JPH03180467A - Method and device for forming thin film - Google Patents

Abstract

PURPOSE:To form a high-quality thin film without damaging its substrate by supplying different high frequency powers to a target and a susceptor holding the substrate and making the frequency of the power on the susceptor side higher. CONSTITUTION:A target 101 is fixed on a target electrode 102 in a vacuum vessel 105, and a high-frequency power of the first frequency f1 (e.g. about 13.56MHz) is applied from an RF power source through a matching circuit. Meanwhile, a high-frequency power of the second frequency f2 (e.g. about 100MHz) is applied on the wafer 103 and susceptor 104. Furthermore, band eliminators 102' and 104' are provided so that only the high-frequency powers respectively of about 13.56MHz and about 100MHz are inputted to the target electrode 102 and the susceptor 104. As a result, the insulating film is formed by bias sputtering without damaging the substrate semiconductor wafer 103.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a thin film forming apparatus and a thin film forming method.

[Prior Art] Currently, sputtering is widely used to form conductive wiring materials and insulating thin films for integrated circuits. The sputtering method is a method in which Ar gas is introduced into a vacuum container, and direct current or high frequency power is applied to a cathode to which a target material is attached to generate glow discharge to form a film. As a result of the glow discharge, the target surface is negatively biased with respect to the plasma (this is called self-biasing), and Ar ions accelerated by this bias voltage impinge on the target surface and sputter-etch the target material. The material particles etched in this way are deposited on wafers placed opposite each other to form a bottom film. In contrast, a method that applies high-frequency power not only to the target but also to the susceptor itself to which the wafer is attached, deposits a film on the wafer surface, and simultaneously performs sputter etching using a self-bias formed on the wafer surface. This method is called high frequency bias sputtering.

FIG. 5 shows a schematic diagram of the cross-sectional structure of a typical conventionally used bias sputtering device.
501 is, for example, Sin.

The target is an insulating material such as S i 3 N4, A1203, AjLN, etc., and 502 is a target electrode to which the target is attached. Also, 503°50
Reference numerals 4 denote electrodes of a semiconductor wafer, a substrate such as glass or quartz, and a susceptor, respectively.

High frequency power is supplied to the target electric current 8i502 and the susceptor electric current 8i504 through matching circuits, and the vacuum vessel 505 is grounded.

Here, the high frequency power supply (RF power supply) has an oscillation frequency of 13.5
6M) (Z) is normally used.In addition to the above, the actual equipment is equipped with a vacuum exhaust unit, gas inlet, and other mechanisms for entering and exiting the wafer. However, it is omitted in this figure for simplicity.

The surfaces of the substrate 503 such as a semiconductor wafer and the susceptor 504 are negatively self-biased with respect to the plasma due to the RF power applied to the susceptor, and Ar ions accelerated by this electric field collide with each other, so that part of the deposited film is By using the zero sputtering method, a thin film with excellent mechanical strength can be obtained. Another feature is that it is possible to form a film with a flat surface by taking advantage of the property that the film formed on the stepped portion is easily sputtered. However, since Ar ions accelerated by self-bias collide with substrates such as semiconductor wafers, the formation of various thin films such as semiconductor N films, conductive thin films, and insulating thin films damages the underlying material and deteriorates the characteristics of devices. This is causing the above problem. These problems have been a major obstacle in putting bias sputtering devices into practical use.

[Problem H to be solved by the invention] The present invention has been made in view of the above points, and provides a thin film manufacturing apparatus and a thin film forming method that can form a high quality thin film without damaging the underlying substrate. It is.

[Means for Solving the Problems] The thin film forming apparatus of the present invention deposits a thin film on the surface of a substrate such as a semiconductor, glass, quartz, metal, etc. by sputtering a target in a reduced pressure atmosphere. In the forming apparatus, high frequency power having a first frequency and a second frequency is supplied to both a target and a susceptor that holds the substrate within the apparatus, and the second frequency is equal to the first frequency. It is characterized by being set to be larger. That is, it is characterized in that high-frequency power having different frequencies can be applied to the image electrodes of the target and the susceptor, respectively.

