Method for classifying and optimizing important performance parameters of recorded target material

Abstract

The invention discloses a method for classifying and optimizing important performance parameters of a recorded target material, which comprises the following steps: firstly, based on a Plackett-Burman experimental method, obtaining a combination of a plurality of influence factor center film thicknesses so as to obtain important performance parameters of an optical medium layer of an optical disc based on the combination of the influence factor center film thicknesses; determining whether the relationship between the important performance parameters and the influence factors is significant or not, obtaining important performance parameter combinations including the same important performance parameters in strongly correlated important performance parameter combinations based on an important performance parameter screening rule, obtaining screened influence factor combinations, and obtaining the important performance parameter combinations including the same important performance parameters based on an OD function. The OD function is optimized through the steepest climbing experiment and the CCD experiment in sequence, and the final value of the influence factor is determined. According to the method, guidance can be provided for subsequent target material localization manufacturing process adjustment, so that the purposiveness is higher when an operator debugs important performance parameters subsequently, the optical disc production quality is guaranteed, and the production takt is accelerated.

Description

Technical Field

[0001] The present invention relates to the field of optical storage technology, and in particular to a method for classifying and optimizing important performance parameters of a recording target material. Background Art

[0002] With the digitization of information resources and the rapid growth of information volume, the requirements for the storage density, access rate and storage life of the medium are constantly increasing. In this case, optical storage technology came into being. Optical storage technology has the advantages of high storage density, long storage life, non-contact reading and writing, high signal-to-noise ratio of information, and low price of information bit.

[0003] The 500GB archive optical disc has the largest capacity among the existing commercially available optical storage media. It is made of two single-sided optical discs bonded together. Each single-sided optical disc includes three optical medium layers, L0, L1, and L2. Each optical medium layer is composed of a recording layer and an upper dielectric layer and a lower dielectric layer on both sides. In addition, there is a protective layer on the surface of the optical disc, an intermediate layer between the three optical medium layers, and a polycarbonate substrate with low absorption rate is used as the substrate material.

[0004] The recording principle is to change the incident light intensity of the recording layer through the upper and lower dielectric layers on both sides of the recording layer. Under the action of the incident light, the oxide in the recording layer decomposes and produces bubbles. The reflectivity at the bubble is significantly different from the reflectivity at the undecomposed part. According to the strength of the reflected light, it is decoded into a binary value to achieve binary recording. Among them, the recording target material used in the recording layer has an important influence on the read and write performance of the optical disc. Its raw materials, ratios, processing technology, etc. are one of the core technologies in optical disc manufacturing technology.

[0005] At present, most of the recording targets for 500GB archive discs are imported from Japan. Globally, the United States, Japan and other countries have a very advantageous position in the industrial chain with their first-mover advantage and technical patent barriers, relying on advanced manufacturing technology, and have strong bargaining power. However, after years of target technology development, some Chinese companies have made breakthroughs in recent years and have begun to gradually achieve domestic substitution.

[0006] The preparation process of recording targets includes four steps: powder synthesis, green blank forming, sintering process, and finished product manufacturing. Among them, the process route, sintering method, sintering atmosphere, forming aids, sintering aids, etc. in each step are different, and the combination methods are diverse, which are unique to Japanese target manufacturers. It is difficult to produce recording targets with completely consistent resistivity, density, roughness, filling rate, crystallinity, optical constants, etc. through reverse development.

[0007] Therefore, in the process of domestic substitution of recording targets for 500GB archive optical discs, in addition to reverse research and development of the targets themselves, the corresponding optical disc performance parameter adjustment and optimization technology is also indispensable. Through the adjustment and optimization of process parameters, the performance parameters of optical discs manufactured by domestic targets can reach a similar level, making up for the performance difference between them and Japanese targets.

[0008] The main process parameter adjusted by the target material during the manufacturing process of the optical disc is the film thickness of each layer of optical thin film formed by sputtering on the substrate. During the development of the optical disc, one of the main considerations for the central film thickness of each layer of optical thin film and the performance design of the target material is the need to eliminate the diffuse reflection generated between the three optical medium layers. Diffuse reflection will cause energy loss when the incident light is transmitted between the layers during recording and reading, and even form multiple focal points during reflection and transmission between the films, making it impossible to achieve normal focusing, which seriously affects the reading and writing performance of the optical disc. By reasonably selecting the film thickness and designing the performance of the target material, the phases of the diffuse reflection light between the optical medium layers can be opposite, thereby canceling each other out and achieving the purpose of eliminating diffuse reflection. If the film thickness is not set properly, the diffuse reflection cannot be canceled out, and the parameter adjustment between the layers will produce unpredictable mutual influence. When the film thickness of each layer of optical thin film is set reasonably, a small adjustment is made to the film thickness of the recording layer and the dielectric layer of the current optical medium layer, which only changes the performance parameters of the current optical medium layer, while the performance parameters of other optical medium layers are basically unaffected.

[0009] In the process of domestic substitution, the performance parameters of 500GB archive optical discs are adjusted mainly by adjusting the film thickness several times, and the adjustment basis is mainly determined by experience. At present, the main difficulties are as follows:

[0010] 1. According to the center film thickness of the optical disc prototype design, when the domestically produced target material is directly used for production, there are large differences in the performance parameters of the optical disc. Nearly half of the performance parameters of the optical disc exceed the specification value, and some performance parameters exceed the warning value;

[0011] 2. When the film thickness of a certain optical medium layer is adjusted separately, the performance parameters of other optical medium layers will change accordingly due to the interlayer influence, and the change is not linear;

[0012] 3. After dozens of adjustments, there are still several performance parameters that cannot be adjusted to meet the requirements, showing a trend of one increasing while the other decreasing. In addition, the relationship between the film thickness of each optical medium layer and the performance parameters of each layer is unclear, resulting in low debugging efficiency and poor results. Summary of the invention

[0013] The invention discloses a method for classifying and optimizing important performance parameters of a recording target material to overcome the above technical problems.

