TWI553693B

TWI553693B - An inductance coil and inductively coupled plasma processing device

Info

Publication number: TWI553693B
Application number: TW103139485A
Authority: TW
Inventors: Jie Liang
Priority date: 2013-11-15
Filing date: 2014-11-14
Publication date: 2016-10-11
Also published as: TW201528324A; CN104637767B; CN104637767A

Description

一種電感線圈及電感耦合等離子體處理裝置Inductor coil and inductively coupled plasma processing device

本發明涉及等離子處理設備，特別涉及一種等離子體處理裝置的電感耦合線圈。The present invention relates to a plasma processing apparatus, and more particularly to an inductive coupling coil of a plasma processing apparatus.

近年來，隨著半導體製造工藝的發展，對元件的集成度和性能要求越來越高，等離子體技術（Plasma Technology）得到了極為廣泛的應用。等離子體技術通過在等離子體處理裝置的反應腔室內通入反應氣體並引入電子流，利用射頻電場使電子加速，與反應氣體發生碰撞使反應氣體發生電離而等離子體，產生的等離子體可被用於各種半導體製造工藝，例如沉積工藝(如化學氣相沉積)、刻蝕工藝(如乾式蝕刻)等。In recent years, with the development of semiconductor manufacturing processes, the integration and performance requirements of components have become higher and higher, and Plasma Technology has been widely used. Plasma technology uses a radio frequency electric field to accelerate electrons by introducing a reaction gas into a reaction chamber of a plasma processing apparatus and introducing a flow of electrons. The reaction gas collides with the reaction gas to ionize the plasma, and the generated plasma can be used. In various semiconductor manufacturing processes, such as deposition processes (such as chemical vapor deposition), etching processes (such as dry etching), and the like.

等離子體處理設備包括常見的電容耦合型和電感耦合型等離子體處理裝置。在需要較高等離子濃度的應用場合，電感耦合型等離子處理裝置是主流，習知技術CN2907173Y和JP2008251830中傳統的電感耦合等離子反應腔包括一個腔體，腔體內下部設置有基座，基座上可以放置待處理的晶圓。反應腔頂部為絕緣材料窗，通常絕緣材料窗是由石英等陶瓷材料製成。絕緣材料窗上方設置有連接到射頻電源的射頻線圈，射頻線圈和絕緣材料窗之間通常還設置有法拉第屏蔽板。這些線圈作為天線產生射頻電磁場，其中電磁場中只有部分磁場能夠穿過法拉第屏蔽板進入反應腔內電離反應氣體形成高濃度等離子體，大部分電場均被法拉第屏蔽板屏蔽在反應腔外。如CN2907173Y說明書第五頁第二段所述，法拉第屏蔽板能夠屏蔽電感線圈向反應腔內的電容耦合，進而減少等離子對絕緣材料層的轟擊，也就減少轟擊產生的顆粒物對待處理基片的污染也提高了絕緣窗的使用壽命和可靠性。Plasma processing equipment includes conventional capacitive coupling and inductively coupled plasma processing devices. In the case of applications requiring a higher plasma concentration, an inductively coupled plasma processing apparatus is the mainstream. The conventional inductively coupled plasma reaction chamber of the prior art CN2907173Y and JP2008251830 includes a cavity, and a pedestal is disposed on the lower portion of the cavity. Place the wafer to be processed. The top of the reaction chamber is an insulating material window, and usually the insulating material window is made of a ceramic material such as quartz. A radio frequency coil connected to the RF power source is disposed above the insulating material window, and a Faraday shield plate is usually disposed between the RF coil and the insulating material window. These coils act as antennas to generate radio frequency electromagnetic fields, in which only part of the electromagnetic field can pass through the Faraday shield plate into the reaction chamber to ionize the reaction gas to form a high concentration plasma, and most of the electric field is shielded by the Faraday shield plate outside the reaction chamber. As described in the second paragraph of the fifth page of CN2907173Y, the Faraday shield can shield the capacitive coupling of the inductor into the reaction chamber, thereby reducing the bombardment of the plasma on the insulating material layer, and reducing the contamination of the particles to be treated by the bombardment. It also improves the service life and reliability of the insulated window.

但是這樣的反應腔結構也會帶來嚴重的問題：由於法拉第屏蔽板的存在，感應線圈上產生的電場無法進入反應腔，只有部分磁場能進入，在點燃等離子體時會造成等離子體無法可靠點燃，需要額外的裝置或者更高能功率輸入射頻線圈才能保證等離子點燃。等離子在點燃前後阻抗是會急劇變化的，從一個高阻抗的物質瞬間變成導體，而調節輸入射頻功率的匹配器需要機械結構來調節阻抗匹配，只能達到秒級，所以匹配器的反應速度遠遠趕不是點燃瞬間的阻抗變化情況，因此為了點燃等離子而施加的額外功率會錯誤的施加到反應腔中一段時間，在這段時間中過高的功率會對反應腔內的部件或者待加工的晶圓造成不利的影響。同時由於法拉第屏蔽板的存在造成只有部分射頻磁場能夠進入反應腔中激發反應氣體形成等離子體，部分射頻能量被浪費了，大幅度降低了電能的使用效率。所以業界需要一種既能夠減小感應線圈對反應腔的電容耦合同時又不會降低感應線圈中磁場能量饋入反應腔的效率，還能實現穩定的點燃等離子的技術方案。However, such a reaction chamber structure also poses a serious problem: due to the presence of the Faraday shield, the electric field generated on the induction coil cannot enter the reaction chamber, and only part of the magnetic field can enter, which causes the plasma to be reliably ignited when the plasma is ignited. Additional equipment or higher power input RF coils are required to ensure plasma ignition. The impedance of the plasma changes sharply before and after ignition, from a high-impedance material to a conductor, and the matcher that regulates the input RF power requires a mechanical structure to adjust the impedance matching, which can only reach the second order, so the matcher's response speed is far. Far-reaching is not a momentary change in impedance, so the extra power applied to ignite the plasma is erroneously applied to the reaction chamber for a period of time during which time too high power will be placed on the components in the reaction chamber or to be processed. Wafers have an adverse effect. At the same time, due to the presence of the Faraday shield, only part of the RF magnetic field can enter the reaction chamber to excite the reaction gas to form a plasma, and part of the RF energy is wasted, which greatly reduces the use efficiency of the electric energy. Therefore, the industry needs a technical solution that can reduce the capacitive coupling of the induction coil to the reaction chamber without reducing the efficiency of the magnetic field energy feeding into the reaction chamber in the induction coil, and achieve stable ignition of the plasma.