Further, the thin film forming method of the present invention is a thin film forming method in which a thin film is deposited on the surface of a substrate by sputtering a target in a reduced pressure atmosphere, which includes a target and a susceptor that holds the substrate in an apparatus. and supplying high frequency power having a first frequency and a second frequency, respectively, and forming a thin film by setting the second frequency to be higher than the first frequency. do.

[Example] The present invention will be described in detail below using the drawings.

Note that, as a matter of course, the scope of the present invention is not limited to the following examples.

FIG. 1(a) is a schematic diagram showing a bias sputtering apparatus for forming an insulating thin film, which is a first embodiment of the present invention. Here, an example will be described in which a semiconductor substrate is used as a base and an insulating film is deposited on the semiconductor substrate.

Reference numeral 101 denotes a target of, for example, S i O, and is attached on the target electrode 102 .

For example, a signal of 13.56 MHz (first frequency f1
) high-frequency power is applied. In addition, the silicon wafer 103 and the susceptor 104 are connected to each other via a matching circuit.
A radio frequency power of a frequency greater than the radio frequency being applied to the target, for example (second frequency f,) 100M) (z) is applied.

Furthermore, a target electrode 102 and a susceptor electrode 104
13.56MHz for each.

A band eliminator (Band E1ia+1nat
or) 102', 104° are provided. The band eliminator used for the susceptor electrode 104 may have the configuration 104b as shown in FIG. 1(b), for example.
The impedance is maximum at the resonant frequency of +)"") (Fig. 1 (C)), and for other frequencies C,
is almost always short-circuited, so the predetermined frequency (in this case f
It is possible to select and supply only a high frequency wave (100 MHz) to the electrodes. That is, for the first frequency fr (here 13.56 MHz), the susceptor is almost completely shorted to ground. Figure 1 shown here (
It goes without saying that the configuration b) merely shows the basic principle and may be modified for various improvements.

For example, FIG. 1(d) is an example of an improvement.

The circuit 104b is grounded in terms of DC, but if you want to make it floating in terms of DC, for example, add a capacitor C1 as shown in 104d in Figure 1(d) to connect the DC path. In this case, the value of 01 is f2 ·L, >17f, C so that the resonant frequency of the circuit does not deviate from f2.

It is necessary to set a value large enough to satisfy the following conditions.

In this case fo = t/ (2yr (Lt Cs)
The impedance of the series circuit of Ll, C, becomes 0 for the frequency of ""), and it becomes a short circuit for the high frequency of the frequency to. Frequency 1 at which this fo can be added to the target
If we set it equal to 3.56MHz, 13
．． It is possible to effectively prevent the high frequency of 56 MHz from being transmitted. In other words, even if the electric field of high-frequency power entering the target terminates vertically from the electrode 102 to the electrode 104, since the electrode 104 is short-circuited to the ground with respect to the frequency f, the voltage of the electrode 104 is The cylindrical magnet 106 provided on the back surface of the target electrode 102, which does not fluctuate at f, generates a magnetic field approximately parallel to the surface of the target material 101, and electrons perform cyclotron motion with respect to this magnetic field. When a perpendicular high-frequency electric field exists between the electrodes 102 and 104, energy is effectively imparted to the cyclotron-moving electrons, and the high-frequency power effectively generates high-density plasma.

Vacuum container 105 is connected to ground. Also, 10
6 is a permanent magnet for magnetron discharge. Furthermore, the apparatus is provided with an exhaust unit that evacuates the vacuum container, a mechanism for introducing gas, and a mechanism for loading and unloading wafers, but these are omitted here for simplicity.

The reason why the present invention makes it possible to form an insulating thin film by bias sputtering without damaging the underlying semiconductor wafer will be explained below.

FIG. 2 is a schematic diagram of an apparatus for measuring the current-voltage characteristics of an electrode. The device itself is the same as that shown in FIG. 1, but the DC power supply 201 and ammeter 202 are
Like the band eliminator 104b shown in FIG. two electrodes (in this figure, they are connected to the susceptor electrode 204. In this state, for example, Ar gas
Fig. 3 shows the relationship between the direct current voltage (2) applied to the electrode and the resulting current that is introduced at a pressure of 'Torr to cause discharge.

