JP6826516B2 - Neutron reflector positioning method, neutron reflector positioning program, and neutron reflector positioning device - Google Patents

Description

The present invention relates to a neutron reflector positioning method, a neutron reflector positioning program, and a neutron reflector positioning device.

In recent years, electronic devices are strongly required to be miniaturized and reduced in power consumption in addition to high functionality and high performance, and high integration of semiconductor devices is required. On the other hand, neutron rays generated by the collision of cosmic rays with the atmosphere are pouring onto the earth. With the increasing integration and miniaturization of semiconductor devices, the charge required to determine bits in the device tends to decrease, and the influence of minute charges of secondary particles generated by cosmic ray-derived neutron rays is affected. It is easy to receive. For this reason, in recent electronic devices, the probability of occurrence of soft errors is increasing as compared with conventional electronic devices.
In response to this increasing tendency of soft errors, electrons are reproduced by irradiating the electronic equipment to be tested with neutrons using the accelerator neutron source that has been used for neutron transmission imaging and the like. A soft error test method for confirming the effect on the device is performed (see Non-Patent Document 1).

H.Iwashita et al., “Accelerated Tests of Soft Errors in Network Systems Using a Compact Accelerator-Driven Neutron Source”, IEEE Transactions on Nuclear Science, Vol.64, pp.689-696, 2017. K.Niita et al., “Analysis of the (N, xN') reactions by quantum molecular dynamics plus statistical decay model”, Physical. Rev. C, 52, No.5, 2620-2635 (1995). S.Furihata, “Statistical analysis of light fragment production from medium energy proton-induced reactions”, Nuclear Instruments and Methods in Physics Research B 171, 251-258 (2000).

For example, as shown in FIG. 6, in the existing method of neutron irradiation for neutron transmission image imaging, in order to increase the amount of neutrons irradiated to the sample 21, the target 11 for neutron generation is surrounded by a neutron reflector 31. , A configuration was adopted in which neutrons generated in directions other than the sample direction were reflected by the sample 21.

When the above configuration is adopted in the soft error test, or when the configuration without using the neutron reflector 31 around the target is adopted in the above configuration, the target 11, that is, the number of neutrons generated from the neutron source is calculated. It decays in inverse proportion to the square of the distance from the source. Therefore, the number of irradiated neutrons differs between the front surface and the rear surface of the test target device (sample) to be irradiated.

In the soft error test, the soft error occurrence rate in the natural environment is estimated from the number of irradiated neutrons and the number of error occurrences. Therefore, if the number of irradiated neutrons is large and the estimation is based on the front surface of the test target device, the soft error occurrence rate in the natural environment is estimated to be low. The soft error rate in the natural environment is highly estimated. As a result, there is a problem that the error of the estimated soft error occurrence rate becomes large.

In view of such a problem, a method of estimating the soft error occurrence rate by calculating the neutron number for each component position in consideration of the component position inside the device with respect to the attenuation of the neutron number can be considered. However, since the structure inside the device is not open to the public, it is difficult to estimate it, and the above method cannot be adopted.

In view of such a background, it is an object of the present invention to reduce the estimation error of the soft error occurrence rate in the soft error test in which neutrons are irradiated.

In order to solve the above-mentioned problems, the invention according to claim 1 is a neutron reflector positioning method for determining the position of a neutron reflector that reflects neutrons irradiated by a neutron source to a test target device in a soft error test. Therefore, the number of first neutrons irradiated from the neutron source to the front surface of the test target device, and the number of second neutrons emitted from the neutron source to the rear surface of the test target device, The number of third neutrons irradiated from the neutron reflector to the rear surface of the device to be tested and the number of fourth neutrons irradiated from the neutron reflector to the front surface of the device to be tested are determined by QMD (Quantum Molecular Dynamics). ) A step calculated using a model or a GEM (Generalized Evaporation Model) model, the total number of the first neutrons and the fourth neutrons, and the total number of the second neutrons and the third neutrons. It is characterized in that the step of determining the position of the neutron reflector in the front-rear direction and the step of determining the position of the neutron reflector are substantially equivalent to each other.

The invention according to claim 2 is a neutron reflector positioning program for causing a computer to execute the neutron reflector positioning method according to claim 1.