[0014] In order to achieve the above object, the technical solution of the present invention is:

[0015] A method for classifying and optimizing important performance parameters of a recording target material comprises the following steps:

[0016] S1: preliminarily determining the influencing factors of important performance parameters of the optical medium layer of the optical disc, as well as the high level value and the low level value of the film thickness of the influencing factors;

[0017] S2: according to the high level value and the low level value of the film thickness of the influencing factor, based on the Plackett-Burman experimental method, obtain a plurality of orthogonal combinations of the high and low level values ​​of the film thickness of the influencing factor, so as to obtain the actual value of the important performance parameter of the optical medium layer of the optical disc based on the orthogonal combination of the high and low level values ​​of the film thickness of the influencing factor; then determine whether the relationship between the important performance parameter and the influencing factor is significant, and obtain the number of influencing factors with significant relationship with the important performance parameter;

[0018] S3: According to the number of influencing factors that are significantly related to the important performance parameters, based on the important performance parameter screening rules, determine the important performance parameter combination that is strongly correlated with the i-th, i=1, ..., I important performance parameters, so as to obtain the important performance parameter combination containing the same important performance parameters, and then obtain the screened influencing factor combination; the screened influencing factor combination includes: influencing factors that are significantly related to the important performance parameters in the important performance parameter combination, and influencing factors of optical medium layers adjacent to the optical medium layer to which the influencing factors that are significantly related to the important performance parameters in the important performance parameter combination belong;

[0019] S4: constructing an OD function according to the combination of important performance parameters including the same important performance parameters; and determining a plurality of screened influencing factor value combinations according to the high level value and the low level value of the influencing factor film thickness, so as to obtain the OD function value of the plurality of screened influencing factor value combinations, and then obtaining the screened influencing factor value combination corresponding to the maximum OD function value;

[0020] S5: according to the value combination of the screened influencing factors, multiple groups of steepest climbing test influencing factor value combinations are obtained to obtain important performance parameters of the optical disk based on the steepest climbing test influencing factor value combination, and the steepest climbing test is performed on the OD function to obtain the local maximum value of the OD function in the fastest rising direction to obtain the local optimal area of ​​the OD function;

[0021] S6, using Minitab software to perform CCD experiments according to the steepest climbing experiment influencing factor value combination corresponding to the local optimal region of the OD function, to obtain multiple CCD experiment influencing factor value combinations, so as to obtain important performance parameters of the optical disc based on the CCD experiment influencing factor combination, and then according to the OD function, to obtain the CCD experiment influencing factor value combination with the maximum OD function value;

[0022] Then the final value of the influencing factor in the screened influencing factor combination is the value of the corresponding influencing factor in the influencing factor value combination of the CCD experiment with the largest OD function value;

[0023] S7: Based on the influencing factors in the non-screened influencing factor combination, repeat S2 to S6 until there are no non-screened influencing factors, and obtain the final values ​​of all the influencing factors.

[0024] Beneficial effect: The method of classifying and optimizing the important performance parameters of the recording target material of the present invention first obtains the orthogonal combination of the high and low level values ​​of the film thickness of the multiple influencing factors based on the Plackett-Burman experimental method, and obtains the actual value of the important performance parameters of the optical medium layer of the optical disc based on the orthogonal combination of the high and low level values ​​of the film thickness of the influencing factors in actual production; then determines whether the relationship between the important performance parameters and the influencing factors is significant, and then obtains the important performance parameter combination with the same important performance parameters in the strongly correlated important performance parameter combination based on the important performance parameter screening rule, and then obtains the screened influencing factor combination, and based on the OD function, the OD function is optimized through the steepest climbing experiment and the CCD experiment in turn, and the final value of the influencing factor is determined. The present invention can provide guidance for the subsequent adjustment of the manufacturing process of the localization of the target material, and then the subsequent operators are more purposeful when debugging the important performance parameters, ensuring the quality of the optical disc production and speeding up the production rhythm. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 A flow chart of a method for classifying and optimizing important performance parameters of a recording target material of the present invention;

[0027] Figure 2 It is a structural diagram of each film layer of a 500GB archive optical disc in an embodiment of the present invention;

[0028] Figure 3 It is a flow chart of the screening of impact factors of the Plackett-Burman experiment in an embodiment of the present invention;

[0029] Figure 4 It is a four-in-one residual diagram of the CCD experiment in the embodiment of the present invention;

[0030] Figure 5 It is a three-dimensional effect surface diagram of the CCD experiment in the embodiment of the present invention;

[0031] Figure 6 It is a contour map of the CCD experiment in the embodiment of the present invention;

[0032] Figure 7 A response optimizer parameter setting diagram for a CCD experiment in an embodiment of the present invention;

[0033] Figure 8 It is a model optimization response diagram of the CCD experiment in an embodiment of the present invention;

[0034] Fig. 9 The figure is a flow chart of loop optimization in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] This embodiment introduces a method for classifying and optimizing important performance parameters of recording target materials, such as Figure 1 As shown, the following steps are included:

[0037] S1: preliminarily determining important performance parameters of each optical medium layer of the optical disc, influencing factors of the important performance parameters, and high and low level values ​​of the film thickness of the influencing factors;

[0038] The optical medium layer of the optical disc includes: an L0 optical medium layer, an L1 optical medium layer and an L2 optical medium layer;

[0039] The influencing factors of the important performance parameters include: L2 lower dielectric film thickness, L2 recording film thickness, L2 upper dielectric film thickness, L1 lower dielectric film thickness, L1 recording film thickness, L1 upper dielectric film thickness, L0 lower dielectric film thickness, L0 recording film thickness, L0 upper dielectric film thickness;

[0040] Specifically, the optical medium layer of the optical disc of the present embodiment includes an L0 optical medium layer, an L1 optical medium layer and an L2 optical medium layer; the L0 optical medium layer, the L1 optical medium layer and the L2 optical medium layer have the same structure, and all include an upper dielectric film, a recording film and a lower dielectric film connected in sequence; the optical disc, from the outside to the inside, is an L2 upper dielectric film, an L2 recording film, an L2 lower dielectric film, an L1 upper dielectric film, an L1 recording film, an L1 lower dielectric film, an L0 upper dielectric film, an L0 recording film and an L0 lower dielectric film; Figure 2 As shown;

[0041] Specifically, in this embodiment, the method used to preliminarily determine the important performance parameters of each film layer that affect the quality of the optical disc (including d-MLSE, recording power, reflectivity, and conversion sensitivity), the influencing factors of the important performance parameters, and the central film thickness value, high-level value, and low-level value of the influencing factors of each important performance parameter is based on the existing relevant Japanese standards and the experience in designing and adjusting the central film thickness of each film layer of the optical disc. This is prior art for those skilled in the art, so it will not be described in detail here.

