13543251354325
(1) 九、發明說明 【發明所屬之技術領域】 本發明係有關一種將經由黏著薄片而被固定於 附加框體之半導體晶圓（以下簡稱「晶圓」）’轉 定於其他框體之狀態的晶圓之轉印方法。 【先前技術】 例如針對電子產業或光學產業之半導體裝置的 程中，於晶圓表面形成特定之電路圖案後，爲了使 之厚度薄且平均，或爲了去除電路形成時所產生之 ，係將晶圓之背面加以硏磨（背向硏磨），之後將 割爲各個電路而製造出期望之半導體晶片（以下簡 片」）。然後，於之後之撿料工程將晶片撿料，將 後之晶片於其次的打線（die bonding)工程中打銲 框等基台，再經過之後的塑型（molding)等工程 出期望之半導體裝置。 然而，近年來半導體裝置係要求極度薄片化， 況下’將極薄化後又未單片化（晶片化）之晶圓加 壞的搬運，或是進行切割等加工，係有困難。 因此，爲了可不對晶圓施加物理力量等而將該 片化，而相當期待一種隱密切割（Stealth Dicing 標）之切割方法，來對應極薄化之晶圓。 隱松切割係於晶圓內部對準焦點而照射雷射光 焦點形成改質且脆弱化的範圍，使的照射雷射光線 體的 至固 造工 晶圓 化膜 圓切 「晶 撿料 導線 製造 此狀 無破 圓單 冊商 ，將 焦點 -5- (2) (2)1354325 的軌跡成爲起點，而切斷晶圓的方法（例如參考專利文件 1 )。進行了隱密切割之晶圓，僅需施加極小的力量來單 純切割被改質之範圍，而不會於其他部分發生不必要之破 裂。故，比起以物理力量進行之通常切割法，更適合極薄 化晶圓之加工。 但是，即使以隱密切割進行加工，爲了進行之後的晶 圓搬運等處理，係必須不直接碰觸晶圓（晶片）地，做爲 經由黏著薄片而固定於環狀框體的工件狀態。 然而，進行隱密切割時，係使焦點不偏移地，避開電 路面或黏著薄片般材質與晶圓本體不同的層，而進行雷射 光線照射者爲佳。故，黏著薄片係被黏合在電路面側，而 由晶圓之背面（硏磨面）進行雷射光線之照射。 〔專利文件1〕日本專利第3 4 0 8 8 0 5號公報 【發明內容】 發明所欲解決之課題 但是’將晶片撿料時，常用之撿料裝置之晶片辨識裝 置，係由工件之上側以攝相機檢測出電路，來辨識晶片之 位置，故電路面黏合有黏著薄片之工件係無法辨識晶片之 正確位置關係。又，因要對電路面進行晶片之推起，故有 多少對電路造成損傷的問題。 本發明係有鑑於上述問題，其目的爲提供一種由黏著 薄片被黏合於晶圓電路面之工件的狀態，轉印至晶圓背面 黏合有黏著薄片之工件的狀態，而可使用常用之撿料裝置 -6 - (3) 1354325 進行fe料的，晶圓之轉印方法。尤其本發明，其目的係提 供一種可由固定有以進行隱密切割之晶圓（晶片）的工件 ’以通常方法進行晶片撿料的晶圓之轉印方法。 用以解決課題之手段 爲達成上述目的’申請專利範圍第1項所記載之發明 ’係將電路面側經由第1黏著薄片而被固定在環狀之第1 • 框體的晶圓’轉印至電路面側之反對側經由第2黏著薄片 而被固定在第2框體的狀態的，附加框體之晶圓之轉印方 法；其特徵係將被固定於上述第1框體之晶圓，於直徑較 該晶圓直徑爲大而較第1框體內徑爲小的轉印桌台上，以 上述第】黏著薄片在下而接觸後，取下上述第】框體；在 該狀態下於上述晶圓上方，配置黏合有第2黏著薄片之第 2框體’將第2黏著薄片黏合於上述晶圓之後，再將上述 第1黏著薄片自上述晶圓剝除，而將晶圓轉印至第2框體 • 側。 申請專利範圍第2項所記載之發明，係針對申請專利 範圍第1項所記載之發明，其中，上述晶圓，係切割線藉 由雷射光線照射，而被改質且脆弱化之晶圓者。 發明效果 若依發明之晶圓轉印方法，則黏著薄片被黏合於晶圓 電路面的工件，會被轉印爲黏著薄片被黏合於晶圓背面的 一般工件狀態，而可使用常用之撿料裝置進行晶片之撿料 -7- (4) (4)1354325 。尤其若依本發明之晶圓轉印方法，因亦可以進行了隱密 切割之晶圓（晶片）其搬運或固定的工件，做爲對象，故 可更簡單的進行極薄化之晶圓（晶片）的搬運或加工》 【實施方式】 以下根據附加圖示，說明本發明之實施方式。 第1圖〜第7圖，係依該工程順序表示本發明方法的 側剖面圖。 第1圖係表示第1工件W1之構成者，該第1工件 w 1，係將自背面被隱密切割的晶圓丨，經由第1黏著薄片 2而與環狀之第1框體3 —體化所構成。 在此，上述晶圓1係以第9圖所示之硏磨工程來研磨 背面，而被極薄化。然後第1工件W1，係將第1黏著薄 片2黏合於被極薄化之晶圓1的電路面側，並黏合於被配 置在晶圓1周圍的環狀第1框體3，而構成之。此狀態下 ，晶圓1係電路面朝下而逆鑲嵌於第1黏著薄片上；接著 ，使用未圖示之隱密切割裝置，由背面（硏磨面）沿著切 割線照射雷射光線。如此一來，切割線會因雷射光線之照 射而改質且脆弱化，晶圓1則成爲可以極小之力量分割出 晶片la的狀態" 接著，本發明中係如第2圖所示，將第I圖所示之第 ]工件W1，以第1黏著薄片2朝下，而放置在轉印桌台5 上。另外，轉印桌台5亦可設置未圖示之吸附固定手段。 在此，轉印桌台5之直徑，係設定爲較晶圓1之直徑 (5) 1354325 大且較第1框體3之內徑小。 其次由第2圖所示之狀態，將第1框體3如第3圖所 示般，沿著轉印桌台5之外緣取下。此第1框體3之取下 ，係爲了於後述轉印工程中，防止其他的第2黏著薄片7 黏合於第1黏著薄片2。另外，取下第1框體3時，上述 真空吸附手段係在關閉狀態。 接著本實施方式中，增加第1框體3之取下量，使隱 B 密切割造成脆弱化的晶圓1之切割線容易斷裂（breaking )’而單片化爲複數晶片la(參考第3圖）。如此將第1 框體3取下而將晶圓1單片化爲晶片I a的同時，晶片i a 之間的空隙會被擴張，而可省略之後撿料裝置的擴張工程 〇 之後如第4圖所示，於晶圓1(被單片化之複數晶片 la)的上方’設置一週邊黏合有第2黏著薄片7的第2框 體6，再如第5圖所示’使第2黏著薄片7不接觸晶圓1 (被單片化之複數晶片la)之背面（上面）地接近之。然 後’自第2黏著薄片7上使黏貼滾輪8旋轉，並將此往第 5圖之箭頭方向移動，而使第2黏著薄片7黏貼於晶圓1 (被單片化之複數晶片】a )之背面（上面）。 又’做爲第2黏著薄片7之黏合方法，亦可使用上述 方法以外的方法。例如將第2框體6,使其上面與複數晶 片la的背面（上面）一樣高地’設置於其周圍，而將第2 黏者薄片7與複數晶片la，一起對第2框體6黏貼亦可。 另外’轉印桌台5設置有吸附固定手段時，則自將第 -9- (6) 1354325 2黏者薄片7黏合於晶圓1(被單片化之複數晶片la)的 階段’到剝除第1黏著薄片2而完成轉印的階段之間，可 使此吸附固定手段成爲開啓狀態，使晶片]a不會偏移或 脫落。 其次如第6圖所示，將第2框體6和被固定於此之第 2黏者薄片7拿往上方，則晶圓1 (被單片化之複數晶片 la)會自第1黏著薄片2脫離’而黏合於第2黏著薄片7 φ 並轉印於此。結果，第1黏著薄片2被貼合於該電路面的 晶圓1 (被單片化之複數晶片1 a )，係如第7圖所示，該 背面（研磨面）側黏合有第2黏著薄片7，而構成此晶圓 1和弟2框體6和弟2黏著薄片7 —體化形成的第2工件 W2。 從而’第7圖所示之第2工件W2，係藉由對第2黏 者薄片7之轉印’將晶圓1(被單片化之複數晶片la)以 其電路面向上的狀％而鑛嵌；故之後的檢料工程中，可簡 • 單以攝相機由上方辨識晶片]3之電路面的圖案，進而可 以其爲基準來精確辨識晶片之位置，使檢料裝置之吸 附筒夾（collet)無偏差的正對於撿料對象物晶片1&!1依 此，將不會有晶片之撿料失誤。 另外，第1黏者薄片2及第2黏著薄片7係分別爲紫 外線硬化型之黏著薄片爲佳。