C. J. Maletskos* and P. R. Hanley C.J. Maletskos* 和 P. R. HanleyVARIAN/Extrion Division VARIAN/Extrion 部門Gloucester, MA 01930
Summary 摘要
Ion implanters produce beams of positive ions that impinge on target materials located in an enclosed vacuum system and are not intended to produce external beams or any other external ionizing radiation. The deceleration of positive ions produces negligible bremsstrahlung external to the implanters. The deceleration of electrons when striking beam-tube components produces bremsstrahlung resulting in significant quantities of unintended external radiation. These electrons are created by the interaction of positive ions with component parts of the implanter and with the residual gas and are subsequently accelerated in the implanter beam tube) At implanter ion energies ( < 500keV)(<500 \mathrm{keV}), the bremsstrahlung is emitted in lobes essentially perpendicular to the electron stream ( 180^(@)180^{\circ} from the ion beam) modified by self-shielding from implanter structures. Experimentally, the radiation exposure rate is generally proportional to the electron current and to the square of the electron energy in essential agreement with theory. Implanter x-ray spectra are also in general agreement with spectra taken under laboratory conditions. Principles for reducing external radiation include the judicious combination of implanter design, materials with low atomic number for electrons to strike, cleanliness in assembly, use of suppression fields to reduce the number of electrons, shielding, interlocks, and operation. The exposure rate limits can vary from the federal and state value of 0.5 milliroentgens per hour for electronic products to various lower values which may be established for other countries or by individual manufacturers. 離子植入器產生的正離子束會撞擊位於密閉真空系統中的目標材料，而不會產生外部離子束或任何其他外部電離輻射。正離子的減速會在離子植入器外部產生可忽略的轫致辐射。電子撞擊束管元件時的減速會產生轫致辐射，導致大量非預期的外部輻射。在植入器離子能量 ( < 500keV)(<500 \mathrm{keV}) 的情況下，轫致辐射以垂直于电子流的裂片形式发射（ 180^(@)180^{\circ} 来自离子束），并通过植入器结构的自屏蔽进行修正。在實驗中，輻射暴露率通常與電子電流和電子能量的平方成正比，這與理論基本一致。植入器的 X 射線光譜也與實驗室條件下的光譜大致相同。減少外部輻射的原則包括植入器設計的明智組合、低原子序數供電子撞擊的材料、組裝時的清潔、使用抑制場以減少電子數量、屏蔽、聯鎖和操作。暴露率限制可從電子產品每小時 0.5 毫倫琴的聯邦和州規定值，到其他國家或個別製造商可能設定的各種較低值不等。
Introduction 簡介
Ion implanters are used to introduce atoms onto or below the surface of materials in order to alter the electrical or mechanical properties of these materials. The implantation is performed by accelerating positive ions of the atom of interest to an energy sufficient to penetrate to the desired depth in the material. The entire operation is performed in an evacuated system with the accelerated ions impinging directly on the target material. Ion implantation systems are intended to produce positive-ion beams and are not intended to produce external beams or any other external ionizing radiation. Ion implanters do produce unintended external ionizing radiation and, therefore, must be designed and built to meet applicable radiation limits. 離子植入器用於將原子導入材料表面或表面以下，以改變這些材料的電氣或機械特性。植入的方式是將相關原子的正離子加速到足以穿透材料到所需深度的能量。整個作業是在抽真空系統中進行，加速離子直接衝擊目標材料。離子植入系統的目的是產生正離子束，而非產生外部束或任何其他外部電離輻射。離子植入器會產生非預期的外部電離輻射，因此其設計與建造必須符合適用的輻射限制。
This report discusses the production and control of the unintended ionizing radiation emitted by ion implanters. Most ion implanters now in use produce ions with energies < 500keV<500 \mathrm{keV}. Some implanters are being developed to operate above this energy, especially in the low MeV region, but these are not discussed in this report. 本報告討論離子植入器所發出的非預期電離輻射的產生與控制。目前使用的大多數離子植入器所產生的離子能量為 < 500keV<500 \mathrm{keV} 。有些植入器正在開發中，可在此能量以上運作，特別是在低 MeV 區域，但本報告不會討論這些植入器。
Bremsstrahlung Production and Characteristics Bremsstrahlung 的產生與特性
Electromagnetic radiation is produced whenever a charged particle is accelerated by deflection from its path or by a change in velocity. This radiation is called bremsstrahlung (braking radiation, i.e. from deceleration of a charged particle on striking a 每當帶電粒子因偏離其路徑或速度改變而加速時，便會產生電磁輻射。這種輻射稱為「轫致辐射」（bremsstrahlung）（煞車輻射，即帶電粒子撞擊軌道時減速所產生的輻射）。
