JP4315884B2 - Metal thin film for semiconductor wiring, semiconductor wiring formed using the metal thin film, and method for manufacturing semiconductor wiring - Google Patents

Description

  The present invention relates to a semiconductor device, and more specifically, a metal thin film used when forming a wiring provided in a semiconductor, a semiconductor wiring formed using the metal thin film, and a semiconductor wiring are manufactured. It is about how to do.

  In recent years, semiconductors have been increasingly improved in performance, and higher speed and higher integration are required. In order to realize a high speed semiconductor, it is effective to reduce the electric resistance of the wiring film that causes a signal transmission delay as much as possible. Therefore, the material of the wiring film has been changed from aluminum or an aluminum alloy (hereinafter sometimes referred to as “Al-based metal”) to copper or a copper alloy (hereinafter sometimes referred to as “Cu-based metal”). In order to enable high-speed operation, it is desirable that the circuit is highly integrated, and it is necessary to make the wiring width as narrow as possible. For this reason, semiconductors with a wiring width of around 0.25 μm have been the mainstream in the past, but in recent years, the wiring width tends to become increasingly narrower.

  On the other hand, in order to realize high integration of semiconductors, in recent years, it has been studied to make a wiring into a multilayer structure. There is a damascene method as a method of forming a multilayer wiring, and this method is used to connect a groove or wiring for embedding wiring in an insulating film (eg, Si oxide film) formed on a semiconductor substrate. After forming a wiring pattern such as a hole (trench / via) (hereinafter sometimes referred to as a “concave portion” collectively), a barrier film is formed on the surface by sputtering, and then Cu is formed by electroplating. After burying the system metal in the recess, wiring is formed by subjecting the excess Cu system metal to chemical mechanical polishing (CMP). In this method, a new insulating film is formed on the polished surface and the above process is repeated to form a multilayer wiring. If the width of the recess (that is, the wiring width) is large, Cu-based metal can be easily embedded in the recess by electroplating.

  However, as described above, the wiring width of semiconductors in recent years tends to be narrower. However, when the wiring width is narrowed, the width of the recess is inevitably narrowed. Therefore, there is a problem that Cu-based metal does not enter the recess and semiconductor wiring cannot be formed.

As a method of embedding a Cu-based metal in the recess, the technique of Patent Document 1 has been proposed previously. This technology is a pressure-injection method for Cu-based wiring films, and the insulating film surface of a substrate in which holes or grooves are formed is covered with a Cu-based wiring film material by physical vapor deposition (specifically, sputtering). After that, a high gas pressure is applied at a temperature lower than the melting point of the wiring film material to plastically flow or diffuse the wiring film material, thereby filling the hole or groove. In this document, it is described that the film formation by the physical vapor deposition method is performed at a high temperature in which the temperature of the target member is about 200 to 400 ° C., and then the indentation process is performed with the high-pressure gas. However, as a result of studies by the present inventors, it has been found that when the width of the hole or groove becomes narrower, the Cu-based wiring film material may not be embedded in the hole or groove, leaving room for improvement. .
JP-A-11-260820 (see [Claims], [0011], [0013])

  In the technique of Patent Document 1, the reason why the Cu-based wiring film material may not be embedded in the recesses provided on the surface of the semiconductor substrate has been studied. The Cu-based wiring film material formed by sputtering is, for example, It has been found that the cause is that the fluidity at a high temperature (hereinafter sometimes referred to as reflowability) is worse than the Cu-based wiring film material formed by plating.

  Therefore, the present invention has been made in view of such a situation, and an object of the present invention is a metal thin film used in manufacturing semiconductor wiring, and even if the semiconductor wiring width is designed to be narrow, the wiring width is reduced. An object of the present invention is to provide a metal thin film for semiconductor wiring that can be reliably embedded in a corresponding recess. Another object of the present invention is to provide a semiconductor wiring formed by embedding the metal thin film for semiconductor wiring in a recess provided in a semiconductor substrate. Still another object is to provide a method of manufacturing such semiconductor wiring.

  With regard to the metal thin film laminated by sputtering on the surface of the semiconductor substrate having the recesses, after intensive investigation from the viewpoint of enhancing the reflow property at high temperature, the Cu-based metal thin film laminated on the surface of the semiconductor substrate is Cu-based. If it is divided by a thin metal layer other than the above, and a Cu-based metal thin layer and a non-Cu-based metal thin layer are laminated in the thickness direction of the metal thin film, the crystal grain size of Cu can be remarkably reduced, and the semiconductor If the crystal grain size of Cu is made small at the stage of film formation on the surface of the substrate, the reflowability is improved by sufficiently growing the crystal grains of Cu when this metal thin film is processed at high temperature and high pressure. The headline and the present invention were completed.

  That is, the metal thin film for semiconductor wiring according to the present invention is a metal thin film laminated on the surface of a semiconductor substrate having a recess, and the metal thin film is a thin film composed of a Cu-based metal other than a Cu-based metal. It has a gist in that it is divided by one or more thin layers made of metal.

  The crystal structure of the non-Cu-based metal thin layer is (a) a face-centered cubic crystal having a lattice constant different by 5% or more from the lattice constant of the Cu-based metal thin film, or (b) other than the Cu-based crystal. When the crystal structure of the metal thin layer is a body-centered cubic crystal or a hexagonal close-packed crystal, defects are introduced into the metal thin film, so that the reflow property can be further enhanced.

