TWI766599B - Wafer Regeneration Process - Google Patents

Abstract

The invention provides a wafer regeneration process, which includes: preparation step, film removal step, annealing step, polishing step and cleaning step; the invention reduces the copper atom concentration on the surface of the regeneration wafer by regulating the temperature of the annealing step. In addition to reducing the risk of copper pollution, the present invention has the advantages of good cost-effectiveness.

Description

Wafer Regeneration Process

The present invention relates to a wafer regeneration process, especially a wafer regeneration process for reducing copper pollution.

Since wafers have extremely high requirements on process stability and dust particle count, in the manufacturing process of semiconductor integrated circuits, fabs need to monitor the process performance and dust-free environment by using monitor wafers. Before the machine is re-launched, it is also necessary to use the dummy wafer to adjust the thermal engine and machine parameters. Based on cost considerations, the dummy wafer will undergo the wafer regeneration process. The more the number of recycling tests, the more helpful In order to reduce the manufacturing cost, more and more attention has been paid to the technology of wafer regeneration.

In addition, in order to meet the demand for miniaturization of electronic products, the process technology of semiconductor chips must also be continuously improved to ensure that the reliability of the circuit can be maintained after the circuit is miniaturized. The replacement of aluminum with copper is a classic example of process technology upgrade. However, even though copper has better electrical conductivity and anti-electromigration (electromigration) ability than aluminum, it can improve the leakage current and circuit heating problems caused by circuit scaling, but at the same time, due to the high activity of copper itself, it can prevent copper from contaminating the semiconductor process. The machine is an important technical threshold. Furthermore, if the wafers are to be recycled and reused, the issue of how to reduce the risk of copper contamination of the wafers becomes more and more important. Therefore, it is necessary to develop a wafer regeneration process that effectively reduces the level of copper contamination.

In view of the above-mentioned technical defects in the prior art, the present invention aims to provide a wafer regeneration process, which can reduce the content of copper atoms on the surface of the regenerated wafer obtained in a simple and effective manner.

In order to achieve the above object, the present invention provides a wafer regeneration process, comprising: a preparation step: preparing a wafer with at least one film layer on the surface, and the wafer contains copper atoms; a film removal step: removing the film layer from The surface of the wafer is peeled off to obtain a de-filmed wafer; annealing step: the de-filmed wafer is placed in a heating environment for annealing treatment to obtain an annealed wafer, and the annealing temperature is greater than or equal to 150 ° C and less than or equal to 500 ° C; polishing step: polishing the annealed wafer to obtain a polished wafer; and cleaning step: cleaning the polished wafer to obtain a regenerated wafer.

According to the present invention, the above-mentioned "wafers" are used wafers, which are converted into reconstituted wafers after the wafer regeneration process of the present invention.

In some embodiments, the regenerated wafer may be a control wafer or a stop wafer.

In the present invention, by performing an annealing step under a specific annealing temperature range to process the stripped wafer, the rate of diffusion of copper atoms contained in the stripped wafer from a high unit content area to a low unit content area can be accelerated , so that the distribution of copper atoms contained in each plane area of the de-filmed wafer is relatively uniform, and can be quickly precipitated on the surface of the de-filmed wafer, and the subsequent polishing step is used to remove the copper. atoms, thereby reducing the concentration of copper atoms in the used wafer.

In one embodiment, the annealing step is furnace heating or oven heating.

Preferably, the annealing step includes heating in a protective atmosphere to avoid oxidation of the wafer caused by oxygen in the air. In one embodiment, the protective atmosphere is nitrogen, but not limited thereto.

Preferably, after the annealing step is completed, the annealed wafer is removed from the heating equipment (such as a furnace tube or an oven), and the annealed wafer is cooled to room temperature in a static manner to Avoid excessive temperature changes affecting the quality of the annealed wafer.

In one embodiment, the duration of the annealing step is at least 1 hour; preferably, the duration of the annealing treatment is at least 2 hours. In addition, the duration of the annealing step of the present invention does not include heating and cooling time.

In one embodiment, the duration of the annealing step is 1 hour to 9 hours; preferably, the duration of the annealing step is 2 hours to 6 hours; more preferably, the duration of the annealing treatment is 3 hours . The duration of the above-mentioned annealing step helps the copper atoms in the regenerated wafer to be uniformly dispersed and moved to the surface of the wafer. After the polishing step and the cleaning step, the concentration of copper atoms on the surface of the regenerated wafer and the precipitation rate can be reduced.