[0042] Specifically, the center film thickness of each film layer of the 500GB archive optical disc is specified by Japanese Panasonic designers through repeated verification. Since the parameters of Japanese-designed optical discs are relatively stable, the adjustment range is usually between ±2nm to meet the performance requirements. For specific structures, see Figure 2 . In the process of adjusting the film thickness of the target material for localization, some film thicknesses were adjusted by 2 to 5 nm, but the expected effect was still not achieved. This was mainly reflected in the fact that the four parameters of d-MLSE, recording power, reflectivity, and conversion sensitivity exceeded the specification value or reached the warning value, resulting in a large difference between the domestic target material and the Japanese target material. Due to the large number of variables in the target material manufacturing process, it is difficult to successfully reverse-develop a domestic target material with the same performance as the Japanese target material. Therefore, it is necessary to adjust the film thickness so that the optical disc produced by the domestic target material can reach the same quality as the current optical disc produced by the Japanese target material. In this embodiment, the L2 lower inductive body film thickness, L2 recording film thickness, L2 upper inductive body film thickness, L1 lower inductive body film thickness, L1 recording film thickness, L1 upper inductive body film thickness, L0 lower inductive body film thickness, L0 recording film thickness, and L0 upper inductive body film thickness are used as influencing factors of important performance parameters, and the four important performance parameters of the optical disc, d-MLSE, recording power, reflectivity, and conversion sensitivity, are studied as responses. The influencing factors of important performance parameters and the high and low level values ​​of the influencing factors of each important performance parameter are shown in Table 1;

[0043] Table 1 Influencing factors of important performance parameters and high and low level values ​​of the influencing factors of each important performance parameter

[0044]

[0045] Specifically, in the subsequent rounds of optimization, since some film thicknesses have been optimized and become fixed values, they no longer exist in the form of high and low values, and the number of influencing factors decreases accordingly. For example, if the first round of optimization determines four of the nine film thicknesses, then the second round of influencing factors becomes five.

[0046] S2: According to the high level value and low level value of the film thickness of the influencing factor, based on the Plackett-Burman experimental method, a plurality of orthogonal combinations of high and low level values ​​of the film thickness of the influencing factor are obtained, so as to actually produce an optical disc based on the orthogonal combination of high and low level values ​​of the film thickness of the influencing factor, and measure the actual value of the important performance parameter of the optical medium layer; then determine whether the relationship between the important performance parameter and the influencing factor is significant, and obtain the number of influencing factors with significant relationship with the important performance parameter;

[0047] Preferably, the important performance parameters include: L0 d-MLSE, L0 recording power, L0 reflectivity, L0 conversion sensitivity; L1 d-MLSE, L1 recording power, L1 reflectivity, L1 conversion sensitivity; L2 d-MLSE, L2 recording power, L2 reflectivity, L2 conversion sensitivity;

[0048] Specifically, this embodiment designs a Plackett-Burman experiment according to the high level value and low level value of the film thickness of the influencing factor, obtains the orthogonal combination of the high and low level values ​​of the film thickness of multiple influencing factors, and obtains the actual value of the important performance parameter of the optical medium layer of the optical disc based on the orthogonal combination of the high and low level values ​​of the film thickness of the influencing factor in actual production; then determines whether the relationship between the response variable (important performance parameter) and the influencing factor is significant; and obtains the number of influencing factors of the important performance parameter whose relationship with the response variable is significant, and the influencing factors of the important performance parameter whose relationship with the response variable is significant;

[0049] Specifically, in this embodiment, the d-MLSE, recording power, reflectivity, and conversion sensitivity of the L0 optical medium layer, the L1 optical medium layer, and the L2 optical medium layer are measured respectively, and the mathematical statistics software Minitab is used to analyze the simulation experimental data to determine whether the relationship between the important performance parameters and the influencing factors is significant;

[0050] Specifically, this embodiment selects d-MLSE, recording power, reflectivity, and conversion sensitivity of each of the L0 optical medium layer, L1 optical medium layer, and L2 optical medium layer of the optical disc, a total of twelve values ​​as response variables, i.e., important performance parameters, and generates a Plackett-Burman experimental design table through Minitab software according to the value range of the influencing factors given in Table 1. In this example, in order to meet the resolution requirements of the experiment, 12 experiments are required for the influencing factors of 9 important performance parameters, as well as their upper and lower limits. The values ​​of the influencing factors of the 9 important performance parameters in the 12 experiments are shown in Table 2;

[0051] Table 2 Plackett-Burman experimental design table

[0052]

[0053]

[0054] Specifically, in subsequent rounds of optimization, as the number of key factors gradually decreases, the Plackett-Burman experiment may no longer need to be conducted 12 times, which can meet the demand.

[0055] In this example, according to the film thickness conditions in Table 2, optical discs with 12 film thickness combinations were produced, and the d-MLSE, recording power, reflectivity, and conversion sensitivity of the L0 optical medium layer, the L1 optical medium layer, and the L2 optical medium layer were measured. The measurement results and the specification values ​​and warning values ​​of each performance parameter are shown in Table 3.

[0056] Table 3 Plackett-Burman experimental design measurement results

[0057]

[0058] Specifically, this embodiment uses the mathematical statistics software Minitab to analyze the simulation experiment data, and screens the influencing factors of the important performance parameters of each layer of the optical disc until the number of influencing factors of each response variable is reduced to a minimum, such as Figure 3 In this example, the relationship between the response variables after the first round of simulation and the influencing factors after screening is shown in Table 4;

[0059] Table 4 Relationship between response variables after the first round of simulation and influencing factors after screening

[0060]

[0061] Specifically, in the subsequent rounds of optimization, as some of the previous key factors become fixed values, the number of remaining key factors gradually decreases, and with each round of optimization, the experimental area gradually moves toward the optimal point along the vertical direction of the contour line, and the functional relationship between the response variable and the influencing factor changes. The relationship in Table 4 will also change in each round.