  As the metal other than the Cu-based metal, for example, at least one metal selected from the group consisting of Au, Pd, W, Mo, Al, or Ag can be suitably used.

  The crystal grain of the Cu-based metal after film formation is preferably as small as possible, and the thickness of the Cu-based metal thin layer formed by being divided by a thin metal layer other than the Cu-based material is a, When the crystal grain size of the Cu-based metal is b, a metal thin film that satisfies the relationship of b ≦ 2a is recommended.

  The thickness of the Cu-based metal thin layer formed by being divided by the thin metal layer other than the Cu-based material is 100 to 2000 mm per layer, and the thickness of the thin metal layer other than the Cu-based material is 1 It is preferable to be 10 to 100 mm per layer.

  The Cu-based metal thin layer preferably includes 2 to 10 layers.

  The semiconductor wiring according to the present invention is formed by laminating the metal thin film on the surface of a semiconductor substrate having a recess and then embedding the metal thin film in the recess by high-temperature and high-pressure treatment.

  The method for producing a semiconductor wiring according to the present invention is that a thin film composed of a Cu-based metal is formed on the surface of a semiconductor substrate having a recess by a sputtering method, and then a thin layer composed of a metal other than a Cu-based metal is sputtered. And forming a thin layer composed of a Cu-based metal by a sputtering method at least once to form a metal thin film for semiconductor wiring, and then subjecting the metal thin film to the inside of the recess by high-temperature and high-pressure treatment. The main point is that the wiring is formed by embedding in the wiring.

  According to the present invention, since the Cu crystal grains in the Cu-based metal thin layer are refined, if the metal thin film including such a Cu-based metal thin layer is processed at high temperature and high pressure, the refined Cu crystal grains are sufficient. Therefore, reflowability is improved. As a result, it is possible to provide a metal thin film for semiconductor wiring that can be reliably embedded in the recess corresponding to the wiring width even if the wiring width of the semiconductor is designed to be narrow. Further, according to the present invention, even if the wiring width is designed to be narrow, the semiconductor thin film for semiconductor wiring is surely embedded in the recess provided in the semiconductor substrate, so that it is possible to provide a semiconductor wiring having good characteristics. Furthermore, according to the present invention, it is possible to provide a method capable of reliably manufacturing such semiconductor wiring.

  In order to improve the reflow property when heated to a high temperature for a metal thin film laminated on the surface of a semiconductor substrate having a recess by sputtering, the crystal grain size of Cu in the metal thin film after film formation should be made as fine as possible. is important.

  That is, the reason why the reflowability at high temperature when the metal thin film formed by sputtering is subjected to high temperature and high pressure treatment is that the polycrystalline structure of the metal thin film is stabilized after the film formation. The present inventors considered. That is, the average crystal grain size of Cu in the Cu-based metal thin film formed by sputtering grows to the same extent as the film thickness. For example, if the film thickness of the Cu-based metal thin film formed by sputtering is 1 μm, the average crystal grain size of Cu in the Cu-based metal thin film grows to about 1 μm. Therefore, in general, the thickness of the Cu-based metal thin film laminated on the semiconductor surface varies depending on the width (opening width) and depth (that is, the volume of the recess) of the recess, but is at least about 1000 mm, and at most about 20000 mm. It is. Therefore, when a Cu-based metal thin film is provided as a single layer by a sputtering method, Cu crystal grains are coarsened to a film thickness of about 1000 to 20000 mm.

  It is considered that the cause of such coarsening is that Cu is a very special metal that causes aging at room temperature (self-phenyl). Therefore, in the state immediately after sputtering (As-deposited state), even if the Cu crystal in the Cu-based metal thin film is a microcrystal, if it is left at room temperature, it will age at room temperature to cause primary recrystallization and the crystal grains will become coarse. . At this time, with the coarsening of the Cu crystal, the crystal grain boundary is formed so as to penetrate in the thickness direction of the metal thin film. The present inventors thought that even when such a metal thin film was subjected to high-temperature and high-pressure treatment, crystal grain boundaries in the metal thin film existed stably, so that the Cu thin film did not move / deform and the reflow property deteriorated. .

  Therefore, in order to improve the reflowability of the metal thin film at high temperatures, the inventors considered that it would be necessary to destabilize the polycrystalline structure of the metal thin film formed by sputtering. As a result, in order to destabilize the polycrystalline structure of the metal thin film, it has been conceived that the Cu crystal grains in the metal thin film need only be refined. In order to refine Cu crystal grains, one or more thin layers in which a thin film composed of a Cu-based metal (hereinafter sometimes abbreviated as a Cu-based metal thin film) is composed of a metal other than a Cu-based metal. It has become clear that it may be divided at

  That is, the metal thin film laminated on the surface of the semiconductor substrate is divided by one or more thin layers in which the Cu-based metal thin film is composed of a metal other than Cu-based, and other than the Cu-based metal thin layer and Cu-based A laminated structure in which thin metal layers are laminated. Metals other than Cu-based metals usually do not cause aging at room temperature, and thus maintain the As-deposited state. Therefore, if a thin metal film composed of a Cu-based metal thin layer and a non-Cu-based metal thin film is formed, Cu crystal grains in the Cu-based metal thin layer are aged and coarsened even if the metal thin film is left at room temperature. However, since the metal in the thin metal layer other than the Cu-based metal does not aging at room temperature, the As-deposited state is maintained. As a result, even if Cu crystal grains are about to grow, the thickness of the Cu-based metal thin layer sandwiched between metals other than the Cu-based metal is small, so the Cu crystal grains in the Cu-based metal thin layer are not coarsened. Remain fine.

