201200613 六、發明說明： 【發明所屬之技術領域】 本發明是有關於一種鋁薄膜製造方法，且特別是有關 於一種可有效降低薄膜沉積時的殘留應力的鋁薄膜製造方 法。 【先前技術】 目前TFT-LCD面板之電極層主要是以南純度铭乾材 > 作為鍍膜原料。然而TFT-LCD面板於製程中會經過高溫熱 處理，其熱能將傳導到面板内之電極層（純鋁薄膜所形 成）。由於鋁薄膜與矽基板之間的熱膨脹係數差異大、降伏 點低，因此濺鍍在矽基板上之鋁薄膜容易在製程中因受熱 (攝氏100〜400度）而產生突起(hillock)，造成線路短路、膜 層剝落等現象。 為了降低突起的產生，有習知技術藉由在鋁薄膜中添 加入其他元素，例如絡或组，以形成一銘合金薄膜，來降 φ 低熱處理時突起的產生。但也因為需要在鋁薄膜中添加其 他元素而增加生產成本，降低了電極層之導電率，也就是 使電極層的電阻值提高，而减慢面板之電訊傳輸速度。 或者，藉由在後續製程中，例如熱退火製程，將熱處 理的溫度降低以減少突起的尺寸與發生機率。但若薄膜沉 積後在未熱處理之前即存在大量的殘留應力，則熱處理溫 度的調降對抑制突起物生成的效果仍然有限。 另一方面，就高純度之鋁薄膜而言，雖然薄膜面電阻 值極低，但在攝氏150度的熱處理下即有突起物形成。$ 201200613 且，隨熱處理溫度增加，薄膜殘留應力增大，突起物之數 量越多、體積越大，越容易讓面板線路短路。 因此，目前亟需一種可有效減少薄膜熱處理後殘留應 力的方法。 【發明内容】 本發明之一目的是在提供一種鋁薄膜的製造方法，可 有效減少薄膜沉積時的殘留應力。 依據本發明之一實施例，提出一種鋁薄膜的製造方 法。首先提供一鋁靶材，鋁靶材純度介於 99.99%〜99.999%。調整鋁靶材面積與濺鍍功率之比值至介 於2.1瓦/平方公分（W/cm2)〜3.3瓦/平方公分之間。提供一 基板，使用一真空磁控濺鍍製程在這基板上形成鋁薄膜。 依據本發明之一實施例，提出一種鋁薄膜的製造方 法。首先提供一鋁靶材，鋁靶材的純度介於 99.99%〜99.999%。提供一基板，接著在基板上沉積鋁薄膜， 鋁薄膜沉積於基板上的沉積速率介於2 9埃/秒至5 0埃/秒之 間。 根據本發明之上述實施例，更包含在一含有惰性氣體 的環境中進行薄膜沉積，其壓力介於0.001托至0.015托之 間。 根據本發明之上述實施例，更包含在氬氣環境中進行 薄膜沉積。 藉由本發明之鋁薄膜製造方法，在相同薄膜製程條件 下，使用具有高濺鍍速率之高純度鋁靶，或適當之靶材面( 201200613 積與濺鍍功率比值，可使薄膜沉積時的殘留應力减小，而 有效降低薄膜突起之發生，進而提升薄膜品質，降低生產 的成本。 【實施方式】 本發明揭露了一種鋁薄膜的製造方法，係調整薄膜製 程參數，因此在薄膜製程中不須添加其他元素也不用降低 後續製程的熱處理溫度，而可有效降低薄膜沉積時的殘留 應力。 請參照第1圖，其係繪示為本發明之一實施例之鋁薄 膜的製造方法之步驟流程圖。首先，在步驟S101中，提供 鋁靶材，其係具有鋁純度介於99.99%至99.999%的鋁靶 材。接著，在步驟S102中，根據所提供紹乾材的面積，調 整鋁靶材與濺鍍功率之比值至介於2.1瓦/平方公分〜3.3瓦/ 平方公分之間。在步驟S103中，提供基板，可例如為矽基 板或玻璃基板。並將基板放置於真空磁控濺鍍製程所需的 腔體中。在步驟S104中，以靶極濺鍍上述鋁靶材，在基板 上沉積鋁薄膜。 在一實施例中，上述的鋁靶材可以是例如直徑為六吋 銘乾材。· 請參照第2圖，其係繪示為本發明之一實施例之鋁薄 膜的製造方法之步驟流程圖。在步驟S201中，提供鋁靶 材，其係具有鋁純度介於99.99%至99.999%的鋁靶材。接 著，在步驟S202中，係提供一基板，可例如為矽基板或玻 璃基板。並將基板放置於真空磁控濺鍍製程所需的腔體 201200613 中。在步驟S203中，以靶極濺鍍上述鋁靶材，在基板上沉 積銘薄膜。上述鋁薄膜係利用鋁靶材及真空磁控濺鍍製程 而形成於上述基板的表面。鋁薄膜沉積於基板上的沉積速 率介於29埃/秒至50埃/秒之間。 根據本發明上述兩實施方式之鋁靶材所形成的鋁薄 膜’在薄膜沉積速率越高的條件下所製備的薄膜，其薄膜 產生突起所需的熱處理溫度就越高，越不容易有突起產 生’因此以本發明之方法所製造的鋁薄膜的可靠率越高。 | 在上述實施例中，基板可為矽基板或玻璃基板。 以下則以實際實施例更具體地說明本發明，惟本發明 的範圍不受這些實施例限制。下列實施例均在真空磁控濺 鍍設備中進行操作。 比較例1 首先預備一鋁靶材，所使用的鋁靶材為純度高於 99.995%的直徑為六吋((182.41平方公分))鋁靶材。接著預 備一矽基板。隨後，將矽基板置入真空磁控濺鍍腔體中。 • 以直流式磁控靶極分別濺鍍上述的鋁靶材，調整濺鍍功率 為500瓦，通入一氬氣至腔體内，通入的氬氣壓力0.003 托’使得沉積速率達到20.1埃/秒。分別在對應之石夕基板的 表面上沉積面積為25厘米*25厘米以及厚度為180奈米之 鋁薄膜。測試溫度為攝氏150度與190度。 實施例1 首先預備一鋁靶材，所使用的鋁靶材為純度高於 99.995%的直徑為六吋鋁靶材。接著預備一矽基板。隨後， 將矽基板置入真空磁控濺鍍腔體中。以直流式磁控靶極分 201200613 別濺鍍上述的鋁靶材，調整濺鍍功率為5〇〇瓦，通入一氬 氣至腔體内，通入的氬氣壓力0.003托，使得沉積速率達 到29.5埃/秒。分別在對應之矽基板的表面上沉積面積為 25厘米*25厘米以及厚度為180奈米之鋁薄膜。 形成面積為25厘米*25厘米以及厚度為18〇奈米的鋁 薄膜試片進行高溫測試，測試溫度為攝氏19〇度與2〇〇度。 實施例2 首先預備一鋁靶材，所使用的鋁靶材為純度高於201200613 VI. Description of the Invention: [Technical Field] The present invention relates to a method for producing an aluminum thin film, and more particularly to a method for producing an aluminum thin film which can effectively reduce residual stress during film deposition. [Prior Art] At present, the electrode layer of the TFT-LCD panel is mainly made of a southern purity material > as a coating material. However, the TFT-LCD panel is subjected to high-temperature heat treatment during the process, and its thermal energy is conducted to the electrode layer (formed of pure aluminum film) in the panel. Since the difference in thermal expansion coefficient between the aluminum thin film and the tantalum substrate is large and the drop point is low, the aluminum thin film sputtered on the tantalum substrate is liable to generate a hillock due to heat (100 to 400 degrees Celsius) during the process, resulting in a line. Short circuit, film