JPH0198976A - Evaluating method for insulation performance of insulating film - Google Patents

Abstract

PURPOSE:To obtain a breakdown charge quantity distribution of the insulation breakdown probability, extending over a wide range, and also, in a short time by increasing a current which is allowed to flow to an insulating film from a current source, as time elapses. CONSTITUTION:By using a current source 4 which can output power having a time characteristic which has been set in advance, a current is set so as to increase gradually to 1X10<-1> amperes in 100sec from 1X10<-8> amperes. Subsequently, the current is allowed to flow to each insulating film 1, and by using the charge quantity which has been allowed to flow before it is brought to dielectric breakdown, as an index, an insulating property of the insulating film 1 is decided. For instance, when the current at the time of starting the application is 1X10<-8> amperes, and the minimum time when the breakdown can be detected is 0.01sec, the minimum breakdown charge quantity which can be detected becomes about 1X10<-10> coulombs. On the other hand, the current at the time of ending the application is 1X10<-1> amperes, therefore, the maximum charge quantity which can be allowed to flow within the measurement time becomes about one coulomb. In such a way, the breakdown charge quantity which can be detected becomes a range of about 10 digits, and a wide breakdown charge quantity distribution extending from an accidental breakdown mode to an intrinsic breakdown mode is obtained surely.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to metal oxide semiconductors (MOS).
) relates to a method for evaluating the electrical insulation performance of an insulation film such as a gate oxide film.

[Conventional technology]

Figure 2 is a circuit diagram showing an insulation evaluation device that implements the conventional insulation performance evaluation method for insulation films. Switch scanner that switches to apply current sequentially,
3 is a voltmeter, 4 is a current source that supplies the above-mentioned current, and 5 is a control device for the switch scanner 2.

Next, the operation will be explained.

The above-mentioned insulation evaluation device is based on, for example, the constant current time dependent dielectric breakdown method shown in IEICE technical research report, 58Ds6-11 (1986).
The insulation properties of the silicon dioxide film are evaluated by the ric breakdown method.

In other words, in this constant current time dependent electric breakdown method, as shown in FIG.
First, the potential difference generated across the insulating film 1 is detected by the voltmeter 3. When the deterioration of the insulating film 1 progresses under such conditions, the potential at both ends of the insulating film 10 decreases rapidly after a certain period of time, leading to dielectric breakdown. The electric current
Calculated from tBD, and this QBD is used as an index of insulation performance. Since the dielectric breakdown phenomenon has a statistical character, the QBD of multiple samples, for example around 100 samples, is investigated and the Q of the dielectric breakdown probability shown in Figure 4 is calculated.
The quality of the insulating film is determined from the BD distribution. The operation of such a determination is performed by the current source 4. Voltmeter 3. A switch scanner 2 that sequentially selects an insulating film 1, which is a sample to which a current is applied.
This is automatically performed by controlling the control device 5.

In FIG. 4, a portion 6 where the probability of failure is flat is an accidental failure mode, and a portion 7 where the probability of failure is steep is a true failure mode. According to this, the smaller the probability of failure in accidental failure mode, and the greater the probability of failure in true failure mode,
It can be said to be a high-quality, highly reliable insulating film. and such accidental destruction.

Knowing the amount of charge at which intrinsic breakdown occurs and the probability of breakdown at that time is very important in evaluating insulation properties.

Furthermore, since QBD is the product of current value and time, the minimum value of QBD that can be detected is determined by the time resolution of destruction detection, and the maximum value is determined by the longest time that the experimenter can tolerate. The lower limit of the destruction detection time is determined by taking into consideration the detection time interval of the voltmeter 3 and the time required for determining destruction by the control device 5.
The limit is around 0.01 seconds, and if you try to make it shorter than that, the structure of the destruction detection device will become complicated. The experimenter's acceptable time is 1ooo QBD of 100 samples.
Considering that the measurement is to be performed within o seconds, the time during which the bt flow can flow per piece is 100 seconds. In this case, the measurable region of Qon is four digits corresponding to 100 seconds from o and oi seconds, which are the limits of the destruction detection time.

