1358538 九、發明說明： 【發明所屬之技術領域】 本發明係有.關於一種半導體晶圓下表面缺陷檢測裝 置，尤指一種基於光學同調斷層掃描的架構，並搭配一寬 頻光源，使該光源足以穿透半導體晶圓下表面，用以分析 晶圓内部不連續的斷面位置及形狀，以達成高靈敏度、高 解析度之半導體晶圓下表面缺陷檢測功能之檢測裝置。 【先前技術】 按，半導體製程的技術，隨著VLSI(超大規模集成電 路）積集度的增加，其線寬已小至奈米尺寸，各種細微的製 程缺陷或沾污’或是蟲晶晶片的品質’均對產品的良率與 效能有嚴重的影響。半導體晶圓缺陷檢測設備的研發與技 術曰新月異，如何提高量測靈敏度與解析度，降低系統成 本，是重要而具有重大產業利益的研究課題。 現今的晶圓缺陷檢測設備中，如矽晶片、砷化鎵及磷 化銦等半導體自動化缺陷檢測方法，大致可分為二種。第 一是光學表面分析技術，利用光學散射的原理來量測晶片 表面的缺陷或雜質，並藉由軟體設計來定義缺陷類型、大 小及數量，進而預測晶片的品質。第二是掃描式電子顯微 鏡與X光能量散佈分析，利用二次電子散射的原理來觀察 半導體表面的形貌及缺陷，並由X光散射的特性譜線來分 析雜質及缺陷種類，藉以判斷各種缺陷的成因。然而，前 者受限於缺陷散射光相對背景雜訊過於微弱，因此只能用 7 1358538 在晶片表面的量測，無法確切得知晶片内部的缺陷資訊； 後者雖可以量測半導體晶圓下表面的缺陷成分，但儀器造 價昂貴，且樣品需放置在真空環境，耗時的量測程序使得 該技術難以用於即時的線上檢測上。 對於光學式半導體晶圓下表面的缺陷分析技術，—般 使用的方法除了上述光學散射式外，亦有共焦顯微鏡及光 學同調斷層掃描術等。其中，紅外光雷射之缺陷散射檢測 技術，其係藉由調整不同的光源強度、波長與極化方向， 量測不同半導體晶圓表面與下表面的缺陷，克服傳統光學 散射系統背景雑訊干擾的問題，然而此種方式所能達到的 斷層影像解析度不足，且小角度收光導致訊號微弱，降低 量測系統的靈敏度。另一種共焦顯微鏡的架構，則可大幅 提高斷層影像的解析度，分析次微米等級的晶體缺陷，唯 系統的靈敏度受限於空間濾波器的數值孔徑，造成影像的 對比不足。 相對而言，光學同調斷層掃描技術，因利用外差式偵 測法可大幅提高訊噪比，而其縱向空間解析度則取決於光 源的頻寬，特別在紅外光波段，可藉由提高光源頻寬克服 繞射極限的問題。其中，光譜掃描式光學同調斷層掃描技 術，乃透過光譜掃描分別記錄各個波長干涉的強度，再將 所得的光譜經由傅立葉變換求出時域上的干涉波形。此種 頻域分析的技術可免除參考光的反射鏡掃描，提高影像擷 取速度。然而，此種方法所用之波長可調式雷射光源，其 可調範圍約只有100〜200nm，因此其對應的縱向解析度並 不高；另一種改進的方法稱為光譜分割平行處理技術，例 8 1358538 如美國發明專利 5905572 號「Sample inspection using interference and/or correlation of scattered superbroad radiation」，可直接將一寬頻雷射的輸出光譜 在空間中展開’各個頻率成分的光束同時進行干涉，並由 對應數目的偵測益所接收，如此平行處理的技術可進一步 省去雷射之波長掃描’提高影像擷取速度。但由於該系統 需使用大量的濾波、耗合與分光元件，光學精密對準要求 甚同，且光缙分割的間距不一與解析度的不足都可能導致 重建後的波形失真，在技術上有其困難；此外，例如中華1358538 IX. Description of the Invention: [Technical Field] The present invention relates to a semiconductor wafer lower surface defect detecting device, and more particularly to an architecture based on optical coherence tomography, and with a wide frequency light source, the light source is sufficient The lower surface of the semiconductor wafer is penetrated to analyze the discontinuous cross-sectional position and shape of the wafer to achieve a high-sensitivity, high-resolution detection device for detecting defects on the surface of the semiconductor wafer. [Prior Art] According to the technology of semiconductor manufacturing, with the increase in the accumulation of VLSI (VLSI), the line width has been as small as nanometer size, various fine process defects or contamination 'or insect crystal wafers The quality of the product has a serious impact on the yield and performance of the product. The research and development and technology of semiconductor wafer defect inspection equipment are changing with each passing day. How to improve measurement sensitivity and resolution and reduce system cost are important research topics with significant industrial interests. In today's wafer defect inspection equipment, semiconductor automated defect detection methods such as germanium wafers, gallium arsenide, and indium phosphide can be roughly classified into two types. The first is optical surface analysis technology, which uses the principle of optical scattering to measure defects or impurities on the surface of the wafer, and defines the type, size and quantity of defects by software design to predict the quality of the wafer. The second is the scanning electron microscope and X-ray energy dispersion analysis. The principle of secondary electron scattering is used to observe the morphology and defects of the semiconductor surface, and the characteristic lines of X-ray scattering are used to analyze the impurity and defect types, so as to judge various kinds. The cause of the defect. However, the former is limited by the fact that the scattered light is too weak relative to the background noise. Therefore, it is only possible to measure the surface of the wafer with 7 1358538 on the surface of the wafer; the latter can measure the lower surface of the semiconductor wafer. Defective components, but the