本發明的主要目的在於克服習知技術的缺陷，提供一種能夠減小感應線圈對反應腔的電容耦合同時又不會降低感應線圈中磁場能量饋入反應腔的效率的技術方案。The main object of the present invention is to overcome the deficiencies of the prior art and to provide a technical solution capable of reducing the capacitive coupling of the induction coil to the reaction chamber without reducing the efficiency of the magnetic field energy feeding into the reaction chamber in the induction coil.

本發明提供一種電感耦合等離子體處理裝置，包括：一個氣密的反應腔，反應腔包括反應腔側壁和頂部的絕緣材料窗，反應腔內其包括一個用於支撐待處理基片的基座；絕緣材料窗上方固定有一個電感線圈，所述電感線圈連接到一個射頻電源；其特徵在於：所述電感線圈包括第一線圈、第三線圈和一個中間線圈，所述第一線圈包括一個第一端連接到所述射頻電源，還包括一個第二端連接到中間線圈第一端；中間線圈還包括一個第二端連接到所述第三線圈第一端；第三線圈還包括一個第二端連接到接地端，其中第一和第三線圈互相平行且位於中間線圈上方，第一和第三線圈的投影在中間線圈上。絕緣材料窗上方還可以包括第二電感線圈圍繞在所述電感線圈外或者在所述電感線圈內。The present invention provides an inductively coupled plasma processing apparatus comprising: a gas-tight reaction chamber comprising a sidewall of the reaction chamber and a top insulating material window, the reaction chamber including a susceptor for supporting the substrate to be processed; An inductor coil is fixed above the insulating material window, and the inductor coil is connected to an RF power source; wherein the inductor coil comprises a first coil, a third coil and an intermediate coil, and the first coil comprises a first The end is connected to the RF power source, and further includes a second end connected to the first end of the intermediate coil; the intermediate coil further comprising a second end connected to the first end of the third coil; the third coil further comprising a second end Connected to the ground terminal, wherein the first and third coils are parallel to each other and above the intermediate coil, and the projections of the first and third coils are on the intermediate coil. The insulating material window may further include a second inductor coil surrounding the inductor coil or within the inductor coil.

優選的，所述第三線圈的第二端通過一個調平衡電路連接到所述接地端。所述調節所述調平衡電路使所述線圈上形成駐波，所述駐波的電壓分佈是第一線圈上任意一點的與第三線圈上相對應位置點的電壓極性相反幅度相同而且所述中間線圈的電壓幅度小於第一和第三線圈的電壓幅度。Preferably, the second end of the third coil is connected to the ground through a balancing circuit. Adjusting the balance circuit to form a standing wave on the coil, the voltage distribution of the standing wave is the same as the voltage polarity of the point on the first coil and the corresponding position on the third coil is opposite The voltage amplitude of the intermediate coil is less than the voltage amplitude of the first and third coils.

其中第一線圈的第二端通過第一連接部（12）連接到下方的中間線圈，中間線圈第二端通過通過第二連接部（23）連接到上方的第三線圈，中間線圈上的第一連接部和第二連接部之間還包括一個開口使第一連接部和第二連接部互相隔離。本發明所述第一線圈、中間線圈或第三線圈的長度和小於射頻電源信號3倍半波長，優選的小於等於於射頻電源信號半波長。Wherein the second end of the first coil is connected to the lower intermediate coil through the first connecting portion (12), and the second end of the intermediate coil is connected to the upper third coil through the second connecting portion (23), the first coil on the middle coil An opening is further included between the connecting portion and the second connecting portion to isolate the first connecting portion and the second connecting portion from each other. The length of the first coil, the intermediate coil or the third coil of the present invention is less than three and a half wavelengths of the radio frequency power signal, preferably less than or equal to half the wavelength of the radio frequency power signal.

本發明還提供一種電感耦合等離子體處理裝置的第二實施例，包括：一個氣密的反應腔，反應腔包括反應腔側壁和頂部的絕緣材料窗，反應腔內其包括一個用於支撐待處理基片的基座；絕緣材料窗上方固定有一個自屏蔽電感線圈，其特徵在於：所述自屏蔽電感線圈包括相互串聯的第一線圈、中間線圈和第三線圈，其中中間線圈位於第一線圈和第三線圈下方且寬度大於第一線圈或第三線圈的寬度，一個射頻電源施加射頻電場到所述自屏蔽電感線圈的第一線圈輸入端和第三線圈輸出端之間，其中所述第三線圈輸出端還連接有一個調平衡電路調節所述調平衡電路使所述自屏蔽電感線圈上形成駐波，所述中間線圈的電壓幅度小於第一線圈或第三線圈上的電壓幅度。所述射頻電源的頻率大於13Mhz，如13.56MHz、27MHz等。The present invention also provides a second embodiment of an inductively coupled plasma processing apparatus comprising: a gas-tight reaction chamber including a sidewall of the reaction chamber and a window of insulating material at the top, the reaction chamber including a support for processing a pedestal of the substrate; a self-shielding inductor is fixed above the insulating material window, wherein the self-shielded inductor comprises a first coil, an intermediate coil and a third coil connected in series, wherein the intermediate coil is located at the first coil And a width below the third coil and having a width greater than a width of the first coil or the third coil, an RF power source applying a radio frequency electric field between the first coil input end and the third coil output end of the self-shielding inductor coil, wherein the The three-coil output end is further connected with a balance adjusting circuit for adjusting the balance adjusting circuit to form a standing wave on the self-shielding inductor coil, and the voltage amplitude of the intermediate coil is smaller than the voltage amplitude on the first coil or the third coil. The frequency of the radio frequency power source is greater than 13 Mhz, such as 13.56 MHz, 27 MHz, and the like.

可選的，所述第一和第三線圈向下投影位於中間線圈上，使中間線圈屏蔽第一線圈和第三線圈上的電壓形成的電場。Optionally, the first and third coils are projected downward on the intermediate coil such that the intermediate coil shields an electric field formed by the voltages on the first coil and the third coil.

可選的，還包括一個法拉第屏蔽板位於所述自屏蔽線圈和絕緣材料窗之間，所述第一和第三線圈的向下投影位於所述法拉第屏蔽板上。Optionally, a Faraday shield is disposed between the self-shielding coil and the insulating material window, and a downward projection of the first and third coils is located on the Faraday shield.

