JP2009266835A - Metal contamination evaluating method of silicon single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal contamination evaluating method of silicon single crystal that speedily confirms a metal contamination situation of a low-resistance silicon single crystal of which lifetime cannot be measured. <P>SOLUTION: Thermal processing is simultaneously performed on a wafer cut from the low-resistance single crystal of which lifetime cannot be measured, in the same thermal processing device as for a metal contamination evaluating wafer. The evaluating wafer getters a contaminated metal of the low-resistance silicon single crystal, and lifetime of the evaluating wafer is measured. Thus, the metal contamination situation of low-resistance silicon single crystal is confirmed. In a method for determining the presence of metal contamination, the wafer having resistance (specific resistance is desirable to be around 10 Ωcm) with which lifetime can be measured is used as the evaluating wafer. If thermal processing is performed at 1,000 to 1,200°C, metal contamination can stably, reliably and easily be evaluated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for evaluating metal contamination of a silicon single crystal, and more particularly, to a method for evaluating metal contamination of a silicon single crystal that can easily confirm the presence or absence of metal contamination in a low-resistance silicon single crystal whose lifetime is difficult to measure. .

  Metal impurities in the silicon single crystal, particularly heavy metals such as iron, copper, and nickel, deteriorate the performance of the semiconductor device, for example, causing deterioration of the oxide film breakdown voltage and increase of leakage current. The problem of contamination due to metal impurities is increasing as device miniaturization and higher integration progress.

  There are various methods for evaluating metal contamination of silicon single crystal, such as atomic absorption spectrometry, DLTS (Deep Level Transient Spectroscopy), secondary ion mass spectrometry (SIMS), etc. Time evaluation is one of them.

  As a conventional technique related to lifetime evaluation, for example, Patent Document 1 discloses the rate of change of the recombination lifetime of carriers of the single crystal with respect to the irradiation time when a P-type silicon single crystal having boron as a dopant is irradiated with a laser. A method is described in which the presence or absence of iron is detected by the change rate obtained by the microwave photoconductivity decay method (microwave PCD method). This change (increase) in lifetime is due to the fact that the Fe-B pair formed by iron and boron mixed in the crystal is dissociated by laser irradiation, and an electronic state different from that of the Fe-B pair is formed. Is due to. Furthermore, the iron contamination concentration can be obtained by preparing a calibration curve indicating the recombination lifetime for each iron concentration by the DLTS method.

  Patent Document 2 discloses that boron (B) -doped P-type silicon is used as a sample, heat treatment is performed to dissociate Fe-B pairs, and lifetimes τ0 and τ1 before and after the dissociation are measured by a photoconductive decay method. On the other hand, the FeTS [Fe] is obtained by DLTS method or SPV method (Surface Photo Voltage) for the same sample, and the proportionality constant α of the following formula is determined in advance. In the subsequent measurements, lifetimes τ0, τ1 and A method for deriving the Fe concentration using the proportionality constant α is disclosed.

        [Fe] = α [(1 / τ0) − (1 / τ1)]

However, in the method described in Patent Document 1, the rate of change of the recombination lifetime with respect to the irradiation time of the laser light depends not only on the iron concentration but also on the concentration of excess carriers generated by light irradiation. In the method described in Patent Document 2, since heat treatment is used for dissociation of Fe-B, the measurement takes time and labor, and a new heat treatment process is used. Since there is a problem that the risk of introducing contamination is high, in Patent Document 3, recombination lifetime τ1 before dissociation of Fe—B (in order to avoid confusion with the code in Patent Document 2 described above, A method has been proposed in which the iron contamination concentration is evaluated as follows by measuring τ _bd ) and the recombination lifetime (saturation value) τ 2 (also expressed as τ _ad ) after dissociation.

That is, when a P-type silicon semiconductor sample contaminated with iron is continuously irradiated with light having energy higher than the forbidden band of silicon, the Fe-B pair is gradually dissociated, and the recombination lifetime measured along with it is Increasingly, the recombination lifetime is saturated when Fe-B is completely dissociated. In the method described in Patent Document 3, the recombination lifetime τ _bd before dissociation of Fe—B and the recombination lifetime (saturation value) τ _ad after dissociation are measured, and the evaluation value DFe obtained thereby is calculated as follows: If DFe = (1 / τ _bd ) − (1 / τ _ad ), DFe has a correlation with the iron concentration. Therefore, this is obtained in advance as a calibration curve, and τ _bd and τ _ad are measured and evaluated. DFe is obtained and the iron contamination concentration is evaluated by collating with the calibration curve. A photoconductive decay method is used to measure the recombination lifetime.