The invention according to claim 3 is a neutron reflector position determining method for determining the position of a neutron reflector that reflects neutrons irradiated by a neutron source to a device to be tested in a soft error test. A step in which the measuring instrument measures the number of first neutrons irradiated from the neutron source to the front surface of the test target device, and a second measuring instrument irradiates the rear surface of the test target device from the neutron source. A step of measuring the number of second neutrons, a step of measuring the number of third neutrons irradiated from the neutron reflector to the rear surface of the device under test, and a fourth measurement. The instrument measures the number of fourth neutrons radiated from the neutron reflector to the front surface of the device under test, and the computer adds the total number of the first neutron and the fourth neutron and the above. It is characterized by performing a step of determining the position of the neutron reflector in the anteroposterior direction, which makes the sum of the second neutron number and the third neutron number substantially equivalent.

The invention according to claim 4 is a neutron reflecting material positioning device for determining the position of a neutron reflecting material that reflects neutrons irradiated by a neutron source to a test target device for a soft error test, and the neutron generation. The first neutron number is obtained from the first measuring instrument that measures the number of first neutrons irradiated from the source to the front surface of the test target device, and the rear surface of the test target device is irradiated from the neutron generation source. The second neutron number was obtained from the second measuring instrument that measured the second neutron number, and the third neutron number was measured from the neutron reflector on the rear surface of the test target device. The third neutron number was obtained from the measuring instrument of the above, and the fourth neutron number was obtained from the fourth measuring instrument that measured the fourth neutron number irradiated to the front surface of the test target device from the neutron reflector. In the anteroposterior direction of the neutron reflector, which is acquired and makes the total of the first neutron number and the fourth neutron number substantially equal to the sum of the second neutron number and the third neutron number. It is characterized by determining the position.

The invention according to claim 5 is a neutron reflector positioning program for causing the computer to function as the neutron reflector positioning device according to claim 4.

According to the inventions of claims 1 to 5, the neutron reflecting material arranged behind the test target device transmits the test target device so that the number of neutrons on the front surface and the rear surface of the test target device are substantially the same. It can complement the decay of neutrons. As a result, when estimating the soft error occurrence rate of the test target device, the number of neutrons irradiated to the test target device corresponding to the estimated soft error occurrence rate can be made constant.
Therefore, it is possible to reduce the estimation error of the soft error occurrence rate in the soft error test in which neutrons are irradiated.

According to the present invention, it is possible to reduce the estimation error of the soft error occurrence rate in the soft error test in which neutrons are irradiated.

It is a block diagram of the system 1 which realizes 1st Embodiment. It is a flowchart which shows the position determination method of the neutron reflector by the system 1. It is a block diagram of the system 2 which realizes the 2nd Embodiment. It is a flowchart which shows the position determination method of the neutron reflector by the system 2. This is an example in the case of a test target device having a depth of 25 cm, in which (a) is a graph showing the relationship between neutron energy and the number of neutrons, and (b) is a table showing the comparison result between the existing method and the proposed method. It is a block diagram of the test system of the existing method.

Hereinafter, embodiments for carrying out the present invention (hereinafter, referred to as “the present embodiment”) will be described with reference to the drawings.

<< First Embodiment >>
In the first embodiment, a neutron reflector is placed on the rear surface of the test target device for the soft error test, neutrons that have passed through the test target device are reflected, and the number of neutrons that have been attenuated is supplemented to supplement the neutron number of the test target device. Determine the position of the neutron reflector that can keep the number of irradiated neutrons on the front and back surfaces constant. By arranging the neutron reflector at the position determined by this, the soft error occurrence rate can be estimated to be constant regardless of the number of irradiated neutrons on the front surface or the rear surface of the device under test.

[Constitution]
As shown in FIG. 1, the system 1 that realizes the first embodiment is composed of a neutron generation source 1, a test target device 2, and a neutron reflector 3.
The neutron generation source 1 is a target with which the accelerating particles P accelerated by the accelerator (not shown) collide, and the neutron N is generated by the collision of the accelerating particles P.

The test target device 2 is a test target of a soft error test, and is, for example, an electronic device including a semiconductor device. The test target device 2 is arranged at the irradiation destination of the neutron N from the neutron source 1. In each embodiment in the present specification, in the linear direction connecting the neutron source 1 and the test target device 2, the direction from the test target device 2 toward the neutron source 1 is defined as "front", and the test is performed from the neutron source 1. The direction toward the target device 2 is defined as "rear". The test target device 2 has a predetermined amount of dimensions (depth) in the front-rear direction.

