JPH06230073A - Radiation resistance testing method for semiconductor device - Google Patents

Abstract

PURPOSE:To carry out a radiation resistant test by setting a distance between a semiconductor device sample and an (alpha) ray source of americium so that average energy of an (alpha) ray falls within a specific intensity range on a device surface in the atmosphere. CONSTITUTION:An (alpha) ray radiating standard sample 1 of americium and an LSI device testing object sample 2 are arranged oppositely to each other, and a shutter 3 is arranged between the materials 1 and 2, and radiation time is controlled. The shutter 3 can be opened and closed electrically, and when a radiation test is carried out on a large quantity of sample, a replacing mechanism of a replacement standby testing object sample 4 is added automatically. Now, in the case of looking at a proportion defective of a leakage current, for example, of a large umber of diode arrays when a distance between the materials 1 and 2 is changed to about 20mm-30mm, with regard to the sample 2 having a difference in (alpha) ray resistance, even if it is a sample having no difference in in-vacuum radiation, a difference becomes large as the distance is changed to 20mm or 25mm in the atmosphere. In this way, when average energy of the (alpha) ray is radiated at a distance in the atmosphere so as to become intensity of about 0-400KeV, degradation by the (alpha) ray is accelerated, and can be recognized easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of accelerating the reliability of a semiconductor device against radiation, especially α rays.

[0002]

2. Description of the Related Art As a conventional α-ray resistance test irradiation method, for example, a method of using americium (Am) as an α-ray source is used for the reliability test of α-ray resistance.
An example of the method is shown in FIG. In FIG. 2, 1 is a standard sample for α-ray irradiation of americium, and 2 is a sample to be tested which is irradiated with α-rays. 3 is a shutter for blocking α rays, and 5 is a vacuum chamber. Since the standard sample 1 such as americium used for standard α-ray irradiation deposits a very thin americium film on a solid surface by vapor deposition, the α-rays emitted from this surface have a uniform high intensity with almost no attenuation. The energy is 4 M to 4.5 MeV, and the result may be quite different from the α-ray acceleration test for the phenomenon that actually occurs, which is a disadvantage.

Therefore, in order to solve the problem that only high-energy irradiation with a uniform spectrum can be performed,
As a conventional method, Japanese Patent Application Laid-Open No. 1-248070 discloses a method of attenuating the energy of α rays by irradiating the sample to be tested and an α ray source at a certain distance in the atmosphere. Here, by irradiating by utilizing the attenuation of the energy of α rays in the atmosphere,
Irradiating a line. When low-energy α-rays are irradiated using this method, α-rays are considerably low due to on-chip materials such as color filters and on-chip lenses formed on the surface of the solid-state image sensor by the element. It becomes an alpha ray. Therefore, there is a difference in the energy distribution of α rays reaching the surface depending on the type of element, and it is difficult to evaluate sufficient characteristics depending on the type of element.

[0004]

As described above, in the above-mentioned structure, the influence of α-rays on the surface condition of the solid-state image pickup device, the thickness of the on-chip material such as the on-chip filter and the lens, and the influence of α-rays on the different materials are tested. Is difficult. Therefore, there is a problem that the α-ray resistance, which is a problem, cannot be actually evaluated.

In view of such a point, the present invention determines the acceleration energy of α-rays irradiated in the atmosphere for the α-ray resistance test of VLSI depending on the thickness of the on-chip material such as an on-chip filter or a lens. It is an object of the present invention to provide a method of irradiating a sample under test while adjusting the distance so that the average energy of α rays is substantially equalized on the element surface.

[0006]

[Means for Solving the Problems] The acceleration energy of α rays generated from an americium standard sample is approximately 4 to 4.5 M.
Since it is eV, most α-ray particles stop in about 30 mm in the atmosphere. Figure 3 shows 4Me in the atmosphere
The calculation result of the distribution of the stopping positions of the α particles of V is shown as 1 × 1
The data of α rays with a number of 0 ¹⁰ cm ^-2 are shown. 10 mm here
In average, the average energy is about 2 MeV, and dispersion occurs at energies near that energy. Almost 2
At a distance exceeding about 0 mm, the average energy is about 1 MeV, which is close to the distribution of the acceleration energy of α rays generated in the VLSI package. However, even in this case, a lot of α rays having high energy remain. Irradiation at about 30 mm is limited to α-rays with low energy, but there is a large decrease in intensity and it is not enough to irradiate a sufficient amount of α-rays in a short time, and the amount of α-rays necessary for evaluation is reached. Therefore, the irradiation time is very long and a lot of time is required for the reliability test. Therefore, it has been found that a distance of about 25 mm is suitable.
However, on-chip materials such as on-chip filters and lenses are mounted on the surface of the solid-state image sensor,
Attenuates according to the film thickness.

Therefore, according to the radiation resistance test method of the present invention, in the atmosphere, the energy of α rays is set to a distance at which the average energy is approximately 0 to 400 KeV on the surface of the semiconductor device, and further, the attenuation amount thereof in air. The distance is converted into 25 mm and the corresponding amount is subtracted from 25 mm, and the distance is shortened for irradiation.

[0008]

With the above-described structure, the present invention can realize an α-ray irradiation acceleration test having an energy distribution of approximately 0 to 400 KeV by fixing the irradiation distance in the atmosphere to a distance of about 25 mm. Further, by making the attenuation distance of the on-chip material closer to each other, it becomes possible to perform the α-ray acceleration resistance test even for elements having different thicknesses of the on-chip material and different materials.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a radiation resistance test method according to an embodiment of the present invention. In FIG. 1, 1 is a standard sample for α-ray irradiation of americium, and 2 is a sample under test of an LSI device, which are arranged opposite to each other as shown in the figure. A shutter 3 is arranged between the α-ray irradiation standard sample 1 and the sample to be tested 2 to control the irradiation time. The shutter 3 has a structure that can be opened and closed electrically and the irradiation time can be set arbitrarily. Further, when performing an irradiation test on a large number of samples, it is possible to add a mechanism for automatically exchanging the sample 4 to be tested waiting for exchange.

