JP5134858B2 - Hazardous element management method in semiconductor sealing resin - Google Patents

Description

The present invention relates to a harmful element management method in a semiconductor encapsulating resin, and relates to a highly accurate harmful element management method using a fluorescent X-ray analyzer.

  In recent years, due to considerations for environmental issues, there has been a strong movement to exclude the use of hazardous substances. For example, regulations such as “restriction of the use of specific hazardous substances (RoHS)” have been implemented in Europe. According to this regulation, it is required to confirm that electronic materials do not contain a specific harmful substance. With this RoHS directive, harmful elements (Br, Sb, As, Bi, It is desired to realize a method capable of measuring Pb and the like easily and with high accuracy, and to realize a highly accurate management method for harmful elements using this analysis method.

  In order to manage harmful elements in the semiconductor sealing resin, it is simple and effective to use a fluorescent X-ray analyzer. In X-ray fluorescence analysis, the fundamental parameter (FP) method is generally used for metal samples, and the calibration curve method is generally used for resin samples. However, the measurement target element is added to create a calibration curve. It is necessary to use a standard resin sample. As this standard sample, what uses polyethylene, ABS resin, vinyl chloride resin, etc. as a matrix resin is marketed.

  By the way, the semiconductor encapsulating resin is compression-molded and has a higher density than those of the above-mentioned standard samples, and is filled with silica or the like to improve the strength, so that primary X-rays are difficult to enter the sample. The measured value tends to be small. Further, when measuring a semiconductor product, fluorescent X-rays of constituent elements inside the sample (frame, chip, wire, etc.) are also detected, which may cause an error depending on the element to be measured.

As a method for inspecting a product in a non-destructive manner, a technique is known in which the presence or absence of Pb in a sample is determined by fluorescent X-rays (see Patent Document 1).
This technique is a method of quantifying Pb by irradiating a sample such as polystyrene with X-rays, determining peaks at all energy positions of Pb, and avoiding inhibition of As, Br, etc., which have close energy positions. By the way, in this method, as described above, in a high-density sample such as a sealing resin of a semiconductor device manufactured by compression molding, it does not solve the problem of measurement accuracy caused by a small measurement value. Absent.

In addition, a method for specifying a material containing a specific substance in an object in which a plurality of materials are formed in a layer form by adopting a fluorescent X-ray analysis method is known (see Patent Document 2). In this document, as an object in which a plurality of materials are formed in layers, a material obtained by subjecting Fe to Zn plating and Cr plating is cited, and Cd, Pb, Hg, Br, Cr, Au, Ag, Pt, Pd, etc. are mentioned. Then, this sample is irradiated with X-rays under different irradiation conditions, and the generated X-ray fluorescence is analyzed to control the X-ray penetration depth and determine the location of a specific substance. . Such a method is an effective method for a sample having a relatively simple layer structure and capable of securing a sufficient amount of the sample to obtain a sufficient amount of measured X-ray intensity. Unlike polyethylene, ABS resin, or plating material, it is a composite material in which a base material (such as DCP (dichloropentadiene) etc.) is mixed with a filler such as silica and is compression molded. It is a high-density material. For this reason, the measured value by fluorescent X-rays becomes small. When the semiconductor product (whole) is a non-destructive measurement object, other members than resin are also measured. There is a problem that a large error occurs.
JP 2007-003331 A JP 2007-017306 A

In the harmful element management method in the semiconductor sealing resin, the management is performed by a simple measurement method with few errors.

  A sample to be measured is placed on the X-ray irradiation surface in the X-ray fluorescence analyzer, and a qualitative analysis is performed to check whether or not the management target element is contained. When the management target element is detected, the sample is arranged over the entire X-ray irradiation surface of the fluorescent X-ray analyzer so that the X-ray irradiation surfaces of the sample are all the same. One side is measured, the opposite side is further measured, and quantitative analysis is performed by a calibration curve method. In order to perform quantitative analysis, a resin sample in which an element to be measured is added to a sealing resin is prepared in advance. These are priced by fine chemical analysis, and used as a standard resin sample for preparing a calibration curve in fluorescent X-ray analysis. Furthermore, the fluorescent X-ray intensity of the element to be measured is normalized by the scattered radiation intensity, and the background is corrected. Based on the obtained two quantitative analysis results, the threshold value is determined using the quantitative result with less influence of the coexisting components.

