JP6340223B2 - Method and apparatus for measuring impurity concentration in thin film - Google Patents

Description

  The present invention mainly relates to a method for measuring an impurity concentration in a thin film provided on a semiconductor wafer and a measuring apparatus therefor.

  A fluorescent X-ray analyzer is an apparatus that detects fluorescent X-rays emitted from a sample by irradiating the sample with primary X-rays, and performs identification analysis and quantitative analysis of elements contained in the sample. Conventionally, X-ray fluorescence analyzers have been used to analyze the composition and film thickness of various thin films on a silicon substrate in the field of semiconductor manufacturing and the like. For example, a fluorescent X-ray analyzer for concentration control of boron (B) or phosphorus (P) in a silicon oxide film (BPSG film) containing boron (B) and phosphorus (P) as impurities formed on a silicon substrate Is used. A block diagram of the X-ray fluorescence analyzer is shown in FIG. The primary X-ray 2 generated in the X-ray tube 1 is irradiated to the sample 3, and the fluorescent X-ray 4 generated from the sample 3 passes through the threat 5 and is then dispersed by the spectral crystal 6, and is detected using a detector 7 such as a goniometer. Detected. Incidentally, this configuration is a schematic configuration of a wavelength dispersive X-ray fluorescence analyzer.

  When quantitative analysis is performed in the fluorescent X-ray analysis apparatus, the X-ray intensity of the apparatus due to a gain shift of the detector 7, a change in ambient environmental temperature, deterioration of the X-ray tube 1, deviation of the spectroscopic system 6, and the like. In order to correct the drift, calibration (intensity correction) is performed by measuring the X-ray intensity of the standard sample for calibration. In particular, in the case of analysis of a BPSG film, calibration is important because the intensity of the fluorescent X-ray of boron (B) is weak. This standard sample is subjected to composition analysis by ICP emission analysis or the like in advance, and a sample having a known concentration and film thickness is used.

  On the other hand, in order to perform analysis with high accuracy, it is necessary to appropriately calibrate in consideration of the drift of the X-ray intensity caused by the standard sample accompanying the alteration of the standard sample. Since the BPSG film is very hygroscopic, a clean and dry atmosphere such as a nitrogen desiccator or a vacuum desiccator is used to store the standard sample in order to prevent alteration. An apparatus having a vacuum storage chamber for storing a sample in the analyzer itself has also been proposed (see, for example, Patent Document 1).

JP-A-6-331574

  However, in the above apparatus, moisture absorption itself can be reduced, but it does not avoid other factors, for example, contamination that the sample has received inside and outside the analyzer. For example, a standard sample used for calibration of a fluorescent X-ray analyzer is subjected to X-ray irradiation every time calibration is performed. When X-rays are repeatedly irradiated, organic matter containing carbon adheres to the sample surface and is contaminated, and the X-ray intensity of the long wavelength spectrum decreases due to absorption of the attached film. By changing the X-ray intensity obtained from the standard sample to be used as a reference at the time of calibration, the measurement value of the daily analytical sample becomes unreliable.

  An object of the present invention is to provide an impurity concentration measurement method in a thin film provided on a semiconductor wafer and a measurement apparatus thereof capable of obtaining a highly reliable measurement value even in an analysis method in which a sample is easily altered. And

In order to solve the above problems, the following means are used in the present invention.
First, in a method for measuring an impurity concentration in a thin film formed on a semiconductor substrate, a step of measuring a thin film thickness of a first analysis sample with a fluorescent X-ray analyzer to obtain a first film thickness value; A step of measuring the thickness of the thin film of the first analysis sample with an optical film thickness meter to obtain a second thickness value; and a ratio of the first thickness value to the second thickness value. Calculating a reference film thickness ratio, determining a management width of the film thickness ratio; measuring a second analysis sample with a fluorescent X-ray analyzer; and measuring a third film thickness value and the impurity concentration in the thin film From the step of obtaining the fourth film thickness value by measuring the second analytical sample with an optical film thickness meter, and the ratio of the third film thickness value to the fourth film thickness value. Calculating a sample film thickness ratio, determining whether the sample film thickness ratio is within the control width, and If the sample thickness ratio is within the control range, and determining the correct the impurity concentration, it was used a method for measuring the concentration of impurities in the thin film characterized consisting.

Further, when the sample film thickness ratio is outside the control range, the measurement method of the impurity concentration in the thin film is used, wherein the analysis sample is remeasured or another analysis sample of the same lot is measured. .
In addition, when the sample film thickness ratio is outside the control range, an X-ray fluorescence analyzer and an optical interference film thickness meter are recalibrated, and the impurity concentration measurement method in the thin film is used.