第1黏著薄片2若爲紫外線. 硬化型之黏著薄片’則因爲可藉由紫外線之照射而控制其 黏著力，故可不勉強的進行擴張工程中晶圓1 (晶片 之固定，和對第2黏著薄片7的轉印。 -10- (7) 1354325 又，第2黏者薄片7右爲紫外線硬化型之黏著薄片， 則可不勉強的進行轉印工程中晶圓1 (晶片la )之固定， 和撿料作業。 然後’第1黏著薄片2及第2黏著薄片7同爲紫外線 硬化型之黏著薄片時’因可使用相同種類之黏著薄片，故 可將材料管理簡單化。如此之紫外線硬化型之黏著薄片， 可將通常之切割工程〜撿料工程所用之切斷膠帶，原樣拿 | 來使用之。 然而本實施方式中’雖說明了背面被隱密切割，切割 線藉由雷射光線照射而被改質且脆弱化的晶圓之轉印方法 ’但本發明對於以其他方法切割並完成單片化的晶圓轉印 ，同樣亦可適用。 第8圖〜第10圖’係表示一準備對以不同於隱密切割 之方法所製造的晶圓，黏合黏著薄片於其電路面的工件之 工程。 桌8圖中，晶圓]係於其電路面側，黏合有晶圓背面 硏磨用之表面保護膠帶4。晶圓1，係以其背面側爲上面 ’而被裝載於未圖示之背面硏磨裝置的處理桌台，而藉由 背面硏磨裝置之旋轉硏磨石9，被硏磨至特定厚度爲止（ 第9圖）。 接著，於晶圓1之外緣配置環狀框體3，且對框體3 和晶圓】之表面保護膠帶4側，以黏著薄片]1 —倂黏合 。更且，藉由將晶圓1加以全切割（full cut )之切割，可 形成第1 0圖所示之工件（第1工件）W1。 -11 - (8) 1354325 如此準備之第1工件W〗，係可藉由本發明之轉印方 法’將表面保護膠帶4整個與黏著薄片11脫離而轉印晶 圓1(被單片化之複數晶片la)，而成爲與第7圖所示之 工件相同的第2工件W2之構成。依此，可由常用之撿料 裝置來撿料晶片la。 產業上之可利用性 B 本發明’係針對電子產業或光學產業中之半導體裝置 的製造工程’尤其做爲極薄之背面切割晶圓的轉印方法是 爲有用。 【圖式簡單說明】 〔第1圖〕表示本發明方法（晶圓被逆鑲嵌之工件） 的側剖面圖 〔第2圖〕表示本發明方法（將第1工件設置於轉印 φ 桌台的工程）的側剖面圖 〔第3圖〕表示本發明方法（取下第1框體之工程） 的側剖面圖 〔第4圖〕表示本發明方法（第2框體和第2黏著薄 片之設置工程）的側剖面圖 〔第5圖〕表示本發明方法（轉印工程）的側剖面圖 〔第6圖〕表示本發明方法（轉印工程）的側剖面圖 〔第7圖〕表示本發明方法（轉印後之第2工件）的 側剖面圖 -12- (9)1354325 〔第8圖〕表示黏合有表面保護膠帶之晶圓的側剖面 圖 〔第9圖〕表示晶圓之背面硏磨工程的側剖面圖 〔第10圖〕表示本發明之其他第1工件之構成的側 剖面圖(1) EMBODIMENT OF THE INVENTION [Technical Field] The present invention relates to a semiconductor wafer (hereinafter referred to as "wafer") that is fixed to an additional frame via an adhesive sheet, and is transferred to another frame. The transfer method of the wafer in the state. [Prior Art] For example, in the process of a semiconductor device in the electronics industry or the optical industry, after a specific circuit pattern is formed on the surface of the wafer, in order to make the thickness thin and average, or to remove the circuit formation, the crystal is formed. The back of the circle is honed (back-grinded), and then cut into individual circuits to produce the desired semiconductor wafer (the following film). Then, after the subsequent processing, the wafer is smashed, and the subsequent wafer is soldered to a base such as a solder frame in a second die bonding process, and then a desired semiconductor device is fabricated through subsequent molding. . However, in recent years, semiconductor devices have been required to be extremely thinned, and it has been difficult to carry out the processing of the wafer which is extremely thinned and not singulated (wafered), or to perform processing such as dicing. Therefore, in order to apply the physical force or the like to the wafer, a dicing method for stealth dicing is expected, which corresponds to an extremely thinned wafer. Concealed cutting is performed by focusing the inside of the wafer to focus on the laser beam to form a modified and fragile range, so that the irradiated laser body is rounded to the solid wafer wafer. The method of cutting off the wafer (for example, refer to Patent Document 1), the method of cutting off the wafer with the focus of the focus -5 (2) (2) 1354325 (for example, refer to Patent Document 1). It takes a very small amount of force to simply cut the modified range without unnecessary cracking in other parts. Therefore, it is more suitable for extremely thin wafer processing than the usual cutting method with physical force. Even if it is processed by