In one embodiment, the annealing temperature is any temperature from 150°C to 500°C, for example: 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 350°C, 400°C, 450° C or 500°C; preferably, the annealing temperature is 250°C.

The present invention controls the range of the annealing temperature, and has the following advantages: (1) accelerating the migration of copper atoms inside the de-filmed wafer and precipitation on the surface of the annealed wafer; (2) avoiding excessive annealing temperature low, the copper atoms cannot be effectively deposited from the surface of the annealed wafer, or the duration of the annealing step must therefore be extended without commensurate with the time cost.

According to the present invention, the methods used in the film removal step include chemical removal methods such as wet etching or physical bombardment methods such as plasma treatment, but are not limited thereto. The stripped wafer obtained after this step may have a rougher surface.

In one embodiment, the wafer regeneration process further includes a cleaning step after the film removal step: cleaning the removed film to obtain a cleaned and removed wafer. In this embodiment, the annealing step involves placing the cleaned, stripped wafer in a heated environment for annealing. The present invention can remove the metals still remaining on the wafer surface after removing the film, such as copper and aluminum, through the cleaning step.

Preferably, between the annealing step and the polishing step, a resting step is additionally performed to wait for the copper atoms inside the wafer to be precipitated onto the surface of the wafer.

Preferably, the standing time of the standing step is 0.5 days to 9 days; more preferably, the standing time of the standing step is 3 days to 7 days.

Preferably, the environment of the standing step is a clean room.

In one embodiment, the clean room complies with Class 1000 of Federal Standard 209 (FED 209), that is, the number of air particles with a particle size greater than or equal to 0.5 microns per cubic foot of air is less than or equal to Equal to 1000 particles; or the clean room complies with ISO 6 of ISO 14644, that is, the number of air particles with a particle size greater than or equal to 0.5 microns per cubic meter of air is less than or equal to 35,200.

Preferably, the methods used in the polishing step include rough polishing and/or fine polishing, but are not limited thereto. In the present invention, the copper atoms precipitated on the surface of the annealed wafer are removed by the polishing step, and since the surface of the polished wafer can have lower surface roughness and higher surface free energy, it can Further slow down the precipitation rate of subsequent copper atoms.

In one embodiment, the polishing step performs rough polishing and fine polishing on both the front and back sides of the annealed wafer, respectively.

In one embodiment, the cleaning step includes: RCA silicon wafer cleaning. The RCA silicon wafer cleaning method uses chemical solutions, which include a mixture of ammonium hydroxide (NH ₄ OH) and hydrogen peroxide (H ₂ O ₂ ), a mixture of hydrochloric acid (HCl) and hydrogen peroxide, hydrofluoric acid (HF) and A mixture of hydrogen peroxide, or a mixture of ozone water (Ozonated DI Water) and hydrogen peroxide, but not limited to this. This cleaning step removes metal impurities as well as particulates.

In one embodiment, the regenerated wafer is finally obtained after the above-mentioned preparation step, the above-mentioned film removal step, the above-mentioned annealing step, the above-mentioned polishing step, and the above-mentioned cleaning step are sequentially performed in the wafer regeneration process.

In one embodiment, the wafer regeneration process sequentially performs the above-mentioned preparation step, the above-mentioned film removal step, the above-mentioned cleaning step, the above-mentioned annealing step, the above-mentioned resting step, the above-mentioned polishing step and the above-mentioned cleaning step, and finally the above-mentioned step is obtained. Recycled wafers.

In one embodiment, the copper atomic concentration on the surface of the de-filmed wafer is at least 10 ¹² /cm ² , and the copper atom concentration on the surface of the regenerated wafer obtained by the wafer regeneration process of the present invention is 1×10 ⁸ pcs/cm ² to 5× ^{10 9} pcs/cm ² . It can be seen that the atomic concentration of copper contained in the stripped wafer is at least 200 times higher than that of the regenerated wafer of the present invention, so the regenerated wafer of the present invention can indeed avoid serious copper pollution.

In one embodiment, the copper atom concentration on the surface of the regenerated wafer obtained by the wafer regeneration process of the present invention is 1×10 ⁹ atoms/cm ² to 5×10 ⁹ atoms/cm ² .

In this specification, the copper atomic concentration refers to the number of copper atoms contained per unit area of the surface of the regenerated wafer. The copper atom concentration on the surface of the regenerated wafer is the result obtained by detecting the solution obtained after acid etching the surface of the regenerated wafer. Preferably, the sampling target is a 12-inch regenerated wafer.