可選的，絕緣材料窗上方還包括第二感應線圈圍繞在所述自屏蔽線圈外或者在所述自屏蔽線圈內。本發明還提供一種用於電感耦合等離子體處理裝置的電感線圈，包括：第一線圈、第三線圈和一個中間線圈，第一線圈和第三線圈位於所述中間線圈上方；所述第一線圈包括一個第一端，和一個第二端，所述第一線圈的第二端連接到下方中間線圈第一端，中間線圈還包括一個第二端連接到所述第三線圈第一端，第三線圈還包括一個第二端，中間線圈寬度大於第一或第三線圈，且第一和第三線圈向下的投影在中間線圈上。其中第一線圈和第三線圈之間存在間隙，且第一線圈圍繞第三線圈。其中所述第一線圈和第二線圈之間的間隙位於所述中間線圈的垂直上方。Optionally, a second induction coil is included above the insulating material window to surround the self-shielding coil or within the self-shielding coil. The present invention also provides an inductor for an inductively coupled plasma processing apparatus, comprising: a first coil, a third coil, and an intermediate coil, the first coil and the third coil being located above the intermediate coil; the first coil a first end, and a second end, the second end of the first coil is connected to the first end of the lower intermediate coil, and the intermediate coil further includes a second end connected to the first end of the third coil, The three coils also include a second end, the intermediate coil width being greater than the first or third coil, and the first and third coils being projected downwardly on the intermediate coil. There is a gap between the first coil and the third coil, and the first coil surrounds the third coil. Wherein a gap between the first coil and the second coil is located vertically above the intermediate coil.

其中所述中間線圈構成一個閉合回路，所述第一線圈和第三線圈與中間線圈具有相同的形狀。Wherein the intermediate coil constitutes a closed loop, and the first coil and the third coil have the same shape as the intermediate coil.

其中所述第一線圈通過一個第一連接部連接到中間線圈第一端，第三線圈通過一個第二連接部連接到中間線圈第二端，中間線圈的第一端和第二端之間存在一個互相隔離的間隙。Wherein the first coil is connected to the first end of the intermediate coil through a first connecting portion, and the third coil is connected to the second end of the intermediate coil through a second connecting portion, and the first end and the second end of the intermediate coil are present A gap that is isolated from each other.

為使本發明的內容更加清楚易懂，以下結合說明書附圖，對本發明的內容作進一步說明。當然本發明並不局限於該具體實施例，本領域中具有通常知識者所熟知的一般替換也涵蓋在本發明的保護範圍內。In order to make the content of the present invention clearer and easier to understand, the contents of the present invention will be further described below in conjunction with the accompanying drawings. It is a matter of course that the invention is not limited to the specific embodiment, and that the general substitutions well known to those skilled in the art are also encompassed within the scope of the invention.

圖1~圖5顯示了本發明的等離子處理裝置的多個實施方式。應該理解，本發明中的等離子體處理裝置可以為等離子體刻蝕、等離子體物理汽相沉積、等離子體化學氣相沉積、等離子體表面清洗等裝置，等離子體處理裝置僅僅是示例性的，其可以包括更少或更多的組成元件，或該組成元件的安排可能與圖中所示相同或不同。1 to 5 show various embodiments of the plasma processing apparatus of the present invention. It should be understood that the plasma processing apparatus in the present invention may be a device such as plasma etching, plasma physical vapor deposition, plasma chemical vapor deposition, plasma surface cleaning, etc., and the plasma processing apparatus is merely exemplary, and Fewer or more constituent elements may be included, or the arrangement of the constituent elements may be the same or different from that shown in the figures.

實施例1Example 1

請參見圖1，其所示為本發明電感線圈結構示意圖。本發明電感線圈包括第一線圈10，通過射頻輸入連接部100連接到射頻電源或其它外部電路。本發明電感線圈還包括一個中間線圈20位於第一線圈10下方，中間線圈10呈平板型，其寬度大於第一線圈10。第一線圈10構成一個圓環，一端為連接部100，另一端通過一個向下的第一中間連接部12連接到中間線圈20。中間線圈10構成一個圓環，一端為第一連接部12，另一端為第二中間連接部32。第二中間連接部32從中間線圈20表面向上延伸連接到一個第三線圈30。第三線圈30呈環型，第一端為第二中間連接部32，另一端通過射頻輸出連接部300連接到第二射頻電源或者其它外部電路。同時參考圖2所示的本發明射頻線圈俯視圖，圖中第一線圈10和第三線圈30位於中間線圈20上方，且第一線圈10和第三線圈30的投影位於中間線圈20內。中間線圈20在第一中間連接部12和第二中間連接部32之間還設置有一個開口21，通過該開口21使第一中間連接部12和第二中間連接部32之間互相隔離。本發明第一線圈10、中間線圈20、第三線圈30具有相同的沿展方向（順時針或逆時針），在施加射頻電源到第一線圈10輸入端時在線圈上產生同方向的電流。Please refer to FIG. 1, which is a schematic structural view of an inductor coil according to the present invention. The inductive coil of the present invention includes a first coil 10 that is connected to a radio frequency power source or other external circuit through a radio frequency input connection 100. The inductor coil of the present invention further includes an intermediate coil 20 located below the first coil 10, and the intermediate coil 10 is of a flat type having a larger width than the first coil 10. The first coil 10 constitutes a circular ring, one end being the connecting portion 100, and the other end being connected to the intermediate coil 20 via a downward first intermediate connecting portion 12. The intermediate coil 10 constitutes a ring having a first connecting portion 12 at one end and a second intermediate connecting portion 32 at the other end. The second intermediate connecting portion 32 extends upward from the surface of the intermediate coil 20 to a third coil 30. The third coil 30 has a ring shape, the first end is a second intermediate connection portion 32, and the other end is connected to a second RF power source or other external circuit through the RF output connection portion 300. Referring to the top view of the RF coil of the present invention shown in FIG. 2, the first coil 10 and the third coil 30 are located above the intermediate coil 20, and the projections of the first coil 10 and the third coil 30 are located in the intermediate coil 20. The intermediate coil 20 is further provided with an opening 21 between the first intermediate connecting portion 12 and the second intermediate connecting portion 32, through which the first intermediate connecting portion 12 and the second intermediate connecting portion 32 are isolated from each other. The first coil 10, the intermediate coil 20, and the third coil 30 of the present invention have the same spanwise direction (clockwise or counterclockwise), and generate a current in the same direction on the coil when a radio frequency power source is applied to the input end of the first coil 10.

