JPH0129062B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for non-destructively inspecting defective insulation of a gate insulator film of a semiconductor device.

[Background of the invention]

Semiconductor random access memory devices often become inoperable suddenly during use. This is mostly due to a drop in breakdown voltage of the gate insulator film of the semiconductor random access memory device. The reason for this is thought to be that the initial screening was incomplete and those with low pressure resistance could not be removed sufficiently.

Conventionally, there are the following methods for inspecting insulator films. The first method is to extract a sample during manufacturing, apply a voltage higher than the breakdown voltage of the current-voltage characteristics, and destructively measure the withstand voltage to determine the lot.The second method is to apply a voltage to the insulator film. A method of measuring withstand voltage (breakdown voltage of current-voltage characteristics) after applying voltage for a certain period of time.Thirdly, after manufacturing of the memory device is completed, after applying a voltage within the operating voltage range of the device or higher than the operating voltage for a certain period of time, There is a way to check the operation.

However, in the first method, the distribution shape of the withstand voltage is unknown because it is not a 100% inspection, and products with different distribution shapes coexist, making it impossible to sufficiently remove products with reduced dielectric breakdown voltage. In addition, in the second method, the inspection time becomes long and insulation deterioration occurs due to breakdown of the insulating film when checking the withstand voltage. Furthermore, the third method not only prolongs the inspection time but also may not be able to remove samples with low dielectric breakdown voltages due to insufficient test voltage.

As described above, with conventional insulator film inspection methods, it is not possible to inspect smoothly during the flow of the manufacturing process, it is impossible to inspect quickly and with high accuracy, and it is difficult to perform inspections during product inspection. There is a disadvantage that the yield is low. This in turn makes it difficult to efficiently and economically obtain a highly reliable semiconductor memory device.

[Purpose of the invention]

An object of the present invention is to provide an inspection method that can non-destructively determine the dielectric breakdown voltage of a gate insulator film.

[Summary of the invention]

The present inventors have experimentally found that the dielectric breakdown voltage of an insulator film for a semiconductor device is lower as the current change ratio in a voltage range lower than the breakdown voltage is larger in the current-voltage characteristics of the insulator film. Based on this, the inspection method of the present invention applies a predetermined voltage smaller than the dielectric breakdown voltage or breakdown voltage to the semiconductor insulator film, measures the current corresponding to the applied voltage, and measures the first predetermined voltage. The ratio of the first predetermined current value corresponding to the voltage and the second predetermined current value corresponding to the second predetermined voltage is determined, and the dielectric breakdown voltage is estimated from the magnitude of the ratio of the current values to determine the dielectric strength voltage. It is characterized by being able to judge and select.

[Embodiments of the invention]

Hereinafter, the present invention will be explained based on embodiments shown in the drawings. FIG. 1 is a schematic diagram of an example of an inspection apparatus for carrying out the inspection method of the present invention, and a sectional view of an example of a semiconductor element that is a sample to be inspected.
In FIG. 1, 1 is a P-type or N-type silicon semiconductor element substrate, 2 is an insulating film of silicon dioxide or silicon nitride, 3 is an aluminum electrode, 4 is a current-voltage characteristic measuring circuit device, and 4a is a current-voltage characteristic measuring circuit device. A detection section, 4b is a voltage setting section, 5 is a control device that can be configured using a microcomputer, for example, for controlling the current detection section 4a and voltage setting section 4b and performing necessary processing, and 5a is a control circuit section thereof. ,
5b is a display device (for example, CRT), and 5c is a printer for recording.

The following is a first embodiment of the inspection method of the present invention.
I will explain based on the diagram. On the surface of the semiconductor element substrate 1,
Silicon dioxide 2 or silicon nitride insulator film 3 created by thermal oxidation or nitridation
is formed, and aluminum is vapor-deposited on its surface to form the electrode 3. The voltage of the voltage setting section 4b of the current-voltage characteristic measuring circuit device 4 is applied to the control circuit section 5.
A first voltage value, for example 0.1V, is applied to the electrode 3 under the selection control of the current detector 4a, and the current is automatically detected by the current detector 4a. The measurement results are taken into the control circuit section 5a, and necessary arithmetic processing is performed. Next, in the same way as above, the voltage setting section 4b is controlled to apply a second voltage value, for example, 1.0V to the electrode 3, the current at that time is automatically detected and measured by the current detection section 4a, and it is The logarithm of the current change ratio with the temporarily recorded current value is calculated in correspondence with the first voltage value which has been fetched into the control circuit section 5a and has been fetched and processed first.

The logarithm value of this current change ratio becomes larger as the dielectric breakdown voltage of the insulator film 2 is smaller, and the insulator film 2 can be evaluated based on this ratio.

FIG. 2 is a graph showing the relationship between dielectric breakdown voltage and current change ratio when the insulating film 2 has a thickness of 400 A in the testing method of the present invention. As is clear from this figure, the larger the current change ratio, the smaller the dielectric breakdown voltage. That is, by determining the ratio of change in current at a very small voltage below the dielectric breakdown voltage, the dielectric breakdown voltage of the insulating film 2 can be estimated, and the dielectric breakdown voltage can be determined and selected.

Although FIG. 2 shows the case where a step-like positive voltage is applied to the electrode 3, a negative voltage may also be applied. Furthermore, although the predetermined voltage is automatically set in this embodiment, it may also be set manually. Furthermore, the voltage may be ramp-like. Moreover, the electrode 3 is indium,
Metal such as gold or polysilicon may also be used.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to test the dielectric breakdown voltage of an insulating film for a semiconductor element quickly and non-destructively. Furthermore, since inspection can be performed non-destructively during the manufacturing process of semiconductor elements, highly reliable semiconductor devices can be obtained at a high yield.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of an inspection device used in the inspection method of the present invention and a sectional view of an example of a semiconductor element to be inspected, and FIG. 2 is a diagram showing the logarithmic ratio of current change and dielectric breakdown in the inspection method of the present invention. It is a graph showing the relationship with voltage. 1... Semiconductor element substrate, 2... Insulator film, 3...
...Electrode, 4...Current-voltage characteristic measurement circuit device, 4
a...Current detection section, 4b...Voltage setting section, 5...
Control device, 5a...control circuit section, 5b...display section, 5c...printer.

Claims (1)

[Claims] 1 Apply predetermined first and second voltages smaller than the dielectric breakdown voltage of the insulator film to the insulator film on the surface of the semiconductor element, and set the first current value corresponding to the first predetermined voltage and the second An insulator characterized in that the logarithmic value of the ratio of the current value to the second current value corresponding to a predetermined voltage is determined, and the dielectric breakdown voltage of the insulating film is determined from the magnitude of the logarithmic ratio of the current value. Membrane inspection method.