TW455525B - Method for improving chemical mechanical polishing of tungsten metal layer - Google Patents

Abstract

A method for improving a chemical mechanical polishing (CMP) of a tungsten metal layer to increase the output of the process and the operation life of a polishing pad is disclosed. The method comprises feeding a wafer; uses a first hard polishing pad to remove the rough surface thereof and increase the productivity. During the first polishing, injects a polishing slurry at an amount more than the later polishing operations and increasing the load thereof; uses a robot arm to transport the wafer to a second polishing pad, which uses a soft polishing for removing the remaining tungsten layer to a specified amount; and transports the wafer to a third polishing pad for using a slurry of a polishing oxide layer to polish the oxide layer for making the tungsten plug and/or wire higher than the peripheral oxide layer.

Description

455525 5. Description of the invention (ο Field of the invention: mechanical polishing process, especially means' fine polishing with a soft polishing pad to improve the life of the polishing pad and wafer polishing in the process] The present invention relates to a chemical / mechanical first hard polishing A method for producing 1 output by polishing metal crane chemical / mechanical polishing pads. BACKGROUND OF THE INVENTION In the ULSI process, as the wafer processes are carried out, the appearance of the dielectric layer with undulations i will be generated. More accurate transfer and metal: the interconnect process becomes easier (prevents disconnection or uneven thickness), usually requires a chemical continuous grinding process after the appropriate process steps to produce; a flat surface The initial stage of the planarization process is usually filled by the high fluidity of spin-coated glass acid SOG—some surface structures that are difficult to cover by chemical vapor deposition, or the gap between the metal layer and the metal layer.通 m broadcasts often need to borrow * retelling to get flattening, but although it is not easy to control the == rate to 1: 1, it is especially difficult for the Fengfeng conductor to enter the sub-micron degree. When transported to the ground, it is frank to say that it is difficult to develop. It is another type—corresponding to the extremely high hardness, not only about 2 to add grinding particles k for mechanical grinding like a sharpening knife, but also because of 455525 | Five, description of the invention (2)

I | utilizes chemical additives such as oxidants and organic solvents to provide chemical reactions for chemical removal, so it has been widely used in various semiconductor processes. In general, as long as the parameters are properly controlled, CM P can provide a flatness of more than 94%. In addition, CMP is also often used to provide a tungsten plug or copper plug metal and interconnect damascene process, with the lead trench and plug metal overflowing the metal layer above the interconnect dielectric layer. It is generally accepted that the widely accepted mechanism of CMP grinding metal layers is that the metal layer first forms a metal oxide layer, and then the removal mechanism is similar to that of the oxide layer (that is, the first generation of hydroxide effect)

J l (hydroxylation) is then bonded to the polishing slurry, and the bond bond is broken and detached), i After the metal oxide layer is removed, it is corroded by the polishing slurry and a oxidation protection layer (passivation) is removed. The above-mentioned polishing slurry is carried by a polishing pad, and the polishing material is a polyurethane cell foamed material j i which can carry a polishing compound to polish the wafer. The wafer is placed on the polishing pad. The wafer is polished by a rotating shaft loaded on the wafer relative to the polishing pad. i As far as various chemical vapor deposition methods are known for depositing tungsten metal layers on substrates, the 'deposited tungsten metal layer not only has high stress and rough surface'; it is believed that the roughness of the tungsten metal layer originates from the Yan film ( Less than 2000 angstroms) From the initial small grains, as the deposition progresses, the Yan grains transform into I columnar crystals along the growth direction and increase the length of the crystalline grains as the thickness of the deposit increases. Rough. And because tungsten metal has high hardness and high stress included in!

Page 5 4 5 5 5 2 5 i. Description of the invention (3) Among them. In order to reduce the impact on polishing 塾 during CMP, traditionally, the CMP process for plug I metal tungsten uses two polishing stages. During the polishing process, the wafer's high point (high spot) and polishing pad are used. The contact 'will therefore be removed and i will be flattened. The first application method is that the first polishing platform and the second polishing platform both use hard polishing pads, such as Taiwan's Applied Materials (AM AT) machine or I. The second application method is that both polishing platforms are soft polishing pads. 'Such as ipec company β

I The first polishing platform in the first method is used to remove the rough surface of the tungsten metal layer. The polishing pad is made of a material with small and many holes, as shown in Figure 1A. The size of the pores is about 3 0-5 0 ν m. For tungsten grinding, the composition of the slurry includes alumina powder, potassium ferricyanide (K3Fe (CN) 6), potassium dihydrogen phosphate (KH2P04), and the like. The pH is controlled between 5 and 6. | 5. The advantage of a hard abrasive pad is that the life of the abrasive pad is generally longer. The polishing rate is high ', however, the throughput is lower than that of the soft polishing pad method. This is because hard grinding pads usually have almost all holes blocked by the grinding mass and the particles after grinding one piece. Therefore, after grinding for about 30-40 seconds, it is necessary to use the grinding pad of the first grinding platform. , To remove the obstructed grinding 塾 activation, or regeneration treatment (condition treatment). At the same time, the wafer is moved to the second polishing platform, and the wafer is again polished and polished with the same formula of the polishing excitation to remove the tungsten metal plug.

