JP6638636B2 - Method for evaluating polymer protection - Google Patents

Description

  The present invention relates to a method for evaluating the protection of a polymer for protecting the surface of a silicon wafer.

  Since processing of a semiconductor silicon wafer requires a plurality of steps, it is necessary to pay attention to a change in the wafer during transfer or storage between the steps. In particular, when the bare silicon is transported to the next step in a submerged state, the bare silicon is easily roughened from pure water in an alkaline pH range (pH 7 or more), and the surface of the bare silicon is highly oxidized such as Cu. Is known to react locally to form pits.

  As a measure for suppressing these phenomena, there is a measure for protecting the bare silicon by means such as forming a natural oxide film on the surface of the bare silicon or adsorbing a polymer on the bare silicon (Patent Document 1). However, the former requires special chemicals such as ozone and a drainage facility, and is therefore difficult in terms of cost. The latter can realize bare silicon surface protection with a simpler method, but has less knowledge than natural oxide films, and is an evaluation technology for e.g. what kind of polymer and which adsorption method will increase the protection. Has not been established.

JP-A-2006-051763

  As a method of evaluating the protective property of the polymer for protecting the silicon wafer surface, for example, a method of analyzing the wafer on which the polymer is adsorbed by a TEM (transmission electron microscope) or the like and evaluating the thickness of the polymer adsorption layer is known. It is conceivable, however, that such a method is difficult to evaluate because the polymer is easily broken by an electron beam. As another method, there is a method of intentionally contaminating a wafer having a polymer adsorbed on the surface thereof with a metal such as Cu and then counting the number of pits generated in a particle counter. This method is not a preferable method because it is contaminated by the metal and affects subsequent experiments. As described above, it is difficult to easily and inexpensively evaluate the protection of a polymer, and there has been a demand for the development of a method that can easily and inexpensively evaluate the protection of a polymer.

  The present invention has been made to solve the above problems, and has as its object to provide an evaluation method capable of easily and inexpensively evaluating the protective property of a polymer for protecting a silicon wafer surface. .

  In order to achieve the above object, the present invention provides a method for evaluating the protective property of a polymer that protects a wafer surface by adsorbing on a wafer surface, the method comprising: A part or all of the wafer whose surface is protected by the polymer is immersed in the above solution, and the difference between the Haze of the wafer after immersion and the Haze of the wafer before immersion, or the immersion part of the wafer after immersion And a method for evaluating the protection of the polymer based on the difference between the Haze of the non-immersed part and the Haze of the non-immersed part.

  With such a method for evaluating the protective property of a polymer, when the wafer whose surface is protected by the polymer is immersed in pure water or a solution having a pH of 7 or more to perform etching, the difference in Haze before and after etching or the etching Based on the difference between the haze of the unetched portion and the haze of the unetched portion, the protection of the polymer can be evaluated easily and inexpensively.

  Further, it is preferable that the haze of the wafer before the immersion is the haze of the wafer before the surface is protected by the polymer.

  By doing so, the haze of the wafer before immersion can be measured more accurately, and as a result, the protection of the polymer can be more accurately evaluated.

  In the method for evaluating the protective property of a polymer according to the present invention, the wafer whose surface has been removed by HF cleaning is immersed in a solution in which the polymer is dissolved as a wafer whose surface is protected by the polymer. Use a wafer on which the polymer is adsorbed, or a wafer on which the polymer is adsorbed on the surface by contacting a wafer made of a cloth impregnated with a solution in which the polymer is dissolved and a surface oxide film removed by the HF cleaning. be able to.

  In the method for evaluating the protective property of a polymer according to the present invention, for example, the protective property of the polymer can be evaluated using a wafer having the polymer adsorbed on the surface by such a method.

