JP2002158271A - Evaluation method of wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably, accurately, and sensitivity evaluating a wafer defect, especially polished damage (a machining-triggering defect), by SC1-RT. SOLUTION: In this evaluation method of a silicon wafer, a silicon surface is etched for a long time by treatment liquid containing ammonia, hydrogen peroxide, and water, and the number of LPDs formed on the surface of the silicon wafer is checked. In this case, a substance is added into the treatment liquid, where the substance sensitizes the wafer defect, especially, machined damage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a wafer, and more particularly to a method for evaluating a process-induced defect generated when processing a semiconductor wafer such as a silicon wafer (hereinafter sometimes simply referred to as a wafer).

[0002]

2. Related Art As the degree of integration of semiconductor devices increases, the quality of wafers has a great influence on the yield and reliability of semiconductor devices. The quality of a semiconductor wafer is determined throughout the crystal growth process, the wafer processing process, and the device manufacturing process. Defects (wafer defects) in a wafer are mainly caused by crystal defects generated during silicon ingot growth. defec
t) and processing-induced defects formed during processing (which are considered to occur in steps other than the crystal growth step) and defects due to external contamination sources.

In general, a silicon wafer is manufactured by a crystal growth process of manufacturing a single crystal ingot using a Czochralski (CZ) method, a floating zone melting (FZ) method, or the like, and a single crystal ingot. Is sliced, and at least one principal surface is processed into a mirror surface through a wafer processing step.

More specifically, the wafer processing step includes a slicing step of slicing a single crystal ingot to obtain a thin disk-shaped wafer and preventing a wafer obtained by the slicing step from cracking or chipping. A chamfering step for chamfering the outer periphery thereof, a lapping step for flattening the wafer, an etching step for removing processing distortion remaining on the chamfered and lapped wafer, and polishing (polishing) for mirror-polishing the wafer surface ) And a cleaning step of cleaning the polished wafer and removing abrasives and foreign substances adhering thereto.
The above-mentioned wafer processing step shows a main step, and other steps such as a heat treatment and a surface grinding step are added, the order of the steps is changed, or the same step is performed in a plurality of steps.

[0005] In each of these steps, a processing-induced defect may occur in each step. In particular, polishing damage formed during processing such as a polishing step is extremely weak and difficult to detect. For example, as damage to a mirror-polished wafer, for example, scratches and latent scratches are known. Scratch is a defect that can be determined visually, but latent scratches cannot be determined visually and evaluation is difficult. In addition, it is thought that there was damage due to polishing, but it could not be clearly detected. The presence of such polishing damage (a defect caused by the polishing process among the process-induced defects) may cause a decrease in yield in a subsequent device manufacturing process. Therefore, it is important to evaluate and manage processing-induced defects (also referred to as processing damage) in a processing step, particularly in a polishing step as final mechanical processing.

As a method for evaluating such a defect, a method has been developed in which a wafer is treated with a chemical solution comprising ammonia, hydrogen peroxide and water to observe the defect (hereinafter, this method is referred to as SC1-RT). .

Defects evaluated by this method are defects in a wafer, mainly COP (Crystal Ori) which is a crystal defect generated during silicon ingot growth.
It is considered that defects due to external contamination sources such as metalized particles and processing damage formed during processing and metal are detected.

[0008]

As described above, S
In C1-RT, it is considered that defects due to external contamination sources such as COP, which is a crystal defect, processing damage formed during processing, and Cu are detected.

When only polishing damage is evaluated among processing-induced defects, for example, if the scratch is minute, CO
Using a wafer without P (for example, an epitaxial wafer or an FZ wafer), after polishing in a process to be evaluated, the polished wafer is washed with HF, and washed with an SC1 cleaning solution,
Thereafter, there is a method of detecting the number of LPDs and evaluating a processing step. As a result, a defect formed in a scratch shape can be evaluated.

However, there is a problem that even if the polishing damage is evaluated by such a method, the expected polishing damage is not detected at all. For example, the polishing step is usually performed in a plurality of stages, but the final polishing step, which is the final stage, is polishing for reducing processing damage, and it is considered that there is almost no processing damage. However, it was suggested that there is a defect that occurs when the processing time of the finish polishing is increased. Such processing-induced defects (processing damage)
It is important to control the manufacturing process and review the manufacturing process. However, such a level of processing damage is very small, and can hardly be detected by simple hydrofluoric acid treatment and SC1 cleaning. Therefore, there is a need for a method capable of evaluating processing damage such as that generated by such finish polishing.

In the present invention, wafer defects, particularly polishing damage (work-induced defects) can be stably performed by the SC1-RT.
It is an object of the present invention to provide an accurate (highly sensitive) evaluation method.

