JP5510022B2 - Wafer evaluation method - Google Patents

Description

  The present invention relates to a wafer evaluation method for evaluating a contact-induced defect caused by contact with an external object at an end surface portion of a wafer.

  In various processes such as a grinding process, a slicing process, a polishing process, and a cleaning process in the wafer manufacturing process, the outer peripheral surface of the wafer is connected to various external objects such as a wire saw, a carrier, a robot arm, abrasive grains, and a cleaning liquid. There are many opportunities to contact. For this reason, the end surface portion of the wafer may be mechanically damaged from an external object, contaminated from the external object, or attached to the external object, which may affect the quality of the wafer.

  In addition, dust generation and trench formation abnormality due to film peeling in device processes (for example, STI (Shallow Trench Isolation) process, HDP (High Density Plasma) process, etc.) also occur due to the state of the end face of the wafer. There are many cases.

  In recent years, the device process may be changed with the higher integration of devices, and it is caused by the quality of the outermost periphery (edge) of the wafer and the vicinity (edge vicinity) that has not been a problem until now. Dust generation in the device process has caused a problem that yield decreases.

  Therefore, there is a need for a method for evaluating the quality of the end face of the wafer in detail. For example, as a device that detects defects on the edge of a wafer, it emits coherent light toward the edge of the wafer, effectively eliminating low-dimensional diffracted light, while blocking the scattered diffracted light. An apparatus for inspecting a flaw on an end surface portion of a wafer by detecting with a detector is known (see Patent Document 1).

Japanese Patent Laid-Open No. 2003-287412

  According to the above-described prior art, only the scratch on the surface of the end face portion of the wafer can be inspected, and a defect caused by contact with an external object potentially existing inside the wafer cannot be detected.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of easily and appropriately evaluating the occurrence of a contact-induced defect due to a contact existing on an end surface portion of a wafer. is there.

  A wafer evaluation method according to a first aspect of the present invention is a wafer evaluation method for evaluating a contact-induced defect caused by contact with an external object at an end surface portion of a predetermined wafer. A dry etching step is performed in which dry etching is performed under conditions that cause different etching rates between an affected part affected by contact with an object and a normal part not affected by contact with an external object, and dry etching is performed. An appearance observation step for observing the appearance of the wafer, and an evaluation step for evaluating a contact-induced defect in the end surface portion of the wafer based on the observation result of the wafer.

  According to such a wafer evaluation method, since dry etching is performed under conditions that result in different etching rates between the affected part affected by contact with an external object and the normal part not affected by contact with an external object, In a dry-etched wafer, the affected part and the normal part are in different states, and by observing the appearance of the wafer, it is possible to appropriately evaluate the contact-induced defects at the end face part of the wafer.

  In the wafer evaluation method, in the appearance observation step, at least one of protrusions or pits formed on the end surface portion of the wafer may be observed. According to such a wafer evaluation method, it is possible to appropriately evaluate the contact-induced defect based on the protrusions or pits formed on the end surface portion of the wafer.

  In the wafer evaluation method, in the appearance observation step, a by-product by dry etching attached to the surface of the wafer may be observed. According to such a wafer evaluation method, it is possible to appropriately evaluate a contact-induced defect based on a by-product generated by dry etching attached to the surface of the wafer.

  In the wafer evaluation method, in the dry etching step, dry etching may be performed under a condition that the etching rate of the affected part is 0.5 times or less, or 2 times or more of the etching rate of the normal part. . According to such a wafer evaluation method, it is possible to make the protrusions or pits that appear on the end face of the wafer relatively easy to observe.

  The wafer evaluation method may further include a heat treatment step for performing a heat treatment simulating a device process performed on the wafer before the dry etching step. According to this wafer evaluation method, it is possible to appropriately evaluate the contact-induced defect of the wafer in consideration of the influence on the wafer in the device process.

  In the above-described wafer evaluation method, in the dry etching step, the etching amount of the portion affected by the dry etching or the normal portion having the higher etching rate may be 0.2 μm or more. According to such a wafer evaluation method, the size of the protrusions or pits that appear on the end face of the wafer can be made relatively large.

