阅读说明：本技术 金属栓塞的形成方法 (Method for forming metal plug ) 是由 不公告发明人 于 2018-06-28 设计创作，主要内容包括：本发明提供一种金属栓塞的形成方法,包括：提供一晶圆,包含基板和在基板上的绝缘层,绝缘层具有空洞；在绝缘层上形成金属层,金属层在空洞里面填充形成为金属栓塞；进行化学机械研磨的主研磨步骤和后研磨步骤,后研磨步骤中金属研磨速率小于主研磨步骤的金属研磨速率；在后研磨步骤之后,金属栓塞的顶面个别的露出于绝缘层在后研磨步骤后的上表面。本发明可在提高金属层研磨效率的同时,有效改善凹陷缺陷,提高产品成品率。(The invention provides a method for forming a metal plug, which comprises the following steps: providing a wafer, wherein the wafer comprises a substrate and an insulating layer on the substrate, and the insulating layer is provided with a cavity; forming a metal layer on the insulating layer, wherein the metal layer is filled in the hollow hole to form a metal plug; a main grinding step and a post grinding step of chemical mechanical grinding are carried out, wherein the metal grinding rate in the post grinding step is less than that in the main grinding step; after the post-polishing step, the top surfaces of the metal plugs are respectively exposed on the upper surface of the insulating layer after the post-polishing step. The invention can improve the grinding efficiency of the metal layer, effectively improve the defect of the depression and improve the yield of products.)

1. A method for forming a metal plug, comprising: providing a wafer, wherein the wafer comprises a substrate and an insulating layer on the substrate, and the insulating layer is provided with a cavity; forming a metal layer on the insulating layer, wherein the metal layer is filled in the hollow hole to form a metal plug; a main polishing step and a post polishing step of performing chemical mechanical polishing, polishing the metal layer on the insulating layer, and supplying a first polishing slurry including a first metal polishing accelerator while polishing the metal layer in the main polishing step; when the thickness of the metal layer removed by the grinding in the main grinding step is 60% or more of the total metal layer thickness of the metal layer on the insulating layer, performing the post-grinding step of grinding the remaining metal layer and part of the insulating layer until the part of the metal layer on the insulating layer is completely removed, and supplying a second grinding slurry including a second metal grinding accelerator while grinding the metal layer in the post-grinding step; the second grinding slurry has a composition ratio different from that of the first grinding slurry, so that the metal grinding rate in the post-grinding step is less than that in the main grinding step; after the post-polishing step, top surfaces of the metal plugs are respectively exposed on the upper surfaces of the insulating layers after the post-polishing step.

2. The forming method according to claim 1, wherein in the main polishing step, when the thickness of the metal layer removed by polishing reaches 70% to 90% of the total thickness of the metal layer on the insulating layer, the post-polishing step is performed.

3. The method of claim 2, wherein the material of the metal layer comprises tungsten metal.

4. The method of forming as claimed in claim 1, wherein the respective flow rates of the first and second abrasive slurries are between 80 ml/min and 120 ml/min.

5. The method as claimed in claim 1, wherein the metal polishing accelerator comprises hydrogen peroxide in a proportion of 3 wt% to 8 wt% based on the weight of the first polishing slurry, and the metal polishing accelerator comprises hydrogen peroxide in a proportion of 0.5 wt% to 1.5 wt% based on the weight of the second polishing slurry.

6. The method according to claim 1, wherein the second polishing slurry is made of the same composition but different composition from the first polishing slurry, and the post-polishing step is performed without any transfer by introducing the second polishing slurry into the same polishing platen in the main polishing step and discharging the first polishing slurry.

7. The method according to claim 6, wherein the first abrasive slurry and the second abrasive slurry each comprise titanium oxide particles having an average particle diameter of 15 nm to 50 nm.

8. The method according to claim 1, wherein the polishing environment of the first polishing slurry and the second polishing slurry is controlled to a pH value ranging from 1 to 4.

9. The forming method according to claim 1, wherein the metal polishing rate in the post-polishing step is 70nm/min to 100nm/min, and the metal polishing rate in the main-polishing step is 90nm/min to 130 nm/min.