[0012]

According to the method for evaluating a wafer, particularly the method for evaluating a process-induced defect of the present invention, a silicon surface is subjected to a long-time etching process using a processing solution comprising ammonia, hydrogen peroxide and water. , LPD (Light Point Det) formed on the surface of the silicon wafer
The method for evaluating a silicon wafer by checking the number of facts is characterized by adding a substance that sensitizes a wafer defect, particularly processing damage, to the processing solution.

[0013] Processing damage, particularly polishing damage caused in the final polishing step, is a defect that is very difficult to detect. Pollution-free ammonia, hydrogen peroxide solution and water system (SC
This polishing damage is not detected when the SC1-RT evaluation is performed using the (one liquid), and the polishing damage can be detected with high sensitivity by evaluating using the SC1 liquid that is appropriately contaminated (for example, contaminated by Cu). It turned out to be. Therefore, in the present invention, a substance (sensitizer) for sensitizing the processing damage is added to the SC1 liquid beforehand for evaluation.

In particular, as a substance for sensitizing processing damage, a Cu compound alone or a Cu compound and a Ca compound,
It is preferable to use a substance obtained by combining at least one compound selected from the group consisting of a compound and a Zn compound. These compounds need only be soluble in an ammonia-based aqueous solution. For example, in the case of a Cu compound, copper nitrate, copper sulfate, copper chloride and the like, and also Ca and Cr,
Compounds such as nitrate may be used for Zn and the like. As long as each metal ionizes in an ammonia-based aqueous solution, it can be used as a substance for sensitizing processing damage in the present invention.

As a metal other than Cu as a substance for sensitizing the processing damage, a compound of a metal such as Au, Ag, or Pt, which has a smaller ionization tendency than Si and can be dissolved in an ammonia-based aqueous solution can be used. . It was also found that the combination of Cu and other metals further affected the sensitivity. For example, Ni,
When contamination such as Fe is present, detection of processing damage is hindered. Conversely, when Cu and Ca, Cr, or Zn are added, even if a small amount of Cu is added, sensitivity is improved due to a synergistic effect of Ca or the like. I understand. Therefore, processing damage can be detected with high sensitivity by adding a Ca compound, a Cr compound, a Zn compound or the like in addition to the Cu compound.

If such a metal compound is excessively added, for example, when the wafer is processed in a chemical solution containing several hundred ppb or more of Cu or the like, pits (defects caused by metal) are generated on the wafer surface. 300ppb as upper limit
The degree is preferred. In addition, since Cu alone has a weak effect at 0.5 ppb or less, it is considered that a higher concentration is necessary for stable evaluation. More preferred addition amount is 3 to
10 ppb. When it is 3 ppb or more, the detection sensitivity is improved, and when it is 10 ppb or less, the generation of defects due to metal contamination is completely suppressed, which is preferable.

In addition, Cu is added within the range of the preferable addition amount.
The sensitivity increases with an increase in the amount of addition, such as the amount of addition, etc., and even those with weak processing damage can be evaluated.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below, but it goes without saying that various modifications can be made without departing from the technical idea of the present invention.

LPD detected by a particle counter
Are counted with a size of 0.12 μm or more. This depends on the capability of the particle counter, but the haze of the wafer is detected when the current apparatus normally counts LPD of about 0.10 μm. This is because it becomes impossible to distinguish between the processing-induced defect and the haze. As long as the haze can be separated by the device, even smaller LPDs may be counted, but it is preferable to detect LPDs with a current size of 0.12 μm or more.

Therefore, in the evaluation method of the present invention, it is possible to prevent the haze from being generated even when the silicon surface is subjected to a long-time etching process using a processing solution comprising ammonia, hydrogen peroxide and water, and to reduce the size of the process-induced defect. Is preferably set to be sufficiently large. Especially from 20 minutes to 60
A processing time on the order of minutes is preferred.

The SC1 solution used for washing is as follows:
Usually, it is a liquid prepared by mixing 28% ammonia water, 30% hydrogen peroxide solution, and water at about 1: 1: 5. In such a composition used for cleaning, the etching effect of processing-induced defects is small and the sensitivity is not good. Therefore, in order to detect with higher sensitivity among the SC1 liquids, the ammonia, hydrogen peroxide and aqueous treatment liquids have an ammonia concentration of 0.3 to 3.0% by weight and a hydrogen peroxide concentration of 0.15 to 0.5%. It is preferably 8% by weight, and the concentration of ammonia is preferably higher than the concentration of hydrogen peroxide.

Further, the etching rate by the processing liquid is 1.
When a processing liquid having a concentration of 0 to 4.0 nm / min is used, defects can be detected with high sensitivity. For example, preferable conditions are to mix 28% by weight of ammonia water, 30% by weight of hydrogen peroxide solution and pure water at a volume ratio of 10: 2: 100, and to treat them at a chemical solution temperature of 80 ° C. for about 40 minutes.