peeling and other phenomena. In order to reduce the generation of protrusions, it is known in the art to reduce the occurrence of protrusions in the low heat treatment by adding other elements such as a layer or a group to the aluminum film to form an alloy film. However, because of the need to add other elements to the aluminum film, the production cost is increased, and the conductivity of the electrode layer is lowered, that is, the resistance value of the electrode layer is increased, and the telecommunications transmission speed of the panel is slowed down. Alternatively, by subsequent processing, such as a thermal annealing process, the temperature of the heat treatment is reduced to reduce the size and probability of occurrence of the protrusions. However, if a large amount of residual stress exists before the film is deposited without heat treatment, the effect of the temperature reduction of the heat treatment on the formation of the protrusion is still limited. On the other hand, in the case of a high-purity aluminum film, although the film surface resistance value is extremely low, protrusions are formed under heat treatment at 150 °C. $ 201200613 Moreover, as the heat treatment temperature increases, the residual stress of the film increases, and the larger the number of protrusions and the larger the volume, the easier it is to short-circuit the panel line. Therefore, there is a need for a method which can effectively reduce the residual stress after heat treatment of a film. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an aluminum thin film, which can effectively reduce residual stress during film deposition. According to an embodiment of the present invention, a method of manufacturing an aluminum film is proposed. First, an aluminum target is provided, and the purity of the aluminum target is between 99.99% and 99.999%. The ratio of the area of the aluminum target to the power of the sputtering is adjusted to be between 2.1 watts/cm<2> (W/cm<2>) and 3.3 watts/cm<2>. A substrate is provided for forming an aluminum film on the substrate using a vacuum magnetron sputtering process. According to an embodiment of the present invention, a method of manufacturing an aluminum film is proposed. First, an aluminum target is provided, and the purity of the aluminum target is between 99.99% and 99.999%. A substrate is provided, followed by deposition of an aluminum film on the substrate, and a deposition rate of the aluminum film deposited on the substrate is between 29 Å/sec and 50 Å/sec. According to the above embodiment of the present invention, the film deposition is further carried out in an atmosphere containing an inert gas at a pressure of between 0.001 Torr and 0.015 Torr. According to the above embodiment of the present invention, it is further included to perform film deposition in an argon atmosphere. By using the aluminum film manufacturing method of the present invention, a high-purity aluminum target having a high sputtering rate, or a suitable target surface (201200613 product and sputtering power ratio) can be used for film deposition residue under the same film processing conditions. The stress is reduced, and the occurrence of the film protrusion is effectively reduced, thereby improving the quality of the film and reducing the cost of production. [Embodiment] The present invention