JP7215412B2 - METHOD FOR DETERMINING TIME TO BEGIN USE OF POLISHING CLOTH FOR SEMICONDUCTOR WAFERS, METHOD FOR POLISHING SEMICONDUCTOR WAFERS USING THE SAME, AND SEMICONDUCTOR WAFER POLISHING SYSTEM - Google Patents

Description

The present invention relates to a method for determining when to start using a semiconductor wafer polishing cloth, a semiconductor wafer polishing method using the same, and a semiconductor wafer polishing system.

Silicon wafers and compound semiconductor wafers such as GaAs wafers are known as semiconductor wafers. Semiconductor wafers generally have a slicing process of slicing a single crystal ingot with a wire saw into thin disc-shaped wafers, a grinding process of flattening the front and back surfaces of the sliced wafers to a predetermined thickness, It can be obtained by sequentially performing a polishing step of performing rough polishing, finishing polishing, and mirror finishing with high flatness. Depending on the application, an epitaxial layer may be formed on the surface of the semiconductor wafer after polishing using a CVD method or the like.

In the above-described semiconductor wafer polishing process, either one or both of a double-sided polishing method in which both surfaces of the semiconductor wafer are polished simultaneously and a single-sided polishing method in which only one side is polished is used. Multistage polishing is also performed in which a single-sided polishing method is sequentially performed after a double-sided polishing method is performed.

For example, in a final polishing process using a single-side polishing method, one side of a semiconductor wafer 290 is subjected to mechanochemical polishing (CMP) by a single-side polishing apparatus 200 as shown in FIG. CMP is a polishing technique for mechanically polishing the wafer with abrasive grains contained in the polishing liquid while etching the semiconductor wafer 290 using a polishing liquid having an etching action on the semiconductor wafer 290 to be polished. The single-side polishing apparatus 200 has a head 202 that holds a semiconductor wafer, and a surface plate 210 having a semiconductor wafer polishing cloth (hereinafter sometimes simply referred to as "polishing cloth") 212 on its surface. The head 202 presses the surface of the wafer to be polished against the polishing cloth 212 . The wafer surface is polished by rotating the head 202 and the platen 210 together while supplying the polishing liquid 228 from the polishing liquid supply unit 226 onto the polishing cloth 212 .

By the way, in general, various impurities adhere to an unused polishing cloth during the manufacturing process of the polishing cloth. These impurities cause damage to the polished surface of the semiconductor wafer. Therefore, a large number of LPDs (Light Point Defects) are detected in the inspection process after polishing from the surface of the wafer polished at the beginning of use of the polishing cloth. Therefore, as described in Patent Document 1, when using a new polishing cloth, a predetermined number of wafers that are not shipped as a product (hereinafter sometimes referred to as "dummy wafers") are polished, and then the product is polished. We polish wafers to be shipped as products (hereinafter sometimes referred to as “product wafers”). Hereinafter, in this specification, polishing performed using a dummy wafer performed at the beginning of use of a new polishing cloth is referred to as "dummy polishing", and a product wafer is polished after that, and the wafer after polishing is used as a product. This polishing is called "main polishing".

In the past, when dummy polishing was performed a predetermined number of times, in other words, after the accumulated number of wafers polished with a new polishing cloth reached a predetermined number, the main polishing process was started. is generally set to a constant value as long as the same type of polishing cloth is used.

However, even with polishing cloths of the same type (polishing cloth of the same material, polishing cloth of the same product, etc.), the polishing result index such as the number of LPD of the wafer after polishing is stabilized at a low level for each individual polishing cloth. The number of times of the dummy polishing process (accumulated number of polished wafers) required until the time is different. Therefore, in order to ensure the quality of product wafers, it was necessary to sufficiently increase the number of times of dummy polishing prior to main polishing. In addition, if the number of times of dummy polishing increases, the number of times the polishing pad can be used (life) will decrease, and it will also affect the production time. . Incidentally, although Patent Document 1 describes that dummy polishing is performed until the concentration of copper in the polishing cloth becomes 0.01 ppm or less, this method uses a polishing cloth to measure the concentration of copper. It involves destructive testing to cut out pieces. Therefore, the method described in Patent Document 1 cannot grasp the state of the polishing cloth in real time, and there is room for improvement in terms of practical use.

