阅读说明：本技术 一种监控钨cmp工艺出现的晶边钨残留的方法 (Method for monitoring tungsten residues on edge of wafer in tungsten CMP process ) 是由 陶仁峰 李协吉 李儒兴 于 2021-07-30 设计创作，主要内容包括：本发明提供一种监控钨CMP工艺出现的晶圆边缘钨残留的方法,包括以下步骤：提供检测晶圆,在检测晶圆的表面形成氧化物膜层,氧化物膜层覆盖中心区域和边缘区域的表面；对氧化物膜层执行钨CMP工艺,并测试晶圆边缘区域处对氧化物膜层的研磨速率；以及根据检测晶圆边缘氧化层研磨速率来监控钨CMP机台的状态,据此判断产品晶圆是否会在边缘区域存在大量的钨残留。本发明通过上述步骤可以通过在线监控氧化物膜层的研磨速率来替代在线监控钨膜层的研磨速率来监控钨CMP工艺出现的晶边钨残留状况,实现提前预防由于钨残留导致钝化层蚀刻制程出现金属线容易被电流击穿并焦化的问题以及电性测试时出现的“烧针”现象造成的晶圆报废和测试设备的损伤。(The invention provides a method for monitoring tungsten residues on the edge of a wafer in a tungsten CMP process, which comprises the following steps: providing a detection wafer, and forming an oxide film layer on the surface of the detection wafer, wherein the oxide film layer covers the surfaces of the central area and the edge area; performing a tungsten CMP process on the oxide film layer, and testing the grinding rate of the edge area of the wafer on the oxide film layer; and monitoring the state of the tungsten CMP machine according to the grinding rate of the oxide layer at the edge of the detected wafer, and accordingly judging whether the product wafer has a large amount of tungsten residues in the edge area. According to the invention, the situation of the grain-side tungsten residue in the tungsten CMP process can be monitored by monitoring the grinding rate of the oxide film layer on line instead of monitoring the grinding rate of the tungsten film layer on line through the steps, so that the problems that a metal wire is easy to be broken down and coked by current in a passivation layer etching process caused by tungsten residue and wafer scrap and damage of test equipment caused by a needle burning phenomenon during an electrical test are prevented in advance.)

1. A method for monitoring edge tungsten residues generated in a tungsten CMP process is characterized by comprising the following steps:

providing a detection wafer, and depositing an oxide film layer on the surface of the detection wafer, wherein the oxide film layer covers the center of the detection wafer and the surface of the edge area;

performing a tungsten CMP process on the oxide film layer, and testing the grinding rate of the edge area of the wafer on the oxide film layer; and

the state of the tungsten CMP machine is monitored according to the grinding rate of the oxide layer at the edge of the detected wafer, and whether a large amount of tungsten residues exist in the edge area of the product wafer is judged according to the state.

2. The method of claim 1, wherein providing a test wafer, forming an oxide film on a surface of the test wafer, the oxide film uniformly covering a surface of a center region and a surface of an edge region of the test wafer, comprises:

providing the detection wafer, wherein the surface of the detection wafer is a plane;

and forming an oxide film layer on the surface of the detection wafer, wherein the oxide film layer is distributed at each position of the detection wafer in a uniform thickness.

3. The method of claim 2, wherein the inspection wafer is a blank wafer.

4. The method of claim 2, wherein the edge region comprises a region 90mm to 99mm from a center point of the inspection wafer.

5. The method of claim 2, wherein the thickness of the oxide film layer is not less than

6. The method of claim 1, wherein performing a chemical mechanical polishing process on an oxide film layer of the test wafer and monitoring a polishing rate of the oxide film layer at an edge region of the test wafer comprises:

and carrying out a chemical mechanical polishing process on the oxide film layer of the detection wafer, and testing the grinding rate of the detection wafer and the area with the distance of 90-99 mm from the center of the detection wafer.

7. The method of claim 6, wherein the chemical mechanical polishing process is performed on the oxide film layer of the test wafer with different mechanical forces, and the polishing rate of the test wafer is monitored in a region 90mm to 99mm away from the center of the test wafer.