[0062] S3: according to the important performance parameter screening rule, determine the important performance parameter combination that is strongly correlated with the i-th, i=1, ..., I important performance parameters, so as to obtain the important performance parameter combination containing the same important performance parameters, and then obtain the screened influencing factor combination, wherein the screened influencing factor combination includes: influencing factors that have significant relationships with the important performance parameters in the important performance parameter combination, and influencing factors of optical medium layers adjacent to the optical medium layer to which the influencing factors that have significant relationships with the important performance parameters in the important performance parameter combination belong;

[0063] Specifically, this embodiment screens out a group of important performance parameter combinations with the highest consistency of strongly correlated influencing factors, where the important performance parameters in the important performance parameter combination are greatly affected by the same or similar influencing factors and are less affected by inter-layer influence;

[0064] Specifically, according to the screening results of the significant influencing factors of the important performance parameters of each layer of the optical disc, this embodiment compares all the important performance parameters of each layer in pairs, and lists the orthogonal table for the number of the same significant influencing factors contained in each other. In this example, taking 3 obtained by orthogonalization of L0 reflectivity and L0 D-Mlse as an example, the significant influencing factors of L0 reflectivity in Table 4 are L0 upper dielectric film thickness, L0 recording film thickness, L0 lower dielectric film thickness, and L2 lower dielectric film thickness, and the influencing factors of L0 D-Mlse in Table 4 are L0 upper dielectric film thickness, L0 recording film thickness, L0 lower dielectric film thickness, and L1 lower dielectric film thickness, among which L0 reflectivity and L0 D-Mlse have the same influencing factors of the three important performance parameters, so the corresponding value is 3, and the rest are shown in Table 5;

[0065] Table 5 Relationship between response variables after the first round of simulation and significant influencing factors after screening

[0066]

[0067] Preferably, the important performance parameter screening rules are as follows:

[0068] Specifically, this embodiment establishes the following rules based on the different numbers of significant influencing factors contained in the important performance parameters of each layer:

[0069] a. When the number of factors that are significantly related to the i-th important performance parameter is 3:

[0070] If among the influencing factors with significant relationship with the jth important performance parameter, there are more than or equal to 2 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is strongly correlated with the jth important performance parameter;

[0071] If among the influencing factors with significant relationship with the jth important performance parameter, there are less than 2 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is not correlated with the jth important performance parameter;

[0072] b. When the number of factors that are significantly related to the i-th important performance parameter is 4:

[0073] If among the influencing factors with significant relationship with the jth important performance parameter, there are more than or equal to 3 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is strongly correlated with the jth important performance parameter;

[0074] If there are two influencing factors with significant relationship with the i-th important performance parameter among the influencing factors with significant relationship with the j-th important performance parameter, then the i-th important performance parameter is weakly correlated with the j-th important performance parameter;

[0075] If among the influencing factors with significant relationship with the jth important performance parameter, there are less than 2 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is not correlated with the jth important performance parameter;

[0076] c. When the number of factors that are significantly related to the i-th important performance parameter is 5:

[0077] If among the influencing factors with significant relationship with the jth important performance parameter, there are more than or equal to 4 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is strongly correlated with the jth important performance parameter;

[0078] If among the influencing factors with significant relationship with the jth important performance parameter, there are 3 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is weakly correlated with the jth important performance parameter;

[0079] If among the influencing factors with significant relationship with the jth important performance parameter, there are less than 3 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is not correlated with the jth important performance parameter;

[0080] d. When the number of significant influencing factors with respect to the i-th important performance parameter is 6:

[0081] If among the influencing factors with significant relationship with the jth important performance parameter, there are more than or equal to 4 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is strongly correlated with the jth important performance parameter;

[0082] If among the influencing factors with significant relationship with the jth important performance parameter, there are 3 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is weakly correlated with the jth important performance parameter;

[0083] If among the influencing factors that have a significant relationship with the jth important performance parameter, there are less than 3 influencing factors that have a significant relationship with the ith important performance parameter, then the ith important performance parameter is not correlated with the jth important performance parameter.

[0084] Specifically, this embodiment classifies a total of 12 important parameters of each optical medium layer according to the important performance parameter screening rules, and obtains 12 important performance parameter combinations. In this embodiment, for performance parameters that have more than 5 significant influencing factors, they are obviously affected by multiple film thicknesses in different optical medium layers and are in an abnormal state of being affected by layers, so they are not involved in this round of classification.

[0085] This embodiment finds an important performance parameter combination containing the same strongly correlated important performance parameters among the 12 important performance parameter combinations, that is, finds a combination with the highest consistency of important performance parameters among multiple strongly correlated important performance parameter combinations.

[0086] Specifically, the important performance parameter combinations that are strongly correlated with each important performance parameter in this embodiment are shown in Table 6, where letters are used as codes due to the large number of characters in each parameter. The code relationships and the first round of classification results in this example are detailed in Table 6.

[0087] Table 6 Classification of important performance parameters of the first round

[0088]

[0089]

[0090] In this example, it is obvious that the combination of A, D, G, and J appears the most times, and the letter combination is the most consistent, that is, L0 d-MLSE, L0 recorded power, L0 reflectivity, and L0 converted sensitivity are a group of categories with the strongest correlation. From Table 4, it can be seen that the common influencing factors of the performance parameters of this group, that is, the factors that have significant relationships with the important performance parameters in the important performance parameter combination are the L0 upper dielectric film thickness, the L0 recording film thickness, and the L0 lower dielectric film thickness. In addition, L0 d-MLSE and L0 recording power are related to the L1 lower dielectric film thickness, and the L1 lower dielectric film thickness is the influencing factor of the optical medium layer adjacent to the optical medium layer to which the important performance parameters in the important performance parameter combination belong; that is, when the film thicknesses of the upper dielectric film, recording film and lower dielectric film of the L0 optical medium layer and the film thickness of the L1 lower dielectric film adjacent to the L0 optical medium layer are adjusted, the four important performance parameters of the L0 optical medium layer, namely, L0 d-MLSE, L0 recording power, L0 reflectivity, and L0 conversion sensitivity, can be effectively adjusted, and they are less affected by the interlayer influence, which is consistent with the ideal situation. After this round of optimization is completed, the corresponding four film thicknesses are optimized, and the interlayer influence of the L0 layer will be further reduced.