Therefore, the applicant of the present application disclosed in Patent Document 2 that the polishing process for polishing the surface of the wafer by bringing the wafer into contact with a polishing cloth provided on the surface of a surface plate and rotating the surface plate and the wafer is performed by: A wafer polishing method performed multiple times with the same polishing cloth, wherein the polishing process includes an initial polishing step in which the polished wafer is not used as a product, and a main polishing step in which the polished wafer is used as a product after the initial polishing step. and measuring the contact angle of the polishing cloth, and determining the switching timing from the initial polishing step to the main polishing step based on the measured value. there is With the wafer polishing method proposed in Patent Document 2, it is possible to reliably reduce wafer loss due to dummy polishing, and to stabilize the number of LPDs on product wafers at a low level.

JP-A-2005-209863 WO2015/092294

However, in the polishing method described in Patent Document 2, it is necessary to measure the contact angle of the polishing pad each time dummy polishing is performed. Considering the preparatory step for accurately measuring the contact angle in the polishing method described in Patent Document 2, there is room for improvement in determining the time to start using the polishing pad for semiconductor wafers in real time.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for determining when to start using a polishing pad for semiconductor wafers, which can accurately and in real time determine when to start using a polishing pad for semiconductor wafers. A further object of the present invention is to provide a semiconductor wafer polishing method and a semiconductor wafer polishing system using this determination method.

In order to solve the above problems, the present inventors have conducted extensive studies and found that there is a correlation between the time waveform data of the surface plate load current value of the surface plate in each successive polishing and the polishing result index of the semiconductor wafer after polishing. I found something. The gist and configuration of the present invention completed based on the above findings are as follows.

(1) A method for determining when to start using a semiconductor wafer polishing cloth placed on a surface plate of a semiconductor wafer polishing apparatus, comprising:
The surface of at least one or more semiconductor wafers is sequentially polished using the first polishing cloth for semiconductor wafers, and the result of waveform analysis of the time waveform data of the surface plate load current value of the surface plate in each polishing, and each time a preliminary step of obtaining a judgment condition based on a correspondence relationship with the polishing result index of the semiconductor wafer after polishing;
a first step of placing a second semiconductor wafer polishing cloth on the surface plate;
a second step of sequentially polishing at least one or more semiconductor wafers using the same polishing conditions as in the preliminary step, acquiring the time waveform data in each polishing step, and analyzing the waveform;
a third step of determining whether the result of waveform analysis in the second step satisfies the determination condition;
A method for determining when to start using a polishing pad for semiconductor wafers, comprising:

(2) The method for determining the time to start using the polishing pad for semiconductor wafers according to (1), wherein the polishing result index is the number of LPDs observed on the polished surface of the semiconductor wafer after polishing.

(3) Using the SAX method, the surface plate load current value in the time waveform data is divided into three or more stages and encoded, and the waveform analysis is performed by obtaining a discrete parameter group corresponding to the time series. and a method for judging when to start using the polishing pad for semiconductor wafers according to (1) or (2) above.

(4) The method for determining the time to start using a polishing cloth for semiconductor wafers according to any one of (1) to (3), wherein the polishing apparatus is a single-sided polishing apparatus for semiconductor wafers.

(5) It is determined that the second polishing cloth for semiconductor wafers can be used according to the method for determining when to start using the polishing cloth for semiconductor wafers according to any one of (1) to (4) above. A method of polishing a semiconductor wafer, wherein the polishing is performed by using a semiconductor wafer for non-product use until the first time, and the polishing is performed by using a semiconductor wafer for product after the time when it is determined that the use can be started. .

(6) Having a holder for holding a semiconductor wafer and a surface plate having a polishing cloth on the surface thereof, and rotating the surface plate and the semiconductor wafer while bringing the semiconductor wafer into contact with the polishing cloth. A semiconductor wafer polishing system that performs a polishing process for polishing the surface of the semiconductor wafer a plurality of times with the same polishing cloth,
The semiconductor wafer polishing system further comprises a control unit, and a waveform analysis unit, a storage unit, a determination unit, and a wafer exchange unit controlled via the control unit,
Time waveform data of the surface plate load current value of the surface plate in each polishing when the surfaces of at least one or more semiconductor wafers are sequentially polished using a polishing cloth of the same kind as the polishing cloth, in the storage unit. and a determination condition based on a correspondence relationship between a result of waveform analysis of and a polishing result index of the semiconductor wafer after each polishing,
The control unit
(i) causing the holder to hold a dummy wafer;
(ii) using the waveform analysis unit to sequentially polish at least one or more dummy wafers using the same polishing conditions as the polishing conditions stored in the storage unit, and the time waveform in each polishing; Acquire data, analyze waveforms,
(iii) using the determination unit to determine whether the result of waveform analysis using the dummy wafer satisfies the determination conditions stored in the storage unit;
(iv) A semiconductor wafer polishing system, wherein after the determination condition is satisfied, the semiconductor wafer is held by the holding section using the wafer exchange section.

