A method measuring interstitial oxygen concentration

Abstract: A silicon wafer measuring method includes: (a) a first step of measuring a light transmission characteristic (I OBS ) of the pulled silicon wafer by incidence of parallel polarized light at Brewster angle into the pulled silicon wafer, (b) a second step of measuring a light transmission characteristic (I O ) of a floating zone silicon wafer functioning as a reference silicon wafer both front and rear sides of which are mirror polished, by incidence of parallel polarized light at Brewster angle into the floating zone silicon wafer, and (c) a third step of calculating an interstitial oxygen concentration [Oic] on the basis of the light transmission characteristic (I OBS ) of the pulled silicon wafer measured during the first step and the light transmission characteristic (I O ) of the floating zone silicon wafer measured during the second step.

Description: The present invention relates to a method of measuring the interstitial oxygen concentration in a pulled silicon wafer according to the preamble of claim 1. Such a method is know from IBM Disclosure Bulletin, Vol. 28, No. 3, August 1985. The present invention relates generally to a method for making a silicon wafer. In particular, the present invention relates to a method for making a silicon wafer in which interstitial oxygen concentration of a pulled silicon wafer is calculated on the basis of a light transmission characteristic measured by incidence of light into the pulled silicon wafer and a further light transmission characteristic measured by incidence of light into a floating zone silicon wafer functioning as a reference silicon wafer and then such a calculated value is compared with a reference value so as to exclude any pulled silicon wafer having defective interstitial oxygen concentration. In this type of conventional method for making silicon wafers, a pulled silicon wafer is picked up from a production line in order to detect it. As a reference silicon wafer, a floating zone type silicon wafer is prepared so as to have substantially the same optical behavior as that of the pulled silicon wafer, for example, by mirror polishing and chemically polishing of the front and rear sides thereof, depending on a treated condition of the pulled silicon wafer when it is picked up. After that, infrared ray enters into both the pulled silicon wafer and the referecnce silicon wafer at the same time to thereby measure a light transmission characteristic of the pulled silicon wafer and the floating zone silicon wafer so that the interstitial oxygen concentration of the pulled silicon wafer is calculated. According to such calculated interstitial oxygen concentration values, it is determined whether or not the pulled silicon wafer is defective. Such a conventional silicon wafer production method has the following disadvantages because the pulled silicon wafer and the floating zone silicon wafer have substantially the same optical behavior. (i) A lot of time and complicated measuring operations are required. In particular, a reference silicon wafer must be treated so as to correspond to the picked-up silicon wafer. (ii) It is not possible in practice to detect all of pulled silicon wafers on a production line. (iii) In addition, it cannot be avoided that some defective pulled silicon wafers are machined during later treatments thereof although it is not necessary. (iv) As a result, it is difficult to improve the production coefficient of the production line. If the method known from the above mentioned IBM Disclosure Bulletin is used, multiple reflections can be avoided. It is said, that in this way, surface conditions of the wafer are of no consequence for the measurement. It is an object of the present invention to improve the method for measuring an interstitial oxygen concentration in a silicon wafer in which a floating zone silicon wafer both front and rear sides of which are mirror polished can be used as a reference silicon wafer without any additional treatment. It is another object of the present invention to provide a silicon wafer measuring method in which a measuring operation is simple. It is a further object of the present invention to provide a method for making interstitial oxygen concentration of a silicon wafer in which all of pulled silicon wafers on a production line can be detected. These objects are achieved by the measuring method as defined in claim 1. According to the present invention, also, a silicon wafer production method in which a pulled silicon wafer sliced from a pulled silicon single crystal is subject to a series of treatments, includes the measuring method as defined in claim 1. The series of treatments include mechanical cutting (slicing), mechanical polishing (lapping), chemical polishing (etching), mirror polishing (mechanochemical polishing), detecting, removing, washing, and gettering. It is preferable that the method of the present invention includes further: (d) a step of comparing the interstitial oxygen concentration [Oic] of the pulled silicon wafer measured during the third step with a reference value, and (e) a step of removing the pulled silicon wafer if its interstitial oxygen concentration [Oic] is out of the reference value so as to be defective in view of the results compared during the fourth step. The light transmission characteristic of the pulled silicon wafer can be measured in various manners. One example of the pulled silicon wafer is a single-side polished wafer which has a mirror polished front side and non-polished rear side. Another example of it is a double-side polished wafer in which both front and rear sides thereof are chemically polished but not mirror polished. In a further example of it, both front and rear sides are mechanically polished but not chemically polished. It can be also measured when it is sliced or cut from a pulled silicon single crystal and then washed but not polished in any manner. The term "pulled silicon wafer" means a silicon wafer which is sliced or cut from a pulled silicon single crystal produced by a pulling method or so called Czochralski method and then treated, if desired, in various manners. Such a silicon wafer is usually made by a series of steps of cutting (slicing), mechanical polishing (lapping), chemical polishing (etching) and mirror polishing (mechanochemical polishing) in order although the present invention is not limited thereto. The chemical polishing step is performed after the mechanical polishing step in order to remove a damaged layer in the front and rear sides of the silicon wafer which are formed during the step of slicing or cutting a single crystal. In addition, the term "floating zone silicon wafer" means a silicon wafer which is sliced or cut from a silicon single crystal made by a floating zone melting method. The present invention can have the following advantageous effects: (i) A floating zone silicon wafer both front and rear sides of which are mirror polished can be used as it is without any additional treatment; (ii) The operation of measuring intersititial oxygen concentration [Oic] of a pulled silicon wafer can be simple; and (iii) The step of measuring interstitial oxygen concentration [Oic] of a pulled silicon wafer can be carried out at a desired position in a production line in order to detect all wafers; and (iv) The production coefficient on the production line can be improved. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a schematic view showing an apparatus for carrying out a preferred silicon wafer production method according to an embodiment of the present invention; Fig. 2 is a schematic view showing a transfer means for use in the embodiment of the present invention; Fig. 3 is a graph explaining and showing a further embodiment of the present invention; Fig. 4 is a graph explaining and showing another embodiment of the present invention; and Figs. 5 to 7 are graphs showing other embodiments, corresponding to Fig. 4. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 A first embodiment of the present invention will be described. According to the first embodiment of the present invention, a method for making a silicon wafer includes the step of measuring interstitial oxygen concentration prior to the steps of gettering and mirror polishing after the washing step accompanied by the chemically polishing step for silicon wafers on a production line. The measuring step in the silicon wafer production method according to the present invention includes a first step of measuring a light transmission characteristic (herein called transmitted light intensity I OBS ) of a pulled silicon wafer both front and rear sides of which are chemically polished during the chemically polishing step within the production line and then washed during the washing step, by incidence of parallel polarized light at Brewster angle B into the pulled silicon wafer, a second step of measuring a light transmission characteristic (herein called transmitted light intensity I O ) of a floating zone silicon wafer functioning as a reference silicon wafer both front and rear sides of which are mirror polished, by incidence of parallel polarized light at Brewster angle B into the reference silicon wafer or floating zone silicon wafer, a third step of calculating an interstitial oxygen concentration [Oic] on the basis of the light transmission characteristic or transmitted light intensity I OBS of the chemically polished pulled silicon wafer measured during the first step and the light transmission characteristic or transmitted light intensity I O of the mirror polished floating zone silicon wafer or reference silicon wafer measured during the second step, a fourth step of comparing the interstitial oxygen concentration [Oic] of the pulled silicon wafer measured during the third step with a reference value, and a fifth step of removing a pulled silicon wafer if its interstitial oxygen concentration [Oic] is out of the reference value so as to be defective in view of the results compared in the fourth step. During the first and second steps, the parallel polarized light enters into both the chemically polished pulled silicon wafer and the mirror polished floating zone silicon wafer at Brewster angle B. This is because any substantial reflection is avoided when the parallel polarized light moves in and out of the chemically polished pulled silicon wafer and the mirror polished floating zone silicon wafer whereby multiple reflections can be avoided within the chemically polished pulled silicon wafer and the mirror polished floating zone silicon wafer. During the second step, the floating zone silicon wafer is used as a reference silicon wafer because the interstitial oxygen concentration [Oi F ] of the floating zone silicon wafer is extremely smaller than that of the pulled silicon wafer. Also, both front and rear side of the floating zone silicon wafer are mirror polished because the incidence light or parallel polarized light is intended to be prevented from being scattered at both front and rear sides thereof. During the third step, how the interstitial oxygen concentration of the pulled silicon wafer is calculated on the basis of the light transmission characteristic or transmitted light intensity I OBS of the chemically polished pulled silicon wafer measured during the first step and the light transmission characteristic or transmitted light intensity I O of the floating zone silicon wafer measured during the second step will be explained hereinafter. First, by using the light absorption coefficient E resulting from the vibration of the interstitial oxygen in the pulled silicon wafer and the conversion coefficient k which is believed at the present time to be 3.03 x 10 17 number/cm 2 , the interstitial oxygen concentration [Oic] of the pulled silicon wafer can be expressed by the following formula: [Oic] = k x E By using the light absorbance A of the silicon wafer having a thickness d with the wave number of 1106 cm -1 resulting from the vibration of the interstitial oxygen and the optical path (L = 1.042d) of the parallel polarized light which enters at Brewster angle B, the light absorption coefficient E of the pulled silicon wafer can be expressed according to Lambert-Beer's law as follows: E = A/L = A/1.042d By using the light transmission characteristic or transmitted light intensity I of the pulled silicon wafer both front and rear sides of which are mirror polished and the light transmission characteristic or transmitted light intensity I O of the floating zone silicon wafer which is mirror polished, the light absorbance A of the pulled silicon wafer can be expressed as follows: A = 1n (I/I O ) -1 Thus, by using the light transmission characteristic or transmitted light intensity I OBS of the chemically polished pulled silicon wafer, the light transmission characteristic or transmitted light intensity I O of the mirror polished floating zone silicon wafer, the light scattering characteristic or scattered light intensity I S1 of the chemically polished pulled silicon wafer at its front side, and the light scattering characteristic or scattered light intensity I S2 of the chemically polished pulled silicon wafer at its rear side, the light absorbance A can be also expressed as follows: A = 1n [(I OBS + I S1 + I S2 )/I O ] -1 Accordingly, the interstitial oxygen concentration [Oic] of the pulled silicon wafer can be calculated as follows: [Oic] = (k/1.042d) x 1n [(I OBS + I S1 + I S2 ) / I O ] -1 The value of ln [(I OBS + I S1 + I S2 ) / I O ] -1 can be