JP2859155B2 - Evaluation equipment for semiconductor devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device evaluation apparatus, and more particularly to a semiconductor device evaluation apparatus for non-destructively evaluating a cross-sectional shape of a semiconductor device to be evaluated using a laser beam.

[0002]

2. Description of the Related Art In a semiconductor device, the accuracy of the cross-sectional shape of electrodes such as gates and sources constituting semiconductor elements such as MOS transistors, the lead wires of these electrodes, or the wirings between semiconductor elements influences the performance and reliability. This is an important requirement. For example, if the gate electrode of a MOS transistor, which should be rectangular, is formed in a trapezoidal cross section, or conversely, if the gate electrode is formed in an inverted trapezoidal shape, performance degradation or variation occurs. In addition, if the wiring is formed in an inverted trapezoidal shape, it causes a problem of reliability that stress migration and electromigration are likely to occur.

Conventionally, as a method for evaluating the cross-sectional shape of an electrode, a wiring, or the like as described above, a target portion of a semiconductor device to be evaluated is cut into a predetermined size, extracted as an evaluation sample, and the evaluation sample is subjected to a first method. A first evaluation method for directly observing and evaluating using a scanning electron microscope as an evaluation device is mainstream.

FIG. 3 shows a first conventional evaluation method in the order of steps.
First, a semiconductor device such as an LSI formed on a semiconductor substrate such as a Si wafer shown in (A) is cut together with the semiconductor substrate as shown in (B) and the cut surface is polished as shown in FIG. As shown in (C), the sample is formed into a sample having a size that can be accommodated in the sample chamber of the scanning electron microscope. Next, this evaluation sample is accommodated in a sample room of a scanning electron microscope, and the above-mentioned polished surface is directly observed and evaluated as an electron microscope image shown in (D). In order to capture a cross section for evaluation as an electron microscope image, it is often necessary to sputter gold on this cross section so that electrons are easily charged.

In this conventional first evaluation apparatus, it is necessary to process and form an evaluation sample of a desired size from a semiconductor wafer or the like to be evaluated in order to perform observation and evaluation. It takes 3 hours.

[0006] Japanese Patent Laid-Open No. 4-17614 for solving this drawback
The second conventional evaluation device, which is a wafer pattern shape inspection device described in Japanese Patent Publication No. 3 (1993) -279, includes a laser light source, a beam expander for expanding a laser beam diameter to cover the outer shape of the wafer, and an expanded laser beam for a wafer to be evaluated. , A condenser lens for collecting the specularly reflected light generated on the wafer to be evaluated and the diffracted light by the pattern of the semiconductor device on the wafer, and a condensed reflected / diffracted laser beam pattern (condensed light beam). Pattern), a storage device for storing the condensing pattern (reference pattern) of the reference semiconductor, and comparing the condensing pattern with the reference pattern to determine which of the semiconductor devices corresponding to the condensing pattern A judgment device for judging whether or not the reflected light / diffraction light corresponds to a reference semiconductor; Manner is that performs shape evaluation including the whole of the three-dimensional pattern wafer.

[0007]

Since the above-mentioned first conventional semiconductor device evaluation apparatus directly observes and evaluates as an electron microscope image, it destroys a semiconductor wafer or the like to be evaluated and evaluates a desired dimension. It is necessary to process the sample,
It requires a lot of man-hours and time, and also has the disadvantage of lowering the yield of the semiconductor device production line.

The second conventional semiconductor device evaluation apparatus which solves this drawback can evaluate the shape of the semiconductor device pattern of the entire wafer, but has a limit in the type of the reference semiconductor. However, it is difficult to specify the actual cross-sectional shape of the semiconductor device alone.

[0009]

According to the present invention, there is provided an apparatus for evaluating a semiconductor device, comprising: a laser light source for irradiating a laser beam at a predetermined angle to one principal surface of a semiconductor substrate on which a semiconductor device having a three-dimensional shape is formed. Reflected light of this laser beam
And process the signals to process the shape of the semiconductor device in the cross-sectional direction.
In the evaluation apparatus of a semiconductor device to be measured, said one main surface
Perpendicular to the irradiation direction of the laser beam projected on
A laser scanning means for scanning the laser light source, and two-dimensionally arranged photoelectric conversion elements, and in a predetermined positional relationship with the laser light source.
2 that is mechanically fixed and receives light reflected from the one main surface
Signal processing means for extracting the dimension light sensor, the maximum charge amount corresponding pixel signals of the photoelectric conversion element receives the primary reflected light corresponding to the signal level of one of the reflected light incident on the front SL two-dimensional photosensor And a storage circuit for storing the pixel signal, and image output means for converting the pixel signal into an image based on the pixel signal read from the storage circuit and the scanning information of the laser beam.

[0010]

FIG. 1 is a block diagram showing an embodiment of the present invention. Referring to FIG. 1, a semiconductor device evaluation apparatus according to this embodiment shown in FIG. A laser light source 1 such as a Ne laser, and a laser light source 1
A two-dimensional CCD sensor 2 which is arranged integrally with the laser beam receiving means 9 for receiving reflected light R from the wafer 9 and a laser scanning unit 3 which can move (scan) a laser beam B in a direction perpendicular to the incident direction.
A signal processing unit 4 for processing an output signal C of the CCD sensor 2 and outputting reflected light data D; a storage unit 5 for storing the reflected light data D; and reading data E from the storage unit 5 to form an image. And an image output unit 6 for displaying on a display.

