201243925 六、發明說明： 【發明所屬之技術領域】 本發明係關於用來將具備SiC基板之板狀的加工對象 物沿著切斷預定線進行切斷之雷射加工方法。 【先前技術】201243925 VI. [Technical Field] The present invention relates to a laser processing method for cutting a plate-shaped object to be processed having a SiC substrate along a line to cut. [Prior Art]
SiC (碳化矽）’是作爲能夠製造耐熱性、耐高電壓 性、省電力性優異的功率元件之半導體材料而受到注目。 然而，由於 SiC是硬度僅次於鑽石之難加工材料，若想 將具備SiC基板之板狀的加工對象物藉由刀片切割進行切 斷，必須進行低速加工且頻繁地更換刀片。於是，藉由對 加工對象物照射雷射光，沿著切斷預定線在SiC基板的內 部形成改質區域，以該改質區域爲起點而沿著切斷預定線 將加工對象物進行切斷之雷射加工方法已被提出（例如參 照專利文獻1 )。 [專利文獻] [專利文獻1]日本特表2007-514315號公報 【發明內容】 然而，藉由上述雷射加工方法，要將具備六方晶系 SiC基板（具有與與c面形成偏離角度的主面）之板狀的 加工對象物予以切斷的情況，本發明人等發現存在著以下 的課題。亦即，若沿著朝與主面及a面平行的方向延伸之 -5- 201243925 第1切斷預定線而在Sic基板內部形成第1改質區域’且 沿著朝與主面及m面平行的方向延伸之第2切斷預定線在 SiC基板內部形成第2改質區域時，沿第1切斷預定線之 切斷精度可能會比沿第2切斷預定線之切斷精度更差。本 發明人等探究的結果得知，這是起因於：龜裂容易從第2 改質區域朝SiC基板的厚度方向伸展，但龜裂不容易從第 1改質區域朝SiC基板的厚度方向伸展。 於是，本發明的目的是爲了提供一種雷射加工方法， 其能夠將具備六方晶系SiC基板（具有與c面形成偏離角 度的主面）之板狀的加工對象物沿著切斷預定線予以高精 度地切斷。 本發明的一觀點之雷射加工方法，是將具備六方晶系 SiC基板（具有與c面形成偏離角度的主面）之板狀的加 工對象物，分別沿著朝與主面及a面平行的方向延伸之第 1切斷預定線以及朝與主面及m面平行的方向延伸之第2 切斷預定線進行切斷之雷射加工方法；該雷射加工方法具 備第1步驟及第2步驟；該第1步驟，是讓雷射光的聚光 點對準SiC基板的內部，沿著第1切斷預定線將雷射光照 射於加工對象物，藉此沿著第1切斷預定線將作爲切斷起 點之第1改質區域形成於SiC基板的內部，以沿Sic基板 的厚度方向排列的方式對於1條第1切斷預定線形成複數 列的第1改質區域：該第2步驟，是讓聚光點對準Sic基 板的內部，沿著第2切斷預定線將雷射光照射於加工對象 物，藉此沿著第2切斷預定線將作爲切斷起點之第2改質 -6 - 201243925 區域形成於Sic基板的內部，以沿SiC基板的厚度方向排 列的方式對於1條第2切斷預定線形成複數列的第2改質 區域：在第1步驟，是以離SiC基板之雷射光入射面第2 近的第1改質區域比離雷射光入射面最近的第1改質區域 更小的方式，依離雷射光入射面從遠到近的順序形成第1 改質區域；在第2步驟，是以離雷射光入射面最近的第2 改質區域比離雷射光入射面第2近的第2改質區域更小的 方式，依離雷射光入射面從遠到近的順序形成第2改質區 域。 在該雷射加工方法，沿著第1切斷預定線，是使離雷 射光入射面第2近的第1改質區域形成相對較小。如此， 即使a面相對於SiC基板的厚度方向形成傾斜，仍能防止 離雷射光入射面第2近的第1改質區域所發生的龜裂朝a 面方向伸展，而能避免以大幅偏離第1切斷預定線的狀態 到達雷射光入射面。而且，沿著第1切斷預定線，是使離 雷射光入射面最近的第1改質區域形成相對較大。如此， 雖然變成龜裂不容易從第1改質區域朝SiC基板的厚度方 向伸展的狀態，但能確實地讓龜裂從離雷射光入射面最近 的第1改質區域到達雷射光入射面。此外，沿著第2切斷 預定線，使離雷射光入射面第2近的第2改質區域形成相 對較大。如此，變成龜裂容易從第2改質區域朝SiC基板 的厚度方向伸展的狀態，並且能讓離雷射光入射面第2近 的第2改質區域所發生的龜裂到達雷射光入射面或其附近 。而且，沿著第2切斷預定線，讓離雷射光入射面最近的 201243925 第2改質區域形成相對較小。如此，可防止在雷射光入射 面發生損傷，並能確實地讓龜裂從第2改質區域到達雷射 光入射面。如以上所述般，沿著第1切斷預定線，能確實 地讓龜裂從第1改質區域到達雷射光入射面，此外，沿著 第2切斷預定線，能確實地讓龜裂從第2改質區域到達雷 射光入射面。因此，依據此雷射加工方法，能夠將具備六 方晶系SiC基板（具有與c面形成偏離角度的主面）之板 狀的加工對象物沿著切斷預定線予以高精度地切斷。又偏 離角是包含0°的情況。在此情況，主面是與c面平行。此 外，可在第1步驟之後實施第2步驟，亦可在第2步驟之 後實施第1步驟。 本發明的一觀點之雷射加工方法，可在第1步驟及第 2步驟之後進一步具備第3步驟；該第3步驟，是以前述 第1改質區域爲起點而沿著第1切斷預定線將加工對象物 切斷，並以第2改質區域爲起點而沿著第2切斷預定線將 前述加工對象物切斷。如此，可獲得沿著切斷預定線被高 精度地切斷後之加工對象物。又能夠在沿著第1切斷預定 線進行切斷之後再實施沿著第2切斷預定線之切斷，也能 夠在沿著第2切斷預定線進行切斷之後再實施沿著第1切 斷預定線之切斷。 本發明的一觀點之雷射加工方法中，第1改質區域及 第2改質區域會有包含熔融處理區域的情況。 依據本發明，能夠將具備六方晶系SiC基板（具有與 c面形成偏離角度的主面）之板狀的加工對象物沿著切斷 -8- 201243925 預定線予以高精度地切斷。 【實施方式】 以下，針對本發明之較佳實施方式，參照圖式進行詳 細的說明。又各圖中對於相同或相當的部分是賦予同一符 號而省略重複的說明。 在本發明的一實施方式之雷射加工方法，是沿著切斷 預定線對加工對象物照射雷射光，藉此沿著切斷預定線在 加工對象物的內部形成改質區域。於是，首先針對此改質 區域的形成，參照第1圖〜第6圖作說明。 如第1圖所示般，雷射加工裝置100係具備：將雷射 光L施以脈衝振盪之雷射光源1 〇 1、配置成讓雷射光L的 光軸（光路）方向改變90°之分光鏡103、以及用來將雷 射光L聚光之聚光用透鏡105。此外，雷射加工裝置100 係具備：用來支承加工對象物1 (被經由聚光用透鏡105 聚光後之雷射光L所照射）之支承台1〇7、讓支承台107 移動之載台111、爲了調節雷射光L的輸出和脈衝寬等而 控制雷射光源1 0 1之雷射光源控制部1 02、以及控制載台 1 1 1的移動之載台控制部1 1 5。 在該雷射加工裝置100，從雷射光源1〇1射出的雷射 光L，經由分光鏡103將其光軸方向改變90。後，藉由聚 光用透鏡105聚光於支承台1〇7上所載置之加工對象物1 的內部。在此同時’讓載令111移動，使加工對象物1相 對於雷射光L沿著切斷預定線5進行相對移動。藉此，讓 201243925 沿著切斷預定線5之改質區域形成於加工對象物1 ° 如第2圖所示般，在加工對象物1上’設定有用來切 斷加工對象物1之切斷預定線5。切斷預定線5是呈直線 狀延伸之假想線。要在加工對象物1內部形成改質區域的 情況，如第3圖所示般，是在聚光點p對準加工對象物1 內部的狀態下，讓雷射光L沿著切斷預定線5 (亦即第2 圖的箭頭A方向）相對地移動。藉此，如第4圖~第6圖 所示般，讓改質區域7沿著切斷預定線5形成於加工對象 物1的內部，沿著切斷預定線5形成之改質區域7成爲切 斷起點區域8 * 又聚光點P是雷射光L所聚光的部位。此外，切斷預 定線5，並不限於直線狀而是曲線狀亦可，並不限於假想 線而是在加工對象物1表面3上實際畫設的線亦可。此外 ，改質區域7，可以是連續形成的情況，也可以是斷續形 成的情況》此外，改質區域7是列狀或點狀皆可，重點是 改質區域7至少形成於加工對象物1的內部即可。此外， 會有以改質區域7爲起點而形成龜裂的情況，龜裂及改質 區域7是露出加工對象物1的外表面（表面、背面、或外 周面）亦可。 附帶一提的，在此的雷射光L，是讓加工對象物1透 過且特別是在加工對象物1內部之聚光點附近被吸收，藉 此在加工對象物1形成改質區域7 (亦即內部吸收型雷射 加工）。如此，在加工對象物1的表面3幾乎不會吸收雷 射光L，因此加工對象物1的表面3不致發生熔融。一般 -10- 201243925 而言，在從表面3被熔融除去而形成孔洞、溝槽等除去部 (表面吸收型雷射加工）的情況，加工區域是從表面3側 逐漸朝背面側進展。 然而，本實施形態所形成的改質區域，是指密度、折 射率、機械強度、其他的物理特性變成與周圍不同的狀態 之區域。作爲改質區域，例如包括熔融處理區域、裂痕區 域、絕緣破壞區域、折射率變化區域等，也可以是其等混 合存在的區域。再者，作爲改質區域，也包括：加工對象 物的材料中改質區域的密度相較於非改質區域的密度發生 改變的區域、形成有晶格缺陷的區域（其等也能統稱爲高 密度差排區域）。 此外，熔融處理區域、折射率變化區域、改質區域的 密度相較於非改質區域的密度發生改變的區域、形成有晶 格缺陷的區域，進一步會有在該等區域的內部、或改質區 域和非改質區域的界面包含龜裂（裂縫、微裂痕）的情況 。所包含的龜裂’可能遍及改質區域的全面、僅形成於一 部分、或是形成於複數部分。 此外，在本實施方式，藉由沿著切斷預定線5形成複 數個改質點（加工痕），而形成改質區域7。改質點，是 藉由脈衝雷射光之1脈衝的照射（亦即1脈衝的雷射照射 :Laser Shot )所形成的改質部分，改質點的集合成爲改 質區域7。作爲改質點，是包含裂痕點 '熔融處理點、折 射率變化點、或是混合存在有該等點之至少一個等。 關於該改質點較佳爲，考慮所要求的切斷精度、所要 -11 - 201243925 求的切斷面之平坦性、加工對象物的厚度、種類、結晶方 位等，來適當地控制其大小、所發生的龜裂長度。 接下來，針對本發明的一實施方式之雷射加工方法作 詳細的說明。如第7圖所示般，加工對象物1係具備SiC 基板12之圓形板狀（例如直徑3吋、厚度3 5 Ομηι )之晶 圓。如第8圖所示般，SiC基板1 2具有六方晶系的結晶構 造，其結晶軸CA相對於SiC基板12的厚度方向以角度Θ (例如4°)形成傾斜。亦即，SiC基板12是具有偏離角 度Θ之六方晶系SiC基板。如第9圖所示般，SiC基板12 具有：與c面形成偏離角度Θ之表面（主面）12a及背面 (主面）12b。在SiC基板12中，a面相對於SiC基板12 的厚度方向（圖中的二點鏈線）以角度Θ形成傾斜；m面 相對於SiC基板12的厚度方向並未形成傾斜。 如第7圖及第9圖所示般，朝與表面12a及a面平行 的方向延伸之複數條的切斷預定線（第1切斷預定線）5a 、和朝與表面12a及m面平行的方向延伸之複數條的切斷 預定線（第2切斷預定線）5 m，是呈格子狀（例如1 mmx lmm)地設定在加工對象物1上。在SiC基板12的表面 12a，在藉由切斷預定線5a，5m畫設之各區域形成功能元 件，在SiC基板12的背面12b，在藉由切斷預定線5a， 5m畫設之各區域形成金屬配線。功能元件及金屬配線， 在沿著切斷預定線5a，5m將加工對象物1切斷而獲得之 各個片狀體中構成功率元件。又在SiC基板12,在與切斷 預定線5a平行的方向形成定向平面6a，在與切斷預定線 -12- 201243925 5m平行的方向形成定向平面6m。 將以上的加工對象物1沿著切斷預定線5a，5m如下 述般進行切斷。首先，如第10圖所示般，以覆蓋siC基 板12的背面12b之金屬配線的方式在加工對象物1上貼 附擴展膠帶2 3。接著，如第n ( a )圖所示般，將以 20ns〜100ns的脈衝寬（更佳爲50ns~60ns的脈衝寬）進行 脈衝振盪後之雷射光L的聚光點p對準SiC基板12內部 ’以脈衝節距爲1 Ομιη〜1 8μιη的方式（更佳爲脈衝節距爲 12μιη〜14μηι的方式）沿著切斷預定線5a將雷射光l照射 於加工對象物1。藉此，沿著切斷預定線5a，將作爲切斷 起點之改質區域（第1改質區域）7a形成於SiC基板12 的內部。該改質區域7a是包含熔融處理區域。又脈衝節 距是指’ 「雷射光L的聚光點P相對於加工對象物丨之移 動速度」除以「脈衝雷射光L的重複頻率」之値。 針對改質區域7a的形成作更詳細地說明。以SiC基 板12的表面12a作爲雷射光入射面而讓雷射光L的聚光 點P位於SiC基板12內部，沿著切斷預定線5a讓聚光點 P相對地移動。而且，讓沿著切斷預定線5a之聚光點P 的相對移動，對於1條切斷預定線5進行複數次（例如8 次）。這時，每次都改變從表面1 2a到聚光點P位置之距 離，藉此以沿SiC基板1 2的厚度方向排列的方式對於1 條切斷預定線5a形成複數列（第1列數，例如8列）的 改質區域7a。在此，以使離SiC基板1 2之雷射光入射 面（表面12a)第2近的改質區域7a比離表面12a最近的 -13- 201243925 改質區域7 a更小的方式，從S i C基板1 2之背面1 2 b側依 序（亦即，依離雷射光入射面從遠到近的順序）形成改質 區域7a。又改質區域7a的大小，例如能藉由改變雷射光 L的脈衝能量而予以調節。 如此，使從各改質區域7a發生的龜裂朝SiC基板12 的厚度方向伸展而互相連結。特別是讓從離SiC基板1 2 的雷射光入射面（表面12a)最近的改質區域7a朝SiC基 板12的厚度方向伸展後的龜裂，到達表面12a。這點，關 於將硬度僅次於鑽石之難加工材料所構成的SiC基板12 沿著切斷預定線5 a予以高精度地切斷方面，是非常重要 的。 當沿著切斷預定線5a形成改質區域7a後，如第1 1 ( b )圖所示般，讓以20ns〜100ns的脈衝寬（更佳爲 50ns~60ns的脈衝寬）進行脈衝振盪後之雷射光L的聚光 點P對準SiC基板12內部，以脈衝節距爲1 〇μιη〜ι 8μηι的 方式（更佳爲脈衝節距爲1 2 μ m〜1 4 μ m )沿著切斷預定線 5 m將雷射光L·照射於加工對象物1。如此，沿著切斷預定 線5m’將作爲切斷起點之改質區域（第2改質區域）7m 形成於SiC基板12的內部。該改質區域7m是包含熔融處 理區域。 針對改質區域7 m的形成作更詳細地說明。以s i c基 板12的表面12a作爲雷射光入射面而讓雷射光l的聚光 點P位於SiC基板12內部，沿著切斷預定線5m。而且， 讓沿著切斷預定線5m之聚光點p的相對移動，對於1條 -14- 201243925 切斷預定線5進行複數次（例如6次）。這時，每次都改 變從表面12a到聚光點P位置之距離，藉此以沿SiC基板 1 2的厚度方向排列的方式對於1條切斷預定線5m形成複 數列（比第1列數更少的第2列數（包含1列的情況）， 例如6列）的改質區域7 m。在此，以使離S i C基板12之 雷射光入射面（表面12a)最近的改質區域7m比離表面 12a第2近的改質區域7m更小的方式，從SiC基板12之 背面1 2 b側依序（亦即，依離雷射光入射面從遠到近的順 序）形成改質區域7 m。又改質區域7 m的大小，例如能藉 由改變雷射光L的脈衝能量而予以調節。 如此，使從各改質區域7m發生的龜裂朝SiC基板12 的厚度方向伸展而互相連結。特別是讓從離SiC基板12 的雷射光入射面（表面12a)最近的改質區域7m朝SiC 基板12的厚度方向伸展後的龜裂，到達表面12a。這點， 關於將硬度僅次於鑽石之難加工材料所構成的SiC基板12 沿著切斷預定線5m予以高精度地切斷方面，是非常重要 的。 沿著切斷預定線5m形成改質區域7m後，如第1 2 ( a )圖所示般讓擴展膠帶23擴張，在此狀態下，沿著各切 斷預定線5m，將刀刃41透過擴展膠帶23按壓在SiC基 板12的背面12b上。藉此，以改質區域7m爲起點沿著切 斷預定線5m將加工對象物1切成棒狀。這時，由於擴展 膠帶2 3處於擴張後的狀態，如第1 2 ( b )圖所示般，切成 棒狀後之加工對象物1會互相分離。 -15- 201243925 沿著切斷預定線5m將加工對象物1切斷後，如第13 (a)圖所示般，在繼續使擴展膠帶23擴張的狀態下，沿 著各切斷預定線5a，將刀刃41透過擴展膠帶23按壓在 SiC基板12的背面12b上。如此，以改質區域7a爲起點 沿著切斷預定線5 a將加工對象物1切成片狀。這時，由 於擴展膠帶2 3處於擴張後的狀態，如第1 3 ( b )圖所示般 ，被切成片狀後的加工對象物1會互相分離。如以上所述 般，將加工對象物1沿著切斷預定線5a，5m切成片狀而 獲得多數個功率元件。 依據以上的雷射加工方法，基於如下的理由，能將具 備六方晶系SiC基板12(具有與c面形成偏離角度的表面 12a)之板狀的加工對象物1沿著切斷預定線5a，5m予以 高精度地切斷，結果可獲得沿著切斷預定線5a，5m被高 精度地切斷後之加工對象物1 (亦即，功率元件）。 首先，以脈衝節距爲10μπι~18μιη的方式沿著切斷預 定線5a，5m對加工對象物1照射雷射光L。若在此條件 下對加工對象物1照射雷射光L，能使龜裂容易從改質區 域7a，7m朝SiC基板12的厚度方向伸展，且使龜裂不容 易從改質區域7a，7m朝c面方向伸展。再者，如果以脈 衝節距爲12μηι〜14μηι的方式沿著切斷預定線5a，5m對加 工對象物1照射雷射光L的話，能使龜裂更容易從改質區 域7a，7m朝SiC基板12的厚度方向伸展，且能使龜裂更 不容易從改質區域7a，7m朝c面方向伸展。 此外’以2〇nS〜l〇〇ns的脈衝寬讓雷射光L進行脈衝 -16- 201243925 振盪。如此，能確實地使龜裂容易從改質區域7a，7m朝 SiC基板12的厚度方向伸展，且確實地使龜裂不容易從改 質區域7a，7m朝c面方向伸展。再者，如果以50ns〜60ns 的脈衝寬讓雷射光L進行脈衝振盪的話，能更確實地使龜 裂容易從改質區域7a，7m朝SiC基板12的厚度方向伸展 ，且更確實地使龜裂不容易從改質區域7a，7m朝c面方 向伸展。 此外，沿著切斷預定線5a，使離SiC基板12之雷射 光入射面（表面12a )第2近的改質區域7a形成相對較小 。如此，即使a面相對於S i C基板12的厚度方向形成傾 斜，仍能防止離表面12a第2近的改質區域7a所發生的 龜裂朝a面方向伸展，而能避免以大幅偏離切斷預定線5a 的狀態到達表面1 2a。而且，沿著切斷預定線5a，使離 SiC基板12之雷射光入射面（表面12a)最近的改質區域 7a形成相對較大。如此，雖然變成龜裂不容易從改質區域 7a朝SiC基板12的厚度方向伸展的狀態，但能確實地讓 龜裂從離表面12a最近的改質區域7a到達表面12a。此外 ，沿著切斷預定線5m，使離SiC基板12之雷射光入射面 (表面1 2 a )第2近的改質區域7 m形成相對較大。如此 ，變成龜裂容易從改質區域7m朝SiC基板12的厚度方向 伸展的狀態，並且能讓離表面12a第2近的改質區域7m 所發生的龜裂到達表面12a或其附近。而且，沿著切斷預 定線5m’讓離SiC基板12之雷射光入射面（表面12a) 最近的改質區域7 m形成相對較小。如此，可防止在表面 -17- 201243925 1 2a發生損傷，並能確實地讓龜裂從改質區域7m到達表 面12a。如以上所述般，沿著切斷預定線5a，能確實地讓 龜裂從改質區域7a到達表面12a，此外，沿著切斷預定線 5m，能確實地讓龜裂從改質區域7m到達表面12a。此效 果，與後述改質區域7a，7m的形成列數、形成順序無關 而能發揮，又依據後述改質區域7a，7m的形成列數、形 成順序則能更顯著地發揮。 此外，比起沿著1條切斷預定線5 m形成改質區域7m 的情況，是沿著1條切斷預定線5 a形成更多列的改質區 域7a。如此，即使a面相對於SiC基板12的厚度方向形 成傾斜，在形成各改質區域7a時可防止龜裂從改質區域 7a朝a面方向大幅伸展，而且成爲在所有的改質區域7a 間使龜裂容易沿著SiC基板12的厚度方向連結的狀態。 此外，比起沿著1條切斷預定線5a形成改質區域7a的情 況，是沿著1條切斷預定線5m形成更少列的改質區域7m 。如此，在形成各改質區域7m時，能使龜裂從改質區域 7m朝SiC基板12的厚度方向大幅伸展。如以上所述般.， 能沿著切斷預定線5a讓龜裂從改質區域7a朝SiC基板12 的厚度方向伸展，此外，能沿著切斷預定線5m讓龜裂從 改質區域7m朝SiC基板12的厚度方向伸展。此效果，與 前述改質區域7a，7m的形成尺寸、後述改質區域7a，7m 的形成順序無關而能發揮，又依據前述改質區域7a，7m 的形成尺寸、後述改質區域7a，7m的形成順序，則能更 顯著地發揮。 -18- 201243925 此外，在形成讓龜裂朝Sic基板12的厚度方向伸展 的條件寬鬆之改質區域7m前，先形成讓龜裂朝SiC基板 12的厚度方向伸展的條件嚴格之改質區域7a。如此，在 形成改質區域7a時，在切斷預定線5a與切斷預定線5m 交叉的部分，能防止龜裂從改質區域7a朝SiC基板12的 厚度方向的伸展受到改質區域7m的阻礙。此效果，與前 述改質區域7a，7m的形成尺寸、形成列數無關而能發揮 〇 再者，以改質區域7m爲起點沿著切斷預定線5m將 加工對象物1切斷，然後以改質區域7a爲起點沿著切斷 預定線5 a將加工對象物1切斷。如此，沿著切斷預定線 5m (由於形成較少列的改質區域7m而想像比較難切斷） 將加工對象物1切斷，然後沿著切斷預定線5 a (由於形成 較多列的改質區域7 a而想像比較容易切斷）將加工對象 物1切斷。因此，能使沿著切斷預定線5 m將加工對象物 1切斷所需的力和沿著切斷預定線5 a將加工對象物1切斷 所需的力均一化，而使沿著切斷預定線5m之切斷精度及 沿著切斷預定線5a之切斷精度都更進一步提高。此效果 ，與前述改質區域7a’ 7m的形成尺寸、形成列數無關而 能發揮。 第14圖係藉由上述雷射加工方法沿著切斷預定線5a 切斷後的SiC基板12切斷面的相片。此外，第15圖係藉 由上述雷射加工方法沿著切斷預定線5m切斷後的SiC基 板12切斷面的相片。