  As described above, according to the method for evaluating the protective property of the polymer of the present invention, when the wafer whose surface is protected by the polymer is immersed in pure water or a solution having a pH of 7 or more to perform etching, the Haze before and after the etching is measured. Based on the difference or the difference between the haze of the etched portion and the haze of the unetched portion, the protection of the polymer can be evaluated cheaply, simply and accurately. In addition, when the evaluation is performed using a plurality of types of polymers, the protective properties of the polymers can be relatively evaluated among the plurality of polymers.

It is a flowchart which shows an example of the protective property evaluation method of the polymer of this invention. It is a flowchart which shows another example of the protective property evaluation method of the polymer of this invention. It is the schematic which shows the state which immersed a part of bare silicon. It is an example of a haze map of bare silicon in which a part was immersed. 5 is a graph showing a difference (ΔHaze) between the haze of the immersed part and the haze of the non-immersed part in Example 1. 9 is a graph showing the number of increased pits due to intentional Cu contamination in Comparative Example 1.

  As described above, the method of evaluating the thickness of the polymer adsorption layer by TEM or the like or the method of counting the number of pits generated due to intentional Cu contamination makes it difficult to easily and inexpensively evaluate the protection of the polymer. There has been a demand for the development of a method that can easily and inexpensively evaluate protection.

  Then, the present inventors paid attention to the roughness change of the wafer on which the polymer was adsorbed. In general, it is known that silicon having a plane orientation of (100) is roughened under neutral to basic conditions of pH 7 or more when hydrogen-terminated by HF treatment or the like. This phenomenon is caused by a difference in etching rate between the (100) direction and the (111) direction.

  As shown in FIG. 3, bare silicon 1 without a surface oxide film is immersed in pure water 2 without polymer protection, leaving only a part (that is, so that immersed part 1a and non-immersed part 1b are formed). After that, when the haze is measured using a particle counter SP2 manufactured by KLA Tencor Co., as shown in FIG. 4, the immersed part 1a is white, the non-immersed part 1b is black, and the immersed part 1a and the non-immersed part 1b are clear. High contrast occurs. Here, the part that looks white is a haze-deteriorated part. This is a result of the fact that the etching proceeds in the immersion part and the surface roughness is promoted. On the other hand, the present inventors have examined that, in a state where the polymer is adsorbed on the surface of bare silicon, the surface is less likely to be roughened even under neutral to basic conditions of pH 7 or more, so that Haze is hardly deteriorated. I understood that. Further, the present inventors have examined and found that the resistance to metal contamination of the polymer is strongly correlated with the resistance to surface roughness due to etching.

  From these facts, the present inventors have found that the difference in Haze before and after etching when a wafer whose surface is protected by a polymer is immersed in pure water or a solution having a pH of 7 or more, or the etched portion The difference between the haze of the unetched portion and the haze (hereinafter also referred to as “ΔHaze”) is regarded as an index of metal contamination resistance and surface roughness resistance by etching (that is, protective property of the polymer), and the amount of ΔHaze is evaluated. And found that the protection of the polymer can be easily and inexpensively evaluated, thereby completing the present invention.

  That is, the present invention is a method for evaluating the protective property of a polymer that protects the wafer surface by adsorbing on the wafer surface, wherein the solution having a pH of 7 or more in which pure water or any alkali is dissolved in pure water is used. Part or all of the wafer whose surface is protected by the polymer is immersed, and the difference between the Haze of the wafer after immersion and the Haze of the wafer before immersion, or the Haze of the immersed part of the wafer after immersion and the non-immersed part This is a method for evaluating the protection of a polymer, wherein the protection of the polymer is evaluated based on the difference from the Haze of the polymer.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

  FIG. 1 shows a flowchart of an example of the method for evaluating the protection of a polymer according to the present invention. In the method of FIG. 1, first, a wafer is prepared (step (A1) in FIG. 1), and a polymer is adsorbed on the wafer surface to protect the wafer surface with the polymer (step (A2) in FIG. 1). Next, a part of the wafer whose surface is protected by the polymer is immersed in pure water (so that an immersion part and a non-immersion part are generated) (step (A3) in FIG. 1). Next, the haze of the immersed part and the haze of the non-immersed part of the immersed wafer are measured (step (A4) in FIG. 1), and a difference (ΔHaze) between the haze of the immersed part and the haze of the non-immersed part is obtained ( (Step (A5) in FIG. 1). Then, the protective property of the polymer is evaluated based on the obtained ΔHaze ((A6) in FIG. 1).

