^3638 3^ 3638 3
五、發明說明（l) 本發明係有關於一種使用光學共焦回饋原理偵測CMP 研磨停止點的方法。 對於次微米的半導體製程而言，為了使微影製程的影 像轉移可以精確地進行，以確保後續進行薄膜蝕刻製程時 的準確度與餘刻後的輪廓，必須對介電層進行全面的平玉曰 化。CM P(化學機械研磨法）便是目前主要的一種全面平土旦 化（global planarization)的技術。不過’CMP製程的控 制卻是相當複雜，影響CMP平坦化技術的主要製程參數， 包括有研漿（s 1 urry )成份、晶片施壓大小、研磨轉速、研 磨塾材質、研漿内之研磨微粒的大小分佈、及研漿的供料 速率、溫度、pH值控制，以及被研磨材質的種類等。這些 參數對於CMP製程都有決定性的影響’另外，不同的被研 磨材料，其最主要的操作參數也會有所不同。雖然，CMp 本身的控制已經相當地複雜，但是在實際的應用上，這項 技術還受限於一些製程整合上的問題，例如：缺乏有效的 CMP停止點偵測系統（End_p〇int Detecti〇n Sys1：em)。 因此，在習知技術中，便提出有許多種CMp製程停止 點的偵測方法，例如：在美國專利第52 34868號中，其利 用在監測結構的周圍形成一溝渠（m〇a t)，再 :測’以溝渠的存在與否’謝否已經研磨 =頂端。也可根據研磨墊與溝渠頂端的電性接觸加以判 =。^美國專利第5240552號中，利聲波即時監測停止 .，並根據反射波型的分析控制研磨製程的國 專利第5308438號中，則是利用監測維持_設定的旋轉速V. Description of the invention (l) The present invention relates to a method for detecting the stopping point of CMP grinding using the principle of optical confocal feedback. For sub-micron semiconductor processes, in order to enable the image transfer of the lithography process to be performed accurately to ensure the accuracy and subsequent contours of the subsequent thin film etching process, a comprehensive flat jade of the dielectric layer must be performed. Said. CM P (Chemical Mechanical Polishing) is currently a major global planarization technology. However, the control of the CMP process is quite complicated. The main process parameters that affect the CMP planarization technology include the s 1 urry composition, the pressure of the wafer, the grinding speed, the grinding material, and the abrasive particles in the grinding slurry. Size distribution, slurry feed rate, temperature, pH control, and the type of material to be ground. These parameters have a decisive influence on the CMP process. In addition, the main operating parameters of different materials to be ground will also be different. Although the control of CMP itself is quite complicated, in practical applications, this technology is also limited by some process integration issues, such as the lack of an effective CMP stop point detection system (End_point Detecti〇n Sys1: em). Therefore, in the conventional technology, there are many methods for detecting the stopping point of the CMP process. For example, in US Patent No. 52 34868, it uses a trench (moat) formed around the monitoring structure, and then : Measure 'existence of the ditch' Thank you for grinding = top. It can also be judged according to the electrical contact between the polishing pad and the top of the trench. ^ In US Patent No. 5,240,552, the sound wave is stopped immediately. And the national patent No. 5308438, which controls the grinding process based on the analysis of the reflected wave pattern, uses monitoring to maintain the set speed.