discloses a method for manufacturing an aluminum film, which is to adjust the process parameters of the film, so that it is not required in the film process. Adding other elements does not reduce the heat treatment temperature of the subsequent process, and can effectively reduce the residual stress during film deposition. Please refer to FIG. 1 , which is a flow chart showing the steps of the method for manufacturing the aluminum film according to an embodiment of the present invention. First, in step S101, an aluminum target having an aluminum target having an aluminum purity of 99.99% to 99.999% is provided. Next, in step S102, the aluminum target is adjusted according to the area of the dried material provided. The ratio to the sputtering power is between 2.1 watts/cm<2> and 3.3 watts/cm<2>. In step S103, the substrate is provided, which may be, for example, 矽a plate or a glass substrate, and placing the substrate in a cavity required for a vacuum magnetron sputtering process. In step S104, the aluminum target is sputtered with a target to deposit an aluminum film on the substrate. The aluminum target may be, for example, a hexagram dry material. Please refer to FIG. 2, which is a flow chart showing the steps of a method for manufacturing an aluminum thin film according to an embodiment of the present invention. In step S201, Providing an aluminum target having an aluminum target having an aluminum purity of 99.99% to 99.999%. Next, in step S202, a substrate is provided, which may be, for example, a germanium substrate or a glass substrate. The substrate is placed in a vacuum. In the cavity 201200613 required for the magnetron sputtering process, in step S203, the aluminum target is sputtered with a target, and a film is deposited on the substrate. The aluminum film is processed by an aluminum target and a vacuum magnetron sputtering process. And forming on the surface of the substrate. The deposition rate of the aluminum thin film deposited on the substrate is between 29 Å/sec and 50 Å/sec. The aluminum thin film formed by the aluminum target according to the above two embodiments of the present invention is in the film. The higher the deposition rate In the prepared film, the higher the heat treatment temperature required for the film to generate the protrusion, the less likely the protrusion is generated. Therefore, the reliability of the aluminum film produced by the method of the present invention is higher. | In the above embodiment, the substrate The present invention may be more specifically described by way of actual embodiments, but the scope of the present invention is not limited by the examples. The following examples are all operated in a vacuum magnetron sputtering apparatus. 1 First prepare an aluminum target, the aluminum target used is a six-inch (182.41 cm2) diameter aluminum target with a purity higher than 99.995%. Then a substrate is prepared. Then, the substrate is placed in a vacuum. In the magnetron sputtering chamber. • The above-mentioned aluminum target is sputtered separately by a DC magnetron target. The sputtering power is adjusted to 500 watts, and an argon gas is introduced into the chamber. The argon pressure is 0.003. The carrier's deposition rate reached 20.1 angstroms per second. An aluminum film having an area of 25 cm * 25 cm and a thickness of 180 nm was deposited on