obtained from light absorbance characteristic which is an inverse number of natural logarithm of the ratio of the total of the light transmission characteristic or transmitted light intensity (I OBS ) of the chemically polished pulled silicon wafer, the light scattering characteristic or scattered light intensity (I S1 ) at the front side of the chemically polished pulled silicon wafer and the light scattering characteristic or scattered light intensity (I S2 ) at the rear side of the chemically polished pulled silicon wafer to the light transmission characteristic or transmitted light intensity (I O ) of the mirror polished floating zone silicon wafer. For example, the value of 1n [(I OBS + I S1 + I S2 ) / I O ] -1 can be obtained as shown in Fig. 3, by using the peak value in case of the wave number of 1106 cm -1 of the light absorption characteristic designated by the solid line when the interstitial oxygen concentration [Oic] is not zero and the value in case of the wave number of 1106 cm -1 of the light absorption characteristic designated by the inclined dotted line when the interstitial oxygen concentration [Oic] is zero. An apparatus for carrying out the first embodiment of the present invention will be explained. Referring to Figs. 1 and 2, a measuring apparatus 10 for carrying out the first embodiment includes a light source 11 such as a globe lamp, a Michelson interferometer 12 for forming interference light by overlapping two separate lights provided from the light source 11 after the light is separated by a semitransparent mirror 12A and then deflected by a movable mirror 12B and a fixed mirror 12C, a polarizer 13 for providing a sample or specimen which is a chemically polished pulled silicon wafer M and a reference silicon wafer which is a mirror polished floating zone silicon wafer R with parallel polarized light which is polarized from the interference light given by the Michelson interferometer 12 in which the sample or specimen M is transferred by a transfer means 20, a detector 14 for detecting the light transmission characteristic which is transmitted light intensity I OBS of the parallel polarized light of the sample M and the light transmission characteristic which is a transmitted light intensity I O of the parallel polarized light of the reference R, a calculator 15 connected to the detector 14 for calculating the interstitial oxygen concentration of the sample M after the light absorbance characteristic is calculated on the basis of the light transmission characteristic or transmitted light intensity I OBS of the sample M and the light transmission characteristic or transmitted light intensity I O of the reference R, and a means 16 for comparing a reference value such as an upper limit reference value and a lower limit reference value with a value of the interstitial oxygen concentration which is calculated by the calcutator 15. If desired, reflecting mirrors 17A, 17B are provided between the sample M and the detector 14 and/or between the reference R and the detector 14. Also, a reflecting mirror (not shown) can be arranged between the Michelson interferometer 12 and the polarizer 13. The transfer means 20 includes a pushing member 21 for pushing the sample M and the reference R from a plurality of transfer containers T 11 , T 12 one by one, a transfer belt 22 for transferring the sample M and the reference R pushed by the pushing means 21 one by one from one end thereof to the other end thereof, a holding means 23 for holding the sample M and the reference R one by one at the other end of the transfer belt 22 and then transferring the same to a measuring area where the sample M and the reference R are rotated by a rotation means 23A until they are held at Brewster angle B with respect to the parallel polarized light. After the interstitial oxygen concentration thereof is measured, the sample M and the reference R are again rotated by the rotation means 23A so as to come back to their original position and then move out of the measuring area. The transfer means 20 further includes another transfer belt 24 for receiving the sample M and the reference R which are released from the measuring area by means of the holding means 23 and then transferring them from one end of the transfer belt 24 to the other end thereof where a plurality of transfer containers T 21 , T 22 , T 23 , T 24 are placed. Although in the illustrated embodiment the reference R is contained in the transfer container T 12 , the reference R and the sample M together can be contained in the transfer container T 11 . In this case, the transfer container T 12 can be omitted. For example, the transfer containers T 21 , T 22 , T 23 , T 24 are used, respectively, as a transfer container for containing defective sample M which has a value of interstitial oxygen concentration more than the upper limit reference value, a transfer container for containing proper sample M which has a value of interstitial oxygen concentration between the upper limit reference value and the lower limit reference value, a transfer container for containing defective sample M which has a value of interstitial oxygen concentration less than the lower limit reference value, and a transfer container for containing the referecne R. Those transfer containers T 21 , T 22 , T 23 are designed to receive the reference R in response to the comparison results of the comparison means 16 in the measuring apparatus 10. Those transfer containers move to the other end of the transfer belt 24 so as to receive the reference R. In the measuring apparatus 10, the Michelson interferometer 12 receives the light from the light source 11 and then produces interference light. This interference light is further filtered so as to obtain parallel polarized light by means of the polarizer 13. After that, the parallel polarized light enters at Brewster angle B into the sample M and the reference R which are transferred to the measuring area by the transfer means 20 after they are pushed one by one from the transfer containers T 11 , T 12 . The light is absorbed and scattered in the sample M and the reference R according to the optical properties thereof. Therefore, the light absorbance characteristic, which can be calculated by the calculator 15 on the basis of the signals detected by the detector 14, is shown in Fig. 3 by way of example. According to Fig. 3 or a table corresponding to it, the calculator 15 calculates the following formula: 1n [(I OBS + I S1 + I S2 ) / I O ] -1 After that, the calculator 15 calculates the light absorbance coefficient E of the chemically polished pulled silicon wafer by the following formula: E = (1 / 1.042d) x 1n[(I OBS + I S1 + I S2 ) / I O ] -1 In addition, the calculator calculates the interstitial oxygen concentration [Oic] of