stealth cutting, in order to perform processing such as wafer transfer, it is necessary to directly touch the wafer (wafer) as a workpiece state fixed to the annular frame via the adhesive sheet. When performing the stealth cutting, the focus is not offset, and the layer of the material other than the circuit surface or the adhesive sheet is avoided, and the laser light is irradiated. Therefore, the adhesive sheet is bonded to the circuit. On the other side, the laser beam is irradiated by the back surface of the wafer (the honing surface). [Patent Document 1] Japanese Patent No. 3,408,058 [Abstract] The problem to be solved by the invention is When the wafer is being used for wafer processing, the wafer identification device of the conventional feeding device detects the circuit by the camera from the upper side of the workpiece to identify the position of the wafer, so that the workpiece with the adhesive sheet on the circuit surface cannot recognize the correct positional relationship of the wafer. Moreover, there is a problem of causing damage to the circuit due to the pushing of the wafer on the circuit surface. The present invention has been made in view of the above problems, and an object thereof is to provide a workpiece bonded to a wafer circuit surface by an adhesive sheet. The state is transferred to the state where the back surface of the wafer is bonded with the workpiece of the adhesive sheet, and the conventional material feeding device -6 - (3) 1354325 can be used for the transfer method of the material, especially the present invention. Provided is a method for transferring a wafer from a workpiece to which a wafer (wafer) for stealth cutting is fixed by a usual method. In the invention of the first aspect of the invention, the invention of the first aspect of the invention is the transfer of the wafer of the first frame to the opposite side of the circuit surface side via the first adhesive sheet. a method of transferring a wafer to a frame by being fixed to the second frame via the second adhesive sheet; the feature is to fix the wafer of the first frame to a diameter of the wafer a transfer table having a large diameter and a smaller inner diameter than the first frame, wherein the first frame is removed after the first adhesive sheet is in contact with the first frame; and in this state, the film is placed over the wafer. After the second adhesive sheet having the second adhesive sheet adheres the second adhesive sheet to the wafer, the first adhesive sheet is peeled off from the wafer, and the wafer is transferred to the second housing. The invention described in claim 2 is the invention described in claim 1, wherein the wafer is modified and fragile by irradiation of a laser beam by a laser beam. Round. According to the invention, in the wafer transfer method of the invention, the workpiece to which the adhesive sheet is bonded to the wafer surface is transferred to a general workpiece state in which the adhesive sheet is bonded to the back surface of the wafer, and the commonly used material can be used. The device performs wafer processing - 7 - (4) (4) 1354325. In particular, according to the wafer transfer method of the present invention, since