JP2000173956A - Polishing agent for semiconductor silicon wafer and polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid a metal contamination, specially a copper contamination, while a polishing rate is maintained by a method wherein an amine having one amino group and a chelate agent are added to a polishing agent component. SOLUTION: This polishing agent for semiconductor silicon wafer is formed by adding an amine having one amino group and a chelate agent to a polishing agent component. As the chelate agent, one having a sufficient chelate agent compound formation capability is preferable and a chelate agent having a formation capability greater than that of nitrilotoriacetic acid is preferable. As amine having one amino group, one selected from among methylamine, ethylamine and propylamine can be used singly or at least two can be combineally used. As the polishing agent component, one containing silica or ceria as an abrasive particle is used, but one containing further sodium hydride and potassium hydride may be used also.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abrasive for polishing a semiconductor silicon wafer (hereinafter, sometimes simply referred to as a wafer, a silicon wafer or a semiconductor wafer) capable of preventing a metal contamination while improving a polishing rate. And a polishing method.

[0002]

2. Related Art In general, a method of manufacturing a semiconductor silicon wafer includes a slicing step of slicing a single crystal ingot to obtain a thin disk-shaped wafer, and a method of preventing cracking and chipping of the wafer obtained by the slicing step. A chamfering step for chamfering the outer peripheral portion, a lapping step for flattening the chamfered wafer, an etching step for removing processing distortion remaining on the chamfered and wrapped wafer, and mirror-polishing the etched wafer surface And a cleaning step of cleaning the polished wafer and removing abrasives and foreign substances adhering thereto.

In the above polishing step, generally, fine SiO 2
₂ (silica) abrasive grains and CeO ₂ (ceria) abrasive grains with pH = 9
A silica-containing abrasive dispersed in a colloidal form in an alkaline aqueous solution of up to about 12 is used, and is polished by a combined action of a mechanical action of SiO ₂ or CeO ₂ and a chemical action of etching silicon with an alkaline solution. . In addition, the silica or ceria-containing abrasive is often used by adding several percent of amines for the purpose of improving the polishing rate.

[0004] However, the alkaline silica or ceria-containing abrasive contains trace amounts of metal impurities. Examples of metal impurities contained in the abrasive include nickel, chromium, iron, copper, and the like.

[0005]

The inventor of the present invention has been studying a polishing process for a semiconductor silicon wafer using a silica-containing abrasive containing these metal impurities. It has become clear that some metal ions, such as nickel, diffuse deeply into the wafer into the polishing agent, degrade the wafer quality, and significantly reduce the characteristics of the semiconductor devices formed by the wafer.

As a countermeasure for preventing the deterioration of wafer quality caused by the above-mentioned silica-containing abrasive, it is conceivable to use a highly purified silica-containing abrasive. However, commercially available high-purity abrasives are extremely expensive, and their use for polishing silicon wafers is not worth the cost.

In order to solve this problem, the present inventors have studied the causes of metal contamination during polishing. As a result, amine added for the purpose of improving the polishing rate promotes metal contamination. It became clear.

From this, it is conceivable to stop the addition of amine to the polishing agent as a measure for preventing metal contamination during polishing. However, when the addition of the amine is stopped, the polishing rate is remarkably reduced, and the productivity is reduced.

Further, as a method for preventing metal contamination, there is disclosed a method in which a chelating agent is added to an abrasive, and heavy metal ions are supplemented by the chelating agent (Japanese Patent Publication No. Hei.
20742). However, when the inventor performed polishing by adding a chelating agent to a commercially available amine-containing polishing agent, it was found that contamination by copper, which is one of the elements easily diffused into the wafer, was not suppressed.

[0010] That is, it is impossible to prevent metal contamination, particularly copper contamination, by simply adding a chelating agent to an abrasive, and it has been necessary to find an amine which can exert the effect of the chelating agent.

The present invention has been made in view of the above-mentioned problems, and provides an abrasive for polishing a semiconductor silicon wafer and a polishing method capable of avoiding metal contamination, particularly copper contamination, while maintaining a polishing rate. The main purpose is to do so.

[0012]

Means for Solving the Problems In order to solve the above problems, an abrasive for polishing a semiconductor silicon wafer according to the present invention comprises:
An amine having one amino group and a chelating agent are added to the abrasive component. The chelating agent preferably has a sufficient ability to form a chelate compound, and is preferably a chelating agent having a greater forming ability than nitrilotriacetic acid (NTA).

As the abrasive component, one containing silica or ceria as abrasive particles is used, and one further containing an inorganic alkali such as sodium hydroxide or potassium hydroxide is also used.

The concentration of silica used in the abrasive of the present invention is 0.01 to 10% by weight. The amount of inorganic alkali added, such as sodium hydroxide and potassium hydroxide, should be between pH 10.0 and
It is added to be in the range of 12.0.

The amine having one amino group (hereinafter sometimes referred to as monoamine) includes methylamine,
Those selected from the group consisting of ethylamine and propylamine can be used alone or in combination of two or more.

