【発明の詳細な説明】[Detailed description of the invention]
本発明は三塩化ホウ素の精製法に関する。
三塩化ホウ素（BCl3）は、陽イオン重合触媒
等として確立された用途を有しているが、さらに
近年、集積回路の微細化要求の高まるにつれて、
半導体素子の配線として用いられるアルミニウム
のドライエツチングにおける塩素の供給源として
の用途が急速にのびている。
BCl3は酸化ほう素（B2O3）をCl2、アルカリ金
属の塩化物または四塩化けい素（SiCl4）等によ
つて塩素化する等公知の方法によつてつくられる
が、生成された粗BCl3中には、N2、O2ホスゲン
（COCl2）、ハロゲン化炭化水素（例えばCCl4、
CHCl3、以下TOCという）Si化合物（例えば
SiCl4、SiCl2H2等）、各種金属（例えばFe、Ni、
Cu、Ｋ、Na等）が含有されている。
ところで、BCl3をアルミニウムのドライエツ
チングに使用するには、上記不純物中各種金属、
COCl2、Si化合物、TOCを1ppm以下まで除去す
る必要がある。各種金属は単に粗BCl3をガス化
（沸点12.5℃）することによつて大半は除去出来
るが、COCl2、Si化合物、TOCを1ppm以下とす
ることは困難である。
従来、BCl3中のCOCl2の除去法としては、活性
炭、その他の接触を用い、H2により還元分解す
る方法、ゼオライトによる吸着除去法、蒸留分離
する方法等が発表されているが、いずれも半導体
用アルミニウムのドライエツチングに用いるため
のBCl3の精製法でなく、数％の不純物含有量を
数百ppmに精製するものである。また、Si化合
物、TOC成分は、これを放電によりラジカル化
し、重合体としてBCl3ガスから除去する方法等
が発表されているが、いずれも実験室的な試みの
域を出ていない。
また、特殊なカラムを用いる精密蒸留によつ
て、上記不純物の含有量を1ppm以下とする可能
性はあるが、高段数の蒸留塔が必要となり、装置
は高価で収率も低い。さらに、含有不純物の濃度
を正確に把握しないと適切な蒸留操作がむずかし
く、不活性ガス雰囲気中の加圧蒸留を行なうなど
操作が繁雑となり、また、BCl3と蒸気圧の近い
COCl2（沸点7.8℃）をH2で還元分解した後、精密
蒸留を行なうことも考えられたが、実際には操作
が繁雑で収率が低い欠点がある。
本発明者等は上記の事情に鑑み、粗BCl3中の
有害不純物を除去し、アルミニウムのドライエツ
チングに使用出来る高純度のBCl3に精製する簡
単な方法を鋭意研究した結果、ガス吸着によつて
上記有害不純物がいずれも除去されることを知見
した。
本発明は上記の知見に基づいてなされたもの
で、その要旨は、粗BCl3を気相状態で活性炭と
接触せしめ、Si化合物、COCl2、TOCを同時に
吸着除去するBCl3の精製法にある。
以下本発明を説明する。
本発明の吸着剤による粗BCl3精製に当つて使
用した装置の代表例を第１図に示す。すなわち、
粗BCl3を入れた容器１を加温槽２に浸漬し、ガ
ス化したBCl3を外部冷却部３を有し、吸着剤を
充填した吸着管４を通して冷媒５によつて冷却さ
れたトラツプ６によつて捕集した。なお、図中７
は圧力計、８はバルブ、９は流量計である。
上記装置の吸着管４に一定量の充分乾燥した各
種充填剤を充填し、これを一定温度に保持しなが
ら、所定の流速でBCl3ガスを通過せしめ、有害
不純物の破過状態を調べた。
その結果、Si化合物は相当部分が気化されず容
器１中に残留し、気相中の濃度は低くなるにもか
かわらず、最も早く破過すること、および活性炭
の有害不純物の除去能力が他の吸着剤に比して格
段に優れていることが判明した。第２図は、各種
吸着剤を用いた場合の結果の一部を示すもので、
Si化合物の破過状態を吸着剤を通過し留出した
BCl3中のSi濃度によつて示した。図中、は活
性炭、はシリカゲル、、はそれぞれゼオラ
イトの一種であるSP115、ゼオロンを用いた場合
の破過曲線である。
同様なことを各種活性炭について行なつたが、
いずれも有害不純物の除去能力に優れ、活性炭の
種類による優劣は殆ど認められなかつた。
本発明におけるBCl3の精製法においては、系
内に水分が存在すると極く微量でも、反応式
BCl3＋3H2O→3HCl＋H3BO3
に示すように反応する。この反応により、生成し
たHClは配管、バルブ等の腐食原因となり、また
H3BO3は微粉状となつて各部に付着し装置閉塞
の原因となる。そのため、実装置を運転する場合
には、前もつて装置係内を完全な乾燥状態にする
必要がある。例えば露点−65℃に乾燥したN2を
係全体に通しながら、あらかじめ乾燥した活性炭
を充填した吸着管を150℃以上に２時間以上保持
し、その後、吸着管を冷却しガス状BCl3を流す。
吸着管の加熱は吸着管に加熱装置を設けても、乾
燥N2を加熱して通してもよい。
また、BCl3は常温で活性炭重量の約1/2量吸着
され、その際多量の吸着熱を発生し、容易に100
℃以上にも達するが、高温下では有害不純物の吸
着能が著しく低下し、破過が早まり、装置効率が
低下する。従つて、吸着管の操作は、BCl3を通
し始めてから、活性炭に飽和吸着される初期吸着
（この間、BCl3は吸着層を通過することなく留出
しない）中に発生する熱をすみやかに除去する
か、初期吸着が終了後BCl3の供給を止め、吸着
層を所定温度に冷却して本吸着に移行するのが望
ましい。この場合、初期吸着の終了温度が所定温
度より高いと、温度を下げることによつてBCl3
はさらに吸着されるが、その量は比較的少ないた
め、吸着層の温度調節は容易である。いずれにし
ても、吸着管には吸着剤を冷却する冷却部を設け
ることが望ましい。所定温度において初期吸着の
終了した活性炭に対するBCl3の吸着は起らずし
たがつて活性炭の温度は上昇せず、有害成分が効
率よく吸着除去される。
上記吸着層の温度は、液化しないかぎり低い方