a workpiece which is transported or fixed by a wafer (wafer) which is secret-cut can be used as a target, it is possible to more easily perform an extremely thinned wafer ( Handling or Processing of Wafers [Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 1 to 7 are side cross-sectional views showing the method of the present invention in the order of the engineering. The first figure shows a structure of the first workpiece W1. The first workpiece w1 is a wafer cassette that is secluded from the back surface, and is connected to the first frame 3 of the ring via the first adhesive sheet 2. The composition of the body. Here, the wafer 1 is polished to the back surface by the honing process shown in Fig. 9, and is extremely thinned. Then, the first workpiece W1 is bonded to the circuit surface side of the wafer 1 which is extremely thinned, and is bonded to the annular first frame 3 disposed around the wafer 1, and is formed. . In this state, the wafer 1 is placed on the first adhesive sheet with the circuit surface facing downward, and then the laser beam is irradiated from the back surface (the honing surface) along the cutting line by a stealth cutting device (not shown). As a result, the cutting line is modified and fragile by the irradiation of the laser light, and the wafer 1 is in a state in which the wafer la can be divided by a very small force. Then, in the present invention, as shown in FIG. 2, The first workpiece W1 shown in Fig. 1 is placed on the transfer table 5 with the first adhesive sheet 2 facing downward. Further, the transfer table 5 may be provided with an adsorption fixing means (not shown). Here, the diameter of the transfer table 5 is set to be larger than the diameter (5) 1354325 of the wafer 1 and smaller than the inner diameter of the first frame 3. Next, in the state shown in Fig. 2, the first housing 3 is removed along the outer edge of the transfer table 5 as shown in Fig. 3. The removal of the first frame 3 is to prevent the other second adhesive sheet 7 from sticking to the first adhesive sheet 2 in the transfer process to be described later. Further, when the first housing 3 is removed, the vacuum suction means is in a closed state. In the present embodiment, the amount of removal of the first housing 3 is increased, and the cutting line of the wafer 1 which is fragile by the hidden B-cutting is easily broken, and singulated into a plurality of wafers la (refer to the third Figure). Thus, when the first frame 3 is removed and the wafer 1 is singulated into the wafer I a , the gap between the wafers ia is expanded, and the expansion of the coating device can be omitted, as shown in FIG. 4 . As shown in the figure, a second frame 6 to which the second adhesive sheet 7 is bonded is provided on the upper side of the wafer 1 (the singulated plurality of wafers la), and the second adhesive sheet is formed as shown in FIG. 7 is not in contact with the back (top) of the wafer 1 (the singulated plurality of wafers la). Then, the adhesive roller 8 is rotated from the second adhesive sheet 7, and is moved in the direction of the arrow in FIG. 5, and the second adhesive sheet 7 is adhered to the wafer 1 (the singulated plurality of