JPS597352B2 - High frequency sputtering equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved high frequency sputtering device, and is particularly effective for forming insulating thin films using the high frequency sputtering device.

Conventional methods for depositing insulating thin films include chemical vapor deposition (C
The VD method (VD method) is widely used, and is mainly used especially in the manufacture of semiconductor devices. However, CVD
When an insulating film is deposited on top of an aluminum wiring layer, the coverage of stepped parts of the wiring is much worse than that of flat parts, and the quality of the film is not dense, so it is easy to crack and is not too thick. There was a defect that it could not be adhered to. On the other hand, high-frequency sputtering has long been known to be an effective method suitable for depositing protective insulating films for interconnects, as it can form dense, thick films. A method has been developed in which a strong magnetic field is formed near the target by placing a magnet with S and N poles on the back side of the target, and charged particles in the discharge atmosphere are concentrated near the target by the action of the magnetic field.
Not only has the deposition rate approached that of the CVD method, the substrate temperature rise during deposition is kept lower than conventional methods, and the damage caused by discharge to semiconductor device characteristics is reduced compared to conventional methods. Regarding the problem of coverage of stepped portions of wiring, the high frequency sputtering method has the same problem as the CVD method, and this is not a problem that can be solved by simply depositing it thickly. That is, when the insulating film 3 is deposited on the sample having the metal wiring 2 on the base substrate 1 as shown in FIG. 1a by, for example, the CVD method,
A constriction occurs at the stepped part. This is said to occur because the deposited insulating film acts as an obstacle and blocks the insulating molecules falling diagonally. In the case of high frequency sputtering, if the insulating film 3 is deposited thickly as shown in FIG. 1b, no constriction will appear at first glance. but,
When the surface of an insulating film is lightly etched (light etch) with an etching solution for the insulating film, the etching progresses rapidly along the dotted line in the figure. This can be verified by scanning electron microscopy (SEM) observation or simply by corrosion testing of metal wiring. The existence of such weak parts is not only a problem from a reliability standpoint, but also the same mechanism can cause a weak insulating film to form around slight irregularities in the underlying surface, such as around billrock on an aluminum wiring surface. It also causes deposits, causing local fluctuations in the etching rate during the etching process of the insulating film, resulting in products with poor appearance such as poor processing dimensions and erosion of the base. Now, in conventional sputtering equipment, various measures have been proposed to overcome this drawback (
For example, Tokuko Sho 48-17592).

In other words, the pressure of argon (Ar) in the sputtering atmosphere is set to an appropriate (small) value, a focusing magnetic field is applied near the substrate holder in a direction perpendicular to the holder, and the substrate holder is not electrically floated. It is said that it is effective to ground through an inductance (coil) and form a resonant circuit with the capacitance between the discharge plasma and the substrate and the coil, or to apply a negative bias to the substrate. These measures strengthen the coupling between the discharge plasma and the substrate holder, the substrate holder becomes at a negative potential although not as much as the target, and the injection of argon ions (Ar+) into the substrate becomes strong and active, which weakens the structure of the deposited film. It is explained that a dense coverage film is obtained as a result of parts being removed by reverse sputtering. However, in the case of sputtering equipment (high-speed sputtering equipment) that improves the deposition rate by forming a specific magnetic field near the target and concentrating the plasma near the target, the above-mentioned methods are basically It was confirmed that the method using a significant focusing magnetic field has difficulties in practical use due to interference between the two magnetic fields, and that the coverage is not sufficiently improved even when the other two methods are used in combination.

This is because the plasma is concentrated very close to the target due to the magnetic field near the target, so the plasma density near the substrate holder is much lower than in conventional equipment, and the coupling between the plasma and the substrate is reduced. This is thought to be because it is weakening. In fact, the spread of plasma can be judged to some extent with the naked eye, but in conventional equipment the plasma spreads uniformly in the space between the target and the substrate holder, whereas in high-speed sputtering equipment the plasma is concentrated near the target. It is observed that The present invention was made in order to eliminate the drawbacks of the above-mentioned high-speed sputtering device,
Coverage can be improved by weakening the electrical coupling between the target and the grounded metal parts around the target, allowing high-frequency current to flow through the substrate holder rather than to ground, and by strengthening the coupling between the charged particles in the plasma and the substrate holder. The present invention provides a method for depositing a good insulating film.

