JP3319055B2 - Quartz crystal type radical beam monitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz crystal for evaluating the amount of radicals irradiated on a substrate for controlling the film formation on the substrate for forming various thin film devices such as semiconductor devices. The present invention relates to an oscillator type radical beam monitor.

[0002]

2. Description of the Related Art As a technique for forming a film on a substrate for forming various thin film devices such as a semiconductor device, a vacuum deposition method, a sputter deposition method and the like are known. In such film formation, a crystal oscillator type film thickness monitor is frequently used for the purpose of controlling the film thickness, the amount of material evaporation, the film formation speed, and the like.

As shown in FIG. 3, a quartz-crystal-type film thickness monitor is provided with gold (A) on both surfaces of an AT-cut (cut in the direction of the smallest thermal expansion coefficient) thickness t quartz crystal 81.
An electrode 82 made of u) or silver (Ag) is provided, and a basic structure is provided in which an AC power supply 83 is connected to this electrode. A high-frequency voltage is applied to the electrodes 82 on both surfaces of the quartz oscillator 81,
When the frequency of the voltage reaches a natural frequency f _q determined by the thickness t and the elastic constant of the crystal resonator 81, a standing wave vibration of a thickness shear is generated. At this time, the following relationship holds: f _q = v / 2t (v: propagation velocity of the standing wave).

If the thickness of the vibrator 81 changes by Δt, the natural frequency changes by Δf, and Δf / f
_q = −Δt / t. If a film having a density ρ and a thickness d is deposited on the surface and the thickness changes by Δt, then Δf / f _q
= -Ρd / ρ _q t: the (ρ _q density of the crystal). Assuming that the frequency becomes f due to the deposition of the film, Δf = ff
_q , and the frequency after the change is f = f _q (1-ρd / ρ
_q t).

As a result, the decrease in the frequency of the vibrator 81 is proportional to the film thickness of the film deposited on the electrode 82, and is used as a monitor for the film thickness during film formation, the amount of material evaporation, the film formation rate, and the like. can do. The film thickness monitor using this crystal unit has a structure and
It is widely used industrially because of its simple operation and sensitivity equal to that of the optical method.

Further, the crystal oscillator type film thickness monitor is also applied to monitoring the amount of radicals irradiated on a substrate in a film forming process including a radical beam irradiation operation on the substrate. For example, as shown in FIG.
Quartz crystal unit 91 of sensor unit 9 of crystal unit thickness monitor
A film 93 containing a substance that is combined with the irradiated radical is formed on the surface of the upper electrode 92, and the change in the frequency of the crystal unit 91 caused by the change in the state of the film due to the reaction with the radical causes the radical Evaluation of the irradiation dose has been performed.
For example, when the radicals used are oxygen radicals,
A g film is used, and the amount of radical irradiation is evaluated by observing a change in the frequency of the vibrator 91 accompanying a change in weight due to oxidation of the film under the irradiation of oxygen radicals.

[0007]

However, in a conventional radical beam monitor utilizing a change in film state due to a chemical reaction of a film on a quartz oscillator, a radical reacts with a constituent atom of the film. Requires that radicals (elements that were radicals) diffuse in the thickness direction of the film. Diffusion rate of radicals (elements that were radicals),
And the rate of the subsequent reaction of the radicals with the constituent atoms of the film is a function of time. Therefore, when monitoring the amount of radical irradiation for a long time, a large error occurs in the measured value of the amount of radicals reacted with the constituent atoms of the film.

In a film-forming apparatus of a load lock type or the like which does not break the vacuum in a film-forming container, when film formation is performed a plurality of times without replacing the crystal oscillator of the monitor, the same conditions are used. It is not possible to measure the amount of radicals with good reproducibility in film formation. Further, the two factors of the film thickness and density change simultaneously with the deposition of the reaction product, so that it becomes more difficult to accurately measure the amount of radicals that have reacted with the constituent atoms of the film.

In the present invention, when a film is formed on a substrate by a process including radical irradiation, the amount of radicals irradiated on the substrate can be stably measured over a long period of time. It is an object of the present invention to provide an inexpensive crystal oscillator type radical beam monitor capable of performing control stably for a long time.