  According to the method for evaluating the protection of a polymer of the present invention, the protection of the polymer can be evaluated based on the difference (ΔHaze) between the haze of the immersed portion of the wafer after immersion and the haze of the non-immersed portion. In this case, if the protective property of the polymer is high, the surface roughness due to the etching in the immersion part of the wafer is suppressed, and the haze of the immersion part becomes small, so that ΔHaze becomes small. On the other hand, if the protective property of the polymer is low, the surface roughness due to the etching in the immersion part is not suppressed, and the haze in the immersion part increases, so that ΔHaze increases. From this, it can be evaluated that the smaller the ΔHaze, the higher the protection of the polymer.

  FIG. 2 shows a flowchart of another example of the method for evaluating the protection of a polymer according to the present invention. In the method of FIG. 2, first, a wafer is prepared (step (B1) of FIG. 2), and the haze of the wafer before the surface is protected by the polymer (that is, the haze of the wafer before immersion) is measured (FIG. 2). (B2) Step). Next, the polymer is adsorbed on the wafer surface and the wafer surface is protected by the polymer (step (B3) in FIG. 2). Next, the entire wafer whose surface is protected by the polymer is immersed in pure water (step (B4) in FIG. 2). Next, the haze of the wafer after immersion is measured (step (B5) in FIG. 2), and the difference (ΔHaze) between the haze after immersion and the haze before immersion is obtained (step (B6) in FIG. 2). Then, the protective property of the polymer is evaluated based on the obtained ΔHaze ((B7) in FIG. 2).

  In the method for evaluating the protection of a polymer according to the present invention, the protection of the polymer can also be evaluated based on the difference (ΔHaze) between the haze of the wafer after immersion and the haze of the wafer before immersion. In this case, if the protection property of the polymer is high, the surface roughness due to the etching when the wafer is immersed is suppressed, and the haze of the wafer after immersion becomes small, so that ΔHaze becomes small. On the other hand, if the protective property of the polymer is low, the surface roughness due to the etching when the wafer is immersed is not suppressed, and the haze of the wafer after immersion increases, so that the ΔHaze increases. From this, it can be evaluated that the smaller the ΔHaze, the higher the protection of the polymer.

  As shown in the flow of FIG. 2, by setting the haze of the wafer before immersion to the haze of the wafer before protecting the surface with the polymer, the haze of the wafer before immersion can be measured more accurately. As a result, the protection of the polymer can be more accurately evaluated, which is preferable.

  In the method for evaluating the protective property of the polymer of the present invention, when the wafer whose surface is protected by the polymer is immersed in pure water or a solution having a pH of 7 or more in which any alkali is dissolved in pure water, the method is not particularly limited. It is preferable to soak for about 12 to 48 hours, for example, it is preferable to soak for about 24 hours. In addition, in order to suppress surface roughness due to light, it is preferable to perform immersion in a dark place.

  In the method for evaluating the protection of a polymer according to the present invention, the measurement of haze is not particularly limited. For example, the haze can be measured using a particle counter SP2 manufactured by KLA Tencor.

  In the method for evaluating the protective property of a polymer according to the present invention, before the haze measurement of the immersed wafer, the wafer is cleaned using a cleaning solution containing hydrogen peroxide (for example, SC1) and adhered to the wafer. It is preferred to remove any polymer present.