  At this time, by dividing the Cu-based metal thin film with a thin metal layer other than Cu-based, the amount of Cu-based metal to be laminated on the surface of the semiconductor substrate is not changed (that is, the total thickness of the Cu-based metal layer is maintained). However, only the thickness of each Cu-based metal thin layer can be reduced. When a metal thin film having such a laminated structure is subjected to high-temperature and high-pressure treatment, the thin metal layer other than Cu is once dissolved in the Cu metal thin layer and disappears, and the metal other than Cu is solid in the Cu metal. It becomes a molten metal thin film. At this time, since the metal thin layer other than the Cu-based metal disappears, Cu crystal grains grow to the thickness of the entire metal thin film and are embedded in the recesses provided on the semiconductor surface. As a result, the reflow property of the metal thin film is increased. In addition, since metals other than Cu-based metals once dissolved form a phase diagram structure during cooling, such metals exist in the form of solid solution, precipitation, eutectic, etc. in the finally formed wiring. it is conceivable that.

  A recess provided on the surface of a semiconductor is a space for forming a semiconductor wiring, and is a general term for a wiring pattern such as a groove for embedding wiring and a hole (trench / via) for connecting wirings. is there. A semiconductor wiring is formed by embedding a metal thin film in the recess.

  The minimum width of the recess is about 0.2 μm or less. When the thickness exceeds 0.2 μm, an ordinary Cu-based metal can be easily embedded in the recess by, for example, electroplating without using the metal thin film for semiconductor wiring of the present invention. On the other hand, the width of the wiring to be formed in the present invention is narrow, and the width of the recess corresponding to the wiring is of a level that cannot be directly embedded with the Cu alloy by electroplating. If the metal thin film for semiconductor wiring of the present invention is used, wiring can be satisfactorily formed even if the minimum width of the recess is reduced to 0.1 μm or less, and further to 0.07 μm or less.

  The depth of the recess is about 0.3 μm or more. If the depth of the recess is shallow, Cu-based metal can be embedded in the recess by, for example, electroplating without using the semiconductor metal thin film of the present invention. On the other hand, if the metal thin film for semiconductor wiring of the present invention is used, the wiring can be reliably formed even if the depth of the recess is about 0.3 μm or more, and further 0.5 μm or more.

  Here, the minimum width of the concave portion refers to the distance of the narrowest portion of the opening of the groove when the object to be embedded with the metal thin film is a groove. On the other hand, when the object for embedding the metal thin film is a hole, it indicates the diameter of the opening of the hole. For example, when the hole is an ellipse, it indicates the short diameter. In the case where a plurality of grooves and holes having different widths are formed in the insulating film, the shortest of the groove widths and hole diameters (or short diameters) only needs to satisfy the above requirements.

  The Cu-based metal refers to a metal mainly composed of Cu, and pure Cu (purity: 99.99 to 99.9999%) or a Cu alloy can be used. The Cu alloy includes an alloy element such as Si or Ti of several mass% or less, and the crystal structure thereof is a face-centered cubic structure (fcc) in an As-positioned state. Preferably, pure Cu is used. A thin film made of a Cu-based metal means a thin film made of pure Cu or a Cu alloy.

  The thin layer composed of a Cu-based metal may be composed of metals having the same component composition, or may be composed of metals having different component compositions.

  The metal other than the Cu-based metal is a metal excluding the Cu-based metal, and the type thereof is not particularly limited as long as Cu crystal grain growth in the Cu-based metal can be suppressed during aging at room temperature. However, the metal must be once dissolved in the Cu-based metal by performing a high-temperature and high-pressure treatment described later. If a metal other than Cu-based metal remains without being dissolved after high-temperature and high-pressure treatment, the metal other than Cu-based metal will cover the recess provided in the semiconductor substrate, and Cu provided on the thin metal layer other than Cu-based metal. This is because the system metal thin layer is not embedded in the recess. Moreover, it is necessary to select a metal other than the Cu-based metal that does not increase the electrical resistance of the Cu-based metal. If the electrical resistance of the Cu-based metal is increased, the electrical resistance of the wiring is increased, and the characteristics as a semiconductor deteriorate.

  From such a viewpoint, the metal other than Cu is preferably at least one metal selected from the group consisting of Au, Pd, W, Mo, Al, or Ag. This metal may be a pure metal (purity: about 99.99%) or an alloy. Preferred is pure Ag or an Ag alloy. The metal other than Cu-based metal may contain a trace amount of Cu as long as it does not impair the effect of dividing the Cu-based metal thin film, but is preferably a metal that does not substantially contain Cu. . “Substantially” means that the Cu content is 0.1% by mass or less or is at an inevitable impurity level. A thin layer composed of a metal other than Cu-based means a thin layer made of pure metal or alloy other than Cu-based.

  The thin layer made of a metal other than the Cu-based metal may be one layer or two or more layers. That is, the Cu-based metal thin film may be divided into at least two layers, and of course, it may be divided into three or more layers. In the case where a plurality of thin layers made of a metal other than Cu are provided, the plurality of thin layers may be made of the same metal or different metals.