INDUSTRIAL APPLICABILITY According to the present invention, there are provided a method for judging the timing of starting use of a polishing cloth for semiconductor wafers, which can accurately and in real time determine the timing for starting use of a polishing cloth for semiconductor wafers, a method for polishing semiconductor wafers using the same, and a semiconductor. A wafer polishing system can be provided.

1 is a schematic diagram of a conventional single-sided polishing apparatus; FIG. 4 is a graph showing the relationship between the polishing time and the platen load current value according to experiments conducted by the present inventors. 3 is a graph obtained by extracting time waveform data of each polishing cycle from the surface plate load current values of FIG. 2 and discretizing the load current values in three steps in time series using the SAX method. FIG. 3B is a bar graph in which the frequency of occurrence of codes for each polishing cycle in FIG. 3A is arranged in the order of polishing; 4 is a graph showing the number of LPDs on the surface to be polished after polishing in each polishing cycle according to experiments conducted by the present inventors; 4 is a flow chart for explaining a determination method and a polishing method according to the present invention; 1 is a block diagram for explaining a semiconductor wafer polishing system according to the present invention; FIG. 5 is a graph obtained by extracting time waveform data of each polishing time from the surface plate load current value and discretizing the load current value in six steps in time series using the SAX method in Example 1. FIG. FIG. 7B is a bar graph in which the code appearance frequencies of each polishing cycle in FIG. 7A are arranged in order of polishing. 10 is a graph obtained by extracting time waveform data of each polishing time from the surface plate load current value and discretizing the load current value in time series in 10 steps using the SAX method in Example 2. FIG. FIG. 8B is a bar graph in which the code appearance frequency of each polishing cycle in FIG. 8A is arranged in the order of polishing. 7 is a graph showing the number of LPDs on the surface to be polished after polishing in each polishing cycle in Example 2. FIG.

Prior to the description of the embodiments of the present invention, a preliminary experimental example that has led to the completion of the present invention will be described first.

[Preliminary experiment example]
Thirty-four silicon wafers having a diameter of 300 mm and a total thickness of 775 μm were prepared. Also, an unused polishing cloth made of suede material was placed on the surface plate of a single-wafer type single-sided polishing apparatus. Using this single-wafer single-sided polishing apparatus, the surface of one silicon wafer is chemically and mechanically polished while supplying an alkaline polishing liquid containing colloidal silica abrasive grains as polishing slurry to the surface of the polishing cloth. The silicon wafers were exchanged, and one-sided polishing of these 34 silicon wafers was sequentially performed under the same polishing conditions. However, in the first polishing and the second polishing, the polishing time was made sufficiently longer than the polishing time after the third time in order to remove impurities from the polishing cloth. Also, the platen load current value was measured during polishing. FIG. 2 shows the measurement result of the surface plate load current value.

From the graph shown in FIG. 2, time waveform data was extracted for each polishing cycle. Next, for each time waveform data, a discrete parameter group corresponding to the time series was obtained using the SAX (Symbolic Aggregate approXimation) method, which is a known discretization method for discretizing time series data. . The SAX method is a well-known approximate expression method for time-series data that is also used in Japanese Patent Application Laid-Open Nos. 2017-156942 and 2016-058027, and these publications are incorporated herein by reference. .

Specific discretization conditions by the SAX method are as follows. The platen load current value is divided into three stages as shown in the graph of FIG. )bottom. As for the time axis, after normalizing the polishing time, it was divided into 53 sections, and after excluding the last 3 sections, it was divided into 5 sections and divided into a total of 10 sections. FIG. 3A shows a graph of the surface plate load current value after discretization by the SAX method, and FIG. 3B shows a band graph in which the code appearance frequency of each polishing cycle in FIG. 3A is arranged in the order of polishing cycles. For example, the discrete parameter group obtained from the surface plate load current value in the first polishing is "ABBBBBBBBB" (1 for A, 9 for B, and 0 for C), and the discrete parameter group obtained from the 8th polishing. is "ABBBBBCCCC" (1 A, 5 B, 4 C). Note that 34 discrete parameter groups obtained from 34 waveform data (see FIG. 2) are superimposed on FIG. 3A.