8. The method of claim 1, wherein monitoring the state of the tungsten CMP tool based on detecting the polishing rate of the oxide layer on the edge of the wafer to determine whether a product wafer has a large amount of tungsten residue in the edge region comprises:

obtaining a final grinding pressure interval and optimizing a grinding process according to the grinding rate of the oxide film and the tungsten residue condition of the edge of the wafer;

after the grinding process is optimized, the state of a tungsten CMP machine is monitored according to the grinding rate of the oxide film layer on the edge of the detected wafer, and whether a great amount of tungsten residues exist in the wafer edge area of a product wafer of the CMP machine for executing the CMP process is judged according to the state.

Technical Field

The invention relates to the field of semiconductor manufacturing, in particular to a method for monitoring tungsten residues on a crystal edge in a tungsten CMP (chemical mechanical polishing) process.

Background

The lapping process of Chemical Mechanical Polishing (CMP) is a combined result of chemical action and mechanical action, wherein the chemical action is mainly provided by a lapping Slurry (Slurry); the mechanical action is related to the pressure applied by the tool to the polishing head, the relative motion of Wafer and polishing platen, and the polishing particles in the Slurry. The Wafer has a Wafer Edge Exposure (WEE) region and an Edge clearance (EBR) region in its Edge region. The WEE area and the EBR area are in a pattern similar to a concave shape relative to the central area of the wafer, so that the mechanical strength of the WEE area and the EBR area in the CMP process is relatively weak, the actual polishing rate is relatively low, and tungsten residues are likely to appear on the wafer edge after the tungsten CMP process is completed (as shown in fig. 1 a).

Tungsten CMP processes were performed using a Mirra _ Ontrak (or Mirra _ Mesa) tool from AMAT and a F × REX200 tool from EBARA, respectively. The conventional tungsten CMP generally uses a blank wafer deposited with a tungsten thin film to test the polishing rate and polishing uniformity of a polishing machine, and for a 200mm tungsten CMP process, the coordinate of the polishing rate test is in a range from-95 mm to 95mm along the diameter direction (21pts linescan). In the test subjects of this patent, the average polishing rate of Mirra _ Ontrak was comparable to that of F × REX200 stations, the tungsten polishing rate at 95mm position of the Mirra _ Ontrak station was 3100A/min, and the polishing rate at 95mm position of the F × REX200 station was 2900A/min, slightly lower than the former. However, in fact, the product wafer has no tungsten residue on the edge after the F × REX200 station is used for tungsten CMP, and instead, the Mirra _ Ontrak station has severe tungsten residue on the edge after the tungsten CMP process. This indicates that the conventional polishing rate test method cannot characterize the tungsten residue at the edge of the product wafer. This is because the WEE and EBR of the product are generally beyond 97mm, and when depositing a metal (e.g. tungsten) film, the thickness of the metal film beyond 97mm (i.e. beyond 97mm from the center point of the wafer) of the conventional blank wafer for tungsten CMP polishing rate test is very thin, and the polishing rate at the edge of the wafer is stronger by the chemical action of the polishing slurry, so that the metal film at the edge is completely removed when testing the polishing rate. Direct testing of the wafer's tungsten polishing rate beyond 97mm of edge is therefore not feasible and of limited utility, and conventional 95mm polishing rate monitoring has little reference to polishing rates beyond 97mm of edge of the wafer.

The tungsten residue causes the subsequent etching process of the passivation layer to have the problem that the metal line is easily broken down and coked by the current (as shown in fig. 1 b) and the "needle burning" phenomenon occurs during the electrical test (e.g., Cp test).

Disclosure of Invention

The invention aims to provide a method for monitoring the tungsten residue on the edge of a tungsten CMP (chemical mechanical polishing) process, which can effectively monitor the condition of a tungsten CMP machine table during daily machine testing, and avoid continuous operation when the machine table is in a deteriorated or unqualified state so as to avoid a large amount of tungsten residue on the edge of a product wafer, so as to avoid the phenomena that a metal wire is easily broken down and coked by current and a needle is burnt during an etching process of a passivation layer.