Next, the operation of the present embodiment will be described with reference to FIG.
A beam B of about 1 μm is irradiated from obliquely above the surface of the wafer 9. Referring also to FIG. 2A showing the relationship between the details of the wafer 9 and the beam B and the reflected light R, the beam B incident on the wafer 9 is reflected by the side surface of the element 10 of the semiconductor device and reflected light R And enters the two-dimensional CCD sensor 2,
A corresponding signal charge is generated. Since the size of one photoelectric element, that is, one pixel of a general two-dimensional CCD sensor of this type is about 3 μm square, incident light having a beam diameter of 0.1 μm is recognized as information for one pixel. However, the reflected light R
Include primary reflected light reflected on the wafer surface and n-order reflected light (n is 2, 3, 4,...) Reflected on a boundary surface such as an insulating film in the lower part of the semiconductor device surface. The physical feature that distinguishes the primary reflected light from the n-order reflected light is energy, and the primary reflected light is the largest. Therefore, of the reflected light R incident on the two-dimensional CCD sensor 2, the one having the largest energy, that is, the one having the largest signal charge amount among the photoelectric elements of the two-dimensional CCD sensor 2 is regarded as the light receiving element of the primary reflected light R. Can be considered. 2 as described above
The two-dimensional CCD sensor 2 is mechanically integrated with the laser light source 1, and depends on which photoelectric element (hereinafter, pixel) the primary reflected light R returns to the cross section of the element 10 on the surface of the wafer 9. Shape can be estimated. That is, FIG.
As shown in (A) and (B), the reflection angle of the beam B incident on the element 10 changes depending on the cross-sectional shape of the element 10.
For example, as shown in (A), when the cross section 11 of the element 10 is an accurate rectangle, that is, perpendicular to the surface of the wafer 9, the element 10 reflects the incident beam B at an angle (hereinafter referred to as a reflection angle) of 0 degree, When the cross section 11 has a trapezoidal shape as shown in FIG. 2D C
The principle is that the reflection angle, that is, the cross-sectional shape of the element 10 can be estimated from the position of the incident pixel of the reflected light R of the CD sensor 2.

The laser light source 1 has a structure that can be scanned by moving in a direction perpendicular to the beam B by the laser scanning unit 3. At the time of evaluation, for example, the reflection angle is measured while moving at a pitch of 0.1 μm, the reflection angle data is stored in the storage device 5, and the stored reflection angle data is synthesized as one image data. Element 10
Can be estimated, and the image output unit 6 displays the image as an image, whereby the shape of the element 10 can be recognized.

Referring to FIG. 2C, which shows an example of a specific output image of the image output control unit 6, the range of the section X of the cross section 11 of the element 10 to be evaluated shown in FIG. It is displayed as an image 12 on the screen 13. A time required for these evaluations of about 10 minutes is sufficient.

As described above, in the present embodiment, only the shape of one side of the element 10 is displayed for evaluation. However, since various element shapes in a semiconductor device are generally symmetrical,
As described above, it is sufficient to display only one side portion. Of course,
It is also possible to accurately evaluate the display of the shape on both sides of the element. In this case, after the display on one side is completed, the incident direction of the beam may be changed to the obliquely upper side on the other side, and the processing may be executed again.

[0015]

As described above, the apparatus for evaluating a semiconductor device according to the present invention uses the laser beam projected onto the wafer surface.
Laser scanning means for scanning in a direction perpendicular to the irradiation direction,
Mechanically fixed in a predetermined positional relationship with the laser light source
And two-dimensional optical sensor for receiving the reflected light from the surface Re,
Comprising a signal processing means for extracting a picture element signal, a memory circuit for storing the pixel signals, and an image output means for converting from from the storage circuit and read out the pixel signal and the scanning information the pixel signal to the image, Conventionally, since the cross-sectional shape of the element of the semiconductor device formed on the wafer can be evaluated very easily.
There is an effect that the time and labor required can be greatly reduced to about 10 minutes.

In addition, since the evaluation of the semiconductor device itself can be performed in a non-destructive manner, there is an effect that the factor of lowering the yield can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a semiconductor device evaluation apparatus of the present invention.

FIG. 2 is an explanatory diagram illustrating a relationship between details of a wafer to be evaluated, a laser beam, and reflected light, and an example of a display image in the semiconductor device evaluation apparatus of the present embodiment.

FIG. 3 is a process chart showing an example of a process of an evaluation method of a conventional semiconductor device evaluation device.

[Explanation of symbols]

 Reference Signs List 1 laser light source 2 two-dimensional CCD sensor 3 laser scanning unit 4 signal processing unit 5 storage unit 6 image output unit 9 wafer 10 element 11 cross section 12 image 13 display screen

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/66 G01B 11/24 H01S 3/00

Claims (2)

(57) [Claims] 1. A laser light source for irradiating a laser beam at a predetermined angle to one principal surface of a semiconductor substrate on which a semiconductor device having a three-dimensional shape is formed, and having a laser beam reflected therefrom.
Detects the emitted light, processes the signal, and detects
In a semiconductor device evaluation device for measuring a shape, a laser beam projected onto the one main surface may be irradiated in a direction in which the laser beam is projected.
Laser scanning means for scanning in the vertical direction; and two-dimensional light, which is composed of two-dimensionally arranged photoelectric conversion elements and is mechanically fixed to the laser light source in a predetermined positional relationship and receives light reflected from the one main surface. signal processing means for extracting sensor and the maximum charge amount corresponding pixel signals of the photoelectric conversion element receives the primary reflected light corresponding to the signal level of one of the reflected light incident on the front SL two-dimensional photosensor, A semiconductor circuit, comprising: a storage circuit that stores the pixel signal; and an image output unit that converts the pixel signal into an image based on the pixel signal read from the storage circuit and scanning information of the laser beam. Evaluation device. 2. The semiconductor device evaluation device according to claim 1 , wherein said two-dimensional optical sensor is a two-dimensional CCD sensor.