
Ar for transportation with flow rate controlled at approximately 100 cc/min
Flow the gas and start bubbling.

At this time, the valve 15 is closed, the valve 20 is opened, and the vaporized gas is introduced into the branch pipe 21. Further, the rotary pump 28 is activated, and the refrigerant is circulated within the heat exchanger 22. Further, the valve 31 is kept closed. Next, the pressure gauge 34 installed at the top of the bubbler container 2 is approximately 100T.
Adjust the variable valve 26 so that it becomes orr. This adjustment may be performed manually or automatically using an adjustment mechanism (not shown).

In this state, the temperature and liquid level inside the bubbler container 2 are stabilized,
Wait until steady state is achieved. In a steady state, the flow rate of the TEOS gas vaporized from the bubbler container 2 (approximately 200 c
Liquid TE01 (approximately 2cc) corresponding to c/LIlin)
/m! n) is continuously supplied by the liquid mass flow controller 13, and approximately the same amount of liquid TE01 is collected into the collection tank 25. At the start of film formation, the substrate 52 is supported by the heater 51 in the reaction chamber by a load-lock chamber and a transport mechanism (not shown), and the reaction chamber is evacuated to a high vacuum (1
0' Torr), O2 gas containing ozone O3 is introduced at a predetermined flow rate (approximately 1000 CC/m1n), and a pressure gauge 5 installed in the CVD reaction chamber 16 is introduced.
3 and variable valve 17, the pressure inside the reaction chamber is approximately 100
Torr is automatically adjusted. Film formation is started by closing the valve 20 of the branch pipe 21 and opening the valve 15. The CVD reaction chamber 16 contains vaporized TEOS gas (
approximately 200 cc/min). To complete the film formation, the valve 15 may be closed and the valve 20 may be opened again.

After long-term use, when TE01 in the recovery tank 25 reaches a predetermined level, stop bubbling and close the valve 20.2.
7 and open the valve 54.31, the recovery tank 25
The TE01 inside is transferred to the TEO3 storage tank 10.

In addition, in the actual device, the bubbler container 2 has a volume of approximately 500.
The liquid volume of TE01 was set to about 200cc using a cc type, but in order to keep the liquid temperature of TE01 constant with high accuracy, TE01 was used.
It is better not to increase the amount of liquid in step 1 too much. This is TE0
This is because the time constant in the temperature control system 1 becomes large (especially in the case of cooling), making it difficult to obtain a fast response. Further, it is desirable that all piping through which the vaporized TEOS gas flows be heated to about 90° C. to prevent dew condensation.

Incidentally, in the above embodiment, the liquid level sensor 6 and the liquid mass flow controller 13 were used to keep the liquid level in the bubbler container 2 constant, but it is not possible to keep the liquid level constant even with the configuration shown in FIG. can. The embodiment shown in FIG. 2 differs from the previous embodiment only in the TEOS gas supply mechanism, and the other parts are the same as in the previous embodiment, so they are designated by the same reference numerals.

That is, in this second embodiment, the TEO5 storage tank 10 is
It also serves as a recovery tank for TE01.

The bottom of the TEO3 storage tank 10 and the bottom of the bubbler container 2 are connected by a thin flexible tube 60. Further, the upper space inside the bubbler container 2 and the upper space of the TEO3 storage tllO are connected by a thin flexible tube 61 so that the pressures in the upper space are equal. The level in the bubbler container 2 is detected by the liquid level sensor 6 and the indicator 7, and the TEO3 storage tank 1 is adjusted so that the liquid level is constant.
0 can be automatically moved in the direction of arrow 63 (up and down). In this embodiment, even if it is used for a long time, there is no need to transfer the recovered TE01 as in the first embodiment (Fig. 1), so as long as TE01 remains in the storage tank. , film formation can be continued.

Next, FIG. 3 shows a third embodiment of this invention.