In this case, the frequency a of the high frequency power supply 205 is variable, and f4
The figure shows results taken for three frequencies: MHz, 40.88 MHz and 100 MHz. Also, the current that positively charged ions flow into the electrode is taken as a positive value.

For example, looking at the characteristics of 100MHz, ■ is approximately -95V
When the value of is expressed as VSa), I=0, and V>V
For sa, I<O, and for V<Vsa, ■>O.

This ■. is called self-bias and is a DC bias voltage generated when high-frequency discharge is performed while the electrode is floating. That is, when the electrode is at this potential, the numbers of ions and electrons flowing into the electrode from the plasma are equal, so they cancel each other out and the current becomes O. When the potential of the electrode is controlled by an externally applied DC bias, a current flows. For example, V>Vs
If it is a, more electrons will flow in and I<O.

On the other hand, when V<Vsa, the potential barrier to electrons increases and the number of electrons flowing in decreases, so that the ionic current becomes larger and a positive current flows. Roughly ■
When increasing in the negative direction, the current value is saturated at V=V,
becomes a constant value.

Considering the fact that the current value is equal to the current value of only ions and is greater than or equal to 0, the slope of the IV characteristic when V>Vo corresponds to the width of the electron energy distribution. In other words, a large slope means that the electron energy distribution is narrow.
In the case of 00 MHz, the energy distribution is reduced to about 1/10. On the other hand, when the ion energy distribution width is ΔElon and the electron energy distribution width is ΔE1, there is a roughly proportional relationship between the two, so the ion energy distribution width is also approximately 1/10. It can be said that it is decreasing.

Furthermore,■! ! The value of 1 is also -400V at 14MHz.
On the other hand, at 100 MHz, the absolute value is about -95 V, which is less than 1/4.

The reason why the conventional bias sputtering method causes damage to the underlying substrate and deteriorates the characteristics of the device is as follows.

That is, in the conventional example, since discharge was performed at a frequency of 13.56 MHz, IVs-b I = 4oov ~ 600
The voltage was 0V, and ions accelerated by this high voltage were hitting the substrate. Furthermore, the energy distribution of ions is large, and even if the average value of energy is controlled, there will be many ions with energy sufficiently higher than the average value, and these high-energy ions will cause a large ion bombardment to the substrate. This was the cause of the damage.

However, in the first embodiment of the present invention, since a high frequency of 100 MHz is used for the quaternary susceptor electrode 104, the IVsa is lower than that of the conventional case of 13.56 MHz.
l is about 1/4 to 115, ΔEta. could be reduced to 1/10 or less. High frequency power applied to the susceptor (
f2) is for controlling the self-bias generated in the susceptor, so by reducing its power, the self-bias can be made small to the extent that it does not damage the substrate.9 In the device of the present invention, The discharge is maintained by the target (high frequency power (f) applied). As a result, damage to the substrate can be eliminated.

VSa decreases as the frequency of the high-frequency power source increases and as the high-frequency power decreases. Therefore, it is only necessary to select the frequency f2 and the power to be applied to the susceptor so as to provide the ion energy and ion irradiation amount necessary to obtain sufficient quality of the thin film deposited on the substrate.

On the other hand, the target electrode 102 has the same 13.
Since 56 MHz is applied, a large self-bias occurs, and sputtering occurs due to large ion energy, so the sputtering speed of the target does not decrease.Furthermore, in the embodiment shown in FIG.
6 is attached, and the ion concentration is increased by causing a magnetron discharge (electrons wrap around magnetic lines of force and move in a cyclotron, receiving energy from a high-frequency electric field and efficiently ionizing neutral Ar atoms) near the target substrate. The structure is such that the sputtering speed is further increased by increasing the sputtering speed.

As described above, according to the dual frequency excitation RF bias sputtering apparatus according to the present invention, while maintaining a high film formation rate,
It has become possible to sputter deposit a high-quality insulating film without damaging the substrate.