が有害不純物の吸着量が増大し、また、吸着管を
通すBCl3の空間速度（SV：hr-1）は小さい程物
質移動量が短くなり、いずれも、破過に致るまで
のBCl3の留出量は増大する。しかし、温度は、
冷媒として水の使用出来る範囲である15〜20℃、
またSVは、吸着管の生産性を考慮して40〜70、
好ましくは40〜50が実装置としては適当である。
次に実施例を示し本発明を具体的に説明する。
実施例 １
内径が28mmのジヤケツト付吸着管に、充分乾燥
した８〜32メツシユの活性炭110ｇを充填した。
この吸着層の長さは350mm、吸着剤容量は215c.c.で
あつた。この吸着層にSi：190ppm、COCl2：
240ppm、TOC：130ppmの粗BCl3を気化させ、
SV50hr-1で流した。この際吸着管ジヤケツトに
は12℃の冷水を流し吸着層を冷却した。初期吸着
の間活性炭のBCl3を吸着しつつある部分は狭い
幅で75℃まで昇温し、その昇温部分が次第に吸着
層出口側に移行して、吸着層の出口側より出ると
初期吸着が終了し、BCl3の留出が始まる。上記
初期吸着において活性炭に吸着されたBCl3は約
55ｇで、充填した活性炭の量の約1/2であつた。
上記留出したBCl3ガスを経時的にサンプリング
し、有害成分であるSi化合物（Siの量として分
析）、COCl2、TOCの濃度を測定したところ、充
填活性炭重量の1.5倍のBCl3が留出するまでは、
いずれの有害成分も検出されず、分析の検出限度
である1ppm以下であつた。この間の活性炭の温
度は13〜15℃であつた。上記結果を第３図に示し
た。図中ａはSi濃度、ｂはCOCl2濃度を示す。
TOCは、ａ，ｂより遅れて破過する。したがつ
て、Siは有害不純物破過を検出する指標となる。
なお、分析法として、Si、COCl2は比色法、
TOCはTOC測定計を用いた。また、参考のため
に各種金属類の粗BCl3中濃度と、留出したBCl3
中の濃度を下表に示した。
The present invention relates to a method for purifying boron trichloride. Boron trichloride (BCl 3 ) has established uses as a cationic polymerization catalyst, but in recent years, as the demand for miniaturization of integrated circuits has increased,
Its use as a source of chlorine in the dry etching of aluminum used as wiring for semiconductor devices is rapidly increasing. BCl 3 is produced by known methods such as chlorinating boron oxide (B 2 O 3 ) with Cl 2 , alkali metal chloride, silicon tetrachloride (SiCl 4 ), etc. The crude BCl 3 contains N 2 , O 2 phosgene (COCl 2 ), halogenated hydrocarbons (e.g. CCl 4 ,
CHCl 3 , hereinafter referred to as TOC) Si compounds (e.g.
SiCl 4 , SiCl 2 H 2, etc.), various metals (e.g. Fe, Ni,
Cu, K, Na, etc.) are contained. By the way, in order to use BCl 3 for dry etching aluminum, various metals,
It is necessary to remove COCl 2 , Si compounds, and TOC to 1 ppm or less. Most of the various metals can be removed simply by gasifying crude BCl 3 (boiling point: 12.5°C), but it is difficult to reduce COCl 2 , Si compounds, and TOC to 1 ppm or less. Conventionally, methods for removing COCl 2 from BCl 3 have been announced, including a method of reductive decomposition with H 2 using activated carbon or other contact, a method of adsorption removal with zeolite, and a method of separation by distillation. This is not a method for purifying BCl 3 for use in dry etching aluminum for semiconductors, but rather purifying impurity content from a few percent to several hundred ppm. In addition, methods have been announced for converting Si compounds and TOC components into radicals by electrical discharge and removing them from BCl 3 gas as polymers, but none of these methods have