再者，第16圖係藉由上述雷射加工 -19- 201243925 方法沿著切斷預定線5a，5m切斷後之SiC基板12的平面 相片。在此，是準備具有4。偏離角之厚度350μπι的六方 晶系SiC基板12。 首先，如第1 4圖所示般，沿著切斷預定線5a ’以沿 SiC基板1 2的厚度方向排列的方式對於1條切斷預定線 5a形成8列改質區域7a。而且以離SiC基板12之雷射光 入射面（表面12a)第2近的改質區域7a比離表面12a最 近的改質區域7a更小的方式，依從SiC基板12之背面 1 2b側的順序形成改質區域7a。從第1 4圖可知，藉由形 成離表面12a第2近的改質區域7a，能將從改質區域7a 發生的龜裂之伸展制止。結果如第1 6圖所示般，相對於 切斷預定線5a之切斷面的蛇行可抑制成±4μηι以下。 又從表面12a到聚光點Ρ位置的距離，依從SiC基板 12的背面 12b側之改質區域 7a的順序爲 314·5μιη、 2 8 0.0 μηι 、 2 4 6.0 μm 、 2 1 2.0 μm 、 1 7 1 . 5 μm 、 1 2 3.5 μm 、 79.0μιη、32.0μιη。此外，雷射光L的脈衝能量，依從SiC 基板12的背面12b側之改質區域7a的順序爲25 μΐ、25 μ J 、25μ] ' 25μΙ > 20μΙ > 1 5μΙ ' 6μΙ > 6μ·ί ° 此外，如第1 5圖所示般，沿著切斷預定線5m，以沿 SiC基板12的厚度方向排列的方式對於1條切斷預定線 5m形成6列改質區域7m »而且，以離SiC基板12之雷 射光入射面（表面12a)最近的改質區域7m比離表面12a 第2近的改質區域7m更小的方式，依從SiC基板12之背 面1 2b的順序形成改質區域7m。從第1 5圖可知，藉由形 -20- 201243925 成離表面12a第2近的改質區域7m，能讓從改質區域7m 發生的龜裂伸展到表面1 2a或其附近。結果如第1 6圖所 示般，相對於切斷預定線5m之切斷面的蛇行可抑制成 ±2μιη以下。 又從表面12a到聚光點Ρ位置的距離，依從SiC基板 12的背面12b側之改質區域7m的順序爲315·5μιη、 264.5μηι、213.5μπι、1 5 5.0 μιη ' 9 5.5 μηι ' 34.5μιη ° 此外， 雷射光L的脈衝能量，依從SiC基板12的背面12b側之 改質區域 7m 的順序爲 25μ】、25μ·ί、20μ：ί、20μ·Γ、15μ：ί、 7 μ J ° 接下來說明，從改質區域7a，7m到達SiC基板12之 雷射光入射面（表面12a)的龜裂（以下稱爲「半切割」 )、與從改質區域7a，7m朝c面方向伸展的龜裂（以下 稱爲「c面裂痕」）的關係。在此，如第17圖及第18圖 所示般，是以改質區域7a爲對象來作說明；該改質區域 7a，在朝SiC基板12的厚度方向讓龜裂伸展的情況，比 起改質區域7m更難發生半切割且更容易發生c面裂痕。 第1 9圖係顯示脈衝寬、ID臨限値、HC臨限値及加 工裕度的關係之表》在此，讓脈衝寬以Ins、10ns〜120ns 的範圍改變，對於每個脈衝寬評價ID臨限値、HC臨限値 及加工裕度。此外，第20圖係顯示脈衝節距、ID臨限値 、H C臨限値及加工裕度的關係之表。在此，讓脈衝節距 以6 μ m ~ 2 2 μ m的範圍改變，對於每個脈衝節距評價I d臨 限値、HC臨限値及加工裕度。 -21 - 201243925 又ID臨限値是指，能發生c面裂痕之雷射光L脈衝 能量的最小値，依從ID臨限値高者（亦即，不容易發生c 面裂痕）的順序評價爲優、良、可、不可。此外，HC臨 限値是指，能發生半切割之雷射光L脈衝能量的最小値’ 依從HC臨限値低者（亦即，容易發生半切割）的順序評 價爲優、良、可、不可◊再者，加工裕度是ID臨限値與 HC臨限値之差，依從加工裕度大者的順序評價爲優、良 、可、不可。而且，綜合是依ID臨限値、HC臨限値、加 工裕度之優先順位進行加權，而評價爲優、良、可、不可 〇 結果·如第19圖所示般，較佳爲以20ns〜100ns的脈衝 寬讓雷射光L進行脈衝振盪，更佳爲以50ns〜60ns的脈衝 寬讓雷射光L進行脈衝振盪。如此，可抑制c面裂痕的發 生並促進半切割的發生。又在脈衝寬l〇ns的情況之ID臨 限値、加工裕度及綜合的各評價，比起脈衝寬20ns的情 況是屬於更接近不可的可。 此外如第20圖所示般，較佳爲以脈衝節距爲ΙΟμηι〜 18μιη的方式沿著切斷預定線5a，5m對SiC基板12照射 雷射光L ;更佳爲以脈衝節距爲1 Ιμηι〜15μιη的方式沿著切 斷預定線5a，5m對SiC基板12照射雷射光L ;特佳爲以 脈衝節距爲12μηι~14μηι的方式沿著切斷預定線5a，5m對 SiC基板1 2照射雷射光L。如此，可抑制C面裂痕的發生 並促進半切割的發生。又因爲脈衝節距爲1 Ομηι時ID臨限 値的評價爲可，如果更重視抑制c面裂痕發生的話，更佳 -22- 201243925 爲使脈衝節距比ΙΟμηι更大。 第21圖〜第23圖係顯示，雷射光L以數値孔徑0.8 聚光的情況之脈衝寬及脈衝節距的加工裕度實驗結果之表 。這些實驗結果，成爲第19圖及第20圖所示的評價根據 。獲得第21圖〜第23圖的實驗結果之實驗條件如下述般 。首先，以具有4°偏離角之厚度100 μηι的六方晶系SiC 基板12爲對象，沿著朝與表面12a及a面平行的方向延 伸之切斷預定線5 a讓雷射光L的聚光點P移動。此外， 將雷射光L以數値孔徑0.8進行聚光，讓聚光點P對準 離SiC基板12之雷射光入射面（表面12a)距離59 μηι的 位置。 使用以上實驗條件作爲前提，讓雷射光L的能量（脈 衝能量）及功率、雷射光L的脈衝節距分別改變，觀察改 質區域7a以及半切割及c面裂痕的狀態。在第21圖~第 23圖，雷射光L的脈衝寬分別爲2 7ns、40ns、57ns，雷 射光L的脈衝寬（重複頻率）分別爲10kHz、20kHz、 35kHz。 在第21圖〜第23圖的實驗結果中，ST表示未發生半 切割，HC表示發生了半切割。此外，ID表示發生了 c面 裂痕，LV1〜LV3表示c面裂痕的發生規模。在沿著2條切 斷預定線5a分別形成改質區域7a的情況，對於40mm的 '區域（20mmx2條的區域），將c面裂痕的發生區域未達 150μιη時以LV1表示，將c面裂痕的發生區域未達450μιη 時以LV2表示，將c面裂痕的發生區域爲450μιη以上時 -23- 201243925 以LV3表示。在LV1，朝與切斷預定線5a垂直的方向之 c面裂痕的伸展爲ΙΟμηι〜20μιη，相對於此，在LV2，LV3 ，朝與切斷預定線5a垂直的方向之c面裂痕的伸展最大 達1 ΟΟμιη左右。 第24圖係顯示脈衝節距和HC臨限値的關係。此外， 第2 5 _係顯示脈衝節距和ID臨限値的關係。再者，第 26圖係顯示脈衝節距和加工裕度的關係。這些圖是根據第 21圖~第23圖的實驗結果所作成的。如第24圖及第25圖 所示般，若脈衝寬變大，HC臨限値及ID臨限値雙方都會 上昇，比起HC臨限値的劣化（上昇），ID臨限値的提高 (上昇）效果更大。這代表著，如第26圖所示般，隨著 脈衝寬變大，加工裕度會變大。例如著眼於脈衝寬27ns 及脈衝寬57ns的情況，當脈衝節距爲12 μηι時，HC臨限 値從15μ1到17μ】而劣化（上昇）2μ;，相對於此，ID 臨限値則是從17μ】到29μ·ί而提高（上昇）12μ〗》而且 ，在脈衝寬40ns的情況，比起脈衝寬27ns的情況，在脈 衝節距10μηι~16μπι的範圍其加工裕度大幅提高。此外， 在脈衝寬57ns的情況，比起脈衝寬27ns的情況，在脈衝 節距6μηι〜20μηι的範圍其加工裕度大幅提高。 第27圖〜第29圖係顯示，將雷射光L以數値孔徑0.6 聚光的情況之脈衝寬及脈衝節距的加工裕度實驗結果之表 。這些實驗結果成爲第19圖及第20圖所示的評價之根據 。獲得第27圖〜第29圖的實驗結果之實驗條件如下所述 •首先，使用具有表面12a (與c面形成偏離角度）之厚 -24- 201243925 度3 5 0μιη的六方晶系SiC基板12作爲對象，沿著朝與表 面12a及a面平行的方向延伸之切斷預定線5a讓雷射光L 的聚光點P移動。此外，將雷射光L以數値孔徑0.6進行 聚光，讓聚光點P對準離SiC基板12之雷射光入射面（ 表面12a)距離50μιη的位置。 使用以上實驗條件作爲前提，讓雷射光L的能量（脈 衝能量）及功率、雷射光L的脈衝節距分別改變，觀察改 質區域7a以及半切割及c面裂痕的狀態。在第27圖~第 29圖，雷射光L的脈衝寬分別爲27ns、40ns、57ns，雷 射光L的脈衝寬（重複頻率）分別爲10kHz、20kHz、 3 5kHz ° 在第27圖〜第29圖的實驗結果中，ST表示未發生半 切割，HC表示發生了半切割。此外，ID表示發生c面裂 痕，LV1〜LV3表示c面裂痕的發生規模。LV1〜LV3的基 準是與上述第21圖〜第23圖的實驗結果的情況相同。再 者，OD表示：當雷射光L能量變大時，改質區域7a也變 大，起因於此而暴走的龜裂大幅偏離切斷預定線5a而到 達SiC基板12的表面12a。在此情況，不對c面裂痕進行 評價。但在脈衝寬40ns及脈衝寬57ns的情況，在脈衝節 距12μιη以上並未發生大規模的c面裂痕》 第3 0圖係顯示脈衝節距和H C臨限値的關係》該圖是 根據第27圖〜第29圖的實驗結果所作成的。如第30圖所 示般，在脈衝寬57ns的情況，比起脈衝寬40ns的情況， HC臨限値劣化2μ〗〜4μ〗左右。比起上述數値孔徑0.8的情 -25- 201243925 況，在數値孔徑0.6的情況，由於雷射光L的聚光點P受 像差的影響變小，在脈衝寬57ns的情況和脈衝寬40ns的 情況成爲同一程度的HC臨限値。如此可說，如果進行像 差修正的話，即使脈衝寬變大（至少到60ns爲止）HC臨 限値也不會劣化。 接下來說明，在SiC基板12之雷射光入射面（表面 12〇附近之HC品質的加工裕度之實驗結果》獲得第31 圖〜第33圖的實驗結果時之實驗條件如下述般。首先，使 用具有4°偏離角之厚度100 μιη的六方晶系SiC基板12作 爲對象，沿著朝與表面12a及a面平行的方向延伸之切斷 預定線5 a讓雷射光· L之聚光點P移動。此外，將雷射光 L以數値孔徑0.8進行聚光。 首先，在第31圖的實驗結果，是分別以27ns，40ns ，5 0ns，5 7ns的脈衝寬照射雷射光L，使用在聚光點位置 25·3μηι會發生半切割且在聚光點位置40.6μηι不會發生半 切割的能量（脈衝能量），讓聚光點位置在 25·3μηι〜40·6μηι的範圍內改變而觀察半切割的狀態。雷射 光L的脈衝節距爲Μμιη而保持一定。又聚光點位置是指 從表面1 2a到聚光點Ρ位置的距離。結果，脈衝寬所造成 之半切割的品質劣化幾乎不會發生，在脈衝寬27ns〜57ns 可形成高品質（半切割相對於切斷預定線之蛇行很小）的 半切割。此外，關於加工裕度，脈衝寬越大則變得越大。 當脈衝寬較小時，一部分的半切割容易發生分岔或裂開（ OD )。 -26- 201243925 此外，在第32圖的實驗結果，是分別以27ns ’ 40ns ，5 0ns，5 7ns的脈衝寬照射雷射光L，讓脈衝能量在7 μ J~ 1 2μ】的範圍內改變而觀察半切割的狀態。雷射光L的脈衝 節距爲14μιη而保持一定，聚光點位置爲34.5μπι而保持一 定。結果，脈衝寬所造成之HC臨限値的變化幾乎不會發 生。此外，相同脈衝能量可發生同一程度品質的半切割。 再者，在第33圖的實驗結果，是分別以ΙΟμιη ’ 12μιη ，14μιη，16μιη，18μπι的脈衝節距照射雷射光L，讓脈衝 能量在7μ·ί〜12 μΐ的範圍內改變化而觀察半切割的狀態。 雷射光L的脈衝寬爲5 7ns而保持一定，聚光點位置爲 3 4.5 μπι而保持一定。結果，脈衝節距所造成之HC臨限値 的變化幾乎不會發生。此外，在聚光點位置爲3 4.5 μιη的 情況，相同脈衝能量可發生同一程度品質的半切割。 接下來說明用來抑制c面裂痕之其他雷射加工方法。 首先，準備具備六方晶系SiC基板12(具有與c面形成偏 離角度的表面12a)之板狀的加工對象物1，設定切斷預 定線5a，5m。接著，如第34(a)圖所示般，讓雷射光L 的聚光點P對準SiC基板12內部，沿著設定於切斷預定 線5 a ( 5 m )的兩側之2條預備線5p將雷射光L照射於加 工對象物1。藉此，沿著各預備線5p將預備改質區域7p 形成於SiC基板1 2內部。該預備改質區域7p是包含熔融 處理區域。 預備線5p，是在與表面12a平行的面內位於切斷預定 線5 a ( 5 m )兩側且朝向與切斷預定線5 a ( 5 m )平行的方 -27- 201243925 向延伸。又在藉由切斷預定線5a，5m所畫設之各區域而 在SiC基板12的表面12a形成有功能元件的情況，從SiC 基板12的厚度方向觀察，較佳爲將預備線5p設定在相鄰 的功能元件間之區域內。 沿著各預備線5p將雷射光L照射於加工對象物1時 ，比起作爲切斷起點之改質區域7a ( 7m )，從預備改質 區域7p更不容易在SiC基板12發生龜裂。預備改質區域 7p，可藉由縮小雷射光L的脈衝能量、脈衝節距、脈衝寬 等，而變得比作爲切斷起點之改質區域7a ( 7m )更不容 易在SiC基板12發生龜裂。 沿著預備線5p形成預備改質區域7p後，讓雷射光L 的聚光點P對準SiC基板12內部，沿著切斷預定線5a ( 5m )將雷射光L照射於加工對象物1。藉此，沿著切斷預 定線5a (5m)將作爲切斷起點之改質區域7a (7m)形成 於SiC基板12內部。該改質區域7a(7m)是包含熔融處 理區域。沿著切斷預定線5a(5m)形成改質區域7a(7m )後，以改質區域7 a ( 7 m )爲起點而沿著切斷預定線5 a (5 m )將加工對象物1予以切斷》 依據以上的雷射加工方法，基於如下的理由，可將具 備六方晶系SiC基板12(具有與c面形成偏離角度的表面 12a)之板狀的加工對象物1沿著切斷預定線5a，5m予以 高精度地切斷，結果可獲得沿著切斷預定線5 a，5 m被高 精度地切斷後之加工對象物1 (亦即，功率元件）。 亦即，要沿著切斷預定線5a(5m)在SiC基板12內 -28- 201243925 部形成改質區域7a ( 7m )時，已沿著各預備線5p在SiC 基板12內部形成有預備改質區域7p。而且，預備線5p是 在與表面12a平行的面內位於切斷預定線5a(5m)的兩 側且朝向與切斷預定線5a ( 5m )平行的方向延伸。因此 ，即使龜裂從改質區域7a ( 7m )朝c面方向伸展，比起 第3 4 ( b )圖所示之未形成預備改質區域7p的情況，如第 34(a)圖所示般，該龜裂（c面裂痕）的伸展會被預備改 質區域7p抑制住。如此，不須考慮龜裂是否容易從改質 區域7a ( 7m )朝c面方向伸展，就能以讓龜裂容易從改 質區域7a ( 7m)朝SiC基板12的厚度方向伸展的方式將 雷射光照射於加工對象物1。又預備改質區域7p，由於不 須發揮作爲切斷起點的作用（亦即，促進從預備改質區域 7p朝SiC基板12的厚度方向之龜裂伸展），能以不容易 在SiC基板12發生龜裂的方式照射雷射光L而形成，因 此在形成預備改質區域7p時，容易抑制從預備改質區域 7 p朝c面方向之龜裂伸展。如此，能夠將具備六方晶系 SiC基板12(具有與c面形成偏離角度的主面）之板狀的 加工對象物沿著切斷預定線5a ( 5m )予以高精度地切斷 〇 此外，當形成改質區域7a(7m)時是讓雷射光l的 聚光點P對準離SiC基板12之雷射光入射面（表面i2a) 既定距離的情況，在形成預備改質區域7p時也是，較佳 爲讓雷射光L的聚光點P對準離表面12a同樣的距離。如 此，可更確實地抑制從改質區域7 a ( 7 m )朝c面方向之 -29- 201243925 龜裂伸展。 又當沿著各預備線5p在SiC基板12內部形成預備改 質區域7p時，同時也沿著設定在該等預備線5p間之切斷 預定線5a(5m)而在SiC基板12內部形成改質區域7a( 7m)的情況，仍能利用預備改質區域7p來抑制c面裂痕 的伸展。在此情況，相較於沿著切斷預定線5a ( 5m )之 改質區域7a ( 7m)的形成，較佳爲讓沿著預備線5p之預 備改質區域7p的形成先進行。 依據本發明，能夠將具備六方晶系SiC基板（具有與 c面形成偏離角度的主面）之板狀的加工對象物沿著切斷 預定線予以高精度地切斷。 明 說 單 簡 式 圖 第1圖係形成改質區域所使用的雷射加工裝置之構造 圖。 第2圖係雷射加工前的加工對象物之俯視圖。 第3圖係沿著第2圖的加工對象物之III-III線的截面 圖。 第4圖係雷射加工後的加工對象物之俯視圖。 第5圖係沿著第4圖的加工對象物之V-V線的截面圖 〇 · 第6圖係沿著第4圖的加工對象物之VI-VI線的截面 圖。 第7圖係作爲本發明一實施方式之雷射加工方法的對 -30- 201243925 象之加工對象物的俯視圖。 第8圖係顯示第7圖的加工對象物之結晶構造。 第9(a) (b)圖係第7圖的加工對象物之局部截面 圖。 第10圖係實施本發明一實施方式之雷射加工方法的 加工對象物之局部截面圖。 第11(a) (b)圖係實施本發明一實施方式之雷射加 工方法的加工對象物之局部截面圖。 第12(a) (b)圖係實施本發明一實施方式之雷射加 工方法的加工對象物之局部截面圖。 第13(a) (b)圖係實施本發明一實施方式之雷射加 工方法的加工對象物之局部截面圖。 第14圖係顯示藉由本發明一實施方式的雷射加工方 法切斷後之SiC基板的切斷面之相片。 第15圖係顯示藉由本發明一實施方式的雷射加工方 法切斷後之SiC基板的切斷面之相片。 第16圖係顯示藉由本發明一實施方式的雷射加工方 法切斷後之SiC基板的平面相片。 第17圖係用來說明SiC基板的內部所發生的c面裂 痕之立體圖。 第1 8圖係發生c面裂痕之SiC基板的切斷面之相片 〇 第1 9圖係顯示脈衝寬、ID臨限値、HC臨限値及加 工裕度的關係表。 -31 - 201243925 第20圖係顯示脈衝節距、ID臨限値、HC臨限値及 加工裕度的關係表。 第21圖係顯示脈衝寬及脈衝節距的加工裕度實驗結 果之表。 第22圖係顯示脈衝寬及脈衝節距的加工裕度實驗結 果之表。 第23圖係顯示脈衝寬及脈衝節距的加工裕度實驗結 果之表。 第24圖係顯示脈衝節距和HC臨限値的關係。 第25圖係顯示脈衝節距和ID臨限値的關係。 第26圖係顯示脈衝節距和加工裕度的關係。 第27圖係顯示脈衝寬及脈衝節距的加工裕度實驗結 果之表。 第28圖係顯示脈衝寬及脈衝節距的加工裕度實驗結 果之表。 第29圖係顯示脈衝寬及脈衝節距的加工裕度實驗結 果之表。 第30圖係顯示脈衝節距和HC臨限値的關係。 第3 1圖係顯示在雷射光入射面附近之HC品質的加工 裕度實驗結果之表。 第32圖係顯示在雷射光入射面附近之HC品質的加工 裕度實驗結果之表。 第3 3圖係顯示在雷射光入射面附近之HC品質的加工 裕度實驗結果之表。 -32- 201243925 第34(a) (b)圖係用來說明本發明的其他實施方式 的雷射加工方法之俯視圖。 