  In the method for evaluating the protective property of the polymer of the present invention, the method of adsorbing the polymer on the wafer surface is not particularly limited. For example, the wafer having the surface oxide film removed by HF cleaning is immersed in a solution in which the polymer is dissolved. A method of adsorbing the polymer on the surface by contacting the surface of the polymer by rubbing a soft cloth material impregnated with a solution in which the polymer is dissolved with a wafer whose surface oxide film has been removed by HF cleaning, etc. And the like.

  According to the method for evaluating the protective property of the polymer of the present invention as described above, when the wafer whose surface is protected by the polymer is immersed in pure water or a solution having a pH of 7 or more to perform etching, the Haze before and after the etching is measured. Based on the difference or the difference between the haze of the etched portion and the haze of the unetched portion, the protection of the polymer can be evaluated cheaply, simply and accurately. In addition, when the evaluation is performed using a plurality of types of polymers, the protection of the polymers can be relatively evaluated among the plurality of polymers.

  Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Example 1]
Based on the difference (ΔHaze) between the haze of the immersed part and the haze of the non-immersed part, the protection properties of the three types of polymers A, B and C were evaluated.

(Polymer adsorption)
The surface oxide film was removed by HF cleaning, and a silicon wafer with a diameter of 300 mm, which was further subjected to normal finish polishing, was prepared. Using a cloth impregnated with an aqueous solution containing each polymer in the final finish polishing, rotating at a load of 10 kPa and rotating. Polishing was performed at several tens of rpm for 10 seconds to adsorb each polymer on the surface of the silicon wafer. In addition, the aqueous solution containing each polymer was supplied to the polishing platen at 1.0 L / min.

(Immersion of silicon wafer)
A pit tank storing pure water was prepared, and a silicon wafer having each polymer adsorbed thereon was immersed therein. At that time, the water level was adjusted so that an immersed part and a non-immersed part were generated. The immersion was performed in the dark for 24 hours in order to suppress surface roughness due to light.

(Haze measurement of silicon wafer after immersion)
In order to remove the polymer adhering to the surface, the immersed silicon wafer was washed using SC1. Next, the haze of the immersed part and the haze of the non-immersed part were measured using a particle counter SP2 manufactured by KLA Tencor Corporation, and the difference (ΔHaze) between the haze of the immersed part and the haze of the non-immersed part was determined. FIG. 5 shows the results.

(Measurement of haze of comparative wafer)
In order to relatively evaluate the protective properties of the polymer, the above description was applied to a silicon wafer from which the surface oxide film was not removed and a silicon wafer from which the surface oxide film was removed by HF cleaning and the subsequent polymer adsorption was not performed. Similarly, the haze of the silicon wafer immersed and the immersed silicon wafer were measured, and the difference (ΔHaze) between the haze of the immersed portion and the haze of the non-immersed portion was obtained. FIG. 5 shows the results.

[Comparative Example 1]
Based on the number of increased pits due to intentional Cu contamination, the protective properties of three types of polymers, polymer A, polymer B and polymer C, were evaluated.

(Measurement of pit increase due to polymer adsorption and intentional Cu contamination)
A silicon wafer on which each polymer was adsorbed was prepared in the same manner as in Example 1, the silicon wafer was immersed in pure water containing 1 ppm of Cu for 5 minutes (Cu intentional contamination), and then the silicon immersed using SC1. The wafer was washed, and the number of increased pits was measured using a particle counter SP2 manufactured by KLA Tencor. FIG. 6 shows the results.

(Measurement of the number of pit increases due to intentional Cu contamination of the comparative wafer)
In order to relatively evaluate the protective properties of the polymer, the above description was applied to a silicon wafer from which the surface oxide film was not removed and a silicon wafer from which the surface oxide film was removed by HF cleaning and the subsequent polymer adsorption was not performed. Similarly, Cu intentional contamination and the number of increased pits were measured. FIG. 6 shows the results.

