Method of detecting semiconductor defects

Details Method of detecting semiconductor defects Method of detecting semiconductor defects

1999-06-09

2001-10-02

Anderson, Bruce (Department: 2881)

Radiant energy

Inspection of solids or liquids by charged particles

Methods

C250S306000, C250S492200, C250S492210, C250S493100, C438S473000

Reexamination Certificate

active

06297503

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the field of semiconductor device manufacturing, and more particularly, this invention relates to the field of detecting defects within a semiconductor device.
BACKGROUND OF THE INVENTION
Electron beam induced contrast (EBIC) is used in quality control of semiconductor device manufacturing because it allows a visual indication of defects in the semiconductor device. The EBIC process is used with a scanning electron microscope (SEM) to observe the semiconductor device and determine errors or quality defects in a specific transistor or junction. EBIC is a well-known non-destructive testing method for semiconductor devices.
Failure analysis methods are essential to determine defects in semiconductor devices. These processes can provide insight to different manufacturing and processing defects and failure modes that have to be corrected. EBIC is used in conjunction with an SEM to provide a focused electron beam and a method for scanning the electron beam over a portion of a semiconductor device, and typically an integrated circuit. The SEM also permits viewing of an image from the semiconductor device by using the secondary electron emission. The EBIC method is used to identify certain types of defects in a semiconductor device by measuring the electron-hole current induced in a semiconductor junction of an integrated circuit by an impinging beam of electrons. One drawback of the EBIC technique is the impinging electrons penetrate a significant distance into the device and also physically spread out into a larger volume in this process. The result of this is that the spatial resolution is substantially reduced making small defects impossible to detect. The primary electron beam must have adequate energy to penetrate through passivation layers to reach the active semiconductor device layer in the integrated circuit having the possible defect. This process also leads to spreading of the beam's effective size.
The EBIC (electron beam induced current) process records the variation of electron hole recombination rates with position by measuring the electrical currents created by the impinging electron beam in local portions of a semiconductor device. These defects include dislocations and defects in the grain boundaries. Electron beams are often used in preference to a laser, e.g., a light beam induced current (LBIC), because the electron beam allows a finer resolution and can create more electron hole pairs. In an EBIC process, the electron beam is scanned perpendicular to the surface of the semiconductor device and the electrons create large numbers of electron-hole pairs within or near to the depletion regions of the semiconductor device. The electrical charges so produced can be collected by the semiconductor device p-n junction induced currents. If the scan includes a grain boundary or other defect, a fraction of the carriers can recombine at different rates, thereby changing the local current generation. Parameters that characterize the defect can be extracted from EBIC line scans, including recombination velocity, V
s
, and minority-carrier diffusion length.
Because of the resolution limitations mentioned above, the EBIC method is commonly used on large semiconductor devices. However, the method does not adequately provide a determination of an exact location of a defect.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of detecting defects within a semiconductor device that allows the detection of defects with more exact certainty than a standard EBIC process.
In accordance with the present invention, a method of detecting defects within a semiconductor device includes the steps of focusing an ion beam in predetermined directions onto an area of a semiconductor device that is believed to have a suspected defect. A portion of the semiconductor device is then milled with the ion beam to form a thin film specimen that is to be removed from the semiconductor device. The thin film specimen is removed from the semiconductor device and placed onto an insulated film mount. Electrical connection points are created on typically what were previously unexposed portions of the thin film specimen by depositing a line of conductive material using a focused ion beam. The surface of the thin film specimen is then scanned with an electron beam in a scanning electron microscope. Internally generated currents as detected by a suitable external amplifier are analyzed. Processing errors of the thin film specimen are then determined and lateral resolution is about the electron beam size.
The focused ion beam allows milling of the semiconductor device such that the thin film specimen has typical dimensions of thickness about 0.1 micrometers, a length of about 20 micrometers, and a width of about 5 micrometers.
In still another aspect of the present invention, the method comprises the steps of depositing a conductive material using a gallium or other appropriate ion emitted from the focused ion beam. The electrical connection points can be created by irradiating gallium or other appropriate ions onto predetermined sections of the thin film specimen by the focused ion beam. A conductive film is then deposited onto the irradiated sections using the focused ion beam to create the electrical connection points. The thin film specimen can be mounted onto a holder, such as a transmission electron microscope grid, before creating the electrical connection points. The method can also include the step of removing the thin film specimen by a charged glass removal tool or metal tip with applied voltage.


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