the surface of the corresponding Shi Xi substrate, respectively. The test temperature is 150 degrees Celsius and 190 degrees Celsius. Example 1 An aluminum target was first prepared, and the aluminum target used was a hexagonal aluminum target having a purity higher than 99.995%. Then prepare a substrate. Subsequently, the germanium substrate is placed in a vacuum magnetron sputtering chamber. The DC magnetron target is divided into 201200613. The above aluminum target is sputtered, the sputtering power is adjusted to 5 watts, an argon gas is introduced into the chamber, and the argon pressure is 0.003 Torr, so that the deposition rate is obtained. It reached 29.5 angstroms per second. An aluminum film having an area of 25 cm * 25 cm and a thickness of 180 nm was deposited on the surface of the corresponding tantalum substrate, respectively. An aluminum film test piece having an area of 25 cm * 25 cm and a thickness of 18 〇 nanometer was subjected to high temperature test at a temperature of 19 degrees Celsius and 2 degrees Celsius. Example 2 First, an aluminum target was prepared, and the aluminum target used was higher in purity.
99.995%的直徑為六吋（182.41平方公分）鋁靶材。接著預備 一矽基板。隨後，將矽基板置入真空磁控濺鍍腔體中。以 直流式磁控靶極分別濺鍍上述的鋁靶材’調整濺鍍功率為 500瓦，通入一氬氣至腔體内，通入的氬氣壓力〇 〇〇3托， 使得沉積速率達到31.8埃/秒。分別在對應之絲板的表面 上沉積面積為25厘米*25厘米以及厚度為副奈米之铭薄 膜0 ，二成面積為25厘来*25厘米以及厚度為18〇奈米的在 薄膜試片進行K測試溫度為攝氏度與攝氏度 氣體在如【Ϊϋί氣f述所通人的氬氣也可以是其他㈣ 鋁薄膜1片St卜其為上述比較例1與實施例1至2白 例\至°2 _ Α面光學金相圖。同時參照比較例1與實方 下陶面積：t片，/以發現在相同的嶋靡 (20.1埃/秒）的比g功率以及氬氣壓力），沉積速率較々 起出現，而洛妖^例1在攝氏150度進行熱處理時即有》 田…、處理溫度增加至攝&携度時所出現的； 201200613 起增大且數量增加。而沉積速率次之的實施例1的鋁薄膜 試片在攝氏190度進行熱處理時仍無明顯的突起出現，而 當熱處理溫度增加至190度時，才有些微的突起出現。而 沉積速率最高的實施例2的鋁薄膜試片在攝氏220度與230 度進行熱處理仍無明顯的突起產生。因此可以推論沉積速 率越高時，則薄膜發生突起所需的熱處理溫度就需要更 高，也就是越不容易有突起產生，鋁薄膜的品質越佳。 請參照第3圖，其繪示依照本發明一實施例之薄膜突 起發生的最低熱處理溫度與濺鍍功率關係圖。在本實施例 > 中，所使用之鋁靶材為六吋鋁靶，其純度介於 99.99%〜99.999%，而在濺鍍腔體内的氬氣壓力介於0.0025 托至0.0045托，分別以300瓦、500瓦、750瓦、1000瓦、 2000瓦以及3000瓦的濺渡功率進行鋁薄膜的沉積。在本 實施例中，可以發現隨著濺鍍功率的提高，薄膜產生突起 所需的熱處理溫度呈現先升後降的趨勢，並且在濺鍍功率 介於約400瓦至600瓦的範圍内所製得的鋁薄膜，其殘留 的應力最小，也就是說薄膜越不易產生突起。在另一實施 • 例中，所使用之鋁靶材為直徑為八吋(324.13平方公分）鋁 靶材，其濺鍍功率與靶材面積之比值介於2.1瓦/平方公分 至3.3瓦/平方公分時，因此所使用的濺鍍功率就必須根據 鋁靶材的面積調整到約650瓦至約1000瓦之間，如此所製 得的鋁薄膜，其殘留的應力最小，薄膜在攝氏200度以上 較不易產生突起。 請參照第4圖，其繪示本發明一實施例之薄膜突起發 生的最低熱處理溫度與沉積速率的關係圖。在本實施例 201200613 中，所使用的鋁靶材為六吋鋁靶，其純度介於 99·99%〜99·999%’而在機鍛腔體内的氮氣壓力介於〇 〇〇1 托至讀15托’而分別以5埃/秒至6〇埃/秒的沉積速率進 行銘薄膜的沉積。在本實施例中，可以發現隨著沉積速率 的增加，薄膜產生突起所需的熱處理溫度呈現先升後降的 趨勢，並且在沉積速率3〇埃/秒至50埃/秒範圍内所製得的 鋁薄膜，其殘留的應力最小，也就是薄膜越不易產生突起， 在約攝氏200度以上才會開始產生突起。99.995% of the diameter is six inches (182.41 square centimeters) of aluminum target. Then prepare a substrate. Subsequently, the germanium substrate is placed in a vacuum magnetron sputtering chamber. The above-mentioned aluminum target is sputtered by a direct current magnetron target to adjust the sputtering power to 500 watts, and an argon gas is introduced into the cavity, and the argon gas pressure is 〇〇〇3 Torr, so that the deposition rate is reached. 31.8 angstroms per second. On the surface of the corresponding silk plate, a film of 25 cm * 25 cm and a thickness of sub-nano film 0, a surface area of 25 cm * 25 cm and a thickness of 18 〇 nanometer were deposited on the surface of the corresponding silk plate. The K test temperature is in Celsius and Celsius. The gas may be other than the argon gas in the system. For example, the first comparative example 1 and the first to the second examples are white to the above. 