DE10122283A1 - Chemical-mechanical polishing (CMP) process for semiconductor wafer includes polishing under pressure with basic agent and post-polishing using basic solution to remove residues - Google Patents

Abstract

The surface is polished under pressure using a basic polishing agent, to cut material from the surface. The surface is after-polished under pressure using a basic solution, to remove polishing residues.

Description

The invention relates to a chemical-mechanical polishing ver drive (CMP process). Such CMP processes are becoming increasingly common in the context of the production of semiconductor components, esp special of the sub-0.5 µm technology for the planarization of the the manufacturing processes occurring topography on the Semiconductor wafer used. The chemical-mechanical Polishing is mainly used to level trenches fillings, metal plugs, intermediate oxides and intermetallic dielectrics.

For chemical-mechanical polishing, the one to be processed Semiconductor wafer from a wafer carrier against a turn bar arranged polishing table on which a elastic perforated pad, a so-called pad, which contains a polishing agent, a so-called slurry. Rotate in the process the semiconductor wafer and the polishing table in opposite Directions, causing the surface of the wafer to rise the outstanding spots are polished off until a completely flat disc surface is reached. One differentiates there in between a so-called blind polishing process, d. H. one Polishing process that takes place within the layer to be polished is held, and a so-called stop-layer polishing process, in which the polishing process is selective to one below the polishing layer is another layer.

The slurries used contain in addition to polishing grains in space mean other active chemical additives that are selective Allow removal of the layers on the semiconductor wafer and are usually very basic.

However, after the chemical mechanical polishing process generally on the surface of the semiconductor wafer Slurry contaminants return before further processing  the semiconductor wafer completely removed have to. This is usually done at the end of the chemical mechanical polishing step of the slurry inflow to the pad switches and the semiconductor surface in a so-called rinse Then white for a short time with deionized water terpoliert. This rinse step is intended to remove slurry residues from the semiconductor surface are removed.

The half is then in a cleaning process conductor disc still with a brush apparatus, a so-called Brush-Cleaner works on the semiconductor surface from the After the rinse step, surface debris remaining exemptions. During the bust cleaning the Semiconductor wafer continuously with distilled water or flushed with ammonia.

Despite the rinse step and the brush cleaning remain but often slurry residues on the semiconductor surface that too Loss of yield in chip production can lead. The reason for this is according to an investigation by James J. Shen et. al. J. Electrochem. Soc., Vol. 145, No. 12, Dec. 1998, p. 4240-4243 that slurry particle agglomerates on the half conductor surface during the rinse step with deionized water can arise. The deionized water in the rinse step namely leads to a sudden decrease in pH and Reduction of the zeta potential on the semiconductor surface surface, which has the consequence that the slurry residues against each other tighten each other or the slurry particles from the half conductor surface are tightened. To such slurry particles Removing agglomerates is known in the known CMP-Ver therefore often drive a second polishing step on one second polishing table with a soft pad using deionized water or ammonia to the Slurry particle agglomerates on the semiconductor surface are liable to be removed by polishing. This procedure has however, the disadvantage that the additional polishing step too a drastic increase in the total process time and the equipment  Leads to effort and thus high process costs gently.

The object of the invention is therefore a chemical mecha African polishing process in which the on a semiconductor wafer remaining during the polishing process Slurry impurities quickly and effectively with little equipment effort can be removed.

This object is achieved by a method according to claim 1 solves. Preferred embodiments are in the dependent An sayings.

According to the invention, when in the polishing step basic slurry used for the rinse step before preferably on the same polishing table as the polishing step instead of deionized water a basic one Solution, preferably ammonia or KOH solution used. By using a basic solution the pH value, which is created by the basic slurry during the polishing process will call, and thus the strong negative zeta potential of the Maintain semiconductor surface in the rinse step so that the slurry particles mutually and also from the Repel semiconductor surface. This makes it reliable without additional equipment, prevents Slurry leftovers, especially large slurry agglomerates on the Semiconductor surface remain.

By the rinse step with a basic preferably An ammonia solution or KOH solution can reduce the defect density clearly on the semiconductor surface after CMP process lowers and thus increases the yield in chip production become. This is particularly with regard to the further Reduction of the structural dimension in semiconductor components and the associated loss of yield through always small other defects of great economic importance.  

You can also by using a basic solution a high cleaning effect can be achieved in the rinse step, because the chemical attack on the semiconductor surface in the is stronger than with deionized water.

It is advantageous at the rinse step with a basic solution also that no additional process time is required, so the process cost over the standard process stay the same or can even be reduced because for the subsequent brush cleaning step no chemicals lien, especially no ammonia solution to improve the Cleaning efficiency is needed.