It is also possible to control the energy of ions flowing into the susceptor by applying a DC bias to the electrodes as shown in FIG. However, this method of applying a DC bias is effective when the thin film to be formed is a conductive material.

Above, we have described only the case where the RF frequencies supplied to the target and susceptor are 13.56 MHz and 100 MHz, respectively, but it goes without saying that it is not necessary to limit the frequency to these.In short, it is sufficient to make the latter larger than the former. The actual value may be determined depending on the purpose, taking into consideration the required film formation rate, the shape of the coating at the 1:H step, etc.

However, for example, when macro waves such as 2.45 GHz are used, the wavelength of the electromagnetic waves becomes smaller than the diameter of the substrate wafer, which may cause variations in film thickness. The material is not limited to insulators, and of course it is also effective for conductive materials C.

From the viewpoint of uniform film formation, the wavelength of the high frequency power source used for high frequency discharge is required to be at least twice the diameter of the wafer. Preferably 100MHz (wavelength 3m) ~t
It is approximately GHz (wavelength: 30 cm).

Further, the structure of the magnet 106 installed on the back surface of the target electrode 102 is not limited to that shown in FIG. 1.

For example, as shown in the second embodiment of the present invention in FIG. It is advantageous to place the scanning system 410 outside the vacuum vessel 405 as shown in Figure (a) to prevent the reaction system from being contaminated by dust generated from mechanical operations. Furthermore, if unnecessary, the magnet 108 may be omitted without departing from the spirit of the present invention.

Furthermore, a magnet may be installed on the wafer susceptor side to increase the efficiency of low-energy ion irradiation without causing damage to the substrate; 41 (Fig. 4(a))
It may be something that can be moved like 0.

Furthermore, in order to further reduce damage to the substrate, it is also possible to take the following method.1 For example, directly inject the exposed silicon surface.

When laminating insulating films such as
During the formation of about 100 films, the RF power supplied to the silicon substrate is set to zero without re-sputtering, and then it is switched to bias sputtering. In this way, resputtering is not performed while the silicon surface is exposed, and sputtering film formation is started after a thin film is formed on the surface, so that damage to the silicon surface of the substrate can be reduced to almost zero. If the kinetic energy of the irradiating ions becomes too great, any material will be damaged. Damage begins to occur in the material when the kinetic energy of the irradiated ions becomes slightly larger than the interatomic bonding force of each material. This interatomic bonding force is usually greater in insulators than in semiconductors.

The energy of the irradiation ions may be determined by matching the properties of the substrate material and film forming material.

FIG. 4(b) shows a third embodiment of the present invention, which shows a method in which damage to the substrate can be suppressed to a minimum and the energy of ions with which the substrate is irradiated can be freely selected. 'M1
The differences compared to the first embodiment shown in Figure (a) are as follows:
The difference is that two different frequencies, fz and fs, can be switched and input to the susceptor, and the band eliminator 401 is also converted depending on the company.

402 and 403 are resonant circuits of C, each with f
,,f, has a resonant frequency.

fz =t/(2π (LI C,)”')t
s = 1 / (2π (L2 C2)""
) Band Eliminator 401, in which two resonant circuits 402 and 403 are connected in series, has a large impedance only for the two frequencies fz and f3, and is short-circuited for other frequencies. It has a function of selectively supplying only two types of high frequencies to the susceptor.

For example, fl is 13.56MHz and f2=100
MHz, f3 = 40 MHz. Then, for example, apply 5i02 directly to the exposed silicon surface.
When growing an insulating film such as
While forming a film of about 00A, the frequency of the high frequency applied to the susceptor 104 is set to fz (100MHz), and thereafter the frequency is set to f3 (40MHz).
to form a thick film (for example, 0.5 to 1 μm). In this way, while the silicon surface is exposed, a small self-bias value of about 10~ corresponding to 100MHz can be maintained.
Ar ions irradiate the substrate surface with 20V, so there is almost no damage to the substrate.When the 0 surface is covered with 5i02 of about 100A, switch the frequency to 40MHz.
Furthermore, if the power is controlled, the self-bias value becomes large, for example, 30 to 250 V, and a large resputtering effect can be obtained. However, already St back surface 5i0
2, so there is no damage to the board.