  By the way, in order to further improve the reflow characteristics of the metal thin film formed by laminating the Cu-based metal thin layer and the non-Cu-based metal thin layer on the surface of the semiconductor substrate, a defect is introduced into the metal thin film. It is effective to do. If there are many defects such as dislocations and atomic vacancies in the metal thin film, the defects are recovered when heated (for example, 300 to 500 ° C.), and at this time, atomic diffusion occurs to promote softening and deformation of Cu crystal grains. Is done. For example, a Cu-based metal thin film formed by electrolytic plating has a large number of vacancies, and the amount of atomic vacancies is such that thermal equilibrium is achieved near the melting point of Bulk-Cu. In contrast, a Cu-based metal thin film formed by a sputtering method is a thin film having a smaller amount of atomic vacancies than a Cu-based metal thin film formed by the electroplating method. Therefore, it is thought that reflowability will fall.

  Therefore, the present inventors examined a method for increasing the amount of defects in the thin film in order to improve the reflow property of the metal thin film formed by sputtering. As a result, the crystal structure of the thin metal layer other than the Cu-based material is (a It was found that it may be a face-centered cubic crystal having a lattice constant that differs by 5% or more from the lattice constant of the Cu-based metal thin film, or (b) a body-centered cubic crystal or a hexagonal close-packed crystal.

  That is, if there is a difference (difference) in the crystal structure between the Cu-based metal thin layer and the non-Cu-based metal thin layer, the crystal lattice constant at the interface between the Cu-based metal thin layer and the non-Cu-based metal thin layer. Inconsistent dislocations occur due to the difference between the two. By increasing defects due to this misfit dislocation, the plastic deformation of the crystal is promoted, the crystal grains are softened, and the reflow property of the metal thin film is improved.

  Since the crystal structure of the Cu-based metal thin layer is a face-centered cubic (fcc), the metal thin layer other than the Cu-based metal has a crystal structure other than the face-centered cubic crystal, that is, a body-centered cubic crystal or a hexagonal close-packed crystal. It is preferable that As the body-centered cubic crystal (bcc) metal, for example, W, Mo, Ta, Cr and the like, and as the dense hexagonal crystal (hcp) metal, for example, Ti, Zr, Co, and the like are preferably used. it can.

  However, the crystal structure of the thin metal layer other than Cu may be a face-centered cubic crystal. In this case, a face-centered cubic crystal having a lattice constant different by 5% or more from the lattice constant of the Cu-based metal thin film is recommended. Even if the crystal structure is a face-centered cubic crystal and the lattice constant differs by 5% or more, misalignment dislocations are often introduced at the interface between the thin film and the thin layer even when such face-centered cubic metal is laminated. As described above, since the epitaxial growth does not occur at the interfaces having different lattice constants by 5% or more, the Cu crystal grains are not coarsened and the reflow property of the metal thin film is improved.

  In general, the lattice constant means the length of the unit cell in the three dimensional directions and the mutual angle. In the present invention, the lattice constant means the value of a (lattice constant a), and the angle α is 90 °. is there. This is because the length that influences the characteristics of the face-centered cubic or body-centered cubic crystal lattice is the lattice constant a. Therefore, the crystal structure of the thin metal layer other than the Cu-based layer may be a face-centered cubic crystal having a lattice constant a different by 5% or more from the lattice constant a of the Cu-based metal thin film.

  Among metals other than Cu, examples of the face-centered cubic metal include Au, Ag, Al, and Pd.

  When the thickness of the Cu-based metal thin layer formed by being divided by a thin metal layer other than Cu-based is a and the maximum crystal grain size of the Cu-based metal in the Cu-based metal thin layer is b, b It is desirable to satisfy the relationship of ≦ 2a. Although the crystal grain of Cu system metal grows to the film thickness grade, it may become coarse in rare cases. When there are many coarse Cu crystal grains, the reflow property at the time of high-temperature and high-pressure processing deteriorates, and the metal thin film formed on the surface of the semiconductor substrate cannot be completely embedded in the recess. Reflowability can be further improved by preventing such coarsening. Preferably, the relationship of b ≦ a is satisfied. It is recommended that this relationship is satisfied in at least one of the Cu-based metal thin layers divided by the metal thin layer other than the Cu-based material, and preferably in all the Cu-based metal thin layers.

  In order for the maximum crystal grain size of the Cu-based metal to satisfy the above range, the thickness of the Cu-based metal thin layer should be as small as possible. Further, the inert gas pressure may be increased during sputtering or the substrate temperature may be lowered.

  The thickness of the Cu-based metal thin layer can be measured by observing with a high-resolution transmission electron microscope (for example, “H900 type” manufactured by Hitachi, Ltd.). The crystal grain size of Cu in the thin layer is 20000 to 30000 times and can be measured by taking a SIM image and analyzing the image. It is only necessary that the number of observation fields is three and the maximum crystal grain size b among the measurement results satisfies the above range.