In order to solve the above problems, the present invention provides a method for monitoring the edge-of-wafer tungsten residue in a tungsten CMP process, comprising the following steps:

providing a detection wafer, and forming an oxide film layer on the surface of the detection wafer, wherein the oxide film layer covers the surface of the central area and the surface of the edge area of the detection wafer;

performing a chemical mechanical polishing process on the oxide film layer of the detection wafer, and monitoring the grinding rate of the oxide film layer at the edge area of the detection wafer; and

the state of the tungsten CMP machine is monitored according to the grinding rate of the oxide layer at the edge of the detected wafer, and whether a large amount of tungsten residues exist in the edge area of the product wafer is judged according to the state.

Optionally, the oxide film layer uniformly covers the surface of the central region and the surface of the edge region of the detection wafer.

Providing the detection wafer, wherein the surface of the detection wafer is a plane;

further, the detection wafer is a blank wafer.

Further, the edge area comprises an area which is 90mm-99mm away from the center point of the detection wafer.

And depositing an oxide film layer on the surface of the detection wafer, wherein the oxide film layer is distributed at each position of the detection wafer in a uniform thickness.

Further, the thickness of the oxide film layer is not less than

Optionally, performing a chemical mechanical polishing process on the oxide film layer of the detection wafer, and monitoring a grinding rate of the oxide film layer at the edge region of the detection wafer, including:

and performing a chemical mechanical polishing process on the oxide film layer of the detection wafer, and monitoring the grinding rate of the detection wafer and the area with the distance of 90-99 mm from the center of the detection wafer.

Further, a chemical mechanical polishing process is carried out on the oxide film layer of the detection wafer by different mechanical acting forces, and the grinding rate of the region with the distance of 90mm-99mm between the center of the detection wafer and the center of the detection wafer is monitored on line.

Optionally, monitoring the state of the tungsten CMP machine according to the detected polishing rate of the edge oxide layer of the wafer, and accordingly determining whether the product wafer has a large amount of tungsten residues in the edge area, the method includes:

obtaining a final grinding pressure interval and optimizing a grinding process according to the grinding rate of the oxide film and the tungsten residue condition of the edge of the wafer;

after the grinding process is optimized, the state of a tungsten CMP machine is monitored according to the grinding rate of the oxide film layer on the edge of the detected wafer, and whether a great amount of tungsten residues exist in the wafer edge area of a product wafer of the CMP machine for executing the CMP process is judged according to the state.

Compared with the prior art, the invention has the following effective effects:

the invention provides a method for monitoring tungsten residues on a crystal edge in a CMP (chemical mechanical polishing) process, which comprises the following steps of: providing a detection wafer, and forming an oxide film layer on the surface of the detection wafer, wherein the oxide film layer covers the surface of the central area and the surface of the edge area of the detection wafer; performing a chemical mechanical polishing process on the oxide film layer of the detection wafer, and testing the grinding rate of the edge area of the detection wafer on the oxide film layer; the state of the tungsten CMP machine is monitored according to the grinding rate of the oxide layer at the edge of the detected wafer, and whether a large amount of tungsten residues exist in the edge area of the product wafer is judged according to the state. According to the invention, the situation of the tungsten residue on the edge of the wafer in the tungsten CMP process can be monitored by monitoring the polishing rate of the oxide film instead of monitoring the polishing rate of the tungsten film through the steps, so that the problems that metal wires are easy to be broken down and coked by current in a passivation layer etching process caused by the tungsten residue and wafer scrap and damage of test equipment caused by the needle burning phenomenon during an electrical test (such as Cptest) are prevented in advance.

Drawings

FIG. 1a is a schematic diagram of tungsten residues occurring at a wafer edge in a conventional tungsten CMP process;

FIG. 1b shows a phenomenon that a metal line is easily broken down by current and coked when a passivation layer is etched due to tungsten residues on a crystal edge in tungsten CMP;

FIG. 2 is a flowchart illustrating a method for monitoring edge tungsten residues in a tungsten CMP process according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of a mirra machine according to an embodiment of the invention;

FIG. 4 is a linear graph illustrating the polishing rate of the same test wafer under different mechanical forces according to one embodiment of the present invention;

FIG. 5 is a diagram illustrating a tungsten residue situation according to an embodiment of the present invention.