圖3所示為本發明在線圈不同長度位置處的電壓幅度分佈示意圖。在兩個同頻率射頻電源分別通入射頻輸入連接部100和連接部300或者一個射頻電源連接到連接部100，在連接部300到接地端之間設置一個調節電路控制反射的射頻功率，這兩種方法均會在本發明第一線圈10、中間線圈20、第三線圈30上形成駐波。駐波的波長與射頻電源的頻率有關，在等離子刻蝕領域典型的射頻電源頻率為13Mhz，對應的波長為23多米，其它如27Mhz，或者60Mhz對應的波長為小於10米。下面以射頻電源的頻率是13Mhz為例來說明本發明的線圈結構，第一線圈10，中間線圈20和第三線圈30的總長度小於等於半波長也就是11.5米，此時通過調節線圈平衡可以獲得如圖3所示的駐波分佈。第一線圈10上的電壓幅度分佈V10是從最高電壓幅度Va逐漸降低到中間電壓，中間線圈上的電壓V20為正向的中間幅度電壓到反向的中間幅度電壓，第三線圈30上的電壓幅度分佈V30為反向的中間幅度電壓到反向的高電壓幅度-Va。在線圈的任意位置處的實際電壓值是以上述曲線為電壓幅值的高頻交流電壓，比如在連接部100處的電壓為輸入電壓的最高幅度，並以13Mhz的頻率在Va和-Va之間交替變換。第一中間連接部12的電壓是在Va/2和-Va/2之間變換，同時流過的電流為I12,同樣的流過第二連接部32的電流為I32。Figure 3 is a schematic view showing the voltage amplitude distribution at different lengths of the coil of the present invention. Two RF power sources of the same frequency are respectively connected to the RF input connection portion 100 and the connection portion 300 or a RF power source is connected to the connection portion 100, and an adjustment circuit is disposed between the connection portion 300 and the ground terminal to control the reflected RF power. Each method forms a standing wave on the first coil 10, the intermediate coil 20, and the third coil 30 of the present invention. The wavelength of the standing wave is related to the frequency of the RF power supply. In the plasma etching field, the typical RF power frequency is 13Mhz, the corresponding wavelength is more than 23 meters, and other wavelengths such as 27Mhz or 60Mhz are less than 10 meters. In the following, the frequency of the RF power source is 13 Mhz as an example to illustrate the coil structure of the present invention. The total length of the first coil 10, the intermediate coil 20 and the third coil 30 is less than or equal to half a wavelength, that is, 11.5 meters. A standing wave distribution as shown in FIG. 3 is obtained. The voltage amplitude distribution V10 on the first coil 10 is gradually decreased from the highest voltage amplitude Va to the intermediate voltage, and the voltage V20 on the intermediate coil is a positive intermediate amplitude voltage to a reverse intermediate amplitude voltage, and the voltage on the third coil 30 The amplitude distribution V30 is the reverse intermediate amplitude voltage to the reverse high voltage amplitude -Va. The actual voltage value at any position of the coil is a high frequency alternating voltage with the above-mentioned curve as the voltage amplitude, for example, the voltage at the connection portion 100 is the highest amplitude of the input voltage, and at frequencies of 13 Mhz at Va and -Va Alternate change. The voltage of the first intermediate connection portion 12 is changed between Va/2 and -Va/2, while the current flowing through is 12, and the current flowing through the second connection portion 32 is I32.

從圖3中所示的駐波電壓幅度可知，在第一線圈10和第三線圈30對應位置處，比如第一線圈10任意一點X1離第三線圈30上最近的點X3上的電壓正好是方向相反電壓幅度相同的，所以這兩個點就形成了偶極電場，對外部的電場強度比如下方的反應腔內施加的電場就是這兩個點之間的合成電場。由於這兩點的電壓極性相反幅度相同，所以這個合成電場非常小，接近與零。由於整個線圈的第一線圈10和第三線圈30上包括無數個這樣一一對應的X1、X3點，所以這兩個線圈形成的綜合的電場也不會對反應腔內產生很大的影響。這種偶極電場可以明顯的減弱遠端的合成電場，但是對於第一線圈10和第三線圈30之間的電場減弱不明顯，比如對於第一線圈10、第三線圈30之間正下方反應腔頂部的電場。設置在第一線圈10、第三線圈30下方的中間線圈20由於具有足夠的寬度能夠遮擋在第一線圈10、第三線圈30和下方絕緣材料窗之間，所以能夠屏蔽上方第一線圈10和第三線圈30之間產生的合成電場，進一步減小線圈整體對下方電場的影響。It can be seen from the amplitude of the standing wave voltage shown in FIG. 3 that at the corresponding position of the first coil 10 and the third coil 30, for example, the voltage at any point X3 of the first coil 10 at the closest point X3 from the third coil 30 is exactly The opposite direction voltage amplitudes are the same, so these two points form a dipole electric field, and the external electric field strength, such as the electric field applied in the lower reaction chamber, is the combined electric field between these two points. Since the voltage polarities of these two points are opposite in magnitude, this synthetic electric field is very small, close to zero. Since the first coil 10 and the third coil 30 of the entire coil include an infinite number of such one-to-one corresponding points X1 and X3, the integrated electric field formed by the two coils does not greatly affect the inside of the reaction chamber. Such a dipole electric field can significantly attenuate the combined electric field at the distal end, but the electric field attenuation between the first coil 10 and the third coil 30 is not significant, such as a reaction directly between the first coil 10 and the third coil 30. The electric field at the top of the cavity. The intermediate coil 20 disposed under the first coil 10 and the third coil 30 can block the first coil 10 and the upper first coil 10 by having a sufficient width to block between the first coil 10, the third coil 30, and the lower insulating material window. The resultant electric field generated between the third coils 30 further reduces the effect of the overall coil on the lower electric field.