[0091] Specifically, in the second and subsequent rounds of optimization, the film thickness of the four influencing factors screened out in the first round has reached the relatively optimal value, and the overall performance parameters have also been improved to a certain extent. The remaining performance parameters that are less affected by the interlayer effect are further extracted, and the corresponding film thicknesses are optimized. Finally, all nine film thicknesses are optimized to certain values, and the interlayer effect is eliminated.

[0092] Specifically, the important performance parameter combination obtained in step S3 with the same important performance parameters is subsequently optimized and adjusted. In this example, the parameters classified in the first round are A, D, G, and J. In the subsequent steps, the four performance parameters A, D, G, and J are optimized.

[0093] S4: constructing an OD function according to the combination of important performance parameters including the same important performance parameters; and determining a plurality of screened influencing factor value combinations according to the high level value and the low level value of the influencing factor film thickness, so as to obtain the OD function value of the plurality of screened influencing factor value combinations, and then obtaining the screened influencing factor value combination corresponding to the maximum OD function value;

[0094] Specifically, in this embodiment, the purpose of constructing the OD function is to find the local optimal region of the experiment through the subsequent steepest ascent method. Next, in step S6, a response surface experiment is performed within the range confirmed as the local optimal region, and then based on the results of the corresponding surface experiment, the response optimizer in the Minitab software is used to obtain the optimal film thickness setting under multiple responses. Among them, the steepest ascent method cannot be used directly when performing multi-objective optimization, so it is necessary to simplify the multi-objective optimization into a single-objective optimization problem through the OD function.

[0095] Preferably, the OD function constructed in this embodiment is as follows:

[0096]

[0097] In the formula, the value of OD is [0, 1], M is the number of response targets; d m To convert the mth response target y m Converted into an expectation function with a value of 0 to 1; m is the index number of the response target;

[0098] Among them, when the response target is d-MLSE / reflectivity / conversion sensitivity,

[0099]

[0100] When the response target is to record power,

[0101]

[0102] Among them, y m，min and m，max are the mth response target y in the experiment m The minimum and maximum values ​​of the specification, that is, y m The lower and upper limits of the tolerance, w is the weight factor, usually set to 0.3;

[0103] Specifically, the OD function is also called the overall normalized value function, where y m As the response target, a one-sided transformation function is used to transform the response target y m Convert to expected function d with value 0 to 1 m In this embodiment, d-MLSE, reflectivity, and conversion sensitivity are response targets that are expected to be as small as possible. m , using formula (1) for conversion, and for the response target y, the larger the expected recording power, the better m Use formula (2) to convert. Then based on the expected function d of each response target m The geometric mean of is used to establish the OD function.

[0104] Specifically, in this embodiment, according to the specification requirements of the four influencing factors in the influencing factor combination after screening in S3, based on the actual measured values ​​of the important performance parameters of the 12 experiments in S2, for the important performance parameter combination ADGJ with the highest consistency of the strongly correlated influencing factors, formulas (1), (2), and (3) are used to calculate the OD function, and the results are shown in Table 7.

[0105] Table 7 First round OD function calculation values ​​(OD values ​​of ADGJ)

[0106]

[0107] Specifically, this embodiment uses the factor analysis function of Minitab and deletes the insignificant items in the t test. The calculated regression equation is shown in formula (4), wherein the variance analysis tables before and after deleting the insignificant items are shown in Tables 8 and 9.

[0108] y=-1.75180+0.0353158×L0 recorded film thickness+0.0387773×L1 dielectric film thickness (4)

[0109] It can be seen from Table 9 that the overall P value of the model is 0.035, which is less than the significant level, that is, the regression effect is significant, the main effect of the factors in the model has a very significant impact on the OD function, and the P value of the lack-of-fit term is 0.418, which is greater than the significant level, and it is believed that this model does not produce a lack-of-fit phenomenon.

[0110] Table 8 Analysis of variance of OD function (before removing insignificant items)

[0111]

[0112]

[0113] Table 9 Analysis of variance of OD function (after removing insignificant items)

[0114]

[0115] Then, the value combination of the filtered influencing factors corresponding to the maximum OD function value is obtained;

[0116] S5: According to the high and low level values ​​of the film thickness recorded at L0 and the dielectric film thickness at L1, as well as the value combination of the screened influencing factors, multiple groups of steepest climbing test influencing factor combinations are obtained to obtain important performance parameters of the optical disc based on the steepest climbing test influencing factor combination, and the steepest climbing test is performed on the OD function to obtain the local maximum value of the OD function in the direction of the fastest rise, so as to obtain the local optimal area of ​​the OD function;

[0117] Preferably, the influencing factor value in the steepest climbing test influencing factor combination is:

[0118] The L0 recorded film thickness and the L1 dielectric film thickness are selected based on the L0 recorded film thickness and the L1 dielectric film thickness values ​​located in the local optimal region of the OD function in the steepest climbing experiment;

[0119] The upper L0 dielectric film thickness and the lower L0 dielectric film thickness are the upper L0 dielectric film thickness and the lower L0 dielectric film thickness in the value combination of the influencing factors after screening;

[0120] The L1 upper dielectric film thickness, L1 recording film thickness, L2 upper dielectric film thickness, L2 recording film thickness, and L2 lower dielectric film thickness are the center film thicknesses of the set L1 upper dielectric film, L1 recording film, L2 upper dielectric film, L2 recording film, and L2 lower dielectric film, respectively.