2 _ Kneading optical metallographic diagram. At the same time, referring to Comparative Example 1 and the actual potting area: t-piece, / to find the same enthalpy (20.1 ang / sec) ratio g power and argon pressure), the deposition rate appears to rise, and Luo demon ^ In Example 1, when heat treatment was performed at 150 degrees Celsius, there was a “field..., the treatment temperature increased to the time when the camera was taken; the increase occurred in 201200613 and the number increased. On the other hand, the aluminum film test piece of Example 1 having the second deposition rate showed no significant protrusions when heat-treated at 190 ° C, and when the heat treatment temperature was increased to 190 degrees, slight protrusions appeared. On the other hand, the aluminum thin film test piece of Example 2 having the highest deposition rate was subjected to heat treatment at 220 ° C and 230 ° C without any significant protrusion generation. Therefore, it can be inferred that the higher the deposition rate, the higher the heat treatment temperature required for the protrusion of the film, that is, the less prone to the occurrence of protrusions, and the better the quality of the aluminum film. Referring to Figure 3, there is shown a graph of the relationship between the minimum heat treatment temperature and the sputtering power at which film protrusions occur in accordance with one embodiment of the present invention. In the present embodiment, the aluminum target used is a hexagonal aluminum target having a purity of 99.99% to 99.999%, and the argon pressure in the sputtering chamber is between 0.0025 Torr and 0.0045 Torr, respectively. The deposition of aluminum thin films is carried out at a sputtering power of 300 watts, 500 watts, 750 watts, 1000 watts, 2000 watts, and 3000 watts. In this embodiment, it can be found that as the sputtering power is increased, the heat treatment temperature required for the film to generate protrusions tends to rise first and then fall, and is produced in a sputtering power of about 400 watts to 600 watts. The obtained aluminum film has the least residual stress, that is, the film is less likely to generate protrusions. In another example, the aluminum target used is an eight-inch (324.13 cm2) aluminum target with a ratio of sputtering power to target area of 2.1 watts/cm 2 to 3.3 watts/square. At the time of centimeters, the sputtering power used must be adjusted to between about 650 watts and about 1000 watts depending on the area of the aluminum target. The aluminum film thus produced has the least residual stress and the film is above 200 degrees Celsius. It is less prone to protrusions. Referring to Figure 4, there is shown a graph showing the relationship between the minimum heat treatment temperature and the deposition rate of a film protrusion according to an embodiment of the present invention. In the present embodiment, 201200613, the aluminum target used is a hexagonal aluminum target with a purity of 99.99% to 99.999%' and the nitrogen pressure in the forging chamber is between 〇〇〇1 Torr. The deposition of the film was carried out at a deposition rate of 5 Å/sec to 6 Å/sec, respectively, up to 15 Torr. In this embodiment, it can be found that as the deposition rate increases, the heat treatment temperature required for the protrusion of the film exhibits a tendency to rise first and then fall, and is obtained at a deposition rate of 3 Å/sec to 50 Å/sec. The aluminum film has the least residual stress, that is, the film is less prone to protrusion, and the protrusion starts to be generated at about 200 degrees Celsius.