The invention will become more apparent from the accompanying drawings explained. Show it:

Fig. 1 shows schematically a chemical mechanical polishing system, can be carried out with an inventive CMP process;

Fig. 2 shows schematically a polisher in cross section;

FIG. 3A is a blind-polishing process;

Fig. 3B is a stop-layer polishing process; and

Fig. 4 results of a comparative measurement of the defect density on an SiO ₂ layer, in which an inventive CMP method with NH ₄ rinse step and a conventional CMP method with a rinse step in which deionized water is used are posed.

The chemical-mechanical polishing system shown in FIG. 1 is composed of a polisher 1 , a wet handler 2 and a cleaning station 3 . The polisher 1 , which is shown schematically in cross section in FIG. 2, has a rotatably arranged polishing table 11 with an elastic perforated support 12 , a so-called pad, which is supplied via a feed 13 with a polishing agent, the so-called slurry is soaked. The semiconductor wafer 4 to be machined is pressed onto the pad 12 by a rotatable wafer carrier 14 , the wafer carrier 14 with the semiconductor wafer 4 fastened thereon and the polishing table 11 rotating in the opposite direction.

The slurry contains polishing grains, so-called abrasive particles, as well as active chemical additives that enable selective removal of layers on the semiconductor wafer 4 . The polishing grains generally have an average of 20 to 500 nm and mostly consist of SiO ₂ , Al ₂ O ₃ or CeO ₂ . The chemical additives are matched to the layer material to be removed. So is a metal layer z. B. to planarize tungsten, a mixture of Al ₂ O ₃ and Fe (NO ₃ ) _{2 used} as a slurry. To planarize an oxide layer, on the other hand, a slurry based on SiO ₂ or CeO _{2 is} used, which is stabilized with KOH or NH ₄ OH. The slurries are all strongly basic, with the pH usually in the range of 9 to 13.

Chemical-mechanical polishing is primarily used to planarize trench fillings, metal plugs in contact holes and vias, and intermediate oxides and intermetallic dielectrics. A distinction is made between two polishing processes, which are shown in FIGS. 3A and 3B. In the so-called blind polishing process, as shown in FIG. 3A using a layer structure consisting of an Si substrate 41 , a thin Si ₃ N ₄ layer 42 and metal conductor tracks 43 arranged thereon, which have a thick SiO ₂ layer 44 are filled, is shown, the planarization of the SiO ₂ layer 44 is controlled such that the polishing process is still stopped within the SiO ₂ layer to be polished. For endpoint detection, z. B. the detection of the thickness of the insulating SiO ₂ layer with the aid of a capacitance measurement.

In the stop-layer polishing process shown in FIG. 3B, which is shown on the basis of a layer structure consisting of a silicon layer 51 with trenches, a thin Si ₃ N ₄ layer 53 arranged thereon and a thick SiO ₂ layer 54 , the polishing process is stopped when the Si ₃ N ₄ layer 52 lying under the SiO ₂ layer 54 is exposed. The endpoint detection can z. B. done by measuring the current consumption of the rotating disc carrier, since the current changes during the transition of the layer materials.

This is basically the case with chemical mechanical polishing Problem that the slurry leftovers after the pressurized guided polishing process with the basic slurry on the Adhere semiconductor surface, must be removed in order Loss of yield in the manufacture of components on the Prevent semiconductor wafer.

According to the invention, this is solved in that an after polishing the semiconductor wafer under pressure with a basic solution is executed, the pH of which is in the essentially with the pH of the basic slurry. There the pH of the basic slurry in the range from 9 to 13 is the pH of the basic solution for polishing set in the same range of values. The polishing the process is preferably carried out with the same polisher as the chemical mechanical polishing process is carried out so that no additional expenditure on equipment by this after polishing process is necessary.

By using a basic solution when polishing to remove the slurry residues from the semiconductor surface prevents a sudden pH-Er low and a decrease in the zeta potential on the Semiconductor surface comes, so it remains guaranteed that the slurry particles counteract each other during the polishing process repel each other from the semiconductor surface. The polishing process with the basic solution ensures a reliable casual removal of the slurry residues from the semiconductor surface surface and also enables that when connecting Brush cleaning process carried out no further chemical  Detergent must be used. The basic solution then ensures already during polishing for additional surface cleaning of other ver impurities, so the brush cleaning step is shortened or can be driven without additional chemicals.

When planarizing an oxide layer on a semiconductor surface in the context of a CMP method according to the invention, the following process sequence is preferably carried out: As a first step, a chemical-mechanical polishing step for planarizing the SiO ₂ layer on the semiconductor surface is carried out using a basic slurry, which is based on SiO ₂ and is stabilized with KOH or NH ₄ OH. After the desired material has been removed, an ammonia solution or KOH solution, the pH of which is preferably in the range from 9 to 13, is fed to the pad instead of slurry. The semiconductor wafer is then polished with this basic solution preferably up to 50 seconds in order to remove the slurry residues from the semiconductor surface. When polishing can be carried out with the same pressure of the semiconductor wafer on the pad as it was in the chemical mechanical polishing process. However, it is also possible to carry out the post-polishing process with a reduced pressure on the semiconductor surface against the pad compared to the chemical-mechanical polishing process. The post-polishing process is then followed by a brush cleaning step with de-ionized water in order to clean the semiconductor surface of the other contaminants.