The neutron reflector 3 reflects the neutron N that has passed through the test target device 2 to the test target device 2. As the neutron reflector 3, for example, a neutron reflector such as lead, iron, or graphite can be used.
The neutron reflector 3 is arranged approximately behind the device 2 to be tested, but the exact arrangement position of the neutron reflector 3 is determined according to the method described below.

The “measurement point A” in FIG. 1 is the position of the neutron source 1 in the front-back direction. Further, the "measurement point B" is a position on the front surface of the test target device 2 in the front-rear direction. The "measurement point C" is the position of the rear surface of the test target device 2 in the front-rear direction. The “measurement point D” is the position of the neutron reflector 3 (front surface) in the front-rear direction.

[Method]
The procedure of the method for determining the position of the neutron reflector 3 by the system 1 will be described with reference to FIG. In this embodiment, the position of the neutron reflector 3 is determined by computer simulation. The computer is equipped with hardware such as an input / output unit, a processing unit, and a storage unit, and a program (neutron reflector position determination program) read by a CPU, which is a specific example of the processing unit, into a memory, which is a specific example of the storage unit. By executing (including), the method of the present embodiment is realized. The computer stores the position of the neutron source 1, that is, the measurement point A as the origin, and the position of the test target device 2, specifically, the data of the measurement points B and C.

When the processing of FIG. 2 is started, the processing unit first calculates the number of neutrons F (x1) generated at the measurement point A for the neutron N generated when the accelerator particle P collides with the neutron generation source 1 (step). A1). F (x) is the number of neutrons at a distance x from the neutron source 1. The distance x = x1 of the measurement point A from the neutron source 1 is 0.

The neutron number F (x1) at the measurement point A can be calculated using, for example, a QMD (Quantum Molecular Dynamics) model. The QMD model is a computational model for the dynamic process of a nuclear reaction, and is an anticlassical model that considers the interaction between nucleons by quantumly handling the state of nucleons. Details of the QMD model are disclosed in, for example, Non-Patent Document 2. F (x1) can be calculated by simulation using each known formula used in the QMD model.

Further, the neutron number F (x1) at the measurement point A can be calculated by using, for example, a GEM (Generalized Evaporation Model) model. The GEM model is a model that deals with the vaporization process and fission. Details of the GEM model are disclosed in, for example, Non-Patent Document 3. F (x1) can be calculated by simulation using each known formula used in the GEM model.

Next, the processing unit uses the calculated neutron number F (x1) to irradiate the neutron number F (x2) (first neutron number), F (1st neutron number) at the measurement points B, C, and D. x3) (the number of second neutrons) and F (x4) are calculated respectively (step A2). x2, x3, and x4 are the distances from the neutron source 1 at the measurement points B, C, and D, respectively. As described above, the number of neutrons generated from the neutron source 1 is attenuated in inverse proportion to the square of the distance from the neutron source 1, so that F (x2) and F ( x3) and F (x4) can be calculated respectively.

Next, the processing unit temporarily sets the material and thickness (depth) of the neutron reflector 3 (step A3). The values of well-known parameters (eg, permittivity, magnetic permeability) that specify the material of the neutron reflector 3 and the values of the thickness parameters are input to the computer.

Next, the processing unit calculates the number of neutrons G (y1) reflected by the neutron reflector 3 from the calculated number of neutrons F (x4) at the measurement point D (step A4). G (y) is the number of reflected neutrons at a distance y from the neutron reflector 3. The distance y = y1 of the measurement point D from the neutron reflector 3 is 0. The neutron number G (y1) at the measurement point D can be calculated by, for example, a QMD model or a GEM model. F (x1) can be calculated by simulation using each known formula used in the QMD model and the GEM model.

Next, the processing unit uses the calculated neutron number G (y1) to irradiate (reflect) the neutron number G (y2) (third neutron number) at the measurement points C and B from the neutron reflector 3. (Y3) (the number of fourth neutrons) are calculated respectively (step A5). y2 and y3 are the distances from the neutron reflector 3 at the measurement points C and B, respectively. Since the number of neutrons reflected from the neutron reflector 3 is attenuated in inverse proportion to the square of the distance from the neutron reflector 3, G (y2) and G (y3) are added to the calculated G (y1), respectively. Can be calculated.

Next, at each of the measurement points B and C, the number of neutrons irradiated from the neutron source 1 and the number of neutrons reflected from the neutron reflector 3 are added. As a result, the processing unit calculates the number of neutrons F (x2) + G (y3) at the measurement point B and the number of neutrons F (x3) + G (y2) at the measurement point C (step A6).