10. The method as claimed in any one of claims 1 to 9, wherein a top surface of the metal plug is recessed within a depth of 100nm of an upper surface of the insulating layer after the post-polishing step.

Technical Field

The present invention relates to the field of semiconductor manufacturing, and more particularly to the field of semiconductor integrated circuits, and more particularly to a method for forming a metal plug.

Background

As the integration of integrated circuits in semiconductor manufacturing increases, the wafer surface does not provide sufficient area to fabricate the desired interconnects. In response to the increased interconnection requirements of scaled mos transistors, the fabrication of multilevel interconnects is becoming a necessary approach for many integrated circuits. The dual damascene technology and the intermetal dielectric layer made of low-k material are the most popular metal interconnect process combination, especially for the high integration, high-speed logic integrated circuit chip manufacturing and deep sub-micron semiconductor process below 0.18 micron, the dual damascene interconnect technology is becoming more and more important in the integrated circuit process and will become the standard interconnect technology in the next generation of semiconductor process.

In the current multilevel interconnect fabrication, the metal plug with higher integration and better step coverage by CVD (chemical vapor deposition) is widely used in the fabrication of the contact plug and via plug for multilevel metallization. For example, a metal plug is used to electrically connect the upper aluminum metal pad and the lower copper dual damascene interconnect to form a complete circuit in series.

In the conventional method, when manufacturing the metal plug, a barrier layer is first formed on the inner surface of the via hole or the plug hole in the dielectric layer, and then the metal is filled into the via hole or the plug hole by chemical vapor deposition to form the metal plug, generally using a titanium/titanium nitride composite layer as the material of the barrier layer. However, since the aforementioned dual damascene process is becoming popular as a metal interconnect, copper with high diffusion capability is filled in the dual damascene structure connected below the metal plug, and tantalum nitride is commonly used as a barrier layer material in the semiconductor industry to ensure better adhesion of the metal to be filled subsequently. After the TaN layer, a metal layer with a thickness of about 300-1500A is deposited on the TaN layer by sputtering to facilitate the growth of the metal deposited by the subsequent CVD method. Then, filling about 2500 to 4000 angstroms of metal into the via hole or plug hole by chemical vapor deposition. Finally, a Chemical Mechanical Polishing (CMP) process is performed to polish the top surface of the metal to be approximately aligned with the surface of the dielectric layer, thereby completing the manufacture of the metal plug.

The CMP process is a polishing method for planarizing a wafer surface by using a polishing pad and a polishing slurry in the manufacture of a semiconductor, and is a mechanical and chemical polishing process for a wafer by dropping a slurry composition onto a polyurethane polishing pad to bring the slurry composition into contact with the wafer and then performing an orbital motion combining a rotational motion and a linear motion.

In the CMP process, the polishing slurry generally contains an abrasive for physical polishing and a polishing accelerator for chemical polishing, such as an etchant or an oxidizing agent, and selectively etches the protruding portions on the wafer surface by a physicochemical method to provide a flat surface.

CMP polishing slurry is classified into slurry for polishing an insulating layer suitable for an ILD (inter-layer dielectric) process and an STI (shallow trench isolation) process in a semiconductor process and slurry for polishing a metal used for a connection point of a tungsten, aluminum or copper wiring and a contact/via plug formation or a dual damascene process, depending on an object to be polished.

The CMP process uses a slurry containing an oxidizing agent, and usually uses a slurry containing an abrasive such as silica or alumina fine particles, and a strong oxidizing agent such as a hydrogen peroxide solution or an iron nitrate. The oxidizing agent in the slurry oxidizes the metal surface to produce metal oxide, which is much weaker than the metal and can be easily removed with an abrasive. In the CMP process, the metal oxide layer is removed by the abrasive in the slurry and mechanical polishing of the CMP pad, the underlying metal is changed into metal oxide by the oxidizing agent and then continuously removed, and this process is repeated to remove the metal layer. Furthermore, the metal barrier film is also removed by a mechanism similar to metal layer polishing.

The CMP process is repeated with the abrasive particles removing the oxide formed by the oxidizing agent. Therefore, in order to increase the polishing rate, the slurry is designed in view of accelerating the oxidation process and smoothly removing the formed oxide.

