JP5510812B2 - Cu alloy film for wiring film and sputtering target material for forming wiring film - Google Patents

Description

  The present invention relates to a wiring film used in a flat display device (Flat Panel Display, hereinafter referred to as FPD) manufactured by forming a thin film on a substrate, and a sputtering target material used for forming the wiring film. .

  Examples of the FPD manufactured by laminating a thin film on a glass substrate or Si wafer include, for example, a liquid crystal display (hereinafter referred to as LCD), a plasma display panel (hereinafter referred to as PDP), and a field emission display (hereinafter referred to as FED). Electroluminescence display (hereinafter referred to as ELD), electronic paper, and the like are known, and various new products are actively researched and developed.

  As a wiring film such as a thin film transistor (TFT) used in these FPDs, high-speed driving for displaying a moving image is required as the display is enlarged, and Al and Al alloys of Al and Al alloys are used as a low resistance wiring film. A membrane is used. In recent years, with further increase in display size and definition, Cu-based wiring has attracted attention as a wiring with lower resistance.

  Cu is considered to have lower resistance than Al and excellent resistance to electromigration and stress migration, and has already been used as a wiring film in the field of LSI. However, with the high integration of LSI, pure Cu is considered to have insufficient electromigration resistance and stress migration resistance, and these migration resistance can be improved by adding Al or Si as additive elements to Cu. (For example, refer to Patent Document 1).

JP-A-6-177117

The Cu alloy film proposed in Patent Document 1 has higher electromigration resistance and stress migration resistance than pure Cu when a device is formed on a Si wafer in the field of LSI or the like. It is a useful Cu alloy film. However, according to the inventor's study, when the proposed Cu alloy film is formed on a glass substrate, it is confirmed that the resistance value does not sufficiently decrease even if the heat treatment during the manufacturing process is performed. did. Further, when heat treatment at about 250 ° C. was performed, protrusions called hillocks and voids called voids were sometimes generated in the Cu alloy film, and it was confirmed that there was a problem in heat resistance.
By the way, in a liquid crystal display (LCD) using amorphous silicon-TFT as a driving element, which is the most common FPD, a device is formed on a transparent glass substrate, and the heating temperature during the manufacturing process is about 250 to 350 ° C. Yes, it is expected to further decrease in the future. For this reason, there is a demand for a Cu alloy wiring film that is optimal for an FPD that can achieve low resistance in heat treatment in a manufacturing process temperature range of about 200 to 250 ° C. while having heat resistance.

  In view of the above problems, an object of the present invention is to reduce the resistance of a wiring film such as an FPD in the process temperature range and to have a heat resistance capable of suppressing hillocks and voids generated in a Cu-based film. It is to provide a sputtering target material for forming an alloy film and its Cu alloy film.

As a result of intensive studies to solve the above problems, the present inventor has a low resistance and heat resistance that can suppress generation of hillocks and voids by adding a suitable amount of B and Ag to Cu. The present inventors have found that a Cu alloy film having properties can be obtained.
That is, the present invention provides a Cu alloy film for a wiring film comprising 0.1 to 1.0 atomic% of B as an additive element and 0.1 to 2.0 atomic% of Ag, and the balance Cu and unavoidable impurities. is there.
Further, the present invention contains 0.1 to 1.0 atomic% of B as additive elements and 0.1 to 2.0 atomic% of Ag as additive elements for obtaining a Cu alloy film for a wiring film having the above composition, with the balance being Cu. And a sputtering target material for forming a wiring film comprising inevitable impurities.

  INDUSTRIAL APPLICABILITY The present invention can realize a Cu alloy film having low resistance, hillock resistance, and void resistance, and is extremely effective as a wiring film for FPDs such as large liquid crystal TVs and electronic papers that require lower resistance in the future. Become.

3 is a field emission scanning electron micrograph of the film surface observed after heat treatment of the Cu alloy film of Sample 1 in Example 1. FIG. 2 is a field emission scanning electron micrograph of a film surface observed after heat treatment of a pure Cu film of Sample 7 in Example 1. FIG. 3 is a field emission scanning electron micrograph of the film surface observed after heat-treating the Cu alloy film of Sample 8 in Example 1. FIG. 2 is a field emission scanning electron micrograph of the film surface observed after heat-treating the Cu alloy film of Sample 9 in Example 1. FIG. It is a figure which shows the relationship between the heating temperature and specific resistance in Example 2. FIG.

