JP2894154B2 - Method for measuring the depth of the affected layer on the silicon wafer surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon wafer obtained by processing a silicon single crystal ingot pulled up by the CZ method, and relates to an etch pit generated on a mirror-polished surface of the silicon wafer by wet etching. The present invention relates to a method for indirectly measuring the depth of a work-affected layer existing on a mirror surface of the silicon wafer by measuring the number of the layers .

[0002]

2. Description of the Related Art A silicon wafer used in the manufacture of a semiconductor device is usually manufactured by subjecting a silicon single crystal ingot to outer diameter grinding, orientation flat processing, slicing, chamfering, lapping, etching, and mirror polishing in this order. . This mirror polishing is usually performed by so-called mechanochemical polishing using a soft polishing cloth and an abrasive containing an alkali component and abrasive grains.In general, a damaged layer is formed on the mechanochemical polished surface. It is said that it does not exist. However, according to the study of the present inventors, in the mirror polishing step,
It has been found that a work-affected layer having a small thickness is present on the surface of a silicon wafer. This work-affected layer is basically the same as the work-affected material, although it differs in that the magnitude and depth of the strain are small when compared with the work-affected material (work strain) caused by machining from the slice to the lapping step. It is. In addition, since the process-affected layer is a cause of generating crystal defects such as microdefects and stacking faults on the surface of a silicon wafer when manufacturing a semiconductor device, its abundance can be suppressed, Abundance (depth) of affected layer
Is critical for the production of high quality semiconductor devices.

[0003]

However, conventionally, it has been difficult to accurately measure the depth of the work-affected layer on the silicon wafer surface as described above. The present invention has been made in view of this point, and an object of the present invention is to provide a method capable of accurately measuring the depth of a work-affected layer on a silicon wafer surface by a simple operation. The present invention relates to (1) COP (crystal originated parti) for an as-grown silicon wafer obtained by the CZ method.
(2) These defects become apparent as etch pits by wet etching. (3) The total number of the etch pits increases almost in proportion to the etching amount (etching depth). And (4) the etching rate of the damaged layer is higher than the etching rate of the bulk layer, and the etching is performed at the boundary between the damaged layer and the bulk layer. The speed, that is, the speed at which the etch pits increase (the rate of increase) decreases , and this is completed.

[0004]

According to a first aspect of the present invention, there is provided a method for measuring the depth of a damaged layer on the surface of a silicon wafer, the method comprising the steps of: processing a silicon single crystal ingot pulled up by a CZ method; Etch the mirror-polished surface with an etchant having a constant component, concentration and temperature, and increase the number of etch pits based on the relationship between the total etching time and the total number of etch pits generated on the surface of the silicon wafer by the etching. Rate falls
A time point of to etching time t from the etching start point to the point where the rate of increase in the etch pits is reduced
d and the etch pit increase rate A1 before the etch pit increase rate is reduced and the etch pit increase rate A2 after the etch pit increase rate is reduced, and the etching rate α of the bulk layer excluding the work-affected layer is separately determined. The method is characterized in that the depth Dd of the damaged layer on the surface of the silicon wafer is obtained by the following equation. Dd (A1 / A2) × α × td

[0005] The surface of the silicon wafer according to claim 2
The method for measuring the depth of the affected layer is characterized in that a mixture of ammonium hydroxide, hydrogen peroxide and water is used as the etching solution.

[0006] The surface of the silicon wafer according to claim 3
The method of measuring the depth of the work-affected layer is characterized in that the number of etch pits is measured with a particle counter.

[0007]

In the measuring method according to claim 1, since the etching rate is constant in the affected layer and the COP is substantially uniform in the affected layer, the total number of generated etch pits is determined by the etching time. And increase almost in proportion. For the same reason, the total number of etch pits that occur in the bulk layer also increases substantially in proportion to the etching time. In this case, since the etching rate of the bulk layer is lower than that of the affected layer, the rate of increase of the etch pits A1 becomes A2 after the entire affected layer is removed by etching.
descend. Here, the etching rate of the affected layer is Rd
If the etching rate of the bulk layer is Rb, the relationship of A1 / A2 = Rd / Rb holds. Here, since Rb can be separately obtained and set to a known value α, Rd = (A1 / A2) × α. Therefore, the depth Dd of the work-affected layer can be obtained as follows: Dd = Rd × td = (A1 / A2) × α × td

In the case of performing etching according to the present invention, the components, concentrations, temperatures and etching rates of the etching solution are not particularly limited. However, when the etching rate is too high, the affected layer is removed in a very short time. Therefore, it is difficult to detect when the rate of increase of the etch pits decreases.Conversely, if the etching rate is too low, it takes a long time to observe the etch pits, and it takes a long time to measure the depth of the affected layer. become. The etchant according to claim 2 has an appropriate etching rate in this sense,
Therefore, it is possible to measure the increase rate of the etch pit in the affected layer without requiring a long time.

In addition, the number of etch pits (COP) can be accurately and simply measured by measuring the number of etch pits with a particle counter.