本發明線圈的第一線圈10和第三線圈30產生的電場在正下方基本被屏蔽，而遠端的合成電場幅度非常小可以忽略不計，只有下方中間線圈20本身產生的電場無法屏蔽。由於本發明線圈的特殊設計和調整使得中間線圈20上的電壓駐波V20的幅度很小，最大也不到最高幅值Va的一半，大部分區域電壓接近於零所以也不會對下方反應腔造成較大影響。通過本發明線圈的設計大幅度減小了感應線圈對反應腔內等離子體的電場耦合效果，所以傳統的法拉第屏蔽板可以省略或者簡化，比如可以選擇導體板上具有更大面積的通孔或者槽，容許更多磁場穿透入反應腔，同時也不會造成反應腔頂部絕緣材料窗的過度損耗。The electric field generated by the first coil 10 and the third coil 30 of the coil of the present invention is substantially shielded directly below, and the amplitude of the combined electric field at the distal end is negligibly small, and only the electric field generated by the lower intermediate coil 20 itself cannot be shielded. Due to the special design and adjustment of the coil of the present invention, the amplitude of the voltage standing wave V20 on the intermediate coil 20 is small, and the maximum is not half of the maximum amplitude Va. Most of the regional voltage is close to zero, so the lower reaction chamber is not Causes a greater impact. The design of the coil of the present invention greatly reduces the electric field coupling effect of the induction coil on the plasma in the reaction chamber, so the conventional Faraday shield can be omitted or simplified. For example, a through hole or a groove having a larger area on the conductor plate can be selected. Allows more magnetic fields to penetrate into the reaction chamber without causing excessive loss of the insulating material window at the top of the reaction chamber.

如圖4所示為本發明線圈在A處的截面圖，圖4a為圖1、圖2所示的本發明第一實施例的截面圖，圖4b和圖4c為本發明第二第三實施例的截面圖，圖4b中第一線圈10位置高於第三線圈30，由於兩個線圈間的電壓關係仍然是極性相反幅度相同所以能夠形成偶極電場，所以仍然能夠實現本發明目的。圖4c中與圖4b類似，第三線圈30與第一線圈10不僅高度不同而且存在部分交疊，同樣由於這樣的線圈排布仍然能夠形成偶極電場所以仍能實現本發明目的，當然由於兩個線圈離反應腔頂部距離不同所以離反應腔頂部較近的第一線圈10會起更大作用，所以線圈產生耦合到反應腔的電場較第一實施例略大，但是仍然遠小於習知技術中傳統線圈耦合到反應腔的電場數值。4 is a cross-sectional view of the coil of the present invention at A, FIG. 4a is a cross-sectional view of the first embodiment of the present invention shown in FIGS. 1 and 2, and FIGS. 4b and 4c are second and third embodiments of the present invention. In the cross-sectional view of the example, the position of the first coil 10 in Fig. 4b is higher than that of the third coil 30, and since the voltage relationship between the two coils is still the same in opposite polarity, a dipole electric field can be formed, so that the object of the present invention can still be achieved. In FIG. 4c, similar to FIG. 4b, the third coil 30 and the first coil 10 are not only different in height but also partially overlapped, and since the coil arrangement can still form a dipole electric field, the object of the present invention can still be achieved, of course, The coils are different from the top of the reaction chamber, so the first coil 10 closer to the top of the reaction chamber will play a greater role, so the electric field coupled to the reaction chamber is slightly larger than that of the first embodiment, but still much smaller than the conventional technology. The electric field value of a conventional coil coupled to a reaction chamber.

中間線圈20的寬度大於第一線圈10、第三線圈30中任意一個的寬度，或者大於兩者的和，這樣能夠更有效的屏蔽兩者產生的電場。根據本發明原理，第一線圈10、第三線圈30之間的電壓差距很大，而且兩者之間距離很近，所以兩者之間的電場很強，如果沒有中間線圈20屏蔽的話仍然會在反應腔內產生較大的耦合電場，影響等離子的能量，縮短絕緣材料窗的壽命。The width of the intermediate coil 20 is larger than the width of any one of the first coil 10 and the third coil 30, or greater than the sum of the two, so that the electric field generated by both can be shielded more effectively. According to the principle of the present invention, the voltage difference between the first coil 10 and the third coil 30 is large, and the distance between the two is very close, so the electric field between the two is very strong, and if there is no shield of the intermediate coil 20, it will still A large coupling electric field is generated in the reaction chamber, which affects the energy of the plasma and shortens the life of the insulating material window.

本發明線圈圖形如第1至3實施例所示多個線圈構成環型外，也可以如圖5所示的第4實施例的俯視圖，線圈構成半圓形，設置兩組本發明第4實施例所示的線圈在反應腔頂部以激發反應腔內的氣體形成等離子體。也可以是其它任意形狀的，如適應方形的反應腔或基板的需要選擇方形的線圈，或者選用多個扇形圖形的線圈構成圓形的線圈組。只要是能構成完整回路的任意形狀的線圈，線圈上能形成偶極電場的，均屬於本發明可實施例。In the coil pattern of the present invention, as shown in the first to third embodiments, the plurality of coils form a ring shape, and the coil may be semicircular as shown in the plan view of the fourth embodiment shown in FIG. 5, and two sets of the fourth embodiment of the present invention are provided. The coil shown in the example forms a plasma at the top of the reaction chamber to excite the gas in the reaction chamber. It can also be any other shape, such as a square coil, or a plurality of fan-shaped coils to form a circular coil group. Any embodiment of the present invention can be made as long as it is a coil of any shape capable of forming a complete loop, and a dipole electric field can be formed on the coil.