That is, the present invention is a harmful element management method in a semiconductor sealing resin,
A content determination step of performing a qualitative analysis of a sample, which is a resin-encapsulated semiconductor device, using a fluorescent X-ray analyzer to determine the presence or absence of the contained element ;
A sample preparation step of aligning the upper and lower surfaces of the plurality of samples and arranging the samples over the entire X-ray irradiation surface;
Measuring one surface of the plurality of samples and the opposite surface thereof with a fluorescent X-ray analyzer to perform quantitative analysis;
A step of determining a threshold value using a quantitative result with less influence of coexisting elements among the two data obtained from the quantitative analysis step;
It is a harmful element management method characterized by having.

  In the quantitative analysis step of the present invention, it is preferable to perform quantitative analysis from a calibration curve prepared using a standard sample in which the base resin contains an epoxy resin.

  In the quantitative analysis step, it is preferable to correct the background by normalizing the fluorescent X-ray intensity of the element to be measured with the scattered X-ray intensity.

Moreover, it is preferable that the sample to be measured contains at least one element of Au, Si, Cu, Fe, Ni, Sn, Bi, Pb, and Ag.

Furthermore, it is preferable to measure at least one of Sb and Br contained in the measurement target sample.

As described above, in the analysis method of the present invention, it is possible to accurately measure and manage the harmful element concentration in the semiconductor sealing resin.
That is, the measurement error is reduced by this method. In addition, since it is a method that is not easily affected by coexisting substances, the semiconductor product (whole) can be measured nondestructively. Therefore, the presence / absence and content of harmful elements in the semiconductor product can be easily determined without performing a detailed analysis, thereby simplifying the management of harmful elements in the semiconductor product.

[Fluorescent X-ray measurement device]
Conventionally, wavelength dispersion type X-ray fluorescence analyzers and energy dispersion type X-ray fluorescence analyzers are known as fluorescent X-ray analyzers used for microanalysis. In the present invention, any apparatus can be used, but an energy dispersive X-ray fluorescence analyzer is preferable because the detector is simple and the apparatus is simple. A conceptual diagram which is an example of this energy dispersive X-ray fluorescence analyzer is shown in FIG. As seen in FIG. 1, this apparatus places a sample 11 on a sample holder 12 and irradiates it with X-rays generated from an X-ray generator 13 such as an X-ray tube. From the sample irradiated with X-rays, fluorescent X-rays corresponding to the element types contained in the sample are generated, and this is used to measure the energy intensity of the fluorescent X-rays with a detector such as the semiconductor detector 14. . The X-ray generation device 13 is controlled by the control device 15, and the signal output from the semiconductor detector 14 is processed by the signal processing device 16 and then configured as a spectrum by the arithmetic processing device 17.

[sample]
(Structure of semiconductor device)
FIG. 2 shows a schematic diagram of a typical example of a semiconductor device which is a sample to be analyzed in the present invention.
As shown in FIG. 2, the semiconductor device includes a semiconductor element 22 made of an iron-based alloy or the like, mounted on a lead frame 24 serving as a terminal of the semiconductor device, and formed on the semiconductor element 22 by an Au wire 23. The terminal portion thus formed and the lead frame 24 are electrically connected. The assembly composed of the lead frame 24, the semiconductor element 22, and the Au wire 23 is covered and sealed with the sealing resin 21, and functions to protect the semiconductor element from moisture and contaminants. .

(Semiconductor element materials)
A sealing resin suitable for use in a semiconductor device as a sample is composed of an epoxy resin, a filler, a curing agent, and the like, and the epoxy resin has two or more epoxy groups in one molecule. Any thing is acceptable. For example, biphenyl type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, naphthol novolac type epoxy resin, bisphenol A type epoxy resin, glycidyl ester type epoxy resin, glycidyl amine type epoxy resin, alicyclic epoxy resin, etc. Can be mentioned.
Examples of the filler include quartz glass, crystalline silica, fused silica, glass, alumina, calcium silicate, barium sulfate, magnesia, silicon nitride, aluminum nitride, aluminum oxide, magnesium oxide, mica, and metal. The filler amount is 70 to 95% by weight.
Examples of the curing agent include a phenol novolak resin, a cresol novolak resin, a phenol aralkyl resin, an allylphenol novolak resin, a naphthol type novolak resin, a biphenyl type novolak resin, and a tris (hydroxyphenyl) alkane compound.