[0121] Specifically, according to the value combination of the screened influencing factors, the steepest climbing experiment is carried out on the OD function to reach the local maximum value of the OD function in the direction of the fastest rise, so as to determine the center point of the multi-response surface experiment:

[0122] According to formula (4), when the step length of the ramp is 1, the unit vector is (0.673, 0.739). Since the film thickness is usually adjusted in integers such as 0.5 nanometers and 1 nanometer, when the step length is 1.485, the amount of each step increase is (1, 1.098), which is approximately (1, 1.1).

[0123] Specifically, after calculating the OD function values ​​of the combination of values ​​of the influencing factors after screening, as shown in Table 7, the influence factor value corresponding to the maximum OD function value of the combination of values ​​of the influencing factors after screening is the value of the 7th row in Table 7, and the influence factor value of this row is used as the first OD function optimal condition; the steepest climbing test is carried out on the OD function, and four climbing tests are carried out in sequence, and each experiment records the film thickness of L0 and the film thickness of the dielectric film under L1 according to the unit vector. Among them, the first experimental values ​​of the dielectric film thickness on L0 and the dielectric film thickness under L0 are taken according to the combination of values ​​of the influencing factors after screening, that is, the film thickness value of the 7th row in Table 7, and the remaining five film thickness values ​​are taken as the central value. After the corresponding optical disc is produced, the four important parameter values ​​of L0 are measured, and the OD function is calculated. The results are shown in Table 9.

[0124] Table 9 Design and results of the first round of steepest climbing experiment

[0125]

[0126] As can be seen from Table 9, the location of Experiment 2 is the optimal region of the OD function;

[0127] S6, using Minitab software to conduct a CCD experiment (central composite bounded design experiment) according to the steepest climbing experiment influencing factor combination corresponding to the local optimal region of the OD function, to obtain the influencing factor combination of multiple CCD experiments, so as to obtain the important performance parameters of the optical disc based on the influencing factor combination of the CCD experiment, and then according to the OD function, to obtain the influencing factor combination of the CCD experiment with the maximum OD function value;

[0128] Then the final value of the influencing factor in the screened influencing factor combination is the value of the corresponding influencing factor in the influencing factor combination of the CCD experiment with the largest OD function value;

[0129] Specifically, this embodiment uses the response variable optimizer in the mathematical statistics software Minitab to adjust the weight and importance of each important performance parameter according to different optimization requirements to obtain the optimal factor setting conditions for the current parameter group;

[0130] Specifically, in this embodiment, according to the steepest climbing experiment influencing factor combination corresponding to the local optimal area of ​​the OD function obtained by the steepest climbing experiment, Minitab software is used for CCD design to obtain 13 CCD experiment influencing factor combinations, and optical discs corresponding to 13 film thickness value combinations are produced. After measuring the important performance parameters of the 13 optical discs, the OD function is calculated. The experimental design and results are shown in Table 10.

[0131] Table 10 CCD experimental results

[0132]

[0133] Minitab software was used to process the data in Table 11. The L0 recording film thickness A' and the L1 dielectric film thickness B' were used as independent variables, and the L0 d-MLSE, L0 recording power, L0 reflectivity, and the total OD function of the L0 converted sensitivity were used as dependent variables. Multiple regression analysis was performed, and variance analysis and goodness of fit analysis were performed. From the model fitting results, it was found that the quadratic polynomial model fitting equation was significant, and the regression equation was:

[0134] OD=-511.541+26.8347×A'-2.34689×B'-0.422327×A' 2 -0.204321×B' 2 +0.300

[0135] 727×A'×B', the variance analysis is shown in Table 11, and the four-in-one residual diagram is shown in Figure 4 , the three-dimensional effect surface diagram and contour diagram of the influence of the L0 recording film thickness A' and the L1 dielectric film thickness B' on the OD value, see Figure 5 , Figure 6.

[0136] Table 11 Variance analysis and goodness of fit analysis of OD function regression model

[0137]

[0138] As shown in Table 11, the regression model P<0.05, the lack of fit term P>0.05, indicating that the equation model has high significance, good fit, no statistical significance of the lack of fit term, and the unknown factors have little interference with the experiment. It can be used to predict the four performance parameters of the first round of L0 layer and the corresponding film thickness condition optimization process. 2 , B' 2 The P values ​​were all less than 0.05, indicating that they all had significant effects on the OD function.

[0139] Depend on Figure 4 It can be seen from the upper left of the residual normal probability plot and the lower left of the residual histogram that the residuals all obey the normal distribution. It can be seen from the upper right of the scatter plot of residuals and fitted values ​​that the residuals of each point maintain equal variance, without obvious "funnel shape" and "trumpet shape". It can be seen from the lower right of the scatter plot of residuals and observation value order that each point randomly fluctuates irregularly above and below the horizontal axis. In summary, it can be determined that the data fits the model well and the residuals are within the normal range.

[0140] The response variable optimizer in Minitab is used, such as Figure 7 As shown in the figure, the local optimal region of the OD function in the CCD experiment is used as the starting point for optimization. The optimization results are shown in Figure 8 As shown, the optimal film thickness setting conditions for the overall evaluation OD function of the current L0 d-MLSE, L0 recording power, L0 reflectivity, and L0 converted sensitivity are: L0 upper dielectric film thickness 6.5nm, L0 recording film thickness 40.28nm, L0 lower dielectric film thickness 16.5nm, L1 upper dielectric film thickness 15.4nm, L1 recording film thickness 36.15nm, L1 lower dielectric film thickness 23.90nm, L2 upper dielectric film thickness 14.95nm, L2 recording film thickness 32.5nm, L2 lower dielectric film thickness 19.45nm.

[0141] Under this film thickness condition, optical discs with corresponding film thickness were produced for actual measurement and verification. The L0 d-MLSE, L0 recording power, L0 reflectivity and L0 conversion sensitivity were all qualified, and the OD function was calculated to be 0.845.

[0142] At this point, the parameters of the L0 upper dielectric film thickness, L0 recording film thickness, L0 lower dielectric film thickness, and L1 lower dielectric film thickness have been set, and the corresponding four important performance parameters of L0 d-MLSE, L0 recording power, L0 reflectivity, and L0 converted sensitivity have been optimized;

[0143] S7: Based on the non-screened influencing factor combinations, repeat S2 to S6 until there are no non-screened influencing factor combinations, and obtain final values ​​of all influencing factors.