wafers) a) The back (top). Further, as the bonding method of the second adhesive sheet 7, a method other than the above method may be used. For example, the second frame body 6 is placed on the upper surface of the second wafer body 6 as high as the back surface (upper surface) of the plurality of wafers la, and the second adhesive sheet 7 and the plurality of wafers la are attached to the second frame body 6 together. can. In addition, when the transfer table 5 is provided with an adsorption fixing means, the stage of the bonding of the -9-(6) 1354325 2 adhesive sheet 7 to the wafer 1 (the singulated plurality of wafers la) is peeled off. Between the stages in which the first adhesive sheet 2 is completed and the transfer is completed, the adsorption fixing means can be turned on, so that the wafer]a does not shift or fall off. Next, as shown in FIG. 6, when the second frame body 6 and the second adhesive sheet 7 fixed thereto are taken upward, the wafer 1 (the singulated plurality of wafers la) will be from the first adhesive sheet 2 It is bonded to the second adhesive sheet 7 φ and is transferred thereto. As a result, the first adhesive sheet 2 is bonded to the wafer 1 on the circuit surface (the plurality of wafers 1 a that are singulated), as shown in Fig. 7, the second adhesive is bonded to the back surface (polishing surface) side. The sheet 7 constitutes a second workpiece W2 formed by forming the wafer 1 and the 2 frame 6 and the 2 adhesive sheet 7 . Therefore, the second workpiece W2 shown in FIG. 7 is obtained by transferring the second adhesive sheet 7 to the wafer 1 (the plurality of wafers singulated) with the circuit surface facing upward. The mine is embedded; therefore, in the subsequent inspection project, the pattern of the circuit surface of the wafer can be identified by the camera alone, and the position of the wafer can be accurately identified based on the reference, so that the suction chuck of the inspection device is clamped. (collet) No deviation is positive for the wafer object 1&!1, and there will be no wafer error. Further, it is preferable that each of the first adhesive sheet 2 and the second adhesive sheet 7 is an ultraviolet-curable adhesive sheet. If the first adhesive sheet 2 is an ultraviolet ray, the hardened type of adhesive sheet can control the adhesion by ultraviolet light, so that the wafer 1 can be stretched without being forced (the wafer is fixed, and the second adhesion is applied). Transfer of the sheet 7. -10- (7) 1354325 Further, the second adhesive sheet 7 is an ultraviolet-curable adhesive sheet on the right side, so that the wafer 1 (wafer la) can be fixed in the transfer process without being forced, and Then, when the first adhesive sheet 2 and the second adhesive sheet 7 are both of the ultraviolet-curable adhesive sheets, the same type of adhesive sheet can be used, so that the material management can be simplified. Adhesive sheet can be used for the cutting tape used in the usual cutting work-forging project. It is used as it is. However, in the present embodiment, 'the back surface is hidden and cut, and the cutting line is irradiated by laser light. Transfer method of modified and fragile wafers. However, the