According to the management method of the present invention, a member constituting a semiconductor device that is a sample to be measured is a semiconductor device containing at least one element of Au, Si, Cu, Fe, Ni, Sn, Bi, Pb, and Ag. It is suitable to apply. This is because these elements are highly likely to act as interference elements in X-ray fluorescence analysis, and it is difficult to expect high-precision analysis according to conventional X-ray fluorescence analysis techniques. .

[Measuring method]
A flowchart of the measurement method of the present invention is shown in FIG. Hereinafter, the method of the present embodiment will be described with reference to FIG.

(S10, S20: qualitative analysis and determination step)
A semiconductor device to be a sample is prepared. As described above, in the fluorescent X-ray analysis of a semiconductor device, since the intensity of the emitted fluorescent X-ray is weak, it is necessary to prepare a large number of samples when analyzing a small semiconductor device. This qualitative analysis is intended to determine whether or not an element to be analyzed exists, and when it is determined in the determination step S20 that the specific element is not contained as a result of this analysis. Therefore, it is determined that the product is non-defective without going through steps S30 and subsequent steps.

(S30: Quantitative analysis sample preparation step)
If it is determined in the previous step that a specific element is contained, a semiconductor device to be a sample is densely arranged on the sample holder with a plurality of upper and lower surfaces aligned as shown in FIG. FIG. 6A shows an example in which the upper surfaces of the semiconductor devices are aligned, and FIG. 6B shows an example in which the lower surfaces of the semiconductor devices are aligned. As seen in FIG. 6, it is preferable that the semiconductor device to be a sample is disposed so that the gap is in close contact with the content.
Generally, in the X-ray fluorescence analysis method, the X-ray irradiation area is about 10 mmφ, so that the semiconductor devices are densely arranged to cover this range. In this step, the top and bottom surfaces of the semiconductor device are aligned for the following reason.
In other words, in X-ray fluorescence analysis, X-rays irradiated on a sample excite elements constituting the sample and generate fluorescent X-rays. The irradiated X-rays are sequentially absorbed from the surface by the constituent elements and excite them, and the irradiated X-rays do not completely penetrate the sample. Therefore, the observed fluorescent X-ray spectrum is strongly influenced by the constituent elements on the irradiation side of the sample.
As shown in FIG. 2, a typical semiconductor device has different constituent members on the upper surface side and the lower surface side of the semiconductor device. When the X-ray is irradiated from the upper surface side, it is affected by the sealing resin material and the Au wire. On the other hand, when the X-ray is irradiated from the lower surface side, the influence of the sealing resin and the lead frame material. Will receive.
When the energy value of the peak of the element to be measured is close to the energy value of the fluorescent X-ray peak of the element included in each of the constituent elements, the analysis value of the element to be measured includes the amount of interfering elements Therefore, it is necessary to conduct analysis from a direction that is not affected by interfering elements. Therefore, in this process, it is necessary to align the vertical direction of the semiconductor device arranged as a sample.

(S40: One aspect analysis)
In this step, the sample aligned in the above step is irradiated with X-rays from one surface thereof to measure fluorescent X-rays. The obtained result is configured and recorded as a fluorescent X-ray spectrum by the signal processing device 14 and the arithmetic processing device 17.

(S50: Analysis of other aspects)
In this step, the opposite surface of the sample measured in the above step is irradiated with X-rays to perform elemental analysis on the opposite surface side. The result in this step is also processed and recorded by the arithmetic processing unit 17.

(S60: determination / threshold judgment)
This process is a process for making a determination based on the result obtained in the analysis step.
Specifically, it is performed as follows. That is, the two spectra obtained up to the above process are compared, and a spectrum with less influence of interfering elements is selected and adopted as quantitative analysis data.
Next, scattered radiation correction is performed on the adopted spectral data. In the scattered ray correction, when a sample is irradiated with X-rays, the X-rays that have entered the sample are reflected by the elements in the sample and emitted as scattered rays. When the region (area / thickness) where X-rays enter the sample changes, it affects the fluorescent X-ray intensity of the element to be measured. In order to cancel the fluctuation of the incident region, scattered radiation correction is performed. Specifically, the peak energy intensity attributed to the element to be measured is divided by the scattered X-ray intensity and normalized. By adopting this correction, the measurement error is reduced and the measurement accuracy is remarkably improved.