Generally, in sputtering equipment, in order to prevent sputtering of the metal parts of the target electrode other than the target material to be sputtered, a ground metal is placed around the target as a shielding jig, and the metal parts of the target electrode other than the target material to be sputtered are grounded. Unnecessary sputtering is prevented by keeping the distance to the shielding jig at a distance that prevents plasma from entering.
407). However, since the front side of the shielding jig or ground metal is exposed to the plasma space, a portion of the high frequency current, or most of the portion depending on the device, ends up flowing here. In the case of conventional equipment, the relative arrangement of the target and the shielding jig or ground metal may not look the same for convenience reasons, such as the way the target material is held differently in equipment that sputters from top to bottom and equipment that sputters from the bottom to the soil. It varies, but is often placed very close to the active part of the target. In conventional devices, where the plasma does not concentrate near the target and spreads uniformly within the device, this poses almost no problem in terms of electrical impedance or film quality. On the other hand, in high-speed sputtering equipment that concentrates plasma near the target by the action of a magnetic field,
In order to avoid temperature rise and damage to the substrate due to the sputter yield and the plasma entering the substrate, a grounded target shield plate is installed closer to the dense plasma near the target, and high-frequency current is applied. It is being done to have the role of absorbing water. In contrast, in the present invention, in order to achieve the above object, in a high-speed sputtering device in which plasma is concentrated near the target by the action of a magnetic field, an effective part of the target measured through the plasma space and a grounded shielding jig or By keeping a sufficiently large distance from an effective grounding metal part and by electrically coupling the substrate holder to the ground, the high-frequency current flowing through the plasma should flow preferentially to the substrate holder rather than to the ground. This made it possible to increase the incidence of Ar ions onto the substrate and improve coverage.

The present invention will be explained in detail below with reference to Examples.

Figure 2 shows the electrode structure in the experimental sputtering chamber. As a target 4, a circular quartz (SlO2, etc.) plate with a thickness of 3 mm is placed on a target electrode 5 with a diameter of 10 (177!), and a 13.56 MHz signal is applied to the target electrode 5 from an external high frequency power source through a metal jig 6. A high-frequency voltage of 100% is applied.A shielding jig 7 for preventing sputtering for the target electrode 5 is placed near the target, and this shielding jig 7 is grounded through the lower wall surface 8 of the sputtering chamber. Immediately on the back side, permanent magnets 9 and 10 are installed with opposite polarities in order to concentrate the plasma near the target.On the other hand, a substrate holder 11 is placed at a distance D facing the target. There is a silicon layer containing aluminum wiring on its surface.
A wafer 12 is placed there. The substrate holder 11 has an electrode 13 taken out to the outside so that the electrode 13 can be grounded directly or through a suitable passive circuit. A shielding jig 14 is also installed around the basic holder, and this is grounded through the soil wall surface 15 of the sputtering room. Argon (Ar) is introduced while the inside of this device is evacuated, the pressure inside the device is maintained at approximately 10-3 to 10-2T0rr, and a high frequency voltage is applied. Discharge plasma is generated throughout the device, but the target The brightness is strong near the center of the magnet, especially near the middle of the magnet.

Now, the high-frequency current applied from the target electrode through the target, which is a capacitor, passes through the plasma, reaches the grounded shielding jig, wall surface, and substrate holder, and flows into the ground. The grounded metal closest to the active portion of the target is the target shield, and this distance is indicated by L in FIG. 16 shows a region with high plasma density, which can be estimated from inspection and how the target quartz glass decreases.It is strongest in the middle of the permanent magnet, and high-density plasma exists on the entire surface facing the target electrode. .

In Figure 2, D≠L-:4C! ! L, and ground the board holder directly or through a 0.1 μF capacitor.
Power density 3.5W/Cd,. Ar pressure 1.2 or 5X
10-3T0rr (Schulz gauge indication), SiO
Two films were deposited to a thickness of about 3μ in 70 minutes.

