JP2847836B2 - Method for improving surface morphology of laser irradiated surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] In a process of irradiating a pulse laser onto a wiring material of a semiconductor device to planarize a film or modify a film, etc., a surface morphology of an irradiation surface generated by irradiation is measured. In order to improve the surface morphology caused by laser irradiation by superposition irradiation and improve the smoothness of the entire area irradiated with laser, the pulsed laser was superposed several times and the conductive film was temporarily In the process of melting and solidifying, a pulse energy density that only melts the entire conductive film in the overlap irradiation is applied, and after the irradiation, a pulse in which only the substantially entire surface layer of the irradiation region melts. It is configured to perform irradiation of energy density.

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is generated by irradiation in a step of irradiating a pulse laser onto a wiring material of a semiconductor device or the like to flatten or modify a film. The present invention relates to improvement of surface morphology of an irradiation surface.

[Prior Art] It is known that a via hole is buried and a wiring is flattened by using a pulse laser (Semicond, monthly publication).
According to this article, the pulse energy density is 5 to 10 J / cm ² , and the melt area obtained by one shot is about 1 × 0.2 cm.

In this method, it is generally performed to irradiate the entire chip with the laser because it is necessary to perform positioning to irradiate only a region such as a via hole which needs to be irradiated with laser.

[Problems to be solved by the invention]

In the case of irradiation with a high energy density (5 to 10 J / cm ² ), the irradiation surface of the conventional pulsed laser has a metal melted on the irradiated surface at the center of one shot, but the energy density is low even in the one shot beam. Since there is a distribution, the energy density is inevitably reduced in the periphery, so that the surface morphology is deteriorated in the periphery. No.
Fig. 14 shows the area 1a that received the beam shot and its surrounding area 1b.When the shot is performed in the direction of the arrow, the wiring is flattened in 1a, but the surface morphology deteriorates in the hatched area 1b around it. Is shown. Also in the following figures, hatched portions indicate morphologically degraded regions, and white regions indicate flattened regions. Furthermore, when the beam size for concentrating energy in the via hole is reduced as in the case of embedding and flattening the via hole, it is difficult to position the beam in the via hole. Irradiation of an area becomes indispensable, and in order to eliminate a non-irradiation area, overlapping irradiation must be performed to increase the area. Therefore, when the superimposition is performed, the morphology of the previous shot located in the peripheral portion of the current shot in the preceding and subsequent shots is deteriorated, and the surface morphology deteriorated region is generated in a large spread.

As described above, even when the entire surface of the wafer is irradiated by superposition using a pulse laser, a region where the surface morphology is deteriorated has occurred. An object of the present invention is to improve surface morphology deterioration caused by a method of performing laser irradiation by superposition irradiation and to smooth the entire region irradiated with laser.

[Means for Solving the Problems] The present invention provides a process for temporarily melting and solidifying a conductive film by superposing and irradiating a pulsed laser a plurality of times, and a pulse which only melts the entire conductive film in the superposing irradiation. The present invention relates to a method for improving the surface morphology of a laser irradiation surface, which comprises irradiating with an energy density and, after the irradiation, irradiating with a pulse energy density at which substantially only the entire surface layer of the irradiation region is melted.

1 (a) and 1 (b) are diagrams for explaining the principle of the present invention. FIG. 1A is a schematic view of an SEM photograph of a cross section in a state where surface morphology is deteriorated by irradiating A1 on an oxide film with an excimer laser at an energy density of about 3 to 4 J / cm ² . SiO ₂
A1 (2) on the layer 3 is entirely melted by the heat of the laser, and solidified in a contracted state around the nucleus 4 instead of solidifying and solidifying over the entire surface, resulting in deterioration of morphology. It is considered that the recess 5 is formed. In addition, it is considered that minute irregularities and defects of the SiO ₂ layer 3 in the region where the laser energy density is low act as nuclei 4. Therefore, the surface morphology of A1 deteriorates after laser irradiation because coagulation is localized around nuclei 4 and nuclei 4
This is considered to be related to the fact that solidification proceeds radially from the surface and that uniform and uniform nucleation is difficult due to the existence of the laser energy density distribution. For it,
After completely melting A1 (2), the surface was further irradiated with a very weak energy density (1-2 J / cm ² ) such that the surface of A1 (2) slightly melted. It is the schematic of the cross-sectional SEM photograph of (b). From the figure, it can be seen that only A1 is melted, and A1 flows by being pulled by the concave portion, so that a smooth surface can be obtained.

The reason why a smooth plane can be obtained despite the energy density distribution of the laser beam in this re-irradiation is considered as follows.

(A) Since the laser does not melt the interface A1 at the interface of the base SiO ₂ layer 3 (FIG. 1A), the nucleus 4 is not generated.
Solidification nuclei also occur in A1 melted by re-irradiation, but directional solidification progresses around these nuclei, and a large amount of molten A1 is formed in the recess 5 (FIG. 1 (a)) sooner than completion. Let it flow. (C) The phenomenon (b) hardly relates to the energy density distribution of the laser beam.