Page 6 455525 V. Description of the invention ¢ 4). Just like the first polishing platform, the second polishing platform also uses hard-type polishing pads. Therefore, after each wafer CMP, a hard-type polishing pad regeneration process is also performed. Therefore, even if the polishing rate of the hard polishing pad is higher than that of the soft polishing pad, the overall output is reduced due to the regeneration process. Finally, a third grinding process is performed to polish the oxide layer with the polishing slurry of the oxide layer, so that the oxide layer is slightly depressed and the tungsten layer is exposed. i | As for the second method, such as the machine sold by IPEC, it is a soft polishing pad for the whole process. Please refer to Figure 1B. The soft polishing pad has large holes to absorb the polishing slurry. The hole size is about 50- 2 0 0 # m. Therefore, the holes are not easily clogged. Naturally, the polishing pad does not need to be regenerated.

The output of I 1 ground wafer is increased. However, soft abrasive pads come at the cost of short pad life. Because when grinding wafers, soft grinding is also consumed, especially the grinding of the rough surface of the tungsten layer, which consumes faster. So in general, a soft polishing pad only needs about 500 wafers to be replaced. Since the second polishing process also uses a soft polishing pad, no reprocessing is required. As in the first method, after the two grinding steps, a third grinding step is performed in which the oxide layer is polished with a polishing slurry for grinding the oxide layer, so that the oxide layer is slightly depressed and the tungsten layer is exposed.

I The traditional method mentioned above is the first one. The service life of the polishing pad is long. However, since the first or second polishing is performed, the wafer must be reconditioned once when the wafer is transferred out. , Refers to grinding the polishing pad with a disc with diamond fine particles, so that the polishing pad

Page 7 455525 V. Description of the invention (5)

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regeneration. However, the regeneration process interrupts the grinding, which is not good for the output. Table 1 shows the comparison of the grinding life and performance of the two polishing methods. D Table 1 The second polishing pad is about 750, about 1000 pieces, the output is 5 5 pieces / hour, 4 2 pieces / hour, and the type of polishing pad is the first. Abrasive pads Soft abrasive pads are about 300 pieces Hard abrasive pads are about 100 pieces. The life of the soft abrasive pads on the first abrasive disc is obviously lower than that of the hard abrasive pads. The second abrasive sheet has a longer life. long. But still below the hard | pad. However, the output of soft polishing pads is relatively high, up to 55 1 pieces per hour, while the output of hard polishing pads is much longer, but the output is much smaller (only about 42 pieces). Another disadvantage of the hard polishing pad is that it is easy to cause the problem of scratching the wafer with the polishing pad. The soft polishing pad is in contact with the surface to be polished of the wafer.

The I i surface is large and may be consistent with the polished surface of the wafer because it is too soft, and the planarization effect may not be achieved. In view of the problems described above, the present invention will provide a method to solve the problems. OBJECTS AND SUMMARY OF THE INVENTION: One object of the present invention is to provide a tungsten metal chemical / mechanical polishing process to solve the problems of tungsten plug scratches, output and polishing pad life. 455525 Description of the invention (6) The invention is a method for improving the output of tungsten metal chemical / mechanical polishing process and increasing the service life of the polishing pad. The present invention is to load the wafer with the first hard polishing pad to remove the rough surface and then transfer it. To the second polishing pad i, remove the remaining tungsten on the smooth surface, and use different polishing conditions for different polishing pads. For example, in the first polishing, the injected polishing is destroyed and the load for I is higher than that. The latter pass grinds more and larger. Finally, it is transferred to the third polishing pad for polishing the oxide layer with a polishing slurry for grinding the oxide layer so that the tungsten plug and / or the wire are higher than the surrounding oxide layer. Since only one polishing pad regeneration is required, the output is higher than that of all hard polishing pads, and because different polishing pads use different polishing conditions. i Detailed description of the invention: In view of the traditional chemical / mechanical polishing process for tungsten wires or plugs, if either the first rough grinding and the second fine grinding use hard polishing pads, or the two grinding processes are all soft The method of polishing pads, and this method, each has its advantages and disadvantages. 1 Therefore, the present invention will provide a method that combines the advantages of both, not only to increase the output (compared to the previous method, and the life of the polishing pad is longer, the inventor conducted a series of studies to improve the traditional method, the results are as follows : First, the inventors found that the grinding removal rate of tungsten is an important key, which will determine the output, the life of the polishing pad, and the use of the polishing slurry.