  The thickness of the Cu-based metal thin layer is 100 to 2000 mm. As the thickness of the Cu-based metal thin layer is smaller, Cu crystal grains do not grow and are effective for miniaturization. However, as described above, the thickness of the metal thin film formed by being laminated on the semiconductor surface varies depending on the opening width and depth of the recess provided on the semiconductor surface, but at least about 1000 mm is necessary. Therefore, assuming that the thickness of the Cu-based metal thin layer is less than 100 mm per layer, for example, when stacking for 1000 mm, it is necessary to provide 10 or more Cu-based metal thin layers. Therefore, productivity is remarkably reduced. Preferably it is 500 mm or more. On the other hand, when the thickness of the Cu-based metal thin layer exceeds 2000 mm per layer, the crystal grains of Cu become coarse as the film thickness increases, so that the reflow property at the time of high-temperature and high-pressure treatment is deteriorated. Preferably it is 1000 mm or less.

  The Cu-based metal thin layer is 2 to 10 layers. In the metal thin film for semiconductor wiring of the present invention, since the thin film composed of Cu-based metal is divided by one or more thin layers composed of metal other than Cu-based, the Cu-based metal thin film is at least 2 Divided into layers. Here, when the film thickness of the metal thin film laminated on the surface of the semiconductor substrate is constant, the number of thin layers composed of a metal other than Cu is increased, and the number of Cu based metal thin layers is increased. The individual thickness of the Cu-based metal thin layer in the metal thin film is reduced. Therefore, Cu crystal grains in the Cu-based metal thin layer are further refined. Therefore, the more Cu-based metal thin layer is, the more preferable. Preferably, there are three or more layers. However, when the number of Cu-based metal thin layers increases, the Cu-based metal thin layer and the metal thin layer other than the Cu-based layer must be repeatedly laminated, which decreases productivity and increases production cost. Therefore, the upper limit of the Cu-based metal thin layer is 10 layers. Preferably it is 6 layers or less.

  The thickness of the metal thin film to be laminated on the surface of the semiconductor substrate is about 20000 mm at the maximum. However, if the average crystal grain size of Cu in the Cu-based metal thin layer is 2000 mm or less, the Cu crystal grains are refined. Therefore, the reflow property at the time of high temperature and high pressure treatment is improved. Also from this viewpoint, the upper limit of the number of Cu-based metal thin layers is 10 layers.

  The thickness of the thin metal layer other than Cu is 10 to 100 mm. The thickness of the thin metal layer other than the Cu-based material is not particularly limited as long as the coarsening of the Cu-based metal crystal grains can be suppressed, but if the thickness of the thin metal layer other than the Cu-based material is too small, Metal crystal grains may grow through the thin layer. Therefore, the thickness of the metal thin film other than Cu-based material needs to be at least 10 mm. Preferably it is 20 mm or more. In order to reliably suppress the growth of Cu-based metal crystal grains, it is preferable to increase the thickness of the thin metal layer other than the Cu-based metal as much as possible. However, if the thickness of the metal thin layer other than Cu-based is too large, the thickness of the metal thin film to be laminated on the surface of the semiconductor substrate is determined to some extent, so the content of the metal other than Cu-based in the metal thin film Will increase. Therefore, the component composition of the wiring obtained by high-temperature and high-pressure treatment and embedding the metal thin film in the recess is an alloy of a Cu-based metal and a metal other than the Cu-based metal. If the wiring is made of an alloy, the electrical resistance of the wiring may increase, which causes the semiconductor characteristics to deteriorate. Therefore, it is preferable to reduce the amount of metal other than Cu-based metal contained in the metal thin film laminated on the surface of the semiconductor substrate as much as possible. Therefore, the thickness of the thin metal layer other than the Cu-based material is 100 mm or less. Preferably it is 50 mm or less.

  Next, a method for manufacturing the semiconductor wiring of the present invention will be described.

  In the semiconductor wiring of the present invention, a thin film composed of a Cu-based metal is formed on the surface of a semiconductor substrate having a recess by a sputtering method, and then a thin layer composed of a metal other than a Cu-based metal is formed by the sputtering method. And forming a thin film composed of Cu-based metal by sputtering one or more times to form a metal thin film for semiconductor wiring, and then performing high temperature and high pressure treatment to embed the metal thin film in the recess A wiring is formed.

  That is, a thin film composed of Cu-based metal is formed on the surface of a semiconductor substrate by sputtering, and then a thin layer composed of metal other than Cu-based is formed by sputtering and Cu-based metal. It is important to repeat the process of forming the thin layer by sputtering one or more times in this order. A Cu-based metal and a metal other than a Cu-based metal are stacked, and a thin film composed of a Cu-based metal is divided into one or more thin layers composed of a metal other than a Cu-based metal.

The sputtering conditions are not particularly limited, and known conditions can be adopted. For example, film formation temperature: -20 to 300 ° C., atmosphere gas during film formation; inert gas (a known gas such as Ar or N ₂ can be used as the inert gas), film formation gas pressure; 0.133 ˜1.33 Pa (1 to 10 mm Torr), discharge power; 1 to 5 W / cm ² , distance between electrodes; 40 to 70 mm.

  The point of the production method of the present invention is to laminate a Cu-based metal thin layer and a metal thin layer other than Cu-based by a sputtering method, and other conditions are not limited, and known conditions can be adopted.

  As the semiconductor substrate having a recess, a semiconductor substrate formed by a known method can be used. That is, an insulating film is formed on the surface of a semiconductor substrate (for example, a silicon wafer), and then a wiring pattern (concave portion) such as a groove for embedding wiring and a hole (trench / via) for connecting wirings is formed. To do.