Note that in this case the target itself acts as an insulating shielding jig. In a Si gate MOS device on a silicon substrate, the aluminum wiring has a thickness of 1
．． It was set to 2μ. This sample was immersed in a 1:6 solution of hydrofluoric acid (HF'):ammonium fluoride (NH4F) at 25°C for a certain period of time, and then immersed in an aluminum corrosive solution. It was found that no aluminum corrosion occurred when the immersion time was up to 3 minutes or 1 minute depending on the Ar pressure. Furthermore, an appropriate coil 17 is connected between the board holder and the ground, and an Ar voltage of 1.2
0rr or 5X10-3T0rr ('When a slightly thin 2μ SiO2 film was deposited, both were mixed with the above A in a 1:6 solution.
It was found that the stepped portion of the aluminum was not exposed even after soaking for 3 minutes or 1 minute under r pressure. By the way, the etching rate of the SiO2 film on the flat part with the 1:6 solution is about 0.15μ/Wt.
It was hot. The number of minutes a film should last with a 1:6 solution is based on the experience gained through the hole-drilling process after depositing the insulating film, subsequent inspections, and reliability tests.
It can be considered a pass of 6.

Further, when it is longer than 2 minutes, it shows a fairly good condition. L was varied by preparing quartz plates with different diameters, and a coverage evaluation test was conducted on the resulting film.

When a quartz plate with a diameter approximately equal to the diameter of the target electrode is used, L is the shortest at about 61 Lm. D=4CT! L
、． Ar pressure 1.2X10-3T0rr1 Power density 3.5
W/Cr! FIG. 3 shows data regarding the time to withstand 1:6 liquid when the No. 11 substrate holder is directly grounded. L is about 2C
It can be seen that coverage deteriorates rapidly below Tn. This distance appears to be related to the thickness of the plasma sheath. Note that the value of D is usually selected to be about 3 to 6 cm from the viewpoint of deposition rate and uniformity of film thickness, but no difference depending on the value of D was observed within this range. shows a typical shape of a structure near a practical target.

This type is commonly used in high-speed sputtering equipment for depositing insulating films currently on the market. That is, a practical sputtering apparatus in terms of ease of holding the substrate is the so-called down sputtering method in which the target is placed above the substrate holder, but in this case holding the target becomes a problem. The same applies to the case of a cylindrical shape that sputters laterally.
In the case of high-speed sputtering equipment, the number of targets decreases rapidly and must be replaced frequently, so replacement is inconvenient using the conventional method of attaching targets to the metal backing with adhesive. The most common method is to screw the target material to the high-voltage electrode with a metal ring, since it is necessary to have good contact with the electrode and also to save on relatively expensive target material. That is, in FIG. 4, the target 4 is the target holding jig 19.
It is fixed to the target electrode 5 using bolts 20. The target shielding jig 21 is fixedly grounded to a wall surface 23 using bolts 22 to prevent the target holding jig 19 from sputtering. In this case, L is L=L1ki61
1, which is extremely small. As expected, the obtained SiO
The coverage with the two films is 10% with a 1:6 solution depending on the deposition conditions.
It took about 30 seconds to 30 seconds, which was completely unsatisfactory. As one of the measures to increase L, as shown in FIG. The electrical connection of the fixture 21 was weakened, and a bolt was passed through a washer 25 with a thickness of 2 mm between the shielding jig 21 and the wall surface 23.

The direct current resistance between the shielding jig 21 and the ground through the three grounded bolts 22 was about 1 MΩ due to leakage resistance due to incomplete application of the sealant. This is sufficiently large compared to the high-frequency impedance of the entire sputtering device, which is said to be about 1KΩ, and except for a small amount of capacitive coupling, the shielding jig is essentially in an electrically floating state with respect to grounding. It can be considered that there is. As a result, the effective L can be considered to be equal to the length L2 beyond the shielding jig. Please understand that L2 is not drawn at the shortest distance in the figure for ease of viewing. Since the grounded bolt head is small in area and located quite far from the target, there is no problem. Needless to say, this enabled the deposition of an insulating film with good coverage. In this way, it is also useful to use a conductor that is not electrically connected effectively to the ground as at least part of the target shielding jig. In the above embodiment, the shielding jig was made of metal, but the main part of the jig could also be made of an insulator.

In FIG. 6, the shielding jig consists of a doughnut-shaped quartz part 26 and a metal part 27 that holds it. In this case as well, by controlling the length of L, a film with good coverage can be deposited. In this case, the advantage is that the degree of capacitive coupling between the plasma and ground is lower than in the case of a metal jig. Furthermore, as shown in FIG. 7, it is even better to use this method in combination with the above-described method of weakening the electrical connection between the metal portion 27 and the ground wall surface 23.

