06 7 06 7 經濟部智慧財產局員工消費合作社印製 A7 B7 五、發明說明（/0 本發明是有關於一種半導體積體電路的製造方法，且 特別是有關於一種小尺度溝渠的製造方法。 在半導體積體電路的集積度不停的提升下，當進入 0.18 μηι甚至線寬更小的製程時，主動區間之元件隔離結 構的寬度也會跟著縮小至0.18 μπι甚至更小的尺度。在這 微小的尺度下1將增加不少微影製程的困難度。 請參照第1圖’基底100上依序形成有墊氧化層110 與氮化矽層120。在罩幕層120之上，形成有曝過光之光 阻層130，因此光阻層130之中形成有開口 140。開口 140 的直徑dl將會和後續在基底1〇〇中欲形成之溝渠(圖上未 示出)寬度相同。在此’罩幕層120可由一層氮化矽所組成， 或是一層氮化矽與位於其上之一層氧化矽所組成。 在此若製程的線寬要求在0.18 μπι以下時，因爲曝光 區域之線寬太小，常會發生光阻層130曝光不足的問題。 光阻層130—旦曝光不足，便會使得顯影過後在光阻層13〇 中所留下之開口 140的底部，常殘留有光阻，且其形狀常 呈圓弧狀，對後面的蝕刻製程影響甚鉅，例如不易控制蝕 刻參數，使得此製程之重複性很差。 因此本發明提供一種小尺度溝渠的製造方法，包括在 基底上依序形成罩幕層與犧牲層’其中犧牲層的材質和基 底的材質相问°然後對犧牲層進丫了弟一縮減飽刻（taper eich) 步驟，以形成第一開口於犧牲層中’暴露出罩幕層之表面。 再對暴露出之罩幕層進行第二飽刻步驟，以形成第二開口 於罩幕層中，暴露出基底表面。接著對犧牲層與暴露出之 3 本紙張尺度適用中國國家標準（CNS)A4規格（210 X 297公釐） ------------(^--------訂---------線d (請先閱讀背面之注意事項再填寫本頁) 經濟部智慧財產局員工消費合作社印製 453337 5 728t\vf.doc/006 A7 五、發明說明（爻） 基底進行第三蝕刻步驟，以罩幕層爲犧牲層之蝕刻終點， 以在基底中形成溝渠。 應用上述本發明之小尺度溝渠的製造方法，利用縮減 蝕刻，可以使原微影製程的線寬較實際所需爲大，以減少 微影參數控制之困難度。另外利用和基底同材質的犧牲 層，以罩幕層爲蝕刻終點，來控制對基底之蝕刻深度。其 中基底的材質例如爲矽時，犧牲層的材質可爲多晶矽。 就另一種觀點來說，本發明提供一種淺溝渠隔離的製 造方法，在利用上述方法於基底中形成溝渠之後，再於溝 渠中與基底上形成一層絕緣層。然後利用化學機械硏磨法 硏磨此絕緣層，形成絕緣插塞於溝渠中，完成淺溝渠隔離 之製作。 應用上述之淺溝渠隔離的製造方法，可以形成比微影 解析度下限還小之淺溝渠隔離。又因爲是以罩幕層爲蝕刻 終點，來控制溝渠的深度，如此可以形成深度統一之溝渠， 使絕緣層塡入溝渠中以及進行化學機械硏磨法時，能得到 更好的控制，獲得更大的製程裕度(process window) ^ 就再一種觀點而言，本發明提供一種小尺度開口的製 造方法，包括於至少形成有一元件的基底上，依序形成物 質層、罩幕層與犧牲層，其中犧牲層的材質和物質層的材 質相同。然後對犧牲層與罩幕層進行縮減蝕刻步驟，以形 成第一開口於犧牲層與罩幕層中，暴露出物質層之表面。 再對犧牲層與暴露出之物質層進行蝕刻步驟，直至暴露出 罩幕層爲止，以在物質層中形成第二開口。 4 本紙張尺度適用中國國家標準（CNS)A4規格（210 X 297公釐） ------------~ 装------ί 訂— _! — ！線 (請先閱讀背面之注意事項再填寫本頁) A7 A b 9 33 7 5 7?8twt. doc/O06 五、發明說明（今） 根據上述本發明之形成小尺度開口的製造方法，可以 突破微影製程解析度的下限，在物質層中形成第二開口》 而桌一開口例如可爲接觸窗開口（contact opening)、介層窗 開口（via opening)或金屬鑲嵌（damascene)開口。 爲讓本發明之上述和其他目的、特徵和優點能更明顯 易懂，下文特舉一較佳實施例，並配合所附圖式，作詳細 說明如下： 圖式之簡單說明： 第1圖是習知要在基底中形成溝渠前之光阻曝光不足 時之結構剖面示意圖；以及 第2A - 2D圖是依照本發明一較佳實施例的一種小尺 度溝渠製造流程剖面示意圖。 圖式之標記說明： 1〇0、200 :基底 1 1 ◦、：墊氧化層 120、220、220a :罩幕層 130、230 :光阻層 140、240、245、245a :開口 225、225a、225b :犧牲層 250、250a :溝渠 D、cU、d2 :開□寬度 tl、t2 :厚度 實施例 請參照第2A - 2D圖，其繪示依照本發明一較佳實施 本紙張尺度適用中國國家標準（CNS)A4規格（210 X 297公釐） ------------~ 表--------訂---------線-' (請先閱讀背面之注意事項再填寫本頁) 經濟部智慧財產局員工消費合作社印製 6J 337 ; 5 72 8iwl'.d oc/() 0 6 A7 B7 五、發明說明（>) 例的一種小尺度溝渠之製造流程剖面示意圖。 請參照第2A圖，在基底200上依序形成墊氧化層2] 0、 罩幕層220與犧牲層225。其中犧牲層225的材質和基底2⑽ 的材質相同，例如基底200的材質爲矽時’犧牲層225的 材質可爲多晶矽或非晶矽。 然後於犧牲層225上形成一層光阻層，經微影製程之 後，形成圖案化之光阻層230。並在光阻層230中形成有 開口 240，開口 240的寬度爲D。在此，開口 240的寬度 爲D可以比實際所需之溝渠寬度還大。 請參照第2B圖，以圖案化的光阻層230爲罩幕，依 序去除暴露出之犧牲層225與位於其下之罩幕層220，於 犧牲層225a與罩幕層220a中形成開口 245。請注意，在 此，開口 245之寬度由上至下，係由原先光阻層230中之 開口 240的寬度D，逐漸縮減至開口 245位於罩幕層220a 中之寬度d2。開口 245底部的寬度d2，可經由選擇適當 的去除方法，做到小於微影解析度之下限。 經濟部智慧財產局員工消費合作社印製 (請先閱讀背面之注意事項再填寫本頁) 去除暴露出之犧牲層225與位於其下之罩幕層220的 方法，例如可爲反應性離子蝕刻法。在此例如可先以縮減 蝕刻(taper etch)的方式來蝕刻犧牲層225，若犧牲層225的 材質爲多晶砂時，可以利用兩段蝕刻方式來達成如第2B 圖所繪示開口 245之縮減輪廓。第一階段蝕刻的參數例如 在約爲4 - 10 mT的壓力與約爲4〇〇 — 6〇〇瓦的功率下，以 流速約爲40 - 80 Sccm的CF4氣體進行蝕刻約10秒鐘然 後第一段蝕刻再於約30 - 70 mT的壓力與約爲500 - 700 6 本紙張尺^適用中國國^標準（CNS)A4規格（210 X 297^^- 經濟部智慧財產局員工消費合作社印製 4 5 3 33 ί , γ ^7281 \ν ί. d ο c / Ο Ο 6 __Β7_ 五、發明説明（5 ) 瓦的功率下，以流速約爲120 - 150 seem的HBr與流速約 爲20 - 40 seem的NF〗氣體來進行蝕刻，直至罩幕層22〇 爲止。 接下來對罩幕層220進行蝕刻，若罩幕層220的材質 爲氮化矽時，例如可在約爲70- 100 mT的壓力與約爲4〇〇 — 500瓦的功率下，以流速約爲40 - 80 seem的CHF、氣體進 行蝕刻，直至墊氧化層210爲止。 請參照第2C圖，然後將光阻層230去除之，例如可 利用氧電漿將其灰化後，再以化學溶液淸洗之。 接著，去除暴露出之犧牲層225a與位於開口 245下方 之墊氧化層210與基底200。在此因爲犧牲層225a與基底 200的材質相同，所以可利用犧牲層225a的厚度tl來控制 基底200被去除的深度。如第2C圖所示，進行去除步驟 一段時間之後，犧牲層225b之厚度將會小於犧牲層225a 原來之厚度tl，同時也於基底200中形成溝渠250。 