200904555 九、發明說明 【發明所屬之技術領域】 本發明係關於一種超音波洗淨方法，尤其是關於一種 液晶顯示裝置用之玻璃基板或光罩用之玻璃基板、光碟用 之基板、半導體晶圓等基板的洗淨之超音波洗淨方法。 【先前技術】 在液晶顯示裝置或半導體之製造步驟中，有被要求以 較高的洗淨度來洗淨玻璃基板或半導體晶圓等基板的步驟 。在此種的步驟中，以往有採用一種反覆進行使用藥品的 洗淨作業與使用超純水的濕潤作業之方法。 但是，一旦以此種方法來洗淨玻璃基板或半導體晶圓 等基板，就有需要大量的藥品與超純水之問題。 因此，近年來廣泛採用一種利用超音波來洗淨的方法 ，亦有提案各種提高其洗淨效果的方法。例如，專利文獻 1中，有提案一種使具機能性之氣體溶解於洗淨液中，並 對使此具機能性之氣體溶解的洗淨液照射超音波’進而供 給至基板的方法。依據此方法，則藉由洗淨液中之溶解氣 體與孔洞（cavity)之生成壓壞效應，即可使反應性高的自 由基產生，並可有效地分解去除基板上的污染物。 (專利文獻）日本特許3 5 2 1 3 93號公報 【發明內容】 (發明所欲解決之問題） -5- 200904555 然而，如專利文獻1所記載的技術，一旦對使氣體溶 解之洗淨液連續照射超音波，隨著時間經過就會在洗淨液 中產生大量的氣泡，又，幾個氣泡會因彼此結合而亦包含 有粗大的氣泡，會有因此產生的大量氣泡之影響而減低洗 淨效果的問題。亦即，一旦在洗淨液中產生大量的氣泡， 超音波就會因此氣泡而散射，其穿透性能會減低，結果， 自由基的生成效率降低，洗淨效果減低。尤其是近年來由 於考慮到對基板的損傷而採用MHz級的超音波，所以在 以往的低頻（0.1 MHz左右）下即使是不會造成問題的氣泡 直徑也會有洗淨效果減低的問題。 本發明係有鑒於此種情事而開發完成者，其目的在於 提高一種可高效率地洗淨被洗淨物的超音波洗淨方法。 (解決問題之手段） 本發明之第一形態，爲了達成前述目的，提供一種超 音波洗淨方法，係以照射過超音波的洗淨液來洗淨被洗淨 物的超音波洗淨方法，其特徵在於：以預定週期（超音波 照射時間+超音波照射停止時間）反覆執行：連續性地照射 超音波至少0.2msec以上的步驟；以及停止超音波照射至 少0.1 m s e c以上的步驟。 依據第一形態，則是反覆進行超音波之照射與停止， 並在連續進行超音波之照射至少0.2msec以上之後’停止 照射至少0 · 1 m s e c以上。如此，藉由設置至少0.1 m s e c以 上之照射停止期間並週期性地照射超音波，即可防止阻礙 -6- 200904555 高效率地洗淨被洗淨 氣泡本身會阻礙超音 因彼此結合而更加粗 但是，藉由設置至少 使該照射停止期間中 解。藉此，防止阻礙 又，藉由設置至少 洞充分成長，獲得較 則可防止阻礙超音波 將超音波能量輸入至 淨的自由基。藉此， 以預定的間隔照射超 況，還可降低所投入 的情況，還可抑制洗 液之氣體溶解度。因 可促進氣體在洗淨液 述目的，係於第一形 〕.3msec以上、未滿 與停止的反覆執行週 500msec。由於連續 超音波穿透的大量氣泡之產生’且可 物。亦即，一旦產生大量氣泡，雖然 波之穿透’但是大量產生的氣泡一旦 大化，就會更加阻礙超音波之穿透。 0.1msec以上之照射停止期間，即可 所產生的細微氣泡在洗淨液中再次溶 超音波穿透的粗大氣泡之形成。 0.2msec以上之照射期間，即可使孔 大的自由基生成效果。 如此，依據本發明之第一形態， 穿透的粗大氣泡之產生，可高效率地 洗淨液中，可高效率地產生有助於洗 可高效率地洗淨被洗淨物。又，由於 音波，所以比起連續照射超音波的情 的能量。更且，比起連續照射超音波 淨液的溫度上升，可保持較高的洗淨 此’比起連續照射超音波的情況，還 中的再次溶解。 本發明之第二形態，爲了達成前 態中，將前述反覆執行的週期設爲< 5 0 0 m s e c ° 依據第二形態，則超音波之照射 期’係被設定爲0.3msec以上、未滿 進行超音波之照射至少0.2msec以上，停止照射至少 200904555 0.1msec以上，所以反覆執行之週期至少需要0.3msec以 上。另一方面，當改變週期觀察關於洗淨性能之作爲重要 參數的自由基之產生狀況時，一旦將週期增加至5 00msec 左右，則自由基產生量會明顯降下來（參照第8圖）。一旦 週期變長，其中連續地照射超音波的時間就會變長，此係 因大量氣泡產生、與其等氣泡之結合所造成的粗大化之影 響，會使超音波之穿透受到阻礙，反而會降低自由基的產 生所致。又，當使週期變化而調查晶圓上之粒子洗淨效果 時，可確認一旦到達週期5〇〇msec左右’效果就會開始往 下掉（參照第9圖）。因而，藉由在此範圍內按照粒子、有 機污染等的污染對象來設定週期，即可設定最適當的洗淨 條件。 本發明之第三形態’爲了達成前述目的，係於第一或 第二形態中，使照射於前述洗淨液的超音波聚焦。 依據第三形態，則藉由使超音波聚焦，就可在聚焦焦 點近旁高效率地使產生有助於洗淨的自由基。另一方面， 一旦如此使超音波聚焦，由於孔洞會在聚焦焦點近旁集中 生成，所以容易形成粗大氣泡。但是，藉由最適當地進行 超音波之照射停止，即可防止粗大氣泡的產生，且可高效 率地使產生有助於洗淨的自由基。 (發明效果） 依據本發明的超音波洗淨方法，可高效率地洗淨被洗 淨物。 -8- 200904555 【實施方式】 以下’按照所附圖式就本發明的超音波洗淨方法之較 佳實施形態加以詳細說明。 第1圖係顯示用以實施本發明超音波洗淨方法的超音 波洗淨裝置之一例的模型圖。 該超音波洗淨裝置1 0，係例如構成作爲液晶顯示裝置 用之大型玻璃基板的洗淨裝置，用以對水平搬運的玻璃基 板G之表面供給照射過超音波的洗淨液來洗淨玻璃基板G 〇 玻璃基板G之搬運，例如係藉由輸送帶來進行，從 被設置於該輸送帶之上方的洗淨用頭1 2簾幕狀地供給照射 過超音波的洗淨液。 第2圖、第3圖係分別顯示洗淨用頭12之槪略構成的正 面剖面圖與側面剖面圖。 如同圖所示，洗淨用頭12，係形成前端被加工成推拔 狀的橫長之箱型形狀’於其前端（下端）形成有呈開縫狀的 洗淨液吐出口 1 4。 在洗淨用頭12之內周部頂面，安裝有呈板狀的超音波 振盪器16，於該超音波振盪器16之下面’安裝有聲波透鏡 18。從超音波振盪器16振盪出的超音波’係藉由該聲波透 鏡1 8聚焦成預定的聚焦焦點，並向洗淨液照射。如此’藉 由使超音波聚焦’就可在聚焦焦點近旁高效率地使產生有 助於洗淨的自由基。因而’該聚焦焦點’較佳爲設定於玻 -9- 200904555 璃基板G之表面近旁。 在洗淨用頭1 2之側面，形成有供給口 1 2 A，從該供給 口 1 2 A供給洗淨液至洗淨用頭內。洗淨液，例如係使用超 純水，從未圖示的供給源經由脫氣膜模組2 0、氣體溶解膜 模組22供給至供給口 12A。 脫氣膜模組20 ’係將溶入於洗淨液中的多餘氣體進行 脫氣，利用氣體溶解膜模組22使具機能性之氣體溶解於由 該脫氣膜模組20所脫氣過的洗淨液中並供給至供給口丨2 a 。如此，將溶入於洗淨液中的多餘氣體進行脫氣之後，供 給具機能性之氣體，藉由使溶解於水中，即可使增加有助 於洗淨的氣體之溶解量，且可更提高洗淨效率。 另外，有關使溶解的氣體，並未被特別限定。 又，亦可形成使空氣飽和於洗淨液中的構成，來取代 使具機能性之氣體溶解於如此脫氣過的洗淨液中的構成。 從供給口 1 2 A供給至洗淨用頭內的洗淨液，係從超音 波振盪器1 6照射超音波’並從洗淨液吐出口 1 4簾幕狀地吐 出。 玻璃基板G ’係以正交洗淨液吐出口 1 4的方式搬運， 當通過該洗淨液吐出口 1 4之下部時’從洗淨液吐出口 1 4吐 出的洗淨液就會供給至表面’表面可獲得洗淨。 如以上所構成的超音波洗淨裝置1 0之作用係如下所述 〇 洗淨對象之玻璃基板<3 ’係藉由未圖示的輸送帶來水 平地搬運於預定的搬運路徑。然後’當通過洗淨用頭12之 -10- 200904555 下部時’從洗淨液吐出口 1 4簾幕狀地吐出的洗淨液就會供 給至表面，表面可獲得洗淨。 該洗淨液’係從未圖示的供給源供給，從該供給源供 給的洗淨液’在利用脫氣膜模組2 0進行脫氣之後，具機能 性之氣體就可利用氣體溶解膜模組2 2來溶解並供給至洗淨 用頭I2。供給至洗淨用頭12的洗淨液，係在從超音波振盪 器1 6照射超音波之後，從洗淨液吐出口 1 4吐出，且供給至 玻璃基板G。 再者’如上所述’玻璃基板G，雖然係被供給照射過 超音波的洗淨液而獲得洗淨，但是一旦連續照射對該洗淨 液照射的超音波，則隨著時間的經過會在洗淨液中產生粗 大的氣泡，而此產生的粗大氣泡之影響會減低洗淨效果。 亦即，一旦連續地對存在有溶解氣體的洗淨液照射超 音波，就會在洗淨液中產生細微的氣泡（參照第4圖（a))。 所產生的細微氣泡群，會隨著時間的經過而增加（參照第4 圖（b))，而氣泡彼此間會相互地結合而形成粗大的氣泡（參 照第4圖（〇)。由於氣體與液體之密度及傳遞於介質中的音 速也大爲不同，所以在此境界面的穿透性能會顯著降低。 因此照射過的超音波，會藉由此種的粗大氣泡而散射。因 此從超音波振盪器16所振盪出的超音波，會隨著遠離超音 波振盪之面而受到洗淨液中所產生的粗大氣泡之影響而衰 減。結果，無法產生有助於洗淨的自由基，而減低了洗淨 效果。 因此，本實施形態的超音波洗淨裝置1 〇，係週期性地 -11 - 200904555 停止超音波之照射，來防止粗大氣泡的產生。亦即，如第 5圖所示，一邊以預定週期反覆進行照射與停止一邊照射 超音波。此時，照射期間A係設定爲至少0 · 2 m s e c以上， 照射停止期間係設定爲至少〇 . 1 msec以上。 如此，藉由設置至少0.1msec以上的照射停止期間， 即可使超音波照射中所產生的細微氣泡在照射停止中再次 溶解於洗淨液中，可有效防止粗大氣泡的產生。