圖6所示為應用了本發明電感耦合線圈的等離子處理裝置，該等離子處理裝置包括反應腔側壁210，反應腔頂部包括一個絕緣材料窗211，反應腔內下方包括一個基座200，基座上放置有待處理的基片。絕緣材料窗211或者側壁210上還設有氣體供應裝置（圖中未示出）如氣體噴頭等。絕緣材料窗211上設置有本發明第一線圈10，第三線圈30和中間線圈20，第一線圈10和第三線圈30分別通過連接部100和300連接到一個射頻電源和一個接地端。其中連接部300和接地端之間還連接有一個調平衡電路220，調平衡電路220可以是一個可變電容，通過調節該電容的容值可以調節流入線圈的射頻能量和從電容反射回線圈的功率或相位，最終獲得穩定的駐波。圖6中線圈安裝在絕緣材料窗211上方，由於本發明線圈具有自屏蔽電場的功能，所以絕緣材料窗211和線圈組之間可以不設習知技術中需要的法拉第屏蔽板。當然本發明仍有如圖3中V20段所示的少量電場會進入反應腔，在部分對電場屏蔽要求特別苛刻的場合，為了取得最佳的屏蔽效果，可以設置部分屏蔽板在本發明線圈和絕緣材料窗211之間，該部分屏蔽板，由於採用本發明線圈後僅需屏蔽圖3中中間線圈對應的少量的電場，所以可以只在本發明線圈下方局部位置設置導電的接地板，無需在絕緣材料窗211上方絕大部分面積覆蓋導電接地板，僅留少量面積的孔或槽供磁場通過。在設置有法拉第屏蔽板的情況下，本發明的中間線圈20寬度也可以減小到與上方的第一線圈10或第三線圈30相類似的寬度。需要更好屏蔽效果時可以選擇更寬的法拉第屏蔽板屏蔽第一線圈10、第三線圈30下方更寬的環狀區域。由於第一線圈10、第三線圈30上的偶極電場存在，所以對於其它部位可以不用進行更嚴格的屏蔽。所以即使採用本發明線圈時仍需設置法拉第屏蔽板也不會像習知技術採用法拉第屏蔽板那樣會影響點火的穩定性。本發明第一線圈10、第三線圈30如上述實施例中所述的在線圈所有圓周角度上具有相同的間隙，也就是兩個線圈相互平行，也可以在部分區域不存在不同的間隙，以抵消下方部分區域的不均一性，最終取得最均一的等離子處理效果。6 is a plasma processing apparatus to which an inductive coupling coil of the present invention is applied. The plasma processing apparatus includes a reaction chamber sidewall 210. The top of the reaction chamber includes an insulating material window 211. The bottom of the reaction chamber includes a base 200 on the base. The substrate to be processed is placed. A gas supply device (not shown) such as a gas jet head or the like is further provided on the insulating material window 211 or the side wall 210. The insulating material window 211 is provided with the first coil 10, the third coil 30 and the intermediate coil 20 of the present invention, and the first coil 10 and the third coil 30 are connected to a radio frequency power source and a ground terminal through the connecting portions 100 and 300, respectively. A balance adjusting circuit 220 is further connected between the connecting portion 300 and the grounding end. The balancing circuit 220 can be a variable capacitor. By adjusting the capacitance of the capacitor, the RF energy flowing into the coil can be adjusted and reflected from the capacitor back to the coil. Power or phase, eventually achieving a stable standing wave. The coil of Fig. 6 is mounted above the insulating material window 211. Since the coil of the present invention has a self-shielding electric field function, the Faraday shield plate required in the prior art may not be provided between the insulating material window 211 and the coil group. Of course, the present invention still has a small amount of electric field as shown in the V20 segment of FIG. 3 entering the reaction chamber. In the case where the electric field shielding is particularly demanding, in order to obtain an optimum shielding effect, a partial shielding plate may be provided in the coil and insulation of the present invention. Between the material windows 211, the partial shielding plate, since only a small amount of electric field corresponding to the middle coil in FIG. 3 needs to be shielded after the coil of the present invention is used, it is possible to provide a conductive grounding plate only at a local position below the coil of the present invention, without being insulated. Most of the area above the material window 211 covers the conductive ground plate, leaving only a small amount of holes or slots for the magnetic field to pass. In the case where the Faraday shield is provided, the width of the intermediate coil 20 of the present invention can also be reduced to a width similar to that of the upper first coil 10 or the third coil 30 above. When a better shielding effect is required, a wider Faraday shield can be selected to shield the wider loop region below the first coil 10 and the third coil 30. Since the dipole electric field on the first coil 10 and the third coil 30 exists, it is not necessary to perform stricter shielding for other parts. Therefore, even if the Faraday shield plate is required to be used in the coil of the present invention, the stability of the ignition may be affected as in the conventional technique using the Faraday shield. The first coil 10 and the third coil 30 of the present invention have the same gap at all circumferential angles of the coil as described in the above embodiments, that is, the two coils are parallel to each other, and there may be no different gaps in the partial regions. The unevenness of the lower part of the area is offset, and the most uniform plasma treatment effect is finally obtained.

本發明線圈的長度最佳地是第一線圈10，中間線圈20和第三線圈30的總長度少於輸入射頻信號的半波長，如果線圈總長度大於半波長，會造成如圖3所示的不能屏蔽的中間線圈的部分V20段的電壓會相應的向兩端擴展，所以在頻率不變的情況下線圈越長則屏蔽效果越差。當線圈總長超過半波長的3倍時，中間不能屏蔽部分電壓達到最大，與習知技術完全沒有屏蔽的效果一樣，必須採用法拉第屏蔽板配合使用才具有工業可利用性。如果線圈總長小於半波長,中間的不能屏蔽部分也會相應縮小，所以本發明效果越明顯。綜合以上結果，本發明線圈總長小於3倍半波長時就能取得縮小感應線圈電容耦合的效果，均屬於本發明範圍。The length of the coil of the present invention is optimally the first coil 10, and the total length of the intermediate coil 20 and the third coil 30 is less than the half wavelength of the input radio frequency signal. If the total length of the coil is greater than half a wavelength, it will result in the same as shown in FIG. The voltage of the V20 section of the intermediate coil that cannot be shielded will expand correspondingly to both ends, so the longer the coil is, the worse the shielding effect is. When the total length of the coil exceeds 3 times of the half wavelength, the voltage of the unshielded part of the middle reaches the maximum, and the effect of the conventional technology is not shielded, and the Faraday shield must be used in combination to have industrial availability. If the total length of the coil is less than a half wavelength, the unshielded portion in the middle will be correspondingly reduced, so that the effect of the present invention is more obvious. Based on the above results, when the total length of the coil of the present invention is less than 3 times and a half wavelength, the effect of reducing the capacitive coupling of the induction coil can be obtained, which is within the scope of the present invention.

當然，如果採用更高頻率的射頻電源如27Mhz，此時半波長縮短一半，相應的可採用的線圈尺寸範圍也會縮小。Of course, if a higher frequency RF power source such as 27Mhz is used, the half wavelength is shortened by half, and the corresponding coil size range can be reduced.

本發明等離子反應腔除了如圖6所示採用一組本發明線圈以外還可以添加其它線圈圍繞本發明線圈週邊或者在本發明線圈第一線圈組內側。其它線圈可以是習知技術的漸開線或者多個圓環組成的線圈，也可以是上述本發明實施例的線圈。The plasma reaction chamber of the present invention may incorporate other coils around the circumference of the coil of the present invention or inside the first coil group of the coil of the present invention, in addition to a set of coils of the present invention as shown in FIG. The other coil may be an involute of a conventional technique or a coil composed of a plurality of rings, or may be a coil of the above-described embodiment of the present invention.