present invention is also applicable to wafer transfer which is cut and completed by other methods. Fig. 8 to Fig. 10 show a preparation To The wafer manufactured by the method of stealth cutting adheres to the work of the workpiece with the adhesive sheet on the circuit surface. In the figure of Table 8, the wafer is attached to the surface of the circuit surface, and the surface for etching the back surface of the wafer is bonded. The protective tape 4. The wafer 1 is mounted on a processing table of a back honing device (not shown) with its back side being the upper side, and is honed by the rotary honing stone 9 of the back honing device. Until the specific thickness (Fig. 9). Next, the annular frame 3 is placed on the outer edge of the wafer 1, and the surface of the surface protection tape 4 of the frame 3 and the wafer is adhered by an adhesive sheet. Further, by cutting the wafer 1 by full cut, the workpiece (first workpiece) W1 shown in Fig. 10 can be formed. -11 - (8) 1354325 The first workpiece thus prepared In other words, the entire surface protection tape 4 can be detached from the adhesive sheet 11 by the transfer method of the present invention, and the wafer 1 (the singulated plurality of wafers la) can be transferred to the same as shown in FIG. The configuration of the second workpiece W2 having the same workpiece. Accordingly, the wafer la can be picked up by a conventional dip device. Utilization B The present invention is useful for a manufacturing process of a semiconductor device in the electronics industry or the optical industry, particularly as a transfer method for an extremely thin back-cut wafer. [Simplified illustration] [Fig. 1] A side cross-sectional view showing a method of the present invention (a workpiece in which a wafer is reversely embedded) (Fig. 2) is a side cross-sectional view showing a method of the present invention (a process of placing a first workpiece on a transfer φ table) (Fig. 3) A side cross-sectional view showing the method of the present invention (the process of removing the first frame) (Fig. 4) shows a side cross-sectional view of the method of the present invention (the installation of the second frame and the second adhesive sheet) [Fig. 5] A side cross-sectional view showing a method (transfer process) of the present invention (Fig. 6) showing a side cross-sectional view of the method (transfer process) of the present invention (Fig. 7) showing the method of the present invention (the second workpiece after transfer) Side section view -12- (9) 1354325 [Fig. 8] shows a side sectional view of a wafer to which a surface protection tape is bonded (Fig. 9) shows a side sectional view of the back side honing process of the wafer [Fig. 10] Side section showing the configuration of the other first workpiece of the present invention Map
【主要元件符號說明】 1 :晶圓 1 a :.晶片 2 :第1黏著薄片 3 :第1框體 5 :轉印桌台 6 :第2框體 7 :第2黏著薄板 8 :黏貼滚輪[Description of main component symbols] 1 : Wafer 1 a :. Wafer 2 : 1st adhesive sheet 3 : 1st frame 5 : Transfer table 6 : 2nd frame 7 : 2nd adhesive sheet 8 : Adhesive roller
9 :旋轉硏磨石 1 1 :黏著薄板 W1 :第1工件 W 2 :第2工件 -13-9: Rotary honing stone 1 1 : Adhesive sheet W1 : 1st workpiece W 2 : 2nd workpiece -13-