JP3441979B2 - Semiconductor wafer processing method and semiconductor wafer - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a semiconductor wafer,
In particular, the present invention relates to improvement of a method for chemically etching and removing a work-affected layer on the surface of a wafer that occurs in the manufacturing process of a single crystal silicon wafer.

[0002]

2. Description of the Related Art Conventionally, a process for producing a semiconductor mirror-finished wafer usually comprises a step of slicing a single crystal rod of silicon or the like and subjecting the obtained semiconductor wafer to at least chamfering, lapping, acid etching, mirror-polishing and washing. ing. Depending on the purpose, some of these steps may be replaced, repeated a plurality of times, or other steps such as heat treatment and grinding may be added or replaced to perform various steps. Here, among the above, acid etching is performed for the purpose of removing the surface-altered layer introduced during mechanical processing such as slicing, chamfering, and lapping,
For example, it is a step of etching the surface from several to several tens of μm with a mixed acid aqueous solution containing hydrofluoric acid, nitric acid, acetic acid, and water, but the following problems have been pointed out.

That is, 1) TTV after wrapping
[Total Thickness Variation] (μm), LTV _max
The flatness of the wafer, which shows the variation in thickness expressed by [Local Thickness Variation] (μm) and the like, is deteriorated as the etching margin increases. 2) Irregularities called mm undulations and peels occur on the etching surface. 3) The etching produces harmful NO _x . Therefore, alkali etching may be used in consideration of these problems.

The advantages and disadvantages of this alkaline etching are listed as follows. First, a) flatness after lapping is maintained after etching, b) generation of harmful gas is suppressed, and the like. A) The surface after etching has a depth of several μm locally.
Since there are pits with a size of several to ten and several μm, if foreign matter enters the pits, it may cause particles or contamination in the subsequent process. (B) There are deep pits or surface roughness. Since (Ra) becomes large, mirror polishing in the subsequent process (mechanochemical polishing)
It is necessary to increase the polishing allowance in C. Since the unevenness of the surface after etching has a sharper shape than that of acid etching, the unevenness itself is a source of particles.

Therefore, the etching process removes the mechanically processed strained layer and improves the surface roughness while maintaining the flatness after lapping, and in particular, makes the local deep pits shallower after the etching, and further If the concavo-convex shape can be made smooth, it is possible to reduce the generation of particles in the subsequent process and the polishing allowance in the mirror polishing process.

[0006]

Therefore, the present invention has been made in view of the above problems, and the mechanically processed strained layer is removed and the surface roughness is maintained while maintaining the flatness of the wafer after lapping. And a method for processing a semiconductor wafer having a shallower local deep pit, a smooth uneven shape, and a chemically etched wafer (CW) having an etching surface that is unlikely to generate particles and contamination. The main purpose is to provide a processed semiconductor wafer.

[0007]

In order to solve the above-mentioned problems, the invention described in claim 1 of the present invention is a semiconductor wafer obtained by slicing a single crystal ingot, at least chamfering, lapping, etching, mirror polishing and In the method for processing a semiconductor wafer consisting of a washing step, after the alkali etching in the etching step, acid etching is performed, in which case the etching allowance of the alkali etching is made larger than the etching allowance of the acid etching, The etching allowance is 10 to 30 μm in alkali etching and 5 to 20 in acid etching.
The method for processing a semiconductor wafer is characterized in that the thickness is set to μm (excluding about 5 μm).

As described above, in the etching process, the wafer after lapping is first subjected to alkali etching to remove the mechanically processed strained layer while maintaining the flatness after lapping, and then subjected to acid etching. It is possible to improve the local deep pits remaining after the alkali etching, the surface roughness and the sharp uneven shape. At that time, it is necessary to make the etching allowance of the alkali etching larger than the etching allowance of the acid etching. The main reason for this is to make the local deep pits remaining after the alkali etching shallower. It is necessary to take a large amount, because the value is larger than the etching amount required to reduce the rate of occurrence of defects such as stains due to uneven etching called stain and the flatness in acid etching. .