It is a flowchart of the wafer evaluation method which concerns on one Embodiment of this invention. It is a figure which shows the mode of the end surface part of the wafer after anisotropic etching which concerns on one Embodiment of this invention. It is a figure explaining the relationship between the by-product on the surface of the wafer which concerns on one Embodiment of this invention, and the protrusion of the end surface part of a wafer. It is a flowchart of the wafer evaluation method which concerns on the 1st modification of this invention. It is a flowchart of the wafer evaluation method which concerns on the 2nd modification of this invention.

  Embodiments of the present invention will be described with reference to the drawings. The embodiments described below do not limit the invention according to the claims, and all the elements and combinations described in the embodiments are essential for the solution of the invention. Is not limited.

  A wafer evaluation method according to an embodiment of the present invention will be described.

  FIG. 1 is a flowchart of a wafer evaluation method according to an embodiment of the present invention.

  In the wafer evaluation method, for example, a defect (contact) caused by contact with an external object using a part (for example, one wafer) selected from a wafer set (for example, lot) created by the same or similar process. (Cause defects) is evaluated.

  In this embodiment, the wafer to be evaluated is a wafer cut from a single crystal ingot, polished with abrasive grains, subjected to a surface treatment by a chemical method, and a chemical abrasive using a polishing abrasive liquid. It may be a polished wafer that has been mechanically polished, an annealed wafer that has been annealed, or an epitaxial wafer in which a silicon layer is vapor-phase grown on the surface of the polished wafer.

  First, anisotropic dry etching is performed on the wafer to be evaluated (step S1).

  This anisotropic etching step is performed by supplying a gas in which halogen (or a halogen compound) and oxygen are mixed using an RIE (Reactive Ion Etching) apparatus.

  In this embodiment, by adjusting the mixing ratio of halogen (or halogen compound) and oxygen, etc., the etching rate (etching rate) in the portion where there is no contact-induced defect (normal portion) and the contact-induced defect are latent. The etching rate in the part (affected part) that has been changed is made different. For example, assuming adhesion of abrasive grains (silicon oxide) as an example of contact, if the etching rate of Si (silicon) is higher than the etching rate of silicon oxide, protrusions are formed on the portion where silicon oxide is adhered. Things are formed.

  In the present embodiment, the etching rate in the normal part is set to 0.5 times or less or twice the etching rate in the affected part. According to this, since the difference in the etching amount between the normal part and the affected part becomes relatively large, it is possible to easily observe the projections, pits and the like caused by the difference in the etching amount between the normal part and the affected part. Further, in the present embodiment, the etching process is performed so that the etching amount at a portion where the etching rate is high is 2 μm or more, more preferably 5 μm or more. According to this, the protrusions and pits caused by the difference in etching amount between the normal part and the affected part can be made to a certain size, and the protrusions and pits can be easily observed.

  Next, the by-product generated in the anisotropic etching process and attached to the surface of the wafer is removed from the wafer (step S2). By-products include, for example, those in which a thin film is rolled.

  Next, the appearance of the wafer (here, the end surface portion of the wafer) is observed (step S3). As an apparatus for observing the appearance of the wafer, for example, a microscope, an end face evaluation apparatus using a laser, an SEM (Scanning Electron Microscope), or the like may be used. In addition, since the edge part of a wafer is a curved surface, SEM with a high focal depth is preferable. In the present embodiment, the size of the protrusions and pits can be made to some extent, so that the protrusions and pits can be observed sufficiently even at a relatively low magnification (for example, about 100 times). Can do.

  Next, the end face is evaluated based on the observation result of the appearance of the wafer (step S4). Here, for example, in the evaluation of the wafer, whether or not there are many contact-induced defects based on the number of occurrences of protrusions (or pits) on the end face of the wafer, the generation density, the width of the dense protrusions, etc. Can be evaluated. Thus, according to the wafer evaluation method, it is possible to appropriately evaluate whether or not there are many contact-induced defects. For this reason, it can estimate appropriately also about the contact-induced defect with respect to the wafer of the same lot.

  FIG. 2 is a diagram illustrating a state of the end surface portion of the wafer after anisotropic etching according to an embodiment of the present invention.

  2A is a diagram showing a state of an end face observed when the evaluation method shown in FIG. 1 is performed on a polished wafer, and FIG. 2B is an evaluation shown in FIG. 1 for an epitaxial wafer. FIG. 2C is a diagram illustrating a state of the end surface portion observed when the method is performed, and FIG. 2C is a diagram illustrating a state of the end surface portion observed when the evaluation method illustrated in FIG. 1 is performed on the annealed wafer. It is.

