JPS63218877A - Evaluating method of semiconductor memory element - Google Patents

Abstract

PURPOSE:To control the dose of alpha rays for a memory element, to evaluate a soft error and thereby to realize a memory being resistive to the soft error, by fixing an alpha-ray source and a semiconductor memory element in a medium and by controlling the density of the medium. CONSTITUTION:An alpha-ray source 1 is fixed on a support 5 so that its relative position with a semiconductor memory element 2 is not varied. Air is used as a medium, and the density of this medium is controlled in an airtight vessel 6 wherein the alpha-ray source 1 and the memory element 2 are set, by means of an air pressure regulator 7 through a tube 8 for feeding and exhausting the air. The energy of alpha rays themselves is thereby varied. Then, a soft error test of the memory element 2 is conducted by using a computer 4. Accordingly, the alpha-ray tolerance critical energy of the memory element 2 can be determined, and the effect of a soft error due to alpha rays can be evaluated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for evaluating soft errors caused by alpha rays in semiconductor memory devices.

Conventional technology When radiation, especially alpha rays, acts on a semiconductor memory device,
Mainly due to the ionization effect of alpha rays, electrons are generated in the semiconductor substrate.
A hole pair is generated. For example, if the same memory is composed of n-channel transistors on an SI P-type substrate,
The generated holes flow toward the substrate electrode, but the electrons gather in the N+ area memory cell due to the electric field, affecting the charge of the memory cell and bit line, resulting in malfunction. Such a phenomenon is called a soft error caused by alpha rays, and is mainly caused by alpha rays emitted from trace amounts of radioactive elements such as uranium and thorium contained in the package material.

Conventionally, as a method for evaluating soft errors caused by alpha rays in semiconductor memory devices, as shown in FIG. The semiconductor memory device 2 is irradiated with α rays from the α ray source 1, and the computer 4
By writing "1" or "0" information into all bits constituting the semiconductor memory element 2, and subsequently reading out the written information, the semiconductor memory element 2 can be adjusted to various alpha rays M (energy). There was a way to evaluate soft errors.

Problems to be Solved by the Invention In the above evaluation method, by changing the distance between the α-ray source 1 and the semiconductor memory element 2, the energy of the α-rays irradiated to the semiconductor device element 2 is changed, and the α-ray source The dose and direction of the α-rays irradiated from the semiconductor memory element 1 to the semiconductor memory element 2 change depending on their distance, and since their shapes are small, the accuracy is high (the solid angle of α-ray irradiation cannot be determined, and the accuracy is high). (It was also difficult to correct the incident dose, which made it difficult to accurately determine the soft error rate.

An object of the present invention is to eliminate the conventional drawbacks, and to accurately control the amount of α rays incident on a semiconductor memory element without changing the incident dose and direction of α rays.
An object of the present invention is to provide a method that can appropriately evaluate soft errors caused by lines.

Means for Solving the Problems The method of evaluating soft errors caused by alpha rays in a semiconductor memory device according to the present invention fixes an alpha ray source and a semiconductor memory device in a medium, and controls the density of the medium. This method evaluates soft errors by controlling the α-ray dose irradiated to semiconductor memory devices.

According to the present invention, the energy of α-rays generated from an α-ray source when incident on a semiconductor memory element is controlled by controlling the medium density, and the evaluation target is determined by examining the energy and information regarding soft errors. α of the semiconductor memory device of
It is possible to evaluate soft errors on lines.

Embodiment An embodiment of the present invention will be explained with reference to a sectional view of a test device shown in FIG.

In FIG. 1, an α-ray source 1 is fixed to a support base 5 so that its position relative to a semiconductor memory device 2 does not change. In this embodiment, air is used as the medium, and the α-ray source 1
By controlling the density of this medium through an air pressure regulator 7 and an exhaust tube 8 in an airtight container 6 containing a semiconductor memory element 2 and a semiconductor memory element 2, the energy of the α ray itself is changed. Then, using computer 4,
A soft error test of the semiconductor memory device 2 is performed. This test pattern includes checkerboard, column bar, row bar, and other check patterns, but for example, information is written to all bits "O" or "1"
After that, reading is performed and soft errors are evaluated. By controlling the medium density in this way and changing the energy of the α rays, only the energy of the α rays incident on the semiconductor memory element 2 can be adjusted accurately without changing the incident dose and direction of the α rays. It is possible to control, obtain the allowable critical energy of α-rays of the semiconductor memory element 2, and evaluate the influence of soft errors caused by α-rays. Although air is used as the medium in this embodiment, other gases or liquids such as oxygen or nitrogen may also be used. Further, when a liquid medium is used, a liquid pressure regulator or the like may be used in place of the air pressure regulator 7 to adjust the density of the medium.

Effects of the Invention According to the present invention, it is possible to control the energy of α-rays without changing the dose or direction of α-rays incident on a semiconductor memory, and this method was used to conduct a test for soft errors caused by α-rays. Based on the evaluation information obtained from
The critical energy for a line can be determined, and even the critical charge can be determined. From such evaluation information and calculation results, it becomes possible to set conditions for α-ray shielding protective films and optimize circuit design to counter soft errors caused by α-rays, and to create semiconductor memories that are resistant to soft errors caused by α-rays. There are effects that can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a test device used in an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional test device. ■...α-ray source, 2... Semiconductor memory element, 4... Computer, 5... Support stand, 6... Airtight container , 7... Barometric pressure regulator, 8... Supply and exhaust tube.

Claims (1)

[Claims] A semiconductor memory device characterized in that an alpha ray source and a semiconductor memory device are fixed in a medium, and the density of the medium is controlled to control the alpha ray dose irradiated to the semiconductor memory device to evaluate soft errors. evaluation method.