  A method for forming the insulating film is not particularly limited, and a known method can be adopted. As the insulating film, silicon oxide, silicon nitride, BSG (Boro-Silicate Glass), PSG (Phospho-Silicate Glass), BPSG (Boro-Phospho-Silicate Glass), or the like may be formed.

  Also, the method for forming the wiring pattern is not particularly limited, and a known method can be adopted. In the present invention, a metal thin film can be embedded in a recess having a minimum width of a wiring pattern of about 0.1 μm or less (not including 0 μm) and a depth of about 0.3 μm or more, thereby forming a wiring.

  A barrier film is formed on the surface of the insulating film by sputtering. If a Cu alloy is directly embedded in the recess formed in the insulating film, Cu may diffuse in the direction of the insulating film and impair the characteristics of the insulating film. Therefore, in order to prevent such diffusion of Cu, a barrier film is formed between the insulating film and the Cu alloy.

  Various materials have been studied as the barrier film, but TiN or TaN may be formed because of excellent barrier properties (that is, a property of suppressing diffusion of Cu at a higher temperature).

  The thickness of the barrier film only needs to be such that Cu can be prevented from diffusing into the insulating film, and is about several nm to several tens of nm. Specifically, it is about 5 to 50 nm. However, if the thickness of the barrier film is excessively large, it is not preferable because it is negative for downsizing of the semiconductor device.

  After the metal thin film is formed on the surface of the semiconductor substrate, high temperature and high pressure treatment is performed. The metal thin film can be embedded in the recess by high-temperature and high-pressure treatment to form a wiring. At this time, by performing the high-temperature and high-pressure treatment, fine pores and bubbles other than the voids disappear.

  Processing temperature shall be 400 degreeC or more. If the temperature is lower than 400 ° C., the temperature is too low, so that the high temperature fluidity of Cu cannot be obtained sufficiently, and even if pressure is applied, the metal thin film cannot be embedded in the recess. Preferably it is 450 degreeC or more. The upper limit of the processing temperature is not particularly limited, but if it exceeds 600 ° C., other parts (for example, the semiconductor substrate itself and the barrier film) constituting the semiconductor device are damaged, which is not practical. Accordingly, the processing temperature is 600 ° C. or lower. Preferably it is 500 degrees C or less.

  The treatment pressure is 150 MPa or more. Since the pressure is too low at less than 150 MPa, the metal thin film cannot be embedded in the recess even if the fluidity of the metal thin film is sufficiently obtained. Preferably it is 170 MPa or more. The upper limit of the treatment pressure is not particularly limited, but it is not practical because it becomes too high when it exceeds 200 MPa. Accordingly, the processing pressure is set to 200 MPa or less. Preferably it is 190 MPa or less.

The treatment time is not particularly limited, but the Cu alloy can be sufficiently embedded in the recess if the holding time at the maximum temperature is about 120 minutes or less. The treatment atmosphere is not particularly limited as long as it is an inert atmosphere, and treatment may be performed in an Ar or N ₂ atmosphere.

  After the high-temperature and high-pressure treatment, an unnecessary Cu alloy is subjected to chemical mechanical polishing (CMP) treatment to form a wiring. Then, by forming a new insulating film on the polished surface and repeating the above process, a multilayer wiring can be formed.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

Experimental example 1
In order to screen the reflowability of the metal thin film during the high temperature and high pressure treatment, the stress-temperature curve of the metal thin film was obtained. The stress-temperature curve shows the change in stress when the metal thin film is heated or cooled. From this stress change, the elasto-plastic deformation behavior of the metal thin film at high temperatures can be predicted. Can judge badness. A metal thin film (specimen) for obtaining a stress-temperature curve was formed by the following procedure.

Specimen A
After forming a TaN film (thickness: 500 mm) as a barrier layer on the surface of a silicon wafer having a diameter of 2 inches, a metal thin film was formed by a DC magnetron sputtering method, and a specimen A was obtained. The metal thin film is formed by repeatedly laminating 4 pure Cu thin layers (thickness: 2000 mm) and 3 pure Ag thin layers (thickness: 40 mm) so that the pure Cu thin layers and the pure Ag thin layers are alternated. did.

The TaN film was formed by sputtering. Pure Ta (purity: 99.99%) was used as a sputtering target, and reactive sputtering was performed in an Ar + N ₂ gas atmosphere. The sputtering conditions were as follows: temperature: 20 ° C., DC magnetron sputtering.

  The pure Cu thin layer and the pure Ag thin layer were formed by a DC magnetron sputtering method. The pure Cu thin layer uses pure Cu with a purity of 99.99% as a sputtering target, and the pure Ag thin layer uses pure Ag with a purity of 99.99% as a sputtering target and performs sputtering in an Ar gas atmosphere. It was. The sputtering conditions at this time were as follows: temperature: 20 ° C., DC magnetron sputtering.

  The film thicknesses of the TaN film, the pure Cu thin layer, and the pure Ag thin layer can be controlled by adjusting the processing time among the sputtering conditions. The film thickness was confirmed by observing the cross section of the metal thin film with a high resolution transmission electron microscope (“H9000 type” manufactured by Hitachi, Ltd .: TEM) at 500,000 times.