In one embodiment, the copper atomic concentration of the present invention is obtained by detecting the acid-etched solution of the sample by inductively coupled plasma mass spectrometry (ICP-MS), and the acid-etching thickness is 5 nm below the surface of the regenerated wafer.

In the present invention, the concentration of copper atoms on the surface of the regenerated wafer can be reduced to less than or equal to 5× ^{10 9} /cm ² by controlling the annealing temperature, the duration of the annealing treatment and the standing time; preferably, the regenerated wafer can be reduced The concentration of copper atoms on the surface is reduced to 1x10 ⁸ /cm ² to avoid the continuous precipitation of a large number of copper atoms during the subsequent standby storage process of the regenerated wafer, resulting in the pollution of high-precision semiconductor processing machines by copper atoms.

In conclusion, the wafer regeneration process of the present invention can not only reduce the precipitation amount of copper atoms on the surface of the recycled wafer and reduce the risk of copper contamination in the subsequent process, but also improve the quality of the recycled wafer; and greatly reduce the process energy consumption, Has better cost-effectiveness.

Hereinafter, those skilled in the art can easily understand the advantages and effects achieved by the present invention from the following examples. Therefore, it should be understood that the description set forth herein is for illustrating preferred embodiments only and not for limiting the scope of the invention, and that various modifications and changes may be made in its implementation or application without departing from the spirit and scope of the invention. content of the present invention.

As shown in FIG. 1 , the wafer regeneration process of the present invention includes step S1: preparation step: preparing a wafer with at least one film layer on the surface, and the wafer contains copper atoms; step S2: removing film step: removing the film The film layer is peeled off from the surface of the wafer to obtain a de-filmed wafer; step S3: annealing step: the de-filmed wafer is placed in a heating environment for annealing treatment to obtain an annealed wafer , and the annealing temperature is greater than or equal to 150 ° C and less than or equal to 500 ° C; Step S4: polishing step: polishing the annealed wafer to obtain a polished wafer; and step S5: cleaning step: cleaning the After polishing the wafer, a regenerated wafer is obtained. Hereinafter, Examples 1 to 5 use the process steps shown in FIG. 1 to perform the wafer regeneration process.

As shown in FIG. 2 , the wafer regeneration process of the present invention includes step S1 : a complete step. Step S2: the step of removing the film. Specifically, the step S2 may adopt wet etching or plasma treatment. Step S3: an annealing step, specifically, step S3 can be heated by a furnace tube or an oven. Step S3-1: a resting step. Specifically, in Step S3-1, the annealed wafer may be placed in a clean room of Class 1000 of Federal Standard 209 for 3 to 7 days. Step S4 : a polishing step. Specifically, in Step S4 , the front and back surfaces of the annealed wafer can be polished with silicon dioxide abrasives, respectively. Step S5: a cleaning step, specifically, step S5 can use a standard RCA silicon wafer cleaning method. Hereinafter, Examples 6 and 7 use the flow steps shown in FIG. 2 to perform the wafer regeneration process.

Reference example 1 : Recycled wafer

Prepare a 12-inch wafer with an oxide film layer on the surface, and the wafer contains copper atoms. Next, the film removal step is performed by chemical removal method, and the oxide film layer is peeled off from the surface of the wafer to obtain a film-removed wafer, which is the regenerated wafer of Reference Example 1.

Example 1 : Recycled wafer

Prepare a 12-inch wafer with an oxide film layer on the surface, and the wafer contains copper atoms. Next, the film removal step is performed by chemical removal method, and the oxide film layer is peeled off from the surface of the wafer to obtain a film-removed wafer. After that, the stripped wafer was placed in a nitrogen-filled atmosphere at 150° C. for continuous 3-hour annealing. After the annealing step is completed, the annealed wafer is subjected to a rough polishing step with silicon dioxide abrasive to obtain a polished wafer; then, the polished wafer is mixed with hydrofluoric acid and hydrogen peroxide The liquid is cleaned, and finally a regenerated wafer is obtained.

Example 2 to example 5 : Recycled wafer

Except that the annealing temperature of embodiment 2 is 200 DEG C, all other steps are the same as those of embodiment 1.

Except that the annealing temperature of embodiment 3 is 250 ℃, all other steps are the same as embodiment 1.