As shown in FIG. 1 (b), the already flat A1
(2) Even if a laser with a very weak energy density of about 1 to ² J / cm ² is irradiated on the surface, only the outermost surface is melted, and the surface is smooth because it does not melt enough to form a nucleus that is the center of shrinkage. It remains. The energy of the laser for the second or final irradiation needs to have a low energy density that does not deteriorate the surface morphology.

The present invention is established based on the above findings, and includes the following steps.

(1) A step of melting the entire wiring layer by overlapping irradiation.

(2) A step of melting only the surface layer after the step (1). In this case, the wiring layer after the step (1) includes a flat portion and a morphologically degraded portion, but the laser beam cannot be aligned with any portion, so that it is necessary to melt substantially the entire surface of the surface. . The energy density of the pulse laser in this surface melting is not high enough to flatten via holes, steps, etc., and not high enough to cause directional solidification due to nucleation, and it is mainly used to eliminate morphology deterioration due to A1 flow on the surface. Works. The pulse laser in the step (2) may be irradiated by superposition irradiation. However, since the periphery of the laser beam trace is considerably close to the melting point, when the fusion between the traces is narrow, the laser beam may be irradiated in a spot form.
Observation of the wiring layer after the step (2) shows that the surface
It can be seen that μm is molten. With a normal thickness of the wiring layer, the concave portion is sufficiently filled and flattened with this amount of melting.

In the present invention, the above (1) and (2) are the basic steps. The number of times of irradiation in each step is completely arbitrary, (1),
Additional irradiation may be performed before and after (2) if the effects of the present invention are not impaired. In addition, although pulse laser irradiation for improving flatness is mainly described, the present invention can be applied to a case where the film quality of a wiring layer such as defects, crystal grain size, and grain boundaries is improved by laser melting.

Even when the surface morphology of the conductive film is deteriorated and the smooth region are mixed on the wafer, or when the entire surface is deteriorated, weak laser energy is applied to the entire region. By doing so, it is possible to improve the surface morphology of the entire laser irradiation area while maintaining a flat surface shape in the area having good morphology.

Also, for semiconductor devices having via holes or steps in multilayer wiring, irradiation is performed at an energy density that melts the entire conductive film, and a certain amount of flattening is performed in the via holes and steps, and then only the surface layer of the conductive film is melted. By irradiating at the same energy density, the surface morphology can be improved by implementing the present invention so that the concave portions caused by the previous irradiation, the via holes that have not yet been completely planarized, and the steps are also planarized by the inflow of the molten A1. Can be improved.

If when the conductive film of the material is A1 or Si is the energy density of the pulsed laser irradiated at the beginning is less than 3J / cm ^2, it is difficult to melt the entire conductive film, whereas when it exceeds 10J / cm ² 3-10 J / cm due to severe morphology deterioration
² needs to be set in the energy density range. On the other hand, if the energy density of the second and subsequent pulse lasers is less than 1 J / cm ^2, it is difficult to melt the conductive film surface, and if it exceeds ² J / cm ² , the tendency to solidify around the nucleus appears. It is necessary to set an energy density range of ² J / cm ² . The above energy density range may be adopted as long as the thickness of the conductive film is within the normal range.

[Action]

In the present invention, as shown in FIG. 1 (e), by irradiating a laser having a very low energy density to an irradiation area of the pulse laser having a concave portion on the surface, as shown in FIG. 1 (b). It is possible to obtain a smooth laser irradiation surface without any.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples.

〔Example〕

Comparative Example 1 Irradiation was performed at a high energy density of 5 to 10 J / cm ² , and then laser irradiation was performed in such a manner that irradiation at a low energy density was not performed.

The beam size is 2 × 2mm on the surface of A1 layer with thickness of 1.0μm
FIG. 2 shows traces of one shot when excimer laser irradiation is performed at an energy density of 5 to 10 J / cm ² in FIG. 2 and traces 9 when superimposed and irradiated continuous shots at 1 mm are shown in FIG. Shown in In the figure, reference numeral 10 denotes a region having good morphology. In the central part (10) of one shot, A1 is sufficiently melted to form a smooth surface, but as the energy density decreases toward the periphery, a concave portion 5 is generated in the periphery and the surface morphology deteriorates. (See FIG. 3). When such shots are superimposed at a pitch of 1.0 mm in the X direction, as shown in FIG. 4, a region having a deteriorated surface morphology (a depth of the concave portion of 1.0 μm) and a smooth region 1 are obtained.
0 and are alternately displayed.

Example 1 The beam size 2 of the A1 layer in the state shown in FIG.
When the laser is irradiated again at the energy density of 1 to ² J / cm2 at the energy density of 1 × 2 mm, the surrounding A1 remelts and flows into the recessed part in the area where the morphology deteriorated in the superimposed part and the surface is smooth. In FIG. 5, in order to maintain the smooth state as it is,
As shown in FIG. 6, the whole becomes smooth.