Even if a monoamine having a molecular size larger than that of propylamine is added, the polishing rate accelerating effect is small. When a diamine such as ethylenediamine or an amino alcohol such as ethanolamine is added, copper contamination cannot be avoided even if a chelating agent is added.

The addition concentration of these monoamines is 0.001 to
1 mol / l is preferred, and 0.01 to 0.5 mol / l is more preferred. If the monoamine concentration is less than 0.001 mol / liter, the polishing rate will not sufficiently increase, and if it exceeds 1 mol / liter, the polishing rate may exceed the environmental standard value.

The above-mentioned chelating agents include nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDT).
A), diethylenetriamine-N, N, N ′, N ″,
N "-pentaacetic acid (DTPA), diaminocyclohexane-
One selected from the group consisting of N, N, N ', N',-tetraacetic acid (CyDTA) and salts thereof can be used alone or in combination of two or more.

Even if a chelating agent having a chelating compound forming ability smaller than that of nitrilotriacetic acid (NTA) is added, a sufficient effect of suppressing copper contamination cannot be obtained. The concentration of these chelating agents is preferably 0.0001 to 0.1 mol / liter.

When the concentration of the chelating agent is less than 0.0001 mol / l, the effect of adding the chelating agent does not increase. When the concentration exceeds 0.1 mol / l, the effect of adding the chelating agent does not change. It is preferable to keep it below.

The method for polishing a semiconductor silicon wafer according to the present invention is a method for polishing a semiconductor silicon wafer using the above-mentioned polishing agent for polishing a semiconductor silicon wafer,
By polishing the semiconductor silicon wafer with the polishing agent for semiconductor silicon wafer polishing described above, a mirror-finished wafer free of copper contamination can be obtained.

It is an object of the present invention to prevent contamination of impurities (heavy metals, particularly Cu), which occurs during wafer polishing, and in particular, contamination of the bulk due to polishing.

Although impurities present on the wafer surface after polishing the wafer can be removed by cleaning in a later step, impurities diffused into the bulk cannot be removed. In particular, the alkaline silica-containing abrasive contains impurities (heavy metals, particularly Cu). In the polishing step, impurities are easily diffused from the wafer surface to the inside. Therefore, a technique for preventing impurities from entering the bulk during wafer polishing has been required.

On the other hand, according to the study of the present inventors, it has been found that the addition of an amine to the polishing agent promotes metal contamination during wafer polishing. In order to prevent this, it was thought that a heavy metal impurity could be removed by adding a chelating agent, but it was not so effective.

The present inventor has further studied in detail that, when polishing a wafer, using amines having a plurality of amino groups together with an abrasive among the amines particularly promotes contamination in the bulk. I understood. Thus, the present inventors have found that when an amine having one amino group (monoamine) is used together with an abrasive, contamination in the bulk is greatly reduced, and the present invention has been completed.

[0026]

Hereinafter, the present invention will be described with reference to experimental examples.
The present invention is not limited to the inventive experimental examples in these experimental examples. In particular, in the following experimental examples, an example of avoiding copper contamination is given, but it has been confirmed that other heavy metal contamination can be avoided by the present invention. In addition, CeO is used as an abrasive.
_The same applies to the case where ₂ is used.

(Experimental example 1: Evaluation of copper contamination level when monoamine or diamine and chelating agent were added)

Abrasive composition (1) Base abrasive: colloidal silica (concentration 3.75 wt.)
%), Inorganic alkali (NaOH), pH = 9 (2) Amine: methylamine, ethylamine (more than monoamine), ethylenediamine, propanediamine (more than diamine) (3) Amine concentration: 0.1 mol / l (4) Chelating agent: EDTA (5) Chelating agent concentration: 0, 0.001 mol / l (6) Copper ion concentration in abrasive: 10 ppb

As described above, the P-type (10) was prepared using eight types of abrasives having different types of amines and different concentrations of chelating agents.
0) Semiconductor silicon wafer (resistivity 0.005 to 0.010 Ω)
.Cm) was polished to 10 μm, and the copper contamination level was investigated.
Polishing was performed using a commercially available single-wafer polishing machine (manufactured by Fujikoshi Machinery Co., Ltd.).

Known SC1 cleaning of the polished wafer [Ammonia: hydrogen peroxide: water volume ratio = 1: 1 to 2: 5 to 5]
75 to 85 ° C, 10 to 20 in the cleaning solution (SC1 solution)
Immersion treatment) and washing with SC2 [washing liquid (SC2: SC2: hydrochloric acid: hydrogen peroxide: water) = 1: 1 to 2: 5 to 7
Liquid) at 75 to 85 ° C. for 10 to 20 minutes to remove impurities on the wafer surface, heat-treat the cleaned wafer at 650 ° C. for 20 minutes, and apply HF / H ₂ O ₂ droplets to the wafer surface. Was recovered and copper contamination levels were evaluated by atomic absorption spectroscopy. By evaluating the copper contamination level by the above method, not only copper on the wafer surface,
Copper diffused inside the wafer can also be evaluated.