Such a method becomes particularly important when controlling the flatness of the surface topography of 111i deposited by bias sputtering. This is because by changing the frequency, the most effective energy of Ar ions for re-sputtering can be controlled, and the optimum energy value can be selected without worrying about damage to the substrate.

Here, only the case of two different frequencies f, , f has been described, but for example, fz and fs.

It goes without saying that three values of f4 may be used; however, in this case, the first frequency f2 to be applied is f
When r>fs and f4, it is important to use the highest frequency to minimize damage. In addition, when using multiple frequencies, these include the target frequency fl,
fl + '2 rf3. It is desirable to select them so that they do not have a harmonic relationship with each other. This is because the discharge space is nonlinear, and therefore the harmonics of fr, fz, fs, etc. may appear in completely different forms depending on the discharge conditions, making the setting of the conditions inaccurate.

Although the embodiments of the present invention have been mainly described above with respect to the deposition of s i 0211i, it is of course not limited to this. This technique is of course effective for forming insulating thin films, but it also applies to An, AIL alloys, W, Mo, Ti, and Ta.
It can also be used for conductive thin films such as Furthermore, film formation is possible regardless of the properties of the substrate material.

This is a particularly effective technique when forming a thin film on a glass plate 1 quartz plate, etc.

So far, we have described an example of application to RF bias sputtering technology using Ar ions. For example, when forming a 513N4 film, a Si substrate is used as the target and N or NH is used as the introduced gas. The present invention can also be directly applied to reactive RF bias sputtering technology for forming films. In forming an AfN film, Aft may be used as a target substrate, and N2 or NH may be introduced as a gas.

It goes without saying that it may also be used for polymeric materials such as polyimide films and resists, if necessary.

Further, it goes without saying that the substrate on which the film is formed is not limited to a semiconductor wafer.

[Effects of the Invention] According to the present invention, it has become possible to easily obtain a thin film of high quality and excellent surface flatness without causing damage to the substrate.

[Brief explanation of drawings]

FIGS. 1(a) to 1(d) are schematic diagrams and explanatory diagrams of an apparatus showing a first embodiment of the present invention. Figure S2 is a schematic diagram showing an apparatus for measuring the current-voltage characteristics of an electrode. FIG. 3 is a graph showing experimental data of current-voltage characteristics of the electrode. FIG. 4 (a) and Cb) are schematic diagrams showing a second embodiment and a third embodiment of the present invention, respectively. FIG. 5 is a schematic diagram showing a conventional example. 101... Target, 102... Target electrode, 103... Wafer, 104... Susceptor electrode,
105...vacuum container, 102°, 104°, 104b
, 104d, 401...Band Eliminator - Fig. 1 (&) Fig. 1 (b) Fig. 1 (d) Fig. 2 Fig. 4 + a) Fig. 4 (b) Fig.

Claims (4)

[Claims] (1) In a thin film forming apparatus that deposits a thin film on the surface of a substrate by sputtering a target in a reduced-pressure atmosphere, both the target and a susceptor that holds the substrate within the apparatus each have a A thin film forming apparatus characterized in that high frequency power having a first frequency and a second frequency is supplied, and the second frequency is set to be higher than the first frequency. (2) The thin film forming apparatus according to claim 1, wherein the first frequency is 13.56 MHz and the second frequency is 100 MHz or more. (3) In a thin film forming method in which a thin film is deposited on the surface of a substrate by sputtering a target in a reduced pressure atmosphere, both the target and a susceptor that holds the substrate in the apparatus are A method for forming a thin film, comprising supplying high frequency power having a first frequency and a second frequency, and forming a thin film by setting the second frequency to be higher than the first frequency. (4) The thin film forming method according to claim 3, wherein the high frequency power supplied to the susceptor is set to approximately 0 in the early stage of film formation, and bisass sputtering is performed after the film is formed to a thickness of approximately several tens of angstroms.