在此所用之去除方法，例如可爲反應離子蝕刻法，以 矽材質的基底200與犧牲層225a來說，在約爲30 — 70 mT 的壓力與約爲500 - 700瓦的功率下，以流速約爲125 - 150 seem的HBr與流速約爲20 - 40 seem的NF3氣體來進行蝕 刻，直至犧牲層225b完全被蝕刻掉，暴露出罩幕層220a 爲止，同時也在基底200中形成溝渠250a，如第2D圖所 示。 因此可知，只要將在基底200中所蝕刻出溝渠25〇a的 深度與犧牲層225的厚度彼此之間的關係找出實驗關係 7 本紙張尺度適用中國國家操準（CNS ) A4規格（210X297公釐） —.--^----—裝------訂------朿 (請先聞讀背面之注意事項再填寫本頁) 337 ?Τ2 ΗI w ί' ϋ o c/(l 0 6 Α7 Β7 經濟部智慧財產局員工消費合作社印製 五、發明説明（厶） 來，就可以很容易地控制溝渠250a深度的均勻度 (umformity)。例如犧牲層225a的材質爲多晶矽，而基底200 的材質爲矽，且溝渠250a的面積約爲犧牲層225a面積之 20 %時，若溝渠250a的深度約爲4000埃，則犧牲層225a 的厚度tl約需3000 - 3500埃。 再將罩幕層220a去除之，然後於溝渠250a中與基底 200上形成一層絕緣層（圖上未示出）。最後利用化學機械 硏磨法硏磨此絕緣層，形成絕緣插塞（圖上未示出）於溝渠 250a中，完成淺溝渠隔離之製作。以上爲熟悉此技藝之人 所熟知，因此不再詳述其過程。 本發明並不限於只能應用在淺溝渠隔離的製造上，也 可應用在製造接觸窗開口、介層窗開口、金屬鑲嵌開口或 其他開口上。只要將欲在其中形成開口之物質層上，依序 形成-層罩幕層與一層犧牲層，再依照上述方法來進行之 即可。也就是上述之基底，可直接替換成一層物質層，並 選用和此物質層材質不同之罩幕層與和此物質層同材質之 犧牲層，即可應用來在物質層中形成比現行使用之微影解 析度下限還小的開口。 由上述本發明較佳實施例可知，應用本發明至少具有 下列優點。 1. 利用縮減蝕刻，可以使原微影製程的線寬較實際所 需爲大，以減少微影參數控制之困難度。 2. 利用和基底同材質的犧牲層，以罩幕層爲蝕刻終點’ 來控制對基底或物質層之蝕刻深度。可改善傳統控制蝕刻 8 (請先聞讀背面之注意事項再填寫本頁) 裝' 訂 線 本紙張尺度適用中國圉家標準（CNS ) A4规格（210 X 297公釐） /1 p； 9 * S72Kt\vl.tloc/00& A7 B7 五、發明説明（"） 時間來控制蝕刻深度時，蝕刻深度不易控制之缺點。 3.當應用在製造淺溝渠隔離時，因爲以罩幕層爲蝕刻 終點，來控制基底中溝渠的深度，可改善同一片晶圓上不 同處、或不同片、甚至不同批晶圓上之溝渠深度的.一致性。 在後續步驟將絕緣層塡入溝渠中以及進行化學機械硏磨 時，能得到更好的控制，獲得更大的製程裕度（process window) ° 雖然本發明已以一較佳實施例揭露如上，然其並非用 以限定本發明，任何熟習此技藝者，在不脫離本發明之精 神和範圍內，當可作各種之更動與潤飾，因此本發明之保 護範圍當視後附之申請專利範圍所界定者爲準。 (請先閲讀背面之注意事項再填寫本頁) 裝 訂 線. 經濟部智慧財產局員工消費合作杜印製 本紙張尺度適用中國國家標準（CNS ) A4规格（21 〇 X 297公釐）06 7 06 7 Printed by A7 B7, Consumer Cooperative of Intellectual Property Bureau of the Ministry of Economic Affairs 5. Description of the Invention (/ 0 The present invention relates to a method for manufacturing a semiconductor integrated circuit, and in particular to a method for manufacturing a small-scale trench. Under the continuous improvement of the integration degree of semiconductor integrated circuits, when entering the process of 0.18 μηι or even smaller line width, the width of the element isolation structure of the active section will be reduced to 0.18 μπm or even smaller. Here At a small scale, 1 will increase the difficulty of the lithography process. Please refer to FIG. 1 'a substrate 100 in which a pad oxide layer 110 and a silicon nitride layer 120 are sequentially formed. On the mask layer 120, there is formed The photoresist layer 130 has been exposed to light, so an opening 140 is formed in the photoresist layer 130. The diameter d1 of the opening 140 will be the same as the width of a trench (not shown) to be formed in the substrate 100 in the future. Here, the mask layer 120 may be composed of a layer of silicon nitride, or a layer of silicon nitride and a layer of silicon oxide above it. If the line width of the process is below 0.18 μπι, line Too small, the problem of underexposure of the photoresist layer 130 often occurs. Once the photoresist layer 130 is underexposed, the bottom of the opening 140 left in the photoresist layer 13 after development will often leave a photoresist, And its shape is often arc-shaped, which has a great influence on the subsequent etching process, for example, it is difficult to control the etching parameters, making the repeatability of this process very poor. Therefore, the present invention provides a method for manufacturing a small-scale trench, including In order to form the mask