Using the calibration curve obtained from the standard sample, the concentration is calculated from the normalized energy intensity obtained by the above method.
A calibration curve is prepared by relating a fluorescent X-ray intensity and a concentration using a standard sample having a known concentration that is usually commercially available. It is preferable to prepare a sample. In normal standard samples, as described above, polyethylene, ABS resin, vinyl chloride resin, and the like are used as the matrix resin that is a base resin. However, these resin materials are used as sealing resins for actual semiconductor devices. Since they are different, it is preferable to use a standard sample in which an epoxy resin that is common as a sealing resin is used as a matrix resin.

  By the above step, the concentration of the measurement target element present in the sample can be determined.

  The process of determination / threshold judgment is performed for each element type to be measured. Production control such as measuring the content of the measured element obtained in this way, comparing it with a threshold acceptable for a non-defective product, judging whether the product is a sample, and stopping the product judged to be defective It can be performed. In addition, when it is determined as defective by this determination, it is possible to perform manufacturing process management such as specifying and improving a process in which an element having a concentration exceeding the standard is mixed in the manufacturing process of the semiconductor sealing resin.

  The above-described method tends to reduce the measurement value in a quantitative analysis of Br having an energy intensity close to a gold element incorporated in a semiconductor device and a high-density sample among harmful elements specified by RoHS. Suitable for quantitative analysis of Sb.

[Modification]
In the above method, an example in which a plurality of semiconductor devices are aligned and measured has been shown. However, in fluorescent X-ray analysis, the intensity of fluorescent X-rays increases as the irradiation area of X-rays increases, and the measurement accuracy increases. In order to improve, an example is shown in which a sufficient amount of sample is densely arranged in the X-ray irradiation area. On the other hand, for example, a semiconductor device such as a power semiconductor is large, and there is a semiconductor device that covers a sufficient irradiation area with one semiconductor device. When analyzing such a semiconductor device, it is not necessary to align a plurality of samples, and it is sufficient if one sample is placed on the sample holder for analysis.

Hereinafter, the present invention will be described by way of examples. In this embodiment, Br contained in the sealing resin is analyzed using a semiconductor device having an Au wire inside the shape shown in FIG.
First, a standard sample was prepared and a calibration curve was prepared. As a standard sample, an epoxy resin was used as a matrix, Br of a known concentration was added thereto, and solidified to obtain a standard sample. For this standard sample, a calibration curve for determining the relationship between the peak intensity of Br and the concentration was prepared using an energy dispersive X-ray fluorescence spectrometer.
Next, the semiconductor device shown in FIG. 2 was prepared, placed on a sample holder at random, and irradiated with X-rays to measure the energy intensity of fluorescent X-rays. For the same semiconductor device, as shown in FIG. 6, the upper and lower surfaces of the semiconductor device are aligned and placed on the sample holder in an orderly manner, and the upper and lower surfaces are irradiated with X-rays, respectively. Was measured. The resulting spectrum is shown in FIG. 4A is an energy intensity spectrum measured by irradiating X-rays from the upper surface of the semiconductor device, and FIG. 4B is energy measured by irradiating X-rays from the lower surface of the semiconductor device. It is a line intensity spectrum. 4A, the Br-Ka line intensity is 544.124 cps, and in FIG. 4B, the Br-Ka line intensity is 315.838 cps.

  The obtained spectrum was normalized using the scattered X-ray intensity, and the bromine content was determined using the calibration curve.

  In addition, a separate precision analysis was performed on the sample.

  Table 1 shows the Br content obtained by the method of this example and the reference example which is a precision analysis.

