JPH104040A - Method for marking semiconductor material and product marked by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate fine projections excellent in visibility restraining dust from being produced by a method wherein the surface of a semiconductor material is irradiated with a pulse laser beam controlling the laser beam at least in either energy or pulse width. SOLUTION: An Nd:YAG laser pulse oscillator projects a laser beam which is nearly uniform in intensity distribution. A metal mask where a pattern to mark is formed is irradiated with a laser beam through an enlarging optical system. The transmitted laser beam is made to irradiate a work through an image forming system to mark the pattern on the work. When an Si wafer 8 as a work is irradiated with a laser beam 109, a large number of fine projections are formed on a part of the Si wafer irradiated with a laser beam. A laser beam irradiating, for instance, the fine projections 105 to 107 is turned to the irregularly reflected laser beams 110 to 113. The fine projections 105 to 107 are very densely distributed, so that a laser-irradiated part and a non- irradiated part are easily discriminated from each other by a light reflection difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for marking a semiconductor material surface or an electronic component with a pulse laser beam.

[0002]

2. Description of the Related Art A method of engraving letters or numbers on the surface of a semiconductor material by a laser beam is known. Known methods include a method of irradiating a laser beam at a position to be imprinted on the surface of the semiconductor material while moving the laser beam, and melting and evaporating the semiconductor material at the irradiated portion to form a continuous concave trace.
As disclosed in Japanese Patent Publication No. 41245/1989, there is a method of forming a circular recess in a laser beam irradiation portion.

[0003]

In the engraving of a semiconductor material, it is required that 1) no dust is generated by the engraving operation, 2) the visibility is excellent, and particularly that it can be easily read by an optical reader. . However, these requirements are conflicting and it is difficult to satisfy both at the same time.

An object of the present invention is to provide an engraving method which suppresses generation of dust and is excellent in visibility in an operation of engraving characters, numerals or patterns on the surface of a semiconductor material by a laser beam.

[0005]

According to the present invention, there is provided an engraving method for engraving a pattern on a semiconductor material surface by irradiating a pulsed laser beam, wherein the laser beam irradiated surface of the semiconductor material surface is melted and recrystallized. In this case, the energy and the pulse width of the pulse laser beam are controlled so that a minute projection is generated at the position.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will now be described with reference to FIGS.
This will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes Nd: Y of pulse oscillation.
An AG laser oscillator that emits a laser beam 2 having a substantially uniform intensity distribution. The laser beam 2 is applied to a metal mask 4 on which a pattern to be imprinted is formed via an enlarging optical system 3. Instead of a metal mask, a glass mask having a partially opaque portion can be used. The transmitted laser light 5 is irradiated onto the work 7 by the imaging optical system 6 to imprint a pattern. 2 shows the state of the engraving 9 formed on the Si wafer 8 as the work 7, FIG. 3 shows an enlarged schematic view of the engraving 9, and FIG. 4 shows a sectional view taken along line IV-IV of FIG.

In FIG. 3, a large number of minute projections 100 to 107 are formed on the right half laser beam irradiation surface.
The minute projections 100 to 107 have a circular or band shape, and have an approximate height of 1 μm or less. The diameter is 0.5-1.0
μm, the spacing between them is approximately 1.5-2.5 μm, and the density is on the order of 1.6-4.5 × 10 ⁷ / cm ² .

As a reason for the formation of the minute projections, according to the experiments of the present inventors, the irradiation of the surface of the semiconductor material with the pulsed laser beam instantaneously causes the portion to be in a molten state. Recrystallization started, and at this time, a phenomenon in which a large number of protrusions having a height of approximately 1 μm or less were formed was observed. It was also found that the intensity distribution, irradiation energy density, and pulse width of the pulsed laser beam were important factors for the occurrence of this phenomenon. In other words, by irradiating a pulsed laser beam having a uniform intensity distribution and maintaining the irradiated surface in a molten state (not evaporating), it is possible to form a large number of projections with a minute height while suppressing generation of dust. It turned out to be.

The character or pattern formed on the surface of the semiconductor material by using this phenomenon becomes a mark having excellent visibility due to the irregular reflection of light due to a large number of minute projections. A marking method utilizing such a phenomenon has not been conventionally known.

That is, as shown in FIG.
When the laser beam 09 is irradiated, it is reflected as it is in the left half of the laser beam non-irradiated portion, but the minute projections such as 105 to 107
Are turned into diffusely reflected lights 110 to 113. As described above, the minute projections 105 to 107 are very densely distributed, so that the laser light irradiated portion and the laser light non-irradiated portion can be easily distinguished by the difference in light reflection.

In this case, the conditions of the pulse laser beam are irradiation energy density = 30 J / cm ² and pulse width = 0.15 ms.
Then, a polished product having a crystal orientation (100) was used for the Si wafer. The lower limit of the irradiation energy density is 18 J / cm ²
In the following, since no melting occurs on the surface,
0 to 107 are not formed. If it is more than 40 J / cm ² , dust is generated due to partial evaporation on the surface, which is not preferable in the manufacturing process. For example, the number of steps for removing dust increases, which is not preferable. Therefore, the irradiation energy density value is 18 J /
cm ^{2 to} 40 J / cm ² , diffused light 110 to
It has minute projections 105 to 107 that generate 113, and can be identified, and no dust is generated.

On the other hand, the upper limit and the lower limit of the pulse width are closely related to the irradiation energy density, and are 18 to 40 J / cm ^2.
In the range, the pulse width is 0.05 to 0.40, and the minute projections 100 to 104 are formed in the range of ms. That is, when the pulse width is shorter than 0.05 ms, the line width of the engraved text, numeral, and the like becomes thin, making it difficult to identify. If the length is longer than 0.40 ms, the line width of the engraved letters and numbers becomes thicker. For example, when engraving two parallel lines, the so-called resolution of the parallel lines appears as if they are the same line, and the resolution decreases. It becomes difficult to do. Therefore, the pulse width is 0.05 to 0.40
In the range of ms, identification becomes easy.

That is, when engraving on a Si wafer, a part or the like, the irradiation energy density value is set to 18 J / cm ^{2 to} 40 J.
/ Cm ² and pulse width 0.05 to 0.40 ms
When a pulse laser beam is irradiated by selecting a value within the range, it is possible to obtain an engraved mark in which dust is not generated and which can be easily identified.

Further, since the intensity distribution of the laser beam emitted from the laser oscillator is required to have a uniformity of about ± 5% on the surface of the mask 4, a single mode, which has been conventionally used for marking on the surface of a semiconductor material, is used. Alternatively, a laser oscillator that oscillates in a low-order mode cannot be used, and a slab laser that easily realizes a uniform intensity distribution is suitable as the oscillator.

FIGS. 5 to 9 show another embodiment of the present invention. A liquid crystal mask 13 is irradiated with a laser beam 12 from a linearly polarized Nd: YAG laser oscillator 11. After the laser beam 15 including the pattern information is separated by the beam splitter 14, the laser beam 15 is irradiated onto the work 7 by the imaging lens 6, and the pattern is engraved. The pattern information is sent to the liquid crystal mask 13 from the control device 16 via the liquid crystal mask controller 17. The unnecessary light 18 is absorbed by the absorbing plate 19.

FIG. 6 is a partially enlarged view of the pattern displayed on the liquid crystal mask 13 and the two-dimensional code 20 is displayed. The two-dimensional code 20, for example, a vericode, a data code, etc., is composed of a collection of regular square patterns called cells 21. Therefore, the liquid crystal mask 13 that displays a pattern for engraving with a set of square pixels is optimal as a mask for generating a pattern for a two-dimensional code.

The display mode of the TN (twisted nematic) liquid crystal mask has two display modes as shown in FIGS. "T" of any character is displayed. The liquid crystal mask 50 is composed of an aggregate of square pixels 51. In a display mode called a normally closed mode shown in FIG.
(Shaded) voltage is applied. However, since a voltage cannot be applied to the gap portion 53 between the pixels, the pattern imprinted on the work (not shown) is a discontinuous collection of squares.

On the other hand, in a display mode called a normally open mode in FIG. 8, a voltage is applied to the pixels 54 (hatched) corresponding to the background portion. That is, in this display mode, a pattern is displayed by the pixels 55 to which no voltage is applied, so that the gap 53 between the pixels also constitutes a part of the pattern. Therefore, a pattern imprinted on a work (not shown) is a continuous square aggregate, and is suitable for imprinting a two-dimensional code in which a connection state between cells is regarded as important. Strictly speaking, a grid-like pattern irrelevant to the engraving pattern will be imprinted on the work. However, the line width on the work in this part is as narrow as about 5 to 10 μm, and due to heat diffused into the work. Since a rise in the temperature of the laser irradiation part is suppressed, no trace is formed on the work.

FIG. 9 is a schematic view of the two-dimensional code 20 engraved on the work 7 by the configuration of FIG. 5, and the pattern of FIG. 6 is displayed on the liquid crystal mask 13. In the present invention, the work 7 is a Si wafer, and the conditions of the pulse laser beam are irradiation energy density = 30 J / cm ² and pulse width = 0.
15 ms was adopted. By employing the above-described normally open mode as the display mode, the adjacent cells 22, 23, and 24 are two-dimensionally formed by a large number of minute projections (not shown) formed on the surface without forming a boundary. The code 20 is represented.

FIG. 10 shows a method for reading the imprinted two-dimensional code.
6 irradiates the workpiece 7 with the reflected light 27 and the minute projection 2.
Of the irregularly reflected light 29 from 8, the former is mainly taken into a two-dimensional CCD sensor (not shown) in the reading device 25, and the pattern is read.

FIG. 11 shows an example of imprinting a two-dimensional code using a conventional laser marker for reference, but one circular recess is made to correspond to one cell on the work 7. For this reason, it is necessary to add a pattern processing function to the reading device in order to distinguish the cell 24A that exists alone and the aggregate 24B of a plurality of cells, which causes an increase in cost. In addition, light reflected from the circular concave portion does not become irregularly reflected light as in the present invention, so that it is necessary to devise light separation. In the present invention, each cell is formed in a square shape, and the light reflected from the engraved portion is irregularly reflected, so that it can be read by a simple reading device.

By the way, in order to improve the reading rate of the imprinted two-dimensional code by the reading device 25, 1) the size of each imprinted cell must be uniform, and 2) the space between adjacent cells must be increased. It is important not to make it, and 3) that the ratio of the reflected light 27 and the irregularly reflected light 29 taken into the two-dimensional CCD sensor is large.

On the other hand, 1),
2) The above-described control of the energy and pulse width of the irradiation pulse laser beam satisfies the conditions 1) and 3), thereby realizing accurate reading of the engraved pattern.

FIG. 12 shows an example in which the present invention is applied to a semiconductor production line. A work 30 is first engraved with a management number (indicated by alphanumeric characters or a two-dimensional code) by an engraving device 31 of the present invention. Are sent to the manufacturing process 32, 33, 34 by the moving device. A reading device 25 is provided between each step as necessary, and the information is sent to the production line control computer 35. If necessary, an engraving device 31 can be arranged between the processes to imprint the information in the previous process on the work 30.

In the above description, the case where the semiconductor material is a Si single crystal has been described. However, a semiconductor wafer having a silicon single crystal surface on which an oxide film or a nitride film is formed, a semiconductor chip, a resin mold type part, or the like. The marking method of the present invention can be applied to electronic components.

[0027]

According to the present invention, an approximately 1 .mu.m height formed on the surface of a semiconductor material by irradiation with a pulsed laser beam.
Since a large number of microprojections less than m are used for engraving, clear engraving can be realized without generating dust at the time of engraving. In addition, since irregular reflection light is generated at the minute projections and identification can be performed, a high reading rate can be realized when a pattern reading device is used.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a liquid crystal laser marker shown as an embodiment of the present invention.

FIG. 2 is a front view of a semiconductor substrate processed by the apparatus of FIG. 1;

FIG. 3 is a partially enlarged surface view of the stamp of FIG. 2;

FIG. 4 is a sectional view taken along line IV-IV of FIG. 3;

FIG. 5 is a schematic explanatory view of a liquid crystal laser marker shown as another embodiment of the present invention.

6 is a partially enlarged view of a pattern displayed on the liquid crystal mask of FIG.

FIG. 7 is a partially enlarged view of a pattern imprinted on the work in FIG. 6;

FIG. 8 is a partially enlarged view of a pattern imprinted on the work of FIG. 6;

FIG. 9 is a partially enlarged view of a pattern imprinted on the work in FIG. 6;

FIG. 10 is an explanatory diagram of a device for reading an engraved pattern.

FIG. 11 is a partially enlarged view of a pattern imprinted on a conventional work.

FIG. 12 is a schematic explanatory view showing a process of arranging a marking device in which the present invention is applied to a semiconductor manufacturing process.

[Explanation of symbols]

1 ... Nd: YAG laser oscillator, 4 ... metal mask, 8 ...
Si wafer, 9: stamp, 10: liquid crystal mask, 20: two-dimensional code, 28: diffusely reflected light, 100 to 107: minute projection.

Claims (7)

[Claims] In a method of imprinting a pattern on a surface of a semiconductor material by irradiating a pulsed laser beam, a microprojection is generated at a location where the surface of the semiconductor material irradiated with the pulsed laser beam is melted and recrystallized. A method of marking on the surface of a semiconductor material, wherein at least one of the energy and the pulse width of the pulsed laser beam is controlled. 2. A method for imprinting a pattern on a surface of a semiconductor material by irradiating a pulsed laser beam, wherein minute projections are generated at the location in the process of melting and recrystallizing the surface of the semiconductor material irradiated with the pulsed laser beam. As described above, a method for imprinting on the surface of a semiconductor material, wherein the pulse width of the pulse laser beam is selected to be 0.05 ms to 0.40 ms. 3. A method for imprinting a pattern on a surface of a semiconductor material by irradiating a pulsed laser beam, wherein a minute projection is generated at a relevant point in the process of melting and recrystallizing the surface of the semiconductor material irradiated with the pulsed laser beam. Thus, the energy density of the pulsed laser beam on the surface of the semiconductor material is set to 18
Marking method of the semiconductor material surface, characterized in that it has selected in ^{J / cm 2 ~40J / cm 2} . 4. while the energy density of the pulsed laser beam to ^{18J / cm 2 ~40J / cm 2} , a semiconductor according to claim 1, wherein the selecting the pulse width 0.05ms~0.40ms How to imprint on the material surface. 5. A process for irradiating an article surface such as a semiconductor material or an electronic component with a pulsed laser beam and melting or recrystallizing the surface irradiated with the pulsed laser beam to form a mark formed of a minute projection formed at the corresponding location. An article characterized by having on the surface. 6. The article according to claim 1, wherein the pattern to be imprinted includes a two-dimensional code, and the means for generating the pattern is a liquid crystal mask. How to engrave on. 7. The article according to claim 5, wherein a pattern to be imprinted on an article such as a semiconductor material or an electronic component includes a two-dimensional code, and the means for generating the pattern is a liquid crystal mask.