亦即，如 上所述，粗大氣泡，雖然係隨著時間的經過而增加超音波 之照射中所產生的細微氣泡群，並藉由相互地結合而形成 (參照第4圖（a)至第4圖（c))，但是藉由設置至少0.1msec以 上的照射停止期間，即可使超音波照射中所產生的細微氣 泡在照射停止中再次溶解於洗淨液中，而可防止粗大氣泡 之產生於未然（參照第6圖（a)至第6圖（〇)。 藉此，就可高效率地使從超音波振盪器1 6所振盪出的 超音波穿透，可高效率地生成有助於洗淨的自由基。亦即 ，藉由超音波不會受到粗大氣泡阻礙而穿透，即可在洗淨 液中高效率地反覆進行孔洞之生成、壓壞。從該壓壞後的 孔洞中，生成氫基（H·)或氫氧基（OH·)，此等的自由基 ’係在乘載於超音波之聲波流而混合後供給至基板表面上 。供給至基板表面上的自由基’係將超苜波振動的效果合 爲一起而與存在於基板表面上的污染物起反應並分解去除 〇 如此’藉由設置至少0.1msec以上的照射停止期間， 即可有效地防止阻礙超音波穿透的粗大氣泡之產生，可高 -12- 200904555 效率地生成有助於洗淨的自由基，可高效率地洗淨玻璃基 板G。 第7圖係將週期設爲lmsec，且進行改變DUTY比而檢 測自由基之產生量的實驗時之實驗結果的圖表。 如同圖所示，一旦連續地照射超音波（DUTY比=1時） ，雖然有助於洗淨的自由基幾乎不會產生，但是藉由週期 性地停止照射（停止至少〇 · 1 m s e c以上），可確認能生成有 助於洗淨的自由基。本例的情況，可確認在DUTY比 0.5〜0.7之範圍（停止期間0.3~0.5msec)內自由基的產生量 變成最大。 另外，照射期間，藉由設爲至少0.2msec以上，就可 使孔洞成長最大限。 因而，照射與停止的週期（=照射期間+照射停止期間） ，係需要至少〇 . 3 m s e c以上。 另一方面，當改變週期觀察關於洗淨性能之作爲重要 參數的自由基之產生狀況時，一旦將週期增加至5 00msec 左右，則自由基產生量會明顯降下來（參照第8圖）。一旦 週期變長，其中連續地照射超音波的時間就會變長，此係 因大量氣泡產生、與其等氣泡之結合所造成的粗大化之影 響，會使超音波之穿透受到阻礙，反而會降低自由基的產 生所致。 又，當使週期變化而調查晶圓上之粒子洗淨效果時， 可確認一旦到達週期5 00msec左右，效果就會開始往下掉 (參照第9圖）。因而，藉由在此範圍內按照粒子、有機污 -13- 200904555 染等的污染對象來設定週期，即可設定最適當的洗淨條件 〇 如以上說明般，依據本實施形態的超音波洗淨方法’ 則在對存在有溶解氣體的洗淨液照射超音波時，藉由週期 性地停止超音波之照射，即可防止阻礙超音波穿透的粗大 氣泡之產生，可高效率地生成有助於洗淨的自由基。藉此 ，可高效率地洗淨玻璃基板G。 另外，近年來，因考慮對基板的損傷，而使用MHz 級之超音波的百萬頻率超音波（Mega-Sonic)洗淨成爲主 流，由於所照射的超音波之波長變短，故而即便在以往的 低頻（0.1 MHz左右）中不造成問題的氣泡直徑也會有阻礙 穿透的問題，但是如本實施形態的超音波洗淨方法’藉由 適當地設置停止期間，並週期性地照射超音波，則即使在 使用MHz級之超音波的情況，亦可防止阻礙超音波穿透 的粗大氣泡之產生，可高效率地洗淨被洗淨物。 又，如此地藉由週期性地停止超音波之照射，比起連 續照射超音波的情況還更能降低所投入的能量。 又，可抑制洗淨液的溫度上升，可保持較高的洗淨液 之氣體溶解度。藉此，比起連續性地照射超音波的情況還 更能促進氣體再次溶解於洗淨液中。 另外，對半導體之細微圖案的損傷較少的超音波之頻 率範圍，係爲1MHz〜3 MHz左右，較適於自由基之產生的 超音波之頻率範圍’係爲0·3ΜΗζ〜1MHz。 另外，本實施形態中，雖係形成藉由聲波透鏡1 8使照 -14 - 200904555 射於洗淨液中的超音波聚焦的構成，但是亦可不聚焦地照 射。藉由使超音波聚焦，可在聚焦焦點近旁高效率地使有 助於洗淨的自由基產生，可更提高洗淨效果。 另一方面，一旦如此地使超音波聚焦，由於孔洞會在 聚焦焦點近旁集中生成，所以容易形成粗大氣泡，但是如 本實施形態之洗淨方法，藉由最適當地進行超音波之照射 停止，即可防止粗大氣泡的產生，可高效率地使有助於洗 淨的自由基產生。 另外，本實施形態中，雖係使用聲波透鏡使從超音波 振盪器所振盪出的超音波聚焦於預定的聚焦焦點，但是使 超音波聚焦的構成，並非被限定於此。例如，藉由將使超 音波振盪器之超音波振盪的面之形狀形成圓弧狀（將超音 波振盪器之形狀形成所謂的桶形），亦可使超音波聚焦於 預定的聚焦焦點。該情況，不需要聲波透鏡。 又，在使超音波聚焦的情況，亦可使超音波聚焦成線 狀，或聚焦成一點。 又，本實施形態中，雖然係形成對水平地搬運的玻璃 基板G從上方簾幕狀地供給照射過超音波的洗淨液而洗 淨玻璃基板G的構成，但是亦可形成對玻璃基板G從下 方簾幕狀地供給照射過超音波的洗淨液而洗淨玻璃基板G 的構成。 又，亦可藉由垂直下降的洗淨頭來掃描保持垂直姿勢 的玻璃基板之表面，形成對玻璃基板之表面供給照射過超 音波的洗淨液，而洗淨玻璃基板之表面的構成。 -15- 200904555 又，本發明如第1 〇圖所示，即使在使被洗淨物30浸漬 於洗淨槽內而洗淨的狀態時亦可同樣地適用。亦即，即使 在使被洗淨物30浸漬於洗淨槽32內所貯留的洗淨液34之中 ，且從設置於洗淨槽32之下部的超音波振盪器36(亦可設 置於洗淨槽內）對洗淨液3 4提供超音波振動而洗淨的狀態 時亦可同樣地適用。該情況，可一次洗淨大量的玻璃基板 〇 另外，如本實施形態，在將從洗淨頭吐出的洗淨液供 給至玻璃基板G之表面而洗淨的構成之情況，較適於以 較高的清淨度洗淨多品種或者少量的洗淨對象時。 又，本實施形態中，雖係舉洗淨液晶顯示裝置用之大 型玻璃基板的情況爲例加以說明，但是本發明之應用，並 非被限定於此，當然可應用在洗淨光罩用之玻璃基板或光 碟用之基板、半導體晶圓等之基板的情況，即使在洗淨其 他的被洗淨物之情況亦可同樣地適用。 【圖式簡單說明】 第1圖係顯不超音波洗淨裝置之一例的模型圖。 第2圖係顯示洗淨用頭之槪略構成的正面剖面圖。 第3圖係顯示洗淨用頭之槪略構成的側面剖面圖。 第4圖（a)係超音波連續照射時的粗大氣泡生成過程（孔 洞產生期）之說明圖。 第4圖（b)係超音波連續照射時的粗大氣泡生成過程（ 孔洞生成效果最大期）之說明圖。 -16- 200904555 第4圖（c)係超音波連續照射時的粗大氣泡生成過程（超 音波穿透阻礙期）之說明圖。 第5圖係超音波照射方法的說明圖。 第6圖（a)係超音波洗淨方法的作用（孔洞產生期）之說 明圖。 第6圖（b)係超苜波洗淨方法的作用（孔洞生成效果最 大期）之說明圖。 第6圖（c)係超音波洗淨方法的作用（孔洞溶解期）之說 明圖。 第7圖係顯示DUTY比與自由基產生量之關係的圖表 〇 第8圖顯示週期與自由基產生量之關係的圖表（輸入 1 00 W ' DUTY0.5)。 第9圖係顯示週期與洗淨效果之關係的圖表。 第10圖係顯示超音波洗淨裝置之另一例的模型圖。 【主要元件符號說明】 1 〇 :超音波洗淨裝置 1 2 ‘·洗淨用頭 1 4 :洗淨液吐出口 1 6 :超音波振盪器 1 8 :聲波透鏡 20 =脫氣膜模組 22 :氣體溶解膜模組 17- 200904555 3 0 :被洗淨物 3 2 :洗淨槽 3 4 :洗淨液 3 6 :超音波振盪器 G :玻璃基板BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic cleaning method, and more particularly to a glass substrate for a liquid crystal display device or a glass substrate for a photomask, a substrate for an optical disk, and a semiconductor wafer. Ultrasonic cleaning method for cleaning the substrate. [Prior Art] In the manufacturing steps of a liquid crystal display device or a semiconductor, there is a step of requiring a substrate such as a glass substrate or a semiconductor wafer to be cleaned with a high degree of cleaning. In such a procedure, a method of repeatedly performing a washing operation using a drug and a wetting operation using ultrapure water has been conventionally employed. However, once the substrate such as a glass substrate or a semiconductor wafer is washed by such a method, there is a problem that a large amount of medicine and ultrapure water are required. Therefore, in recent years, a method of washing with ultrasonic waves has been widely used, and various methods for improving the washing effect