layer and the sacrificial layer, the material of the sacrificial layer and the material of the substrate are interposed. Then, the sacrificial layer is subjected to a taper eich step to form a first opening in the sacrificial layer. The surface of the mask layer is then subjected to a second saturation step to form a second opening in the mask layer to expose the surface of the substrate. Then the sacrificial layer and the exposed 3 paper sizes Applicable to China National Standard (CNS) A4 specification (210 X 297 mm) ------------ (^ -------- Order --------- line d (Please read the notes on the back before filling out this page.) Company printed 453337 5 728t \ vf.doc / 006 A7 V. Description of the invention (ii) The substrate is subjected to a third etching step, and the mask layer is used as the sacrifice layer to etch the end point to form a trench in the substrate. The manufacturing method of small-scale trenches uses reduced etching to make the line width of the original lithography process larger than actually needed to reduce the difficulty of lithography parameter control. In addition, a sacrificial layer of the same material as the substrate is used to cover the screen. The layer is the end point of the etch to control the etching depth to the substrate. When the material of the substrate is silicon, for example, the material of the sacrificial layer may be polycrystalline silicon. In another aspect, the present invention provides a manufacturing method for shallow trench isolation. After the above method forms a trench in the substrate, an insulation layer is formed in the trench and on the substrate. Then, the insulating layer is honed by a chemical mechanical honing method to form an insulating plug in the trench, and the isolation of the shallow trench is completed. By applying the above-mentioned manufacturing method of shallow trench isolation, shallow trench isolation smaller than the lower limit of the lithographic resolution can be formed. Because the depth of the trench is controlled by using the mask layer as the end point of etching, a trench with uniform depth can be formed, and the insulating layer can be inserted into the trench and the chemical mechanical honing method can be better controlled to obtain more Large process window ^ In another aspect, the present invention provides a method for manufacturing a small-scale opening, which includes sequentially forming a material layer, a mask layer, and a sacrificial layer on a substrate on which at least one element is formed. , Where the material of the sacrificial layer and the material layer are the same. Then, a reduction etching step is performed on the sacrificial layer and the mask layer to form a first opening in the sacrificial layer and the mask layer to expose the surface of the material layer. Then, an etching step is performed on the sacrificial layer and the exposed material layer until the mask layer is exposed to form a second opening in the material layer. 4 This paper size is in accordance with China National Standard (CNS) A4 (210 X 297 mm) ------------ ~ Packing ------ ί Order — _! —! (Please read the precautions on the back before filling this page) A7 A b 9 33 7 5 7? 