The structure of the CVD reaction chamber 16 is the same as that in the previous example, so it is omitted. Mako, this third embodiment is bubbler container 2
The only difference is the mechanism that keeps the TEOS liquid level within the
Since it has the same structure as the embodiment, the same reference numerals are given. Inside the bubbler container 2, there is a TEO3 storage tank 1.
A tube 80 for injecting TE01 is inserted from 0, and its tip position matches the liquid level in the bubbler container 2. This liquid level is the bubbler container 2
The pressure inside (measured by pressure gauge 34) P.

(Torr) and the pressure in the upper space inside the TEO3 storage tank 10 (measured by the pressure gauge 81) Pl (Torr), which is maintained constant by the differential pressure. That is, if the level difference between the liquid level in the bubbler container 2 and the liquid level in the TEOS storage tank 10 (arrow 82 in the figure) is h (mm), then Pl is automatically set so that PQ - pm always holds. It has a mechanism to control the A pressure control unit 83 performs this control.

Here, the pressure gauge 34 installed in the bubbler container 2 and the T
Pressure gauge 81 installed in EO3 storage tank 10, and further TEO
3. A liquid level sensor 32 installed in the storage tank 10,
A variable flow valve 84 connected to the gas cylinder 11 and a variable flow valve connected to the rotary pump 28 are set so that the indicated value of the pressure gauge 81 always satisfies the above relationship. 85 is controlled.

In the three embodiments described above, a capacitance detection type level meter can be used as the liquid level meter, but level meters of other types can also be used. Furthermore, the heat exchanger 22 is not limited to the one shown in the embodiment.
Various modifications are possible. Furthermore, although the examples have been described using TEOS gas as a specific example, the type of raw material is not limited to TE01, and any material can be used as long as it does not undergo deterioration due to heating in the bubbler container.

In the embodiment shown above, approximately 1 in the TEO3 storage tank 10
Using 0g of liquid raw material, the flow rate was kept constant within ±5% (~200cc/ll1i) over a period of 75 hours or more.
n). Moreover, the variation in the thickness of the 5i02 thin film produced was also within ±5% within the above-mentioned time. If the liquid material in the storage tank is made larger, it can be used for a longer period of time.

(Effects of the Invention) As explained above, according to the present invention, it is possible to repeatedly supply a constant amount of raw material gas to the CVD reaction chamber, so it is possible to create a thin film with good reproducibility under the required control. It has significant industrial value.

Further, in addition to the above-mentioned effects, the invention as set forth in claim 3 has the effect that the recovered raw material gas can be reused and the replenishment period of the raw material gas can be extended.

[Brief explanation of drawings]

Fig. 1 is a system diagram of the first embodiment of the present invention, Fig. 2 is a system diagram of the second embodiment, and Fig. 3 is a system diagram of the third embodiment with a part omitted. FIG. 4 is an explanatory diagram of a conventional bubbler container, and FIG. 5 is a graph showing temporal changes in the flow rate of vaporized gas supplied by the conventional bubbler container. 1... Liquid raw material 2... Bubbler container 10
...TEO8 storage tank 15...Valve 16...C
VD reaction chamber 20... Valve 21... Branch pipe

Claims (1)

[Claims] 1. In a method for forming a thin film on a substrate surface by introducing a raw material gas into a CVD reaction chamber using a bubbler method, a constant amount of raw material gas can be supplied at all times by keeping the raw material contained in a bubbler container constant. A method for producing a thin film characterized in that the source gas is allowed to be supplied to a CVD reaction chamber, and the source gas is guided to the CVD reaction chamber when forming a thin film, while the source gas is guided to a place other than the CVD reaction chamber when forming a non-thin film. 2. In a thin film production apparatus comprising a bubbler-type gas supply mechanism and a CVD reaction chamber, the gas supply mechanism includes:
It consists of a bubbler container, a mechanism for controlling the amount of raw material inside the bubbler container, and piping connecting the bubbler container and the CVD reaction chamber, and the piping is provided with a branch pipe, and the piping and Thin film forming apparatus 3 characterized in that each branch pipe is provided with a valve. The thin film forming apparatus according to claim 2, wherein the branch pipe is connected to a recovery device for raw material gas sent from a bubbler container.