【主要元件符號說明】 1 :加工對象物 5a，5m :切斷預定線 5 p :預備線 7 a，7 m :改質區域 7p :預備改質區域 1 2 : SiC基板 12a :表面（主面） 12b :背面（主面） L :雷射光 P :聚光點 -33-SiC (tantalum carbide) is attracting attention as a semiconductor material capable of producing a power element excellent in heat resistance, high voltage resistance, and power saving. However, since SiC is a hard-to-machine material that is second only to diamonds in hardness, it is necessary to perform low-speed processing and frequently replace the blade if the object to be processed having a plate shape having a SiC substrate is cut by blade cutting. Then, by irradiating the object with the laser light, a modified region is formed inside the SiC substrate along the line to cut, and the object to be processed is cut along the line to cut with the modified region as a starting point. A laser processing method has been proposed (for example, refer to Patent Document 1). [Patent Document 1] [Patent Document 1] Japanese Laid-Open Patent Publication No. 2007-514315. SUMMARY OF THE INVENTION However, the above-described laser processing method is required to have a hexagonal SiC substrate (having a main angle deviating from the c-plane) The present inventors have found that the following problems have been found in the case where the object to be processed in the form of a plate is cut. That is, the first modified region ' is formed inside the Sic substrate along the -5 - 201243925 first cutting line extending in a direction parallel to the main surface and the a-plane, and along the main surface and the m-plane When the second planned cutting line is formed in the parallel direction, when the second modified region is formed inside the SiC substrate, the cutting accuracy along the first cutting planned line may be worse than the cutting accuracy along the second cutting planned line. . As a result of investigation by the inventors of the present invention, it is found that the crack easily spreads from the second modified region toward the thickness direction of the SiC substrate, but the crack does not easily extend from the first modified region toward the thickness of the SiC substrate. . Accordingly, an object of the present invention is to provide a laser processing method capable of providing a plate-shaped object to be processed having a hexagonal SiC substrate (having a main surface deviated from the c-plane) along a line to be cut. Cut off with high precision. A laser processing method according to a point of view of the present invention is a plate-shaped object to be processed having a hexagonal SiC substrate (having a main surface deviated from the c-plane), and is parallel to the main surface and the a-plane a first laser cutting method in which the first cutting line and the second cutting line extending in a direction parallel to the main surface and the m surface are cut; the laser processing method includes the first step and the second step In the first step, the condensing point of the laser light is aligned with the inside of the SiC substrate, and the laser beam is irradiated onto the object to be processed along the first line to cut, thereby along the first line to cut. The first modified region, which is the starting point of the cutting, is formed inside the SiC substrate, and the first modified region is formed in a plurality of rows for one first cutting planned line so as to be aligned in the thickness direction of the Sic substrate: the second step The illuminating point is aligned with the inside of the Sic substrate, and the laser beam is irradiated onto the object to be processed along the second line to cut, whereby the second modification is used as the cutting start point along the second line to cut. -6 - 201243925 The area is formed inside the Sic substrate to follow the SiC substrate A method of arranging in the thickness direction forms a second modified region in a plurality of rows for one second planned cutting line: in the first step, the first modified region is closer to the second closest to the laser light incident surface of the SiC substrate The first modified region closest to the incident surface of the laser light is smaller, and the first modified region is formed from the far side to the near side of the incident surface of the laser light; in the second step, the closest to the incident surface of the laser light is 2 The modified region is smaller than the second modified region which is closer to the second incident laser light incident surface, and the second modified region is formed in order from the far side to the near laser light incident surface. In the laser processing method, along the first line to cut, the first modified region which is second closest to the incident surface of the laser light is formed relatively small. In this way, even if the a-plane is inclined with respect to the thickness direction of the SiC substrate, it is possible to prevent the crack generated in the first modified region which is second closest to the incident surface of the laser light from extending in the a-plane direction, and it is possible to avoid a large deviation from the first one. The state of cutting the predetermined line reaches the laser light incident surface. Further, along the first line to cut, the first modified region closest to the incident surface of the laser light is relatively large. In this manner, the crack does not easily extend from the first modified region toward the thickness of the SiC substrate, but the crack can be surely brought to the laser light incident surface from the first modified region closest to the incident surface of the laser light. Further, along the second planned cutting line, the second modified region which is second closest to the incident surface of the laser light is relatively large. In this way, the crack tends to extend from the second modified region toward the thickness direction of the SiC substrate, and the crack generated in the second modified region near the laser light incident surface can reach the laser light incident surface or Near it. Further, along the second planned cutting line, the second modified region of 201243925 which is closest to the incident surface of the laser light is relatively small. In this way, damage to the incident surface of the laser light can be prevented, and the crack can be reliably caused to reach the laser light incident surface from the second modified region. As described above, it is possible to surely allow the crack to pass from the first modified region to the laser light incident surface along the first line to cut, and to reliably cause the crack along the second line to cut. The laser light incident surface is reached from the second modified region. Therefore, according to the laser processing method, a plate-shaped object to be processed having a hexagonal SiC substrate (having a main surface which is offset from the c-plane) can be cut with high precision along the line to cut. The deviation angle is also the case of 0°. In this case, the main surface is parallel to the c-plane. Further, the second step may be carried out after the first step, or the first step may be carried out after the second step. The laser processing method according to one aspect of the present invention may further include a third step after the first step and the second step, and the third step is to follow the first modified region as a starting point and to follow the first cutting schedule The line cuts the object to be processed, and cuts the object to be processed along the second line to cut along the second modified region. In this way, the object to be processed which has been cut with high precision along the line to cut can be obtained. Further, after cutting along the first line to cut, the cutting along the second line to cut can be performed, and the cutting along the second line to cut can be performed along the first line. Cut off the cut of the predetermined line. In the laser processing method according to one aspect of the invention, the first modified region and the second modified region may include a molten processed region. According to the present invention, a plate-shaped object to be processed having a hexagonal SiC substrate (having a main surface which is offset from the c-plane) can be cut with high precision along a predetermined line of -8-201243925. [Embodiment] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. In the respective drawings, the same or corresponding components are designated by the same reference numerals, and the description thereof will not be repeated. In the laser processing method according to the embodiment of the present invention, the object to be processed is irradiated with the laser light along the line to cut, whereby the modified region is formed inside the object along the line to cut. Therefore, first, the formation of the modified region will be described with reference to Figs. 1 to 6 . As shown in Fig. 1, the laser processing apparatus 100 includes a laser light source 1 〇1 that pulsates the laser light L, and a light beam that is arranged to change the optical axis (light path) direction of the laser light L by 90°. The mirror 103 and the condensing lens 105 for concentrating the laser light L are provided. Further, the laser processing apparatus 100 includes a support table 1〇7 for supporting the object 1 to be processed (irradiated by the laser light L collected by the collecting lens 105), and a stage for moving the support table 107. 