the sample M of the chemically polished pulled silicon wafer M by the following formula: [Oic] = (k / 1.042d) x 1n[(I OBS + I S1 + I S2 ) / I O ] -1 After that, the comparison means 16 compares the reference value (for example, the upper limit reference value and the lower limit reference value) with the value of the interstitial oxygen concentration [Oic] of the sample or chemically polished pulled silicon wafer M which is calculated by the calculator 15. The compared results of the comparison means 16 are sent to means for controlling the transfer means 20 so as to be used during the operation of containing the sample M and the reference R into the transfer containers T 21 , T 22 , T 23 , T 24 . Examples 1 to 22 Working examples of the first embodiment will be explained so that a method for making a silicon wafer according to the present invention will be fully understood. As shown in Table 1, interstitial oxygen concentration [Oic] of plural pulled silicon wafers were measured according to the present invention. First, after both front and rear sides of the silicon wafers were chemically polished, interstitial oxygen concentration [Oic] thereof were measured. After that, both front and rear sides of those pulled silicon wafers were mirror polished. In such a mirror polished condition, the interstitial oxygen concentration [Oic]* of each pulled silicon wafer was measured according to the present invention. Such measured results of the interstitial oxygen concentration [Oic] of the chemically polished pulled silicon wafers and the interstitial oxygen concentration [Oic]* of the mirror polished pulled silicon wafers are plotted along the Y-axis and X-axis, respectively, in Fig. 4. This graph shows that the former reasonably corresponds to the latter so that the test results are positioned along the line X = Y. It is apparent from the examples 1 to 22 that, according to the present invention, the chemically polished pulled silicon wafers and the mirror polished floating zone silicon wafers can be used as sample and references, respectively, in order to directly measure interstitial oxygen concentration [Oic] of the pulled silicon wafers on the production line. Example No. interstitial oxygen concentration [O ic ] of chemically polished pulled silicon wafer (x 10 17 number/cm 3 ) interstitial oxygen concentration [Oic]* of mirror polished pulled silicon wafer (x 10 17 number/cm 3 ) 1 7.51 7.55 2 7.87 7.77 3 7.66 7.68 4 7.98 7.99 5 7.93 8.00 6 9.41 9.46 7 9.54 9.55 8 9.73 9.76 9 9.85 9.79 10 9.44 9.54 11 9.32 9.37 12 9.36 9.42 13 9.27 9.35 14 7.99 8.02 15 8.02 8.05 16 8.64 8.70 17 8.80 8.91 18 9.79 9.70 19 9.88 9.85 20 9.65 9.64 21 8.83 8.98 22 8.83 8.84 Although the above-stated embodiment is limited to the Michelson interferometer 12, the present invention is not restricted to such an embodiment only. For example, a spectrometer can be used in place of the Michelson interferometer. Although in the above-stated embodiment the interstitial oxygen concentration [Oic] is measured prior to the gettering step following the chemically polishing step, the present invention is not restricted to such embodiments only. For example, the interstitial oxygen concentration [Oic] can be measured at any position or place after the chemically polishing step and prior to the mirror polishing step. For instance, the interstitial oxygen concentration [Oic] can be measured during the silicon wafer detecting step. Embodiment 2 A second embodiment of the present invention will be explained with respect to the construction and operation thereof. The second embodiment of the present invention has substantially the same construction as that of the first embodiment except that, in addition to the interstitial oxygen concentration measuring step prior to the gettering step, the interstitial oxygen concentration measuring step is carried out after the gettering step. The interstitial oxygen concentration measuring step after the gettering step has the same construction as that of the interstitial oxygen concentration measuring step prior to the gettering step which corresponnds to the measuring step in the first embodiment. The operation of the second embodiment can be easily understood by taking into consideration that of the first embodiment. Thus, the explanation thereof is omitted. Embodiment 3 A third embodiment of the present invention will be explained with respect to the construction and operation thereof. The third embodiment of the present invention has substantially the same construction as that of the first embodiment except that, in place of the interstitial oxygen concentration measuring step prior to the gettering step, the interstitial oxygen concentration measuring step is carried out after the gettering step. The interstitial oxygen concentration measuring step after the gettering step has the same construction as that of the measuring step in the first embodiment. The operation of the third embodiment can be easily understood by taking into consideration that of the first embodiment. Thus, the explanation thereof is omitted. Embodiment 4 Embodiment 4 of the present invention has substantially the same construction as that of the embodiment 1 except that the fourth comparing step and the fifth removing step of the embodiment 1 are omitted. The operation of the embodiment 4 can be easily understood by taking into consideration that of the embodiment 1. Embodiment 5 A fifth embodiment of the present invention is similar to the first embodiment. In the fifth embodiment, however, a sample has a mirror polished front side and non-polished rear side during the step of measuring it. The light path L is 1.041d in place of 1.042d. In order to easily ascertain front and rear sides of a silicon wafer during subsequent treatments thereof, a front side of it is mirror polished while a rear side of it is not polished. Therefore, in Fig. 3, the light absorbance A is expressed as follows: A = 1n [(I OBS + I S )/I O ] -1 where I S is the light scattering characteristic or scattered light intensity of the one-side mirror polished pulled wafer at its rear side. The measuring step includes a first step of measuring a light transmission characteristic or transmitted light intensity I OBS of a pulled silicon wafer (herein called one-side polished silicon wafer) only a front side of which is mirror polished during the mirror polishing step within the production line and then washed during the washing step, by incidence of parallel polarized light at Brewster angle B into the pulled silicon wafer, a second step of measuring a light transmission characteristic or transmitted light intensity I O of a floating zone silicon wafer functioning as a reference silicon wafer both front and rear sides of which are mirror polished, by