target), is also called xx rays, and its amplitude is proportional to the acceleration: Thus, 目標），也稱為 xx 射線，其振幅與加速度成正比：因此、
where a is the acceleration, Ze is the nuclear charge of the atom of atomic number ZZ involved in the interaction, ze is charge of the incident particle and mm its mass. The intensity of the radiation per atom is proportional to the square of the amplitude and is 其中 a 是加速度，Ze 是參與互動的原子序數 ZZ 原子的核電荷，ze 是入射粒子的電荷， mm 是其質量。每個原子的輻射強度與振幅的平方成正比，為
Equation (2) indicates that the intensity per atom is proportional to the square of the atomic number and inversely proportional to the square of the mass of the incident particle. Therefore lower-Z materials will produce less bremsstrahlung. Protons and heavier charged particles will produce more than 10^(6)10^{6} times less radiation than electrons. 等式 (2) 顯示每個原子的強度與原子序數的平方成正比，與入射粒子質量的平方成反比。因此，Z 值較低的材料會產生較少的轫致辐射。質子和較重的帶電粒子所產生的輻射會比電子少 10^(6)10^{6} 倍以上。
The incident charged particle can radiate any amount of energy from zero up to its total kinetic energy: i.e., a spectrum of energies, with maximum energy equal to the charged particle energy, E_(e)\mathrm{E}_{\mathrm{e}}. 入射的帶電粒子可以輻射從零到其總動能的任何能量：即能量光譜，最大能量等於帶電粒子能量 E_(e)\mathrm{E}_{\mathrm{e}} 。
Figure 1 shows a schematic representation of the two general types of ion implanters. In both cases, the positive ions striking the target material and other materials will produce negligible bremsstrahlung and, with the intrinsic self-shielding by the components of the implanter, the emitted radiation is of no concern from the standpoint of radiation protection. On the other hand electrons (created by the interaction of the positive ions with component parts of the implanter or with the residual gas in the beam tube) can be accelerated by potentials in various parts of the implanter and can produce bremsstrahlung or xx rays in amounts significant enough to require attention. An important region in both systems is the ion sources. In the system with acceleration after analysis, the slit and acceleration tube are also important. Focusing and deflection systems can also be sources of xx rays if they utilize electric fields, 圖 1 顯示兩種一般離子植入器的示意圖。在這兩種情況下，正離子撞擊目標材料和其他材料所產生的轫致辐射可以忽略不计，而且由於植入器的部件具有固有的自屏蔽功能，因此從輻射防護的角度來看，所釋放的輻射是無關緊要的。另一方面，電子 (由於正離子與植入器的元件或束管中的殘留氣體互動而產生) 會被植入器各部分的電位加速，並可能產生轫致辐射或 xx 射線，其數量之大足以引起注意。這兩個系統中的一個重要區域是離子源。在分析後加速的系統中，狹縫和加速管也很重要。如果聚焦和偏轉系統利用電場，它們也可能是 xx 射線的來源、
ACCELERATION AFTER ANALYSIS (UPPER) 分析後的加速度 (上圖)
ACCELERATION BEFORE ANALYSIS (LOWER) 分析前加速度 (較低)
Figure 1. Schematic representation of two general types of ion implanters showing x-ray source regions. 圖 1.兩種一般類型離子植入器的示意圖，顯示 X 射線源區域。
In implanters, electrons strike materials considerably thicker than the range of these electrons in these materials, and, hence, bremsstrahlung production from thick targets is the practical condition. When radiative and ionization energy losses are considered in thick-target bremsstrahlung theory, the total bremsstrahlung intensity per electron, I_(e,T)\mathrm{I}_{\mathrm{e}, \mathrm{T}}, is given by 在植入器中，電子撞擊材料的厚度遠大於這些材料中這些電子的射程，因此，從厚靶產生轫致辐射是實際條件。在厚靶轫致辐射理论中考虑辐射和电离能量损失时，每个电子的总轫致辐射强度 I_(e,T)\mathrm{I}_{\mathrm{e}, \mathrm{T}} 由以下公式给出
I_(e,T)=kZE_(e)^(2),\mathrm{I}_{\mathrm{e}, \mathrm{~T}}=k Z \mathrm{E}_{\mathrm{e}}^{2},
where kk is a constant and E_(e)E_{e} is the initial electron energy. The fraction, ff, of the initial electron energy that is converted to x rays is 其中 kk 是常數， E_(e)E_{e} 是初始電子能量。轉換成 X 射線的初始電子能量的分數 ff 為
f=(I_(e,T))/(E_(e))=kZE_(e)f=\frac{I_{e, T}}{E_{e}}=k Z E_{e}
The value of k prop(0.7+-0.2)xx10^(-6)k \propto(0.7 \pm 0.2) \times 10^{-6} for E_(e)E_{e} in keV. Thus for 10w-Z10 \mathrm{w}-\mathrm{Z} materials and E_(e)=<500keV,f≃1-2%E_{\mathrm{e}}=<500 \mathrm{keV}, \mathrm{f} \simeq 1-2 \%. Nevertheless, this small conversion to bremsstrahlung (the rest of the electron energy is lost by ionizationat these low electron energies) can result in a substantial radiation exposure rate. 對於 E_(e)E_{e} 的 k prop(0.7+-0.2)xx10^(-6)k \propto(0.7 \pm 0.2) \times 10^{-6} 值，單位為 keV。因此，對於 10w-Z10 \mathrm{w}-\mathrm{Z} 材料和 E_(e)=<500keV,f≃1-2%E_{\mathrm{e}}=<500 \mathrm{keV}, \mathrm{f} \simeq 1-2 \% 。儘管如此，這一小部分轉換為轫致辐射（其餘的電子能量會在這些低電子能量時因電離而損失），就會造成相當大的輻射暴露率。