  An important feature of the present invention is that, as an optimum alloy configuration for obtaining a wiring film having sufficient hillock resistance and void resistance while realizing the low resistance required for the wiring film for FPD, A Cu alloy film in which Ag is added in combination is found.

The reason for selecting B and Ag as additive elements and the reason for selecting the addition amount in the Cu alloy film for wiring films of the present invention will be described below.
First, the effect of adding B to Cu is that when a Cu alloy film is formed by sputtering, even when heat treatment is performed at a low temperature range of 200 to 250 ° C., the resistance value can be significantly reduced as compared with the time of film formation. It is in the point which can improve the hillock tolerance at the time of heat-processing. The reason why the effect is obtained is not clear, but is presumed as follows. When a thin film is formed on a substrate by sputtering, the additive element is dissolved in a non-equilibrium state. Since B has almost no solid solution region with respect to Cu, and B is a light element, the resistance value can be reduced because B is ejected from the Cu matrix to the grain boundaries and the film surface even by heat treatment at a low temperature. It is considered a thing. In addition, it is considered that the hillock resistance is improved because B is discharged from the Cu matrix to the grain boundaries and the film surface during the heat treatment, thereby reducing the compressive stress of the film.
The above effect becomes clear when B is added in an amount of 0.1 atomic% or more. If B is added in excess of 1.0 atomic%, the film tends to peel off, which is undesirable. 0.0 atomic%.

Furthermore, the high effect which suppresses the void which generate | occur | produces in Cu film | membrane is acquired by adding 0.1-2.0 atomic% of Ag with respect to Cu. The reason is presumed as follows. Ag is an element that dissolves approximately 5 atomic% in Cu at a high temperature range of 800 ° C. When a Cu alloy film is formed by sputtering, Ag dissolves in Cu to suppress the movement of Cu atoms during heating. As a result, the generation of voids is considered to be suppressed.
Furthermore, obtaining Cu alloy which has the effect that resistance value falls by 200-250 degreeC heat processing, suppressing generation | occurrence | production of a hillock or a void by combining and adding B and Ag with respect to Cu. Can do. Although the reason is not clear, it is considered that B is an element that expresses Ag and a compound, so that B and Ag are combined by heat treatment and discharged as a compound from a Cu matrix. The above effects appear from 0.1 atomic% as the addition amount of Ag. However, if the addition amount exceeds 2.0 atomic%, the resistance value increases and it becomes difficult to obtain a low resistance value even after heating. The amount is 0.1 to 2.0 atomic%.
Further, in order to obtain a Cu alloy film having a lower resistance while suppressing generation of hillocks and voids, Ag is set to 0.1 to 1.0 atomic% and B is set to 0.1 to 0.5 atomic%. Is desirable.

  Moreover, when forming the Cu alloy film for wiring films of the present invention, sputtering using a wiring film forming sputtering target material having the same composition as the Cu alloy film is optimal. This is because sputtering can form a film having almost the same composition as the target material, and the Cu alloy film of the present invention can be formed stably.

  Although there are various methods for producing the target material, any method may be used as long as it can achieve the high purity, uniform structure, high density and the like generally required for the target material. For example, a molten metal adjusted to a predetermined composition by a vacuum melting method is cast into a metal mold, and then processed into a plate shape by plastic processing such as forging and rolling, and finished to a target having a predetermined shape by machining. Can be manufactured. In order to obtain a more uniform structure, an ingot rapidly solidified by a powder sintering method or a spray forming method (droplet deposition method) may be used.

  In the sputtering target material for forming a Cu alloy film and a wiring film of the present invention, component elements other than additive elements are Cu and inevitable impurities. That is, inevitable impurities such as oxygen, nitrogen, and carbon, which are gas components, may be included as long as the effects of the present invention are not impaired. For example, oxygen, nitrogen, and carbon in the gas components are each 50 ppm or less, and the purity excluding the gas components is preferably 99.9% or more.