Next, the processing unit calculates the difference h with respect to the number of neutrons at the measurement points B and C calculated in step A6 (step A7). The formula for calculating the difference h is, for example, as follows.
h = 1- {F (x2) + G (y3)} / {F (x3) + G (y2)}

Next, the processing unit determines whether or not the difference h is within 5%, that is, whether or not the relational expression | h | ≦ 0.05 is satisfied (step A8). When the condition is satisfied (step A8 / Yes), the number of neutrons in the processing unit is substantially the same between the front surface and the rear surface of the device 2 to be tested, so that the position of the neutron reflector 3 from the neutron source 1 is appropriate. Is determined, and the position of the neutron reflector 3 is determined (step A9). After the determination, the process of FIG. 2 is terminated.

On the other hand, when the relational expression | h | ≤0.05 is not satisfied (step A8 / No), the processing unit satisfies whether or not the difference h exceeds + 5%, that is, the relational expression h> 0.05 is satisfied. Whether or not it is determined (step A10). It is considered that the failure to satisfy the relational expression | h | ≤0.05 is mainly due to the influence of the black boxed test target device 2 itself.

When the relational expression h> 0.05 is satisfied (step A10 / Yes), it means that the number of neutrons on the front surface of the device 2 to be tested is larger than the number of neutrons on the rear surface. In this case, the processing unit takes an approach of thickening the neutron reflector 3 or bringing the neutron reflector 3 closer to the test target device 2 (step A11). Specifically, a larger value is input to the computer for the depth parameter of the neutron reflector 3, or a smaller value is input to the computer for the parameter of the position of the neutron reflector 3 from the neutron source 1. .. After inputting each value, the processing unit recalculates the neutron number G (y1) based on the input value (step A4), and the subsequent steps are repeated. When the neutron reflector 3 is brought closer to the device 2 to be tested, the value of F (x4) at the measurement point D calculated in step A2 is changed, so that the processing unit changes the F (x4) after the change. ) Is used to recalculate the neutron number G (y1).

When the relational expression h> 0.05 is not satisfied (step A10 / No), h <-0.05, which means that the number of neutrons on the front surface of the device 2 to be tested is smaller than the number of neutrons on the rear surface. doing. In this case, the processing unit takes an approach of thinning the neutron reflector 3 or keeping the neutron reflector 3 away from the test target device 2 (step A12). Specifically, a smaller value is input to the computer for the depth parameter of the neutron reflector 3, or a larger value is input to the computer for the parameter of the position of the neutron reflector 3 from the neutron source 1. .. After inputting each value, the processing unit recalculates the neutron number G (y1) based on the input value (step A4), and the subsequent steps are repeated. When the neutron reflector 3 is moved away from the test target device 2, the value of F (x4) at the measurement point D calculated in step A2 is changed, so that the processing unit changes the F (x4). ) Is used to recalculate the neutron number G (y1).

According to the first embodiment, the neutron reflector 3 arranged behind the test target device 2 has passed through the test target device 2 so that the number of neutrons on the front surface and the rear surface of the test target device is substantially the same. It can complement the decay of neutrons. As a result, when estimating the soft error occurrence rate of the test target device 2, the number of neutrons irradiated to the test target device 2 corresponding to the estimated soft error occurrence rate can be made constant.
Therefore, it is possible to reduce the estimation error of the soft error occurrence rate in the soft error test in which neutrons are irradiated.

<< Second Embodiment >>
In the second embodiment, a movable neutron reflector is placed on the rear surface of the test target device for the soft error test, and the neutrons transmitted through the test target device are measured while measuring the number of neutrons on the front and rear surfaces of the test target device. The number of neutrons reflected and attenuated is complemented, and the number of irradiated neutrons on the front and rear surfaces of the device under test is kept constant. As a result, the soft error occurrence rate can be estimated to be constant regardless of the number of irradiated neutrons on the front surface or the rear surface of the device to be tested.

[Constitution]
As shown in FIG. 3, the system 2 that realizes the second embodiment includes a neutron source 1, a test target device 2, a neutron reflector 3, a neutron number measuring device 41 to 44, and a neutron number determination system. It is composed of 5 and a movable lift 6. Since the neutron generation source 1, the test target device 2, and the neutron reflector 3 are common to the first embodiment, the description thereof will be omitted.