—iliMa 五、發明說明（2) 度所需的功率的變化’來決定停止點的位置。在美國專利 第5337015號中’其利用設置在研磨墊中的電極，高頻、 低電壓的訊號，及偵測裝置，來偵測已研磨之介電層的厚 度°在美國專利第51 9 6 3 5 3號中，則利用紅外線輕射偵 測’來偵測研磨中之半導體晶圓的表面溫度變化，以決定 停止點的位置。 上述習知方法要不是準確度不高，就是過於複雜。因 此’在習知技術中’另有利用光學偵測的方法，其以雷射 光入射至半導體基材，然後根據所量測到的反射光強度， 決定停止點的位置。此種光學偵測方法具有較高的準確 度’不過其僅能適用於内層介電層（ILD)。請參閱第la圖 及第1 b圖，其中，第1 a圖係繪示以上述光學方法偵測内層 介電層之研磨停止點的反射光強度曲線；第lb圖係繪示以 上述光學方法偵測内金屬介電層之研磨停止點的反射光強 度曲線。在第la圖中，曲線只有一個拗折點，所以可輕易 地判斷出停止點的位置。但在第lb圖中，由於多層訊號反 射會造成相當大的雜訊，因此無法根據曲線判斷出研磨停 止點的位置。 有鑑於此，為了改進上述習知技術的缺點，本發明乃 提出一種使用光學共焦回饋原理偵測C Μ P研磨停止點的方 法’其利用光學回饋的方法取代習知的干涉方法’可準確 地偵測到研磨停止點。 本發明之另一目的在於提出一種使用光學共焦回饋原 理偵測CMP研磨停止點的方法，其可適用於内層介電層—IliMa V. Description of the invention (2) Change in power required by degrees' to determine the position of the stopping point. In U.S. Patent No. 5,337,015, it uses electrodes disposed in a polishing pad, high-frequency, low-voltage signals, and a detection device to detect the thickness of a polished dielectric layer. In U.S. Patent No. 51 9 6 In No. 3, No. 3, the infrared light detection is used to detect the surface temperature change of the semiconductor wafer during polishing to determine the position of the stopping point. The above-mentioned conventional methods are either inaccurate or too complicated. Therefore, in the conventional technology, there is another method using optical detection, in which laser light is incident on a semiconductor substrate, and then the position of the stopping point is determined according to the measured reflected light intensity. This optical detection method has high accuracy ', but it can only be applied to the inner dielectric layer (ILD). Please refer to FIG. 1a and FIG. 1b, wherein FIG. 1a shows the reflected light intensity curve for detecting the grinding stop point of the inner dielectric layer by the above-mentioned optical method; and FIG. Lb shows the above-mentioned optical method The reflected light intensity curve of the grinding stop point of the inner metal dielectric layer is detected. In Figure la, the curve has only one inflection point, so the position of the stopping point can be easily determined. However, in Figure lb, because the multilayer signal reflection causes considerable noise, the position of the grinding stop point cannot be judged from the curve. In view of this, in order to improve the shortcomings of the above-mentioned conventional techniques, the present invention proposes a method for detecting the CMP grinding stopping point using the principle of optical confocal feedback, 'which uses the optical feedback method instead of the conventional interference method', which can accurately The ground stop was detected. Another object of the present invention is to provide a method for detecting a CMP polishing stop point using an optical confocal feedback principle, which is applicable to an inner dielectric layer.
第5頁 436383 五、發明說明（3) - (ILD)及内金屬介電層等各種介電層之研磨停止點的偵 測。 本發明之使用光學共焦回饋原理偵測Μ?研磨停止點 的方法對於介電層的厚度之偵測，具有高解析度。同時， 利用本發明之方法，可簡化硬體的架構。 ^發明主要疋利用光學共焦回饋系統偵測製程的 研磨停止點’冑參閱第2圖’習知的光學共焦回饋系統主 要係包括：-雷射光源10 ’帛以產生雷射光束；第一針孔 12，上述雷射光束被聚焦於第一針孔12上；一透鏡14，闬 以將上述針孔12上之點光源聚焦至透明的待測物16上；— 物鏡1 8，用以將穿透待測物1 6的光線聚焦；第二針孔2 〇， 經上述物鏡1 8聚焦的光點位於第二針孔2 〇上；—偵測裝置 22，接收穿過第二針孔20的光線。上述透鏡14與物鏡18具 有相同的數值孔徑。 μ - 〃 圖式之簡要說明 為了更進一步聞明本發明之方法、架構及特點，兹配 合附圖說明較佳實施例如下，其中： 第la圖係繪示以習知光學方法偵測内層介電層之研磨 停止點的反射光強度曲線。 第1 b圖係繪示以習知光學方法偵測内金屬介電層之研 磨停止點的反射光強度曲線。 第2圖係繪示一習知的光學共焦回饋系統的架構圖 式。 ’、 第3a圖係繪示根攄本發明之一實施例的使用光學共焦Page 5 436383 V. Description of the invention (3)-(ILD) and detection of the grinding stop points of various dielectric layers such as the inner metal dielectric layer. The method of using the optical confocal feedback principle of the present invention to detect the M? Grinding stop point has a high resolution for the detection of the thickness of the dielectric layer. At the same time, the method of the present invention can simplify the hardware architecture. ^ The invention mainly uses the optical confocal feedback system to detect the grinding stop point of the process. 胄 Refer to Figure 2. The conventional optical confocal feedback system mainly includes:-a laser light source 10 'to generate a laser beam; A pinhole 12, the laser beam is focused on the first pinhole 12; a lens 14, which focuses the point light source on the pinhole 12 onto the transparent object 16 to be tested; To focus the light penetrating the object under test 16; the second pinhole 20; the light spot focused by the objective lens 18 is located on the second pinhole 20;-the detection device 22 receives the second pin Light from the hole 20. The above-mentioned lens 14 and the objective lens 18 have the same numerical aperture. μ-〃 Brief description of the drawings In order to further understand the method, architecture and characteristics of the present invention, the preferred embodiments are described below with reference to the accompanying drawings, in which: Figure la is a diagram showing the detection of the inner layer by conventional optical methods Reflected light intensity curve at the grinding stop point of the electrical layer. Figure 1b shows the reflected light intensity curve of the grinding stop point of the inner metal dielectric layer detected by conventional optical methods. FIG. 2 is a structural diagram of a conventional optical confocal feedback system. ′, FIG. 3a illustrates the use of optical confocal according to an embodiment of the present invention.
第6頁 436383 五、發明說明（4) 回饋原理偵測CMP研磨停止點的架構之圖式。 第3b圖係繪示根據本發明之另—實/例的使用光學共 焦回饋原理偵測CMP研磨停止點的架構之圖式。 第4圖係繪示使用於本發明中的光學共焦回饋系統之 一實施例的架構圖式。 第5圖係繪示使用於本發明中的光學共焦回饋系統之 另一實施例的架構圖式。 參考標號之說明 10、40 雷射光源，12 針孔；14、gg、36a、36b、 50、62透鏡；16、45待測物；18、44物鏡；2〇、52針 孔；22彳貞測裝置；30金屬層；32晶圓表面；34研磨 墊：38a、38b光學共焦回饋系統；42偏振分光鏡；46 四分之一波片，4 8偏振器’ 5 4光偵測器；6 〇半導體雷 射；64 電流摘測器。 實施例之說明 光學共焦回饋系統的原理已簡述如上，所以對於CMp 製程而言’自針孔射出的點光源，若被聚焦在待測晶圓的 反射面上，則其反射光束也會聚集在偵測裝置端的針孔 ^ =用光學共焦、回饋系統中光源端與谓測端均應為光強 &最向的光點，可以決定CMP研磨停止點。其操作方式有 下列兩種：首先，當研磨墊與透鏡間的距離固定時，請參 閱第3a圖’若研磨停止點為自金屬層3〇至晶圓表面32距離 3的位置’則使研磨墊34與透鏡36間的距離固定為f-s(其 中，f為透鏡焦距）。如此，當進行研磨至偵測到反射光強Page 6 436383 V. Description of the invention (4) A schematic diagram of the structure of the feedback principle to detect the stopping point of CMP polishing. Fig. 3b is a diagram showing a structure for detecting a CMP polishing stop point using an optical confocal feedback principle according to another embodiment of the present invention. Fig. 4 is a schematic diagram showing an embodiment of an optical confocal feedback system used in the present invention. Fig. 5 is a schematic diagram showing another embodiment of an optical confocal feedback system used in the present invention. Explanation of reference numerals 10, 40 laser light sources, 12 pinholes; 14, gg, 36a, 36b, 50, 62 lenses; 16, 45 test objects; 18, 44 objective lenses; 20, 52 pinholes; 22 