  In connection with metal contamination, Patent Document 4 describes contamination of a wafer due to a metal contained in a member used in the semiconductor substrate (wafer) heat treatment apparatus, in particular, a heat treatment tube, in the process. In order to reduce the temperature, a method is described in which a heat-treated tube is cleaned by previously introducing a metal-contaminated getter substrate (dummy wafer) into the heat-treated tube and performing a heat treatment. This method will be mentioned again in the context of the present invention.

JP-A-9-218175 JP-A-6-69301 JP 2000-183123 A JP 2002-252179 A

  As described above, the lifetime measurement of the carrier is used for evaluating the metal contamination of the silicon single crystal. In particular, the photoconductivity (ratio) attenuation method (microwave PCD method) is capable of nondestructive and quick measurement. Therefore, it is widely used for quality evaluation of wafers.

  However, due to the measurement principle, a silicon single crystal having a low resistance (resistivity of about 1 Ωcm or less) has a very low resistivity, and therefore has a very high microwave reflectance. Therefore, since the output of the microwave PCD detector is saturated or microwave noise is superimposed, it becomes difficult to detect a change in reflectivity due to excess carrier injection, regardless of whether it is P-type or N-type. Measurement is not possible. Therefore, when evaluating metal contamination of a low-resistance silicon single crystal, atomic absorption spectrometry or SIMS is used. However, it is expensive and takes too much time to evaluate, so it can be used on a production line. There was a problem that I could not.

  The present invention relates to a metal contamination state of a low resistance silicon single crystal for which lifetime measurement cannot be performed, in other words, it is possible to quickly confirm whether or not the silicon single crystal is contaminated with metal. It aims to provide a method.

  The diffusion coefficient of heavy metals is extremely large compared to boron (B) and phosphorus (P) which are dopant materials. Since it diffuses even at room temperature, if a metal-contaminated wafer flows through the wafer processing process, the process line itself may be contaminated. In the heat treatment step, the diffusion of the contaminated metal is further promoted, so that the inside of the heat treatment furnace is contaminated.

  The present inventor obtained the idea of using this contamination in reverse to confirm the metal contamination status of a low-resistance silicon single crystal that cannot measure lifetime. The idea is to use the metal-contaminated getter wafer used for cleaning the heat-treated tube described in Patent Document 4 described above for the evaluation of metal contamination. As a result of repeated studies based on this idea, a relatively high resistance wafer capable of measuring lifetime was used as a metal contamination evaluation wafer, and this wafer has a low resistance silicon single crystal contamination metal that cannot be measured for lifetime. It was confirmed that the metal contamination status of the low resistance silicon single crystal can be evaluated by transferring (ie, “transferring” the contamination).

  The gist of the present invention is that a wafer cut from a low-resistance silicon single crystal whose lifetime cannot be measured is simultaneously heat-treated in the same heat treatment apparatus as the metal contamination evaluation wafer, and the metal contamination evaluation wafer is applied to the low resistance silicon single crystal. A method for evaluating metal contamination of a silicon single crystal, characterized by confirming the metal contamination status of a low-resistance silicon single crystal by gettering the contaminated metal of the crystal by diffusion and measuring the lifetime of the wafer for metal contamination evaluation It is.

  The “low resistance silicon single crystal” refers to a silicon single crystal having a resistivity of 1 Ωcm or less. It is the object of metal contamination assessment.

  On the other hand, the “metal contamination evaluation wafer” is a wafer used for confirming the metal contamination state of the low resistance silicon single crystal to be evaluated. Here, “confirmation of metal contamination status” means checking (inspecting) whether or not there is metal contamination in the silicon single crystal ingot manufacturing process and wafer processing process.