Further, the evaluation method of the present invention can evaluate from a large defect to a small defect generated in any of the processing steps and after the polishing step. Particularly suitable for evaluating very small processes. Although it is generally considered that there is no processing damage in the finish polishing step, very weak polishing damage can be detected by the evaluation method of the present invention. Therefore, by examining the polishing conditions and the like based on the evaluation results, the operating conditions can be improved to the optimal ones.

Specifically, a mirror-polished wafer without COP is prepared, the wafer is processed in a process to be polished (polishing process to be evaluated), and the wafer is processed by an evaluation method using the SC1 liquid to which Cu or the like is added. The process-induced defect may be evaluated, and the polishing process may be controlled so that the process to be polished is adjusted based on the number of detected LPDs.

As the mirror-polished wafer without COP, for example, a wafer on which an epitaxial layer is formed or an FZ wafer can be used. The adjustment of the polishing process means, for example, the evaluation of processing conditions such as processing pressure and equipment used such as an abrasive when the apparatus is started up, and the review (replacement) of a deteriorated member such as a polishing cloth during operation. May be adjusted (improved) based on the evaluation result of the present invention.

The evaluation method of the present invention can also be used for daily process management. In other words, since the present invention is a stable evaluation method, the amount of the sensitizer is fixed, controlled under the same processing conditions, the LPD level of a normal wafer is grasped, and an extremely large number of LPDs is detected. In this case, it is judged as abnormal and the process is reviewed.

[0027]

The present invention will be described more specifically with reference to the following examples.

(Example 1) As a raw material wafer, a wafer having no COP, for example, an 8-inch epitaxial wafer (hereinafter also referred to as an epi-wafer) in which a 3-μm epitaxial layer is stacked on a P-type substrate was used. This epiwafer was confirmed using a particle counter LS-6500 (manufactured by Hitachi Electronics Engineering Co., Ltd.) to confirm that no crystal-induced COP was present.

This epiwafer was introduced into a process to be evaluated, for example, a final polishing process in which a polishing pad of about 0.1 μm was polished using a suede-type polishing cloth and an abrasive containing colloidal silica, and the wafer surface was polished. In addition,
In this example, in order to evaluate a wafer having polishing damage, a very small amount of foreign matter (zinc oxide) was added to the polishing agent.
Polishing damage is intentionally caused.

Thereafter, evaluation was performed using the SC1 solution of the present invention. In other words, to evaluate stable polishing damage,
First, the processing vessel used for the SC1-RT was washed with an acid solution such as hydrochloric acid, and then the ammonia concentration was 2.27% by weight.
Hydrogen peroxide concentration 0.59 wt%, residual water treatment liquid (SC1
Liquid) 30 liters was prepared and placed in the processing vessel. Further, copper nitrate was added so that the Cu ion concentration became 5 ppb.

Using such SC1 solution, the previously polished epiwafer is immersed in a chemical solution, and the etching time is about 4 hours.
Performed at 0 minutes.

After rinsing with pure water and drying with IPA (isopropyl alcohol), a particle counter LS-6500 (manufactured by Hitachi Electronics Engineering Co., Ltd.)
The number of LPDs of 0.12 μm or more on the wafer was counted. As a result, the number of LPDs was 20,000 or more, and very many defects were observed.

(Embodiment 2) A wafer polished by using the same raw material wafer as in Embodiment 1 and minimizing polishing damage without mixing foreign matter into the polishing agent using the same processing liquid as in Embodiment 1. When similarly evaluated, the number of LPDs is 500
The number was about 0 to 8000.

As is clear from the first and second embodiments,
Difference due to polishing damage when using a treatment solution to which Cu is added (difference when polishing is performed with foreign matter in the polishing agent)
Was clearly observed. Although it depends on the amount of copper added and the processing conditions, about 5000 LPDs were detected in Example 2 above. As described above, many LPDs are detected. However, these are very weak, and processing-induced defects that do not affect the quality at the current level are detected.

Comparative Example 1 An epiwafer polished in the same manner as in Example 1 was subjected to the same composition as in Example 1 by using a high-purity chemical solution (chemical solution to which Cu was not added) used in ordinary cleaning and the like. In other words, ammonia concentration 2.27% by weight, hydrogen peroxide concentration 0.59% by weight, residual water treatment liquid (SC1 liquid)
Was prepared, processed under the same conditions, and evaluated. As a result, L
The number of PDs was not so large at 50 to 100.

From the evaluation results of Comparative Example 1, it cannot be clearly determined whether a work-induced defect has been detected.