[0010]

Next, the present invention will be described in more detail with reference to examples. Example 1 Two silicon wafers (125 mm in diameter) after processing a silicon single crystal ingot obtained by the CZ method and having a pulling orientation of <100> in a conventional processing step, and mirror-polished with a polishing solution of pH 10 , And a resistivity of 8 to 12 Ωcm). Hydrofluoric acid having a concentration of 20% by weight (room temperature) was used, and the volume ratio of the etching solution was ammonium hydroxide (28% by weight): hydrogen peroxide (30% by weight): water = 0.05: 1: 10. Using the mixture (at room temperature), each wafer was processed according to the following procedure, and the number of etch pits was measured as the number of COPs with a particle counter (Hitachi LS6000). Treatment 1: After washing with the hydrofluoric acid, etching with the etching solution for 30 seconds, observing the etched surface with the particle counter. Treatment 2: After treating with the etching solution for 1 minute, observing the etched surface with the particle counter. Hereinafter, the same operation as the process 2 is repeated n times in total. In this case, the cleaning treatment with hydrofluoric acid is for removing abrasives and foreign matters remaining on the wafer surface after mirror polishing. It should be noted that hydrofluoric acid does not have an effect of etching the affected layer or the bulk layer.

[0011] Then, the above operation is repeated, and a particle map for each operation is superimposed on the basis of the particle map after the etching has been performed for a sufficiently long time so that the deteriorated layer is considered to be completely removed. Particles at the same position were determined to be etch pits generated due to the COP, and the relationship between the total etching time in processes 1 to n and the total number of etch pits was plotted. Once an etch pit is generated, it will be present at the same position, but particles that adhere at the time of etching will be detached and adhered before and after etching, and the position will not be at the same position. Becomes possible. The above processes 1 to n and the plotting work were repeatedly performed for the same sample, and a point at which a graph showing the relationship between the total etching time and the total number of etch pits was sharply bent was obtained. The total etching time at this point indicates the etching time during which the entire affected layer was dissolved and removed by etching.

FIG. 1 shows the above results. In this figure, the horizontal axis represents the total etching time, and the vertical axis represents the total number of generated etch pits. From this figure, it can be seen that when the total etching time is t _d = 5 minutes, the entire affected layer is dissolved and removed, and thereafter, the bulk layer is etched, and the etch pit increase rate of the affected layer is 30.9. / M
in, the etch pit increase rate of the bulk layer is 3.6 / min. On the other hand, according to another experiment, the etching rate of the bulk layer of the silicon wafer after the mirror polishing was 0.15 nm /
min. Therefore, damaged layer depth D _d of the silicon wafer surface is determined by the following equation. D _d = R _d × t _d = (A ₁ / A ₂ ) × α × t _d = (30.9 / 3.6) × 0.15 × 5 = 6.4 nm

[0013]

As is apparent from the above description, claim 1
According to the method for measuring the depth of a damaged layer on a silicon wafer surface described in the above section, by repeating the operation of measuring the number of etch pits generated by wet etching, the depth of the affected layer can be accurately determined by a simple operation. There is an effect that can be measured. According to the method for measuring the depth of a damaged layer on the surface of a silicon wafer according to claim 2, the time at which the etching rate of the damaged layer becomes appropriate and the time at which the generation rate of the etch pits decreases falls within a shorter time. Therefore, there is an effect that the time required for measuring the depth of the affected layer can be reduced. According to the method for measuring the depth of a damaged layer on a silicon wafer surface according to the third aspect, since the number of etch pits is measured by a particle counter, there is an effect that accurate measurement can be performed by a simple operation.

[Brief description of the drawings]

FIG. 1 is a graph showing a result of an example of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaki Nakano 150 Odakura Odaikura, Nishigo-mura, Nishishirakawa-gun, Fukushima Prefecture Shin-Etsu Semiconductor Co., Ltd. Semiconductor Shirakawa Research Laboratory (56) References JP-A-2-130848 (JP, A) JP-A-4-125946 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/66 G01N 21/88

Claims (3)

(57) [Claims] 1. A mirror polished surface of a silicon wafer obtained by processing a silicon single crystal ingot pulled up by a CZ method is etched with an etching solution having a constant component, concentration and temperature, and a total etching time And, based on the relationship between the total number of etch pits generated on the surface of the silicon wafer due to etching, the point at which the rate of increase of the etch pits decreases, and from the time of etching start to the point at which the rate of increase of the etch pits decreases And the etch pit increase rate A1 before the etch pit increase rate is reduced and the etch pit increase rate A2 after the etch pit increase rate is reduced, and the etching rate α of the bulk layer excluding the work-affected layer is determined. Separately, the depth Dd of the damaged layer of the silicon wafer surface processing is calculated by the following equation. Method of measuring the damaged layer depth of the silicon wafer surface, characterized in Rukoto. Dd = (A1 / A2) × α × td As claimed in claim 2 wherein said etching solution, and ammonium hydroxide, hydrogen peroxide and, a silicon wafer surface according to claim 1 which comprises using a mixture of water pressure
How to measure the depth of damaged layer . 3. A damaged layer depth measurement methods of the silicon wafer surface according to claim 1, characterized by measuring the number of etch pits in a particle counter.