111. The laser light source control unit 102 for controlling the laser light source 1 0 1 and the stage control unit 1 15 for controlling the movement of the stage 1 1 1 in order to adjust the output of the laser light L and the pulse width. In the laser processing apparatus 100, the laser light L emitted from the laser light source 1〇1 is changed by 90 in the optical axis direction via the beam splitter 103. Thereafter, it is condensed on the inside of the object 1 placed on the support table 1〇7 by the condenser lens 105. At the same time, the carrier 111 is moved, and the object 1 is relatively moved with respect to the laser beam L along the line to cut 5 . In this way, the modified region of the 201243925 along the line to cut 5 is formed in the object to be processed 1°. As shown in Fig. 2, the cutting object 1 is cut by the cutting object 1 Schedule line 5. The line to cut 5 is an imaginary line extending in a straight line. When the modified region is formed in the object 1 to be processed, as shown in FIG. 3, the laser light L is placed along the line to cut 5 in a state where the light-converging point p is aligned with the inside of the object 1 . (that is, the direction of the arrow A in Fig. 2) relatively moves. As a result, as shown in FIG. 4 to FIG. 6, the modified region 7 is formed inside the object 1 along the line to cut 5, and the modified region 7 formed along the line to cut 5 becomes The cutting start point region 8* and the light collecting point P are portions where the laser light L is concentrated. Further, the cutting of the predetermined line 5 is not limited to a linear shape but a curved shape, and may not be limited to the imaginary line but may be a line actually drawn on the surface 3 of the object 1 to be processed. Further, the modified region 7 may be formed continuously or in a case where it is intermittently formed. Further, the modified region 7 may be in the form of a column or a dot, and the emphasis is that the modified region 7 is formed at least in the object to be processed. The inside of 1 can be. Further, cracks may be formed from the modified region 7 as a starting point, and the cracked and modified region 7 may expose the outer surface (surface, back surface, or outer peripheral surface) of the object 1 to be processed. Incidentally, the laser light L here is such that the object 1 is transmitted, and particularly absorbed in the vicinity of the condensing point inside the object 1 to form a modified region 7 in the object 1 (also That is, internal absorption type laser processing). As described above, since the laser light L is hardly absorbed on the surface 3 of the object 1 to be processed, the surface 3 of the object 1 does not melt. In the case where the surface 3 is melted and removed to form a removal portion such as a hole or a groove (surface absorption type laser processing), the processing region gradually progresses from the surface 3 side toward the back surface side. However, the modified region formed in the present embodiment means a region in which the density, the refractive index, the mechanical strength, and other physical properties are different from the surroundings. The modified region may include, for example, a molten processed region, a cracked region, an insulating fracture region, a refractive index change region, or the like, or a region in which the mixture is mixed. Further, the modified region includes: a region in which the density of the modified region in the material of the object to be processed is changed from that in the non-modified region, and a region in which a lattice defect is formed (these can also be collectively referred to as High density difference row area). Further, the region where the density of the molten processed region, the refractive index change region, and the modified region is changed compared to the density of the non-modified region, and the region where the lattice defect is formed may further be internal to the regions, or may be modified. The interface between the qualitative region and the non-modified region includes cracks (cracks, micro-cracks). The included cracks may be comprehensive throughout the modified region, formed only in one portion, or formed in a plurality of portions. Further, in the present embodiment, the modified region 7 is formed by forming a plurality of modified spots (machining marks) along the line to cut 5 . The modified spot is a modified portion formed by one pulse of pulsed laser light (i.e., one pulse of laser irradiation: Laser Shot), and the set of modified spots becomes the modified region 7. The modified point includes a crack point "melting point, a change point of the refractive index, or at least one of the points in the mixture." It is preferable to appropriately control the size and the size of the object to be corrected in consideration of the required cutting accuracy, the flatness of the cut surface to be determined by -11 to 201243925, the thickness, the type, and the crystal orientation of the object to be processed. The length of the crack that occurred. Next, a laser processing method according to an embodiment of the present invention will be described in detail. As shown in Fig. 7, the object 1 is provided with a circular disk shape (for example, a diameter of 3 吋 and a thickness of 3 5 Ομηι) of the SiC substrate 12. As shown in Fig. 8, the SiC substrate 12 has a hexagonal crystal structure in which the crystal axis CA is inclined at an angle Θ (for example, 4°) with respect to the thickness direction of the SiC substrate 12. That is, the SiC substrate 12 is a hexagonal SiC substrate having an off angle Θ. As shown in Fig. 9, the SiC substrate 12 has a surface (main surface) 12a and a back surface (main surface) 12b which are formed at an angle Θ from the c-plane. In the SiC substrate 12, the a-plane is inclined at an angle 相对 with respect to the thickness direction of the SiC substrate 12 (the two-dot chain line in the drawing); the m-plane is not inclined with respect to the thickness direction of the SiC substrate 12. As shown in Fig. 7 and Fig. 9, a plurality of planned cutting lines (first cutting planned lines) 5a extending in a direction parallel to the surface 12a and the a surface are parallel to the surface 12a and the m surface. The cutting line (second cutting planned line) 5 m of a plurality of lines extending in the direction is set in a lattice shape (for example, 1 mm x 1 mm) on the object 1 to be processed. On the surface 12a of the SiC substrate 12, functional elements are formed in the respective regions drawn by the predetermined lines 5a, 5m, and the regions on the back surface 12b of the SiC substrate 12 are cut by the predetermined lines 5a, 5m. Metal wiring is formed. The functional element and the metal wiring constitute a power element in each of the sheet-like bodies obtained by cutting the object 1 along the line to cut 5a, 5m. Further, in the SiC substrate 12, an orientation flat 6a is formed in a direction parallel to the line to cut 5a, and an orientation flat 6m is formed in a direction parallel to the line to cut -12-201243925 5m. The above-described object 1 is cut along the line to cut 5a, 5m as follows. First, as shown in Fig. 10, the expanded tape 2 is attached to the object 1 so as to cover the metal wiring of the back surface 12b of the siC substrate 12. Next, as shown in the nth (a) diagram, the condensed spot p of the laser light L pulse-oscillated with a pulse width of 20 ns to 100 ns (more preferably, a pulse width of 50 ns to 60 ns) is aligned with the SiC substrate 12 In the internal portion, the laser light 1 is irradiated onto the object 1 along the line to cut 5a in such a manner that the pulse pitch is 1 Ομηη to 18 μm (more preferably, the pulse pitch is 12 μm to 14 μm). Thereby, a modified region (first modified region) 7a as a cutting start point is formed inside the SiC substrate 12 along the line to cut 5a. The modified region 7a is a molten processed region. Further, the pulse pitch is defined as "the moving speed of the focused spot P of the laser light L with respect to the object to be processed" divided by the "repetition frequency of the pulsed laser light L". The formation of the modified region 7a will be described in more detail. The surface 12a of the SiC substrate 12 serves as a laser light incident surface, and the condensed spot P of the laser light L is positioned inside the SiC substrate 12, and the condensed spot P is relatively moved along the line to cut 5a. Further, the relative movement of the condensed spot P along the line to cut 5a is made plural times (for example, eight times) for one line to cut. At this time, the distance from the surface 1 2a to the position of the condensing point P is changed each time, thereby forming a plurality of columns (the number of the first column) for one planned cutting line 5a so as to be aligned in the thickness direction of the SiC substrate 12. For example, 8 columns) of the modified region 7a. Here, the modified region 7a which is second closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is smaller than the -13-201243925 modified region 7a which is closest to the surface 12a, from S i The back surface 1 2 b side of the C substrate 1 2 is sequentially formed (that is, in order from the far side to the near side of the laser light incident surface) to form the modified region 7a. The size of the modified region 7a can be adjusted, for example, by changing the pulse energy of the laser light L. In this manner, the cracks generated from the respective modified regions 7a are extended toward the thickness direction of the SiC substrate 12 to be connected to each other. In particular, the crack extending from the modified region 7a closest to the laser light incident surface (surface 12a) of the SiC substrate 1 toward the thickness direction of the SiC substrate 12 reaches the surface 12a. In this regard, it is very important to cut the SiC substrate 12 composed of the hard-to-machine material having a hardness second only to the diamond along the line to cut 5a with high precision. After the modified region 7a is formed along the line to cut 5a, as shown in Fig. 1 (b), pulse oscillation is performed with a pulse width of 20 ns to 100 ns (more preferably, a pulse width of 50 ns to 60 ns). The condensed spot P of the laser light L is aligned with the inside of the SiC substrate 12, and