Page 9 45 55 25 ⑺ It is necessary to design an appropriate grinding formula to produce the best grinding removal speed test such as 圊 t. The diagram of the grinding removal rate (removal amount vs. time) shows whether the rotation is reversed using a soft polishing pad The removal rate curve 10 of the removal rate curve polishing pad is non-linear, and the performance of the curve uniformity shows that — it is better to start the hard polishing pad, but the removal rate of the two polishing pads is about 20 seconds before the beginning. It is comparable to the linear curve range> The removal rate curve of the hard polishing pad 1 0 represents the removal rate curve of the polishing pad 2 0 is good. Using the tracing electron microscope, the original surface roughness of tungsten is quite T% (such as the curve Grind 5 results below the graph). Therefore, the removal amount is not significant more than 20 seconds before the beginning, and the straight roughness is removed to a considerable degree (for example, the result of the research below the graph is quite flat). Removal rate (rougher surfaces must be softer The polishing pad has great lethality. The soft polishing pad grinds the wafer, and the polishing removal rate declines. The polishing pad is much faster. Because the first polishing pad is relatively flat. The first wafer polishing is performed with a soft polishing pad. , Will reduce the life only, and the second wafer polishing pad, there is no such I. V, the description of the amount of I. Because of the rate. Please refer to the figure. Figure 2 丨 2 0 or hard! 1 2 and 2 2 are the last two of I The person who j i opened i, although it is relatively soft to find out, the knot after 丨 seconds! J to the surface 丨 grind 3 Q seconds later (large).

I | | Second i therefore the first 丨 Shen is smoother than the second table. Therefore, based on the results shown in Figure 3, the grinding method provided by the present invention is 4555 25. 15. Description of the invention (8) i The hard grinding pad is used in the first grinding, and the following conditions are used, for example, grinding | refining flow 120- 180 seem 'pH value is controlled at 2-3' polishing pad and wafer; the angular velocity of the tape is 113-1 15 RPMA 1 1 1 1 5 RPM load I is about 5.0-5 · 5 broken. In order to completely remove the rough surface (the height difference is greater than 60 angstroms) of tungsten before the first polishing pad is regenerated. After the rough surface of the wafer is removed, the first polishing pad is regenerated, and the I wafer is moved to the second polishing pad for polishing at this time. The second polishing pad is a soft 丨 type polishing pad. At this time, the polishing slurry conditions are as follows: slurry flow 1 〇〇_ 1 2 [} | sccm 'p Η value is controlled at 2-3' angular velocity carried by polishing pad and wafer respectively | are 113-1151 ?? "and 111- 115 1 ^ 1 ^, effective load is 4.5-5_〇 crushed, I can effectively remove fine scratches. Table 2 Comparison of the present invention and the two previous cases. Polishing pad type polishing pad life output (per hour) Regeneration treatment (pHp2) Hard pad + soft pad about 1500 pieces 52 pieces only pi (invention) Hard pad + hard pad about 1 0 0 0 pieces 42 pieces Pi and P2 soft pad + soft pad less than 1 0 0 0 pieces 55 pieces Not required; The method of the present invention is shown to make the polishing pad longer than the previous one. The tube is either a hard polishing pad or a soft polishing pad, which is longer. This is because the present invention i's polishing conditions during the first polishing Different from the first

Page 11 455525! V. Description of the invention (9) The polishing pad, for example, has a large flux, so the polishing pad has less damage. Because the rough surface of the tungsten layer is completely removed when the second polishing pad is replaced, the soft polishing pad is only used to polish the smooth surface, and the rough pad surface will not scratch the polishing pad, which naturally achieves the purpose of extending its service life. The following Ruming said ¾ under the best is to have Ming Fa with the French method to send the film to ten temples and four temples Θ h dagger / / 1 come again every live 塾 原 磨 Yuken can be about one, the promotion is done to mention Shao Danli, Production of tablet grinding and more research ten} May 1-IC to lifting, soft lifting, lifting pads are grinding. Shou-type pad with a hard grinding to soften each type of cymbals. Ο ο 2 2 each type of soft out of 00 5 and up to 1 pad raised to grinding to improve the life of the shovel} also hard 塾 points} 磨 部 2 C 研磨 type grinding hard research. If the question is not asked, the damage caused by the grinding pad is made into a grinded grinding mark. It is useful to make the pad grinded and grinded. The second rule is to pass the reason. Disclose tr CM and state that 'the hair has already been issued but the exception is not implemented. It is better and more extraordinary *' Ming Wai issued Fan Benli for the purpose of describing only the application of the application. The package should be decorated or modified. Fan Shenli Jingzhu, page 12b ______- 丨 a brief illustration of the diagram i I The preferred embodiment of the present invention will be supplemented by the following [I figure for more detailed explanation: i