However, as the etching rate increases, portions where the wiring layer needs to be formed in order to etch the electrical characteristics of the device such as pits and contact portions are also etched, which in turn decreases the reliability and yield of the device.

The metal polishing slurry requires a polishing rate difference between the metal layer and the insulating layer, that is, a high polishing rate is required for the metal wiring, and a low polishing rate is required for the insulating layer. This is because, when the difference in the polishing rate is small, the polishing rate is partially increased only in a portion where the pattern density is high, and thus, a defect such as erosion occurs in a portion where the pattern density is high. Therefore, it is necessary to reduce the polishing rate of the insulating layer to prevent a partial increase in the polishing rate.

However, there are problems as follows: since the filled metal is ductile, H must be added₂O₂To assist oxidation and facilitate removal. Therefore, the property of metal CMP is chemical reaction, in which the polishing rate of metal is deeply influenced by H in the polishing liquid₂O₂The concentration is influenced by the chemical reaction. H₂O₂Lower concentration the lower the metal polishing rate, H₂O₂The higher the concentration, the higher the polishing rate of the metal, however, such a polishing rate causes a more serious recess depth of the metal wire terminal portion by the end stage of polishing, resulting in a high wire resistance and even a defect of serious metal oxide on the surface of the metal wire terminal.

Patent publication No. CN103228756A discloses a CMP slurry composition for metal polishing involving an abrasive comprising colloidal silica dispersed in ultrapure water and a polishing accelerator comprising a hydrogen peroxide solution, ammonium persulfate and ferric nitrate, which is free from the problem of slurry discoloration, excellent in etching selectivity and applicable to CMP process, and an unsatisfactory improvement effect because metal oxides cannot be effectively removed due to a great influence of the concentration of an oxidizing agent.

The patent publication (publication: CN104066807A) discloses a polishing slurry for metal polishing process and a polishing method using the same. The slurry comprises: an abrasive for grinding, the abrasive comprising titanium oxide particles, and an oxidation promoter for promoting oxide formation. The method is complex to operate and is not beneficial to large-scale popularization.

In order to avoid the dishing defect and the high resistance of the conductive line, a method for forming a metal plug capable of avoiding the dishing defect is developed.

Disclosure of Invention

The invention aims to provide a method for forming a metal plug, which can improve the metal recess defect while increasing the grinding rate and improving the wafer output. In order to achieve the technical purpose, the invention adopts the specific technical scheme that:

a method for forming a metal plug includes: providing a wafer, wherein the wafer comprises a substrate and an insulating layer on the substrate, and the insulating layer is provided with a cavity; forming a metal layer on the insulating layer, wherein the metal layer is filled in the hollow hole to form a metal plug; a main polishing step and a post polishing step of performing chemical mechanical polishing, polishing the metal layer on the insulating layer, and supplying a first polishing slurry including a first metal polishing accelerator while polishing the metal layer in the main polishing step; when the thickness of the metal layer removed by the grinding in the main grinding step is 60% or more of the total metal layer thickness of the metal layer on the insulating layer, performing the post-grinding step of grinding the remaining metal layer and part of the insulating layer until the part of the metal layer on the insulating layer is completely removed, and supplying a second grinding slurry including a second metal grinding accelerator while grinding the metal layer in the post-grinding step; the second grinding slurry has a composition ratio different from that of the first grinding slurry, so that the metal grinding rate in the post-grinding step is less than that in the main grinding step; after the post-polishing step, top surfaces of the metal plugs are respectively exposed on the upper surfaces of the insulating layers after the post-polishing step.

As an improved technical scheme, in the main grinding step, when the thickness of the metal layer removed by grinding reaches 70% -90% of the total thickness of the metal layer on the insulating layer, the post-grinding step is carried out.

As an improved technical scheme, the material of the metal layer comprises tungsten metal.

As a modified technical scheme, the individual flow rates of the first grinding slurry and the second grinding slurry are between 80 ml/min and 120 ml/min.