The neutron counting instruments 41 to 44 are, for example, well-known radiation dose counters.
The neutron number measuring device 41 (first measuring device) is arranged in front of the test target device 2. The neutron number measuring device 41 measures the number of neutrons irradiated from the neutron source 1 to the front surface of the test target device 2.
The neutron number measuring device 42 (second measuring device) is arranged on the rear surface of the test target device 2. The neutron number measuring device 42 measures the number of neutrons radiated to the rear surface of the test target device 2 through the test target device 2 from the front.
The neutron number measuring device 43 (third measuring device) is arranged on the rear surface of the test target device 2. The neutron number measuring device 43 passes through the test target device 2 and measures the number of neutrons reflected from the neutron reflector 3 arranged behind the test target device 2 to the rear surface of the test target device 2.
The neutron number measuring device 44 (fourth measuring device) is arranged in front of the test target device 2. The neutron number measuring device 44 measures the number of neutrons that pass through the test target device 2 from behind and are reflected on the front surface of the test target device 2.

The neutron number determination system 5 (neutron reflector position determining device) is a computer communicatively connected to the neutron number measuring devices 41 to 44 and the movable lift 6. The neutron number determination system 5 determines the position of the test target device 2 based on the number of neutrons obtained from each of the neutron number measuring devices 41 to 44. The neutron number determination system 5 includes hardware such as an input / output unit, a processing unit, and a storage unit, and a program (neutron reflection) read by a CPU, which is a specific example of the processing unit, into a memory, which is a specific example of the storage unit. The method of the present embodiment is realized by executing the material position determination program).
The movable lift 6 is a mounting table for the neutron reflector 3. The movable lift 6 moves in the front-rear direction according to an instruction from the neutron number determination system 5.

In the system 2, the movable lift 6 is moved to determine the position of the neutron reflector 3 in the front-rear direction while performing the test, and the number of neutrons is adjusted.
The procedure of the method for determining the position of the neutron reflector 3 by the system 2 will be described with reference to FIG.
When the processing of FIG. 4 is started, first, the processing unit of the neutron number determination system 5 temporarily sets the material and thickness (depth) of the neutron reflector 3 (step B1). The values of well-known parameters (eg, permittivity, magnetic permeability) for specifying the material of the neutron reflector 3 and the values of the thickness parameters are input to the neutron number determination system 5.

Next, the neutron number measuring device 41 measures the neutron number F (x2) (first neutron number) irradiated on the front surface of the test target device 2. The neutron number measuring device 42 measures the neutron number F (x3) (second neutron number) irradiated on the rear surface of the device 2 to be tested. The neutron number measuring device 43 measures the neutron number G (y2) (third neutron number) reflected on the rear surface of the device 2 to be tested. The neutron number measuring device 44 measures the neutron number G (y3) (fourth neutron number) reflected on the front surface of the device 2 to be tested (step B2). The neutron number determination system 5 acquires data of neutron numbers F (x2), F (x3), G (y2), and G (y3) from each of the neutron number measuring instruments 41 to 44, respectively.

Next, the processing unit of the neutron number determination system 5 calculates F (x2) + G (y3) and F (x3) + G (y2) (step B3). Step B3 corresponds to step A6 (FIG. 2). F (x2) + G (y3) is the total number of neutrons on the front surface of the device 2 under test. F (x3) + G (y2) is the total number of neutrons on the rear surface of the test target device 2.

Next, the processing unit calculates the difference h with respect to the number of neutrons on the front surface and the rear surface of the test target device 2 calculated in step B3 (step B4). Step B4 corresponds to step A7 (FIG. 2), and the difference h is, for example, the same as that used in step A7.

Next, the processing unit determines whether or not the difference h is within 5%, that is, whether or not the relational expression | h | ≦ 0.05 is satisfied (step B5). Step B5 corresponds to step A8 (FIG. 2). When the condition is satisfied (step B5 / Yes), the number of neutrons in the processing unit is substantially the same between the front surface and the rear surface of the device 2 to be tested, so that the position of the neutron reflector 3 from the neutron source 1 is appropriate. Is determined, and the position of the neutron reflector 3 is determined (step B6). After the determination, the process of FIG. 4 is terminated.

On the other hand, when the relational expression | h | ≤0.05 is not satisfied (step B5 / No), the processing unit satisfies whether or not the difference h exceeds + 5%, that is, the relational expression h> 0.05 is satisfied. Whether or not it is determined (step B7). Step B7 corresponds to step A10 (FIG. 2).