have been proposed. For example, Patent Document 1 proposes a method in which a functional gas is dissolved in a cleaning liquid, and a cleaning liquid which dissolves the functional gas is irradiated with ultrasonic waves and supplied to the substrate. According to this method, a highly reactive free radical can be generated by the formation of a crushing effect of dissolved gas and cavity in the cleaning liquid, and the contaminants on the substrate can be efficiently decomposed and removed. (Patent Document) Japanese Patent No. 3 5 2 1 3 93 [Inventive Contents] (Problems to be Solved by the Invention) -5-200904555 However, as in the technique described in Patent Document 1, once the cleaning liquid for dissolving the gas is used Continuously irradiating ultrasonic waves, a large amount of bubbles are generated in the washing liquid over time, and several bubbles are also combined with each other to contain coarse bubbles, which may reduce the influence of a large number of bubbles generated thereby. The problem of net effect. That is, once a large amount of bubbles are generated in the cleaning liquid, the ultrasonic waves are scattered by the bubbles, and the penetration performance is lowered. As a result, the generation efficiency of the radicals is lowered, and the washing effect is reduced. In particular, in recent years, ultrasonic waves of the order of magnitude have been used in consideration of damage to the substrate. Therefore, even in the conventional low frequency (about 0.1 MHz), even if the bubble diameter does not cause a problem, the cleaning effect is reduced. The present invention has been developed in view of such circumstances, and an object thereof is to improve an ultrasonic cleaning method capable of efficiently cleaning a laundry. (Means for Solving the Problem) In the first aspect of the present invention, in order to achieve the above object, an ultrasonic cleaning method for cleaning an object to be washed by a cleaning liquid that has been irradiated with ultrasonic waves is provided. It is characterized in that the predetermined period (ultrasonic irradiation time + ultrasonic irradiation stop time) is repeatedly performed: a step of continuously irradiating the ultrasonic wave for at least 0.2 msec or more; and a step of stopping the ultrasonic irradiation for at least 0.1 msec or more. According to the first aspect, the ultrasonic irradiation and the stop are repeated, and after the ultrasonic irradiation is continuously performed for at least 0.2 msec or more, the irradiation is stopped at least 0 · 1 m s e c or more. In this way, by providing an irradiation stop period of at least 0.1 msec or more and periodically irradiating the ultrasonic waves, it is possible to prevent the -6-200904555 from efficiently washing the washed bubbles themselves, which prevents the supersonics from being thicker due to the combination of each other. By setting at least the solution during the stop of the illumination. In this way, by preventing at least the hole from being formed, it is possible to prevent the supersonic wave from being input into the net free radical by preventing the ultrasonic wave from being sufficiently grown. Thereby, the irradiation is irradiated at predetermined intervals, the input can be reduced, and the gas solubility of the washing liquid can be suppressed. The purpose of promoting the gas in the cleaning liquid is to be 500 msec in the first form of .3 msec or more, and the over-execution week of the stop and stop. The generation of a large number of bubbles penetrating by continuous ultrasonic waves is ok. That is, once a large number of bubbles are generated, although the wave penetrates, the large number of generated bubbles become larger, which hinders the penetration of the ultrasonic waves. During the irradiation stop period of 0.1 msec or more, the generated fine bubbles are again dissolved in the cleaning liquid to form the formation of coarse bubbles penetrated by the ultrasonic waves. During the irradiation period of 0.2 msec or more, the radical generating effect of the pores can be made large. As described