Detailed Description

As described in the background, the WEE tool (including other tools with similar polishing head structures) is prone to have more serious tungsten residue in the WEE region and the EBR region of the wafer edge (i.e., the wafer edge) when used in a metal CMP (e.g., tungsten CMP) process, which results in the problem that metal lines are prone to be broken down and charred by current in the subsequent passivation layer etching process and the "needle burning" phenomenon in the electrical test (e.g., Cp test). However, in the current industry, the tungsten film layer is formed on the blank wafer for monitoring the polishing rate of tungsten CMP, and the tungsten film layer is subjected to a CMP process, which cannot effectively determine the performance of the wafer edge at 99mm by Offline Monitor; and Defect Scan or metal thickness measurement on the line cannot effectively characterize the problem; and the manual inspection mode can not be used for mass production.

In order to solve the above problems, the present invention provides a method for monitoring the edge-of-wafer tungsten residue in a tungsten CMP process, in which an oxide film layer is used to replace a tungsten film layer to indirectly test the polishing rate of a metal CMP process in a 90mm-99mm region, the widths of the tungsten residue in a WEE region and an EBR region of the wafer edge of an on-line product can be effectively characterized, and the problems that the metal line is easily broken down and coked by current in a passivation layer etching process due to the tungsten residue and wafer scrap and damage of test equipment due to a "needle burning" phenomenon during an electrical test (e.g., Cp test) can be prevented in advance.

A method of monitoring the occurrence of edge-to-edge tungsten residues in a tungsten CMP process according to the present invention will be described in further detail below. The present invention will now be described in more detail with reference to the accompanying drawings, in which preferred embodiments of the invention are shown, it being understood that one skilled in the art may modify the invention herein described while still achieving the advantageous effects of the invention. Accordingly, the following description should be construed as broadly as possible to those skilled in the art and not as limiting the invention.

In the interest of clarity, not all features of an actual implementation are described. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific details must be set forth in order to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art.

In order to make the objects and features of the present invention more comprehensible, embodiments of the present invention are described in detail below with reference to the accompanying drawings. It is to be noted that the drawings are in a very simplified form and are all used in a non-precise ratio for the purpose of facilitating and distinctly aiding in the description of the embodiments of the invention.

Fig. 2 is a flowchart illustrating a method for monitoring edge tungsten residues in a tungsten CMP process according to this embodiment. As shown in fig. 2, the present embodiment provides a method for monitoring edge tungsten residues occurring in a tungsten CMP process, including the following steps:

step S1: providing a detection wafer, depositing an oxide film layer on the surface of the detection wafer, wherein the oxide film layer covers the center of the detection wafer and the surface of the edge area, and defining an edge measuring point according to the WEE or EBR design of a wafer factory, such as 97-99 mm;

step S2: performing a tungsten CMP process on the oxide film layer, and testing the grinding rate of the edge area of the wafer on the oxide film layer;

step S3: the state of the tungsten CMP machine is monitored according to the grinding rate of the oxide layer at the edge of the detected wafer, and whether a large amount of tungsten residues exist in the edge area of the product wafer is judged according to the state.

A method for monitoring the occurrence of the edge tungsten residue in the CMP process according to this embodiment is described in detail below with reference to fig. 2 to 5.

Step S1 is performed to provide a test wafer, and an oxide film is deposited on a surface of the test wafer, where the oxide film covers a center of the test wafer and a surface of the edge region.

The method comprises the following steps:

firstly, providing the detection wafer, wherein the detection wafer is a blank wafer for testing, only comprises a silicon substrate, does not form a device structure or forms a wafer with a pattern, and the surface of the wafer is a plane.