incidence of parallel polarized light at Brewster angle B into the reference silicon wafer or floating zone silicon wafer, a third step of calculating a interstitial oxygen concentration [Oic] on the basis of the light transmission characteristic or transmitted light intensity I OBS of the one-side polished pulled silicon wafer measured during the first step and the light transmission characteristic or transmitted light intensity I O of the mirror polished floating zone silicon wafer or reference silicon wafer measured during the second step, a fourth step of comparing the interstitial oxygen concentration [Oic] of the pulled silicon wafer measured during the third step with a reference value (for example, upper limit reference value and/or lower limit reference value), and a fifth step of removing a pulled silicon wafer if its interstitial oxygen concentration [Oic] is not within the reference value (for example, between the upper limit reference value and the lower limit reference value) so as to be defective in view of the results compared in the fourth step. During the first and second steps, the parallel polarized light enters into both the one-side polished pulled silicon wafer and the mirror polished floating zone silicon wafer at Brewster angle B because any substantial reflection is avoided when the parallel polarized light moves in and out of the one-side polished pulled silicon wafer and the mirror polished floating zone silicon wafer whereby multiple reflections can be avoided within the one-side polished pulled silicon wafer and the mirror polished floating zone silicon wafer. During the third step, how the interstitial oxygen concentration of the one-side polished pulled silicon wafer is calculated on the basis of the light transmission characteristic or transmitted light intensity I OBS of the chemically polished pulled silicon wafer measured during the first step and the light transmission characteristic or transmitted light intensity I O of the floating zone silicon wafer measured during the second step is substantially the same as that of the first embodiment. Examples 23 to 40 Working examples of the fifth embodiment will be explained so that a method for making a silicon wafer according to the present invention will be fully understood. As shown in Table 2, interstitial oxygen concentration [Oic] of plural pulled silicon wafers were measured according to the present invention. First, a silicon wafer only a front side of which was mirror polished, that is, one-side polished silicon wafer was measured with respect to its interstitial oxygen concentration [Oic]. After that, the pulled silicon wafer was mirror polished. In such a condition in which both front and rear sides thereof were mirror polished, the interstitial oxygen concentration [Oic]* of each pulled silicon wafer was measured according to the present invention. Such measured results of the interstitial oxygen concentration [Oic] of the one-side polished pulled silicon wafers and the interstitial oxygen concentration [Oic]* of the two-side mirror polished pulled silicon wafers are plotted along the Y-axis and X-axis, respectively, in Fig. 5. Thus, the former reasonably corresponds to the latter so that the test results are positioned along the line X = Y. It is apparent from the examples 23 to 40 that, according to the present invention, the one-side polished pulled silicon wafers and the mirror polished floating zone silicon wafers can be used as sample and references, respectively, in order to directly measure interstitial oxygen concentration [Oic] of the pulled silicon wafers on the production line. Example No. interstitial oxygen concentration [O ic ] of one-side polished pulled silicon wafer (x 10 17 number/cm 3 ) interstitial oxygen concentration [Oic]* of two-side polished pulled silicon wafer (x 10 17 number/cm 3 ) 23 11.57 11.67 24 11.64 11.82 25 9.21 9.27 26 9.36 9.42 27 11.45 11.48 28 5.33 5.39 29 6.42 6.54 30 6.51 6.58 31 10.12 10.12 32 10.12 10.12 33 10.15 10.18 34 9.51 9.57 35 7.24 7.21 36 7.21 7.18 37 8.03 8.03 38 7.09 7.06 39 10.12 10.09 40 10.27 10.33 Embodiment 5A Another embodiment 5A of the present invention will be explained with respect to the construction and operation thereof. The embodiment 5A of the present invention has substantially the same construction as that of the above-stated embodiment 5 except that, in addition to the interstitial oxygen concentration measuring step prior to the gettering step, the interstitial oxygen concentration measuring step is carried out after the gettering step. The interstitial oxygen concentration measuring step after the gettering step has the same construction as that of the interstitial oxygen concentration measuring step prior to the gettering step which corresponnds to the measuring step in the above-stated embodiment 5. The operation of the second embodiment can be easily understood by taking into consideration that of the above-stated embodiment 5. Thus, the explanation thereof is omitted. Embodiment 5B A further embodiment 5B of the present invention will be explained with respect to the construction and operation thereof. The embodiment 5B of the present invention has substantially the same construction as that of the above-stated embodiment 5 except that, in place of the interstitial oxygen concentration measuring step prior to the gettering step, the interstitial oxygen concentration measuring step is carried out after the gettering step. The interstitial oxygen concentration measuring step after the gettering step has the same construction as that of the measuring step in the above-stated embodiment 5. The operation of the embodiment 5B can be easily understood by taking into consideration that of the above-stated embodiment 5. Thus, the explanation thereof is omitted. Embodiment 6 A sixth embodiment of the present invention will be explained with respect to the construction and operation thereof. The sixth embodiment of the present invention has substantially the same construction as that of the fifth embodiment except that the fourth comparing step and the fifth removing step are omitted. Embodiment 7 A seventh embodiment of the present invention has the same construction as that of the first embodiment of the present invention except that both front and rear sides of a sample are mechanically polished but not chemically polished. A method for making a silicon wafer includes the step of measuring interstitial oxygen concentration prior to the step of chemically polishing after the washing step accompanied by the mechanically polishing step for silicon wafers on a production line. The measuring step includes a first step of measuring a light transmission characteristic (herein called transmitted light intensity I OBS ) of a pulled silicon