Table 1 shows the measurement results of copper contamination on the polished wafer. As is evident from the results in Table 1, the diamine-added abrasive could not avoid copper contamination even when the chelating agent was added, as well as when no chelating agent was added. On the other hand, the monoamine-added abrasive could not avoid copper contamination when the chelating agent was not added, but could avoid copper contamination when the chelating agent was added.

[0032]

[Table 1]

(Experimental Example 2: Evaluation of copper contamination level when methylamine and various chelating agents were added)

Abrasive composition (1) Base abrasive: Colloidal silica concentration (3.75 wt.
%), Inorganic alkali (NaOH), pH = 9 (2) amine: methylamine (monoamine) (3) amine concentration: 0.1 mol / l (4) chelating agent: pyrocatechol, NTA, EDTA,
DTPA, CyDTA (5) Chelating agent concentration: 0.001 mol / l (6) Copper ion concentration in abrasive: 10 ppb

As described above, a P-type (100) semiconductor silicon wafer (resistivity 0.005 to 0.010 Ω · cm) is formed by using five types of abrasives having different types of chelating agents.
and the copper contamination level was investigated. Polishing was performed using a commercially available single-wafer polishing machine (manufactured by Fujikoshi Machinery Co., Ltd.). Known SC1, S in the polished wafer as in Experimental Example 1
After performing C2 cleaning, the cleaned wafer is heated at 650 ° C. for 2 hours.
0 min heat treatment, the copper wafer surface was collected with HF / H ₂ 0 ₂ droplets was evaluated copper contamination level by atomic absorption spectrometry.

Table 2 shows the measurement results of copper contamination on the polished wafer. As is clear from the results in Table 2, copper contamination could not be avoided in the case of pyrocatechol, a chelating agent having a smaller chelate compound formation than NTA, but a chelating agent having a larger chelate compound forming ability than NTA. By adding, copper contamination could be avoided.

[0037]

[Table 2]

(Experimental example 3: Evaluation of polishing rate when various amines were added)

Abrasive composition (1) Base abrasive: Colloidal silica concentration (3.75 wt.
%), Inorganic alkali (NaOH), pH = 10.5 (2) Amine: methylamine, ethylamine, propylamine, butylamine (more than monoamine), ethylenediamine (more than diamine) (3) Amine concentration: 0, 0.1 mol / liter (4 ) Chelating agent: EDTA (5) Chelating agent concentration: 0.001 mol / l

As described above, P-type (100)
Semiconductor silicon wafer (resistivity 0.005 to 0.010 Ω · c
m) was polished and the polishing rate was investigated. Polishing was performed using a commercially available single-wafer polishing machine (manufactured by Fujikoshi Machinery Co., Ltd.). The evaluation of the polishing rate was calculated by measuring the thickness of the wafer before and after polishing with a capacitance-type thickness measuring device (manufactured by Nippon ADI Co., Ltd.) and dividing by the polishing time.

Table 3 shows the measurement results of the polishing rate. In Table 3, the polishing rate when various amines are added is shown as 1 when the amine is not added. In the amine names in Table 3, the molecular size increases as one moves to the right.

[0042]

[Table 3]

From the results shown in Table 3, it was confirmed that by adding a monoamine having a molecular size smaller than that of butylamine, a higher polishing rate can be obtained than when no amine was added.

A similar effect was obtained with ammonia having a structure similar to that of monoamine. However, ammonia is highly volatile, and monoamine is preferred in view of the stability of the abrasive.

[0045]

As described above, according to the present invention, by adding an amine having one amino group and a chelating agent to a silica-containing polishing agent, it is possible to improve the polishing rate when polishing a wafer. A remarkable effect that metal contamination, particularly copper contamination, can be avoided can be achieved.

Claims (6)

[Claims] An abrasive for polishing a semiconductor silicon wafer, characterized by adding an amine having one amino group to the abrasive component and a chelating agent having a higher chelating compound generating ability than nitrilotriacetic acid (NTA). 2. The abrasive for polishing a semiconductor silicon wafer according to claim 1, wherein the abrasive particles contained in the abrasive component are made of silica. 3. The polishing agent for polishing a semiconductor silicon wafer according to claim 1, wherein the polishing agent component contains an inorganic alkali. 4. The amine according to claim 1, wherein the amine having one amino group is at least one selected from the group consisting of methylamine, ethylamine, and propylamine. Polishing agent for polishing semiconductor silicon wafers. 5. The chelating agent includes nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriamine-N, N, N ′, N ″, N ″ -pentaacetic acid (DTPA), and diaminocyclohexane-N , N,
5. The semiconductor silicon wafer polishing method according to claim 1, wherein at least one selected from the group consisting of N ', N',-tetraacetic acid (CyDTA) and salts thereof. Abrasive. 6. A method for polishing a semiconductor silicon wafer, comprising polishing a semiconductor silicon wafer using the polishing agent according to claim 1. Description: