JP3627562B2 - Evaluation method of trace organic substances on silicon wafer surface - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for evaluating trace organic substances on the surface of a silicon wafer, and more particularly to a method for evaluating trace organic substances on the surface of a silicon wafer, for example, measuring the number of organic aggregates generated on the surface of a silicon wafer stored for a long time in a wafer case.
[0002]
[Prior art]
After polishing and cleaning, the silicon wafer shipped to the device factory is stored in a wafer case, transported and stored.
By the way, if this wafer case consists of a case body and core made of polypropylene and a lid made of polycarbonate, for example, if stored for a long period of one month or longer, the cause has not been elucidated, In some cases, a minute amount of organic aggregates having a perfect circle shape with a diameter of 10 μm and a thickness of 0.1 μm may be generated.
[0003]
Such organic aggregates greatly affect the product yield and reliability of the device as the device is further miniaturized and the chip area is increased. This is because the appearance shape defect on the wafer surface is the largest cause of a decrease in product yield. As a result, if there are many organic substance aggregates, it becomes a defective product, and the product yield and the like are reduced.
Therefore, it is necessary to detect this organic aggregate and discharge the silicon wafer, which has been found to have a large amount of organic aggregate, from the device manufacturing line. For example, re-cleaning is performed.
[0004]
[Problems to be solved by the invention]
By the way, in the conventional wafer surface inspection performed before the device process, the particle inspection may be performed using a low-angle incident particle detection apparatus.
However, this organic aggregate has a problem that it is difficult to be detected by a low-angle incident particle detection device because the height is as low as about 0.1 μm.
[0005]
OBJECT OF THE INVENTION
Therefore, the present invention provides a method for evaluating a small amount of organic matter on the surface of a silicon wafer by measuring the number of organic matter aggregates present on the surface of the silicon wafer and evaluating the number of organic matter aggregates. That is the purpose.
Another object of the present invention is to evaluate a situation (for example, a plastic case) in which a silicon wafer is stored.
[0006]
[Means for Solving the Problems]
According to the first aspect of the present invention, the surface of a silicon wafer having no COP is irradiated with laser light from two directions of a vertical direction and an inclination direction of 20 to 40 degrees, and the thickness of the wafer surface obtained by the normal incidence is obtained. Silicon that measures and evaluates the number of organic substance aggregates by subtracting the number of particles that do not contain organic substance aggregates obtained by oblique incidence from the number of particles that contain organic substance aggregates less than 0.1 μm in thickness. This is an evaluation method for trace organic substances on the wafer surface.
The silicon wafer to be evaluated is not limited to what causes the organic aggregates on the wafer surface. For example, a wafer case having parts made of polypropylene and parts made of polycarbonate may be mentioned.
Moreover, the particle detection apparatus which irradiates a laser beam to a silicon wafer surface from a perpendicular direction is not specifically limited. For example, “SS6200”, “SP-1” manufactured by Tencor Corporation, “LS-6310” manufactured by Hitachi, Ltd., “WIS-CR80” manufactured by ADE, and the like can be given.
[0007]
Further, the particle detection apparatus that irradiates laser light from the tilt direction is not particularly limited. For example, “SS6420” manufactured by Tencor Corporation may be used.
The incident angle of the laser beam is preferably 20 to 80 degrees, particularly preferably 20 to 40 degrees. If it is less than 20 degrees, minute particles cannot be detected accurately. On the other hand, when it exceeds 80 degrees, the target organic substance aggregate is measured.
[0008]
[Action]
According to the present invention, first, a silicon wafer having no COP on the surface is set at a predetermined inspection position. Thereafter, for example, the wafer surface is irradiated with laser light from the vertical direction, and the total number of particles such as fine dust including organic substance aggregates existing on the wafer surface is measured.
Next, laser light is irradiated to the wafer surface from the tilt direction. As a result, the number of particles excluding organic aggregates present on the wafer surface is measured.
Then, by subtracting the number of particles not including the latter organic substance aggregate from the number of particles including the former organic substance aggregate, the number of the organic substance aggregates can be obtained by a simple calculation. In addition, from this calculation result, it is possible to evaluate the multiple state of the organic aggregate that has a height as low as about 0.1 μm and is difficult to detect by the conventional method.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory view during particle detection by vertical incidence in the method for evaluating a trace amount of organic substance on the surface of a silicon wafer according to one embodiment of the present invention. FIG. 2 is an explanatory view during particle detection by oblique incidence in the method for evaluating a trace amount of organic substance on the surface of a silicon wafer according to one embodiment of the present invention.