I Figure 1 shows the difference between the holes of a hard polishing pad (Figure 1A) and a soft polishing pad (Figure 1B) observed by a scanning electron microscope. Figure 2 shows that the removal rate at the initial stage of grinding is non-linear in the early stage (first 20 seconds). The curve is regardless of the soft or hard polishing pad, and the latter stage. After 20 seconds, the removal rate is linear, below the curve. SEM observation research

I 丨 Surface image after grinding for 5 seconds (rough) and after grinding for 30 seconds (smooth).

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Claims (1)

45 55 25 VI. Scope of patent application | l. A method for improving the output of tungsten metal chemical / mechanical polishing process and increasing the service life of grinding pads, the method includes at least the following steps: I Put a tungsten-containing metal layer on top The wafer on the surface is loaded on a first polishing pad. The first polishing pad is a hard polishing pad and is subjected to a chemical / mechanical polishing process to remove tungsten I metal with a roughness amplitude of about 60 ° angstroms or more. Except; and i | transfer the wafer to a second polishing pad, which is a soft polishing pad used to remove the remaining tungsten layer to a set removal amount. | 2. The method according to item 1 of the patent application scope further includes performing a regeneration process on the first polishing pad when the wafer is transferred to the second polishing pad. j | 3. The method according to item 1 of the patent application range, wherein the above-mentioned hard polishing pad j during grinding includes at least the following conditions, the polishing slurry injection flow rate is about 120-180 seem, and the pH value is controlled at 2-3, The angular velocities carried by the polishing pad and wafer are 113-115 RPM and 111-115 RPM, respectively, and the load is about 5. I 0-5. 5 pounds. I | 4. The method according to item 1 of the scope of patent application, wherein the above-mentioned soft polishing pad | during grinding, at least include the following conditions, the injection flow of the polishing slurry is about j 100-120 seem, and the pH value is controlled at 2-3, The angular | velocity carried by the polishing pad and wafer are 113-115 RPM and 111-115 RPM, respectively, and the load is about 4. I 5-5.0. Page 14 455525 6. Scope of patent application ^ ~ —— I 5 · If the method of the scope of patent application is the first item, it will make the above-mentioned town metal layer system | the wires and interconnects formed on the interconnect dielectric layer Plugs in the dielectric layer. I i 6. The method according to item 5 of the scope of patent application, further comprising transferring the wafer polished into a second polishing pad to a third polishing pad, so as to interconnect the wafer with the i under the tungsten metal layer. The electrical layer is partially removed so that it belongs to the surrounding k interconnect dielectric layer. 7. —A method for improving the output of the chemical / mechanical polishing process of tungsten metal plugs on the wafer and increasing the service life of the polishing pad, the method includes at least the following steps:, a crystal containing a crane metal layer on the upper surface The circle is loaded on the first polishing pad. The first polishing pad is a hard polishing pad 'wherein the polishing slurry injection flow rate is about 120-180 seem' The pH value is controlled at 2-3, and the angular velocity carried by the polishing pad and the wafer are 1 1 3-11 5 RPM and 1 11-1 1 5 rpm for chemical / mechanical | polishing process; and I transfer the wafer to a second polishing pad, which is a soft grinding | The slurry injection flow is about 0 0 ~ 1 2 0 sccm, the P face is controlled at 2-3, and the angular velocities carried by the polishing pad and wafer are 113-U5 RPM and 111-115 RPM, respectively, to remove the remaining town layers to Up to the set removal amount. 8 _ The method according to item 7 of the scope of patent application further includes performing a regeneration process on the first polishing pad when the wafer is transferred to the second polishing pad. Page 15 455525 I. Application scope of patent ί 9. The method according to item 7 of the scope of patent application, in which the above-mentioned hard polishing pad I is about 5.0 to 5-5 pieces when grinding. j 1 0. The method according to item 7 of the scope of patent application, wherein the above-mentioned hard grinding I pad grinding removes at least about 60 angstroms of tungsten (r ughnessamp 1 amplitude) before transferring to soft grinding pad. i 11. The method according to item 7 of the scope of patent application, wherein the above-mentioned soft grinding | loading of the pad is about 4.5 to 5.0 pieces. Page 16