Specimen B
After forming a TaN film (thickness: 500 mm) as a barrier layer on the surface of a silicon wafer having a diameter of 2 inches, a metal thin film was formed by a DC magnetron sputtering method to obtain a test material B. As the metal thin film, a pure Cu thin film (thickness: 8000 mm) was formed as a single layer. The conditions for forming the TaN film and the pure Cu thin film were the same as those for the specimen A.

  The obtained specimens A and B were heated and cooled from room temperature to 500 ° C. at a heating / cooling rate of 5 ° C./min. At this time, the stress change of the metal thin film was measured in situ (in-situ) to obtain a stress-temperature curve. The in-situ stress of the metal thin film was measured by an optical lever method. FIG. 1 shows a stress-temperature curve of the metal thin film laminated on the specimen A, and FIG. 2 shows a stress-temperature curve of the metal thin film laminated on the specimen B, respectively.

  As is clear from FIG. 2, when the metal thin film is a single layer of pure Cu, the degree of stress relaxation in the heating process (Heating) is small, and the stress changes linearly with temperature in the cooling process (Cooling). It can be seen that it is elastically deformed.

  On the other hand, as is clear from FIG. 1, when the metal thin film is laminated so that the pure Cu thin film is divided by the pure Ag thin layer, the stress in the heating process is always smaller than 0, and in the cooling process, the stress is up to 200 ° C. It can be seen that the stress is smaller than 0, and when the temperature is lower than 200 ° C., the stress changes linearly with respect to the temperature and elastically deforms. That is, it can be seen that when the metal thin film has a laminated structure of a pure Cu thin layer and a pure Ag thin layer, stress relaxation (that is, softening of the thin film) occurs.

Experimental example 2
Using the test materials A and B obtained in Experimental Example 1, the samples were heat-treated, and the change in the structure of the metal thin film before and after the heat treatment was observed.

  The heat treatment was performed in vacuum at 500 ° C. for 5 minutes. At this time, the heating / cooling rate was 5 ° C./min.

  The structure of the metal thin film is exposed by processing a cross section in the thickness direction with respect to the metal thin film using an FIB apparatus (“SMI9200 type” manufactured by SII Nanotechnology Co., Ltd.), and this cross section is exposed to a SIM image (excited by ions) of the FIB apparatus. Secondary electron image). FIG. 3 shows a cross-sectional photograph of the specimen A as a drawing substitute photograph, and FIG. 4 shows a sectional photograph of the specimen B as a drawing substitute photograph.

  The crystal grain size of Cu in the metal thin film before and after the heat treatment was measured by taking a SIM image at 50,000 times and analyzing the image. The observation visual field was 5 μm × 5 μm, and an arbitrary position in the cross section.

  As can be seen from FIG. 4, when a pure Cu thin film is formed as a single layer, Cu crystal grains before heat treatment (As-deposited state) are large, and there are crystal grain boundaries penetrating in the thickness direction of the metal thin film. Many were observed. The average crystal grain size of Cu of the metal thin film was calculated to be 8200 mm, and the average crystal grain size was almost the same as the film thickness. However, a number of coarse Cu crystal grains having a crystal grain size equivalent to about four times the film thickness were observed, and the maximum crystal grain size was 37000 mm.

  On the other hand, the average crystal grain size of Cu after the heat treatment is almost the same as that before the heat treatment, and the grain growth (recrystallization) hardly occurs even after the heat treatment. That is, it can be seen that it has the same polycrystalline structure as the As-deposited state.

  On the other hand, as is clear from FIG. 3, when the pure Cu thin layer and the pure Ag thin layer are laminated, the metal thin film (pure Cu thin film) is divided into four layers by the pure Ag thin layer before the heat treatment. I understand that When the average crystal grain size of Cu in each pure Cu thin layer was calculated, the average crystal grain size of Cu in each pure Cu thin layer was 1650 mm, which was almost the same as the thickness of each thin layer. However, coarse Cu crystal grains having a crystal grain size exceeding twice the film thickness are not recognized, and the maximum crystal grain size is 1900 mm, which indicates that the crystal grain has a fine polycrystalline structure.

  On the other hand, when heat treatment is performed, Cu crystal grains become coarse and have a large polycrystalline structure. At this time, the pure Ag thin layer disappears, and remarkable Cu grain growth occurs.

  From the above results, when the Cu-based metal thin film is divided by a thin metal layer other than Cu-based, the Cu crystal grains before heat treatment can be refined, and if the heat treatment is performed, the Cu crystal grains grow significantly, and at this time, atomic diffusion occurs. Reflowability is improved.

Experimental example 3
An insulating film (TEOS film: SiOF film) is formed on the surface of a 2-inch diameter silicon wafer with a thickness of 8000 mm, and vias having a diameter of 0.18 μm, a depth of 0.55 μm, and a pitch of 450 nm are formed on the insulating film. A plurality of evaluation elements (TEG) were obtained by providing a plurality.

A TaN film was provided as a barrier layer on the surface of the obtained TEG. The TaN film was formed by a sputtering method, pure Ta was used as a sputtering target, and reactive sputtering was performed in an Ar + N ₂ gas atmosphere. The sputtering conditions were known conditions. The thickness of the TaN film provided on the bottom and side surfaces of the via was 50 nm.

  Next, after forming a pure Cu thin layer on the TEG provided with the barrier layer by sputtering, sputtering is performed so that the pure Ag thin layer and the pure Cu thin layer alternate in this order, and the opening of the via is made of metal. Bridging with a thin film. At this time, the film thicknesses of the pure Cu thin layer and the pure Ag thin layer and the number of the pure Cu thin layers were changed as shown in Table 1 below. The film thickness was measured by TEM observation of the cross section at 500,000 times.

