JP4610595B2 - Method of forming compound barrier film in silicon semiconductor - Google Patents

Description

  The present invention relates to a method for forming a compound barrier film applied to a metal wiring process of a silicon semiconductor device.

  Conventionally, in a metal wiring process of a silicon semiconductor device, a compound barrier film such as TiN is formed on the surface of a silicon semiconductor substrate as a base for preventing diffusion before forming a main wiring metal. As a method of forming this compound barrier film, a formation method by a sputtering method using a planar magnetron cathode and a formation method by a CVD method are known. In the sputtering method, a compound barrier film is formed directly on the base by reactive sputtering, or a metal layer is first deposited on the base by simple sputtering in a sputtering chamber, and then a reactive gas atmosphere such as nitrogen gas in the reaction chamber. A method of forming a compound barrier film by reacting the metal layer with the atmospheric gas only by heating, or forming a metal layer first by simple sputtering in the sputtering chamber on the base, and then exciting with plasma in the reaction chamber A method of forming a compound barrier film by reacting the metal layer with the atmospheric gas in a reactive gas atmosphere is used. In the case of the CVD method, the compound barrier film is formed directly on the base.

In addition, as a sputter cathode, an inductively coupled RF plasma assisted magnetron cathode in which a magnet is provided behind the target and an RF coil is provided in front of the target has been proposed by the applicant (Patent Document 1). This cathode has the advantage that it can sustain the generation of plasma in a high vacuum and has less generation of impurities and secondary products.
JP-A-6-41739

In the above reactive sputtering method, a compound barrier film can be formed. However, if a stepped portion such as a contact hole or a via hole is formed on the surface of the substrate, it is often as shown in FIG. 1 near the entrance of the hole. A so-called “step break” occurs in which the TiN compound barrier film a does not cleanly cover the base layer b of the insulator (SiO ₂ ), and the barrier property is broken from there. This is because the compound barrier film such as silica or its compound and TiN used for the base has a large interfacial tension and so-called “wetting”, so that the compound barrier film is cut at a step portion pulled from two different directions. Conceivable.

  On the other hand, in the method of thermally reacting the metal layer, the metal layer deposited on the base by sputtering is “wet” with the base silica and its compound, so the base is cleanly covered, and then the metal layer is thermally reacted. Since it is compounded, the formed compound barrier film covers the base cleanly and no step breakage occurs. However, this method requires two processes, ie, sputtering and thermal reaction, and separate apparatuses for performing the process for forming the barrier film, which disadvantageously increases the production cost.

  Further, in the method in which the metal layer is subjected to plasma reaction, a compound barrier film having no step difference similar to the thermal reaction method of the metal layer can be formed. However, this method has the following two problems. One of the problems is that two processes of sputtering and plasma reaction and separate apparatuses for performing the process are required, and the production cost is high. The other is the thickness of the compound barrier film that can be formed by the plasma reaction. This is a problem that the barrier property is often insufficient as shown in FIG. That is, the surface layer portion of the metal layer only becomes a compound barrier film, and the entire metal layer does not become a compound barrier film. The reason why the thickness of the barrier film is limited is that, in the plasma reaction, the plasma-excited atmospheric gas component enters the layer by diffusion from the surface of the metal layer, and the reaction proceeds. This is considered to be because the reaction layer cannot be formed in the plasma reaction at a lower temperature because the diffusion into the metal layer becomes insufficient.

  Furthermore, although the above-mentioned CVD method can form a compound barrier film without step breakage, the CVD method has a completely different apparatus configuration from the sputtering method, and the consistency of the apparatus with the main metal wiring process performed by the sputtering method after the barrier film is formed. Since it cannot be made into a multi-chamber apparatus, a completely different independent apparatus is required, resulting in an increase in production cost.

  An object of the present invention is to provide a method for forming a compound barrier film without step breakage by a single apparatus in one process.

In the present invention, a magnetron cathode having a metal target connected to a DC power source, a magnet behind it and an RF coil for increasing the ionization rate in front of the target is provided in the vacuum chamber, and power is supplied to the target and the RF coil. Forming a metal film, and maintaining the power to the RF coil and reducing the input power to the target to zero, and introducing a reactive gas into the vacuum chamber to compound the metal film, The above object is achieved by forming a compound barrier film by alternately repeating the formation of a metal film and the compounding of the metal film on the surface of a silicon semiconductor substrate provided facing the target. To achieve. It is convenient to manufacture the RF coil from the same material as the metal target, and it is preferable to connect the metal target to a DC power source through an abnormal discharge prevention circuit.