Measuring device; 30 metal layers; 32 wafer surface; 34 polishing pads: 38a, 38b optical confocal feedback system; 42 polarization beam splitter; 46 quarter wave plate, 4 8 polarizer '5 4 light detector; 6 0 semiconductor laser; 64 current pick-up. The description of the embodiment The principle of the optical confocal feedback system has been briefly described above. Therefore, for the CMP process, a point light source emitted from a pinhole is focused on the reflective surface of the wafer to be tested, and its reflected beam will also be The pinholes gathered at the end of the detection device ^ = With the optical confocal, feedback system, both the light source end and the measurement end should be the light intensity & the most direct light spot, which can determine the CMP polishing stop point. There are two methods of operation: First, when the distance between the polishing pad and the lens is fixed, refer to Figure 3a, 'If the polishing stop point is a distance of 3 from the metal layer 30 to the wafer surface 32', the polishing is performed. The distance between the pad 34 and the lens 36 is fixed at fs (where f is the focal length of the lens). In this way, when grinding is performed until the reflected light intensity is detected
436383 五、發明說明（5) 度最大時’停止研磨，此時透鏡36與金屬層30間的距離為 f，可得到金屬層30至晶圓表面32的距離為s。 其次’當研磨墊與透鏡間的距離無法固定時，請參閱 第3b圖’同樣假設研磨停止點為自金屬層3〇至晶圓表面32 距離s的位置’則必須使用兩組光學共焦回饋系統3 8 a、 38b ’其透鏡36a、36b的焦距均為；f，同時使兩個透鏡相距 s的距離。第一個透鏡3 6a是用以偵測研磨中的晶圓表面32 之位置’第二個透鏡36b則是用以偵測金屬層3〇的位置。 如此，第一個透鏡36a的光學共焦回饋系統始終維持在反 射光強度最大，而當第二個透鏡36b的光學共焦回饋系統 達到反射光強度最大時，即停止研磨，此時金屬層3〇至晶 圓表面32的距離為s。 接下 饋系統的 共焦回饋 束； 偏 44，用以 46，設置 偏振方向 上述偏振 器48 ，用 向，以控 通過上述 光點位於 來，說明上述 架構。請參閱 系统係包括： 振分光鏡42， 將上述光束聚 於上述物鏡44 ’使得光束經 分光鏡42時， 以配合穿透上 制通過該偏振 偏振器4 8的光 該針孔52上； 兩個實施例中所使用的光學共焦回 第4圖，根據第一個實施例，光學 —雷射光源40，用以產生一雷射光 用以將經偏振的光 焦至待測物4 5上； 與待測物45之間， 待測物45反射，並 可穿透上述偏振分 述偏振分光鏡42的 器48的光強度；一 線聚焦；一針孔5 2 ~光偵測器5 4，用 束反射；一物鏡 一四分之一波片 用以改變 經物鏡4 4 光鏡42 ; 光線之偏 透鏡50， ，使上述 以偵測接 光束的 投射至 一偏振 振方 用以將 聚焦之 收到的 436383 五、發明說明¢6) 光強度訊號。 請參閱第5圖，根據第二個實施例，光學共焦回饋系 統係包括：一半導體雷射60，經電流驅動會產生雷射光 束；一透鏡62，可將上述半導體雷射60產生之光束聚焦； 一電流偵測器64，用以偵測流經上述半導體雷射60的電 流。由於經上述透鏡62聚焦之雷射光束在被反射時，會再 聚集至上述半導體雷射及用以偵測半導體雷射之背向光的 光感測器上，如此會影響流經半導體雷射的電流大小，且 此電流大小與反射回來的光強度成比例關係。因此，利用 上述電流偵測器彳貞測流經上述半導體雷射的電流大小，可 推知經反射之雷射光束的強度，並可據以判斷出上述透鏡 之焦點是否位於反射面上。 上述光學共焦回饋系統亦可用以掃瞄出晶圓的拓樸結 構’其操作方式是利用上述光學共焦回饋系統，以不同的 深度水平掃瞄晶圓，再將各個光反射強度最大的區域連 接。 利用本發明上述方法，由於根據反射光的強度變化， 可準確地測知每一層的介面位置，所以可精確地掌握晶圓 表面至内部某一層間的距離，換言之，可以精確地決定 CMP研磨停止點的位置。436383 V. Description of the invention (5) The grinding is stopped when the degree is maximum. At this time, the distance between the lens 36 and the metal layer 30 is f, and the distance from the metal layer 30 to the wafer surface 32 is s. Secondly, 'when the distance between the polishing pad and the lens cannot be fixed, please refer to Figure 3b.' Similarly, it is assumed that the polishing stop point is at a distance of s from the metal layer 30 to the wafer surface 32. Then two sets of optical confocal feedback must be used. The systems 3 8 a and 38 b ′ have the focal lengths of the lenses 36 a and 36 b; f, at the same time, the distance between the two lenses is s. The first lens 36a is used to detect the position of the wafer surface 32 during polishing ', and the second lens 36b is used to detect the position of the metal layer 30. In this way, the optical confocal feedback system of the first lens 