Finally, the total power, P_(T)P_{T}, (intensity/unit time) is obtained by multiplying by the electron flow per unit time, tt, i.e., the electron current, as 最後，將總功率 P_(T)P_{T} （強度/單位時間）乘以單位時間內的電子流量 tt ，即電子電流，可得到如下結果
P_(T)=(I_(e,T))/(t)=k_(1)ZE_(e)^(2_(i))P_{T}=\frac{I_{e, T}}{t}=k_{1} Z E_{e}^{2_{i}}
where i\mathbf{i} is the electron current. The total power is proportional to i and E_(e)^(2)\mathrm{E}_{\mathrm{e}}^{2}. Thus, the x -ray exposure rate (directly related to P_(T)\mathrm{P}_{\mathrm{T}} ) can be reduced by using low-Z materials, by keeping the electron current low, and especially by maintaining as low an electron energy as possible. 其中 i\mathbf{i} 是電子電流。總功率與 i 和 E_(e)^(2)\mathrm{E}_{\mathrm{e}}^{2} 成正比。因此，X 射線曝光率（與 P_(T)\mathrm{P}_{\mathrm{T}} 直接相關）可通過使用低 Z 材料、保持低電子電流，尤其是保持盡可能低的電子能量來降低。
At low electron energies, the momentum of the photon is very low and the momentum distribution between the electron and the atom results in an angular distribution of the photon intensity predominantly at 90^(@)90^{\circ} to the electron direction (Figure 2, theoretical curve A). As the energy increases, the photon momentum increases and the angular distribution of the photons moves forward and eventually is predom- 在低電子能量時，光子的動量非常低，電子和原子之間的動量分佈導致光子強度的角度分佈主要在 90^(@)90^{\circ} 到電子方向（圖 2，理論曲線 A）。隨著能量的增加，光子動量也會增加，光子的角度分佈也會向前移動，並最終在 90^(@)90^{\circ} 與電子方向的角度分佈為前導（圖 2，理論曲線 A）。
Figure 2. Relative angular distributions of bremsstrahlung intensity. Curve A is theoretical for an interaction of a very low energy electron with an atom or very thin target. Curve BB is experimental for 2350-keV electrons on a copper target slightly thicker than the maximum range of the electrons (from Buechner et al ^(1){ }^{1} ). 圖 2.轫致辐射强度的相对角分布。曲線 A 是理論上能量非常低的電子與原子或非常薄的靶的相互作用。曲線 BB 是 2350-keV 電子在比電子最大射程稍厚的銅靶上的實驗結果（來自 Buechner 等人的 ^(1){ }^{1} ）。
inantly in the direction of the electrons (Figure 2, experimenmtal curve B). The angular distribution of electrons impinging on thick targets, as is the case for implanters, is a complicated function of electron energy and absorber atomic number, but results in similar lobe characteristics. Figure 3 shows the angular distribution from an implanter operating at 200 keV . Although it is difficult to make measurements of lobe characteristics on implanters because of selfshielding, other measurements made on units operating in the 80-80- to 100-keV100-\mathrm{keV} range have indicated a locus of points of maximum intensity around the implanter that lie in a plane nearly perpendicular to the electron stream and intersecting the stream at about the expected source of the bremsstrahlung. 在電子的方向上（圖 2，實驗曲線 B）。電子撞擊厚靶的角度分佈與植入器的情況一樣，是電子能量和吸收體原子序數的複雜函數，但會產生相似的波束特徵。圖 3 顯示了在 200 keV 下運作的植入器的角度分佈。儘管由於自屏蔽的關係，很難在植入器上測量瓣葉特徵，但在 80-80- 到 100-keV100-\mathrm{keV} 範圍內工作的設備上進行的其他測量顯示，在植入器周圍有一個最大強度點的位置，它位於幾乎垂直於電子流的平面上，並與電子流相交於轫致辐射的預期來源。
Figure 3. Relative intensity of bremsstrahlung lobe from an ion implanter. Lobe is dotted to imply general shape because factory conditions limit number of points. 圖 3.來自離子植入器的轫致辐射波束的相對強度。由於工廠條件限制了點數，因此輻射線以虛線表示一般形狀。
Figure 4. X-ray spectra from electrons on thick targets. Electron energies not large enough to result in characteristic tungsten xx rays. (calculated from Ul rey ^(2){ }^{2} ). 圖 4.厚靶上電子產生的 X 射線光譜。電子能量不足以產生特徵性的鎢 xx 射線。(根據 Ul rey ^(2){ }^{2} 計算）。
Typical bremsstrahlung spectra are shown in Figure 4 obtained under laboratory conditions. Depending on the ZZ of the absorber and the electron energy, electrons can be emitted from the target atoms which in turn will emit characteristic xx rays. These xx rays will appear as sharp peaks superposed on the bremsstrahlung spectrum but their total intensity will be small compared to that of the bremsstrahlung . 典型的轫致辐射光谱如图 4 所示，是在实验室条件下获得的。根據吸收器的 ZZ 和電子能量，電子可以從目標原子中發射出來，而目標原子反過來又會發射出特徵性的 xx 射線。這些 xx 射線會在轫致辐射光譜上出現尖銳的峰值，但與轫致辐射相比，其總強度很小。