As an improved technical solution, the first metal polishing accelerator includes hydrogen peroxide, and accounts for 3 wt% to 8 wt% of the first polishing slurry, and the second metal polishing accelerator includes hydrogen peroxide, and accounts for 0.5 wt% to 1.5 wt% of the second polishing slurry.

As an improved technical solution, the second polishing slurry has the same components but different proportions from the first polishing slurry, so that the second polishing slurry and the first polishing slurry are mutually soluble, the second polishing slurry is introduced into the same polishing disk in the main polishing step, the first polishing slurry is discharged, and the post-polishing step is performed in a non-transferring manner.

As an improved technical scheme, the first grinding slurry and the second grinding slurry both comprise titanium oxide particles, and the average particle size of the titanium oxide particles is 15-50 nanometers.

As an improved technical scheme, the grinding environment of the first grinding slurry and the second grinding slurry is controlled within the pH value range of 1-4.

As an improved technical scheme, the metal grinding speed in the post-grinding step is 70 nm/min-100 nm/min, and the metal grinding speed in the main grinding step is 90 nm/min-130 nm/min.

As an improved technical solution, the depth of the top surface of the metal plug recessed in the upper surface of the insulating layer after the post-polishing step is within 100 nm.

Advantageous effects

The forming method of the metal embolism provided by the invention comprises the following steps of firstly, carrying out a main grinding step, supplying first grinding slurry while grinding, wherein the first grinding slurry comprises a first metal grinding accelerator, and stopping main grinding when the thickness of a metal layer removed by grinding reaches more than 60% of the total thickness of the metal layer on an insulating layer; and performing a post-grinding step, grinding the residual metal layer until the metal layer is completely removed, and supplying a second grinding slurry while grinding, wherein the second grinding slurry comprises a second metal grinding accelerator. The metal layer polishing method has the advantages that the first grinding slurry with high metal polishing selection ratio is given to the metal layer in the initial grinding stage, high mass production efficiency is provided, the second grinding slurry with low metal polishing selection ratio is given to the metal layer in the later grinding stage, the end part of a metal wire is prevented from being seriously sunken, low wire resistance is maintained, and the metal grinding speed in the later grinding step is smaller than that in the main grinding step, so that the sunken defect is effectively improved while the metal layer grinding efficiency is improved, and the product yield is improved.

Drawings

FIG. 1 is a schematic diagram illustrating the operation of polishing a metal layer.

FIG. 2 is a graph showing the relationship between the concentration of hydrogen peroxide in the polishing slurry and the polishing rate when different materials are polished.

FIG. 3 is a graph showing the relationship between the hydrogen peroxide concentration and the metal polishing rate in the polishing slurry under different polishing pressures.

FIG. 4 is a cross-sectional view of a wafer without filling metal plugs and metal layers according to an embodiment of the present invention.

FIG. 5 is a cross-sectional view of a wafer filled with metal plugs and metal layers according to an embodiment of the present invention.

FIG. 6 is a cross-sectional view of a metal plug formed by a conventional method.

FIG. 7 is a schematic cross-sectional view of a wafer after a metal layer is polished by a main polishing step according to the present invention.

FIG. 8 is a schematic cross-sectional view of a metal plug formed by the method of the present invention.

FIG. 9 is a schematic view of an apparatus corresponding to the main polishing step in the embodiment of the present invention.

FIG. 10 is a schematic view of an apparatus corresponding to the post-polishing step in the embodiment of the present invention.

In the figure, 1, wafer; 2. a metal plug; 3. a metal oxide layer; 4. a polishing pad; 5. a metal layer polishing rate curve; 6. an insulating layer polishing rate profile; 7. metal layer polishing rate profile at 4psi polishing pressure; 8. metal layer polishing rate profile at 3psi polishing pressure; 9. an insulating layer; 10. a barrier layer; 11. a grinding platform; 12. a first abrasive slurry; 13. a substrate; 14. a metal layer; 15. a void; 16. and a second abrasive slurry.