wafer both front and rear sides of which are mechanically polished during the mechanical polishing step within the production line and then washed during the washing step, by incidence of parallel polarized light at Brewster angle B into the pulled silicon wafer, a second step of measuring a light transmission characteristic (herein called transmitted light intensity I O ) of a floating zone silicon wafer functioning as a reference silicon wafer both front and rear sides of which are mirror polished, by incidence of parallel polarized light at Brewster angle B into the reference silicon wafer or floating zone silicon wafer, a third step of calculating an interstitial oxygen concentration [Oic] on the basis of the light transmission characteristic or transmitted light intensity I OBS of the mechanically polished pulled silicon wafer measured during the first step and the light transmission characteristic or transmitted light intensity I O of the mirror polished floating zone silicon wafer or reference silicon wafer measured during the second step, a fourth step of comparing the interstitial oxygen concentration [Oic] of the pulled silicon wafer measured during the third step with a reference value, and a fifth step of removing a pulled silicon wafer if its interstitial oxygen concentration [Oic] is out of the reference value so as to be defective in view of the results compared in the fourth step. In order to obtain a desired flatness, the mechanical polishing step is carried out piror to the chemical polishing step. A damaged layer formed on each side of a silicon wafer during the step of cutting a silicon single crystal is deleted by chemical polishing thereof. Examples 41 to 46 Working examples of the seventh embodiment will be explained so that a method for making a silicon wafer according to the present invention will be fully understood. As shown in Table 3, interstitial oxygen concentration [Oic] of plural pulled silicon wafers were measured according to the present invention. First, after both front and rear sides of the silicon wafers were mechanically polished, interstitial oxygen concentration [Oic] thereof were measured. After that, both front and rear sides of those pulled silicon wafers were chemically polished and then mirror polished. In such a mirror polished condition, the interstitial oxygen concentration [Oic]* of each pulled silicon wafer was measured according to the present invention. Such measured results of the interstitial oxygen concentration [Oic] of the mechanically polished pulled silicon wafers and the interstitial oxygen concentration [Oic]* of the mirror polished pulled silicon wafers are plotted along the Y-axis and X-axis, respectively, in Fig. 6. This graph shows that the former reasonably corresponds to the latter so that the test results are positioned along the line X = Y. It is apparent from the examples 41 to 46 that, according to the present invention, the mechanically polished pulled silicon wafers and the mirror polished floating zone silicon wafers can be used as sample and references, respectively, in order to directly measure interstitial oxygen concentration [Oic] of the pulled silicon wafers on the production line. Example No. interstitial oxygen concentration [O ic ] of mechanically polished pulled silicon wafer (x 10 17 number/cm 3 ) interstitial oxygen concentration [Oic]* of mirror polished pulled silicon wafer (x 10 17 number/cm 3 ) 41 11.60 11.90 42 9.23 9.30 43 5.35 5.40 44 9.05 9.28 45 5.92 6.01 46 10.10 9.94 Embodiment 7A A further embodiment 7A of the present invention will be explained with respect to the construction and operation thereof. The embodiment 7A of the present invention has substantially the same construction as that of the embodiment 7 except that, in addition to the interstitial oxygen concentration measuring step prior to the gettering step, the interstitial oxygen concentration measuring step is carried out after the gettering step. The interstitial oxygen concentration measuring step after the gettering step has the same construction as that of the interstitial oxygen concentration measuring step prior to the gettering step which corresponds to the measuring step in the embodiment 7. The operation of the embodiment 7A can be easily understood by taking into consideration that of the embodiment 7. Thus, the explanation thereof is omitted. Embodiment 7B Another embodiment 7B of the present invention will be explained with respect to the construction and operation thereof. This embodiment 7B of the present invention has substantially the same construction as that of the embodiment 7 except that, in place of the interstitial oxygen concentration measuring step prior to the gettering step, the interstitial oxygen concentration measuring step is carried out after the gettering step. The interstitial oxygen concentration measuring step after the gettering step has the same construction as that of the measuring step in the embodiment 7. The operation of the embodiment 7B can be easily understood by taking into consideration that of the embodiment 7. Thus, the explanation thereof is omitted. Embodiment 8 An eighth embodiment of the present invention will be explained as follows: A method for making a silicon wafer includes the step of measuring interstitial oxygen concentration which comprises a first step of measuring a light transmission characteristic (herein called transmitted light intensity I OBS ) of a pulled silicon wafer which is not chemically polished, by incidence of parallel polarized light at Brewster angle B into the pulled silicon wafer, a second step of measuring a light transmission characteristic (herein called transmitted light intensity I O ) of a floating zone silicon wafer functioning as a reference silicon wafer both front and rear sides of which are mirror polished, by incidence of parallel polarized light at Brewster angle B into the reference silicon wafer or floating zone silicon wafer, and a third step of calculating an interstitial oxygen concentration [Oic] on the basis of the light transmission characteristic or transmitted light intensity I OBS of the mechanically polished pulled silicon wafer measured during the first step and the light transmission characteristic or transmitted light intensity I O of the mirror polished floating zone silicon wafer or reference silicon wafer measured during the second step. During the first and second steps, the parallel polarized light enters into both non chemically-polished pulled silicon wafer and the mirror polished floating zone silicon wafer at Brewster angle B. This is because any substantial reflection is avoided when the parallel polarized light moves in and out of non chemically-polished pulled silicon wafer and the mirror polished floating zone