An implanter bremsstrahlung spectrum, shown in Figure 5, has the same general features of the spectra in Figure 4. In addition, a characteristic peak appears at ∼30keV\sim 30 \mathrm{keV} due to the iodine in the NaI detector. Lower energy characteristic x rays from component materials of the implanter do not appear because of nearly complete absorption of these photons. The bremsstrahlung spectrum of Figure 5 is, in fact, a “hardened” spectrum favoring the higher- 圖 5 所示的植入器轫致辐射光譜具有與圖 4 光譜相同的一般特徵。此外，由於 NaI 探測器中的碘，在 ∼30keV\sim 30 \mathrm{keV} 處會出現一個特徵峰。來自植入器元件材料的較低能量特徵 X 射線不會出現，因為這些光子幾乎完全被吸收。圖 5 的轫致辐射光譜實際上是一種「硬化」光譜，偏向於高能量的 X 射線。
energy xx rays because the lower-energy xx rays have been partially absorbed by the implanter structures. 能量 xx 射線，因為能量較低的 xx 射線已被植入器結構部分吸收。
Figure 5. X-ray spectrum from implanter operating at acceleration voltage of 200 kV . The small peak at 30 keV is the characteristic x-ray peak of iodine in the sodium iodide detector used for the measurement. The collimated detector was perpendicular to the electron stream and pointed at the x-ray source region. 圖 5.在加速電壓為 200 kV 時，來自植入器的 X 射線光譜。在 30 keV 處的小峰是碘化鈉探測器中碘的特徵 X 射線峰。准直探測器垂直於電子流，並指向 X 射線源區域。
Operating Characteristics 操作特性
The relative bremsstrahlung intensities as a function of several operating variables are shown in Figures 6, 7 and 8. 相對轫致辐射强度与几个操作变量的函数关系如图 6、图 7 和图 8 所示。
Figure 6 shows the dependence of the relative intensity on the acceleration voltage. The intensity drops dramatically with decreasing voltage and therefore decreasing electron energy. The relation is much greater than E^(2)E^{2} shown by the theoretical curve of y=y=ax^(2)a x^{2} adjusted to be equal to the experimental curve at 100 kV . As the voltage is decreased, the electron energy decreases, the bremsstrahlung spectrum energies decrease and these lower photon energies can be absorbed more readily by the implanter structures. Because of this strong dependence on voltage, radiation surveys must be made at the maximum energy of the implanter. 圖 6 顯示相對強度與加速電壓的關係。隨著電壓的降低，電子能量也隨之降低，相對強度急劇下降。這個關係遠大於 E^(2)E^{2} 所顯示的理論曲線 y=y=ax^(2)a x^{2} 調整為等於 100 kV 時的實驗曲線。隨著電壓降低，電子能量降低，轫致辐射光譜能量降低，這些較低的光子能量可以更容易地被植入器結構吸收。由於這種對電壓的強烈依賴性，輻射測量必須在植入器的最大能量下進行。
Figure 7 shows the dependence of the relative intensity on the positive ion beam current (the electron current being somewhat proportional to the ion current). The relative intensity is nearly proportional to the current. The break in the slope between 4 and 6 mA is probably due to changes in the 圖 7 顯示相對強度對正離子束電流的依賴關係（電子電流與離子電流成一定比例）。相對強度幾乎與電流成正比。斜率在 4 mA 到 6 mA 之間的中斷可能是由於正離子束電流的變化造成的。
Figure 6. Relative bremsstrahlung intensity vs acceleration voltage. The dependence of intensity on E_(e)^(2)\mathrm{E}_{\mathrm{e}}^{2} is given by the curve y=ax^(2)y=a x^{2}. 圖 6.相對轫致辐射强度 vs 加速度电压。曲線 y=ax^(2)y=a x^{2} 表示強度對 E_(e)^(2)\mathrm{E}_{\mathrm{e}}^{2} 的依賴關係。
Figure 7. Relative bremsstrahlung intensity vs positive ion beam current. The electron current is nearly proportional to the ion current. The bend in the curve is probably due to a change in beam optics. 圖 7.相對轫致辐射强度 vs 正離子束流。電子電流與離子電流幾乎成正比。曲線中的彎曲可能是由於光束光學的改變。
Figure 8 Relative bremsstrahlung intensity vs suppression voltage. The current for the point bar(at)\overline{\mathrm{at}} -3.85 kV could not be maintained at 8 mA ; the upper value at this voltage has been increased by the current ratio of 8//6.28 / 6.2. 圖 8 相對轫致辐射强度 vs 抑制电压。 bar(at)\overline{\mathrm{at}} -3.85 kV 點的電流無法維持在 8 mA；此電壓下的上限值已由 8//6.28 / 6.2 的電流比率增加。
optics of the ion beam. Because the radiation increases with current, radiation surveys must be made at the maximum sustainable current consistent with not damaging the implanter. 離子束的光學。由於輻射會隨著電流增加，因此必須在不損壞植入器的最大持續電流下進行輻射檢測。