gone beyond laboratory trials. Furthermore, it is possible to reduce the content of the above impurities to 1 ppm or less by precision distillation using a special column, but this requires a distillation column with a high number of plates, making the equipment expensive and yielding low. Furthermore, if the concentration of impurities contained is not accurately known, it is difficult to carry out appropriate distillation operations, resulting in complicated operations such as pressurized distillation in an inert gas atmosphere .
It has been considered to perform precision distillation after reductive decomposition of COCl 2 (boiling point 7.8°C) with H 2 , but in practice this method has the drawbacks of complicated operations and low yields. In view of the above circumstances, the present inventors have conducted extensive research on a simple method to remove harmful impurities from crude BCl 3 and purify it into high-purity BCl 3 that can be used for dry etching of aluminum. It was found that all of the above harmful impurities were removed. The present invention was made based on the above findings, and its gist lies in a BCl 3 purification method in which crude BCl 3 is brought into contact with activated carbon in a gaseous state, and Si compounds, COCl 2 and TOC are simultaneously adsorbed and removed. . The present invention will be explained below. FIG. 1 shows a typical example of an apparatus used for purifying crude BCl 3 using the adsorbent of the present invention. That is,
A container 1 containing crude BCl 3 is immersed in a heating tank 2, and the gasified BCl 3 is passed through an adsorption tube 4, which has an external cooling section 3 and is filled with an adsorbent, into a trap 6 cooled by a refrigerant 5. Collected by. In addition, 7 in the figure
is a pressure gauge, 8 is a valve, and 9 is a flow meter. The adsorption tube 4 of the above apparatus was filled with a certain amount of various sufficiently dried fillers, and while the temperature was maintained at a constant temperature, BCl 3 gas was passed through the tube at a certain flow rate, and the state of breakthrough of harmful impurities was investigated. As a result, a considerable portion of the Si compound remains in the container 1 without being vaporized, and although the concentration in the gas phase is low, it breaks through the earliest, and activated carbon's ability to remove harmful impurities is superior to other compounds. It was found to be significantly superior to adsorbents. Figure 2 shows some of the results when using various adsorbents.