  As shown in FIG. 5, according to the method of Example 1, when polymer A was adsorbed, ΔHaze was at the same level as when the surface oxide film was not removed, and when polymer B was adsorbed, ΔHaze is larger than when polymer C is adsorbed, ΔHaze is larger when polymer C is adsorbed than when polymer B is adsorbed, and larger than when polymer C is adsorbed when polymer is not adsorbed. ΔHaze was large. From this, the progress of surface roughness differs depending on the type of polymer, and when polymers B and C are adsorbed, surface roughness due to immersion can be significantly suppressed as compared with the case where polymers are not adsorbed. It can be seen that the surface roughness due to immersion is advanced as compared with the case where polymer A is adsorbed.

  On the other hand, as shown in FIG. 6, in the method of Comparative Example 1, the number of pits was about the same level when polymer A was adsorbed as when the surface oxide film was not removed, and when polymer B was adsorbed. Means that the number of pit increases is larger than that when polymer A is adsorbed, that when polymer C is adsorbed, the number of pits is larger than when polymer B is adsorbed, and that when polymer is not adsorbed, polymer C is The result obtained was that the number of pits increased significantly more than in the case of adsorption. From this, the degree of pit generation differs depending on the type of polymer, and when polymers B and C are adsorbed, the generation of pits due to Cu intentional contamination can be significantly suppressed as compared with the case where polymers are not adsorbed. However, it can be seen that pits are generated due to intentional Cu contamination as compared with the case where polymer A is adsorbed. In the method of Comparative Example 1, since intentional contamination with Cu was actually performed, metal contamination of equipment used for the analysis (immersion tank or cleaning tank) was generated.

  From the comparison between the results of Example 1 and Comparative Example 1, ΔHaze of Example 1 which is an index of surface roughness resistance due to etching strongly correlates with the number of pit increases of Comparative Example 1 which is an index of metal contamination resistance. You can see that there is. That is, by obtaining ΔHaze as in the first embodiment, not only the surface roughness resistance due to etching but also the metal contamination resistance correlated therewith can be evaluated. Further, in the method of Example 1, since intentional contamination by Cu is not performed, there is no possibility that metal contamination occurs in equipment used for analysis as in the method of Comparative Example 1. Furthermore, according to the method of Example 1, it is possible to relatively compare the different protective properties among the polymer types, and to compare the case where the surface oxide film is not removed or the case where the polymer is not adsorbed. Thereby, the protective property of the polymer can be relatively evaluated.

  From the above, it has been clarified that the evaluation method of the present invention in which the protective property of a polymer is evaluated based on ΔHaze can evaluate the protective property of a polymer for protecting the surface of a silicon wafer at low cost and easily.

  Note that the present invention is not limited to the above embodiment. The above embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and has the same effect. Within the technical scope of

  1: bare silicon, 1a: immersion part, 1b: non-immersion part, 2: pure water.

Claims (3)

A method for evaluating the protective properties of a polymer that protects the wafer surface by adsorbing on the wafer surface,
Part or all of the wafer whose surface is protected by the polymer is immersed in pure water or a solution having a pH of 7 or more in which pure alkali is dissolved in pure water, and the Haze of the wafer from which the polymer is removed after the immersion is removed. Evaluating the protective property of the polymer based on the difference between the Haze of the wafer before immersion or the difference between the Haze of the immersed part and the Haze of the non-immersed part of the wafer after removing the polymer after the immersion. Method for evaluating the protective properties of polymers.   The method of claim 1, wherein the haze of the wafer before immersion is set to the haze of the wafer before the surface is protected by the polymer.   As a wafer whose surface is protected by the polymer, a wafer in which the polymer is adsorbed on the surface by immersing the wafer whose surface oxide film has been removed by HF cleaning in a solution in which the polymer is dissolved, or the polymer is dissolved 3. A wafer having the polymer adsorbed on the surface thereof by contacting a cloth material impregnated with the solution and a wafer from which a surface oxide film has been removed by the HF cleaning. A method for evaluating the protection of the described polymer.