  In the method for evaluating metal contamination of a silicon single crystal according to the present invention, if the wafer for metal contamination evaluation has a resistance capable of lifetime measurement, the evaluation of metal contamination of the low resistance silicon single crystal can be performed stably and reliably. Can be done.

  Further, in the method for evaluating metal contamination of a silicon single crystal according to the present invention, a wafer cut out from a low-resistance silicon single crystal and a metal contamination evaluation wafer are overlapped or slightly spaced, for example, in a state in which two wafers are arranged. If the heat treatment is performed in this step, the transfer (transfer) of the contaminated metal to the contamination evaluation wafer can be easily performed.

  According to the method for evaluating metal contamination of a silicon single crystal according to the present invention, a low-resistance silicon single crystal that has not been able to be easily performed because the lifetime cannot be measured. The metal contamination can be easily evaluated in a short time and at a low cost.

  In the method for evaluating metal contamination of a silicon single crystal according to the present invention, a wafer cut out from a low-resistance silicon single crystal whose lifetime cannot be measured is simultaneously heat-treated in the same heat treatment apparatus as the metal contamination evaluation wafer to evaluate metal contamination. A method for confirming a metal contamination state of a low resistance silicon single crystal by causing gettering of the contamination metal of the low resistance silicon single crystal to the wafer for diffusion by diffusion and measuring a lifetime of the wafer for metal contamination evaluation It is.

  The wafer cut from the low-resistance silicon single crystal that cannot measure the lifetime is subjected to the heat treatment in the same heat treatment apparatus as the metal contamination evaluation wafer at the same time. This is for transferring (transferring) to. Contaminating metals contained in the low-resistance silicon single crystal are easily gettered in a short time by the evaluation wafer by performing high-temperature treatment simultaneously in the same heat treatment apparatus.

  In the metal contamination evaluation method of the present invention, the presence or absence of metal contamination in a single crystal ingot manufacturing process or wafer processing process is checked by measuring the lifetime of an evaluation wafer gettered with a contaminated metal as described above. Indirectly, the metal contamination status of the low resistance silicon single crystal can be confirmed.

  There is no particular limitation on the heat treatment temperature. This is because the transition of the contaminated metal to the wafer for evaluation proceeds by heat treatment regardless of the temperature, so that it is possible to confirm the metal contamination status of the low resistance silicon single crystal. Conventionally, the lifetime measurement has been performed in a temperature range of about 1100 ° C., and the higher the temperature, the more the transition of the contaminated metal from the low-resistance silicon single crystal to the evaluation wafer is promoted. Therefore, it is desirable to hold the heat treatment conditions at 1000 to 1200 ° C. for 10 minutes to 2 hours. When the holding time is less than 10 minutes, the growth of the surface oxide film and the transfer of the contaminated metal to the wafer for evaluation are not necessarily sufficient. When the holding time exceeds 2 hours, the processing takes time and oxidation-induced stacking fault (OSF) Occurrence increases the carrier generation speed and decreases the lifetime.

There is no particular limitation on the atmosphere during the heat treatment. An argon atmosphere, a dry oxygen (O ₂ ) atmosphere, or the like, which is usually used in a silicon single crystal manufacturing process or a wafer processing process, or any other atmosphere in which contamination to the evaluation wafer hardly occurs. An atmosphere containing chlorine (Cl ₂ ) or chlorine compounds should be avoided.

  There is also no particular limitation on the arrangement of wafers cut out from a low-resistance silicon single crystal in the heat treatment apparatus and the wafer for contamination evaluation (positional relationship between both wafers in the heat treatment apparatus). This is because metal diffusion (that is, migration of contaminating metal from the low-resistance silicon single crystal to the evaluation wafer) occurs even when both wafers are not in contact with each other.

  As described above, the contamination evaluation wafer is a wafer used for confirming the metal contamination state of the low-resistance silicon single crystal to be evaluated. Therefore, it is only necessary to clarify that there is no metal contamination. There is no limitation on what kind of wafer is used. For example, the evaluation wafer does not have to be the same size as the wafer cut out from the low-resistance silicon single crystal to be evaluated, and may be any size and shape that allows lifetime measurement. However, since the lifetime is measured to evaluate the contamination state of the low-resistance silicon single crystal, it is necessary to know in advance the lifetime of the evaluation wafer to be used.