The breakthrough state of Si compounds was passed through an adsorbent and distilled.
It is shown by the Si concentration in BCl3 . In the figure, indicates the breakthrough curve when activated carbon, silica gel, and SP115 and zeolon, which are a type of zeolite, are used, respectively. The same thing was done with various activated carbons, but
All of them had excellent ability to remove harmful impurities, and there was almost no discernible superiority or inferiority depending on the type of activated carbon. In the BCl 3 purification method of the present invention, if water is present in the system, even if it is in a very small amount, a reaction occurs as shown in the reaction formula BCl 3 +3H 2 O→3HCl+H 3 BO 3 . The HCl generated by this reaction causes corrosion of pipes, valves, etc.
H 3 BO 3 becomes fine powder and adheres to various parts, causing equipment blockage. Therefore, before operating the actual device, it is necessary to completely dry the inside of the device. For example, an adsorption tube filled with pre-dried activated carbon is held at 150°C or above for 2 hours or more while dry N2 with a dew point of -65°C is passed through the entire chamber, and then the adsorption tube is cooled and gaseous BCl3 is passed through it. .
The adsorption tube may be heated by providing a heating device in the adsorption tube, or by passing heated dry N 2 through it. In addition, BCl 3 is adsorbed in an amount of approximately 1/2 of the weight of activated carbon at room temperature, generating a large amount of heat of adsorption and easily absorbing 100
However, at high temperatures, the ability to adsorb harmful impurities is significantly reduced, breakthrough is accelerated, and equipment efficiency is reduced. Therefore, the operation of the adsorption tube is such that the heat generated during the initial adsorption of saturated adsorption onto activated carbon (during this period, BCl 3 does not pass through the adsorption layer and is not distilled out) after BCl 3 starts passing through is quickly removed. Alternatively, it is desirable to stop the supply of BCl 3 after the initial adsorption is completed, cool the adsorption layer to a predetermined temperature, and then proceed to main adsorption. In this case, if the initial adsorption end temperature is higher than the predetermined temperature, BCl 3 can be reduced by lowering the temperature.
is further adsorbed, but the amount is relatively small, so the temperature of the adsorption layer can be easily controlled. In any case, it is desirable that the adsorption tube be provided with a cooling section for cooling the adsorbent. At a predetermined temperature, BCl 3 is not adsorbed on the activated carbon that has completed its initial adsorption, so the temperature of the activated carbon does not rise, and harmful components are efficiently adsorbed and removed. As long as the temperature of the adsorption layer is low, the amount of harmful impurities adsorbed increases as long as it does not liquefy, and the smaller the space velocity (SV: hr -1 ) of BCl 3 passing through the adsorption tube, the shorter the amount of mass transfer. In either case, the amount of BCl 3 distilled out increases until breakthrough occurs. However, the temperature
15-20℃, which is the range where water can be used as a refrigerant.
In addition, the SV is 40 to 70, considering the productivity of the adsorption tube.
Preferably, 40 to 50 is suitable for actual equipment. Next, the present invention will be specifically explained with reference to Examples. Example 1 A jacketed adsorption tube with an inner diameter of 28 mm was filled with 110 g of sufficiently dried activated carbon of 8 to 32 meshes.