Detailed Description

In order to make the purpose and technical solutions of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without any inventive step, are within the scope of protection of the invention.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

As shown in fig. 1, the conventional CMP process includes: the surface of the semiconductor wafer 1 is brought into contact with a polishing pad 4, polished while the polishing pad 4 is rotated, and the surface of the wafer 1 is planarized by using a slurry containing an abrasive and a plurality of compounds. Because of the ductility of the metal, an oxidizing agent (e.g., H) is added to the polishing slurry during polishing of the metal layer 14₂O₂) To assist the oxidation, a metal oxide layer 3 is formed to facilitate the removal. In the polishing process, the process of forming the metal oxide layer 3 by using the oxidizing agent and the metal layer 14 is repeated, and the formed metal oxide layer 3 is removed by using the polishing material.

Since the nature of metal CMP is a chemical reaction, the polishing rate of metal is strongly influenced by the chemical reaction caused by the concentration of the oxidizing agent in the polishing slurry. E.g. H in abrasive slurries₂O₂Lower concentration the lower the metal polishing rate, H₂O₂The higher the concentration, the higher the polishing rate of the metal, however, such a polishing rate causes more serious recess defect to the terminal portion of the metal wire by the end stage of polishing (FIG. 6), resulting in a high resistance of the wire even a defect of a serious metal oxide layer 3 on the surface of the terminal portion of the metal wireAnd (4) generating. As shown in fig. 2 and 3, when the hydrogen peroxide concentration in the polishing slurry is different, the polishing rate of the metal layer 14 shows a sharp change (as shown in the metal layer polishing rate curve 5 in fig. 2), but the polishing rate of the metal oxide layer 3 does not change much (as shown in the insulating layer polishing rate curve 6 in fig. 2), at a 3psi polishing pressure, the polishing rate of the metal layer 14 increases with increasing hydrogen peroxide concentration in the polishing slurry (as shown by metal layer polishing rate curve 8 at 3psi polishing pressure in FIG. 3), at a 4psi polishing pressure, the polishing rate of the metal layer 14 increases with increasing hydrogen peroxide concentration in the polishing slurry (as shown by metal layer polishing rate curve 7 at 4psi polishing pressure in FIG. 3), the polishing rate rise slope of the metal layer 14 at 4psi polishing pressure is slightly higher than the polishing rate rise slope of the metal layer 14 at 3psi polishing pressure. The inventor of the present application finds that if the concentration of the oxidizing agent in the polishing slurry is low, the polishing slurry has the advantage of being less prone to causing a dishing phenomenon after polishing; however, the disadvantage is that the grinding time is long, which directly increases the probability of scratching defects and increases the production cost.

In order to solve the problem of the recess defect after metal grinding, the invention provides a method for forming a metal plug 2, which comprises the following steps: as shown in fig. 4 and 5, a wafer 1 is provided, which includes a substrate 13 and an insulating layer 9 on the substrate 13, wherein the insulating layer 9 has a cavity 15; a metal layer 14 is formed on the insulating layer 9, the metal layer 14 is filled in the cavity 15 to form a metal plug 2, the metal layer 14 is filled above the cavity 15 to form a metal layer 14, the metal layer 14 and the metal plug 2 contain the same metal, which may be tungsten metal, so that the cavity 15 is completely filled. In order to make the metal layer 14 and the metal plug 2 have good adhesion with the insulating layer 9, a titanium adhesive layer is formed on the surface of the substrate 13 before the metal layer 14 and the metal plug 2 are deposited, and a barrier layer 10 is further formed on the adhesive layer to block the metal layer 14 in order to prevent the bonding between the source material and the titanium having high reactivity when the metal layer 14 and the metal plug 2 are formed, wherein the barrier layer 10 may be titanium nitride; a main polishing step and a post polishing step of chemical mechanical polishing are performed to polish the metal layer 14 on the insulating layer 9.

As shown in fig. 7 and 9, the wafer 1 is placed on the polishing platen 11, the first polishing slurry 12 is supplied while the metal layer 14 is polished in the main polishing step, the first polishing slurry 12 includes a first metal polishing accelerator, the flow rate of the first polishing slurry 12 may be between 80 ml/min and 120 ml/min, the polishing environment of the first polishing slurry 12 may be controlled within a pH range of 1 to 4, the first polishing slurry 12 includes a first metal polishing accelerator, the weight ratio of the first metal polishing accelerator to the first polishing slurry 12 may be between 12% and 22%, the first metal polishing accelerator may include hydrogen peroxide, and the weight ratio of the hydrogen peroxide to the first polishing slurry 12 is between 3% and 8% by weight. The first polishing slurry 12, which gives a high metal polish selectivity to the metal layer 14 in the main polishing step, improves the polishing efficiency, providing high mass production efficiency.