Figure 8 shows the dependence of the relative intensity on the suppression voltage. The suppression voltage is a negative potential placed at appropriate locations in the implanter (as shown in Figure 1) to decrease the number of electrons that get past the these suppression regions which can then be accelerated. Figure 8 shows the increase in relative intensity as the negative suppression voltage is decreased. Suppression voltages should be fixed at large enough negative values sufficient to minimize bremsstrahlung production. Since the suppression voltage can fail, the voltage indication on the suppressor itself must be interlocked with the acceleration voltage power supply to prevent high voltage from being turned on when there is insufficient suppression voltage. Because bremsstrahlung production is strongly dependent on the presence of adequate suppression voltage, radiation surveys must be made only when this condition is met. 圖 8 顯示相對強度與抑制電壓的關係。抑制電壓是放置在植入器中適當位置的負電位 (如圖 1 所示)，以減少通過這些抑制區域的電子數量，進而加速這些電子。圖 8 顯示當負抑制電壓降低時相對強度的增加。抑制電壓應固定在足夠大的負值，以減少轫致辐射的產生。由於抑制電壓可能會失效，因此抑制器本身的電壓指示必須與加速電壓電源互鎖，以防止在抑制電壓不足時開啟高壓。由於轫致辐射的产生在很大程度上取决于是否存在足够的抑制电压，因此只有在满足这一条件时才能进行辐射测量。
Practical Considerations 實務考量
This section contains a series of items that pertain directly and practically to the radiation safety of ion implanters. 本節包含一系列直接與離子植入器輻射安全有關的項目。
Radiation Quantities and Units 輻射量和單位
A summary of the current terminology is given in Table 1 based on ICRU Report 33 of the International Commission on Radiation Units and Measurements ^(3){ }^{3} (ICRU) where the exact definitions and qualifications are to be found. The following points should be noted. Exposure refers to the charge of all the electrons produced by photons ionizing a mass of air when those electrons are stopped in air. The currently recommended units are the S. I. units. (The special units are those now in use and which are intended to be phased out.) The derivatives with respect to time give the rates, such as exposure rate. Radiation survey instruments generally measure exposure rate. 根據國際輻射單位與量測委員會 ^(3){ }^{3} (ICRU) 的第 33 號報告，表 1 提供了目前術語的摘要，其中可以找到確切的定義和限定。應注意以下幾點。暴露量指的是光子電離一團空氣所產生的所有電子，當這些電子停止在空氣中時所帶的電荷。目前推薦的單位是 S. I. 單位。(特殊單位是指現在使用的單位，並打算逐步淘汰）。與時間有關的導數會得出速率，例如暴露率。輻射測量儀器通常測量暴露率。
Absorbed dose is the mean energy imparted to a mass of matter. The matter can be anything including air and, of specific interest,biological tissues and organs. The dose equivalent provides the means for inferring a biological effect from a given absorbed dose. This relationship is shown by the equation in the bottom of Table I where QQ is the quality factor (based on many factors relating on the biological effectiveness of different radiations) and NN is the product of other modifying factors, if any, (at present N=1N=1 ). For the low-energy xx rays of implanters Q=1Q=1 and, therefore, dose equivalent and absorbed dose are numerically equal. It turns out that 1 R in air is approximately equal to 1 rad in air which in turn is approximately equal to 1 rad in most tissues for photon energies less than a few MeV, and, hence, all three quantities in terms of special units are nearly numerically equal. Thus, these quantities are used interchangeably, but this practice is incorrect and the distinction should be observed. Radiation emission limits for devices such as implanters are specifically set in terms of exposure rate. 吸收劑量是指傳遞給大量物質的平均能量。該物質可以是任何東西，包括空氣，以及特別感興趣的生物組織和器官。劑量當量提供了從特定吸收劑量推斷生物效應的方法。此關係由表 I 底部的等式所顯示，其中 QQ 是品質因子（基於許多與不同輻射的生物效應有關的因素），而 NN 是其他修正因子（如有）的乘積（目前為 N=1N=1 ）。對於植入器的低能量 xx 射線 Q=1Q=1 ，因此劑量當量和吸收劑量在數字上相等。事實證明，對於小於幾 MeV 的光子能量，空氣中的 1 R 大約等於 1 拉德，而在大多數組織中，空氣中的 1 R 又大約等於 1 拉德，因此，以特殊單位表示的這三個量在數值上幾乎相等。因此，這些量被交替使用，但這種做法並不正確，應注意區分。植入器等裝置的輻射放射限值是以暴露率來特別設定的。
Table 1. Radiation Quantities and Units 表 1.輻射量與單位
Quantity 數量
S. I. Unit ^("a "){ }^{\text {a }} S.I. Unit ^("a "){ }^{\text {a }}
Special Unit 特別單位
Name 名稱
Symbol 符號
Name Symbol 名稱 符號
Name 名稱
Symb01
Exposure 曝光
x
庫倫 C/kg 每公斤
coulombs
C/kg
per kilogram
coulombs
C/kg
per kilogram| coulombs |
| :--- |
| C/kg |
| per kilogram |
Quantity S. I. Unit ^("a ") Special Unit
Name Symbol Name Symbol Name Symb01
Exposure x "coulombs
C/kg