  According to these FIG. 2A to FIG. 2C, the generation amount of the rice granular projections in the polished wafer is larger than that in the epitaxial wafer and the annealed wafer.

  This is because the epitaxial wafer is obtained by growing an epitaxial layer on the polished wafer, and the affected part that generates defects due to contact existing in the polished wafer is covered by the epitaxial layer. There seems to be little generation of things. In addition, the annealed wafer has been improved to a normal part due to the rearrangement of the affected part due to the annealing process and the contamination source of the affected part being annealed out. It is done. 2B and 2C are steps generated by anisotropic etching and are common to both the normal part and the affected part, and are not used in this evaluation.

  From this situation, it can be seen that the protrusions generated on the wafer appropriately indicate defects caused by contact.

  Next, the state of the end face observed when the evaluation method shown in FIG. 1 is performed on wafers having different processing processes will be described.

  FIG. 2D shows the state of the end face observed when the evaluation method shown in FIG. 1 is performed on the wafer that has been subjected to the cleaning process without performing the mirror chamfering process. FIG. 2E shows the mirror chamfering process. FIG. 2F is a view showing the state of the end face observed when the evaluation method shown in FIG. 1 is performed on the wafer subjected to the double-side polishing process and the final cleaning process. FIG. 2G is a diagram showing the state of the end face portion observed when the evaluation method shown in FIG. 1 is performed on the wafer that has been processed, mirror-finished, and subjected to the final cleaning process. It is a figure which shows the mode of the end surface part observed when performing the evaluation method shown in FIG. 1 with respect to the wafer which performed the polishing process, performed the mirror chamfering process on the wafer, and performed the water washing process.

  The wafer shown in FIG. 2D has many protrusions observed. This is probably because the mirror chamfering process is not performed, and is caused by the contact with an external object that has occurred in the previous process (for example, grinding process, slicing process, etc.). In addition, the wafer shown in FIG. 2E has many observed protrusions. This is considered to be due to the contact with the carrier in the subsequent double-side polishing process, although the affected part that becomes the contact-induced defect of the end face part of the wafer can be removed by the mirror chamfering process. In addition, the wafer shown in FIG. 2F has very few observed protrusions. This is considered to be because the affected part that becomes a contact-induced defect due to contact with an external object in the grinding process or the double-side polishing process can be appropriately removed by the mirror chamfering process. In addition, the wafer shown in FIG. 2G has many protrusions observed. This is because the mirror chamfering process can appropriately remove the affected part that causes a contact-induced defect due to contact with an external object in the grinding process or the double-sided polishing process. This is considered to be because it remains in contact with the end face of the wafer.

  From this situation, it can be seen that the protrusions generated on the wafer appropriately indicate defects caused by contact. Therefore, the contact-induced defect of the wafer can be appropriately evaluated by the protrusion generated on the wafer.

  In the above embodiment, the wafer contact defect is evaluated based on the number of protrusions (or pits). However, the present invention is not limited to this, as in the following first modification. You can also In other words, the contact-induced defect of the wafer may be evaluated based on the by-product generated in the etching process that has adhered to the surface of the wafer after anisotropic etching.

  FIG. 3 is a view for explaining the relationship between by-products on the surface of the wafer and protrusions on the end surface portion of the wafer according to an embodiment of the present invention. FIG. 3A shows the number of by-products adhering to the wafer surface after etching and the positions thereof, and FIG. 3B shows the relationship between the observation plane orientation and the projection density observed on that plane. FIG. 3C shows the protrusion density, and FIG. 3D shows the plane orientation.

  After the anisotropic etching, by-products generated by the etching adhere to the surface of the wafer. For example, as shown in FIG. 3A, this multi-product has a large number of by-products in the direction corresponding to the plane orientations of <0-10>, <100>, and <010>. Here, the plane orientation is expressed as shown in FIG. 3D. On the other hand, with respect to the end surface portion of the wafer, the projection density in the plane orientations <0-10>, <100>, and <010> is large. Here, as shown in FIG. 3C, the protrusion dense width indicates a width where protrusions are densely packed in the end surface portion (chamfered portion) of the wafer, and the protrusion dense width is large. It means that there are many occurrences of. From the above, a tendency similar to the number of by-products and the number of protrusions on the edge of the wafer is observed, which means that wafer contact-induced defects can be evaluated based on the by-products. ing.