Except that the annealing temperature of embodiment 4 is 250 DEG C, and the duration of annealing treatment is 1 hour, all other steps are the same as those of embodiment 1.

Except that the annealing temperature of embodiment 5 is 250 DEG C, and the duration of annealing treatment is 9 hours, all other steps are the same as those of embodiment 1.

Example 6 is the same as Example 3 except that a resting step is added between the annealing step and the polishing step; wherein, the environment of the resting step is a clean room that meets the Class 1000 of the US Federal Standard 209, and the resting time is 3 days.

In Example 7, all other steps are the same as in Example 6 except that the standing time reaches 7 days.

Comparative example 1 to the comparative example 3 : Recycled wafer

The remaining steps of Comparative Example 1 are the same as those of Example 1, except that the annealing step is not performed.

The remaining steps of Comparative Example 2 are the same as those of Example 6, except that the annealing step is not performed.

The steps of Comparative Example 3 are the same as those of Example 7 except that the annealing step is not performed.

analyze 1 : Process Variation and Copper Atomic Concentration

Whether the 12-inch reconstituted wafers of Reference Example 1, Examples 1 to 5, and Comparative Example 1 used in this analysis have undergone an annealing step, as well as the annealing temperature and duration of the annealing treatment set by each are shown in Table 1. The rolling machine uses hydrofluoric acid diluent to dissolve the oxide layer on the surface of each group of samples, and the sampling range is the interval from the surface to 5 nanometers below the surface of each group of samples to obtain the samples to be tested in each group; The samples to be tested in each group were analyzed for the concentration of copper atoms in the solution by a high-resolution inductively coupled plasma mass spectrometer, and the analysis results of each group are shown in Table 1.

Table 1: Whether the reconstituted wafers of Reference Example 1, Examples 1 to 5 and Comparative Example 1 have undergone the annealing step, the annealing temperature in the annealing step, the duration of the annealing treatment, and the copper atomic concentration group Annealing temperature Duration of annealing treatment Copper atomic concentration (pieces/cm ² ) Reference Example 1 Only stripped wafers, no annealing step. 1x10 ¹² Example 1 150°C 3 hours 5x10 ⁹ Example 2 200°C 3 hours 2.5x10 ⁹ Example 3 250°C 3 hours 1.5x10 ⁹ Example 4 250°C 1 hour 4x10 ⁹ Example 5 250°C 9 hours 1x10 ⁹ Comparative Example 1 Without the annealing step. 2x10 ¹¹

It can be seen from Table 1 that the concentration of copper atoms on the surface of Reference Example 1 before the annealing step is 1×10 ¹² /cm ² , and after the wafer regeneration process of the present invention in Examples 1 to 5, the surface copper atoms of the regenerated wafers obtained are The atomic concentrations are all greatly reduced, for example, Example 1 is reduced to 0.005 times compared to Reference Example 1, and even Example 5 can be reduced to 0.001 times compared to Reference Example 1.

Compared with Examples 1 to 5, the surface copper atomic concentration of the regenerated wafer of Comparative Example 1 is 2×10 ¹¹ /cm ² , which is also 40 to 200 times that of Examples 1 to 5. It can be proved that the annealing step in the wafer regeneration process of the present invention can indeed reduce the copper atomic concentration on the surface of the obtained regenerated wafer.

Furthermore, from the comparison results of the surface copper atomic concentration of the regenerated wafers of Example 1 to Example 3, it can be seen that increasing the annealing temperature helps to reduce the copper atomic concentration on the surface of the regenerated wafer.

In addition, from the comparison results of the surface copper atomic concentrations of the regenerated wafers in Example 3 to Example 5, it can be seen that increasing the duration of the annealing treatment helps to reduce the copper atomic concentration on the surface of the regenerated wafers.

Finally, although the copper atom concentration on the surface of Example 5 is lower than that of Example 3, the difference is not significant. Therefore, if the annealing step adopts the parameters that the annealing temperature is 250° C. and the duration of the annealing treatment is 3 hours, it can be It is more cost-effective to reduce the required energy.

analyze 2 : Difference in standing steps and copper atomic concentration

Table 2 shows the difference in standing time between Examples 3, 6, and 7 used in this analysis and Comparative Examples 1 to 3. The sampling and preparation methods of each group of samples to be tested are the same as the samples to be tested in Example 1 above; Each sample to be tested was analyzed for the concentration of copper atoms in the dissolved solution with a high-resolution inductively coupled plasma mass spectrometer. The results are shown in Table 2.

