阅读说明：本技术 一种纳米级静电保护器件失效微区的表征方法 (Characterization method of failure micro-area of nanoscale electrostatic protection device ) 是由 吴幸 陈新倩 徐何军 杨鑫 于 2020-05-07 设计创作，主要内容包括：本发明公开了一种纳米级静电保护器件失效微区的表征方法,选取一个静电失效的纳米级静电保护器件,该器件对比失效前,在工作电压下测得漏电流发生突增,此为失效样品；通过激光扫描该器件表面,利用光致电阻的变化,定位缺陷位置,得到失效热点；根据失效热点,原位切割器件,通过SEM窗口实时观察并调整适合的束流大小,得到最有分析价值的失效TEM样品；最后通过TEM完成对失效区域原子级的表征,综合分析,找出失效机理。本发明对纳米级静电保护器件的内部失效微区精确定位并得到失效的高分辨图像和元素的信息,可以对失效部位进行有效的失效分析,得到失效机理,最终达到改进器件性能的目的。(The invention discloses a characterization method of a failure micro-area of a nanoscale electrostatic protection device, which comprises the steps of selecting a nanoscale electrostatic protection device with electrostatic failure, comparing the device with the device before failure, and measuring the sudden increase of leakage current under working voltage, wherein the device is a failure sample; scanning the surface of the device by laser, and positioning the defect position by utilizing the change of the photoinduced resistor to obtain a failure hot spot; according to the failure hot spot, cutting the device in situ, observing in real time through an SEM window and adjusting the size of a proper beam to obtain a failure TEM sample with the most analysis value; and finally, completing representation and comprehensive analysis of the atomic level of the failure region through the TEM and finding out a failure mechanism. The invention accurately positions the inner failure micro-area of the nano-scale electrostatic protection device and obtains the information of failure high-resolution images and elements, can effectively analyze failure of failure parts to obtain failure mechanisms, and finally achieves the aim of improving the performance of the device.)

1. A characterization method of a failure micro-area of a nanoscale electrostatic protection device is characterized by comprising the following specific steps:

step 1: selecting a nanoscale electrostatic protection device with electrostatic failure, comparing leakage current of the failed device under the same working voltage, wherein the leakage current of the failed device is suddenly increased, the surface of the failed device is free of defects, but the inside of the failed device is short-circuited, and the failed device is a failed sample;

step 2: placing the failure sample obtained in the step 1 in a laser beam resistance abnormity detection instrument, connecting the positive electrode with constant voltage, and connecting the negative electrode with ground to form a loop; wherein the voltage is 0.1-0.6V; irradiating the surface of the failure sample by laser, and absorbing partial energy of the laser by a device to convert the energy into heat; the change of resistance values caused by internal defects of the device can be converted into the change of current, the current change is converted into the brightness of the imaged pixel and recorded, and a failure hotspot is obtained by superposing the position of the pixel change and an optical microscope picture under the same visual angle;

and step 3: placing the failure sample into an instrument of a double-beam focused ion beam-scanning electron microscope, and depositing a Pt protective layer on the surface of the failure sample according to the position of the failure hot spot obtained in the step 2, wherein the length of the failure sample is 8-10 times that of the failure hot spot, the width of the failure sample is 3-5 times that of the failure hot spot, and the thickness of the failure sample is 100-120 nm; digging grooves on two sides of the Pt protective layer by adopting large beams to obtain a roughly cut sample; wherein the current value is 50-70 nA;

and 4, step 4: observing the interfaces at two sides of the rough-cut sample obtained in the step (3) in real time from a window of a scanning electron microscope, and cutting the sample by using a middle beam when the metal layer of the interface at one side is observed to have abnormal appearance; wherein the current value is 20-50 nA;

and 5: when one side of the sample interface obtained in the step (4) has the abnormal appearance of the active region, stopping the ion beam cutting of the side, and continuously cutting the other side by adopting the middle beam until the abnormal appearance of the active region with the same degree appears; wherein the current value is 20-50 nA;

step 6: moving the probe to the upper surface of the failure sample obtained in the step 5, depositing a layer of Pt adhesion probe and sample, cutting off the connection between the failure sample and the substrate, transferring the failure sample on a molybdenum column by using the probe, and finely thinning by using a small beam to obtain a TEM sample; wherein the current is 8-15 nA, and the thinned thickness is 80-100 nm;

and 7: placing the molybdenum column provided with the TEM sample in the step 6 on a sample rod of a transmission electron microscope, inserting the sample rod into a sample cavity of the transmission electron microscope, and shooting a high-resolution image of an internal failure area of the failure sample; switching a scanning transmission electron microscope mode, and collecting element types and contents of the failure area; and finishing the representation of the failure micro-area of the nanoscale electrostatic protection device.