In order to planarize a metal layer, preferably a tungsten plug, with the aid of the CMP method according to the invention, the procedure is as follows:
The chemical mechanical polishing process is carried out on the polisher with an Al ₂ O ₃ based slurry until the desired material removal for tungsten has taken place. An oxide polishing step is then usually carried out with an SiO ₂ -based basic slurry in order to free the inter-metal dielectric (SiO ₂ ) from tungsten slurry impurities. Then this basic slurry is again switched to a dilute ammonia solution, the pH value of which is preferably in the range from 9 to 13, and the rinse step, in which the semiconductor surface is subsequently polished under pressure, is carried out. Post-polishing times of up to 50 seconds have also proven to be advantageous here. The post-polishing process is then followed by a brush cleaning process with deionized water to remove the remaining surface contaminants.

Through the two process sequences presented with diluted Ammonia solution or KOH solution in the rinse step, can Defect density on the semiconductor surface with the Invention according to the CMP process and thus the yield can be significantly increased in chip production. This is especially with regard to the constantly downsized construction partial dimensions and the associated losses in yield due to smaller and smaller defects of large economic loading interpretation. It is particularly important that the Rinse step with the basic solution no additional pro time compared to conventional CMP processes process costs will not increase. In Ge Quite the opposite, it can be compared to the standard CMP process Cost reduction can be achieved because it is more conventional here use ammonia solution for verbs when cleaning brushes cleaning efficiency is needed. According to the Er it is sufficient to clean the brush with ent perform ionized water so that in the brushes cleaning equipment no chemicals need to be used leads to increased process costs.

Fig. 4 shows results of a comparative measurement of the defect density on a part of a CMP planarising th SiO ₂ surface, in which an inventive CMP process with an ammonia-rinse step of a conventional CMP process with a rinse step, where deionized water is used, is compared. The comparative investigation was carried out using a silicon semiconductor wafer on which a 750 nm thick SiO ₂ layer had been applied. The CMP process was carried out using a standard polisher, as shown in FIG. 2, using a slurry based on SiO ₂ . After the chemical-mechanical polishing process, a rinse step was carried out, using deionized water for a first test series and dilute ammonia solution with a pH of 11 for a second test series. Then a brush cleaning was carried out, with the standard CMP method, in which the rinse step was carried out with deionized water, a brush cleaning with ammonia was carried out. In contrast, deionized water was used in the CMP process according to the invention with an ammonia rinse step for brush cleaning. Fig. 4 shows the total defect density, which was measured on six different areas of the semiconductor surface where polishing times of 10, 20 and 30 seconds were carried out within each test series. The comparison results in FIG. 4 clearly show that the number of surface defects in the CMP process according to the invention with an ammonia rinse process is significantly reduced compared to the conventional CMP process with a water rinse step.

Claims (8)

1. Method for chemical-mechanical polishing of a surface of a semiconductor wafer with the method steps:
Polish the surface of the disc under pressure with a basic polishing agent to remove material from the surface of the disc; and
Polishing the surface of the wheel under pressure with a basic solution to remove polishing agent residues. 2. The method of claim 1, wherein the basic polishing medium and the basic solution essentially the same pH Have value. 3. The method of claim 2, wherein the basic polishing medium and the basic solution has a pH in the range of 9 up to 13. 4. The method according to any one of claims 1 to 3, wherein the Polishing step and the post-polishing step with the same Buffers are run. 5. The method according to any one of claims 1 to 4, wherein the basic solution for the post-polishing step an ammonia solution is. 6. The method according to claim 5, wherein with the chemical-mechanical polishing step an oxide is planarized and carried out according to the following process steps:
Polishing the wafer surface under pressure with a SiO _2- based polishing agent to remove oxide from the wafer surface; and
Repolish the slide surface with a dilute ammonia solution that has a pH of approximately 11. 7. The method according to claim 5, wherein the chemical-mechanical polishing step is used to planarize a metal layer on the semiconductor wafer and the following method steps are carried out:
Polishing the wafer surface under pressure with a polish based on a mixture of Al ₂ O ₃ and Fe (NO ₃ ) _{2 in} order to remove oxide from the wafer surface; and
Repolish the slide surface with a dilute ammonia solution that has a pH of approximately 11. 8. The method according to any one of claims 5 to 7, wherein including brush cleaning of the semiconductor surface deionized water is carried out.