(Comparative Example 2) When an epitaxial wafer polished by minimizing polishing damage without mixing foreign matter into the polishing agent was evaluated in the same manner with the same processing liquid as Comparative Example 1, LP
The D number was about 50 to 100.

As is clear from Comparative Examples 1 and 2,
The difference due to the polishing damage (the difference when polishing was performed with foreign matter in the polishing agent) was not clearly seen. In other words, it can be seen that when copper was not added, the presence or absence of polishing damage could not be evaluated in some cases.

From the above results, it was found that when the SC1 solution containing Cu or the like was used, the detection sensitivity was improved.

[Experimental Example 1: The effect of a substance (sensitizer) for sensitizing processing damage was confirmed. Using the same epiwafer as the wafer used in Example 1, and using the same processing conditions except for the sensitizer, the substances to be added to the processing solution were as follows:
(G) was changed and evaluated.

(A) No sensitizer (b) Addition of 0.5 ppb of Cu (copper nitrate) (sensitizer 1) (c) Addition of 5 ppb of Cu (sensitizer 2) (d) 0.5 ppb of Cu + 1 p of Ca (calcium nitrate)
Addition of pb (sensitizer 3) (e) 0.5 ppb of Cu + 1 ppb of Cr (chromium nitrate)
Addition (sensitizer 4) (f) Cu5ppb + Ni (nickel nitrate) 1ppb addition (sensitizer 5) (g) Cu5ppb + Fe (iron nitrate) 1ppb addition (sensitizer 6)

FIG. 1 shows the evaluation results. As is clear from FIG. 1, when no sensitizer was used and when Cu was 0.5 pp.
Below m, LPD is hardly detected. 5 ppm of Cu
When added, Cu is 0.5 ppb and at least C
When Ca and Cr are added together with u, the sensitivity is improved. Conversely, it can be seen that even if a large amount of Cu is added, if Ni or Fe is mixed in the processing solution, the sensitivity is lowered.

(Example 3) Polishing damage was evaluated under environmental conditions 1 to 7 shown in FIG. 2 by changing the environment such as the date and time and the measurement place under the same epiwafer and processing conditions as in Example 1. As a result, it was found that stable evaluation was possible as shown in FIG.

Note that the embodiment of the present invention is not limited to the above example. In Example 2, although the wafer itself was a good product, 5000 LPDs were detected as many as possible. This can be made smaller or larger by adjusting the amount of sensitizer added, and by making the amount of sensitizer smaller than in Example 2 (for example, by making Cu about 1 ppb). It is also possible to reduce the number of non-defective LPDs and adjust them so that they appear as large numbers only when there is a work-induced defect. This addition amount may be appropriately adjusted.

Normally, the amount of the sensitizer to be added is fixed, the level of a non-defective product is grasped, and if a numerical value extremely larger than the level is obtained, it is sufficient to manage it so that it is judged to be abnormal.

[0046]

As described above, according to the evaluation method of the present invention, polishing damage which cannot be sufficiently evaluated by the conventional wafer evaluation can be evaluated with high sensitivity. The use of the evaluation method of the present invention makes it possible to evaluate stable processing-induced defects (processing damage), particularly polishing damage such as finish polishing. As a result, in order to reduce polishing damage, it is possible to make an evaluation useful for improving the polishing process.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the type of sensitizer and the number of detected LPDs in Experimental Example 1.

FIG. 2 is a graph showing a relationship between environmental conditions 1 to 7 and the number of detected LPDs in Example 3.

Continued on the front page F term (reference) 4M106 AA01 BA05 CB19 CB20 DH12 DH32

Claims (5)

[Claims] 1. A silicon wafer is subjected to an etching process for a long time using a processing solution comprising ammonia, hydrogen peroxide and water, and the number of LPDs formed on the silicon wafer surface is examined to evaluate the silicon wafer. A method for evaluating a wafer, comprising: adding a substance that sensitizes a wafer defect to the processing solution; 2. The wafer evaluation method according to claim 1, wherein said wafer defect is processing damage. 3. A substance that sensitizes the processing damage is a Cu compound alone or a Cu compound and a Ca compound,
3. The wafer evaluation method according to claim 2, wherein a substance obtained by combining at least one compound selected from the group consisting of a compound and a Zn compound is used. 4. The method for evaluating a wafer according to claim 2, wherein the material for sensitizing the processing damage is added to the processing liquid as Cu ions at 3 ppb to 10 ppb. 5. The treatment liquid comprising ammonia, hydrogen peroxide and water, wherein the concentration of ammonia is 0.3 to 3.0% by weight, the concentration of hydrogen peroxide is 0.15 to 0.8% by weight, The method for evaluating a wafer according to any one of claims 1 to 4, wherein a processing solution having a concentration higher than the concentration of hydrogen peroxide is used.