  FIG. 4 is a flowchart of the wafer evaluation method according to the first modification of the present invention. In addition, the same code | symbol shall be attached | subjected about the part similar to FIG.

  First, anisotropic dry etching is performed on the wafer to be evaluated (step S1). By this dry etching, a by-product may adhere to the surface of the wafer.

  Next, the appearance of the wafer (here, the surface of the wafer) is observed (step S5). As an apparatus for observing the appearance of the wafer, for example, a microscope, an end face evaluation apparatus using a laser, an SEM (Scanning Electron Microscope), or the like may be used. Moreover, you may observe using a particle counter. In this observation, the number and density of by-products on the wafer surface are observed.

  Next, the end face is evaluated based on the observation result of the appearance of the wafer (step S6). Here, for example, as the evaluation of the wafer, whether or not there are many contact-induced defects is evaluated based on the number of by-products on the wafer surface, the density, and the like. For example, when the number of by-products on the wafer surface is a predetermined number or more, it is evaluated that there are many contact-induced defects. Thus, according to the wafer evaluation method, it is possible to appropriately evaluate whether or not there are many contact-induced defects.

  Next, a wafer evaluation method according to a second modification of the present invention will be described. The wafer evaluation method according to the second modification is a method for evaluating an end surface portion of a wafer based on by-products attached to the surface of the wafer and protrusions (or pits) generated on the end surface portion of the wafer. It is.

  FIG. 5 is a flowchart of the wafer evaluation method according to the second modification of the present invention. In addition, the same code | symbol shall be attached | subjected about the part similar to FIG. 1, FIG.

First, anisotropic dry etching is performed on the wafer to be evaluated (step S1). Next, the appearance of the wafer (here, the surface of the wafer) is observed (step S5). Next, the by-product generated in the etching process and attached to the surface of the wafer is removed from the wafer (step S2). Next, the appearance of the wafer (here, the end surface portion of the wafer) is observed (step S3).
The

  Next, the end face is evaluated based on the observation results of the wafer appearance (by-products on the wafer surface and protrusions on the end face portion of the wafer) (step S7). Here, for example, in the evaluation of the wafer, the contact-induced defect is determined based on the number of protrusions (or pits) generated on the end face of the wafer, the generation density, the number of by-products on the wafer surface, the density, and the like. It can be evaluated whether there are many. Thus, according to the wafer evaluation method, it is possible to appropriately evaluate whether or not there are many contact-induced defects.

  As mentioned above, although this invention was demonstrated based on embodiment, this invention is not restricted to embodiment mentioned above and a modification, It can apply to other various aspects. For example, in the above-described embodiment and modification, before performing anisotropic etching (before step S1 in FIGS. 1, 4, and 5), heat treatment simulating a device process to be performed on the wafer is performed. You may do it. In this way, the contact-induced defects of the wafer can be evaluated in consideration of the influence of the heat treatment in the device process.

  Further, in the above embodiment, one wafer is taken out and evaluated for each lot unit, but the present invention is not limited to this. For example, for a plurality of lots manufactured by the same line, wafers are obtained. One piece may be taken out and evaluated. In short, a part of wafers may be taken out and evaluated at least in units of a plurality of wafers that can be considered to have similar tendencies.

Claims (4)

A wafer evaluation method for evaluating a contact-induced defect caused by contact with an external object at an end surface portion of a predetermined wafer,
Dry etching is performed on a predetermined wafer under conditions that cause different etching rates between an affected part affected by contact with the external object and a normal part not affected by contact with the external object. A dry etching step;
Appearance observation step for observing at least one of protrusions or pits formed on the end surface portion of the wafer subjected to dry etching and a by-product by dry etching attached to the surface of the wafer ;
A wafer evaluation method comprising: an evaluation step of evaluating the contact-induced defect in the end surface portion of the wafer based on an observation result of the wafer. In the dry etching step, dry etching is performed under a condition that the etching rate of the affected part is 0.5 times or less, or 2 times or more the etching rate of the normal part.
The wafer evaluation method according to claim 1 . The wafer evaluation method according to claim 1, further comprising a heat treatment step of performing a heat treatment simulating a device process performed on the wafer before the dry etching step. In the dry etching step,
The wafer evaluation method according to any one of claims 1 to 3 , wherein an etching amount of the affected part or the normal part by dry etching having a higher etching rate is 0.2 µm or more.