JPS626639B2 - - Google Patents

Description

Detailed Description of the Invention The present invention enables high-quality films to be formed at high speed by using a hollow container-shaped target having at least one opening in the sputtering method, which is a type of thin film manufacturing method. The present invention relates to a sputtering device that can be used for sputtering.

The sputtering method is widely used as a method for forming various metal films or compound films. In particular, in recent years, various high-speed sputtering methods have been developed, and significant improvements are being made in terms of film formation speed, and they are expected to be used in a wide variety of fields, including thin-film electronic components.

The most common sputtering method is a two-pole sputtering method using a flat target, but this method has the drawbacks of slow film formation and the tendency to contain impurities in the film. To improve the film formation speed, there is a magnetron sputtering method that uses so-called magnetron discharge, where the electric and magnetic fields are orthogonal, to promote ionization of the atmospheric gas, or a hot cathode (tungsten filament) for thermionic emission. A three-pole sputter method has been proposed.

However, the following problems still remain in sputtering apparatuses employing this new method. In other words, in both the magnetron method and the three-electrode method, the discharge plasma necessary for sputtering is in contact with the film formation area, so the effects of the plasma (especially destruction of the film structure by high-speed ions or impurity gas in the film) etc.)
is difficult to avoid. Furthermore, in the three-pole sputtering method, the temperature inside the sputtering tank becomes extremely high due to heat generation from the tungsten filament, and an increase in temperature at the film forming portion is unavoidable. This temperature increase is undesirable for film formation. Furthermore, there is a drawback that tungsten vapor generated from a tungsten filament for emitting thermionic electrons mixes into the film as an impurity.

An object of the present invention is to provide a sputtering device that eliminates the drawbacks of the conventional devices.

The present invention provides a sputtering apparatus comprising a substrate holder, a target holder disposed opposite to the substrate holder, and a target supported by the target holder, wherein the target has a hollow container shape to confine secondary electrons. and is characterized in that the surface facing the substrate holder is provided with an opening for sustaining discharge having an area smaller than the area of the hollow part of the target on the side facing the substrate holder. be.

By confining the discharge plasma in a hollow container-shaped target, the present invention can extremely increase the effective ionization efficiency of the sputtering gas by electrons, and as a result of separating the discharge plasma from the film forming part, it is possible to improve the efficiency during film formation. This is based on the recognition that it is not affected by electrical discharge.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 shows an embodiment in which the present invention is applied to a conventional two-pole sputtering device. This sputtering device includes a cylindrical sputtering tank 1, which has a sputtering gas inlet 2 and an exhaust port 3. This exhaust port 3 is connected to a vacuum exhaust system (not shown). Inside this sputtering tank 1, a cylindrical substrate holder 4 at the top and a cylindrical target holder 5 at the bottom are provided facing each other. The interiors of the substrate holder 4 and target holder 5 are constructed to allow circulation of cooling water, and water pipes 6 and 7 pass through the top wall 8 and bottom wall 9 of the sputtering tank. The target holder 5 and the sputtering tank 1 are electrically insulated.

A substrate 10 is provided on the lower surface of the substrate holder 4. On the other hand, a hollow cylindrical container-shaped target 11 is provided on the upper surface of the target holder 5. This target has a circular opening 12 in its upper wall. Target holder 5 and target 11
The target is surrounded by a shield plate 13, except for the upper wall part, and this shield plate is connected to a sputtering tank. This shield plate 13 is for suppressing unnecessary spatter discharge on the outer wall surface of the target. Substrate 10 and target 11
are cooled by a substrate holder 4 and a target holder 5, respectively.

A circular flat shutter 14 and a circular shield plate 16 having a circular opening 15 in the center are provided between the substrate 10 and the target 11. To simplify the drawing, mechanisms for supporting the shutter 14 and shield plate 16 are omitted. The shutter 14 is for removing vapor of the first sputtered particles containing impurities, and is supported so as to be rotatably movable parallel to the bottom wall 9, as shown by an arrow 17 in the figure. Further, the shield plate 16 is
This is to suppress unnecessary discharge occurring on the target surface, stabilize the discharge occurring inside the target, and partially control the discharge conditions.

The target holder 5 is connected to the negative terminal of a DC voltage power source 18 to serve as a cathode. On the other hand, the sputtering tank 1 and therefore the substrate holder 4 are grounded and serve as an anode.

Next, the operation of the sputtering apparatus having the above structure will be explained.

The interior of the sputtering tank is evacuated through the exhaust port 3, and a fixed amount of sputtering gas, such as argon gas, is supplied through the gas inlet 2. Since the target holder 5 is connected to the negative terminal of the DC high voltage source 18, a negative potential is applied thereto. Prior to setting the desired sputtering conditions, it is necessary to ignite the discharge, which can be done by increasing the gas pressure or
Alternatively, this can be done by applying a high voltage to the target holder 5.