Furthermore, for each of the 34 silicon wafers after polishing, a commercially available laser particle counter (SP2; manufactured by KLA-Tencor) was used to measure the number of LPDs having an LPD size of 35 nm or more on the surface to be polished/wafer. The results are shown in FIG.

First, comparing the graph of FIG. 2 with the graph of FIG. 4, it is confirmed that the surface plate load current value increases as the number of polishing times increases, and the number of LPDs decreases as the number of polishing times increases. Furthermore, after the number of LPDs is significantly reduced once compared to the number of LPDs at the initial stage of polishing, the number of LPDs does not exceed the practical allowable value in subsequent polishing. This tendency is consistent with the conventional empirical rule that dummy polishing is necessary because LPD occurs frequently in the initial stage of use of the polishing cloth, and is obtained by waveform analysis of the time waveform data of the surface plate load current value. It was confirmed that there is a significant correlation between the parameter and the number of LPDs.

In this preliminary experiment, it was confirmed from FIG. 4 that the number of LPDs was 10 or less per wafer after the eighth polishing (the ninth and subsequent polishing). According to FIGS. 3B and 4, since level C appears for the first time in the discrete parameter group at the eighth time, when level C appears, the number of LPDs is 10 or less per wafer in subsequent polishing. become. Therefore, in this example, an example of a criterion for judging whether dummy polishing can be finished, that is, whether actual polishing can be started is the level If the determination condition is whether or not one or more C appear, it can be determined that the number of LPDs will be 10 or less per wafer in subsequent polishing. Even when the same type of suede polishing cloth as used in this preliminary experiment was used, if level C appeared when the same discretization process was performed, the number of LPDs in the subsequent polishing was 10/10. It was confirmed to be below the wafer.

Thus, the present invention shows that there is a significant correlation between the discrete parameter group obtained by waveform analysis from the time waveform data of the platen load current value and the number of LPDs on the polished surface of the semiconductor wafer after polishing. they confirmed. In addition, the discrete parameter group corresponding to time series according to this preliminary experiment example is an example, and the parameter obtained by waveform analysis of the time waveform data of the surface plate load current value in each polishing time, and the polished surface of the semiconductor wafer after polishing. A significant correlation is also recognized with the number of LPDs, and the number of LPDs in this preliminary experiment can be replaced by a polishing result index such as surface roughness. Since the surface plate load current value is data that can be acquired in real time during polishing, the present inventors have found that it is possible to accurately and in real time determine when to start using the polishing cloth for semiconductor wafers by considering this experimental fact. bottom.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that each configuration in the drawing is a schematic diagram, and differs from the actual aspect ratio.

(Method for Determining When to Start Using Polishing Cloth for Semiconductor Wafers)
Please refer to the flow chart of FIG. A method for determining when to start using a polishing pad for semiconductor wafers according to an embodiment of the present invention includes at least a preliminary step S10, a first step S21, a second step S22 and a third step S23. In this preliminary step S10, the surfaces of at least one or more semiconductor wafers are sequentially polished using the first polishing cloth for semiconductor wafers, and the time waveform data of the surface plate load current value of the surface plate in each polishing is analyzed. A judgment condition is obtained based on the correspondence relationship between the result of polishing and the polishing result index of the semiconductor wafer after each polishing. Separately from this preliminary step, in the first step S21, a second semiconductor wafer polishing cloth is placed on a surface plate. Next, in the second step S22, at least one or more semiconductor wafers are successively polished using the same polishing conditions as in the preliminary step S10, and time waveform data is acquired and analyzed for each polishing step. Then, in the third step S23, it is determined whether or not the result of the waveform analysis in the second step S22 satisfies the determination condition. Details of each step will be described below. Further, hereinafter, the first polishing cloth for semiconductor wafers is referred to as "pre-polishing cloth", and the second polishing cloth for semiconductor wafers is referred to as "determination target polishing cloth".