  According to the present invention, a magnetron cathode equipped with an RF coil for increasing the ionization rate is provided, and the input power to the target and the RF coil and the flow rates of the inert gas and the reactive gas for sputtering introduced into the vacuum chamber are controlled. In addition, since the formation of the metal film on the substrate and the compounding of the metal film are alternately repeated, a compound barrier film having no step difference can be formed in one process with a single apparatus, and the film formation cost can be reduced. Has the effect of becoming inexpensive.

The embodiment of the present invention will be described with reference to the drawings. FIG. 3 shows a sputtering apparatus used for carrying out the present invention. Reference numeral 1 in FIG. 3 denotes an exhaust port 2 connected to a vacuum pump and sputtering gas such as argon gas. 1 shows a vacuum chamber provided with an inlet 3 and a reactive gas inlet 4 for introducing a reactive gas such as N ₂ . In the vacuum chamber 1, a metal target 6 made of Ti or the like connected to a DC power source 5 via an abnormal discharge prevention circuit 10, a magnet 7 behind it, and an RF coil 8 that increases the ionization rate in front of the target 6. A magnetron cathode 9 is provided. The cathode 9 is known as the above-described inductively coupled RF plasma assisted magnetron cathode, and the RF coil 8 is provided so as to surround the front periphery of the metal target 6, and is supplied with power from the RF power source 12 via the matching box 11. Is supplied. Reference numeral 13 denotes a substrate for a silicon semiconductor device having a diameter of 2 inches, for example, which is provided to face the target 6 so as to form a compound barrier film for preventing diffusion, and has a step such as a contact hole, a via hole or a groove on its surface. The portion is formed in advance, and the metal wiring film is formed after the formation of the compound barrier film. The RF coil 8 is made of, for example, Ti made of the same material as that of the metal target 6. If necessary, cooling water is circulated therein. Reference numeral 14 denotes a heater for heating the substrate.

  In order to form a compound barrier film on the substrate 13 by reactive sputtering using the apparatus shown in FIG. 3, first, the vacuum chamber 1 is evacuated and an appropriate amount of sputtering argon gas is introduced from the inlet 3 near the cathode 9. After the pressure is adjusted, the substrate 13 is heated by the heater 14 to bring the substrate temperature to the required film formation temperature. DC power is supplied to the metal target 6 and high-frequency power is supplied to the RF coil 8. As a result, plasma is generated in front of the target 6, the target 6 is sputtered by the ions, and the sputtered metal particles are deposited on the substrate 13. When the metal is deposited in a very thin film of, for example, several tens of millimeters, the reaction gas is introduced from the reaction gas introduction port 4 with the input power to the target 6 set to zero and only the high-frequency power applied to the RF coil 8. To do. As a result, the target 6 is hardly sputtered, and the introduced reactive gas is excited and ionized by the plasma of the RF coil 8, so that it reacts quickly with the deposited metal film and becomes a compound barrier film. Since the deposited metal film is extremely thin, it becomes a compound film that is almost completely combined up to the inside of the thin film.

  Thereafter, the sputtering process of the target 6 and the compounding process by introduction of the reaction gas are repeated to form an extremely thin compound barrier film of about 100 mm on the substrate 13. The compound barrier film thus obtained has an excellent barrier property while being extremely thin. Various metals that form compound barrier films can be used for the target 6. For example, if Ta or W is used, a barrier film of TaN or WN can be formed, and the target material and reactive gas are appropriately selected. By doing so, various compound barrier films can be formed.

The deposition rate of the metal on the substrate 13 mainly depends on the DC power supplied to the target 6, and the degree of ionization and excitation of the sputtered metal particles and reactive gas mainly depends on the high frequency power supplied to the RF coil 8. To do. The reason for the latter is considered to be due to a post ionization mechanism similar to ion plating in which the sputtered neutral metal particles are ionized when passing through the plasma zone formed by the RF coil 8. Since the degree of ionization and excitation mainly depends on the collision frequency between electrons and gas particles, generally, the higher the gas pressure, the greater. However, in the so-called long throw sputtering in which the distance between the substrate and the target is about 3 to 8 times the distance in the conventional planar magnetron sputtering apparatus, even if excited with plasma in the RF coil, the target is high when the gas pressure is high. As a result, the amount of ions reaching the substrate is reduced. Therefore, in such an arrangement, the amount of ions reaching the substrate becomes more conspicuous under a low pressure of 2 × 10 ⁻³ Torr or less. When depositing the metal film, not only direct current power to the target 6 but also high frequency power is simultaneously applied to the RF coil 8 to increase the ionization efficiency, and the substrate 13 is densely coated with good coverage. An extremely thin metal film having a good crystallinity of about several tens of millimeters can be deposited. When the reactive gas is introduced in a state where the direct current power to the target 6 is zero and only the high frequency power to the RF coil 8 is introduced, there is almost no metal to be sputtered, and it is excited and ionized by the plasma from the RF coil 8. It reacts rapidly with the deposited ultra-thin metal film, making it almost completely a compound barrier film.