the pulse pitch is 1 〇μιη to ι 8 μηι (more preferably, the pulse pitch is 12 μm to 1 4 μm). The laser beam L· is irradiated onto the object 1 at a predetermined line of 5 m. In this manner, a modified region (second modified region) 7m as a cutting start point is formed inside the SiC substrate 12 along the cutting planned line 5m'. The modified region 7m is a region containing a molten treatment. The formation of the modified region 7 m will be described in more detail. The surface 12a of the s i c substrate 12 is used as a laser light incident surface, and the condensed spot P of the laser light 1 is placed inside the SiC substrate 12 along the line to cut 5m. Further, the relative movement of the condensed spot p along the line to cut 5m is made plural times (for example, six times) for one line of the -14-201243925 cut line 5 . At this time, the distance from the surface 12a to the position of the light-converging point P is changed each time, whereby a plurality of columns (more than the first column) are formed for one planned cutting line 5m so as to be aligned in the thickness direction of the SiC substrate 12. The number of second columns (including one column), for example, six columns, is the modified region 7 m. Here, the modified region 7m closest to the laser light incident surface (surface 12a) of the Si C substrate 12 is smaller than the modified region 7m which is second closest to the surface 12a, from the back surface 1 of the SiC substrate 12. The 2b side is sequentially formed (i.e., in order from the far side to the near side of the incident surface of the laser light) to form the modified region 7m. The size of the modified region 7 m can be adjusted, for example, by changing the pulse energy of the laser light L. In this manner, the cracks generated from the respective modified regions 7m are extended toward the thickness direction of the SiC substrate 12 to be connected to each other. In particular, the crack extending from the modified region 7m closest to the laser light incident surface (surface 12a) of the SiC substrate 12 toward the thickness direction of the SiC substrate 12 reaches the surface 12a. In this regard, it is very important that the SiC substrate 12 composed of the hard-to-machine material having a hardness second only to the diamond is cut with high precision along the line to cut 5m. After the modified region 7m is formed along the line to cut 5m, the expanded tape 23 is expanded as shown in Fig. 1 (a), and in this state, the blade 41 is expanded along the respective planned cutting lines 5m. The tape 23 is pressed against the back surface 12b of the SiC substrate 12. Thereby, the object 1 is cut into a rod shape along the line to cut 5m from the modified region 7m. At this time, since the expanded tape 2 3 is in an expanded state, as shown in Fig. 1 (b), the objects 1 to be cut into a rod shape are separated from each other. -15-201243925 After cutting the object 1 along the cutting line 5m, as shown in Fig. 13(a), in the state where the expansion tape 23 is continuously expanded, along the respective cutting planned lines 5a, The blade 41 is pressed against the back surface 12b of the SiC substrate 12 through the spread tape 23. In this manner, the object 1 is cut into a sheet shape along the line to cut 5a starting from the modified region 7a. At this time, since the expanded tape 23 is in an expanded state, as shown in Fig. 1 (b), the objects 1 to be cut into pieces are separated from each other. As described above, the object 1 is cut into a sheet shape along the line to cut 5a, 5m to obtain a plurality of power elements. According to the above-described laser processing method, the object 1 having a plate shape including the hexagonal SiC substrate 12 (having a surface 12a which is deviated from the c-plane) can be along the line to cut 5a. 5 m is cut with high precision, and as a result, the object 1 (that is, the power element) which is cut with high precision along the line to cut 5a, 5m can be obtained. First, the object 1 is irradiated with the laser light L along the cutting predetermined lines 5a, 5m so that the pulse pitch is 10 μm to 18 μm. When the object 1 is irradiated with the laser light L under these conditions, the crack can be easily extended from the modified regions 7a and 7m toward the thickness direction of the SiC substrate 12, and the crack is not easily changed from the modified region 7a, 7m toward The c-plane extends. In addition, when the laser beam L is irradiated to the object 1 along the line to cut 5a, 5m so that the pulse pitch is 12 μm to 14 μm, the crack can be more easily changed from the modified region 7a, 7m toward the SiC substrate. The thickness direction of 12 is extended, and the crack is less likely to extend from the modified region 7a, 7m toward the c-plane. In addition, the laser beam L is pulsed with a pulse width of 2〇nS to l〇〇ns. -16-201243925 Oscillation. In this way, it is possible to reliably cause the crack to easily extend from the modified regions 7a, 7m in the thickness direction of the SiC substrate 12, and it is possible to surely prevent the crack from extending from the modified regions 7a, 7m toward the c-plane direction. In addition, when the laser beam L is pulse-oscillated with a pulse width of 50 ns to 60 ns, it is possible to more reliably cause the crack to easily extend from the modified region 7a, 7m toward the thickness direction of the SiC substrate 12, and more reliably make the turtle The crack does not easily extend from the modified region 7a, 7m toward the c-plane. Further, along the line to cut 5a, the modified region 7a which is second closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is formed relatively small. In this manner, even if the a-plane is inclined with respect to the thickness direction of the S i C substrate 12, it is possible to prevent the crack generated in the modified region 7a which is second from the surface 12a from extending in the a-plane direction, and it is possible to avoid a large deviation from the cut. The state of the predetermined line 5a reaches the surface 12a. Further, along the line to cut 5a, the modified region 7a closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is relatively large. In this manner, the crack does not easily extend from the modified region 7a toward the thickness direction of the SiC substrate 12. However, the crack can be reliably caused to reach the surface 12a from the modified region 7a closest to the surface 12a. Further, along the line to cut 5m, the modified region 7 m which is second closest to the laser light incident surface (surface 1 2 a ) of the SiC substrate 12 is relatively large. In this way, the crack easily spreads from the modified region 7m toward the thickness direction of the SiC substrate 12, and the crack generated in the modified region 7m which is second from the surface 12a can reach the surface 12a or its vicinity. Further, the modified region 7 m closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is formed relatively small along the cutting predetermined line 5 m'. Thus, damage to the surface -17-201243925 1 2a can be prevented, and the crack can be surely allowed to reach the surface 12a from the modified region 7m. As described above, along the line to cut 5a, it is possible to surely allow the crack to reach the surface 12a from the modified region 7a, and further, along the line to cut 5m, the crack can be reliably made from the modified region 7m. Reach the surface 12a. This effect can be exhibited irrespective of the number of formation rows and the order of formation of the modified regions 7a and 7m to be described later, and can be more prominently exhibited in accordance with the number of formation rows and the order of formation of the modified regions 7a and 7m which will be described later. Further, in the case where the modified region 7m is formed along the one line cutting line 5 m, a plurality of modified regions 7a are formed along one planned cutting line 5a. In this way, even if the a-plane is inclined with respect to the thickness direction of the SiC substrate 12, it is possible to prevent the crack from being greatly extended from the modified region 7a toward the a-plane direction when the modified regions 7a are formed, and to make the between all the modified regions 7a The crack is easily connected to the SiC substrate 12 in the thickness direction. Further, in comparison with the case where the modified region 7a is formed along one line to be cut 5a, a modified region 7m having fewer rows is formed along one planned cutting line 5m. As described above, when each modified region 7m is formed, the crack can be greatly extended from the modified region 7m toward the thickness direction of the SiC substrate 12. As mentioned above. The crack can be extended from the modified region 7a toward the thickness direction of the SiC substrate 12 along the line to cut 5a, and the crack can be made from the modified region 7m toward the thickness of the SiC substrate 12 along the line to cut 5m. Stretch in the direction. This effect can be exerted regardless of the formation size of the modified regions 7a, 7m and the order of formation of the modified regions 7a, 7m described later, and depending on the formation size of the modified regions 7a, 7m, and