[Problem that the invention seeks to solve]

Since the conventional method for evaluating the insulation performance of an insulating film is configured as described above, the detectable range of QBD varies depending on the performance of the equipment used for measurement or the time allowed by the experimenter, but the simple equipment configuration However, since QBD is normally distributed very widely depending on the manufacturing conditions of the insulating film, a range of four digits is insufficient in some cases. For this reason, if the insulating film 1 is of good quality, the QBD will be larger than the detectable area, and if the insulating film 1 is of bad quality, the QBD will be smaller than the detectable area. There were problems such as not being able to do enough. In other words, the conventional method of obtaining QBD by flowing a constant current has the drawback that the detectable region of QBD is small, and when trying to widen the detectable region of C1QnD, the time required for measurement becomes longer. However, there were problems such as a complicated device configuration.

This invention was made to solve the above-mentioned problems, and aims to provide a method for evaluating the insulation performance of an insulation film that can obtain the QBD distribution of insulation breakdown probability over a wide range and in a short time. purpose.

[Means for solving problems]

The method for evaluating the insulation performance of an insulating film according to the present invention increases the current flowing from a current source to the insulating film over time, calculates the amount of charge that can flow until dielectric breakdown occurs as the amount of breakdown charge, and The insulation properties are evaluated using the quantity as an index.

[For production]

Since the current source in this invention increases the current with time, the minimum detectable amount of destructive charge can be reduced by setting the current at a low value at the start of application, and
By setting a large current at the end of application, the maximum amount of destructive charge that can be detected can be increased. In this way, by gradually increasing the current, the range of detectable destructive charge amount is expanded, and by setting the rate of current increase appropriately, it is possible to complete the measurement in a short time. .

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. The basic configuration of the insulation performance evaluation device for examining the breakdown charge distribution is the same as that shown in Figure 2.
has the current-time output characteristics shown below. That is, in the insulation performance evaluation method of the present invention, a current source 4 capable of outputting a current with preset time characteristics is used, and as shown in FIG.
Set to gradually increase to 1xlO amps in seconds. This current is passed through each insulating film 1, and the insulating properties of the insulating film 1 are determined using the amount of charge that can be passed until dielectric breakdown occurs.

In this embodiment, if the current at the start of application is 1xlO ampere and the minimum time for detectable destruction is 0.01 seconds, the minimum detectable amount of destructive charge is about 1xlO coulombs. On the other hand, since the current at the end of application is lXl0"-" ampere, the maximum amount of charge that can be passed within the measurement time is approximately 1
It becomes a coulomb. Thus, in this embodiment, the detectable amount of destructive charge QBD spans a range of approximately 10 orders of magnitude. Therefore, regardless of the quality of the insulating film 1, a wide breakdown charge distribution from the accidental breakdown mode to the true breakdown mode can be reliably obtained.

In addition, since the applied current can be applied to the insulating film 1 while gradually increasing as described above, by setting the increase rate of the applied current arbitrarily, insulation can be achieved in a short time. Performance measurements can be completed.

〔Effect of the invention〕

As described above, according to the present invention, the amount of breakdown charge is measured by increasing the current applied from the current source to the insulating film to be evaluated over time. There is an effect that the breakdown charge amount distribution can be obtained and therefore the breakdown probability distribution of the breakdown charge amount can be sufficiently and accurately measured and evaluated.

[Brief explanation of the drawing]

FIG. 1 is a current-time characteristic diagram of a current source illustrating a method for evaluating insulation properties of an insulating film according to an embodiment of the present invention, and FIG. 2 is an insulation evaluation device for implementing the present invention and a conventional method for evaluating insulation films. FIG. 3 is a time characteristic diagram of the current flowing through the insulating film in the conventional insulating film evaluation method, and FIG. 4 is a characteristic diagram showing the breakdown charge amount distribution of dielectric breakdown probability. 1 is an insulating film, and 4 is a current source. Visiting tribute cargo volume (Qeo)

Claims (1)

[Claims] Determine the amount of breakdown charge from the current flowing into the insulating film from the current source and the time it takes for this insulating film to break down, and evaluate the insulation performance of the insulating film from the magnitude of this breakdown charge. A method for evaluating the insulation performance of an insulating film, characterized in that a current that increases with time is caused to flow through the insulating film from the current source.