36a always maintains the maximum reflected light intensity, and when the optical confocal feedback system of the second lens 36b reaches the maximum reflected light intensity, grinding is stopped, and at this time, the metal layer 3 The distance from 0 to the wafer surface 32 is s. The confocal feedback beam of the feed-back system is connected; the polarization 44 and 46 are used to set the polarization direction, and the above-mentioned polarizer 48 is used to control the location of the light point to explain the above structure. Please refer to the system including: a vibrating beam splitter 42 for condensing the above-mentioned light beam onto the objective lens 44 'so that the light beam passes through the beam splitter 42 to cooperate with penetrating the light passing through the polarization polarizer 48 on the pinhole 52; two The optical confocal used in this embodiment returns to FIG. 4. According to the first embodiment, the optical-laser light source 40 is used to generate a laser light to focus the polarized light onto the object 45 to be measured. Between the object 45 and the object 45, the object 45 reflects and can penetrate the light intensity of the device 48 of the polarization segmentation polarization beam splitter 42; one-line focusing; one pinhole 5 2 ~ light detector 54, Beam reflection; an objective lens and a quarter wave plate are used to change the objective lens 4 4 light mirror 42; the polarizing lens 50 of the light, so that the above-mentioned detection of the projection of the beam onto a polarization side is used to focus the 436383 received V. Description of invention ¢ 6) Light intensity signal. Please refer to FIG. 5. According to the second embodiment, the optical confocal feedback system includes: a semiconductor laser 60, which is driven by a current to generate a laser beam; a lens 62, which can convert the beam generated by the semiconductor laser 60 described above. Focusing; a current detector 64 for detecting a current flowing through the semiconductor laser 60. Since the laser beam focused by the lens 62 is reflected, it will be focused on the semiconductor laser and the light sensor for detecting the back light of the semiconductor laser, which will affect the flow of the semiconductor laser. The magnitude of the current is proportional to the intensity of the reflected light. Therefore, by measuring the magnitude of the current flowing through the semiconductor laser using the current detector, the intensity of the reflected laser beam can be inferred, and it can be judged whether the focal point of the lens is located on the reflective surface. The above-mentioned optical confocal feedback system can also be used to scan the topology of the wafer. The operation method is to use the above-mentioned optical confocal feedback system to scan the wafer at different depth levels, and then to reflect the areas with the highest light intensity. connection. With the above method of the present invention, since the interface position of each layer can be accurately detected according to the intensity change of the reflected light, the distance from the wafer surface to an inner layer can be accurately grasped, in other words, the CMP polishing stop can be accurately determined The location of the point.
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