8twt. Doc / O06 V. Description of the invention (today) According to the above-mentioned manufacturing method of forming a small-scale opening, it can break through The lower limit of the resolution of the lithography process forms a second opening in the material layer. The opening of the table can be, for example, a contact opening, a via opening, or a damascene opening. In order to make the above and other objects, features, and advantages of the present invention more comprehensible, a preferred embodiment is given below in conjunction with the accompanying drawings for detailed description as follows: Brief description of the drawings: FIG. 1 is It is known that a schematic sectional view of the structure when the photoresist is not exposed before the trench is formed in the substrate; and FIGS. 2A to 2D are schematic sectional views of a small-scale trench manufacturing process according to a preferred embodiment of the present invention. Explanation of the marks of the drawings: 100, 200: substrate 1 1 ◦: pad oxide layers 120, 220, 220a: mask layer 130, 230: photoresist layer 140, 240, 245, 245a: openings 225, 225a, 225b: sacrificial layers 250, 250a: trenches D, cU, d2: opening width t1, t2: thickness For an example, please refer to Figures 2A-2D, which shows a preferred implementation according to the present invention. This paper scale is applicable to Chinese national standards. (CNS) A4 specification (210 X 297 mm) ------------ ~ Table -------- Order --------- Line- '(please first Read the notes on the back and fill in this page) Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs 6J 337; 5 72 8iwl'.d oc / () 0 6 A7 B7 5. A small-scale example of the invention (>) Schematic cross-section of the manufacturing process of a ditch. Referring to FIG. 2A, a pad oxide layer 2], a mask layer 220, and a sacrificial layer 225 are sequentially formed on the substrate 200. The material of the sacrificial layer 225 is the same as that of the substrate 2⑽. For example, when the material of the substrate 200 is silicon, the material of the sacrificial layer 225 may be polycrystalline silicon or amorphous silicon. Then, a photoresist layer is formed on the sacrificial layer 225. After the lithography process, a patterned photoresist layer 230 is formed. An opening 240 is formed in the photoresist layer 230, and the width of the opening 240 is D. Here, the width D of the opening 240 may be larger than the actually required trench width. Referring to FIG. 2B, the patterned photoresist layer 230 is used as a mask, and the exposed sacrificial layer 225 and the mask layer 220 below it are sequentially removed, and openings 245 are formed in the sacrificial layer 225a and the mask layer 220a . Please note that the width of the opening 245 from top to bottom is gradually reduced from the width D of the opening 240 in the original photoresist layer 230 to the width d2 of the opening 245 in the mask layer 220a. The width d2 at the bottom of the opening 245 can be less than the lower limit of the lithographic resolution by selecting an appropriate removal method. Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs (please read the precautions on the back before filling this page) The method of removing the exposed sacrificial layer 225 and the mask layer 220 below it, such as reactive ion etching . Here, for example, the sacrificial layer 225 can be etched by tape etch. If the material of the sacrificial layer 225 is polycrystalline sand, two-stage etching can be used to achieve the opening 245 as shown in FIG. 2B. Reduce the outline. The parameters of the first-stage etching are, for example, etching at a pressure of about 4-10 mT and a power of about 400-600 watts with CF4 gas having a flow rate of about 40-80 Sccm for about 10 seconds, and then A piece of etching is performed at a pressure of about 30-70 mT and about 500-700 6 This paper rule ^ applies to the Chinese National Standard (CNS) A4 specification (210 X 297 ^^-printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs) 4 5 3 33 ί, γ ^ 7281 \ ν ί. D ο c / Ο Ο 6 __Β7_ V. Description of the invention (5) At a power of watts, HBr with a flow rate of about 120-150 seem and a flow rate of about 20-40 seem NF〗 gas to etch until the mask layer 22. Next, the mask layer 220 is etched. If the material of the mask layer 220 is silicon nitride, for example, it can be about 70-100 mT. Under pressure and a power of about 400-500 watts, etching is performed with CHF and gas at a flow rate of about 40-80 seem until the pad oxide layer 210 is formed. Please refer to FIG. 2C, and then remove the photoresist layer 230 For example, it can be ashed with an oxygen plasma, and then washed with a chemical solution. Next, the exposed sacrificial layer 225a is removed. The pad oxide layer 210 and the substrate 200 under the opening 245. Because the material of the sacrificial layer 225a and the substrate 200 are the same, the thickness t1 of the sacrificial layer 225a can be used to control the depth of the substrate 200 to be removed. As shown in FIG. 2C It is shown that after the removal step is performed for a period of time, the thickness of the sacrificial layer 225b will be smaller than the original thickness t1 of the sacrificial layer 225a, and a trench 250 is also formed in the substrate 200. The removal method used here may be, for example, a reactive ion etching method, With silicon substrate 200 and sacrificial layer 225a, under the pressure of about 30-70 mT and the power of about 500-700 watts, the flow rate of HBr is about 125-150 seem and the flow rate is about 20-40 NF3 gas seems to be etched until the sacrificial layer 225b is completely etched away, and the cover layer 220a is exposed, and a trench 250a is also formed in the substrate 200, as shown in FIG. 2D. Therefore, as long as the substrate 200 The relationship between the depth of the etched trench 25 〇a and the thickness of the sacrificial layer 225 is found in the experimental relationship. 7 This paper size is applicable to China National Standard (CNS) A4 (210X297 mm) —.-- ^ ------ Install ------ Order ------ 朿 (Please read the notes on the back before filling this page) 337? Τ2 ΗI w ί 'ϋ oc / (l 0 6 Α7 Β7 Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs. 5. Description of Invention (厶) With this, the umformity of the depth of the trench 250a can be easily controlled. For example, when the material of the sacrificial layer 225a is polycrystalline silicon and the material of the substrate 200 is silicon, and the area of the trench 250a is about 20% of the area of the sacrificial layer 225a, if the depth of the trench 250a is about 4000 angstroms, the thickness of the sacrificial layer 225a is t1. It takes about 3000-3500 angstroms. Then, the