請參照第5圖，其綠示本發明一實施例之薄膜厚度與 突起密度以及突起直__圖。在本實關中，所使用 的錄輕材、乾材面積、機錄功率以及沉積速率均相同，相 異處僅在於所沉積薄膜的厚度不同，介於奈米至麵 奈米。，本實％例中’可以發現隨著薄膜厚度的增加，突 起的數量減>、了 ’但每顆突起的密度卻增加了。*在膜厚 400奈米至6GG奈料，突起的直徑與密度可達到較平 的姑果三也就是薄膜厚度與突起的密度是成正比的趨勢， 但薄膜密度賴突起的直徑成反比的趙勢。 例可知’藉由在相同薄獏製程條件下，ί 用之高純度_ ’或適當之輕材面積-鍍m可使薄膜沉積時的殘留應力减小而有效降< 薄藤突起之發生，進而提升薄膜品質，降低生產的成本。 =本：明已以實施方式揭露如上，然其並非 定本r二此技藝者，在不脫離本發明之㈣Referring to Figure 5, the green color shows the film thickness and the protrusion density and the protrusions in an embodiment of the present invention. In this actual case, the recorded light materials, dry material area, machine recording power, and deposition rate are the same, and the difference is only in the thickness of the deposited film, ranging from nanometer to nanometer. In the present example, it can be found that as the thickness of the film increases, the number of protrusions decreases, but the density of each protrusion increases. * In the film thickness of 400 nm to 6 GG ingot, the diameter and density of the protrusion can reach a flattening effect, that is, the thickness of the film is proportional to the density of the protrusion, but the film density is inversely proportional to the diameter of the protrusion. Potential. For example, by using the same high-purity _ ' or the appropriate light material area - plating m can reduce the residual stress during film deposition and effectively reduce the occurrence of thin vine protrusions, In turn, the film quality is improved and the cost of production is reduced. =本:明 has been exposed as above in the implementation, but it is not intended to be a skilled person, without departing from the invention (4)
範二Γ 更動與―’因此本發明之保護I 園當祝後附之申請專利範園所界定者為準。 畢 201200613 【圖式簡單說明】 為讓本發明之上述和其他目的、特徵、優點與實施例 能更明顯易懂，所附圖式之說明如下： 第1圖係繪示依照本發明之一實施例之鋁薄膜的製造 方法之步驟流程圖。 第2圖係繪示依照本發明之一實施例之鋁薄膜的製造 方法之步驟流程圖。 p 第3圖係繪示依照本發明之一實施例之薄膜突起的最 低熱處理溫度與濺鍍功率關係圖。 第4圖係繪示依照本發明之一實施例的薄膜突起發生 的最低熱處理溫度與沉積速率的關係圖。 第5圖係繪示依照本發明之一實施例的薄膜厚度與突 起密度以及突起直徑的關係圖。 【主要元件符號說明】 # S101 〜S104 ··步驟 S201〜S203 :步驟Fan Erzhen is more motivated and “therefore, the protection I Park of the present invention is subject to the definition of the patent application park attached to it. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features, advantages and embodiments of the present invention will become more <RTIgt; A flow chart of the steps of the method for producing an aluminum film. Fig. 2 is a flow chart showing the steps of a method for producing an aluminum film according to an embodiment of the present invention. Fig. 3 is a graph showing the relationship between the minimum heat treatment temperature and the sputtering power of the film protrusions according to an embodiment of the present invention. Fig. 4 is a graph showing the relationship between the minimum heat treatment temperature and the deposition rate of film protrusions according to an embodiment of the present invention. Figure 5 is a graph showing film thickness versus protrusion density and protrusion diameter in accordance with an embodiment of the present invention. [Description of main component symbols] # S101 to S104 ··Steps S201 to S203: Steps