  In the method for evaluating metal contamination of a silicon single crystal according to the present invention, it is desirable to adopt an embodiment in which the evaluation wafer is a wafer having a resistance capable of lifetime measurement (this is referred to as Embodiment 1). Low-resistance silicon single crystals are often used for specific applications such as epitaxial wafer substrates, and are managed separately from normal resistivity silicon single crystals. Although a wafer is not used as an evaluation wafer, a wafer having a resistance capable of measuring a lifetime (that is, a resistance higher than that, not a low resistance mentioned here) is used as an evaluation wafer. Then, the metal contamination of the low resistance silicon single crystal can be constantly and reliably evaluated.

  It is more desirable to use a wafer having a high lifetime value reliability and a resistivity of around 10 Ωcm as an evaluation wafer, because the reliability of the evaluation of the contamination state of the low-resistance silicon single crystal can be increased.

  There is no limitation on the method of measuring the lifetime. For example, a microwave PCD method that is commercially available for non-destructive and quick measurement and is widely used for quality evaluation of wafers may be used.

  In the metal contamination evaluation method of the present invention and the evaluation method of the first embodiment, the wafers cut from the low-resistance silicon single crystal are further heat-treated simultaneously in the same heat treatment apparatus as the contamination evaluation wafer. It is desirable to adopt an embodiment (this is referred to as Embodiment 2) in which heat treatment is performed in a state where two sheets are arranged, for example, in a stacked state or with a slight gap.

  The method for arranging both wafers in the second embodiment may be either an arrangement method in which part or all of the respective surfaces are opposed to each other, or an arrangement method in which the peripheral edges are close to each other. Diffusion of the metal in the heat treatment apparatus occurs even in a non-contact state. However, it is more difficult to disperse the contaminated metal (that is, when two wafers are overlapped and adhered to each other or heat treatment is performed with two gaps arranged as little as possible) , Absorption into the evaluation wafer) is further promoted, and the contamination metal can be easily transferred to the evaluation wafer.

  The silicon single-crystal metal contamination evaluation method (including the evaluation methods of Embodiments 1 and 2) of the present invention is a method for confirming the metal contamination status of a low-resistance silicon single crystal, that is, a method for determining the presence or absence of metal contamination. It can also be used in production lines. When actually applying the evaluation method of the present invention, for example, if a wafer cut out from the silicon single crystal to be evaluated is evaluated as “with metal contamination” at a certain stage (process) in the wafer processing process, The silicon single crystal to be removed is removed from the process line to prevent contamination of the line itself, and quantitative evaluation is performed on the contamination state of the silicon single crystal by the SIMS method or the like.

  According to the method for evaluating metal contamination of a silicon single crystal according to the present invention, the contamination metal of the low resistance silicon single crystal is gettered to the metal contamination evaluation wafer by diffusion and the lifetime of the evaluation wafer is measured. This is a method for confirming the metal contamination status of crystals. According to this evaluation method, the lifetime can not be measured because of its low resistance, and it is easy to evaluate metal contamination in a low resistance silicon single crystal that had to rely on atomic absorption spectrometry or SIMS. Moreover, it can be performed at low cost. Application in production lines is also possible.

  Therefore, the method for evaluating metal contamination of a silicon single crystal according to the present invention can be widely used in the field of manufacturing semiconductor substrate materials.

Claims (3)

  A wafer cut from a low-resistance silicon single crystal, whose lifetime cannot be measured, is simultaneously heat-treated in the same heat treatment equipment as the metal contamination evaluation wafer, and the contamination metal of the low resistance silicon single crystal is diffused into the metal contamination evaluation wafer. A metal contamination evaluation method for a silicon single crystal, wherein the metal contamination state of the low resistance silicon single crystal is confirmed by measuring the lifetime of the wafer for metal contamination evaluation.   2. The method for evaluating metal contamination of a silicon single crystal according to claim 1, wherein the metal contamination evaluation wafer has a resistance capable of lifetime measurement.   3. The silicon single crystal according to claim 1, wherein the heat treatment is performed by superposing the wafer cut from the low-resistance silicon single crystal and the wafer for metal contamination evaluation or by providing a slight gap therebetween. Metal contamination assessment method.