  In addition, an apparatus for measuring the impurity concentration in the thin film is assumed to have an optical film thickness meter incorporated in the fluorescent X-ray analyzer.

  By using the above means, the measurement reliability of the impurity concentration in the thin film can be improved.

The figure which shows the management method of the analyzer of this invention Control chart explaining the management method of the present invention Example diagram illustrating the management method of the present invention Configuration of X-ray fluorescence analyzer

Examples of the present invention will be described below.
FIG. 1 is a diagram showing a method for measuring an impurity concentration in a thin film formed on a semiconductor substrate according to an embodiment of the present invention.

  In the measurement method of this example, first, a fluorescent X-ray analyzer calibrated using a standard sample in which a BPSG film is formed on a silicon substrate and an optical interference film thickness meter are prepared. Then, the thickness of the BPSG film of the first analysis sample in which a thin film, for example, a BPSG film is formed on the silicon substrate, is measured with a fluorescent X-ray analyzer, and a film thickness value A is obtained (Step 1).

  Next, the film thickness of the BPSG film of the same first analysis sample is measured with an optical interference film thickness meter to obtain a film thickness value B (Step 2). The first analysis sample was measured immediately after film formation to reduce the exposure time to the atmosphere and minimize surface contamination. In addition, a spectroscopic ellipsometer may be used instead of the optical interference film thickness meter, and the measurement of Step 1 and Step 2 is continuously performed by incorporating the optical interference film thickness meter in the fluorescent X-ray analyzer. And it is good also as a structure performed automatically.

  Next, as shown in Step 3, a reference film thickness ratio (film thickness value A / film thickness value B) is calculated from the obtained film thickness values A and B. If the fluorescent X-ray analyzer and the optical interference film thickness meter are calibrated normally, the film thickness values A and B will be close, but the film thickness range of the BPSG film, boron (B), phosphorus (P) Depending on the concentration range, it may be somewhat different, and it is important to calculate and record each film thickness region and the reference film thickness ratio in each concentration region for each film type (film thickness, concentration). A management width of the sample film thickness ratio is set based on the measured reference film thickness ratio.

  Step 4 is a step of periodically calibrating a fluorescent X-ray analyzer or an optical interference film thickness meter using a standard sample. The standard sample for the optical interference type film thickness meter is not deteriorated so much, but the standard sample for the fluorescent X-ray analyzer is that the intensity of the fluorescent X-ray emitted from the sample is lowered by the long-time irradiation of the X-ray. Become. Therefore, management of the standard sample used here is important, and if it is judged that it is contaminated, it must be replaced.

  Next, the concentration measurement of the second analysis sample performed in the daily production activity of the semiconductor device is performed by the following procedure. The second analysis sample is a film formed under the same conditions as the first analysis sample.

  First, as shown in step 5, a second analytical sample in which a thin film, for example, a BPSG film is formed on a silicon substrate is measured with a fluorescent X-ray analyzer, and the film thickness value C of the BPSG film and boron ( B) Obtain the concentration and phosphorus (P) concentration.

  Next, the film thickness of the same BPSG film sample is measured with an optical interference film thickness meter to obtain the film thickness value D of the BPSG film (Step 6). Then, a sample film thickness ratio consisting of film thickness value C / film thickness value D is calculated, and it is determined whether or not it is within the previously determined management width (Step 7). If it is within the control range, it is determined that the boron (B) concentration and phosphorus (P) concentration obtained in Step 4 are correct, and the concentration values are recorded (Step 8).

  FIG. 2 shows a control chart for correctly carrying out the method for measuring the impurity concentration in a thin film formed on a semiconductor substrate according to the present invention. (A) is a figure using the management upper limit (UCL) and the management lower limit (LCL). In this example, the reference film thickness ratio obtained from the standard sample is 98%, UCL is 100%, and LCL is 96%. If UCL or LCL is exceeded or the number of reams is counted, it is necessary to correct it. To be judged.

  Points 1 to 7 in the figure are within the management range, and the number of reams does not exceed the predetermined number, so that it can be determined to be normal. At points 8 and 12, an abnormal point 8 is exceeded beyond the control range, and it can be determined that there is an abnormality in the second analysis sample, the standard sample, the fluorescent X-ray analyzer or the optical interference film thickness meter.