In the radiation resistance test method of the embodiment configured as described above, the distance from the standard sample 1 for α-ray irradiation of americium when the sample 2 to be tested having no on-chip material is used is from 20 mm. The electrical characteristics when the thickness is 30 mm will be described. Here, as an example of the evaluation, the result of the defect rate due to the leakage current in the diode array having a large number of test samples is shown. When the diode array is irradiated with α-rays, defects remain due to an increase in leak current. The evaluation was performed by this slight increase in current.

FIG. 4 shows the results of comparing the increase of the actual defective rate of the sample which causes a difference in the effect of the six kinds of α ray resistance of the leakage current remaining in the diode array when irradiated in the conventional vacuum. FIG. 5 shows the average value of the number of defective samples due to leakage current when irradiated with a distance of 20 mm by the method according to the present invention for each of 10 samples having 6 kinds of α ray resistance.
FIG. 6 shows that the number of defects due to leakage current when irradiated with a distance of 25 mm by the method according to the present invention is 6 kinds of α-resistant.
The average value of 10 samples each having a line difference is shown. Regarding the irradiation in vacuum in FIG. 4, no difference was observed under the six conditions, but in FIG. 5, there is a clear difference.
As for the above, the difference becomes larger and larger, and it can be seen that it has the same tendency as the difference in the data obtained by natural α-ray irradiation over the actual two-month long term.

As described above, according to this embodiment, the long-term reliability of the leak current, which is considered to be due to α rays, can be easily examined in a short time by irradiating the atmosphere at an appropriate distance. The effect as an accelerated test is very large. The data difference between Fig. 5 and Fig. 6 is 20m
This is due to the fact that α-ray components with high energy of about 1 MeV still remain at a distance of about m.

Further, in the spectrum of α-rays from the actual package, the proportion of high-energy mixed is different depending on the state. Therefore, when only low-energy α-rays are irradiated, there is a difference from the actual case. There is also. Therefore, the distance between the sample to be tested of the semiconductor device and the α-ray source may be changed continuously or in several steps to intentionally form an energy spectrum and irradiate, so that a more realistic acceleration test can be performed. At this time, the method of controlling the irradiation time is the easiest.
Also, instead of changing the distance, there is also a method of changing the energy by placing an attenuation thin film between the sample under test and the α-ray source for a fixed time. In this case, there is a method of rotating the thin film and putting it in and out.

Further, the distance a to the sample in the air is given with respect to the total thickness b × 10 ⁻³ (mm) of the on-chip material such as the on-chip lens and the filter on the surface of the semiconductor device.
By setting mm to be a = 23− (10/9) b ± 5, the influence of the on-chip material can be eliminated. This value is 27
This is because the micron on-chip filter corresponds to 30 mm in air. For example, when the thickness of the on-chip material is 9 mm, a = 13 ± 5 (mm). Needless to say, when the on-chip material is different, the value of 10/9 in the above equation is naturally changed according to the stopping power. Also, when using a standard sample different from americium, it is necessary to change the distance of 23 mm in the formula according to the energy, and the average α-ray energy on the sample surface under the on-chip is almost 0 to 0. Select a distance that gives 400 KeV.

[0015]

As described above, according to the present invention,
By irradiating in air with a fixed distance of about 25 mm, it is possible to easily realize an α-ray irradiation acceleration test with relatively low acceleration energy α-rays and an energy distribution with a width of several hundred keV. It is possible and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a radiation resistance test method according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a conventional radiation resistance test method in a vacuum.

FIG. 3 shows the distance from a standard α-ray source in the atmosphere of 24-28.
Diagram showing stop distribution of α-rays when separated by mm

FIG. 4 is a diagram illustrating a leak current defect rate when irradiation is performed in a vacuum at a distance of 100 mm.

FIG. 5 is a diagram illustrating a leak current defect rate when irradiation is performed in the atmosphere at a distance of 20 mm.

FIG. 6 is a diagram illustrating a leak current defect rate when irradiation is performed in the atmosphere at a distance of 25 mm.

[Explanation of symbols]

 1 Standard sample for α-ray irradiation 2 Sample to be tested 3 Shutter 4 Standby replacement evaluation sample

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuya Ishikawa 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electronics Industrial Co., Ltd.

Claims (5)

[Claims] 1. The distance between the sample to be tested of the semiconductor device and the α-ray source in the atmosphere is such that the energy of α-rays is about 0 to 400 keV on the surface of the semiconductor device.
A radiation resistance test method for a semiconductor device, characterized in that: 2. The radiation resistance test method for a semiconductor device according to claim 1, wherein the α-ray source is americium. 3. The radiation resistance test method for a semiconductor device according to claim 1, wherein the semiconductor device to be irradiated is a solid-state image sensor. 4. The semiconductor according to claim 1, wherein the distance between the sample to be tested and the α-ray source in the atmosphere is shortened according to the thickness of the on-chip material formed on the surface of the semiconductor device. Radiation resistance test method for equipment. 5. The distance a (mm) between the sample to be tested and the α-ray source in air is a with respect to the total thickness b × 10 ⁻³ (mm) of the on-chip material formed on the surface of the semiconductor device. = 2
The radiation resistance test method for a semiconductor device according to claim 4, wherein the radiation resistance test method is 3- (10/9) b ± 5.