per kilogram" Roentgen R
1R=2.58 xx10^(-4)c//kg (exactly)
"Absorbed
Dose" 0 Gray "GGy
(=1J//kg)" rad rad
1rad=10^(-2)Gy
"Dose
Equivalent" H Sievert " Sv
(=1J//kg)" ren rem
1 rem =10^(-2)Sv
H=DQN | Quantity | | S. I. Unit ${ }^{\text {a }}$ | Special Unit | |
| :---: | :---: | :---: | :---: | :---: |
| Name | Symbol | Name Symbol | Name | Symb01 |
| Exposure | x | coulombs <br> C/kg <br> per kilogram | Roentgen | $R$ |
| | | $1 R=2.58 \times 10^{-4} \mathrm{c} / \mathrm{kg}$ (exactly) | | |
| Absorbed <br> Dose | 0 | Gray $\begin{array}{ll} G \mathrm{~Gy} \\ (=1 \mathrm{~J} / \mathrm{kg}) \end{array}$ | rad | rad |
| | | $1 \mathrm{rad}=10^{-2} \mathrm{~Gy}$ | | |
| Dose <br> Equivalent | H | Sievert $\begin{aligned} & \text { Sv } \\ & (=1 \mathrm{~J} / \mathrm{kg}) \end{aligned}$ | ren | rem |
| | | 1 rem $=10^{-2} \mathrm{~Sv}$ | | |
| | | $H=D Q N$ | | |
a “S.I.” refers to the International System of Units based on the rules developed by the international Conmittee for Weights and Measures. a "S.I. "指基於國際度量衡委員會制定的規則的國際單位制。
Estimate of Exposure Rate 暴露率估算
Estimates of exposure rate to be anticipated by a particular implanter design are useful in developing the design concepts, the structural layout and the potential shielding requirements. Such estimates can be made by use of Equation (5), by assuming the intensity is emitted isotropically, by knowledge of the spectral shape, and by converting power to exposure rate. Details for making this calculation can be 估算特定植入器設計所預期的曝露率，有助於發展設計概念、結構佈局和潛在的屏蔽要求。此類估算可使用公式 (5)、假設強度是等向發射、了解光譜形狀，以及將功率轉換為曝光率來進行。進行此計算的詳細資訊可參考
found in a number of books on dosimetry and radiation protection. This method of calculation can be inaccurate because of the complex theory producing uncertainties in the constant k_(1)\mathrm{k}_{1} in Equation (5) and in the spectral shape,and because angular distribution and self-absorption of photons in thick targets are important but not easily accountable effects. 可在許多有關放射量測定與輻射防護的書籍中找到。由於公式 (5) 中的常數 k_(1)\mathrm{k}_{1} 和光譜形狀的複雜理論會產生不確定性，而且厚目標中光子的角度分佈和自吸收是重要但不易統計的效應，因此此計算方法可能不準確。
An alternative and more realistic method is to use experimental data obtained from thick target sources such as medical x-ray units. X-ray emission rates from high-Z targets and modifications for low-Z targets can be found in NCRP Report ^(4){ }^{4} No. 51. The attenuation of xx rays produced at various potentials (corresponding to effective electron energies) in various materials can be found in NCRP Report ^(5){ }^{5} No. 49 as well as in NCRP Report No. 51. These attenuation data are for broad-beam conditions directly applicable to ion implanters. As an example, a 100-keV100-\mathrm{keV} electron beam of 1 mA striking an aluminum structure perpendicularly will give an exposure rate of about 290mR//h290 \mathrm{mR} / \mathrm{h} at one meter perpendicular to the electron beam. A steel structure 6.4 mm thick ( 0.25 inches) will reduce the exposure rate to ∼30mR//h\sim 30 \mathrm{mR} / \mathrm{h} and 1.6 mm ( 1//16inch1 / 16 \mathrm{inch} ) of lead will further reduce this to ∼0.14mR//h\sim 0.14 \mathrm{mR} / \mathrm{h}. The exposure rate in the forward direction would be negligible. 另一種更現實的方法是使用從厚靶源（如醫療 X 射線裝置）獲得的實驗數據。高Z靶的X射線發射率和對低Z靶的修正可在NCRP報告 ^(4){ }^{4} 第51號中找到。 xx 射線在各種電位（相當於有效電子能量）下在各種材料中產生的衰減，可在 NCRP 報告 ^(5){ }^{5} No.這些衰減數據是直接適用於離子植入器的寬光束條件。舉例來說，一束 1 mA 的 100-keV100-\mathrm{keV} 電子束垂直打在鋁金屬結構上，在垂直於電子束的一公尺處的曝光率約為 290mR//h290 \mathrm{mR} / \mathrm{h} 。6.4 mm 厚 (0.25 英寸) 的鋼結構會將曝光率降低到 ∼30mR//h\sim 30 \mathrm{mR} / \mathrm{h} ，而 1.6 mm ( 1//16inch1 / 16 \mathrm{inch} ) 的鉛會進一步降低到 ∼0.14mR//h\sim 0.14 \mathrm{mR} / \mathrm{h} 。正向的曝光率可以忽略不计。
Principles for Reducing Radiation 減少輻射的原則
Many factors are involved in reducing the radiation external to ion implanters. Fortunately, most of these factors affect the quality of the positive ion beam, and anything that improves the implanter beam generally acts to reduce the production of xx rays. 減少離子植入器的外部輻射涉及許多因素。幸運的是，這些因素大多數都會影響正離子束的品質，任何能改善植入器光束的因素通常都能起到減少 xx 射線產生的作用。