silicon wafer whereby multiple reflections can be avoided within non chemically-polished pulled silicon wafer and the mirror polished floating zone silicon wafer. During the second step, the floating zone silicon wafer is used as a reference silicon wafer because the interstitial oxygen concentration [Oic] of the floating zone silicon wafer is extremely smaller than that of the pulled silicon wafer. Also, both front and rear sides of the floating zone silicon wafer are mirror polished because the incidence light or parallel polarized light is intended to be prevented from being scattered at both front and rear sides thereof. During the third step, how the interstitial oxygen concentration of the pulled silicon wafer is calculated on the basis of the light transmission characteristic or transmitted light intensity I OBS of non chemically-polished pulled silicon wafer measured during the first step and the light transmission characteristic or transmitted light intensity I O of the floating zone silicon wafer measured during the second step is substatially the same as that of the first embodimemt. Examples 47 to 55 Working examples of the eighth embodiment will be explained so that a method for making a silicon wafer according to the present invention will be fully understood. First, interstitial oxygen concentration [Oic] of plural pulled silicon wafers were measured according to the present invention when both front and rear sides of the silicon wafers were mechanically polished but not yet chemically polished. The measured data of the interstitial oxygen concentration [Oic] thereof were substantially the same as those of Examples Nos. 41 to 46 shown in Table 3. After that, those pulled silicon wafers were chemically polished and then mirror polished. In such a mirror polished condition, the interstitial oxygen concentration [Oic]* of each pulled silicon wafer was measured according to the present invention. The measured data of the interstitial oxygen concentration [Oic]* thereof were substantially the same as those of Examples Nos. 41 to 46 shown in Table 3. Such measured results of the interstitial oxygen concentration [Oic] of the mechanically polished pulled silicon wafers and the interstitial oxygen concentration [Oic]* of the mirror polished pulled silicon wafers are plotted along the Y-axis and X-axis, respectively, as in Fig. 6. Thefore, it can be recognized that the former reasonably corresponds to the latter so that the test results are positioned along the line X = Y. It is apparent that, according to the present invention, the mechanically polished pulled silicon wafers and the mirror polished floating zone silicon wafers can be used as sample and references, respectively, in order to directly measure interstitial oxygen concentration [Oic] of the pulled silicon wafers on the production line. On the other hand, interstitial oxygen concentration [Oic] of plural pulled silicon wafers were measured according to the present invention after the pulled silicon wafers were cut or sliced and before both front and rear sides of the silicon wafers were chemically polished. After that, those pulled silicon wafers were chemically polished and then mirror polished. In such a mirror polished condition, the interstitial oxygen concentration [Oic]* of each pulled silicon wafer was measured according to the present invention. The measured data are shown in Table 4. Such measured results of the interstitial oxygen concentration [Oic] of non chemically-polished pulled silicon wafers and the interstitial oxygen concentration [Oic]* of the mirror polished pulled silicon wafers are plotted along the Y-axis and X-axis, respectively, in Fig. 7. This graph shows that the former reasonably corresponds to the latter so that the test results are positioned along the line X = Y. It is apparent from the examples 47 to 55 that, according to the present invention, non mechanically-polished pulled silicon wafers and the mirror polished floating zone silicon wafers can be used as sample and references, respectively, in order to directly measure interstitial oxygen concentration [Oic] of the pulled silicon wafers on the production line. Example No. interstitial oxygen concentration [O ic ] of non-chemically polished pulled silicon wafer (x 10 17 number/cm 3 ) interstitial oxygen concentration [Oic]* of mirror polished pulled silicon wafer (x 10 17 number/cm 3 ) 47 11.60 11.50 48 11.50 11.60 49 9.32 9.16 50 8.89 8.77 51 10.7 10.80 52 6.45 6.37 53 5.85 5.79 54 6.35 6.44 55 9.96 10.10 Embodiment 9 Embodiment 9 of the present invention has the same construction as that of the embodiment 1 except that both front and rear sides of a sample are not mechanically polished. According to the embodiment 9 of the present invention, a method for making a silicon wafer includes the step of measuring interstitial oxygen concentration prior to the gettering step before the mechanically polishing and after the washing step accompanied by the step of cutting a single crystal so as to produce silicon wafers on a production line. The measuring step in the silicon wafer production method according to the present invention includes a first step of measuring a light transmission characteristic (herein called transmitted light intensity I OBS ) of a pulled silicon wafer which is cut from a single crystal and then washed but not mechanically polished (herein called non-mechanically polished silicon wafer) within the production line, by incidence of parallel polarized light at Brewster angle B into the pulled silicon wafer, a second step of measuring a light transmission characteristic (herein called transmitted light intensity I O ) of a floating zone silicon wafer functioning as a reference silicon wafer both front and rear sides of which are mirror polished, by incidence of parallel polarized light at Brewster angle B into the reference silicon wafer or floating zone silicon wafer, a third step of calculating an interstitial oxygen concentration [Oic] on the basis of the light transmission characteristic or transmitted light intensity I OBS of the non-polished pulled silicon wafer measured during the first step and the light transmission characteristic or transmitted light intensity I O of the mirror polished floating zone silicon wafer or reference silicon wafer measured during the second step, a fourth step of comparing the interstitial oxygen concentration [Oic] of the pulled silicon wafer measured during the third step with a reference value, and a fifth step of removing a pulled silicon wafer if its interstitial oxygen concentration [Oic] is out of the reference value so as to be defective in view of the results compared in the fourth step. Examples 56 to 64 Working examples of a ninth embodiment will be explained so that a method for