[0144] Specifically, after determining the remaining optimal factor setting conditions, redesign the Plackett-Burman experiment, obtain the new regression equation of the remaining important performance parameters and screen the influencing factors, reclassify the parameter groups with small interlayer effects, recalculate the OD function, ramp, CCD experiment and search for the best, until all important performance parameters are classified and optimized, all film thickness values ​​are determined, and interlayer effects are eliminated.

[0145] Specifically, in the second round of screening, compared with the first round, some film thickness values ​​have changed, and the regression equation between film thickness and performance parameters will also change. In this example, there are five remaining influencing factors and eight remaining important performance parameters.

[0146] Repeat S2 to S6. After determining the remaining influencing factors, redesign the Plackett-Burman experiment to obtain new regression equations for the remaining important performance parameters and screen the influencing factors. Reclassify the parameter groups with small interlayer effects, recalculate the OD function, ramp, CCD experiment and search for the best. Until all important performance parameters are classified and optimized, all film thickness values ​​are determined, and interlayer effects are eliminated. The process of cyclic optimization is as follows: Fig. 9 shown.

[0147] The purpose of this embodiment is to provide a method for classifying and optimizing the important performance parameters of the recording target material of a 500GB archived optical disc, which can identify the influencing factors of each important performance parameter, that is, the degree of influence of the film thickness of each layer of optical film on each optical disc performance parameter, and find the main influencing factors of each optical disc performance parameter by excluding non-critical factors, and extract a group of optical disc performance parameters that are least affected by the interlayer according to the important performance parameter screening rules. Through the steepest climbing experiment and response variables, the film thickness that affects the performance parameters of this group of optical discs is optimized and adjusted to achieve the relative optimal performance parameters of this group of optical discs. By gradually extracting the performance parameters of the optical disc and optimizing the corresponding film thickness, the optimal setting of all film thicknesses is finally achieved, so as to eliminate the interlayer influence and optimize all important performance parameters.

[0148] This embodiment is to design a Plackett-Burman experiment, calculate the functional relationship between each important performance parameter and the film thickness value, and screen the factors to extract a group of important performance parameters, which are characterized by being affected by a group of common film thickness values ​​and less affected by other layers. Construct the OD function of this group of performance parameters, find the fastest rising direction, and find the local optimal area through the steepest climbing experiment. Design a CCD experiment in this area, and optimize the response variables to obtain the influencing factors corresponding to this group of important performance parameters, that is, the optimal settings of some film thickness values. The optimal settings of all film thickness values ​​can be completed through several rounds of cycles. This embodiment mainly uses quantitative analysis of a small amount of experimental data to quickly find the optimal settings of film thickness values ​​with a small number of adjustments, effectively improving the accuracy and economy of parameter adjustment in the localization process of recording target materials for 500GB archive optical discs, and solving problems such as low adjustment efficiency, poor adjustment effect, and unclear direction of target material differences.

[0149] This embodiment has the following beneficial effects:

[0150] In this embodiment, the nine film thickness values ​​of the L0 upper dielectric film, L0 recording film, L0 lower dielectric film, L1 upper dielectric film, L1 recording film, L1 lower dielectric film, L2 upper dielectric film, L2 recording film, and L2 lower dielectric film of the recording target material of the 500GB archived optical disc during the sputtering film forming process of the optical disc production are adjusted to achieve the optimization of the important performance parameters of the optical disc. In order to verify the influence relationship between each film thickness value and each important performance parameter, the influencing factors of each important performance parameter are firstly screened by the Plackett-Burman experiment, and then a group of important performance parameters with less interlayer influence are extracted based on the important performance parameter screening rules, and the OD function for evaluation is constructed. Next, the steepest climbing experiment is used to reach the local maximum value of the OD function in the direction of the fastest rise, so as to determine the center point of the multi-response surface experiment, and finally the response variable optimizer in the mathematical statistics software Minitab is used to adjust the weight and importance of each important performance parameter according to different optimization requirements to obtain the optimal factor setting conditions for the current parameter group. After several cycles, all important performance parameters can be precisely controlled to eliminate inter-layer effects.

[0151] This embodiment uses the mathematical statistics software Minitab to analyze the simulation experiment data. According to the analysis results, it can provide guidance for the subsequent adjustment of the manufacturing process for the localization of the target material. For example, it can obtain the difference between the optimized film thickness of the three optical medium layers of the domestic target material and the film thickness of the current quality optical disc produced by the Japanese target material, so as to understand the degree of closeness between the performance of the recording target material of the three optical medium layers and the Japanese target material.