Positive argon ions existing in the internal space of the target 11 are accelerated by the potential gradient and collide with the inner wall surface of the target. The target atoms (or molecules) on the inner wall of the target that are repelled by the accelerated argon ions diffuse through the target opening 12, pass through the opening 15 of the shield plate 16, and reach the substrate 10. Forms a film. At this time, a large number of secondary electrons simultaneously fly out from the inner wall of the target, but these secondary electrons are confined within the hollow part of the target, and the neutral argon atoms are ionized by these electrons and converted into positive argon ions. While repeating the above process, a donut-shaped stable discharge plasma with relatively high density is formed inside the target. In equilibrium,
A fixed number of electrons are ejected through the target aperture and a stable discharge is established. The resulting number of sputtered particles allows stable film formation on the substrate.

Note that the shutter 14 removes the vapor of the first sputtered particles containing impurities.
The shutter is placed at a position where it cuts between the target 11 and the substrate 10, and then the shutter is rotated parallel to the bottom wall 9 to open a passage so that the target atoms can reach the substrate.

The present applicant conducted various experiments by changing the shape of the target, etc., in order to confirm the effects of the above-described embodiment apparatus. As shown in FIGS. 2a and 2b, the experiment was carried out using a hollow cylindrical container-shaped target 11 having one circular opening 12 as described in the above embodiment, and a hollow rectangular parallelepiped container having one circular opening 19. The target was 20.

When changing the argon pressure P _Ar (10 mTorr and
Figure 3 shows the DC discharge characteristics obtained at 20mTorr). The vertical axis of the graph shown in FIG. 3 represents the applied voltage V (volts), and the horizontal axis represents the discharge current I (amperes). The target is a rectangular parallelepiped container-shaped target made of tungsten W and having an opening diameter of about 7 mm.
The experiment was carried out using a cylindrical container-shaped target made of niobium Nb and having an opening diameter of about 6 mm.

According to this experimental result, in the case of Nb, the characteristic I
∝V ⁿ characteristics are observed. Here, n is an index reflecting the electron ionization efficiency, and is approximately 20 when P _Ar =20 mTorr. This value is higher than the value (n9) reported for high-speed coaxial magnetrons, and it can be seen that highly efficient ionization is performed inside the target. For example, in the case of Nb, the current reaches a value exceeding 1A at a voltage of 200 to 500V. This is different from normal abnormal glow discharge where the current slowly increases as the voltage rises, but a new discharge mode is observed where the voltage is almost constant and the current increases rapidly. The difference in discharge characteristics seen in the experimental results is thought to be related to the difference in thermionic emission coefficient of each metal at high temperatures. In any case, it is noteworthy that high power can be input with a relatively low applied voltage.

Next, the maximum film deposition rate R _D on the substrate obtained when the argon pressure P _Ar is kept constant (20 mTorr)
FIG. 4 shows the relationship between (Å/min) and input power (watts). The tested targets were a hollow rectangular container made of tungsten with an opening diameter of approximately 7 mm, a hollow rectangular container made of niobium with an opening diameter of approximately 6 mm, and a hollow rectangular container made of Nb with an opening diameter of approximately 6 mm. It is a hollow cylindrical container with a diameter of about 12 mm. The experimental results for each of these targets are shown in the graph of FIG. 4 by lines a, b, and c, respectively. According to the above experimental results, the maximum film deposition rate R _D increases linearly as the power increases. With tungsten, it was possible to deposit a film of about 1000 Å per minute. This value is compared to the value obtained by direct current two-pole sputtering on a flat target with approximately the same area.
More than 10 times higher. Note that when comparing the R _D obtained with tungsten and niobium, which have approximately the same shape, tungsten has a value about 1.5 times higher. Under equal accelerating voltages, the sputtering rates of both metals are approximately equal. However, as shown in FIG. 3, under the condition of constant input power, a higher voltage was applied than in the case of tungsten, and as a result, it is understood that the spatter rate increased and R _D increased. It was also found that R _D tends to decrease as the diameter of the opening increases. This corresponds to a decrease in plasma density.

As is clear from the above explanation, in the conventional two-pole sputtering device, the efficiency of ionizing neutral argon atoms by secondary electrons was extremely low, and the number of sputtered particles that could be taken out was small. According to this method, since the inner wall surface of the target has a shape that confines the plasma, the effective ionization efficiency of the argon gas by secondary electrons becomes extremely high, which has the effect of realizing high-speed film formation. Experiments have confirmed that the film formation rate is more than 10 times higher than that of a normal two-pole sputtering device.

In addition, while both the magnetron sputtering method and the three-pole sputtering method require complicated device configurations such as magnets or tungsten filaments, this example device can be used in conventional two-pole sputtering devices by changing only the shape of the target. Since the desired performance can be achieved, the electrode configuration can be extremely simplified, and the device itself and its handling can therefore be extremely simple.