2. The characterization method according to claim 1, wherein the electrostatic protection device of step 1 is a silicon controlled rectifier, a diode or a bipolar transistor.

3. The characterization method according to claim 1, wherein the operating voltage of step 1 is a standard of an input/output pin for which the electrostatic protection device is designed.

Technical Field

The invention relates to the field of failure analysis of nanometer devices, in particular to a method for characterizing failure micro-regions of a nanometer electrostatic protection device.

Background

With the continuous reduction of the process size and the continuous increase of the circuit scale, the influence of the electrostatic discharge on the integrated circuit is more and more remarkable. When an electrostatic discharge occurs, when a high voltage is discharged in about 100ns, the integrated circuit is instantaneously destroyed and irreversible due to the huge energy dissipation. Because the electrostatic protection device itself has the ability to discharge large currents, the industry is equipped with electrostatic protection devices or electrostatic protection circuits at the integrated circuit pins or inside. Therefore, ESD protection is one of the key factors for improving the reliability of integrated circuits.

The gradual reduction of the process leads to the design window and application conditions of the electrostatic protection device becoming more and more severe, and in order to meet the application requirements, various novel electrostatic protection devices emerge endlessly, and the research on the reliability of the novel electrostatic protection devices mostly depends on simulation and modeling, and a method for researching the device performance from a microscopic physical structure failure mechanism is lacked. Furthermore, at the nanoscale, it is difficult to accurately locate and acquire failed tem samples. "a semiconductor laser electrostatic failure analysis method" (CN105425136A) is an electrostatic failure method proposed for a larger-sized semiconductor laser, and the patent can use a high-resolution optical microscope and a scanning transmission microscope to observe failures and analyze failure causes, and is not suitable for a nano-scale device with no damage on the surface. How to accurately locate the failure point on a nanometer scale, shoot a corresponding high-resolution image and analyze a failure mechanism is a technical problem. Therefore, it is desirable to provide a method for characterizing the failure micro-region of a nanoscale electrostatic protection device.

Disclosure of Invention

The invention aims to provide a method for representing a failure micro-area of a nanoscale electrostatic protection device, wherein the method comprises the following steps of firstly selecting a nanoscale electrostatic protection device with electrostatic failure, wherein the surface of the device is free of defects, but the leakage current of the device is suddenly increased compared with that before the device fails, and the device is a failure sample; the position of a failure point is obtained by superposing an optical microscope picture through the change of the photoinduced resistance, wherein the size of the current change under constant voltage corresponds to the brightness of the imaged pixel; cutting the sample by using the double-beam focused ion beam to obtain an ultrathin transmission electron microscope sample; finally, the transmission electron microscope is used for shooting the physical appearance of the microscopic failure and capturing the change of chemical elements, which is the key of the method. The method is used for researching the origin efficiency of the failure of the electrostatic protection device, has good ductility, and can accurately position the failure position and visualize the appearance of physical failure.

The specific technical scheme for realizing the purpose of the invention is as follows:

a characterization method of failure micro-area of nano-scale electrostatic protection device is characterized in that the method comprises the following steps:

step 1: selecting a nanoscale electrostatic protection device with electrostatic failure, comparing leakage current of the failed device under the same working voltage, wherein the leakage current of the failed device is suddenly increased, the surface of the failed device is free of defects, but the inside of the failed device is short-circuited, and the failed device is a failed sample;

step 2: placing the failure sample obtained in the step 1 in a laser beam resistance abnormity detection instrument, connecting the positive electrode with constant voltage, and connecting the negative electrode with ground to form a loop; wherein the voltage is 0.1-0.6V; irradiating the surface of the failure sample by laser, and absorbing partial energy of the laser by a device to convert the energy into heat; the change of resistance values caused by internal defects of the device can be converted into the change of current, the current change is converted into the brightness of the imaged pixel and recorded, and a failure hotspot is obtained by superposing the position of the pixel change and an optical microscope picture under the same visual angle;