instrument is expensive, and the sample needs to be placed in a vacuum environment. The time-consuming measurement procedure makes the technology difficult to use for on-line inspection. For the defect analysis technology of the lower surface of an optical semiconductor wafer, in general, in addition to the above optical scattering type, there are confocal microscopy and optical coherence tomography. Among them, the infrared light laser defect scattering detection technology overcomes the defects of the traditional optical scattering system background by adjusting the intensity, wavelength and polarization direction of different light sources to measure the defects of the surface and the lower surface of different semiconductor wafers. However, the resolution of the tomographic image that can be achieved by this method is insufficient, and the light receiving at a small angle causes the signal to be weak, which reduces the sensitivity of the measurement system. Another confocal microscope architecture can greatly improve the resolution of tomographic images and analyze sub-micron crystal defects. The sensitivity of the system is limited by the numerical aperture of the spatial filter, resulting in insufficient image contrast. Relatively speaking, the optical coherence tomography technique can greatly improve the signal-to-noise ratio by using the heterodyne detection method, and the longitudinal spatial resolution depends on the bandwidth of the light source, especially in the infrared light band, by increasing the light source. The bandwidth overcomes the problem of diffraction limits. Among them, the spectral scanning optical coherence tomography technique records the intensity of interference of each wavelength through spectral scanning, and then obtains the interference waveform in the time domain by Fourier transform. This technique of frequency domain analysis eliminates the need for mirror scanning of reference light and improves image capture speed. However, the wavelength-tunable laser source used in this method has an adjustable range of only about 100 to 200 nm, so its corresponding longitudinal resolution is not high; another improved method is called spectral segmentation parallel processing technique, Example 8 1358538, for example, "Sample inspection using interference and/or correlation of scattered superbroad radiation", which can directly expand the output spectrum of a wide-band laser in space to simultaneously interfere with the beam of each frequency component, and the corresponding number The detection of the benefits, such parallel processing technology can further eliminate the laser wavelength scanning 'improve the image capture speed. However, since the system needs to use a large number of filtering, consuming and splitting elements, the optical precision alignment requirements are very different, and the spacing of the pupil division and the lack of resolution may lead to waveform distortion after reconstruction, and technically Its difficulty; in addition, for example, China
民國發明專利申請帛94145579號「混合寬頻光源與相干光 源之光馳組」’藉由帶㈣波H對寬頻光源產生作用並與 相干光源相耦合’當應用於低同調斷層掃描儀時，可使掃 像具可魏度解析之功效；然而，目前的光學同調 描技術所採用的寬頻光源，主要仍為自光光源或超 :於座光一極體’其對應的縱向空間解析度大約數微米， —半導體晶圓下表面的奈米級缺陷仍無法檢測。此外， 的㈣均有固定的光譜，只適用特定的缺陷種類 無法涵蓋各種半導體元㈣需求，因此在實用上有 其限制。 【發明内容】 減i鏗於習知技術之缺失，本發明之目的在於提出一種 =晶圓下表面缺陷檢測裝置，基於光學同調斷層掃描 主’亚&配—寬頻光源’使該光源足以穿透半導體晶 、面，用以分析晶圓内部不連續的斷面位置及形狀， 9 1358538 以達成高靈敏度、高解析度之半導體晶圓下表面缺陷檢測 - 功能。 • 為達到上述目的，本發明提出一種半導體晶圓下表面 ' 缺陷檢測裝置，其包含一超寬頻光纖雷射、一光譜調制系 . 統、一光學同調斷層掃描系統及一處理單元；該超寬頻光 纖雷射可產生超寬頻雷射，該光譜調制系統係用以調制超 寬頻雷射輸出光譜；該光學同調斷層掃描系統包括至少一 ΐ光器、二物鏡及至少一光偵測器，超寬頻雷射透過分光 籲 °。及物鏡後產生散射光與參考光，並可由該光偵測器取得 政射光與參考光之干涉訊號；該處理單元則用以控制該檢 測裝置作動及進行訊號或資料處理。 、為使#審查委員對於本發明之結構目的和功效有更 進-步之了解與認同’茲配合圖示詳細說明如后。 【實施方式】 用^lit照^附之圖式來描述本發明為達成目的所信 、何手段與功效，而以下圖式所 助說明，以利眚逶杏禾。认4 千〜貝犯里两朝 於所列舉圖式。