The length of this adsorption layer was 350 mm, and the adsorbent capacity was 215 c.c. This adsorption layer contains Si: 190ppm, COCl 2 :
240ppm, TOC: 130ppm crude BCl3 is vaporized,
It was flushed with SV50hr -1 . At this time, 12°C cold water was flowed through the adsorption tube jacket to cool the adsorption layer. During the initial adsorption, the temperature of the part of the activated carbon that is adsorbing BCl 3 rises to 75℃ in a narrow width, and this heated part gradually moves to the outlet side of the adsorption layer, and when it exits from the outlet side of the adsorption layer, the initial adsorption is completed. is completed, and the distillation of BCl 3 begins. In the above initial adsorption, BCl 3 adsorbed on activated carbon is approximately
The amount was 55g, which was about 1/2 of the amount of activated carbon packed.
When the BCl 3 gas distilled above was sampled over time and the concentrations of harmful components such as Si compounds (analyzed as the amount of Si), COCl 2 and TOC were measured, it was found that 1.5 times the weight of the charged activated carbon was distilled . Until you put it out,
No harmful components were detected, and they were below the detection limit of 1 ppm. The temperature of the activated carbon during this period was 13-15°C. The above results are shown in FIG. In the figure, a indicates the Si concentration, and b indicates the COCl 2 concentration.
TOC breaks through later than a and b. Therefore, Si serves as an indicator for detecting the breakthrough of harmful impurities. The analytical methods for Si and COCl 2 are colorimetric,
TOC was measured using a TOC meter. Also, for reference, the concentrations of various metals in crude BCl 3 and the distilled BCl 3
The concentrations are shown in the table below.
【表】
実施例 ２
実施例１において吸着管ジヤケツトに冷水を通
さない外は、同じ操作によりBCl3の精製を行つ
た。この場合初期吸着の終つた活性炭の温度は35
℃で、経時的にSiの分析を行なつた結果、活性炭
量の0.7倍のBCl3が留出するまでは、Siの破過は
認められなかつた。
以上述べたように、本発明に係るBCl3の精製
法は、アルミニウムのドライエツチングに対して
有害なSi化合物、COCl2、TOCを同時に吸着操
作によつて、ほぼ完全に除去することが出来る極
めて優れた方法である。[Table] Example 2 BCl 3 was purified using the same procedure as in Example 1 except that cold water was not passed through the adsorption tube jacket. In this case, the temperature of activated carbon after initial adsorption is 35
As a result of conducting Si analysis over time at ℃, Si breakthrough was not observed until BCl 3 0.7 times the amount of activated carbon was distilled out. As mentioned above, the BCl 3 purification method according to the present invention is an extremely effective method that can almost completely remove Si compounds, COCl 2 and TOC, which are harmful to aluminum dry etching, by simultaneous adsorption operation. This is an excellent method.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は、本発明の装置の代表例を示すフロー
図、第２図は、粗BCl3を気化し、各種吸着剤を
通過し、留出させた場合のSiの破過する状態を示
す図、第３図は、粗BCl3を気化し、活性炭を通
過し、留出させた場合のSi、COCl2の破過状態を
示す図である。
１……容器、２……加温槽、３……冷却部、４
……吸着管、５……冷媒、６……トラツプ、７…
…圧力計、８……バルブ、９……流量計、……
活性炭、……シリカゲル、……ゼオライト
SP115、……ゼオロン、ａ……Si、ｂ……
COCl2。
Fig. 1 is a flow diagram showing a typical example of the apparatus of the present invention, and Fig. 2 shows the Si breakthrough state when crude BCl 3 is vaporized, passed through various adsorbents, and distilled. FIG. 3 is a diagram showing the breakthrough state of Si and COCl 2 when crude BCl 3 is vaporized, passed through activated carbon, and distilled. 1... Container, 2... Warming tank, 3... Cooling section, 4
...Adsorption tube, 5...Refrigerant, 6...Trap, 7...
...Pressure gauge, 8...Valve, 9...Flowmeter,...
Activated carbon, silica gel, zeolite
SP115,...Zeoron, a...Si, b...
COCl2 .