雖然本發明已以較佳實施例揭示如上，然所述諸多實施例僅為了便於說明而舉例而已，並非用以限定本發明，本領域中具有通常知識者在不脫離本發明精神和範圍的前提下可作若干的更動與潤飾，本發明所主張的保護範圍應以申請專利範圍所述為準。The present invention has been described in the above preferred embodiments, and the present invention is not intended to limit the scope of the present invention, and is not intended to limit the scope of the invention. A number of changes and refinements may be made, and the scope of protection claimed by the present invention shall be as described in the scope of the patent application.

100、300‧‧‧連接部
10‧‧‧第一線圈
12‧‧‧第一中間連接部
20‧‧‧中間線圈
21‧‧‧開口
30‧‧‧第三線圈
32‧‧‧第二中間連接部
200‧‧‧基座
210‧‧‧反應腔側壁
211‧‧‧絕緣材料窗
220‧‧‧調平衡電路
X1、X2、X3‧‧‧點100, 300‧‧‧ Connections
10‧‧‧First coil
12‧‧‧First intermediate connection
20‧‧‧ intermediate coil
21‧‧‧ openings
30‧‧‧third coil
32‧‧‧Second intermediate connection
200‧‧‧Base
210‧‧‧Reaction chamber sidewall
211‧‧‧Insulation window
220‧‧‧balance circuit
X1, X2, X3‧‧ points

［圖1］為本發明射頻線圈結構示意圖；［圖2］為本發明射頻線圈俯視圖；［圖3］為本發明在線圈不同長度位置處的電壓幅度分佈示意圖；［圖4a］為圖2中本發明等離子體處理裝置A處的射頻線圈截面圖；［圖4b］為本發明第二實施例射頻線圈截面圖；［圖4c］為本發明第三實施例射頻線圈截面圖；［圖5］為本發明第四實施例射頻線圈俯視圖；［圖6］為應用本發明射頻線圈後的等離子處理裝置示意圖。1 is a schematic structural view of a radio frequency coil according to the present invention; [FIG. 2] is a top view of a radio frequency coil according to the present invention; [FIG. 3] is a schematic diagram of voltage amplitude distribution at different lengths of a coil of the present invention; [FIG. 4a] is FIG. A cross-sectional view of a radio frequency coil at a plasma processing apparatus A of the present invention; [Fig. 4b] is a cross-sectional view of a radio frequency coil according to a second embodiment of the present invention; [Fig. 4c] is a cross-sectional view of a radio frequency coil according to a third embodiment of the present invention; [Fig. 5] A top view of a radio frequency coil according to a fourth embodiment of the present invention; [Fig. 6] is a schematic view of a plasma processing apparatus after applying the radio frequency coil of the present invention.

100、300‧‧‧連接部 100, 300‧‧‧ Connections

10‧‧‧第一線圈 10‧‧‧First coil

12‧‧‧第一中間連接部 12‧‧‧First intermediate connection

20‧‧‧中間線圈 20‧‧‧ intermediate coil

30‧‧‧第三線圈 30‧‧‧third coil

32‧‧‧第二中間連接部 32‧‧‧Second intermediate connection

200‧‧‧基座 200‧‧‧Base

210‧‧‧反應腔側壁 210‧‧‧Reaction chamber sidewall

211‧‧‧絕緣材料窗 211‧‧‧Insulation window

220‧‧‧調平衡電路 220‧‧‧balance circuit

Claims

一種電感耦合等離子體處理裝置，包括：一個氣密的反應腔，反應腔包括反應腔側壁和頂部的絕緣材料窗，反應腔內其包括一個用於支撐待處理基片的基座；絕緣材料窗上方固定有一個電感線圈，所述電感線圈連接到一個射頻電源；其中，所述電感線圈包括第一線圈、第三線圈和一個中間線圈，所述第一線圈包括一個第一端連接到所述射頻電源，還包括一個第二端連接到中間線圈第一端；中間線圈還包括一個第二端連接到所述第三線圈第一端；第三線圈還包括一個第二端連接到接地端，其中第一線圈和第三線圈之間存在間隙且位於中間線圈上方，第一線圈和第三線圈的投影在中間線圈上，其中所述第一線圈的第二端通過第一連接部(12)連接到下方的中間線圈，中間線圈第二端通過通過第二連接部(23)連接到上方的第三線圈，中間線圈上的第一連接部和第二連接部之間還包括一個開口使第一連接部和第二連接部互相隔離。 An inductively coupled plasma processing apparatus comprising: a gas-tight reaction chamber including a sidewall of the reaction chamber and a window of insulating material at the top, the reaction chamber including a base for supporting the substrate to be processed; and an insulating material window An inductor is fixed on the upper side, and the inductor is connected to an RF power source; wherein the inductor coil includes a first coil, a third coil and an intermediate coil, and the first coil includes a first end connected to the The RF power supply further includes a second end connected to the first end of the intermediate coil; the intermediate coil further includes a second end connected to the first end of the third coil; and the third coil further includes a second end connected to the ground end, Wherein a gap exists between the first coil and the third coil and is located above the intermediate coil, and the projection of the first coil and the third coil is on the intermediate coil, wherein the second end of the first coil passes through the first connecting portion (12) Connected to the lower intermediate coil, the second end of the intermediate coil is connected to the upper third coil by the second connecting portion (23), and the first connecting portion on the intermediate coil Between the second connection portion further comprises a first opening and a second portion connected to the connecting portion isolated from each other.

如請求項1所述的等離子體處理裝置，其中所述第三線圈的第二端通過一個調平衡電路連接到所述接地端。 The plasma processing apparatus of claim 1, wherein the second end of the third coil is connected to the ground through a balancing circuit.

如請求項1所述的等離子體處理裝置，其中絕緣材料窗上方還包括第二電感線圈圍繞在所述電感線圈外或者在所述電感線圈內。 The plasma processing apparatus of claim 1, wherein the insulating material window further comprises a second inductive coil surrounding the inductive coil or within the inductive coil.

如請求項2所述的等離子體處理裝置，其中調節所述調平衡電路使所述線圈上形成駐波，所述駐波的電壓分佈使第一線圈上任意一點的與第三線圈上相對應位置點的電壓極性相反幅度相同。 The plasma processing apparatus of claim 2, wherein the balance circuit is adjusted to form a standing wave on the coil, and the voltage distribution of the standing wave is such that any point on the first coil corresponds to the third coil The voltage polarity of the position point is the same in the opposite magnitude.