[0152] This embodiment also uses the mathematical statistics software Minitab to analyze the simulation experiment data, which can obtain the primary and secondary order of each film thickness affecting important performance parameters and the proportion of interaction between film thicknesses, so that subsequent operators can be more purposeful when debugging important performance parameters, ensuring the quality of optical disc production and speeding up the production rhythm.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for classifying and optimizing important performance parameters of a recording target, characterized in that: The steps include: S1: preliminarily determining the influencing factors of important performance parameters of the optical medium layer of the optical disc, as well as the high level value and the low level value of the film thickness of the influencing factors; S2: according to the high level value and the low level value of the film thickness of the influencing factor, based on the Plackett-Burman experimental method, obtain a plurality of orthogonal combinations of the high and low level values ​​of the film thickness of the influencing factor, so as to obtain the actual value of the important performance parameter of the optical medium layer of the optical disc based on the orthogonal combination of the high and low level values ​​of the film thickness of the influencing factor; then determine whether the relationship between the important performance parameter and the influencing factor is significant, and obtain the number of influencing factors with significant relationship with the important performance parameter; S3: according to the number of influencing factors that are significantly related to the important performance parameters, based on the important performance parameter screening rules, determine the important performance parameter combination that is strongly correlated with the i-th, i=1,…,I-th important performance parameters, so as to obtain the important performance parameter combination containing the same important performance parameters, and then obtain the screened influencing factor combination; The screened influencing factor combination includes: influencing factors that have significant relationships with the important performance parameters in the important performance parameter combination, and influencing factors of optical medium layers adjacent to the optical medium layer to which the influencing factors have significant relationships with the important performance parameters in the important performance parameter combination belong; I represents the total number of important performance parameters; S4: constructing an OD function according to the combination of important performance parameters including the same important performance parameters; and determining a plurality of screened influencing factor value combinations according to the high level value and the low level value of the influencing factor film thickness, so as to obtain the OD function value of the plurality of screened influencing factor value combinations, and then obtaining the screened influencing factor value combination corresponding to the maximum OD function value; S5: according to the value combination of the screened influencing factors, multiple groups of steepest climbing test influencing factor value combinations are obtained to obtain important performance parameters of the optical disk based on the steepest climbing test influencing factor value combination, and the steepest climbing test is performed on the OD function to obtain the local maximum value of the OD function in the fastest rising direction to obtain the local optimal area of ​​the OD function; S6, using Minitab software to perform CCD experiments according to the steepest climbing experiment influencing factor value combination corresponding to the local optimal region of the OD function, to obtain multiple CCD experiment influencing factor value combinations, so as to obtain important performance parameters of the optical disc based on the CCD experiment influencing factor combination, and then according to the OD function, to obtain the CCD experiment influencing factor value combination with the maximum OD function value; Then the final value of the influencing factor in the screened influencing factor combination is the value of the corresponding influencing factor in the influencing factor value combination of the CCD experiment with the largest OD function value; S7: Based on the influencing factors in the non-screened influencing factor combination, repeat S2 to S6 until there are no non-screened influencing factors, and obtain the final values ​​of all the influencing factors.

2. A method for classifying and optimizing important performance parameters of a recording target material according to claim 1, characterized in that: The important performance parameter screening rules are as follows: a. When the number of factors that are significantly related to the i-th important performance parameter is 3: If among the influencing factors with significant relationship with the jth important performance parameter, there are more than or equal to 2 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is strongly correlated with the jth important performance parameter; If among the influencing factors with significant relationship with the jth important performance parameter, there are less than 2 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is not correlated with the jth important performance parameter; b. When the number of factors that are significantly related to the i-th important performance parameter is 4: If among the influencing factors with significant relationship with the jth important performance parameter, there are more than or equal to 3 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is strongly correlated with the jth important performance parameter; If there are two influencing factors with significant relationship with the i-th important performance parameter among the influencing factors with significant relationship with the j-th important performance parameter, then the i-th important performance parameter is weakly correlated with the j-th important performance parameter; If among the influencing factors with significant relationship with the jth important performance parameter, there are less than 2 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is not correlated with the jth important performance parameter; c. When the number of factors that are significantly related to the i-th important performance parameter is 5: If among the influencing factors with significant relationship with the jth important performance parameter, there are more than or equal to 4 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is strongly correlated with the jth important performance parameter; If among the influencing factors with significant relationship with the jth important performance parameter, there are 3 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is weakly correlated with the jth important performance parameter; If among the influencing factors with significant relationship with the jth important performance parameter, there are less than 3 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is not correlated with the jth important performance parameter; d. When the number of significant influencing factors with respect to the i-th important performance parameter is 6: If among the influencing factors with significant relationship with the jth important performance parameter, there are more than or equal to 4 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is strongly correlated with the jth important performance parameter; If among the influencing factors with significant relationship with the jth important performance parameter, there are 3 influencing factors with significant relationship with the ith important performance parameter, then the ith important performance parameter is weakly correlated with the jth important performance parameter; If among the influencing factors that have a significant relationship with the jth important performance parameter, there are less than 3 influencing factors that have a significant relationship with the ith important performance parameter, then the ith important performance parameter is not correlated with the jth important performance parameter.

3. A method for classifying and optimizing important performance parameters of a recording target material according to claim 1, characterized in that: The optical medium layer of the optical disc includes: an L0 optical medium layer, an L1 optical medium layer and an L2 optical medium layer; The influencing factors of the important performance parameters include: L2 lower dielectric film thickness, L2 recording film thickness, L2 upper dielectric film thickness, L1 lower dielectric film thickness, L1 recording film thickness, L1 upper dielectric film thickness, L0 lower dielectric film thickness, L0 recording film thickness, L0 upper dielectric film thickness.

4. A method for classifying and optimizing important performance parameters of a recording target material according to claim 1, characterized in that: The important performance parameters include: L0 d-MLSE, L0 recorded power, L0 reflectivity, L0 converted sensitivity; L1 d-MLSE, L1 recorded power, L1 reflectivity, L1 converted sensitivity; L2 d-MLSE, L2 recorded power, L2 reflectivity, L2 converted sensitivity.

5. A method for classifying and optimizing important performance parameters of a recording target material according to claim 1, characterized in that: The OD function is established as follows: In the formula, the value of OD is [0, 1], M is the number of response targets; d m To convert the mth response target y m Converted into an expectation function with a value of 0 to 1; m is the index number of the response target; Among them, when the response target is d-MLSE / reflectivity / converted sensitivity, When the response target is to record power, Among them, y m，min and m，max are the mth response target y in the experiment m The lower and upper limits of the specification, w is the weight factor.

6. A method for classifying and optimizing important performance parameters of a recording target material according to claim 1, characterized in that: The values ​​of the influencing factors in the steepest climbing test influencing factor value combination are as follows: The film thickness recorded at L0 and the film thickness of the dielectric under L1 are selected within the local optimal region of the OD function; The upper L0 dielectric film thickness and the lower L0 dielectric film thickness are the upper L0 dielectric film thickness and the lower L0 dielectric film thickness in the value combination of the influencing factors after screening; The L1 upper dielectric film thickness, L1 recording film thickness, L2 upper dielectric film thickness, L2 recording film thickness, and L2 lower dielectric film thickness are the center film thicknesses of the set L1 upper dielectric film, L1 recording film, L2 upper dielectric film, L2 recording film, and L2 lower dielectric film, respectively.

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