、讀解’但本案之技㈣段並不阳 月多閱第圖所示，本發明所提供之半導體s圓下# 面缺陷檢測裝-置，h a 土々 導圓下表 制系統20、一光學n包周;Γ風超寬頻光纖雷射10、一光勒 該處理單元掃描系統％以及—處理單天 動及進行㈣«料處理腦錢，心控職檢測裝置竹 1358538 =射路徑進入該光譜調制⑷〇，再透過反射鏡％ 改支运射路㈣域光學同輯層抑线3G;關於該光 暗调制糸統2G可採用之架構不限，如第三圖所示實施例， 邊光譜調制系統2G係由-極化分❹2卜—反 22、-拋物面鏡23及一空間光調制器24所組成，其中， 該極化分光器21與空間光調制器24形成一振幅調制系 統，而該反射式光柵22與抛物面鏡23則分別作為空間頻 譜展開f耦合之元件，前述該空間光調制器24係連接電腦 或處理單元（圖中未示出），該電腦或處理單元可採用或整 合於第-圖所示該處理單元4〇 ;藉此，使得該超寬頻光纖 雷射10產生之超寬頻雷射各個頻率成份可經由相位調制 而達到光譜平坦化之效果。關於光譜調制之目的在於，由 於超連續光譜導因於孤立子之分裂^“^加“^沁幻其 伴隨高階色散與受激拉曼散射（Stimulated如出时 Scattering，SRS)等效應所造成之頻譜強度分佈不均。利 用電腦產生之灰階影像控制該空間光調制器24每一像素 之相位延遲，即可調制各個頻率成份之濾波效果，如此不 但能使光譜平坦化並趨於高斯分佈，亦可針對不同半導體 材料及元件之缺陷吸收與散射特性，提供多樣化光譜。 請參閱第四圖所示光譜調制系統另一架構實施例，該 光譜調制系統20a包括兩極化分光器21a、一半波片25a、 兩反射式光栅22a、兩拋物面鏡23a及一空間光調制哭 24a ’由該兩極化分光器21 a、該半波片25a及該空間光調 制器24a形成一振幅調制系統，而該兩反射式光柵22a與 兩拋物面鏡23a則分別作為空間頻譜展開與耦合之元件； 1358538 可針對不同半導體元件調整參考光L2之色散補償，使得散 射光L1可與參考光L2之群速度色散始終保持匹配，維持 最佳縱向解析度，藉此，再搭配樣品5 0之二維掃描，即可 取得該樣品50之三維空間斷層影像。 再者，本發明之另一特點在於採用平衡偵測系統 (dual-balanceddetection)，如第一圖所示，該平衡偵測 系統係使用了兩個光偵測器35a、35b，分別連接該極化分 光器.32及分光器33，並搭配一個減法電路37，再搭配相 關之放大濾波器371，可以消除因雷射強度隨時間變化所 引入的雜訊，進而提高訊噪比，相對提高量測系統的靈敏 度。 根據上述各實施例，可歸納出本發明具有以下優點： 一、 超寬頻光纖雷射不但能取代傳統白光或低同調性光源 之同調長度不足的缺點，提高光學同調斷層掃描系統 的縱向解析度外；亦由於其波長涵蓋紅外光的範圍， 可提高各種半導體材料的穿透深度。 二、 光譜調制系統以電腦產生的灰階影像來調制光譜，不 但能將超寬頻光纖雷射的光譜平坦化並趨於高斯分 佈，亦可針對不同半導體材料及元件之缺陷吸收與散 射特性，提供多樣化的光譜。 三、 光學同調斷層掃描系統所引入的色散補償元件與平衡 偵測系統，可以有效提升量測系統的縱向解析度與靈 敏度，適合用於半導體内部更細微缺陷結構的檢測。 四、 超短脈衝光源所具有的高功率、低熱量等特性，可避 免半導體元件的熱效應，提高系統的掃描速度，符合 14 1358538 半導體製程中線上即時檢測之需求。 綜上所述，本發明所提供之半導體晶圓下表面缺陷檢 測裝置，基於光學同調斷層掃描的架構，並搭配一寬頻光 源，使該光源足以穿透半導體晶圓下表面，用以分析晶圓 内部不連續的斷面位置及形狀，可達成高靈敏度、高解析 度之半導體晶圓下表面缺陷檢測功能，此外，本發明可依 使用狀況而做各種變化，例如光纖雷射之波長與頻寬，超 連續光譜產生所使用之光纖，光譜調制系統所使用之元件 等。 惟以上所述者，僅為本發明之實施例而已，當不能以 之限定本發明所實施之範圍。即大凡依本發明申請專利範 圍所作之均等變化與修飾，皆應仍屬於本發明專利涵蓋之 範圍内，謹請貴審查委員明鑑，並祈惠准，是所至禱。 【圖式簡單說明】 第一圖係本發明實施例之架構示意圖。 第二圖係本發明超寬頻光纖雷射另一實施例之架構示 意圖。 第三圖係本發明光譜調制系統之一實施例之架構示意 圖。 第四圖係本發明光譜調制系統另一實施例之架構示意 圖。 【主要元件符號說明】The invention patent application No. 94145579 of the Republic of China "mixing a broadband source and a coherent light source" "by using a (four) wave H to act on a broadband source and coupling it with a coherent source" can be used when applied to a low coherence tomography scanner Sweeping images have the effect of Weidu analysis; however, the current wide-frequency light source used in optical and modulating techniques is mainly self-light source or super: in the photo-polar body's corresponding longitudinal spatial resolution is about several micrometers. — Nano-level defects on the underside of the semiconductor wafer are still undetectable. In addition, (4) has a fixed spectrum, and only a specific defect type cannot cover various semiconductor elements (4), so there are practical limitations. SUMMARY OF THE INVENTION The present invention aims to provide a = wafer lower surface defect detecting device based on optical coherence tomography scanning of the main 'sub & wide-frequency source' to make the light source sufficient to wear Through the semiconductor crystal and surface, to analyze the discontinuous cross-section position and shape inside the wafer, 9 1358538 to achieve high sensitivity, high resolution semiconductor wafer lower surface defect detection - function. In order to achieve the above object, the present invention provides a semiconductor wafer lower surface 'defect detecting device comprising an ultra-wideband fiber laser, a spectral modulation system, an optical coherence tomography system and a processing unit; the ultra-wideband The fiber laser can generate an ultra-wideband laser, and the spectral modulation system is used to modulate an ultra-wideband laser output spectrum; the optical coherence tomography system includes at least one chopper, two objective lenses, and at least one photodetector, ultra-wideband The laser passes through the split light. The objective lens generates scattered light and reference light, and the optical detector