[0010]
In FIG. 1, reference numeral 10 denotes an inspection device 10 for a trace organic substance on the surface of a silicon wafer to which the method for evaluating a trace organic substance on the surface of a silicon wafer according to one embodiment of the present invention is applied (hereinafter sometimes simply referred to as a trace organic matter inspection apparatus 10). ). This trace organic matter inspection apparatus 10 injects a laser beam from a vertical direction into a minute amount of an organic substance aggregate a (diameter d = 10 μm, thickness t = 0.1 μm), fine dust, etc. present on the surface of a silicon wafer W. The inspection is performed by irradiating the surface of the wafer with the first particle detection device 11 to be inspected and other fine dust excluding organic aggregates existing on the surface of the silicon wafer W at an inclination angle of 20 degrees. And a second particle detection device 12. The second particle detection device 12 is installed downstream from the first particle detection device 11.
[0011]
The silicon wafer W used here is obtained, for example, by subjecting a silicon single crystal rod pulled up by the CZ method to block cleaning, wafer cutting, chamfering, mechanical chemical polishing, and final cleaning by RCA cleaning, and then These silicon wafers were stored and shipped in a wafer case consisting of a polypropylene case body and core and a polycarbonate lid, and were kept in a device factory warehouse for about one month. The silicon wafer W to be evaluated has a mirror finished surface.
The first particle detection device 11 is specifically “SS6200” manufactured by Tencor Corporation. That is, it is an apparatus for detecting the minimum number of particles of 0.10 μm existing on the surface of the silicon wafer W by irradiating the surface of the silicon wafer W with a laser beam from the vertical direction.
[0012]
In this apparatus configuration, a light source 13 of laser light arranged orthogonally to the wafer surface and two channels (for bright field and dark field) are radiated and arranged on the left and right in the vertical plane with the light source 13 as the center. The photomultiplier 14 is provided. The laser beam irradiated at 90 ° from the upper light source 13 toward the wafer surface strikes and diffusely reflects particles such as organic aggregate a and fine dust adhering to the mirror-finished wafer surface. The reflected light spreads radially as shown by the arrows in FIG. This is captured by an arbitrary photomultiplier 14 so that the total number of particles including the organic aggregate a existing on the surface of the silicon wafer W is detected.
[0013]
The second particle detection device 12 shown in FIG. 2 is specifically “SS6420” manufactured by Tencor Corporation. That is, the surface of the silicon wafer W is irradiated with laser light obliquely from above, and particles such as fine dust having a minimum size of 0.15 μm excluding the organic aggregate a on the wafer surface are counted.
The apparatus configuration is arranged on one upper side of the silicon wafer W, and a light source 15 for irradiating laser light upward in parallel with the silicon wafer W, and a mirror 16 for bending the laser light downward toward the silicon wafer W side. And a beam expander 17, a lens 18 for condensing the laser beam that has passed through the beam expander 17, and a large photomultiplier that is disposed on the other upper side of the silicon wafer W and captures the laser beam reflected from the wafer surface. 19.
[0014]
The laser light emitted from the light source 15 is bent at an angle of 20 degrees with respect to the surface of the wafer W by the mirror 16, and then irradiated to the wafer surface via the beam expander 17 and the lens 18. Of these, the reflected light reflected by the particles is captured by the photomultiplier 19 of two channels (for bright field and for dark field), and this particle is detected.
However, as described above, the organic substance aggregate a cannot be detected here. This is because the thickness t of the organic aggregate a is an extremely thin particle of 0.1 μm, and therefore, when the light is from the inclined direction, the side detector can capture the aggregate a. This is because the reflected light cannot be obtained.
[0015]
Here, the scanning technique by SS6420 will be described. The focus mechanism moves the target silicon wafer W up and down with the wafer surface placed on the scan plane. The silicon wafer W moves in a high-speed telecentric scanning laser beam having a wavelength of 488 nm at a constant speed. The laser beam is focused so as to project a 75 μm diameter circle when traversing the substrate surface at an angle of 20 °. Further, the scanning beam crosses a straight path on the silicon wafer W back and forth, and reliably samples the entire silicon wafer W.