<Preliminary process>
The preliminary step S10 is a step performed prior to the determination of the use start time of the main polishing cloth in the first to third steps, and uses a pre-polishing cloth of the same kind as the polishing cloth to be judged, and prepares at least one or more semiconductor wafers. The surface of each is polished sequentially. The term "same type" as used herein refers to polishing cloths made of the same material and having the same polishing cloth as a product, but having different manufacturing dates and the like. In addition, polishing conditions such as polishing methods such as single-wafer single-side polishing and batch-type single-side polishing, applied pressure, surface plate rotation speed, and type of slurry used inevitably change when polishing a large number of semiconductor wafers in sequence. Except for the conditions, the polishing conditions for polishing with the pre-polishing cloth are the same as the polishing conditions for polishing with the judgment target polishing cloth. The number of semiconductor wafers to be polished is not particularly limited, but is approximately 5 to 20 as an example.

In the preliminary step S10, time waveform data of the surface plate load current value in each polishing time obtained when the semiconductor wafers are sequentially polished using the pre-polishing cloth is obtained. Next, waveform analysis is performed on this time waveform data. For example, using the SAX method in the same manner as in the preliminary experiment described above, the surface plate load current value in the time waveform data is divided into three or more stages and encoded, and a discrete parameter group corresponding to the time series is obtained. By doing so, the above waveform analysis can be performed.

Then, separately from the waveform analysis, a polishing result index after each polishing is obtained when polishing is performed sequentially using the pre-polishing cloth. As a polishing result index, the number of LPDs on the surface to be polished after polishing may be used as in the preliminary experiment example described above, or surface roughness, SFQR (Site front least squares range), GBIR (Global backside ideal range), etc. Any quality parameter for polishing can be used, such as flatness.

Further, determination conditions are obtained based on the correspondence relationship between the result of waveform analysis of the time waveform data and the polishing result index after each polishing. For example, in the subsequent polishing, it is sufficient to obtain a judgment condition under which the polishing result index is equal to or less than a predetermined threshold value. In the above-described preliminary experiment example, if level C appears, the determination condition is that the number of LPDs corresponding to the polishing index is 10 or less per wafer in subsequent polishing. It may be appropriately determined by comparing the correspondence between the analysis result and the polishing result index.

The method of waveform analysis is not limited to the SAX method, and a unit space is a set of time waveform data of a pre-polishing cloth having a good polishing result index such as the number of LPDs. How far the current value is from the unit space may be analyzed by applying the MT method. Although actually measured time waveform data may be used as the object of analysis, the number of times the waveform crosses a specific value or the time during which the value is within a specific range is used as a feature quantity. may be analyzed. In addition, the time waveform data measured in advance is divided into several groups using a clustering method such as the k-means method, and to which group the time waveform data of dummy polishing in the main polishing belongs. , and based on whether or not the past performance of the polishing result index of the group was good, it is possible to determine the dummy polishing end point of the polishing cloth to be determined in the main polishing.

<First step>
After performing the preliminary step S10, in the first step S21, a polishing cloth to be judged (second polishing cloth for semiconductor wafers) is placed on a surface plate. At this stage, the polishing cloth to be judged is in an unused state in which it has never been polished, including the polishing of dummy wafers.

<Second step>
Subsequent to the first step S21, in a second step S22, at least one or more semiconductor wafers are sequentially polished using the same polishing conditions as in the preliminary step S10. During polishing, time waveform data is obtained for each polishing, and the time waveform data is analyzed using the same method as in the preliminary step S10.

<Third step>
Then, in the third step S23, it is determined whether or not the result of the waveform analysis in the second step S22 satisfies the determination condition obtained in the preliminary step S10. If the result of waveform analysis when polishing with the polishing cloth to be judged satisfies the judgment conditions, if the use of the polishing cloth to be judged is started after this, the polishing result index of the semiconductor wafer will be obtained in the next and subsequent polishing. can be determined to produce good results as product wafers. Conversely, if the result of waveform analysis when polishing is performed using the polishing cloth to be judged does not satisfy the judgment conditions, the polishing result index of the next semiconductor wafer will not necessarily be sufficient as a product wafer. Not exclusively. Therefore, in the latter case, it can be determined that a further dummy polishing process must be performed prior to the main polishing in order to apply the judgment target polishing cloth to the main polishing.

The determination result may be notified to the operator via a notification unit such as a display, a speaker, or a lamp, or the determination result may be notified to the polishing apparatus or its control unit as a result signal.