can obtain an interference signal between the political light and the reference light; the processing unit controls the operation of the detecting device and performs signal or data processing. In order to make the # review committee have a more advanced understanding and recognition of the structural purpose and efficacy of the present invention, the detailed description of the figure is as follows. [Embodiment] The drawings of the present invention are used to describe the meaning, the means and the effects of the present invention for achieving the purpose, and the following figures help to illustrate the benefits of the apricot. Recognize the pattern of the four thousand ~ Bei dynasty. Read the solution, but the technique of the case (4) is not as shown in the figure. The semiconductor s round under the invention is provided with the surface defect detection device, and the ha earthworm guide circle system is 20 Optical n-package week; Hurricane ultra-wideband fiber laser 10, a light-learning unit scanning system% and - processing single-day movement and carry out (four) «material processing brain money, heart control job detection device bamboo 1358538 = shooting path into the Spectral modulation (4) 〇, and then through the mirror% change the branching path (4) domain optical coherent layer suppression line 3G; the structure of the light and dark modulation system 2G can be used, as shown in the third figure, the side The spectral modulation system 2G is composed of a polarization bin 2 - a 22, a parabolic mirror 23 and a spatial light modulator 24, wherein the polarization beam splitter 21 and the spatial light modulator 24 form an amplitude modulation system. The reflective grating 22 and the parabolic mirror 23 respectively serve as elements for spatially uncoupling f-coupling, and the spatial light modulator 24 is connected to a computer or a processing unit (not shown), and the computer or processing unit can adopt or Integrated into the processing unit 4 shown in the figure - The ultra-wideband laser generated by the ultra-wideband fiber laser 10 can achieve spectral flattening effect through phase modulation. The purpose of spectral modulation is that super-continuous spectroscopy is caused by the splitting of solitons, which is caused by effects such as high-order dispersion and stimulated Raman scattering (Stimulated Scattering, SRS). The intensity of the spectrum is unevenly distributed. By using the gray-scale image generated by the computer to control the phase delay of each pixel of the spatial light modulator 24, the filtering effect of each frequency component can be modulated, so that the spectrum can be flattened and tend to be Gaussian, and can also be used for different semiconductor materials. And the defect absorption and scattering properties of the components provide a diverse spectrum. Referring to another architectural embodiment of the spectral modulation system shown in FIG. 4, the spectral modulation system 20a includes a dual polarization beam splitter 21a, a half wave plate 25a, a two reflection grating 22a, two parabolic mirrors 23a, and a spatial light modulation cry 24a. The amplitude modulation system is formed by the polarization beam splitter 21a, the half wave plate 25a and the spatial light modulator 24a, and the two reflection gratings 22a and the two parabolic mirrors 23a are respectively used as spatial spectrum expansion and coupling components. 