making a silicon wafer according to the present invention can be fully understood. Like in Table 4, interstitial oxygen concentration [Oic] of plural pulled silicon wafers were measured according to the present invention. First, after the silicon wafers was cut from a single crystal, before it was mechanically polished, interstitial oxygen concentration [Oic] thereof was measured. After that, both front and rear sides of the pulled silicon wafers were first mechanically polished and then chemically polished and finally mirror polished. In such a mirror polished condition, the interstitial oxygen concentration [Oic]* of each pulled silicon wafer was measured according to the present invention. Such measured results of the interstitial oxygen concentration [Oic] of the mechanically polished pulled silicon wafers and the interstitial oxygen concentration [Oic]* of the mirror polished pulled silicon wafers are plotted in Fig. 7. Embodiment 10 A tenth embodiment of the present invention will be explained with respect to the construction and operation thereof. The tenth embodiment of the present invention has substantially the same construction as that of the ninth embodiment except that, in addition to the interstitial oxygen concentration measuring step prior to the gettering step, the interstitial oxygen concentration measuring step is carried out prior to the mechanical polishing subsequent to the gettering step. The interstitial oxygen concentration measuring step after the gettering step has the same construction as that of the interstitial oxygen concentration measuring step prior to the gettering step which corresponnds to the measuring step in the ninth embodiment. The operation of the tenth embodiment can be easily understood by taking into consideration that of the ninth embodiment. Thus, the explanation thereof is omitted. Embodiment 11 An eleventh embodiment of the present invention will be explained with respect to the construction and operation thereof. The eleventh embodiment of the present invention has substantially the same construction as that of the ninth embodiment except that, in place of the interstitial oxygen concentration measuring step prior to the gettering step, the interstitial oxygen concentration measuring step is carried out prior to the mechanical polishing step following the gettering step. The interstitial oxygen concentration measuring step after the gettering step has the same construction as that of the measuring step in the ninth embodiment. The operation of the eleventh embodiment can be easily understood by taking into consideration that of the ninth embodiment. Thus, the explanation thereof is omitted.

Claims: A method for measuring an interstitial oxygen concentration (O ic ) in a pulled silicon wafer (M), said method comprising the steps of: providing the pulled silicon wafer (M), said pulled silicon wafer (M) having an interstitial oxygen concentration (O ic ) to be measured and having a front face and a rear face, said front face having one of a plurality of predetermined finishes and said rear face having one of said plurality of predetermined finishes; providing a floating zone silicon wafer (R), said floating zone silicon wafer (R) functioning as a reference silicon wafer; measuring a first light transmission of said pulled silicon wafer (M) ; measuring a second light transmission I o of said floating zone silicon wafer (R); and measuring said interstitial oxygen concentration (O ic ) throughout said pulled silicon wafer on the basis of said first light transmission and said second light transmission I o , wherein both said first light transmission of said pulled silicon wafer (M) and said second light transmission (I o ) of said floating zone silicon wafer (R) are measured by utilizing polarized light from a light source (11), incident at the Brewster angle into said wafers (M,R), characterized in that said light source (11) is a lamp (11) for producing various wavelengths, such as a globar lamp (11), said light is parallel polarized before entering the wafers (M, R), the front and the rear sides of the floating zone silicon wafer (R) are mirror polished, a first light transmission characteristic being the sum of the intensities I OBS , I S1 and I S2 of the pulled silicon wafer (M) and a second light transmission characteristic I o of the floating zone silicon wafer (R) are measured, and said interstitial oxygen concentration (O ic ) is calculated from said characteristics, wherein I OBS : transmitted light intensity of the pulled silicon wafer (M); I S1 : scattered light intensity of the pulled silicon wafer (M) at its front side; and I S2 : scattered light intensity of the pulled silicon wafer (M) at its rear side. The method of claim 1, characterized in that, before said parallel polarized light enters into a wafer, the light provided from said lamp (11) becomes an interference light. The method of claim 2, characterized in that the light is changed into the interference light before the light is polarized. The method of claim 1, characterized in that said parallel polarized light is polarized from an interference light, and said interference light is given by a Michelson interferometer (12). The method of claim 1, characterized in that said parallel polarized light is polarized from an interference light, and said interference light is formed by overlapping two separate lights provided from a light source (11). The method of claim 1, characterized in that said plurality of predetermined finishes include a mechanically polished finish, a chemically polished finish, and a mirror polished finish. The method of claim 1, characterized in that the method further includes a step of comparing the interstitial oxygen concentration (O ic ) of the pulled silicon wafer with a reference value. The method of claim 8, characterized in that the method further includes a step of removing the pulled silicon wafer if its interstitial oxygen concentration (O ic ) is out of the reference value so as to be defective. A silicon wafer production method in which a pulled silicon wafer cut from a pulled silicon single crystal is subject to a series of treatments including a measuring method as defined in anyone of claims 1 to 9. The method of claim 10, characterized in that the series of treatments include mechanical cutting, mechanical polishing, chemical polishing, mirror polishing, detecting, removing, washing, and gettering.

Inventors: SHIRAI HIROSHI, TAKASU SHINICHIRO, WATANABE MIKIO, SHIRAI, HIROSHI, TAKASU, SHINICHIRO, WATANABE, MIKIO, Shirai, Hiroshi, c/o Research and Dev. Center, Takasu, Shinichiro, c/o Toshiba Ceramics Co., Ltd.
Applicants: TOSHIBA CERAMICS CO, TOSHIBA CERAMICS CO., LTD.
Application year: 1991
Main classification: G01N21
IPC codes: G01N21