A feature of the present invention is that it can be applied to a ready-made high-speed sputtering device by making simple modifications to the structure near the target.

Another major feature of the present invention is that there are very few restrictions on the focusing magnetic field and the method of electrical connection between the substrate holder and ground.

With the countermeasures known for conventional equipment, 5X is the most advantageous in terms of preventing impurity contamination, stability of deposition rate, and uniformity of film thickness.
At an Ar pressure around 10-3T0rr, in order to obtain good coverage, a concentrating magnetic field is applied, and an inductance (coil) is inserted between the substrate holder and the ground.
It was necessary to arrange for some of the RF current to flow into the substrate holder by creating a resonant circuit for the capacitance between the plasma and the substrate holder. Aside from the fact that this measure alone is insufficient in the case of high-speed sputtering equipment, commercially available high-speed sputtering equipment does not have a focusing magnetic field,
It is true that in some products the substrate holder is electrically floated, but in some other products the substrate holder is grounded in advance due to reasons such as a feeding mechanism for mass production or a rotation mechanism to obtain uniformity of the film. has been done. In this case, modification is quite difficult. According to the present invention, at normal Ar pressure, not only when an inductance is inserted between the substrate holder and the ground, but also when the ground is directly grounded (DC grounding) or grounded through a capacitor (AC grounding). An insulating film with sufficient coverage can be obtained. It must be said that the contribution of the present invention, which allows modification of film quality by simply modifying the target or target shielding jig, is extremely large. In addition, among the conventional measures, the method of lowering the Ar pressure to about 1 to 2 x 10-3 T0rr and further applying a magnetic field near the substrate holder is a method that creates a specific magnetic field near the target in high-speed sputtering equipment. Therefore, although it is desirable to avoid introducing a second magnetic field because the magnetic fields will interfere with each other, lowering the Ar pressure will greatly increase the influence of residual gas (oxygen, moisture, etc.). , instability of the operating point, variation in deposition rate, etc. will inevitably occur.

When the present invention is applied to a high-speed sputtering device, it is very useful because a film with good coverage to some extent can be obtained without a focusing magnetic field even at a commonly used pressure of about 5.times.10@-3 T0rr. One of the reasons why the present invention has less restrictions on the focusing magnetic field, substrate grounding method, and Ar pressure is that the power density per unit area of the target is several times higher in high-speed sputtering equipment than in conventional sputtering equipment. I think it depends on that.

The deposition rate is improved by increasing the power density, but a higher power density means that the current density between the plasma and the substrate holder can be relatively higher. It is thought that the degree of coupling between the plasma and the substrate holder can be made relatively large as long as measures are taken to shield the target. In this embodiment, a typical case of sputtering technology that is actually used has been described, but it goes without saying that the gist of the present invention can be applied to several cases other than those described in detail here.

For example, in terms of equipment, cylindrical sputtering equipment, continuous sputtering equipment, etc., sputtering materials can be made of various insulating materials such as SiO2, various glasses and alumina, and for example, silicon targets can be used to insulate in nitrogen gas. This method can be applied to the case of depositing a silicon nitride film as a body. The deposition conditions, such as the size and shape of the target electrode, or the power density, can also be used within a wider range than those used in the examples. However, it is necessary to avoid making the substrate holder floating, using a thick insulator, such as a quartz plate of Im or more, as the substrate holder, and setting the Ar pressure to more than 1x10-3T0rr, as these will significantly impair the effects of the present invention. be. Although the present invention increases the rate at which high-frequency current flows into the substrate, no change in deposition rate, increase in substrate temperature, or increase in damage to the substrate due to this was observed.

[Brief explanation of the drawing]

Figures 1A and b are cross-sectional views of an insulating film coated on a base substrate with steps, Figure 2 is a cross-sectional view of a high-speed high-frequency sputtering device showing one embodiment of the present invention, and Figure 3 is a cross-sectional view of step coverage. Diagrams showing test results, Figures 4, 5, 6 and 7
The figure shows another embodiment of the invention.

Claims (1)

[Claims] 1. In a high-frequency sputtering device having means for forming a magnetic field near the target and concentrating charged particles in the discharge atmosphere near the target, the distance from the effective part of the target to the ground metal measured through the discharge atmosphere is 2 cm or more, A high frequency sputtering apparatus characterized in that a substrate holder is electrically coupled to ground.