  The pure Cu thin layer was sputtered in an Ar atmosphere using pure Cu and the pure Ag thin layer was pure Ag, respectively. The sputtering conditions for providing the pure Cu thin layer and the pure Ag thin layer were set to 20 ° C. and DC magnetron sputtering.

  When the crystal structure of the pure Cu thin layer and the pure Ag thin layer was measured by TEM limited-field electron diffraction, the pure Cu thin layer was a face-centered cubic crystal having a lattice constant a of 3.6150, and the pure Ag thin layer was a lattice constant. a was a face-centered cubic crystal having 4.0861.

  Next, the bridged TEG was subjected to a high-temperature and high-pressure treatment. The processing conditions were as follows: processing pressure: 200 MPa, processing temperature (maximum temperature reached): 600 ° C., holding time at the maximum temperature reached: 15 minutes, temperature rising / falling speed: 20 ° C./min.

  For each TEG subjected to high-temperature and high-pressure treatment, the cross section of 15 via parts was processed and exposed with an FIB apparatus (“SMI9200 type” manufactured by SII Nanotechnology), and the SIM image (excited by ions) of the FIB apparatus. (Secondary electron image) was observed to evaluate whether the metal thin film was embedded in the via portion (embedding characteristics). The evaluation standard for the embedding characteristics is that, among the 15 vias that were arbitrarily observed, all the vias were completely embedded with the metal thin film (O), and one via that was not completely embedded with Cu. In the case of (2), it was determined to be acceptable (Δ), and if there were two or more vias not completely embedded with Cu, it was determined to be unacceptable (x). The evaluation results are shown in Table 1 below.

  As is clear from Table 1, in the example satisfying the requirements defined in the present invention, the metal thin film could be completely embedded in all the vias. No. No. 2 is an example in which the film thickness of the pure Cu thin layer is large, and since the crystal grains of Cu are coarsened, the embedding result is not excellent. No. 7 is an example in which the thickness of the pure Ag thin layer is large, and the metal thin film cannot be completely embedded. No. No. 11 is an example in which the film thickness of the pure Ag thin layer is too small, and the effect of dividing the Cu-based metal thin layer by a metal thin layer other than the Cu-based layer was hardly obtained.

It is a graph which shows the result of having measured the stress-temperature curve of the laminated thin film laminated | stacked on the test material A. It is a graph which shows the result of having measured the stress-temperature curve of the single layer thin film laminated | stacked on the test material B. FIG. 3 is a cross-sectional photograph (drawing substitute photograph) of specimen A. 3 is a cross-sectional photograph (drawing substitute photograph) of Specimen B.

Claims (8)

A metal thin film laminated on the surface of a semiconductor substrate having a recess,
In the metal thin film, a thin film made of a Cu-based metal is divided by one or more thin layers made of a metal other than a Cu-based metal,
The metal other than the Cu-based metal is a metal that can suppress the grain growth of Cu crystals in the Cu-based metal during aging at room temperature, and is once dissolved in the Cu-based metal by performing high-temperature and high-pressure treatment.
The thickness of the Cu-based metal thin layer formed by being divided by the metal thin layer other than the Cu-based material is 100 to 2000 mm per layer,
A metal thin film for semiconductor wiring, wherein the thickness of the thin metal layer other than the Cu-based material is 10 to 100 mm per layer.   2. The metal thin film for semiconductor wiring according to claim 1, wherein the crystal structure of the thin metal layer other than Cu-based is a face-centered cubic crystal having a lattice constant that differs by 5% or more from the lattice constant of the Cu-based metal thin film.   2. The metal thin film for semiconductor wiring according to claim 1, wherein a crystal structure of the thin metal layer other than the Cu-based material is a body-centered cubic crystal or a hexagonal close-packed crystal.   The metal thin film for semiconductor wiring according to any one of claims 1 to 3, wherein the metal other than the Cu-based metal is at least one metal selected from the group consisting of Au, Pd, W, Mo, Al, or Ag.   When the thickness of the Cu-based metal thin layer formed by being divided by the thin metal layer other than the Cu-based material is a, and the maximum crystal grain size of the Cu-based metal in the thin layer is b, b ≦ 2a The metal thin film for semiconductor wiring according to any one of claims 1 to 4, which satisfies the relationship:   The metal thin film for semiconductor wiring according to claim 1, comprising 2 to 10 Cu-based metal thin layers.   It is formed by laminating the metal thin film according to any one of claims 1 to 6 on the surface of a semiconductor substrate having a recess, and then embedding the metal thin film in the recess by high-temperature and high-pressure treatment. And semiconductor wiring. Forming a thin layer composed of a Cu-based metal on the surface of a semiconductor substrate having a recess by a sputtering method, and then forming a thin layer composed of a metal other than a Cu-based metal by a sputtering method and a Cu-based metal The metal thin film for semiconductor wiring according to any one of claims 1 to 6 is formed by repeating the step of forming a thin layer to be formed by a sputtering method at least once in this order,
Next, a method for producing a semiconductor wiring, wherein the wiring is formed by performing a high-temperature and high-pressure treatment and embedding the metal thin film in the recess.

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