the modified regions 7a, 7m described later. The order of formation can be played more prominently. -18-201243925 In addition, a modified region 7a is formed which allows the crack to extend in the thickness direction of the SiC substrate 12 before forming a modified region 7m in which the crack is extended in the thickness direction of the Sic substrate 12. . When the modified region 7a is formed, the portion where the planned cutting line 5a and the planned cutting line 5m intersect with each other can prevent the crack from being extended from the modified region 7a toward the thickness direction of the SiC substrate 12 by the modified region 7m. Obstruction. This effect can be achieved irrespective of the formation size and the number of rows of the modified regions 7a and 7m, and the object 1 is cut along the line to cut 5m with the modified region 7m as a starting point, and then The modified region 7a is a starting point that cuts the object 1 along the line to cut 5a. In this way, along the line to cut 5m (the imaginary is difficult to cut due to the formation of the modified region 7m of a small number of rows), the object 1 is cut, and then along the line to cut 5 a (due to the formation of more columns) In the modified region 7 a, it is easy to cut off the image. Therefore, the force required to cut the object 1 along the line to cut 5 m and the force required to cut the object 1 along the line to cut 5 a can be made uniform along the line The cutting accuracy of the cutting planned line 5m and the cutting accuracy along the cutting planned line 5a are further improved. This effect can be exerted regardless of the formation size of the modified region 7a' 7m and the number of columns to be formed. Fig. 14 is a photograph of the cut surface of the SiC substrate 12 cut along the line to cut 5a by the above-described laser processing method. Further, Fig. 15 is a photograph of the cut surface of the SiC substrate 12 cut along the line to cut 5m by the above-described laser processing method. Further, Fig. 16 is a plan view of the SiC substrate 12 cut along the line to cut 5a, 5m by the above-described laser processing -19-201243925 method. Here, it is prepared to have 4. A hexagonal SiC substrate 12 having an off-angle thickness of 350 μm. First, as shown in Fig. 14, three rows of modified regions 7a are formed for one planned cutting line 5a so as to be aligned along the thickness direction of the SiC substrate 12 along the line to cut 5a'. Further, the modified region 7a which is second closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is formed smaller than the modified region 7a closest to the surface 12a, in accordance with the order of the back surface 1 2b side of the SiC substrate 12. The modified area 7a. As is apparent from Fig. 4, by forming the modified region 7a which is second closest to the surface 12a, the stretching of the crack generated from the modified region 7a can be stopped. As a result, as shown in Fig. 16, the meandering of the cut surface of the cut line 5a can be suppressed to ±4 μm or less. Further, the distance from the surface 12a to the position of the condensing point , is in accordance with the order of the modified region 7a on the side of the back surface 12b of the SiC substrate 12 of 314·5 μm, 280. 0 μηι, 2 4 6. 0 μm, 2 1 2. 0 μm , 1 7 1 . 5 μm, 1 2 3. 5 μm, 79. 0μιη, 32. 0μιη. Further, the pulse energy of the laser light L is in the order of 25 μΐ, 25 μ J, 25 μ] '25 μΙ > 20 μΙ > 1 5 μΙ ' 6 μΙ > 6 μ·ί according to the order of the modified region 7a on the back surface 12b side of the SiC substrate 12. Further, as shown in FIG. 5, six rows of modified regions 7m are formed for one planned cutting line 5m so as to be aligned along the cutting line 5m in the thickness direction of the SiC substrate 12. The modified region 7m closest to the laser light incident surface (surface 12a) of the SiC substrate 12 is smaller than the modified region 7m which is second closest to the surface 12a, and the modified region is formed in the order of the back surface 1 2b of the SiC substrate 12. 7m. As is apparent from Fig. 5, the shape of the modification region 7m which is second to the surface 12a by the shape -20-201243925 allows the crack generated from the modified region 7m to extend to or near the surface 12a. As a result, as shown in Fig. 16, the meandering of the cut surface with respect to the cutting line of 5 m can be suppressed to ±2 μm or less. Further, the distance from the surface 12a to the position of the condensing point , is 315·5 μιη, 264 in accordance with the order of the modified region 7m on the back surface 12b side of the SiC substrate 12. 5μηι, 213. 5μπι, 1 5 5. 0 μιη ' 9 5. 5 μηι ' 34. 5μιη ° In addition, the pulse energy of the laser light L follows the order of the modified region 7m on the back surface 12b side of the SiC substrate 12 by 25 μ, 25 μ·ί, 20 μ: ί, 20 μ·Γ, 15 μ: ί, 7 μ J ° Next, the cracks (hereinafter referred to as "half-cut") of the laser light incident surface (surface 12a) of the SiC substrate 12 from the modified regions 7a and 7m and the extension from the modified regions 7a and 7m toward the c-plane are described. The relationship between cracks (hereinafter referred to as "c-plane cracks"). Here, as shown in FIGS. 17 and 18, the modified region 7a is described as an object; the modified region 7a is formed by causing the crack to extend in the thickness direction of the SiC substrate 12, as compared with the case of the modified region 7a. It is more difficult for the modified region 7m to be half-cut and the c-plane crack is more likely to occur. The 19th figure shows the relationship between the pulse width, the ID threshold, the HC threshold, and the processing margin. Here, the pulse width is changed in the range of Ins, 10 ns to 120 ns, and the ID is evaluated for each pulse width. Restricted HC, HC 値 値 and processing margin. In addition, Fig. 20 shows a table showing the relationship between pulse pitch, ID threshold H, H C threshold, and processing margin. Here, the pulse pitch is changed in the range of 6 μm to 2 2 μm, and the I d threshold, the HC threshold, and the processing margin are evaluated for each pulse pitch. -21 - 201243925 The ID 临 値 値 値 値 ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临 临Good, OK, not. In addition, the HC limit 値 means that the minimum 値' of the laser energy of the half-cut laser light can be evaluated as the order of the HC threshold (ie, the half cut is easy to occur). Furthermore, the processing margin is the difference between the ID threshold and the HC threshold, and the order of the processing margin is excellent, good, acceptable, and not acceptable. Moreover, the integration is weighted according to the priority of the ID threshold, the HC threshold, and the processing margin, and the evaluation is excellent, good, acceptable, and unsatisfactory. As shown in Fig. 19, it is preferably 20 ns. The pulse width of ~100 ns causes the laser light L to oscillate, and it is more preferable to pulse the laser light L with a pulse width of 50 ns to 60 ns. Thus, the occurrence of c-plane cracks can be suppressed and the occurrence of half-cutting can be promoted. In addition, in the case of the pulse width l〇ns, the ID limit, the processing margin, and the comprehensive evaluation are closer to the pulse width than 20 ns. Further, as shown in Fig. 20, it is preferable that the SiC substrate 12 is irradiated with the laser light L along the line to cut 5a, 5m in such a manner that the pulse pitch is ΙΟμηι 18 to 18 μm; more preferably, the pulse pitch is 1 Ιμηι. The SiC substrate 12 is irradiated with the laser light L along the line to cut 5a, 5m in a manner of 15 μm; particularly preferably, the SiC substrate 1 2 is irradiated along the line to cut 5a, 5 m with a pulse pitch of 12 μm to 14 μm. Laser light L. Thus, the occurrence of cracks on the C surface can be suppressed and the occurrence of half cut can be promoted. Also, since the pulse pitch is 1 Ομηι, the ID threshold is evaluated. If it is more important to suppress the occurrence of c-plane cracks, it is better -22-201243925 to make the pulse pitch larger than ΙΟμηι. Figure 21 to Figure 23 show that the laser light L has a number of apertures of 0. 8 Table of results of experimental results of pulse width and pulse pitch processing margin in the case of concentrating light. The results of these experiments are based on the evaluations shown in Figs. 19 and 20. The experimental conditions for obtaining the experimental results of Figs. 21 to 23 are as follows. First, a hexagonal SiC substrate 12 having a thickness of 100 μm with an off angle of 4° is applied, and a spot for the laser light L is arranged along a line to cut 5 a extending in a direction parallel to the surfaces 12 a and a. P moves. In addition, the laser light L is measured by a number of apertures of 0. 