above, according to the first aspect of the present invention, the generation of the coarse bubbles that are penetrated can be efficiently washed in the liquid, and the washed matter can be efficiently washed to facilitate the washing. Moreover, due to the sound wave, it is compared with the energy of the continuous illumination of the ultrasonic wave. Further, compared with the temperature rise of the continuous irradiation of the ultrasonic cleaning liquid, it is possible to maintain a high degree of cleaning. This is re-dissolved in the case of continuously irradiating the ultrasonic wave. In the second aspect of the present invention, in order to achieve the state of the front state, the period of the repeated execution is set to < 5 0 0 msec °. According to the second aspect, the irradiation period of the ultrasonic wave is set to be 0.3 msec or more and less than Ultrasonic irradiation is performed for at least 0.2 msec or more, and irradiation is stopped for at least 200,904,555 for 0.1 msec or more. Therefore, the cycle of repeating execution is required to be at least 0.3 msec or more. On the other hand, when the period of the radical generation as an important parameter regarding the cleaning performance is observed by changing the period, once the period is increased to about 500 msec, the amount of radical generation is remarkably lowered (refer to Fig. 8). As the period becomes longer, the time for continuously irradiating the ultrasonic wave becomes longer. This is caused by the coarsening caused by the combination of a large number of bubbles and the combination of the bubbles, which may hinder the penetration of the ultrasonic wave. Reduce the production of free radicals. In addition, when the cycle cleaning is performed to investigate the effect of cleaning the particles on the wafer, it is confirmed that the effect is started when the cycle is about 5 〇〇 msec (see Fig. 9). Therefore, by setting the cycle in accordance with the contamination target such as particles or organic contamination within this range, the most appropriate cleaning conditions can be set. According to a third aspect of the present invention, in order to achieve the above object, in the first or second aspect, the ultrasonic waves irradiated to the cleaning liquid are focused. According to the third aspect, by focusing the ultrasonic waves, it is possible to efficiently generate radicals which contribute to washing in the vicinity of the focus of the focus. On the other hand, once the ultrasonic waves are focused as such, since the holes are concentratedly generated near the focus of the focus, it is easy to form coarse bubbles. However, by appropriately stopping the irradiation of the ultrasonic waves, generation of coarse bubbles can be prevented, and radicals contributing to washing can be efficiently produced. (Effect of the Invention) According to the ultrasonic cleaning method of the present invention, the object to be washed can be efficiently washed. -8-200904555 [Embodiment] Hereinafter, a preferred embodiment of the ultrasonic cleaning method of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 is a model diagram showing an example of an ultrasonic cleaning apparatus for carrying out the ultrasonic cleaning method of the present invention. The ultrasonic cleaning device 10 is, for example, a cleaning device that is a large-sized glass substrate for a liquid crystal display device, and is configured to supply a cleaning liquid that has been irradiated with ultrasonic waves to the surface of the glass substrate G that is conveyed horizontally to clean the glass. The conveyance of the substrate G and the glass substrate G is carried out, for example, by a conveyance belt, and the cleaning liquid irradiated with the ultrasonic waves is supplied from the cleaning head 12 provided above the conveyor belt in a curtain shape. Fig. 2 and Fig. 3 are a front sectional view and a side sectional view, respectively, showing a schematic configuration of the cleaning head 12. As shown in the figure, the cleaning head 12 has a horizontally long box shape in which the tip end is processed into a