Then, forming an oxide film layer on the surface of the detection wafer, wherein the oxide film layer is distributed at each position of the detection wafer in uniform thickness, and the thickness of the oxide film layer is not less than that of the detection waferThe thickness of the oxide film layer used in the examples was aboutThe pre-polishing thickness is measured (multiple measurement points distributed along the diameter, e.g., -99mm-99mm, edge measurement points defined by the wafer fab's WEE or EBR design, e.g., 97-99 mm).

Then, in step S2, a tungsten CMP process is performed on the oxide film and the polishing rate of the oxide film at the edge area of the wafer is tested.

Firstly, carrying out a chemical mechanical polishing process on an oxide film layer of the detected wafer;

then, the thickness of the oxide film layer after the tungsten CMP process is measured, the measurement points correspond to the previous values one by one, and the polishing rate of each point, namely (the previous value-the next value)/the polishing time is calculated.

Specifically, a chemical mechanical polishing process is performed on the silicide film layer of the detection wafer, the thickness of the oxide film before and after grinding is measured, and the grinding rate of each position of the detection wafer is calculated, particularly the grinding rate of a region with a distance of 90mm-99mm between the center of the detection wafer and the center of the detection wafer.

In the polishing mechanism of CMP, since the polishing pad is an elastic pad, the polishing rate of the depression (edge region) of the wafer is related to the deformation of the polishing pad under pressure. In this embodiment, the F × REX200 machine of EBARA uses Guide Ring, the Ring (positioning Ring) has a surface height lower than the surface of the wafer during polishing, and does not directly act on the polishing pad to cause additional deformation, the pressure applied to the wafer by the polishing head is not offset by the deformation of the polishing pad, but the pressure applied to the polishing pad by the wafer causes the polishing pad to contact with the edge of the wafer more sufficiently, and the polishing rate is higher. The surface of the Retaining Ring (positioning Ring 1) of the Mirra machine is higher than the surface of the wafer, the deformation of the polishing pad caused by the applied pressure can cause the polishing pad to generate the separation effect with the edge of the wafer, the position of the deformation area can change along with the change of the Retaining pressure, and the effective pressure acting on the edge of the wafer is the superposition of the pressure applied by the polishing head and the deformation degree and position of the polishing pad. For the tungsten CMP process of the production wafer, the tungsten residue at the edge of the wafer depends more on whether the mechanical force of the polishing process can be effectively applied to the area. For the oxide film, the polishing rate is mainly determined by the mechanical action of polishing, so that the action size and position of the mechanical action can be reflected.

As shown in fig. 3, the mechanical pressure is changed by adjusting the pressure of the positioning ring 1, so as to affect the deformation degree and position of the polishing pad, and the change of the mechanical pressure has a significant effect on the polishing rate of the oxide film in the region where the distance between the center of the detection wafer and the center of the detection wafer is 90mm to 99mm, especially in the region where the distance between the center of the detection wafer and the center of the detection wafer is 95mm to 99mm, wherein the polishing rate at the position where the distance between the center of the detection wafer and the center of the detection wafer is 99mm is not increased along with the increase of the mechanical pressure.

FIG. 4 is a linear graph illustrating the polishing rates of the present embodiment under different mechanical forces. As shown in fig. 3, fig. 3 is a linear diagram illustrating the polishing rate of the same detected wafer under different mechanical forces when a CMP process is performed on a Mirra machine, where the horizontal axis is the distance (in mm) from the center point of the detected wafer, the vertical axis is the normalized polishing rate, and the curves (i) to (c) are the polishing rate curves of different mechanical forces on the detected wafer, where (i) the polishing rate curve under a mechanical pressure of 4.9PSI, (ii) the polishing rate curve under a mechanical pressure of 5.2PSI, (iii) the polishing rate curve under a mechanical pressure of 5.5PSI, (iv) the polishing rate curve under a mechanical pressure of 5.8PSI, (iv) the polishing rate curve under a mechanical pressure of 6.1PSI, (iv) the polishing rate curve under a mechanical pressure of 7.0PSI, and (iv) the polishing rate curve under a mechanical pressure of 7.8 PSI.