FIG. 6 is a schematic view of an SEM image of a cross section taken along the line bb of FIG. 5, and shows that a flat surface 10 having an accuracy of 0.2 μm was obtained.

Comparative Example 2 Irradiation was performed at a laser energy density of 3 to 4 J / cm ² , and then laser irradiation was performed at a low energy density in such a manner that irradiation was not performed.

When the surface of A1-Si (1.0 μm) is irradiated at an energy density of ³ to 4 J / cm 2 at a beam size of 2 × 2 mm, the trace of one shot is superimposed and the continuous shot is superimposed at 1 mm in FIG. Figure 9 shows the trace of the above operation in a simplified manner. 1
In the shot, melting occurs due to low energy density, but the surface morphology deteriorates as a whole due to insufficient flattening action by fluidization of A1, as shown in the cross section of FIG. The recess 5 is formed with a depth of about 1.0 μm. When such shots are superimposed at a pitch of 1.0 mm in the X direction, a region 10 with slightly improved surface morphology is formed at the beam edge in a region 11 with poor surface morphology as shown in FIG. ing. this is,
This is because the energy density decreases by 1 to ² J / cm ² at the beam edge, so that a portion having an appropriate energy density is formed just to improve the surface morphology.

The A1 wiring in the state shown in FIG. 9 has many regions where the flatness is insufficient, and the morphology improvement effect is insufficient.

Example 2 In the state shown in FIG. 9, the beam size was 2 × 2 mm, and 1 to 2 J /
When laser irradiation is performed again with an energy density of cm ² , the surface morphology of the entire surface is improved except for the region corresponding to the second irradiation beam edge as shown in FIG. At the edge of the second beam, the energy density was too low, and the surface of A1-Si could not be melted, leaving the x-direction recess as it was. In this case, the third irradiation was necessary become. When the position is set so that the center of the beam hits the remaining concave portion and irradiation is performed again under the same conditions as the second time, the entire A1-Si surface can be smoothed as shown in FIG.

Example 3 (continuous irradiation of the same area) The beam shown in FIG. 2 (5 to 10 J / cm) in which the irradiation surface is melted at the center of the beam and the surface morphology is deteriorated at the periphery of the beam
² ) After irradiating one shot of a fixed area (2 × 2 mm) in a certain area (2 × 2 mm), the beam setting is changed to set the beam size to 3 × 3 mm, the energy density to 1 J / cm ² , and the center to coincide with the 2 × 2 mm area. Irradiation. The region where the morphology of the beam edge is deteriorated at the beginning formed by this irradiation is improved and becomes smooth as a whole as shown in FIG. In the figure, 12 is a region smoothed by the first beam, 13 is a trace of the first beam,
14 shows the trace of the second beam.

In this way, by repeating the irradiation of the high pulse energy density (12) and the irradiation of the low pulse energy density (13) alternately and overlapping the irradiation areas, a smooth laser irradiation as shown in FIG. You can get a surface.

〔The invention's effect〕

As described above, according to the present invention, deterioration of surface morphology generated in a semiconductor material by pulsed laser irradiation can be improved, and this significantly contributes to improvement in reliability of the semiconductor material after pulsed laser irradiation. .

[Brief description of the drawings]

1 (a) and 1 (b) are diagrams for explaining the principle of the present invention,
2 shows the surface morphology after irradiation at a high energy density and a low energy density, respectively. FIG. 2 is a view showing a trace of a one-shot laser in Comparative Example 1, and FIG. 3 is a sectional view taken along aa of FIG. FIG. 4 is a diagram showing the state of the surface after superposition irradiation in Comparative Example 1, FIG. 5 is a diagram showing the state of the surface after irradiation in Example 1, and FIG. 6 is bb in FIG. 7 is a view showing traces of a one-shot laser in Comparative Example 2, FIG. 8 is a sectional view taken along the line cc of FIG. 7, and FIG. 9 is a surface state after superposition irradiation in Comparative Example 2. FIGS. 10 and 11 are diagrams showing the surface condition after irradiation in Example 2, FIGS. 12 and 13 are diagrams showing the surface condition after irradiation in Example 3, and FIG. FIG. 4 is a diagram showing deteriorated surface morphology. 2 ... A1 ₁ 4 ... core, 5 ... recess, 10 ... morphology
Good area, 11: Morphology-worse area

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/3205 H01L 21/3213 H01L 21/768

Claims (1)

(57) [Claims] In a process for temporarily melting and solidifying a conductive film by overlappingly irradiating a pulse laser a plurality of times, irradiation with a pulse energy density sufficient to melt the entire conductive film in the overlap irradiation is performed. A method for improving the surface morphology of a laser irradiation surface, comprising, after irradiation, performing irradiation with a pulse energy density at which substantially only the entire surface layer of the irradiation region is melted.