push-out shape, and a washing liquid discharge port 14 having a slit shape is formed at the tip end (lower end). On the top surface of the inner peripheral portion of the cleaning head 12, a plate-shaped ultrasonic oscillator 16 is attached, and an acoustic lens 18 is attached to the lower surface of the ultrasonic oscillator 16. The ultrasonic wave oscillated from the ultrasonic oscillator 16 is focused by the sonic lens 18 into a predetermined focus focus, and is irradiated to the cleaning liquid. Thus, by focusing the ultrasound, it is possible to efficiently generate free radicals that contribute to washing near the focus of focus. Therefore, the 'focus focus' is preferably set near the surface of the glass substrate G of the glass -9-200904555. On the side of the cleaning head 12, a supply port 1 2 A is formed, and the cleaning liquid is supplied from the supply port 1 2 A to the cleaning head. The cleaning liquid is supplied to the supply port 12A via a degassing membrane module 20 and a gas dissolving membrane module 22, for example, using ultrapure water. The degassing membrane module 20' degases the excess gas dissolved in the cleaning liquid, and dissolves the functional gas in the degassing membrane module 20 by the gas dissolving membrane module 22. The cleaning solution is supplied to the supply port 2 a. In this way, after the excess gas dissolved in the cleaning liquid is degassed, the functional gas is supplied, and by dissolving in the water, the amount of the gas contributing to the cleaning can be increased, and the gas can be increased. Improve washing efficiency. Further, the gas to be dissolved is not particularly limited. Further, a configuration in which air is saturated in the cleaning liquid may be formed instead of dissolving the functional gas in the degassed cleaning liquid. The cleaning liquid supplied from the supply port 1 2 A to the cleaning head is irradiated with ultrasonic waves from the ultrasonic oscillator 16 and discharged from the cleaning liquid discharge port 14 in a curtain shape. The glass substrate G' is transported so as to cross the cleaning liquid discharge port 14 and is supplied to the lower portion of the cleaning liquid discharge port 14 when the cleaning liquid is discharged from the cleaning liquid discharge port 14 The surface 'surface can be washed. The operation of the ultrasonic cleaning device 10 configured as described above is as follows. The glass substrate <3' to be cleaned is transported horizontally to a predetermined conveyance path by a conveyance belt (not shown). Then, when the lower portion of the cleaning head 12 is -10-200904555, the washing liquid discharged from the washing liquid discharge port 14 is supplied to the surface, and the surface is washed. The cleaning liquid is supplied from a supply source (not shown), and the cleaning liquid supplied from the supply source is degassed by the deaeration membrane module 20, and then the gas can be dissolved by the functional gas. The module 22 is dissolved and supplied to the cleaning head I2. The cleaning liquid supplied to the cleaning head 12 is irradiated with ultrasonic waves from the ultrasonic oscillator 16 and then discharged from the cleaning liquid discharge port 14 and supplied to the glass substrate G. In addition, as described above, the glass substrate G is supplied with a cleaning liquid that has been irradiated with ultrasonic waves, and is cleaned. However, when the ultrasonic wave irradiated to the cleaning liquid is continuously irradiated, it will be over time. Large bubbles are generated in the washing liquid, and the effect of the coarse bubbles generated by this will reduce the washing effect. In other words, when the cleaning liquid in which the dissolved gas is present is continuously irradiated with ultrasonic waves, fine bubbles are generated in the cleaning liquid (see Fig. 4(a)). The generated fine bubble group increases with time (see Fig. 4(b)), and the bubbles combine with each other to form coarse bubbles (see Fig. 4 (〇). Due to gas and The density of the liquid and the speed of sound transmitted to the medium are also