It should be noted that fig. 3 and 4 do not correspond one-to-one, and fig. 3 and 4 include different numbers of mechanical forces, but they do not affect the connection between step 2 and step 3.

Therefore, step S3 is executed, and step S3 is executed to monitor the state of the tungsten CMP machine according to the polishing rate of the edge oxide layer of the wafer, so as to determine whether the product wafer has a large amount of tungsten residue in the edge area.

Firstly, according to the polishing rates of the oxide film (such as the silicon dioxide film) obtained by different mechanical acting forces and different CMP machines and different consumable service times, and the tungsten residue condition of the edge area of the wafer in the tungsten CMP process, a final polishing pressure interval (namely an optimal polishing pressure interval) is obtained and a polishing program (namely the polishing process) is optimized, so that the overall level of the tungsten residue of the wafer of the tungsten CMP product is improved.

Then, after the overall level of the manufacturing process is optimized, the state of a tungsten CMP machine is monitored according to the polishing rate of the oxide layer at the edge of the detected wafer, and whether the product wafer has a large amount of risks of tungsten residues in the edge area of the wafer under the condition of the machine is judged according to the state.

In this example, the average of the polishing rates of the points at the edge (e.g., the average of the polishing rates of the points in the 97-99mm area) is subtracted from the average of the polishing rates of the points other than the edge point, and the difference between the polishing rates is divided by the average of the polishing rates of the points other than the edge point to obtain a percentage of rate deviation. When the deviation is within a certain range, we can determine that there is no risk of a large amount of tungsten remaining in the edge region of the wafer under the machine condition.

Fig. 5 is a schematic diagram of the mechanical force versus tungsten residual width. As shown in fig. 5, the horizontal axis of the graph is the mechanical force Retain ring pressure in PSI, the vertical axis is the tungsten residual width of the distance detection wafer in um, a 1-a 7 in the graph are ranges of the tungsten residual width under different mechanical forces, and a 11-a 71 are averages of the tungsten residual widths under different mechanical forces. In this embodiment, by obtaining online monitoring of a plurality of inspection wafers, a plurality of sets of data can be obtained, and these data are processed to obtain the tungsten residue width ranges corresponding to different mechanical forces, so as to obtain the optimal tungsten residue condition of the edge area of the production wafer in the tungsten CMP process. The mechanical pressure optimum pressure corresponding to the width of tungsten residue appearing in the edge area of the pattern wafer here differs from the experimental optimum pressure from the loading effect of the WEE and EBR areas, but the trend is consistent.

In summary, the present invention provides a method for monitoring edge tungsten residue in a CMP process, comprising the following steps: providing a detection wafer, and forming an oxide film layer on the surface of the detection wafer, wherein the oxide film layer covers the surface of the central area and the surface of the edge area of the detection wafer; performing a chemical mechanical polishing process on the oxide film layer of the detection wafer, and monitoring the grinding rate of the oxide film layer at the edge area of the detection wafer; and monitoring the state of the tungsten CMP machine according to the grinding rate of the oxide layer at the edge of the detected wafer, and accordingly judging whether the product wafer has a large amount of tungsten residues in the edge area. According to the invention, the condition of the grain-side tungsten residue in the CMP process can be monitored by monitoring the grinding rate of the silicon oxide film layer instead of monitoring the grinding rate of the tungsten film layer on line through the steps, so that the problems that metal wires are easy to be broken down and coked by current in a passivation layer etching process caused by the tungsten residue and wafer scrap and damage of test equipment caused by a needle burning phenomenon during an electrical test (such as Cptest) are prevented in advance.

In addition, unless otherwise specified or indicated, the description of the terms "first" and "second" in the specification is only used for distinguishing various components, elements, steps and the like in the specification, and is not used for representing logical relationships or sequential relationships among the various components, elements, steps and the like. It is to be understood that while the present invention has been described in conjunction with the preferred embodiments thereof, it is not intended to limit the invention to those embodiments. It will be apparent to those skilled in the art from this disclosure that many changes and modifications can be made, or equivalents modified, in the embodiments of the invention without departing from the scope of the invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.