[0010]

A crystal oscillator type radical beam monitor according to the present invention which solves the above-mentioned problems is provided with an electrode on a crystal oscillator, applies an AC electric field to the crystal oscillator via the electrode, and By observing the change in the oscillation frequency of the quartz oscillator due to the substance attached to the electrode, the electrode of the quartz oscillator type film thickness monitor capable of monitoring the thickness of the film formed on the substrate on which the film is to be formed is provided. A film containing a substance which becomes a gas by being combined with a radical irradiated upon film formation on the film formation substrate is formed and formed, and the film formed on the electrode is
To analyze the composition of the gas generated by exposure to
It is characterized by combining stages .

It is also conceivable to provide a heater for heating the quartz oscillator in order to promote the reaction between radicals and a substance contained in the film to be irradiated with radicals. In addition, when using the monitor of the present invention, as a film forming technique, vacuum deposition,
Various methods such as sputtering can be considered.

[0012]

According to the monitor of the present invention, a film containing a substance which becomes a gas by being combined with radicals is formed on the surface of the electrode on the quartz crystal resonator to be irradiated with radicals. When the monitor is irradiated with radicals, the radicals combine with the radical-irradiated substances contained in the film to form a gas, and the film thickness of the film is reduced accordingly. The amount of radical irradiation is evaluated by detecting a change in the frequency of the quartz oscillator due to a decrease in the thickness of the film. Specifically, for example, the weight (the number of atoms or the number of molecules) of the substance to be irradiated with the radical is determined from the frequency change. On the other hand, the composition of the gas generated from the monitor by the radical irradiation is analyzed by a means for analyzing the gas (gas composition analyzer or the like), and the ratio of the constituent elements of the gas molecules obtained by the gas composition analyzing means, that is, the irradiation target substance and the radical The amount (number) of radicals combined with the substance contained in the film is determined from the composition ratio with the existing element and the weight (atom number or molecular number) of the substance irradiated with radicals that has disappeared by reacting with the radical. That is, the amount (number) of irradiated radicals is evaluated.

When a heater for heating the quartz oscillator is provided, the reaction between the radical and the substance to be irradiated with the radical is promoted.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an experimental apparatus for measuring the amount of radicals using a quartz oscillator type radical beam monitor 500 according to one embodiment of the present invention, and FIG. 2 shows a configuration of a sensor unit 5 of the monitor 500. I have.

The sensor section 5 has almost the same structure as the sensor section 8 of the conventional crystal resonator type film thickness monitor shown in FIG. A
T-cut crystal unit 51 (resonance frequency 5 MHz)
An electrode 52 made of gold (Au) is provided on both surfaces of the device, and a high-frequency voltage is applied to the crystal unit 51 via this electrode. A film (radical irradiated film) 53 containing a substance which reacts with irradiated radicals and turns into a gas is formed on one of the radical irradiation surfaces of the electrode 52. An AC power supply 54 is connected to both electrodes 52.

According to this experimental apparatus for measuring the amount of radicals, the radicals 4a are irradiated from the radical source 4 onto the film 53 of the sensor section 5 in the vacuum vessel 1 maintained at a predetermined degree of vacuum by the operation of the exhaust device 2 in advance. The thickness of the film 53 decreases in accordance with the irradiation amount of the radicals 4a, and the vibration frequency of the crystal unit 51 changes. By monitoring the change in the frequency with the measuring circuit of the measuring unit 50 of the radical beam monitor 500, the number of atoms or molecules of the substance contained in the film 53 that has reacted with the radical 4a can be monitored. In addition, the gas composition analyzer 3 detects the types of elements contained in the gas generated from the monitor sensor unit 5 and their atomic ratios. From the atomic ratio and the number of atoms or molecules of the substance contained in the film 53 that has reacted with the radicals 4a, the amount (number) of the radicals 4a that have been irradiated and contributed to the reaction with the film 53 can be determined.