如請求項1所述的等離子體處理裝置，其中所述第一線圈、中間線圈或第三線圈的長度和小於射頻電源信號的3倍半波長長度。 The plasma processing apparatus of claim 1, wherein the length of the first coil, the intermediate coil or the third coil is less than a length of three and a half wavelengths of a radio frequency power signal.

如請求項2所述的等離子體處理裝置，其中所述中間線圈的電壓幅度小於第一線圈和第三線圈的電壓幅度。 The plasma processing apparatus of claim 2, wherein a voltage amplitude of the intermediate coil is smaller than a voltage amplitude of the first coil and the third coil.

一種電感耦合等離子體處理裝置，包括：一個氣密的反應腔，反應腔包括反應腔側壁和頂部的絕緣材料窗，反應腔內其包括一個用於支撐待處理基片的基座；絕緣材料窗上方固定有一個自屏蔽電感線圈，其中所述自屏蔽電感線圈包括相互串聯的第一線圈、中間線圈和第三線圈，其中中間線圈位於第一線圈和第三線圈下方且寬度大於第一線圈或第三線圈的寬度，一個射頻電源施加射頻電場到所述自屏蔽線圈的第一線圈輸入端和第三線圈輸出端之間，其中所述第三線圈輸出端還連接有一個調平衡電路，調節所述調平衡電路使所述自屏蔽線圈上形成駐波，所述中間線圈的電壓幅度小於第一線圈或第三線圈上的電壓幅度。 An inductively coupled plasma processing apparatus comprising: a gas-tight reaction chamber including a sidewall of the reaction chamber and a window of insulating material at the top, the reaction chamber including a base for supporting the substrate to be processed; and an insulating material window Fixedly, a self-shielding inductor coil is fixed, wherein the self-shielded inductor coil comprises a first coil, an intermediate coil and a third coil connected in series with each other, wherein the intermediate coil is located below the first coil and the third coil and has a width greater than the first coil or a width of the third coil, an RF power source applies a radio frequency electric field between the first coil input end and the third coil output end of the self-shielding coil, wherein the third coil output end is further connected with a balance adjusting circuit, and is adjusted The balance circuit forms a standing wave on the self-shielding coil, and the voltage amplitude of the intermediate coil is smaller than the voltage amplitude on the first coil or the third coil.

如請求項7所述的等離子體處理裝置，其中所述第一和第三線圈向下投影位於中間線圈上，使中間線圈屏蔽第一線圈和第三線圈上的電壓形成的電場。 The plasma processing apparatus of claim 7, wherein the first and third coils are projected downwardly on the intermediate coil such that the intermediate coil shields an electric field formed by voltages on the first coil and the third coil.

如請求項7所述的等離子體處理裝置，其中還包括一個法拉第屏蔽板位於所述自屏蔽線圈和絕緣材料窗之間，所述第一和第三線圈的向下投影位於所述法拉第屏蔽板上。 The plasma processing apparatus of claim 7, further comprising a Faraday shield between the self-shielding coil and the insulating material window, the downward projection of the first and third coils being located on the Faraday shield on.

如請求項7所述的等離子體處理裝置，其中所述絕緣材料窗上方還包括第二感應線圈圍繞在所述自屏蔽電感線圈外或者在所述自屏蔽電感線圈內。 The plasma processing apparatus of claim 7, wherein the insulating material window further comprises a second induction coil surrounding the self-shielding inductor coil or within the self-shielding inductor coil.

如請求項7所述的等離子體處理裝置，其中所述射頻電源的頻率大於13Mhz。 The plasma processing apparatus of claim 7, wherein the frequency of the radio frequency power source is greater than 13 Mhz.

一種用於電感耦合等離子體處理裝置的電感線圈，包括：第一線圈、第三線圈和一個中間線圈，第一線圈和第三線圈位於所述中間線圈上方；所述第一線圈包括一個第一端，和一個第二端，所述第一線圈的第二端連接到下方中間線圈的第一端，中間線圈還包括一個第二端連接到所述第三線圈第一端，第三線圈還包括一個第二端，所述中間線圈寬度大於第一線圈或第三線圈，且第一線圈和第三線圈向下的投影位於中間線圈上。 An inductor for an inductively coupled plasma processing apparatus, comprising: a first coil, a third coil, and an intermediate coil, the first coil and the third coil being located above the intermediate coil; the first coil including a first And a second end, the second end of the first coil is connected to the first end of the lower intermediate coil, and the intermediate coil further comprises a second end connected to the first end of the third coil, the third coil further A second end is included, the intermediate coil width being greater than the first coil or the third coil, and the downward projection of the first coil and the third coil is located on the intermediate coil.

如請求項12所述的電感線圈，其中第一線圈和第三線圈之間存在間隙，且第一線圈圍繞第三線圈。 The inductive coil of claim 12, wherein there is a gap between the first coil and the third coil, and the first coil surrounds the third coil.

如請求項12所述的電感線圈，其中所述中間線圈構成一個閉合回路，所述第一線圈和第三線圈與中間線圈具有相同的形狀。 The inductive coil of claim 12, wherein the intermediate coil constitutes a closed loop, and the first coil and the third coil have the same shape as the intermediate coil.

如請求項12所述的電感線圈，其中所述第一線圈通過一個第一連接部連接到中間線圈第一端，第三線圈通過一個第二連接部連接到中間線圈第二端，中間線圈的第一端和第二端之間存在一個互相隔離的間隙。 The inductor of claim 12, wherein the first coil is connected to the first end of the intermediate coil by a first connection, and the third coil is connected to the second end of the intermediate coil by a second connection, the middle coil There is a gap between the first end and the second end that is isolated from each other.

如請求項13所述的電感線圈，其中所述第一線圈和第二線圈之間的間隙位於所述中間線圈的上方。 The inductor of claim 13, wherein a gap between the first coil and the second coil is above the intermediate coil.

如請求項12所述的電感線圈，其中第一線圈、中間線圈、第三線圈沿相同的方向延展，所述方向選自順時針和逆時針。 The inductive coil of claim 12, wherein the first coil, the intermediate coil, and the third coil extend in the same direction, the direction being selected from clockwise and counterclockwise.