If this judgment method is used, it is possible to start applying the polishing cloth to be judged in real time to the main polishing by non-destructive inspection based on the judgment conditions obtained in advance and the surface plate load current value obtained during polishing (in other words, It is possible to determine whether the dummy polishing may be terminated. A polishing method according to one embodiment of the present invention will now be described below with reference to the flow chart of FIG.

(Semiconductor wafer polishing method)
In the method for polishing a semiconductor wafer according to one embodiment of the present invention, it is determined that the use of the polishing cloth to be determined (second polishing cloth for semiconductor wafers) can be started according to the above-described method for determining the time to start using the polishing cloth for semiconductor wafers. Polishing is performed using dummy wafers (semiconductor wafers for non-products) until the next time (S21 to S23). Until the judgment is completed, it corresponds to performing so-called dummy polishing.

Then, after it is determined that the polishing cloth to be determined can be used, polishing is performed using a semiconductor wafer for production (S30). The main polishing may be started from the next time when it is determined that the use can be started, or the main polishing may be started after several times of dummy polishing from the next time when it is determined that the use can be started. .

According to the present embodiment, the present polishing method is also useful in that the number of times of dummy polishing can be reduced without substantially stopping polishing to determine when to start using the polishing pad.

As the dummy wafer, a semiconductor wafer of the same type (same material, same shape) as the product semiconductor wafer can be used. However, the thickness of the dummy wafer may be thinner than the product semiconductor wafer as long as it can be polished. Impurities may be attached as long as they do not contaminate the polishing cloth to be judged and the polishing apparatus. Unlike product wafers, dummy wafers may be repeatedly subjected to dummy polishing as long as they have a thickness that enables polishing.

(semiconductor wafer polishing system)
Referring to FIG. 6, a semiconductor wafer polishing system according to one embodiment of the invention is described. The semiconductor wafer polishing system 100 has a holder 120 that holds a semiconductor wafer 190 and a surface plate 110 having a polishing cloth 112 on the surface thereof. By rotating 110 and semiconductor wafer 190 , polishing processing for polishing the surface of semiconductor wafer 190 is performed multiple times with the same polishing pad 112 . The semiconductor wafer polishing system 100 further includes a control section 130 , and a waveform analysis section 140 , a storage section 150 , a determination section 160 and a wafer exchange section 170 which are controlled via the control section 130 . The wafer exchange unit 170 can have a dummy wafer storage unit 171 and a product wafer storage unit 172. The dummy wafer storage unit 171 stores dummy wafers for dummy polishing, and the product wafer storage unit 172 stores actual polishing. A semiconductor wafer 190 for is stored.

The storage unit 150 stores the time of the surface plate load current value of the surface plate 110 at each polishing time when the surfaces of at least one or more semiconductor wafers are successively polished using a polishing cloth of the same kind as the polishing cloth 112. A determination condition based on the correspondence relationship between the result of waveform analysis of the waveform data and the polishing result index of the semiconductor wafer 190 after each polishing is stored. The waveform analysis method, polishing result index, and determination conditions in this embodiment are the same as in the case of using the pre-polishing cloth in the embodiment of the determination method described above, and the above description is used for details.

The control unit 130 first (i) causes the holding unit 120 to hold a dummy wafer. The dummy wafer may be acquired from the dummy wafer storage section 171 of the wafer exchange section 170 .

Next, the control unit 130 (ii) uses the waveform analysis unit 140 to sequentially polish at least one or more dummy wafers using polishing conditions similar to the polishing conditions stored in the storage unit 150, Acquire the time waveform data in each polishing and analyze the waveform. The waveform analysis unit 140 may also serve as an acquisition unit that acquires the waveform data of the surface plate load current value. The platen load current value can be obtained from a motor or the like that rotates the platen 110 .

Subsequently, (iii) the control unit 130 uses the determination unit 160 to determine whether or not the result of the waveform analysis using the dummy wafer satisfies the determination conditions stored in the storage unit 150 .

After (iv) the determination condition is satisfied, the control unit 130 causes the holding unit 120 to hold the semiconductor wafer 190 using the wafer exchange unit 170 . Therefore, the object to be polished is switched from the dummy wafer to the semiconductor wafer.

By using the semiconductor wafer polishing system 100, the above polishing method can be performed.

The determination method, polishing method, and polishing system described above can be applied to any polishing cloth used in a polishing apparatus for semiconductor wafers, but it is particularly preferable to apply them to a polishing cloth for a single-sided polishing apparatus.