very different, so the penetration performance at this interface is significantly reduced. Therefore, the irradiated ultrasonic waves are scattered by such coarse bubbles. Therefore, from the ultrasonic wave The ultrasonic waves oscillated by the oscillator 16 are attenuated by the coarse bubbles generated in the cleaning liquid as they move away from the surface of the ultrasonic oscillation. As a result, free radicals contributing to washing cannot be produced, and the radicals are reduced. Therefore, the ultrasonic cleaning device 1 of the present embodiment periodically stops the irradiation of the ultrasonic waves by -11 - 200904555 to prevent the generation of coarse bubbles. That is, as shown in Fig. 5, The ultrasonic wave is irradiated while repeatedly irradiating and stopping at a predetermined cycle. At this time, the irradiation period A is set to be at least 0 · 2 msec or more, and the irradiation stop period is set to at least 〇 1 msec or more. By providing an irradiation stop period of at least 0.1 msec or more, the fine bubbles generated in the ultrasonic irradiation can be dissolved again in the cleaning liquid during the irradiation stop, and the generation of coarse bubbles can be effectively prevented. As described above, the coarse bubbles are formed by increasing the number of fine bubbles generated during the irradiation of the ultrasonic waves over time, and are formed by mutual bonding (refer to Figs. 4(a) to 4(c)). However, by providing an irradiation stop period of at least 0.1 msec or more, it is possible to prevent the fine bubbles generated in the ultrasonic irradiation from being dissolved again in the cleaning liquid during the irradiation stop, thereby preventing the occurrence of coarse bubbles (see the 6(a) to 6(〇). By this, the ultrasonic waves oscillated from the ultrasonic oscillator 16 can be efficiently penetrated, and the freedom for washing can be efficiently generated. In other words, the ultrasonic wave can be efficiently and repeatedly generated and crushed in the cleaning liquid by the ultrasonic wave being prevented from being blocked by the coarse air bubbles, and a hydrogen base is generated from the crushed hole ( H·) or hydroxyl (OH·) These radicals are supplied to the surface of the substrate after being mixed by the acoustic wave of the ultrasonic wave, and the radicals supplied to the surface of the substrate combine the effects of the super-chopper vibration with the substrate. The contaminants on the surface react and decompose and remove. Therefore, by setting the irradiation stop period of at least 0.1 msec or more, the generation of coarse bubbles that hinder the penetration of ultrasonic waves can be effectively prevented, and can be efficiently generated by high-12-200904555. The glass substrate G can be washed with high efficiency, and the glass substrate G can be cleaned with high efficiency. Fig. 7 is a graph showing experimental results of an experiment in which the cycle is changed to lmsec and the DUTY ratio is changed to detect the amount of radical generation. As shown in the figure, once the ultrasonic waves are continuously irradiated (when DUTY ratio = 1), the radicals contributing to the washing are hardly generated, but the irradiation is stopped periodically (stopping at least 〇 1 msec or more). It is confirmed that it can generate free radicals that contribute to washing. In the case of this example, it was confirmed that the amount of generation of radicals was maximized in the range of DUTY ratio of 0.5 to 0.7 (0.3 to 0.5 msec in the stop period). Further, by setting the irradiation period to at least 0.2 msec or more, the pore growth can be maximized. Therefore, the period of irradiation and stop (=irradiation period + irradiation stop period) is required to be at least 〇3 m s e c or more. On the other hand, when the period of the radical generation as an important parameter regarding the cleaning performance is observed by changing the period, once the period is increased to about 500 msec, the amount of radical generation is remarkably lowered (refer to Fig. 8). As the period becomes longer, the