As described above, Au wire is used inside the sample, and Au is detected in the fluorescent X-ray analysis when the sample is randomly arranged and measured. As can be seen from FIG. 4, since the Kα line of Br and the Lβ line of Au are energetically adjacent to each other, if Au is detected, the Br is apparently measured to cause a positive error. . On the other hand, if samples are arranged in an orderly manner and the sample is arranged so that only the lower surface is irradiated with primary X-rays, almost no Au is detected. When measured at random or when the upper surface is measured, the error with respect to the precision analysis value of Br content is 20% or more due to the influence of Au, whereas when the lower surface is measured, Au is hardly detected, The error was about 7%, and measurement was possible with very high accuracy.
As a result of the above analysis of Br, the top and bottom surfaces of the semiconductor device as a sample are arranged in an orderly manner, and the two spectra measured by irradiating each surface with X-rays are used to use the spectrum that is less affected by interfering elements. It was found that a more accurate analysis is possible by performing a quantitative analysis. It has been found that it is possible to make a highly accurate determination by determining whether a semiconductor device is good or bad by using this analysis technique.
That is, in the example in which the measurement of Example Br described above is performed, Br is close to the fluorescent X-ray of Au in energy intensity and is easily affected by Au. Therefore, it is preferable to perform the measurement from the surface where the gold wire of the semiconductor device does not exist.

Subsequently, Sb fluorescent X-ray analysis was performed using the same sample of the semiconductor device. The result is shown in FIG. FIG. 5A is a spectrum showing fluorescence X-ray intensity measured by irradiating X-rays from the upper surface of the semiconductor device, and FIG. 5B is a spectrum measured by irradiating X-rays from the lower surface. In the case of FIG. 5A, the intensity of the Sb-Ka line was 181.954 cps, whereas in the case of FIG. 5B, the intensity of the Sb-Ka line was 138.015 cps. . Thus, in the case of Sb, since it is not influenced by Au, it is preferable to irradiate more sealing resin with X-rays. In the case of the semiconductor device shown in FIG. 2, a large amount of sealing resin exists on the upper surface, and it is preferable to analyze the upper surface. In the case of the semiconductor device shown in FIG. 6, lead terminals are disposed on the lower surface, and in this case as well, it is possible to irradiate more sealing resin with X-rays by irradiating X-rays from the upper surface. More preferable.

1 is a conceptual diagram of a fluorescent X-ray analyzer used in the present invention. 1 is a schematic cross-sectional view of a semiconductor device that serves as a sample. The flowchart which shows the method of this invention. The graph which shows the result of having analyzed Br in the Example of this invention. The graph which shows the result of having analyzed Sb in the Example of this invention. FIG. 4 is a diagram showing an example of measuring semiconductor devices side by side in an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Sample 12 ... Sample holder 13 ... X-ray tube 14 ... Semiconductor detector 15 ... Control device 16 ... Signal processing device 17 ... Arithmetic device 21 ... Sealing resin 22 ... Semiconductor element 23 ... Gold wire 24 ... Lead frame

Claims (5)

A method for managing harmful elements in a semiconductor sealing resin,
A content determination step of performing a qualitative analysis of a sample which is a resin-encapsulated semiconductor device by a fluorescent X-ray analyzer to determine the presence or absence of an element to be analyzed ;
A sample preparation step of aligning the upper and lower surfaces of the plurality of samples and arranging the samples over the entire X-ray irradiation surface;
A step of performing quantitative analysis by measuring one surface of the plurality of samples and the opposite surface thereof with a fluorescent X-ray analyzer;
A step of determining a threshold value using a quantitative result with less influence of coexisting elements among the two data obtained from the quantitative analysis step;
A hazardous element management method characterized by comprising:   2. The method for managing harmful elements in a semiconductor encapsulating resin according to claim 1, wherein in the quantitative analysis step, quantitative analysis is performed from a calibration curve prepared using a standard sample in which the base resin contains an epoxy resin.   2. The harmful element management in a semiconductor encapsulating resin according to claim 1, wherein in the quantitative analysis step, the background is corrected by normalizing the fluorescent X-ray intensity of the element to be measured with the scattered X-ray intensity. Method. 2. The harmful element management in a semiconductor sealing resin according to claim 1, wherein the sample contains at least one element selected from the group consisting of Au, Si, Cu, Fe, Ni, Sn, Bi, Pb, and Ag. Method. The method for managing harmful elements in a semiconductor sealing resin according to claim 1, wherein at least one of Sb and Br contained in the sample is measured.