The semiconductor wafers to be polished by the present invention are preferably silicon wafers, but the present invention can also be applied to any other semiconductor wafers such as SiC wafers and sapphire wafers. . The semiconductor wafer may be a bulk wafer, may have a homoepitaxial layer or heteroepitaxial layer formed on its surface, or may be a bonded wafer.

In addition, for the surface plate 110 and the polishing cloth 112, a general configuration used in a polishing apparatus for semiconductor wafers can be applied. Also, in the single-side polishing apparatus, a polishing head can be applied to the holding portion 120 . In both polishing apparatuses, a robot hand and a wafer chuck attached thereto can be applied to the holding part 120, and the semiconductor wafer 190 can be loaded onto the carrier plate using the holding part 120. FIG.

EXAMPLES The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples.

A group of discrete parameters was obtained by the SAX method from the platen load current values obtained in the preliminary experimental example described above. Specific discretization conditions are as follows. The platen load current value was divided into six levels and coded into levels A to F (level A is a low current value region and level F is a high current value region). As for the time axis, after normalizing the polishing time, it was divided into 53 sections and the last 6 sections were excluded. FIG. 7A shows a graph of the surface plate load current value after discretization by the SAX method, and FIG. 7B shows a band graph in which the code appearance frequencies of each polishing cycle in FIG. 7A are arranged in the order of polishing cycles. In FIG. 7A, 34 discrete parameter groups obtained from 34 waveform data (see FIG. 2) are superimposed as in the preliminary experiment example described above. The number of LPDs per wafer after polishing each time is as shown in FIG. 4 already described.

By comparing FIG. 4 and FIG. 7B, in Example 1, the following three types of determination conditions were obtained.
Judgment condition 1: If 10 or more levels E appear in the discrete parameter group, it is judged that the main polishing can be started.
This is because the number of LPDs in the eighth polishing batch rapidly decreased from the number of LPDs before that, and 10 or more level E appeared for the first time in this polishing batch.
Judgment condition 2: If there are two consecutive polishing batches in which 10 or more levels E appear in the discrete parameter group, it is judged that the main polishing can be started.
This is because in the 9th polishing batch, 10 or more levels E appeared following the 8th polishing batch.
- Judgment condition 3: If level F appears in the discrete parameter group, it is judged that the main polishing can be started.
This is because level F appeared for the first time in the 12th polishing batch.

In order to more reliably reduce the number of LPDs after the start of main polishing, judgment condition 3 is the most preferable, followed by condition 2. Even under condition 1, the number of LPDs after the start of main polishing can be reliably reduced.

Conventionally, the number of times of dummy polishing was set to 20 times. It was also confirmed that the level of the number of LPDs after completion of the dummy polishing was the same as in the conventional case where the dummy polishing was performed 20 times. From this, it was confirmed that the determination conditions of the present invention can be applied.

Thirty-four silicon wafers having a diameter of 300 mm and a total thickness of 775 μm were prepared. Also, on the surface plate of the single-wafer single-sided polishing apparatus, an unused suede polishing cloth having the same model number as that of the preliminary experiment was set. Using this single-wafer single-sided polishing apparatus, the surface of one silicon wafer is chemically mechanically polished while supplying an alkaline polishing liquid containing colloidal silica abrasive grains further containing a water-soluble polymer component as a polishing slurry onto the surface of the polishing cloth. Each time polishing was completed, the silicon wafers were exchanged, and one-side polishing of these 34 silicon wafers was sequentially performed under the same polishing conditions. The platen load current value was measured during polishing.

A group of discrete parameters was obtained by the SAX method from the obtained platen load current values. Specific discretization conditions are as follows. The platen load current value was divided into 10 levels and coded into levels A to J (level A is a low current value region and level J is a high current value region). The time axis was divided into 50 sections after normalizing the polishing time. FIG. 8A shows a graph of the surface plate load current value after discretization by the SAX method, and FIG. 8B shows a band graph in which the code appearance frequency of each polishing cycle in FIG. 8A is arranged in the order of polishing cycles. 34 discrete parameter groups are superimposed on FIG. 8A.

In addition, the number of LPDs per wafer after each polishing was measured in the same manner as in the preliminary experiment. The results are shown in FIG.