1358538 The dispersion compensation of the reference light L2 can be adjusted for different semiconductor components, so that the scattered light L1 can always match the group velocity dispersion of the reference light L2, maintaining the optimal longitudinal resolution, thereby matching the sample 50 with the two-dimensional Scanning, a three-dimensional spatial tomographic image of the sample 50 can be obtained. Furthermore, another feature of the present invention is that a dual-balanced detection system is used. As shown in the first figure, the balance detection system uses two photodetectors 35a and 35b to respectively connect the poles. The splitter .32 and the splitter 33, together with a subtraction circuit 37, and the associated amplification filter 371, can eliminate the noise introduced by the laser intensity with time, thereby improving the signal-to-noise ratio and the relative increase. Measure the sensitivity of the system. According to the above embodiments, the present invention has the following advantages: 1. The ultra-wideband fiber laser can not only replace the shortcomings of the conventional white light or the low-coherence light source, but also improve the longitudinal resolution of the optical coherence tomography system. Also, because its wavelength covers the range of infrared light, the penetration depth of various semiconductor materials can be improved. Second, the spectral modulation system modulates the spectrum with computer-generated gray-scale images, which not only flattens the spectrum of the ultra-wideband fiber laser and tends to Gaussian distribution, but also provides the absorption and scattering characteristics of defects of different semiconductor materials and components. A diverse spectrum. 3. The dispersion compensating element and balance detection system introduced by the optical coherence tomography system can effectively improve the longitudinal resolution and sensitivity of the measurement system, and is suitable for the detection of finer defect structures in semiconductors. Fourth, the ultra-short pulse light source has high power, low heat and other characteristics, which can avoid the thermal effect of the semiconductor components, improve the scanning speed of the system, and meet the requirements of on-line real-time detection in the semiconductor process of 14 1358538. In summary, the semiconductor wafer lower surface defect detecting device provided by the present invention is based on an optical coherence tomography structure and is matched with a broadband source such that the light source is sufficient to penetrate the lower surface of the semiconductor wafer for analyzing the wafer. The discontinuous cross-sectional position and shape of the internality can achieve high sensitivity and high resolution semiconductor wafer lower surface defect detection function. In addition, the present invention can be variously changed according to the use condition, such as the wavelength and bandwidth of the fiber laser. The supercontinuum spectrum produces the fiber used, the components used in the spectral modulation system, and the like. However, the above description is only for the embodiments of the present invention, and the scope of the invention is not limited thereto. That is to say, the equivalent changes and modifications made by the applicant in accordance with the scope of application of the present invention should still fall within the scope covered by the patent of the present invention. I would like to ask your reviewing committee to give a clear understanding and pray for it. BRIEF DESCRIPTION OF THE DRAWINGS The first figure is a schematic diagram of the architecture of an embodiment of the present invention. The second drawing is an architectural illustration of another embodiment of the ultra-wideband fiber laser of the present invention. The third figure is a schematic illustration of one embodiment of an embodiment of a spectral modulation system of the present invention. Figure 4 is a schematic illustration of another embodiment of a spectral modulation system of the present invention. [Main component symbol description]