Next, specific examples of the present invention will be described.
First, a Cu alloy target material was manufactured by the method described below.
After mixing the raw materials having a purity of 99.9% or more and melting them in a vacuum melting furnace so as to be substantially the same as the target composition of the Cu alloy film obtained by adding various additive elements shown in Table 1 to Cu, A Cu alloy ingot was produced by casting. Next, a sputtering target material having a diameter of 100 mm and a thickness of 5 mm was produced by machining a Cu alloy ingot.
As a comparative example, a pure Cu target having the same dimensions was produced by the same method.
A sputtering material is used to form a Cu alloy film having a thickness of 200 nm and a pure Cu film on a smooth glass substrate having a size of 100 × 100 mm, using the target materials having various compositions prepared above. Resistance was measured. The measurement results are shown in Table 1.
As a result of quantitative analysis of the oxygen content and carbon content of the target materials of Samples 1, 2, 3 and 4 by the infrared absorption method and nitrogen content by the thermal conductivity method, the oxygen content was 18 ppm, 18 ppm, 21 ppm, 20 ppm and carbon, respectively. The amounts were 7 ppm, 6 ppm, 5 ppm, and 10 ppm, respectively, and the nitrogen amounts were 10 ppm, 10 ppm, 10 ppm, and 10 ppm, respectively.

Further, the Cu alloy film and the pure Cu film formed above were cut into a size of 25 × 50 mm and subjected to heat treatment at a temperature of 250 ° C. for 1 hour in a vacuum atmosphere reduced to 1 × 10 ⁻¹ Pa or less. The specific resistance was measured later. Furthermore, the surface conditions of the Cu alloy film and the pure Cu film were observed with a field emission scanning electron microscope (hereinafter referred to as FE-SEM). The film surface observation by FE-SEM was performed from a direction oblique to the film surface at an angle of 45 °, and the observation magnification was 50,000 times. Evaluate that the film surface does not have hillocks, voids, or film peeling as good, and evaluate the film surface that has hillocks, voids, or film peeling as x, and the specific resistance after heat treatment In addition, Table 1 shows the film surface evaluation.
In addition, FE-SEM images obtained by observing the film surface conditions after heat treatment of Samples 1, 7, 8, and 9 are shown in FIGS. 1 to 4, respectively.

  As shown in Table 1 and FIGS. 1 to 4, pure Cu has a low resistance value, but it can be seen that voids are generated along with the growth of crystal grains after the heat treatment. Further, in the Cu—Al alloy or Cu—Si alloy, hillocks are generated after the heat treatment, and at the same time, the specific resistance after the heat treatment exceeds 4 μΩcm, and the resistance cannot be sufficiently lowered. On the other hand, it can be seen that the Cu-Ag-B alloy of the present invention does not generate voids or hillocks after the heat treatment and can reduce the specific resistance to less than 4 μΩcm. Further, if the added amount of Ag is large, hillocks are likely to occur, and if the added amount of B is large, the adhesiveness is lowered and film peeling is likely to occur. Since Ag has a low solid solution region with respect to Cu at a low temperature, it is considered that when the amount of Ag added is large, it precipitates during heating and tends to generate hillocks.

Cu-0.3% Ag-0.5% B (atomic%) of the present invention example produced in Example 1, pure Cu, Cu-1.0 Al (atomic%), Cu-1.0 Si (comparative example) Samples in which a Cu alloy film and pure Cu were formed on a glass substrate were prepared in the same manner as in Example 1 using each atomic target. Then, the specific resistance was measured after heat-processing for 1 hour in the temperature range of 100-250 degreeC in the vacuum atmosphere which pressure-reduced each sample to 1x10 < ^-1 > Pa or less. From the measurement results, the relationship between the heating temperature and the specific resistance is shown in FIG.
From FIG. 5, it can be seen that the specific resistance of the Cu—Ag—B alloy film of the present invention gradually decreases with increasing heating temperature, and the specific resistance decreases particularly with heat treatment at 200 ° C. or higher.

Claims (2)

  A Cu alloy film for a wiring film comprising 0.1 to 1.0 atomic% of B as an additive element and 0.1 to 2.0 atomic% of Ag, and the balance being Cu and inevitable impurities.   A sputtering target material for forming a wiring film, comprising 0.1 to 1.0 atomic% of B as an additive element and 0.1 to 2.0 atomic% of Ag, and the balance being Cu and inevitable impurities.