and step 3: placing the failure sample into an instrument of a double-beam focused ion beam-scanning electron microscope, and depositing a Pt protective layer on the surface of the failure sample according to the position of the failure hot spot obtained in the step 2, wherein the length of the failure sample is 8-10 times that of the failure hot spot, the width of the failure sample is 3-5 times that of the failure hot spot, and the thickness of the failure sample is 100-120 nm; digging grooves on two sides of the Pt protective layer by adopting large beams to obtain a roughly cut sample; wherein the current value is 50-70 nA;

and 4, step 4: observing the interfaces at two sides of the rough-cut sample obtained in the step (3) in real time from a window of a scanning electron microscope, and cutting the sample by using a middle beam when the metal layer of the interface at one side is observed to have abnormal appearance; wherein the current value is 20-50 nA;

and 5: when one side of the sample interface obtained in the step (4) has the abnormal appearance of the active region, stopping the ion beam cutting of the side, and continuously cutting the other side by adopting the middle beam until the abnormal appearance of the active region with the same degree appears; wherein the current value is 20-50 nA;

step 6: moving the probe to the upper surface of the failure sample obtained in the step 5, depositing a layer of Pt adhesion probe and sample, cutting off the connection between the failure sample and the substrate, transferring the failure sample on a molybdenum column by using the probe, and finely thinning by using a small beam to obtain a TEM sample; wherein the current is 8-15 nA, and the thinned thickness is 80-100 nm;

and 7: placing the molybdenum column provided with the TEM sample in the step 6 on a sample rod of a transmission electron microscope, inserting the sample rod into a sample cavity of the transmission electron microscope, and shooting a high-resolution image of an internal failure area of the failure sample; switching a scanning transmission electron microscope mode, and collecting element types and contents of the failure area; and finishing the representation of the failure micro-area of the nanoscale electrostatic protection device.

And (3) the electrostatic protection device in the step 1 is a silicon controlled rectifier, a diode or a bipolar transistor.

The working voltage stated in step 1 is the standard of the input/output pin suitable for the design of the electrostatic protection device.

The beam size in the step 3-6 is characterized in that the range of the large beam is 50-70 nA, the range of the medium beam is 20-50 nA, and the range of the small beam is 8-15 nA.

The invention can accurately position the electrostatic failure position of the nano device with no damage on the surface, obtains a sample of the transmission electron microscope by cutting through the focused ion beam, observes the physical appearance of the failure part and provides better analysis data for failure mechanism research. The failure characterization method has great significance for improving the reliability of the electrostatic protection device.

1) The invention solves the problem of accurate positioning of failure points when the electrostatic protection device with the nanoscale has no surface damage, adopts a laser beam resistance abnormity detection instrument, and has no influence on the device by utilizing the positioning mode of photoinduced resistance change without introducing secondary damage.

2) According to the invention, when a transmission sample is prepared, the beam current is changed according to different stages, so that excessive damage caused by ion reduction is reduced, the integrity and the flatness of the surface can be maintained, the serious result of missing a failure area due to excessively fast sample cutting can be reduced, and the subsequent reliability research is facilitated.

3) The invention can obtain the physical morphology information of the electrostatic protection device at the internal atomic level, is beneficial to analyzing the failure cause from the microscopic angle, and provides possibility for exploring the influence of factors such as process, design size, material and the like on the device performance.

4) The method has the advantages of high accuracy, high efficiency, strong extensibility and the like.

Drawings

FIG. 1 is a flow chart of the present invention;

FIG. 2 is a graph showing electrical tests of square-wave pulse application in example 1 of the present invention;

FIG. 3 is a failure hotspot graph captured in example 1 of the present invention;

FIG. 4 is a scanning electron microscope image of a sample preparation process in example 1 of the present invention;

FIG. 5 is a diagram of a transmission electron microscope sample finally obtained in example 1 of the present invention;

fig. 6 is a local high-resolution image of a failure region and a corresponding element distribution map taken in embodiment 1 of the present invention.

Detailed Description

The invention is described in detail below with reference to the figures and examples.