When the relational expression h> 0.05 is satisfied (step B7 / Yes), it means that the number of neutrons on the front surface of the test target device 2 is larger than the number of neutrons on the rear surface. In this case, the processing unit further determines whether or not the neutron reflector 3 is closest to the test target device 2 (step B8). The fact that the neutron reflector 3 is closest to the device 2 to be tested means that the neutron reflector 3 is located most forward within the allowable range of the position of the neutron reflector 3. The permissible range of the position of the neutron reflector 3 is a design matter.

In the case of the closest approach (step B8 / Yes), it is desired to reduce the number of neutrons in front of the test target device 2, but this means that it cannot be realized by moving the neutron reflector 3 by the movable lift 6. In this case, the processing unit takes an approach of thickening the neutron reflector 3 or changing the material type of the neutron reflector 3 (step B9). Specifically, a larger value is input to the neutron number determination system 5 according to the depth parameter of the neutron reflector 3, or a value of the material parameter of the neutron reflector 3 is changed and input to the neutron number determination system 5. After inputting each value, the neutron number measuring instrument 41 recalculates the neutron numbers F (x2), F (x3), G (y2), and G (y3) (step B2), and the position of the neutron reflector 3 is determined. Subsequent steps are repeated until determined (step B6).

On the other hand, when they are not closest to each other (step B8 / No), the processing unit takes an approach of bringing the neutron reflector closer to the test target device 2 (step B10). Specifically, a smaller value is input to the neutron number determination system 5 for the parameter of the position of the neutron reflector 3 from the neutron generation source 1. Further, the neutron number determination system 5 controls the movable lift 6 to bring the neutron reflector 3 closer. After that, the neutron number measuring device 41 measures the neutron numbers F (x2), F (x3), G (y2), and G (y3) again (step B2) until the position of the neutron reflector 3 is determined. (Step B6), the subsequent steps are repeated.

When the relational expression h> 0.05 is not satisfied (step B7 / No), h <-0.05, but the number of neutrons on the front surface of the device 2 to be tested is smaller than the number of neutrons on the rear surface. Means. In this case, the processing unit takes an approach of moving the neutron reflector 3 away from the test target device 2 (step B11). Specifically, a larger value is input to the computer for the parameter of the position of the neutron reflector 3 from the neutron source 1. Further, the neutron number determination system 5 controls the movable lift 6 to keep the neutron reflector 3 away. After that, the neutron number measuring device 41 measures the neutron numbers F (x2), F (x3), G (y2), and G (y3) again (step B2) until the position of the neutron reflector 3 is determined. (Step B6), the subsequent steps are repeated.

The effect of the second embodiment is the same as the effect of the first embodiment. Further, in the second embodiment, it is sufficient that the number of neutrons measured by the neutron number measuring devices 41 to 44 can be obtained, and as in the first embodiment, the number of neutrons generated at the measurement point A and the reflection at the measurement point D. There is no need to find the number of neutrons. Therefore, the calculation load by the neutron number determination system 5 of the second embodiment can be reduced as compared with the first embodiment.

<< Example >>
FIG. 5 shows the results when the second embodiment is applied to the test target device 2 having a depth of 25 cm. The distance from the neutron source 1 to the front surface of the test target device 2 is 150 cm, and the distance to the rear surface is 175 cm. FIG. 5 shows the result of the existing method in which the neutron reflector 3 is not arranged behind the test target device 2 and the result of the proposed method in which the neutron reflector 3 is arranged behind the test target device 2.

With respect to the neutrons generated by the neutron source 1, the number of neutrons on the front surface (150 cm) of the test target device 2 (reference numeral L1 in FIG. 5 (a)) and the number of neutrons on the rear surface (175 cm) (FIG. 5 (a)) Medium code L2), the number of neutrons on the front surface (150 cm) of the device 2 under test by the proposed method (medium code L3 in FIG. 5 (a)), and the number of neutrons on the rear surface (175 cm) (medium code L4 in FIG. 5 (a)). The distribution from 1.0 MeV to 6.0 MeV is as shown in FIG. 5 (a).