  In the compounding process using the RF coil 8, since the metal film is not coated on the surface of the RF coil 8 by the sputtered particles from the target 6, the exposed surface of the RF coil 8 is subjected to inductively coupled plasma discharge. Contamination is considered that the sputtered particles of the coil material adhere to the surface of the substrate 13. Such contamination can be prevented by preparing the RF coil 8 with the same material as the target 6.

  In addition, when the reactive gas is excited and ionized by plasma, the surface of the target 6 also reacts to form a compound layer there, and the DC discharge in the next sputtering process may become unstable. This is because when a compound or insulator with low electrical conductivity is formed on the target surface, a positive charge is charged on the surface in DC discharge, and the potential difference between the cathode (target) and the anode (substrate) disappears. As a result, the discharge becomes unstable or the discharge stops. In order to eliminate this state, the positive charges accumulated on the surface of the target may be neutralized with electrons from the plasma. Therefore, an abnormal discharge prevention circuit 10 is interposed in the DC power source 5 of the target 6 as shown in FIG. Thus, a positive potential is generated at a constant rate, and when this positive potential is reached, electrons from the plasma are drawn into the target surface to neutralize the positive charges accumulated on the target surface.

An apparatus with an inductively coupled RF plasma assisted magnetron cathode shown in FIG. 3 was used to form a very thin TiN compound barrier film of about 100 シ リ コ ン on a substrate 13 of a silicon semiconductor device. The RF coil 8 is made of Ti which is water-cooled, and the DC power source 5 is connected to the Ti target 6 via the abnormal discharge prevention circuit 10. Further, argon gas as a sputtering gas can be introduced from the inlet 3, and N ₂ gas as a reactive gas can be introduced from the reactive gas inlet 4. The diameter of the cathode 6 is 2 inches. The distance between the substrate and the target was 200 mm.

Prior to the formation of the compound barrier film, the argon sputtering gas pressure in the vacuum chamber 1 is set to 6 × 10 ⁻⁴ Torr, the target input power is kept constant at 50 W DC, and the input power to the RF coil 8 is changed to move onto the substrate 13. The changes in the Ti film deposition rate and the ionic current flowing into the substrate were measured. Note that a direct current of −50 V was applied to the substrate 13 so that ion current (Ti ⁺ , Ar ⁺ ) flowing into the substrate could be measured. The result is as shown in FIG. 5, and it can be seen that the Ti film deposition rate does not depend much on the input power to the RF coil 8. FIG. 6 shows changes in the Ti film deposition rate when the target DC power is changed using the input power to the RF coil 8 as a parameter. Thus, under this condition, it can be seen that the Ti film deposition rate is proportional to the electric power applied to the target 6 and is hardly affected by the electric power applied to the RF coil 8, which is consistent with the result of FIG. On the other hand, the ion current flowing into the substrate 13 increases rapidly with the input power to the RF coil 8, indicating that this inductively coupled RF plasma assisted magnetron sputtering method is extremely effective in promoting ionization of sputtered particles. . The ions flowing into the substrate are Ti ions and Ar ions. FIG. 7 shows the result of examining which ion is how much. In this measurement, a quadrupole mass spectrometer with an energy analyzer is attached to the position of the substrate 13, and when the Ti target is sputtered, the type of ions flowing into the substrate and the energy distribution of the amount are measured. Here, an example is shown in which the input power to the RF coil 8 is constant at 40 W and the target input DC power is changed. From FIG. 7, it can be seen that when the DC power is suppressed and the input power to the RF coil is relatively increased (the DC power is decreased), the gas is mainly ionized and the ion energy is shifted to the higher energy side. . Similarly, when a reactive gas such as nitrogen is added as an atmospheric gas, it is considered that the excitation of the reactive gas preferentially occurs, so this is caused by reacting the deposited metal film with the reactive gas to form the compound film. It is a very favorable condition to create. On the other hand, when the DC power is relatively increased, ionization of the sputtered metal particles proceeds, and it can be seen that a dense and high-quality metal film can be deposited under this condition (no reactive gas is added).