Table 2: Resting time and copper atomic concentration of Examples 3, 6, 7 and Comparative Examples 1 to 3 group Rest time Copper atomic concentration (pieces/cm ² ) Example 3 0 days 1.5x10 ⁹ Example 6 3 days 1.3x10 ⁹ Example 7 7 days 1x10 ⁹ Comparative Example 1 0 days 2x10 ¹¹ Comparative Example 2 3 days 3.2x10 ¹¹ Comparative Example 3 7 days 4x10 ¹¹

From the comparison results of the surface copper atomic concentrations of the regenerated wafers in Example 3, Example 6 and Example 7 in Table 2, it can be seen that adding a resting step between the annealing step and the polishing step can further reduce the surface concentration of the regenerated wafer. Copper atomic concentration; meanwhile, the longer the standing step lasts, the better the effect.

From the comparison of the surface copper atomic concentration of the regenerated wafers of Comparative Example 1 to Comparative Example 3 in Table 2, it can be seen that if the annealing step is not performed, the resting step not only does not help to reduce the copper atomic concentration on the surface of the regenerated wafer, but even on the contrary By increasing the concentration of copper atoms on the surface of the regenerated wafer, it can be seen that the annealing step of the present invention can indeed accelerate the precipitation of copper atoms inside the regenerated wafer.

From the comparison of the surface copper atomic concentration of the regenerated wafers of Example 6 and Comparative Example 2 in Table 2, it can be seen that after the wafer regeneration process of the present invention in Example 6 is carried out, that is, the annealing step is performed, and the surface copper atoms of the regenerated wafers are obtained. The concentration was greatly reduced and decreased by a factor of 0.004.

From the comparison of the surface copper atom concentration of the regenerated wafers of Example 7 and Comparative Example 3 in Table 2, it can be seen that in Example 6, after the wafer regeneration process of the present invention, the annealing step is performed, and the surface copper atoms of the regenerated wafer are obtained. The concentration is greatly reduced and reduced by a factor of 0.0025.

To sum up, the wafer regeneration process of the present invention can indeed effectively reduce the concentration of copper atoms on the surface of the regenerated wafer by the combination of the annealing step and the subsequent polishing step. In addition, when the wafer regeneration process of the present invention further includes a resting step, the concentration of copper atoms on the surface of the regenerated wafer can be further reduced, so as to avoid the precipitation of copper atoms on the surface of the regenerated wafer during the subsequent standby storage period of the regenerated wafer. Copper contamination occurs in subsequent processes.

S1: Step S2: Step S3: Step S3-1: Steps S4: Steps S5: Steps

FIG. 1 is a flow chart of the wafer regeneration process of Embodiments 1 to 5. As shown in FIG. FIG. 2 is a flow chart of the wafer regeneration process of Embodiments 6 and 7. FIG.

none

S1: Step

S2: Step

S3: Step

S4: Steps

S5: Steps

Claims (8)

A wafer regeneration process, comprising: a preparation step: preparing a wafer with at least one film layer on the surface, and the wafer contains copper atoms; a film removal step: peeling off the film layer from the surface of the wafer, Obtaining a de-filmed wafer; annealing step: placing the de-filmed wafer in a heating environment for annealing treatment to obtain an annealed wafer, and the annealing temperature is greater than or equal to 150° C. and less than or equal to 500° C. ℃; polishing step: polishing the annealed wafer to obtain a polished wafer; and cleaning step: cleaning the polished wafer to obtain a regenerated wafer; wherein, between the annealing step and the polishing step period, and also includes a resting step. The wafer regeneration process according to claim 1, wherein the duration of the annealing treatment in the annealing step is at least 1 hour. The wafer regeneration process according to claim 2, wherein the duration of the annealing treatment in the annealing step is 2 hours to 6 hours. The wafer regeneration process according to claim 1, wherein the annealing temperature is 250°C. The wafer regeneration process according to claim 1, wherein the resting time of the resting step is 3 days to 7 days. The wafer regeneration process according to claim 1, wherein the environment of the resting step is a clean room. The wafer regeneration process of claim 6, wherein the clean room complies with Class 1000 of Federal Standard 209 (FED 209) or ISO 6 of ISO 14644. The wafer regeneration process according to claim 1, wherein the copper atom concentration on the surface of the regenerated wafer is 1×10 ⁸ /cm ² to 5× ^{10 9} /cm ² .

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