As shown in FIG. 5 (b), in contrast to the existing method in which the number of irradiated neutrons decreases between the front surface and the rear surface of the device 2 to be tested (3.72E + 5 → 2.77E + 5), the proposed method has the number of irradiated neutrons. Was confirmed to be constant (3.85E + 5 → 3.98E + 5). The proposed method of arranging the neutron reflector 3 behind the test target device 2 described in the first embodiment and the second embodiment has a soft error occurrence rate in the soft error test as compared with the existing method. It can be said that the estimation error can be improved by about 30% (74% → 103%) and works effectively.
Even when the first embodiment is applied, the same result as that shown in FIG. 5 can be obtained.

≪Others≫
(A): The determination based on the difference h does not have to be limited to 5% or less (step A8 in FIG. 2 and step B5 in FIG. 4), and a minute amount smaller than 5% (the number of neutrons on the front and rear surfaces of the device under test). Is an amount that can be set to be substantially equivalent), or may be a minute amount larger than 5%.
(B): In the comparison between F (x2) + G (y3) and F (x3) + G (y2), the difference h is not calculated (step A7 in FIG. 2 and step B4 in FIG. 4), for example. , {F (x2) + G (y3)}-{F (x3) + G (y2)} may be determined whether or not the value exceeds a predetermined value.

It is also possible to realize a technique in which various techniques described in the present embodiment are appropriately combined.
In addition, the system configuration, flowchart, and the like can be appropriately changed without departing from the spirit of the present invention.

1 Neutron source 2 Test target device 3 Neutron reflector 41-44 Neutron number measuring instrument (1st to 4th measuring instruments)
5 Neutron number determination system (computer: neutron reflector position determination device)
6 Movable lift

Claims (5)

It is a neutron reflector position determination method that determines the position of the neutron reflector that reflects the neutrons that the neutron source irradiates the test target device of the soft error test.
The calculator
The number of first neutrons irradiated from the neutron source to the front surface of the device to be tested, the number of second neutrons irradiated from the neutron source to the rear surface of the device to be tested, and the neutron reflector. The number of third neutrons irradiated on the rear surface of the device under test and the number of fourth neutrons irradiated on the front surface of the device under test from the neutron reflector are calculated by using a QMD (Quantum Molecular Dynamics) model or GEM (Generalized). Evaporation Model) Steps to calculate using the model and
Determine the position of the neutron reflector in the anteroposterior direction so that the sum of the first neutron number and the fourth neutron number is substantially equal to the sum of the second neutron number and the third neutron number. Steps to and perform,
A method for determining the position of a neutron reflector. A neutron reflector positioning program for causing a computer to execute the neutron reflector positioning method according to claim 1. It is a neutron reflector position determination method that determines the position of the neutron reflector that reflects the neutrons that the neutron source irradiates the test target device of the soft error test.
A step in which the first measuring instrument measures the number of first neutrons irradiated from the neutron source to the front surface of the device under test.
A step in which the second measuring instrument measures the number of second neutrons irradiated from the neutron source to the rear surface of the device under test.
A step in which the third measuring instrument measures the number of third neutrons irradiated from the neutron reflector to the rear surface of the device under test.
A step in which the fourth measuring instrument measures the number of fourth neutrons irradiated from the neutron reflector to the front surface of the device under test.
The computer obtains each of the first neutron number to the fourth neutron number from each of the first measuring device to the fourth measuring device, and obtains the first neutron number and the fourth neutron number. Performing a step of determining the position of the neutron reflector in the anteroposterior direction, which makes the sum of the numbers substantially equal to the sum of the second neutrons and the third neutrons.
A method for determining the position of a neutron reflector. It is a neutron reflector positioning device that determines the position of the neutron reflector that reflects the neutrons that the neutron source irradiates the test target device of the soft error test.
The first neutron number was obtained from the first measuring instrument that measured the first neutron number irradiated to the front surface of the test target device from the neutron source.
The second neutron number was obtained from the second measuring instrument that measured the second neutron number irradiated from the neutron source to the rear surface of the test target device.
The third neutron number was obtained from the third measuring instrument that measured the third neutron number irradiated to the rear surface of the test target device from the neutron reflector.
The fourth neutron number was obtained from the fourth measuring instrument that measured the fourth neutron number irradiated to the front surface of the test target device from the neutron reflector.
Determine the position of the neutron reflector in the anteroposterior direction so that the sum of the first neutron number and the fourth neutron number is substantially equal to the sum of the second neutron number and the third neutron number. To do,
A neutron reflector positioning device characterized by this. A neutron reflector positioning program for causing a computer to function as the neutron reflector positioning device according to claim 4.

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