The design of the implanter sets out the main themes of construction and operation and the arrangement of structures and of beam production and control mechanisms. Materials that are struck by accelerated electrons should have as low an atomic number as is compatible with other requirements. Cleanliness in the assembly of the vacuum system will minimize residual gas which produces electrons from collisions with the positive ion beam. The location of suppression fields and the magnitude of the negative voltage are important. In particular, the acceleration voltage interlock system must sense the suppression voltage on the suppressor itself for maximum effectiveness of the interlock. Interlocks on the highvoltage enclosure doors provide electrical as well as radiation safety. Measured radiation increases in the following order for the ions: boron, phosphorus, arsenic and argon. A good vacuum favors a good beam and at the same time reduces the number of electrons that are formed. 植入器的設計規定了構造和操作的主題，以及結構和束流產生與控制機制的安排。被加速電子撞擊的材料，其原子序數應盡可能低，以符合其他要求。真空系統組裝的潔淨度可將與正離子束碰撞產生電子的殘留氣體減至最少。抑制場的位置和負電壓的大小非常重要。尤其是加速電壓互鎖系統必須感應到抑制器本身的抑制電壓，才能發揮最大的互鎖效果。高壓機櫃門上的互鎖裝置可提供電氣以及輻射安全。測得的輻射依下列離子順序增加：硼、磷、砷和氬。良好的真空有利於產生良好的光束，同時減少形成的電子數量。
The structures of the implanter are generally not sufficient to attenuate the radiation to acceptable exposure rates and, hence, extra shielding is required. Of the three processes involved in the attenuation of photons (photoelectric, Compton and pair production), the photoelectric process (proportional to z^(4)z^{4} ) is the dominant one for the x-ray energies involved with implanters. Hence, lead is usually the material of choice. In all cases, it is important that the lead be installed in a permanent, and not easily removable, manner. 植入器的結構通常不足以將輻射衰減至可接受的暴露率，因此需要額外的遮蔽。在光子衰減所涉及的三個過程 (光電、康普頓和成對生產) 中，光電過程 (與 z^(4)z^{4} 成比例) 是植入器所涉及的 X 射線能量的主要過程。因此，鉛通常是首選的材料。在任何情況下，鉛都必須以永久性且不易移除的方式安裝。
The operation of the implanter can sometimes affect the radiation emitted. It is possible for a defocused ion beam or a beam striking unintended structures to produce excess electrons. Sufficient shielding must be installed to account for this condition if it can occur. 植入器的操作有時會影響所發出的輻射。偏焦的離子束或衝擊非預期結構的離子束有可能產生過量電子。如果可能發生這種情況，則必須安裝足夠的遮罩。
The final test for an implanter to meet the acceptable emission exposure rate is to make a radiation survey. 植入器是否符合可接受的放射暴露率的最後測試是進行輻射檢測。
Principles of Radiation Surveys 輻射測量原則
Only a few points pertinent to the survey of implanters are discussed. Surprisingly, presumably identical ion implanters do not always have identical external radiation patterns. Therefore, a complete radiation survey must be made of each ion implanter. A complete survey requires that all the implanter surfaces be measured including the end station, the top, and especially the bottom if the implanter is to be located on a floor other than the ground floor. Areas of concern include the high voltage enclosure, and the focusing and deflecting structures when electric fields are used. Sharp lobes and streaming through hinges, cracks and door handles are typical points that may require additional shielding. A complete survey will also pick up peculiarities of component installation and changes in geometry of structures. 僅討論與植入器調查相關的幾點。令人驚訝的是，假定相同的離子植入器並不總是具有相同的外部輻射模式。因此，必須對每個離子植入器進行完整的輻射檢測。完整的輻射測量需要測量所有植入器的表面，包括端站、頂部，尤其是底部（如果植入器位於地面以外的樓層）。需要注意的地方包括高壓電罩，以及使用電場時的聚焦和偏轉結構。尖銳的裂片和流經鉸鏈、縫隙和門把是可能需要額外屏蔽的典型點。完整的調查也會發現元件安裝的特殊性以及結構幾何形狀的變化。
Thin sodium iodide detectors, with a high sensitivity for the low-energy photon spectra, can be used for rapid surveys of all the surfaces to locate areas that need attention. Measurements of areas of interest with a calibrated Geiger-Müller (GM) counter and/or ionization chamber can then be used to determine the exposure rate. At these low photon energies the energy response of the GM counter and ionization. chamber can be important. 薄型碘化鈉探測器對低能量光子光譜具有高靈敏度，可用於快速檢測所有表面，以找出需要注意的區域。使用校準過的蓋革-繆勒 (GM) 計數器和/或電離室測量有興趣的區域，就可以用來確定曝光率。在這些低光子能量下，GM 計數器和電離室的能量反應可能很重要。