  If it is outside such a management range, first, the same wafer is remeasured or another wafer of the same lot is measured according to the route of Step 9 in FIG. If a normal sample film thickness ratio is obtained in this way, the process proceeds to Step 8, but if the desired sample film thickness ratio is still not obtained, recalibration with a new standard sample is performed according to the route of Step 10, and the final Thus, the process proceeds to Step 8 to complete the measurement.

  If this does not solve the problem, if there is an investigation on whether there is an abnormality in the fluorescent X-ray analyzer and the optical interference type film thickness meter, the abnormality is removed. However, since the second analysis sample is measured immediately after the film formation, it is unlikely that the second analysis sample is contaminated. Rather, the standard sample used for periodic calibration is used continuously. Therefore, the surface is often contaminated. The present invention is an effective technique for detecting abnormalities in both the standard sample and the daily second analytical sample.

FIG. 2B shows an example in which the upper limit standard value / lower limit standard value is used instead of UCL / LCL. Whether the control upper limit (UCL) and the control lower limit (LCL) are used or whether the upper limit specification value and the lower limit specification value are used may be properly used according to the accuracy required for the product or process.
In the above description, the BPSG film has been described as an example. Needless to say, the present invention can also be used for measuring the boron concentration in the BSG film and the phosphorus concentration in the PSG film.

  For reference, FIG. 3 shows the difference in film thickness ratio (fluorescence X-ray / optical film thickness meter) with and without contamination of the standard sample. In the case of a normal standard sample having no surface contamination, the value is around 98%, whereas in the case of a deteriorated standard sample having contamination, the value is reduced to about 86%. If it is calibrated with a deteriorated standard sample, it can be easily understood that the measured value of the second analytical sample deviates greatly from the original value. In this case, the B and P concentrations of the second analysis sample are higher than the original, and the film thickness value is shifted in the thinner direction. The reason why the film thickness value is shifted in the thin direction is that the film thickness value has a negative correlation with the Si-Kα line which is a fluorescent X-ray of Si.

  Note that the normal standard sample is a sample that is measured immediately after film formation and is free from contamination. Moreover, the deterioration standard sample uses the sample which irradiated the X-ray to the surface for a long time, and was in the state which can confirm the color nonuniformity of a deposit | attachment on the surface visually.

As described above, the B and P concentrations of the BPSG film can be correctly measured by managing the process according to the above procedure.
Also, by managing the film thickness ratio, it is possible to detect not only the calibration deviation caused by the standard sample but also the sudden change in the intensity of the excitation X-ray of the apparatus, so it is used as an index of the reliability of the overall analysis. It is possible.

  The present invention is not limited to a thin film on a semiconductor wafer, but can be used for management of analysis accuracy of a fluorescent X-ray analyzer used for analyzing other thin films.

1 X-ray tube 2 Primary X-ray 3 Sample 4 Fluorescent X-ray 5 Slit 6 Spectroscopic crystal 7 Detector 8 Abnormal point

Claims (4)

In the method for measuring the impurity concentration in a thin film formed on a semiconductor substrate,
Measuring the thickness of the thin film of the first analysis sample with a fluorescent X-ray analyzer to obtain a first thickness value;
Measuring the film thickness of the thin film of the first analysis sample with an optical film thickness meter to obtain a second film thickness value;
Calculating a reference film thickness ratio composed of a ratio of the first film thickness value to the second film thickness value, and determining a management width of the sample film thickness ratio based on the reference film thickness ratio;
Measuring a second analysis sample with a fluorescent X-ray analyzer to obtain a third film thickness value and the impurity concentration in the thin film;
Measuring the second analysis sample with an optical film thickness meter to obtain a fourth film thickness value;
Calculating the sample film thickness ratio comprising the ratio of the third film thickness value to the fourth film thickness value;
Determining whether the sample thickness ratio is within the control range;
If the sample film thickness ratio is within the control range, determining that the impurity concentration is correct;
For measuring the impurity concentration in a thin film comprising:   2. The thin film according to claim 1, wherein if the sample film thickness ratio is outside the control range, the second analysis sample is remeasured or another second analysis sample of the same lot is measured. Method for measuring the impurity concentration of water. 3. The measurement of impurity concentration in a thin film according to claim 1, wherein if the sample thickness ratio is outside the control range, the X-ray fluorescence analyzer is recalibrated with a new standard sample. Method.   4. The impurity concentration in the thin film according to claim 1, wherein in the step of determining the management width of the sample film thickness ratio, the management width is determined by an upper limit specification value and a lower limit specification value. Measuring method.

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