Furthermore, although magnetron sputtering equipment cannot sputter ferromagnetic materials at high speed, this example equipment is effective even for ferromagnetic materials because it uses a method that essentially does not utilize a magnetic field. It is.

It goes without saying that the present invention is not limited to the embodiments described above, and that various modifications and changes can be made.

For example, if the target material is an insulator, an RF (Radio) source is used instead of a DC high voltage source.
Frequency) can be used as a power source.

In addition, the present invention is not limited to the two-pole sputter method.
It can also be applied to a flat plate magnetron sputter method. In this case, Figures 5a and 5
As shown in figure b, a central cylindrical magnet 21, an annular magnet 22 surrounding it, and a yoke 2 between these magnets.
It is also possible to provide a hollow container-shaped target 25 above the flat magnetron electrode consisting of 3. The rest of the structure is the same as that in FIG. 1, so it is omitted in the drawing.

Further, the shape of the target may be a hollow cylindrical container, a hollow rectangular parallelepiped container, or a hollow polyhedral container, and may be of any shape as long as it can confine the plasma. The openings can be provided at any desired location, and the number of openings is not particularly limited as long as it serves the function of confining plasma.

Furthermore, a reactive gas such as nitrogen or oxygen can be supplied in cases where nitrogen compounds, oxides, etc. are to be formed. In this case, the sputtering tank must be provided with an inlet for the reactive gas.

As explained above, according to the sputtering apparatus of the present invention, the discharge is confined within the target, so that the discharge plasma does not come into contact with the film forming portion.
Therefore, the effects of plasma such as destruction of the film structure by high-speed ions or incorporation of impurity gas into the film can be significantly alleviated.

In addition, in the three-electrode sputtering method, not only does the tungsten vapor generated from the tungsten filament mix with impurities in the film, but also the temperature inside the sputtering tank becomes extremely high due to heat generation from the tungsten filament, causing an increase in the temperature of the film forming area. However, since the apparatus of the present invention does not use a tungsten filament, there is no possibility that substances other than the target become vapor, and there is no problem of temperature increase due to the tungsten filament.

Since the present invention confines secondary electrons in a hollow part of the target and utilizes a new discharge phenomenon different from conventional abnormal glow discharge, high-speed sputtering can be easily realized. Further, since the secondary electron beam can be extracted from the opening of the target, this is advantageous when heating the film deposition surface. Furthermore, by trapping the secondary electron beam at the front surface of the substrate using a magnetic field, the sputtering gas is activated, the chemical reaction is greatly promoted on the substrate surface, and a compound film can be formed efficiently. In addition, since the sputtered neutral particles travel a long distance until they escape from the hollow part of the target, they are scattered with sputter gas molecules (atoms) or other sputtered particles while traveling, and their kinetic energy is significantly reduced. However, since high-energy particles disturb the film growth surface and prevent good crystal growth, the present target in the form of a hollow container is advantageous in forming a high-quality compound crystal film.

Furthermore, in the apparatus of the present invention, by avoiding irradiation of the substrate with electrons, it is possible to suppress the temperature rise in the film forming portion to a constant low temperature.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway sectional view showing an embodiment of the sputtering apparatus of the present invention, and FIGS. 2a and 2b are
FIG. 3 is a perspective view showing the shape of the target, FIG. 3 is a graph showing the DC discharge characteristics, and FIG.
The figure is a graph showing the relationship between film deposition rate and input power, Figure 5a is a diagram showing another embodiment of the sputtering apparatus of the present invention, and Figure 5b is a diagram showing the flat magnetron electrode used in this embodiment. FIG. 1... Spatter tank, 4... Substrate holder, 5...
...Target holder, 10...Substrate, 11,2
0,25...Hollow container-shaped target, 12,19...
...Target opening, 13...Shield plate, 1
6... Circular shield plate, 18... DC high voltage source,
24... Flat magnetron electrode.

Claims (1)

[Claims] 1. A sputtering apparatus comprising a substrate holder, a target holder disposed opposite to the substrate holder, and a target supported by the target holder, wherein the target is hollow in order to confine secondary electrons. A sputtering device formed in a container shape and provided with an opening for sustaining a discharge, the surface facing the substrate holder having an area smaller than the area of the hollow part of the target on the side facing the substrate holder. . 2. The sputtering apparatus according to claim 1, wherein the substrate holder serves as an anode, the target holder serves as a cathode, and a high DC voltage is applied between these electrodes. 3. The sputtering apparatus according to claim 1, wherein the target holder is a flat magnetron electrode. 4. A sputtering apparatus according to claim 1, 2 or 3, wherein the target is a hollow cylindrical container-shaped target or a hollow rectangular parallelepiped container-shaped target.