time for continuously irradiating the ultrasonic wave becomes longer. This is caused by the coarsening caused by the combination of a large number of bubbles and the combination of the bubbles, which may hinder the penetration of the ultrasonic wave. Reduce the production of free radicals. Further, when the periodicity of the particles is examined and the effect of cleaning the particles on the wafer is examined, it is confirmed that the effect starts to fall as soon as the cycle reaches about 500 msec (see Fig. 9). Therefore, by setting the cycle in accordance with the contamination target such as particles or organic stains-13-200904555 in this range, the most appropriate washing conditions can be set. As described above, the ultrasonic cleaning according to the present embodiment is performed. In the method, when the ultrasonic wave in which the dissolved gas is present is irradiated with the ultrasonic wave, by periodically stopping the irradiation of the ultrasonic wave, the generation of coarse bubbles that hinder the penetration of the ultrasonic wave can be prevented, and the generation can be efficiently performed. Free radicals for washing. Thereby, the glass substrate G can be cleaned efficiently. In addition, in recent years, Mega-Sonic cleaning using ultrasonic waves of the MHz level has become mainstream because of damage to the substrate, and since the wavelength of the ultrasonic wave to be irradiated is shortened, even in the past The bubble diameter which does not cause a problem in the low frequency (about 0.1 MHz) may also have a problem of hindering penetration, but the ultrasonic cleaning method of the present embodiment "irradiates the ultrasonic wave periodically by appropriately setting the stop period" In addition, even when a supersonic wave of the MHz level is used, the generation of coarse bubbles that block the penetration of ultrasonic waves can be prevented, and the object to be washed can be efficiently washed. Further, by periodically stopping the irradiation of the ultrasonic waves, the energy input can be further reduced as compared with the case of continuously irradiating the ultrasonic waves. Further, it is possible to suppress an increase in the temperature of the cleaning liquid and maintain a high gas solubility of the cleaning liquid. Thereby, it is possible to further promote the gas to be dissolved again in the cleaning liquid than when the ultrasonic wave is continuously irradiated. Further, the frequency range of the ultrasonic wave having less damage to the fine pattern of the semiconductor is about 1 MHz to 3 MHz, and the frequency range of the ultrasonic wave suitable for the generation of radicals is 0·3 ΜΗζ 1 MHz. Further, in the present embodiment, the ultrasonic lens is used to focus the ultrasonic waves incident on the cleaning liquid by the acoustic lens 18, but it may be irradiated without focusing. By focusing the ultrasonic waves, the radicals contributing to the cleaning can be efficiently generated in the vicinity of the focus of the focus, and the washing effect can be further improved. On the other hand, when the ultrasonic waves are focused in this way, since the holes are concentrated in the vicinity of the focus of the focus, it is easy to form coarse bubbles. However, as in the cleaning method of the present embodiment, the irradiation of the ultrasonic waves is most appropriately stopped, that is, It can prevent the generation of coarse bubbles, and can efficiently generate free radicals that contribute to washing. Further, in the present embodiment, the ultrasonic wave oscillated from the ultrasonic oscillator is focused on a predetermined focus focus using an acoustic lens, but the configuration in which the ultrasonic waves are focused is not limited thereto. For example, by forming the shape of the surface oscillating the ultrasonic wave of the ultrasonic oscillator into an arc shape (forming the shape of the ultrasonic oscillator into a so-called barrel shape), the ultrasonic wave can be focused on a predetermined focus focus. In this case, an acoustic lens is not required. Further, in the case of focusing