mask layer 220a is removed, and then an insulation layer is formed in the trench 250a and the substrate 200 (not shown in the figure). Finally, the insulating layer is honed using a chemical mechanical honing method to form an insulating plug (not shown in the figure) in the trench 250a to complete the production of shallow trench isolation. The above is well known to those familiar with this technique, so the process will not be described in detail. The present invention is not limited to the manufacturing of shallow trench isolation, but can also be applied to manufacturing contact window openings, interlayer window openings, metal inlaid openings or other openings. As long as the material layer in which openings are to be formed, a layer-curtain layer and a sacrificial layer are sequentially formed, and then the method is performed in accordance with the above method. That is, the above substrate can be directly replaced with a material layer, and a mask layer different from the material layer and a sacrificial layer of the same material as the material layer can be used to form a material layer that is more than the currently used material. The lower limit of the lithographic resolution is still small. As can be seen from the above-mentioned preferred embodiments of the present invention, the application of the present invention has at least the following advantages. 1. By reducing the etching, the line width of the original lithography process can be made larger than the actual need, so as to reduce the difficulty of lithography parameter control. 2. Use a sacrificial layer of the same material as the substrate and use the mask layer as the end point to control the etching depth of the substrate or material layer. Can improve the traditional control of etching 8 (Please read the precautions on the back before filling in this page) Binding 'The paper size is applicable to the Chinese standard (CNS) A4 specification (210 X 297 mm) / 1 p; 9 * S72Kt \ vl.tloc / 00 & A7 B7 V. Description of the invention (") When the time is used to control the etching depth, the disadvantage is that the etching depth is not easy to control. 3. When applied in the manufacture of shallow trench isolation, the depth of the trench in the substrate is controlled by using the mask layer as the end point of the etching, which can improve the trenches on different parts of the same wafer, or on different wafers, and even in different batches of wafers. Deep. Consistency. In the subsequent steps, when the insulating layer is inserted into the trench and chemical mechanical honing, better control can be obtained and a greater process window can be obtained. Although the present invention has been disclosed as above with a preferred embodiment, However, it is not intended to limit the present invention. Any person skilled in the art can make various modifications and retouches without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be regarded as the scope of the attached patent application. Defined shall prevail. (Please read the precautions on the back before filling this page) Binding line. Printed by the consumer cooperation of the Intellectual Property Bureau of the Ministry of Economic Affairs. This paper size applies the Chinese National Standard (CNS) A4 specification (21 0 X 297 mm).