8 condensing is performed so that the condensed spot P is aligned to a position away from the laser light incident surface (surface 12a) of the SiC substrate 12 by a distance of 59 μm. Using the above experimental conditions as a premise, the energy (pulse energy) and power of the laser light L and the pulse pitch of the laser light L are changed, and the state of the modified region 7a and the half-cut and c-plane cracks are observed. In Fig. 21 to Fig. 23, the pulse widths of the laser light L are 2 7 ns, 40 ns, and 57 ns, respectively, and the pulse width (repetition frequency) of the laser light L is 10 kHz, 20 kHz, and 35 kHz, respectively. In the experimental results of Figs. 21 to 23, ST indicates that half cut did not occur, and HC indicates that half cut occurred. Further, ID indicates that a c-plane crack occurred, and LV1 to LV3 indicate the occurrence scale of the c-plane crack. In the case where the modified region 7a is formed along the two planned cutting lines 5a, for the 40 mm 'region (20 mm x 2 regions), when the c-plane crack occurrence region is less than 150 μm, it is represented by LV1, and the c-plane crack is formed. When the occurrence region is less than 450 μηη, it is represented by LV2, and when the occurrence region of the c-plane crack is 450 μm or more, -23-201243925 is represented by LV3. In LV1, the extension of the c-plane crack in the direction perpendicular to the line to cut 5a is ΙΟμηι~20μηη, whereas in LV2, LV3, the extension of the c-plane crack in the direction perpendicular to the line to cut 5a is the largest. Up to 1 ΟΟμιη or so. Figure 24 shows the relationship between pulse pitch and HC threshold. In addition, the 25th _ system shows the relationship between the pulse pitch and the ID threshold. Furthermore, Figure 26 shows the relationship between pulse pitch and machining margin. These figures are based on the experimental results of Figures 21 to 23. As shown in Fig. 24 and Fig. 25, if the pulse width becomes larger, both the HC threshold and the ID threshold will rise, and the ID threshold will increase compared to the deterioration (rise) of the HC threshold. Rise) is more effective. This means that as shown in Fig. 26, as the pulse width becomes larger, the processing margin becomes larger. For example, when the pulse width is 27 ns and the pulse width is 57 ns, when the pulse pitch is 12 μηι, the HC threshold is from 15 μ1 to 17 μm and deteriorates (rises) by 2 μ; in contrast, the ID threshold is from Further, when the pulse width is 40 ns, the processing margin is greatly increased in the range of the pulse pitch of 10 μm to 16 μm compared to the case where the pulse width is 40 ns. Further, in the case where the pulse width is 57 ns, the processing margin is greatly increased in the range of the pulse pitch of 6 μm to 20 μm compared to the case where the pulse width is 27 ns. Fig. 27 to Fig. 29 show that the laser light L has a number of apertures of 0. 6 Table of results of experimental results of pulse width and pulse pitch processing margin in the case of concentrating light. These experimental results are the basis for the evaluations shown in Figs. 19 and 20. The experimental conditions for obtaining the experimental results of Figs. 27 to 29 are as follows. First, a hexagonal SiC substrate 12 having a thickness of -24 - 201243925 degrees 3 5 0 μηη having a surface 12a (deviated from the c-plane) is used as the first embodiment. The object moves the light-converging point P of the laser light L along the line to cut 5a extending in a direction parallel to the surfaces 12a and a. In addition, the laser light L is measured by a number of apertures of 0. 6 condensing is performed so that the condensed spot P is aligned at a position away from the laser light incident surface (surface 12a) of the SiC substrate 12 by a distance of 50 μm. Using the above experimental conditions as a premise, the energy (pulse energy) and power of the laser light L and the pulse pitch of the laser light L are changed, and the state of the modified region 7a and the half-cut and c-plane cracks are observed. In Fig. 27 to Fig. 29, the pulse widths of the laser light L are 27 ns, 40 ns, and 57 ns, respectively, and the pulse width (repetition frequency) of the laser light L is 10 kHz, 20 kHz, and 3 5 kHz °, respectively, in Fig. 27 to Fig. 29 In the experimental results, ST indicates that half cut did not occur, and HC indicates that half cut occurred. Further, ID indicates that a c-plane crack occurs, and LV1 to LV3 indicate the occurrence scale of the c-plane crack. The criteria of LV1 to LV3 are the same as those of the experimental results of Figs. 21 to 23 described above. Further, OD indicates that when the energy of the laser light L becomes large, the modified region 7a also becomes large, and the crack which is caused by the collision is largely deviated from the line to cut 5a to reach the surface 12a of the SiC substrate 12. In this case, the c-plane crack is not evaluated. However, in the case of a pulse width of 40 ns and a pulse width of 57 ns, a large-scale c-plane crack does not occur above the pulse pitch of 12 μm. The third graph shows the relationship between the pulse pitch and the HC threshold 》. The results of the experiment in Figure 27 ~ Figure 29 were made. As shown in Fig. 30, in the case where the pulse width is 57 ns, the HC threshold is degraded by about 2 μ to 4 μ when compared with the case where the pulse width is 40 ns. Compared to the above number 値 aperture 0. The situation of 8 -25- 201243925, in the number of apertures 0. In the case of 6, the condensed point P of the laser light L is less affected by the aberration, and the HC threshold is the same degree in the case of a pulse width of 57 ns and a pulse width of 40 ns. In this way, if the aberration correction is performed, the HC threshold will not deteriorate even if the pulse width becomes large (at least to 60 ns). Next, the experimental conditions when the experimental results of the 31st to 33rd drawings are obtained on the laser light incident surface of the SiC substrate 12 (the experimental result of the processing margin of the HC quality in the vicinity of the surface 12A) are as follows. First, The hexagonal SiC substrate 12 having a thickness of 100 μm with an off angle of 4° is used as a target, and the spot light 5 of the laser light L is arranged along a line to cut 5 a extending in a direction parallel to the surfaces 12 a and a. Move. In addition, the laser light L is measured by a number of apertures of 0. 8 to collect light. First, in the experimental result of Fig. 31, the laser light L is irradiated with a pulse width of 27 ns, 40 ns, 50 ns, and 5 7 ns, respectively, and half cut is performed at the spot position 25·3 μηι and at the condensed spot position 40. . The 6 μηι does not undergo half-cutting energy (pulse energy), and the position of the focused spot is changed within the range of 25·3 μηι to 40·6 μηι to observe the state of the half cut. The pulse pitch of the laser light L is Μμιη and remains constant. The position of the condensed spot is the distance from the surface 1 2a to the position of the condensed spot. As a result, the deterioration of the quality of the half cut caused by the pulse width hardly occurs, and the half cut of the high quality (the half cut is small with respect to the line to cut) can be formed at a pulse width of 27 ns to 57 ns. Further, regarding the processing margin, the larger the pulse width, the larger. When the pulse width is small, a part of the half cut is prone to splitting or splitting (OD). -26- 201243925 In addition, the experimental result in Fig. 32 is that the laser light L is irradiated with a pulse width of 27 ns ' 40 ns , 50 ns , and 5 7 ns , respectively , so that the pulse energy is changed within the range of 7 μ J to 1 2 μ]. Observe the state of the half cut. The pulse pitch of the laser light L is 14 μm and remains constant, and the spot position is 34. Keep it at 5μπι. As a result, the change in the HC threshold due to the pulse width hardly occurs. In addition, the same pulse energy can produce a half cut of the same degree of quality. Furthermore, in the experimental result of Fig. 33, the laser light L is irradiated with a pulse pitch of ΙΟμιη ' 12μιη, 14μιη, 16μιη, and 18μπι, respectively, and the pulse energy is changed in the range of 7μ·ί~12 μΐ to observe half. The state of the cut. The pulse width of the laser light L is 5 7 ns and remains constant, and the position of the condensed spot is 3 4. 