When the thickness of the metal layer 14 removed by the grinding in the main grinding step is more than 60% of the total thickness of the metal layer 14 on the insulating layer 9, preferably, when the thickness of the metal layer 14 removed by the grinding is more than 70% to 90% of the total thickness of the metal layer, the main grinding step is stopped, as shown in fig. 10, the post-grinding step is performed, the wafer 1 is placed on the grinding platform 11, the residual metal layer 14 and part of the insulating layer 9 are ground until the part of the metal layer 14 on the insulating layer 9 is completely removed, the second grinding slurry 16 is supplied while the metal layer 14 is ground in the post-grinding step, the second grinding slurry 16 includes a second metal grinding accelerator, the grinding environment of the second grinding slurry 16 can be controlled within a pH range of 1 to 4, and the flow rate of the second grinding slurry 16 can be 80 ml/min to 120 ml/min, the weight ratio of the second metal grinding accelerator to the second grinding slurry 16 can be between 2% and 5%, the second metal grinding accelerator can contain hydrogen peroxide, and the weight ratio of the hydrogen peroxide to the second grinding slurry 16 is between 0.5% and 1.5%; the second polishing slurry 16 has a composition ratio different from that of the first polishing slurry 12 so that the metal polishing rate in the post-polishing step is smaller than that in the main polishing step; after the post-polishing step, as shown in fig. 8, in the metal plug 2 formed in the present embodiment, the top surface of the metal plug 2 is respectively exposed on the upper surface of the insulating layer 9 after the post-polishing step, and preferably, the depth of the top surface of the metal plug 2 recessed in the upper surface of the insulating layer 9 after the post-polishing step is within 100 nm. Preferably, the second polishing slurry 16 has the same composition but different mixture ratio as the first polishing slurry 12, the second polishing slurry 16 is mutually soluble with the first polishing slurry 12, the second polishing slurry 16 is introduced into the same polishing disc in the main polishing step, the first polishing slurry 12 is discharged, the post-polishing step is performed in a non-transfer manner, the second polishing slurry 16 with low metal polishing selectivity is given to the metal layer 14 in the post-polishing step, so that the end of the metal wire is prevented from being seriously recessed, the resistance of the metal wire is maintained to be low, and the generation of defects is prevented.

In the grinding process, the metal grinding speed in the post-grinding step can be 70 nm/min-100 nm/min (nanometer/min), the metal grinding speed in the main grinding step can be 90 nm/min-130 nm/min, and the metal grinding speed in the post-grinding step is smaller than that in the main grinding step, so that the grinding efficiency of the metal layer 14 can be improved, the recess defect can be effectively improved, and the product yield can be improved.

The first polishing slurry 12 and the second polishing slurry 16 may contain titanium oxide particles, the average particle diameter of the titanium oxide particles may be 15 nm to 50 nm, the weight ratio of the titanium oxide particles to the first polishing slurry 12 may be 0.2% to 10%, and the weight ratio of the titanium oxide particles to the second polishing slurry 16 may be 0.2% to 10%, and in the above range, the metal polishing effect is more excellent. The first metal grinding accelerator and the second metal grinding accelerator can also contain ammonium persulfate, the weight ratio of the ammonium persulfate to the first metal grinding accelerator or the second metal grinding accelerator can be 0.005-0.01 wt%, the first metal grinding accelerator and the second metal grinding accelerator can also contain ferric nitrate, and the weight ratio of the ferric nitrate to the first metal grinding accelerator or the second metal grinding accelerator can be 0.005-0.01 wt%, so that better grinding effect can be achieved.

The above are merely embodiments of the present invention, which are described in detail and with particularity, and therefore should not be construed as limiting the scope of the invention. It should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the spirit of the present invention, and these changes and modifications are within the scope of the present invention.