Assuming that the accuracy of the survey meter is appropriately accounted for by calibration and the energy response factor, the precision of the measurement must still be considered. To account for the precision, the working limit is set below the standard limit by, for example, two standard deviations of the survey meter measurement, a practice that makes it unlikely that the exposure rate limit will be exceeded by odds of one in twenty. 假設測量儀器的精確度已透過校準和能量反應係數適當計算，則仍必須考慮測量的精確度。為了考量精確度，工作限值會設定在標準限值之下，例如測量儀測量值的兩個標準差，這種做法使得暴露率限值不太可能超過二十分之一的機率。
Finally, because parameters can be varied in the operation of the implanter, the survey must be made under conditions that will produce maximum radiation. These conditions are maximum acceleration voltage, maximum sustainable beam current consistent with not damaging the unit, adequate suppression voltage, and use of that ion, included in the implanter specifications, that produces maximum radiation. 最後，由於植入器的操作參數可以改變，因此必須在能夠產生最大輻射的條件下進行檢測。這些條件包括最大加速電壓、不會損壞裝置的最大持續束流、足夠的抑制電壓，以及使用植入器規格中可產生最大輻射的離子。
Exposure Limits 暴露限值
Exposure limits, defined in terms of emission exposure rate, can vary over a wide range depending on who sets them. To maintain consistency, these measurements are made at a specified distance from the external surface with a detector of specified area and dimensions. In the United States, the Bureau of Radiological Health** (BRH) sets the exposure limits at the federal level for electronic products that emit radiation, currently 0.5mR//h0.5 \mathrm{mR} / \mathrm{h} for those products for which it has set performance standards. Standards have not been set for particle accelerators but presumably the same value of 0.5mR//h0.5 \mathrm{mR} / \mathrm{h} should be acceptable. The radiation control programs of the various states follow this limit. Some foreign countries and manufacturers use lower values. 暴露限值是以發射暴露率來定義的，會因設定者的不同而有很大的差異。為了保持一致性，這些測量是在距離外部表面指定的距離，使用指定面積和尺寸的偵測器進行的。在美國，放射衛生局 (Bureau of Radiological Health**, BRH) 在聯邦層級設定放射輻射電子產品的暴露限值，目前 0.5mR//h0.5 \mathrm{mR} / \mathrm{h} 是針對其已設定效能標準的產品。目前尚未針對粒子加速器設定標準，但據推測， 0.5mR//h0.5 \mathrm{mR} / \mathrm{h} 的相同值應該是可以接受的。各州的輻射控制計畫都遵循此限制。有些外國國家和製造商則使用較低的數值。
In a well-designed, well-built and properlytested ion implanter, the exposure rate from emitted ionizing radiation should easily be able to be kept within acceptable limits. 在設計完善、建造精良且經過適當測試的離子植入器中，所釋出的電離輻射照射率應可輕易維持在可接受的範圍內。
References 參考資料
W.W. Buechner, R.J. Van der Graaff, E.A. Burrill and A. Sperduto, Thick-Target X-Ray Production in the Range 1250 to 2350 kV, Phys. Rev. 74, 1348 (1948). W.W. Buechner, R.J. Van der Graaff, E.A. Burrill and A. Sperduto, Thick-Target X-Ray Production in the Range 1250 to 2350 kV, Phys. Rev. 74, 1348 (1948)。
C.T. Ulrey, An Experimental Investigation of the Energy in the Continuous X-Ray Spectra of Certain Elements, Phys. Rev. 11, 401 (1918). C.T. Ulrey，《某些元素連續 X 射線光譜能量的實驗研究》，Phys. Rev. 11, 401 (1918)。
International Commission on Radiation Units and Measurements, Radiation Quantities and Units (International Commission on Radiation Units and Measurements, Washington, D.C., 1980, ICRU Report 33).
National Council on Radiation Protection and Measurements, Radiation Protection Design Guidelines for 0.1-100MeV0.1-100 \mathrm{MeV} Particle Accelerator Facilities (National Council on Radiation Protection and Measurements, Washington, D.C., 1977, NCRP Report No. 51). 美國國家輻射防護與測量委員會，《 0.1-100MeV0.1-100 \mathrm{MeV} 粒子加速器設施的輻射防護設計指南》（美國國家輻射防護與測量委員會，華盛頓特區，1977 年，NCRP 第 51 號報告）。
National Council on Radiation Protection and Measurements, Structural Shielding Design and Evaluation for Medical Use of XX Rays and Gamma Rays of Energies up to 10 MeV (National Council on Radiation Protection and Measurements, Washington, D.C., 1976, NCRP Report No. 49). 國家輻射防護與測量委員會，《能量高達 10 MeV 的 XX 射線和伽馬射線的醫療用途結構屏蔽設計與評估》（國家輻射防護與測量委員會，華盛頓特區，1976 年，NCRP 第 49 號報告）。
**Food and Drug Administration, U.S. Department of Human and Health Services. ** 美國人類與健康服務部食品與藥物管理局。