Based on this result, the sputtering process for depositing a Ti metal film and the compounding process for compounding the film by plasma nitriding are repeated according to the procedure shown in FIG. A TiN compound barrier film having excellent barrier properties was formed. The sputtering argon gas pressure was 8 × 10 ⁻⁴ Torr, and the temperature of the Si substrate was constant at 300 ° C.

Specifically, the direct current power to the target 6 is 80 W, the high frequency power to the RF coil 8 is 30 W, Ar gas is 20 sccm, N ₂ gas is 0 sccm, and sputtering is performed for 30 seconds under these conditions. A Ti metal film was deposited on the substrate. Subsequently, the DC power to the target is maintained at 0 V, the high-frequency power to the RF coil 8 is maintained at 30 W as it is, the flow rate of the sputter argon gas is reduced to 5 sccm, N ₂ gas is introduced into the 20 sccm vacuum chamber, and the RF coil 8 The Ti metal film deposited by generating only inductively coupled plasma for 60 seconds was plasma nitrided to obtain a TiN film. Further, a next metal film having a thickness of about 20 mm was deposited on the TiN film under the sputtering conditions of the Ti metal film, and the next metal film was nitrided under the same conditions as the compounding conditions. In this manner, the sputtering process and the compounding process were repeated four times to form a TiN film of about 100 mm on the substrate.

  FIG. 9 shows an example of a result obtained by measuring the distribution in the depth direction of the constituent elements of the TiN film formed on the Si wafer substrate under the same conditions by Auger electron spectroscopy (AES). It can be seen that the entire deposited film is TiN, which is significantly different from the conventional film (FIG. 2) in which only the surface is nitrided.

  Although an example of TiN is shown here, the present invention can be applied to the formation of various compound barrier films such as TaN and WN. The present invention can be applied in principle as long as it has both a mechanism for sputtering metal and a mechanism for plasma excitation of atmospheric gas in the same chamber, and they can be controlled almost independently. It is. Accordingly, it goes without saying that the present invention can be applied to a sputtering apparatus, an ECR sputtering apparatus, or the like in which the RF coil is installed between the target and the substrate, for example, other than the apparatus shown in FIG. Although the silicon substrate metal wiring process has been described here, the present invention can be applied to various electronic device device thin film manufacturing processes such as a flat display and a thin film magnetic head. Further, here, the compound barrier film was alternately subjected to the metal deposition sputtering process and the plasma reaction compounding process. Instead, the base layer and the first layer or the next second layer having poor “wetting” were removed. After that, the compound layer may be formed all at once by reactive sputtering.

  INDUSTRIAL APPLICABILITY The present invention can be used industrially in the technical field of forming a compound barrier film applied to a metal wiring process of a silicon semiconductor device.

Sectional drawing which shows the film-forming state of the conventional compound barrier film Distribution of constituent elements in the depth direction of conventional compound barrier films Cutaway side view of the apparatus used to carry out the method of the present invention Characteristic diagram of voltage applied to cathode in FIG. Relationship diagram between RF coil power and film deposition rate Changes in film deposition rate when changing target power with RF coil power as parameter Correlation diagram of target power, RF coil power, and ion energy Diagram of the procedure for carrying out the method of the invention Distribution diagram of constituent elements in the depth direction of the film obtained by the method of the present invention

Explanation of symbols

1 Vacuum chamber 2 Exhaust port 3 Sputter gas inlet 4 Reactive gas inlet 5 DC power source 6 Metal target,
7 magnets,
8 RF coil 9 Magnetron cathode 10 Abnormal discharge prevention circuit 11 Matching box 12 High frequency power supply 13 Substrate 14 Lamp heater

Claims (3)

In the vacuum chamber, a metal target connected to a DC power source, a magnet behind it and a magnetron cathode equipped with an RF coil that increases the ionization rate in front of the target are provided , and power is supplied to the target and the RF coil to form a metal film. Control is performed to repeat the film forming process and the process of maintaining the power to the RF coil and reducing the input power to the target to zero and introducing the reactive gas into the vacuum chamber to compound the metal film. And forming a compound barrier film by alternately repeating the formation of a metal film and the compounding of the metal film on the surface of a silicon semiconductor substrate provided opposite to the target. Barrier film formation method.   2. The method of forming a compound barrier film in a silicon semiconductor according to claim 1, wherein the RF coil is made of the same material as the metal target.   2. The method of forming a compound barrier film in a silicon semiconductor according to claim 1, wherein the metal target is connected to a DC power source through an abnormal discharge prevention circuit.

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