The atoms or molecules of the substance contained in the film 53 that have reacted with the radicals 4a disappear from the film as one constituent element of the gas molecules, so that the sequentially irradiated radicals are emitted at the surface layer of the film. Reacts with substances contained in. Therefore, it is not affected by the diffusion rate of radicals (elements that were radicals) as a function of time, and the radical irradiation amount (number) can be accurately calculated over a long period of time or many times (total of a long time). Can be measured.

The radical irradiation amount (number) can be accurately measured because the density of the film 53 is not changed by the radical irradiation, and only the film thickness or the film weight is changed. next,
A specific example in which the radical irradiation amount is measured using the radical beam monitor 500 of the present invention and oxygen radicals as the radicals 4a will be described. In the vacuum vessel 1, as a radical beam monitor 500, a thickness of 1 μm was formed on one surface of the crystal unit electrode 52 of the sensor unit 5 by a vacuum evaporation method.
m having a carbon (C) film 53 formed thereon.
Oxygen radicals 4a were irradiated at a power of 500 W using the radical source 4 from a position 300 mm away from. During this time, the inside of the container 1 is operated at 5 × 10 ⁻⁵ Torr by operating the exhaust device 2.
r. During this time, a linear relationship was observed between the irradiation time of the radicals 4a and the frequency of the quartz oscillator 51 for one hour, and stable monitoring of the oxygen radicals 4a was performed.

As a comparative example, a thickness of 1 μm was applied to one surface of the crystal unit electrode 92 of the sensor unit 9 by a vacuum evaporation method.
The irradiation amount of the oxygen radicals 4a was measured for one hour using a radical beam monitor on which an Ag film 93 of m was formed in the same manner as in the specific example of the present invention. During this time, the irradiation time of the oxygen radical 4a and the quartz oscillator 5
The frequency of 1 had a linear relationship for 5 minutes after the start of radical irradiation, but then became unstable gradually, and stable monitoring of oxygen radicals was not performed.

From the above results, it can be seen that in the embodiment using the radical beam monitor 500 of the present invention, more stable monitoring can be performed for a longer time than in the comparative example. Although the radical beam monitor of the present invention has been used in the radical amount measurement experimental apparatus in the above description,
Actually, it is used in a film forming apparatus including radical irradiation means.

Further, the radical beam monitor of the present invention comprises:
Compared with a means for optically monitoring the amount of radical irradiation, the structure is simpler and can be provided at low cost. .

[0022]

According to the present invention, when a film is formed on a substrate by a process including radical irradiation, the amount of radicals irradiated on the substrate can be measured stably over a long period of time. It is possible to provide an inexpensive crystal oscillator type radical beam monitor capable of performing film formation control stably for a long time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a radical amount measurement experiment apparatus provided with an embodiment of the present invention.

FIG. 2 is a configuration diagram of a main part of one embodiment of the present invention used in the apparatus of FIG. 1;

FIG. 3 is a configuration diagram of a main part of a conventional crystal resonator type film thickness monitor.

FIG. 4 is a configuration diagram of a main part of a conventional crystal oscillator type radical beam monitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Exhaust device 3 Gas composition analyzer 4 Radical source 4a Radical 500 Radical beam monitor 50 Measurement part of monitor 500 5 Sensor part of monitor 50 51 Quartz crystal oscillator 52 Au electrode 53 Radical irradiation film

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-318909 (JP, A) JP-A-57-106113 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21 / 203,21 / 363 C23C 14/00-14/58 G01B 17/02

Claims (2)

(57) [Claims] 1. An electrode is provided on a crystal oscillator, an AC electric field is applied to the crystal oscillator via the electrode, and a change in the oscillation frequency of the crystal oscillator due to the attachment of a substance on the electrode is observed. A substance which becomes a gas by being combined with radicals irradiated at the time of film formation on the film formation substrate is applied to the electrode of the crystal oscillator type film thickness monitor capable of monitoring the thickness of the film formed on the film formation substrate. on the electrode as well as constructed by forming a film comprising
Occurs when the film formed on the surface is exposed to radical irradiation
1. A crystal oscillator type radical beam monitor characterized by combining means for analyzing the composition of a gas to be changed. 2. The crystal oscillator type radical beam monitor according to claim 1, further comprising a heater for heating said crystal oscillator.