5 μπι and keep it constant. As a result, the change in the HC threshold due to the pulse pitch hardly occurs. In addition, the position at the spotlight point is 3 4. In the case of 5 μιη, the same pulse energy can produce a half cut of the same quality. Next, other laser processing methods for suppressing c-plane cracks will be described. First, a plate-shaped object 1 having a hexagonal SiC substrate 12 (having a surface 12a having a deviation angle from the c-plane) is prepared, and the cutting predetermined lines 5a and 5m are set. Next, as shown in Fig. 34(a), the condensed spot P of the laser light L is aligned with the inside of the SiC substrate 12, and is prepared along two sides set on the cutting line 5 a ( 5 m ). The line 5p irradiates the object 1 with the laser light L. Thereby, the preliminary modified region 7p is formed inside the SiC substrate 1 2 along each of the preliminary lines 5p. The preliminary reforming region 7p is a molten processing region. The preparatory line 5p is located on both sides of the cutting planned line 5a (5 m) in a plane parallel to the surface 12a and extends in a direction parallel to the planned cutting line 5a (5 m) -27-201243925. Further, when the functional elements are formed on the surface 12a of the SiC substrate 12 by cutting the respective regions drawn by the predetermined lines 5a, 5m, it is preferable to set the preliminary line 5p when viewed from the thickness direction of the SiC substrate 12. Within the area between adjacent functional components. When the laser light L is irradiated onto the object 1 along each of the preparatory lines 5p, it is less likely to be cracked on the SiC substrate 12 from the preliminary modified region 7p than the modified region 7a (7m) which is the starting point of the cutting. By preparing the modified region 7p, it is possible to reduce the pulse energy, the pulse pitch, the pulse width, and the like of the laser light L, and it is less likely to cause a turtle on the SiC substrate 12 than the modified region 7a (7m) which is the starting point of the cutting. crack. After the preliminary modified region 7p is formed along the preliminary line 5p, the light-converging point P of the laser light L is aligned with the inside of the SiC substrate 12, and the laser beam L is irradiated onto the object 1 along the line to cut 5a (5m). Thereby, the modified region 7a (7m) as the cutting start point is formed inside the SiC substrate 12 along the cutting predetermined line 5a (5m). The modified region 7a (7m) is a region containing a molten treatment. After the modified region 7a (7m) is formed along the line to cut 5a (5m), the object 1 is processed along the line to cut 5 a (5 m ) with the modified region 7 a ( 7 m ) as a starting point. According to the above-described laser processing method, the object 1 having a plate-like shape including the hexagonal SiC substrate 12 (having a surface 12a having an off-angle from the c-plane) can be cut along the following reason. The predetermined lines 5a and 5m are cut with high precision, and as a result, the object 1 (i.e., the power element) which is cut with high precision along the line to cut 5 a, 5 m can be obtained. That is, when the modified region 7a (7m) is formed in the -28-201243925 portion of the SiC substrate 12 along the line to cut 5a (5 m), a preliminary modification has been formed inside the SiC substrate 12 along each of the preliminary lines 5p. Quality area 7p. Further, the preliminary line 5p is located on both sides of the line to cut 5a (5m) in a plane parallel to the surface 12a and extends in a direction parallel to the line to cut 5a (5m). Therefore, even if the crack extends from the modified region 7a (7m) toward the c-plane direction, as shown in Fig. 34(a), the preliminary modified region 7p is not formed as shown in the third figure (b). In general, the extension of the crack (c-crack) is suppressed by the preparatory modified region 7p. In this way, it is possible to make the crack easily extend from the modified region 7a (7m) toward the thickness direction of the SiC substrate 12 without considering whether the crack is easily extended from the modified region 7a (7m) toward the c-plane direction. The emitted light is irradiated onto the object 1 to be processed. Further, since the modified region 7p is not required to function as a cutting start point (that is, it promotes crack propagation from the preliminary modified region 7p toward the thickness direction of the SiC substrate 12), it is not easy to occur on the SiC substrate 12. Since the crack is formed by irradiating the laser light L, it is easy to suppress the crack extension from the preliminary modified region 7p toward the c-plane direction when the preliminary modified region 7p is formed. In this way, it is possible to cut the object to be processed in a plate shape including the hexagonal SiC substrate 12 (having a main surface which is offset from the c-plane) along the line to cut 5a (5 m). When the modified region 7a (7 m) is formed, the condensed spot P of the laser light 1 is aligned with a predetermined distance from the laser light incident surface (surface i2a) of the SiC substrate 12, and when the preliminary modified region 7p is formed, Preferably, the spot P of the laser light L is aligned at the same distance from the surface 12a. Thus, the crack extension from the modified region 7 a ( 7 m ) toward the c-plane -29-201243925 can be more reliably suppressed. Further, when the preliminary modified region 7p is formed inside the SiC substrate 12 along each of the standby lines 5p, the cut line 5a (5 m) set between the preliminary lines 5p is also formed inside the SiC substrate 12. In the case of the mass region 7a (7 m), the pre-modified region 7p can still be used to suppress the stretching of the c-plane crack. In this case, it is preferable to form the preparation modified region 7p along the preliminary line 5p first in comparison with the formation of the modified region 7a (7m) along the line to cut 5a (5m). According to the present invention, it is possible to cut the object to be processed in a plate shape having a hexagonal SiC substrate (having a main surface which is offset from the c-plane) with high precision along the line to cut. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a structural view of a laser processing apparatus used to form a modified region. Fig. 2 is a plan view of the object to be processed before laser processing. Fig. 3 is a cross-sectional view taken along line III-III of the object to be processed in Fig. 2 . Fig. 4 is a plan view of the object to be processed after laser processing. Fig. 5 is a cross-sectional view taken along the line V-V of the object to be processed in Fig. 4; Fig. 6 is a cross-sectional view taken along line VI-VI of the object of Fig. 4. Fig. 7 is a plan view showing an object to be processed of -30-201243925 as a laser processing method according to an embodiment of the present invention. Fig. 8 is a view showing the crystal structure of the object to be processed in Fig. 7. Fig. 9(a) and (b) are partial cross-sectional views of the object to be processed in Fig. 7. Fig. 10 is a partial cross-sectional view showing an object to be processed which is subjected to a laser processing method according to an embodiment of the present invention. 11(a) and 11(b) are fragmentary cross-sectional views showing the object to be processed which is subjected to the laser processing method according to the embodiment of the present invention. Fig. 12 (a) and (b) are partial cross-sectional views of the object to be processed which is subjected to the laser processing method according to the embodiment of the present invention. Fig. 13 (a) and (b) are partial cross-sectional views of the object to be processed which is subjected to the laser processing method according to the embodiment of the present invention. Fig. 14 is a photograph showing a cut surface of a SiC substrate cut by a laser processing method according to an embodiment of the present invention. Fig. 15 is a photograph showing a cut surface of a SiC substrate cut by a laser processing method according to an embodiment of the present invention. Fig. 16 is a plan view showing a SiC substrate cut by a laser processing method according to an embodiment of the present invention. Fig. 17 is a perspective view for explaining a c-plane crack occurring inside the SiC substrate. Fig. 18 is a photograph of the cut surface of the SiC substrate in which the c-plane crack occurs. 〇 Figure 19 shows the relationship between the pulse width, the ID threshold, the HC threshold, and the processing margin. -31 - 201243925 Figure 20 shows the relationship between pulse pitch, ID threshold, HC threshold, and machining margin. Figure 21 is a table showing the experimental results of the processing margins of pulse width and pulse pitch. Figure 22 is a table showing the experimental results of the processing margins of pulse width and pulse pitch. Figure 23 is a table showing the experimental results of the processing margins of pulse width and pulse pitch. Figure 24 shows the relationship between pulse pitch and HC threshold. Figure 25 shows the relationship between pulse pitch and ID threshold. Figure 26 shows the relationship between pulse pitch and machining margin. Figure 27 is a table showing the experimental results of the processing margins of pulse width and pulse pitch. Figure 28 is a table showing the experimental results of the processing margins of pulse width and pulse pitch. Figure 29 is a table showing the experimental results of the processing margins of pulse width and pulse pitch. Figure 30 shows the relationship between pulse pitch and HC threshold. Fig. 3 is a table showing experimental results of processing margins of HC quality near the incident surface of the laser light. Fig. 32 is a table showing experimental results of processing margins of HC quality in the vicinity of the incident surface of the laser light. Fig. 3 is a table showing the experimental results of the processing margin of HC quality near the incident surface of the laser light. -32- 201243925 Section 34(a)(b) is a plan view for explaining a laser processing method according to another embodiment of the present invention. [Description of main component symbols] 1 : Object to be processed 5a, 5m : Line to be cut 5 p : Preliminary line 7 a, 7 m : Modified region 7p : Pre-modified region 1 2 : SiC substrate 12a : Surface (main surface ) 12b : Back side (main side) L : Laser light P : Spot light point -33-