By comparing FIG. 9 and FIG. 8B, the following two determination conditions were obtained in Example 2.
- Judgment condition 1: If level J appears in the discrete parameter group, it is judged that the main polishing can be started.
This is because the number of LPDs in the 10th polishing batch decreased rapidly from the number of LPDs before it, and level J appeared for the first time in this polishing batch.
Judgment condition 2: It is judged that the main polishing can be started when there are two continuous polishing batches in which level J appears in the discrete parameter group.
This is because level J appeared in the 13th polishing batch following the 12th polishing batch.

In order to more reliably reduce the number of LPDs after the start of main polishing, determination condition 2 is preferable, and even with determination condition 1, the number of LPDs after the start of main polishing can be reliably reduced.

INDUSTRIAL APPLICABILITY According to the present invention, there are provided a method for judging the timing of starting use of a polishing cloth for semiconductor wafers, which can accurately and in real time determine the timing for starting use of a polishing cloth for semiconductor wafers, a method for polishing semiconductor wafers using the same, and a semiconductor. A wafer polishing system can be provided.

110 surface plate 112 semiconductor wafer polishing cloth 120 holder 130 control unit 140 waveform analysis unit 150 storage unit 160 determination unit 170 wafer exchange unit 171 dummy wafer storage unit 172 product wafer storage unit 190 semiconductor wafer

Claims (6)

A method for determining when to start using a semiconductor wafer polishing cloth placed on a surface plate of a semiconductor wafer polishing apparatus, comprising:
The surface of at least one or more semiconductor wafers is sequentially polished using the first polishing cloth for semiconductor wafers, and the result of waveform analysis of the time waveform data of the surface plate load current value of the surface plate in each polishing, and each time a preliminary step of obtaining a judgment condition based on a correspondence relationship with the polishing result index of the semiconductor wafer after polishing;
a first step of placing a second semiconductor wafer polishing cloth on the surface plate;
a second step of sequentially polishing at least one or more semiconductor wafers using the same polishing conditions as in the preliminary step, acquiring the time waveform data in each polishing step, and analyzing the waveform;
a third step of determining whether the result of waveform analysis in the second step satisfies the determination condition;
A method for determining when to start using a polishing pad for semiconductor wafers, comprising: 2. The method for determining when to start using a polishing cloth for semiconductor wafers according to claim 1, wherein said polishing result index is the number of LPDs observed on the polished surface of the semiconductor wafer after polishing. The waveform analysis is performed by dividing the surface plate load current value in the time waveform data into three or more stages using the SAX method, encoding the values, and obtaining a discrete parameter group corresponding to the time series. 3. A method for determining when to start using the polishing pad for semiconductor wafers according to 1 or 2. 4. The method for judging when to start using a polishing cloth for semiconductor wafers according to claim 1, wherein said polishing apparatus is a single-sided polishing apparatus for semiconductor wafers. According to the method for determining when to start using the polishing cloth for semiconductor wafers according to any one of claims 1 to 4, the second polishing cloth for semiconductor wafers is for non-product use until it is determined that it is possible to start using it. and performing the polishing using a product semiconductor wafer after the time when it is determined that the use can be started. A holding part for holding a semiconductor wafer and a surface plate having a polishing cloth on the surface thereof are provided. A semiconductor wafer polishing system that performs polishing processing for polishing the surface of a semiconductor wafer multiple times with the same polishing cloth,
The semiconductor wafer polishing system further comprises a control unit, and a waveform analysis unit, a storage unit, a determination unit, and a wafer exchange unit controlled via the control unit,
Time waveform data of the surface plate load current value of the surface plate in each polishing when the surfaces of at least one or more semiconductor wafers are sequentially polished using a polishing cloth of the same kind as the polishing cloth, in the storage unit. and a determination condition based on a correspondence relationship between a result of waveform analysis of and a polishing result index of the semiconductor wafer after each polishing,
The control unit
(i) causing the holder to hold a dummy wafer;
(ii) using the waveform analysis unit to sequentially polish at least one or more dummy wafers using the same polishing conditions as the polishing conditions stored in the storage unit, and the time waveform in each polishing; Acquire data, analyze waveforms,
(iii) using the determination unit to determine whether the result of waveform analysis using the dummy wafer satisfies the determination conditions stored in the storage unit;
(iv) A semiconductor wafer polishing system, wherein after the determination condition is satisfied, the semiconductor wafer is held by the holding section using the wafer exchange section.

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