the ultrasonic waves, the ultrasonic waves may be focused in a line shape or focused at a point. In addition, in the present embodiment, the glass substrate G which is conveyed horizontally is supplied with the cleaning liquid which has been irradiated with ultrasonic waves from the upper curtain, and the glass substrate G is washed. However, the glass substrate G may be formed. The structure in which the glass substrate G is washed by supplying the cleaning liquid irradiated with the ultrasonic waves from the lower curtain shape. Further, the surface of the glass substrate held in the vertical posture can be scanned by the vertically falling cleaning head to form a structure in which the surface of the glass substrate is supplied with the ultrasonic wave irradiated with the ultrasonic wave to wash the surface of the glass substrate. -15-200904555 Further, the present invention is similarly applied to the state in which the object to be washed 30 is immersed in the washing tank and washed as shown in Fig. 1 . In other words, even if the object to be washed 30 is immersed in the cleaning liquid 34 stored in the cleaning tank 32, the ultrasonic oscillator 36 (which may be provided in the lower portion of the cleaning tank 32) may be provided. The same applies to the case where the cleaning liquid 34 is supplied with ultrasonic vibration and cleaned. In this case, a large number of glass substrates can be washed at a time. In the present embodiment, the cleaning liquid discharged from the cleaning head is supplied to the surface of the glass substrate G and washed. High cleanliness when washing a large variety or a small amount of washing objects. Further, in the present embodiment, a case where a large-sized glass substrate for a liquid crystal display device is washed is described as an example. However, the application of the present invention is not limited thereto, and it is of course applicable to a glass for cleaning a photomask. In the case of a substrate such as a substrate or a substrate for a compact disc or a semiconductor wafer, the same can be applied even when other cleaned materials are washed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a model diagram showing an example of a non-ultrasonic cleaning device. Fig. 2 is a front cross-sectional view showing a schematic configuration of a cleaning head. Fig. 3 is a side cross-sectional view showing a schematic configuration of a cleaning head. Fig. 4(a) is an explanatory diagram of a coarse bubble generation process (hole generation period) in the case of continuous ultrasonic irradiation. Fig. 4(b) is an explanatory diagram of the process of generating a large bubble (the maximum period of the hole generation effect) when the ultrasonic wave is continuously irradiated. -16- 200904555 Fig. 4(c) is an explanatory diagram of a coarse bubble generation process (ultrasonic penetration inhibition period) during continuous ultrasonic irradiation. Fig. 5 is an explanatory diagram of a method of ultrasonic irradiation. Fig. 6(a) is an explanatory diagram of the action of the ultrasonic cleaning method (hole generation period). Fig. 6(b) is an explanatory diagram of the action of the ultra-wave cleaning method (the maximum period of hole formation effect). Fig. 6(c) is an explanatory diagram of the action of the ultrasonic cleaning method (hole dissolution period). Fig. 7 is a graph showing the relationship between the DUTY ratio and the amount of radical generation. Fig. 8 is a graph showing the relationship between the period and the amount of radical generation (input 1 00 W 'DUTY0.5). Figure 9 is a graph showing the relationship between cycle and cleaning effect. Fig. 10 is a model diagram showing another example of the ultrasonic cleaning device. [Description of main component symbols] 1 〇: Ultrasonic cleaning device 1 2 '· Washing head 1 4 : Cleaning liquid discharge port 1 6 : Ultrasonic oscillator 1 8 : Acoustic lens 20 = Degassing membrane module 22 : Gas Dissolving Membrane Module 17- 200904555 3 0 : Washed material 3 2 : Washing tank 3 4 : Cleaning liquid 3 6 : Ultrasonic oscillator G : Glass substrate