[0016]
When the laser beam illuminates the LPD (foreign matter) on the silicon wafer W, the light is scattered in all directions from the incident point. Part of this scattered light is collected and guided to a low noise photomultiplier tube for amplification. The analog signal output from the low noise photomultiplier tube PMT is digitized by a high-speed analog-to-digital converter. Data acquisition electronics periodically sample the digital converter to generate a raster image of the surface of the silicon wafer W. The raster image is then analyzed by a pipeline processor and a dedicated general purpose computer to create, display and manipulate surface measurement data.
[0017]
Next, a method for evaluating a trace organic substance on the silicon wafer surface using the trace organic substance inspection apparatus 10 will be described.
As shown in FIG. 1, the silicon wafer W is placed in a horizontal state on the detection stage of the first particle detector 11.
Thereafter, the organic agglomerates a, fine dust, etc. present on the surface of the silicon wafer W are inspected. That is, in the particle inspection of the wafer surface, laser light is irradiated from the light source 13 of the first particle detection device 11 toward the wafer surface at 90 °, and the reflected light is captured by the photomultiplier 14. The particles containing the organic substance aggregate a adhering to the surface are counted.
Thus, in the first particle detection device 11, the laser beam is incident from the direction perpendicular to the wafer surface. Therefore, as shown in the partially enlarged view of FIG. 1, the reflected light from the organic aggregate a having a low height can be well captured using the photomultiplier 14.
[0018]
Next, the silicon wafer W is transferred to the detection stage of the first particle device 12.
Here, the second particle detection device 12 irradiates the wafer surface with laser light from the light source 15 from an inclined direction. Then, the reflected light is captured by the photomultiplier 19. Thereby, particles such as fine dust existing on the wafer surface are detected.
However, in the second particle detector 12, since the incident angle of the laser beam is small, as shown in the partially enlarged view of FIG. 2, the organic aggregate a having a thickness of about 0.1 μm is not used. The reflection angle of the reflected light is small. Therefore, the photomultiplier 19 cannot capture the reflected light well. As a result, the particles that can be detected by the second particle detection device 12 are fine dust and the like excluding the organic aggregate a.
[0019]
Thereafter, in the control unit (not shown) of the trace organic matter inspection device 10, the number of particles of the second particle detection device 12 is simply subtracted from the number of particles obtained by the first particle detection device 11. The number of organic aggregates a present on the surface of the silicon wafer W is measured by calculation, and the number of organic aggregates a on the silicon wafer W as a specimen is evaluated based on the obtained result.
In this way, when measuring the number of organic aggregates a on the wafer surface, the surface of the wafer is irradiated with laser light from the vertical direction and the tilt direction, and then the organic aggregates a are obtained by performing simple calculations. Since the number is measured, it is possible to easily evaluate the state in which the organic substance a is abundant or in a state in which the organic agglomerates a are small.
[0020]
【The invention's effect】
According to the present invention, the surface of the wafer is irradiated with the laser beam from the vertical direction and the tilt direction to measure the organic aggregates existing on the wafer surface. It is possible to easily evaluate whether or not there is much above. In particular, it is possible to easily evaluate the cleanliness of the wafer surface stored in the resin case. Therefore, the cleanliness of the resin case itself can be evaluated. In addition, wafer cleaning can be evaluated.
[Brief description of the drawings]
FIG. 1 is an explanatory view during particle detection by normal incidence in a method for evaluating a trace amount of organic matter on a silicon wafer surface according to an embodiment of the present invention.
FIG. 2 is an explanatory view during particle detection by oblique incidence in the method for evaluating a trace amount of organic substance on the surface of a silicon wafer according to one embodiment of the present invention.
[Explanation of symbols]
10 Inspection device for trace organic matter on silicon wafer surface,
11 1st particle | grain detection apparatus,
12 Second particle detection device,
W silicon wafer,
a Organic aggregate.

Claims (1)

Irradiate the surface of a silicon wafer having no COP with laser light from two directions, a vertical direction and an inclination direction of 20 to 40 degrees ,
This organic matter is obtained by subtracting the number of particles that do not contain organic matter aggregates obtained by oblique incidence from the number of particles that contain organic matter aggregates having a thickness of less than 0.1 μm on the wafer surface obtained by normal incidence. A method for evaluating trace organic substances on the surface of silicon wafers, which measures and evaluates the number of aggregates.

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