In this case, as described in claim 2, the etching step is performed by alkali etching, then immersing in an aqueous solution of hydrogen peroxide, and then acid etching. This is because the surface of the wafer after alkali etching is active and becomes hydrophobic so that foreign substances are easily attached and contaminated, so if the surface is oxidized and made hydrophilic by immersion in an aqueous solution of hydrogen peroxide, particles will be attached. This is because it becomes difficult to do so.

In the present invention, the etching allowance is 10 to 30 μm in alkali etching,
In acid etching, the thickness is preferably 5 to 20 μm (excluding about 5 μm). In alkali etching, the depth of local deep pits remaining after etching tends to become shallower as the etching margin increases, and on the contrary, the surface roughness tends to deteriorate, but the above range is an appropriate value. In acid etching, the flatness deteriorates as the etching margin increases, but the stain generation rate greatly decreases, so the above range is appropriate.

According to the third aspect of the present invention, the etching solution for alkali etching is a NaOH aqueous solution or a KOH aqueous solution, and the etching solution for acid etching is a mixed acid aqueous solution of hydrofluoric acid, nitric acid, acetic acid and water. With such an etching solution, even in alkaline etching,
Even in the acid etching, the effect of the etching treatment is surely exhibited, the control of the etching allowance can be performed relatively easily, and the cost is low. It should be noted that the specific numerical values of the etching allowances in the present invention are all total values obtained by adding the etching allowances of both surfaces of the wafer.

Next, in the invention described in claim 4 of the present invention, the acid etching is a reaction-controlled acid etching. When the acid etching is of the reaction-controlled type as described above, in addition to the improvement of the local deep pits remaining after the alkali etching, the surface roughness and the sharp uneven shape, the waviness can be improved and further flattened.

In this case, as described in claim 5, an etching solution for the reaction rate-controlled acid etching is added to a mixed acid aqueous solution of hydrofluoric acid, nitric acid, acetic acid, and water to have a silicon concentration of 2
The solution was dissolved in 0 to 30 g / L (liter). By using such an etching solution, the effect of the etching treatment can be more reliably exhibited, the control of the etching allowance can be performed relatively easily, and the adjustment can be performed at low cost.

The invention according to claim 6 of the present invention is a semiconductor wafer processed by the method according to any one of claims 1 to 5 . In this way, by performing alkali etching, the mechanically processed strained layer is removed while maintaining the flatness after lapping, and then acid etching is performed, whereby local deep pits remaining after alkali etching and surface roughness and It is possible to obtain a semiconductor wafer having an improved sharp uneven shape. In particular, the reaction rate-controlled acid etching can improve the waviness and obtain a flatter semiconductor wafer.

Next, the invention described in claim 7 of the present invention is a semiconductor wafer chemically etched according to claim 4 or 5 , wherein the cell size is 20 × 20 mm.
LTVmax is 0.3 μm or less and the maximum pit depth is 6 μm or less.

In this case, as described in claim 8 , the average value of the waviness of the semiconductor wafer is set to 0.04 μm or less. Thus, according to the present invention, it is possible to obtain a semiconductor wafer which is extremely flat and has a small pit depth.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto. Here, FIG. 1, FIG. 2 and FIG.
The relationship between the etching depth of the wafer which is alkali-etched after lapping the inch wafer and the local deep pit depth (FIG. 1), TTV (FIG. 2) and surface roughness [Ra] (FIG. 3) is shown. . FIG. 4 shows the relationship between the etching allowance of a wafer obtained by acid etching after lapping an 8-inch wafer and TTV. FIG. 5 shows the relationship between the etching allowance due to general acid etching and the rate of occurrence of defects such as stains due to uneven etching called stain.

The inventors of the present invention have variously studied a semiconductor wafer processing method, particularly an etching method, for maintaining the flatness of the wafer after lapping and producing a chemical etching wafer having an etching surface which is unlikely to generate particles or contamination. As a result, first, alkali etching was performed to remove the strained layer while maintaining the flatness after lapping, and acid etching was performed to improve the deep pits, surface roughness, or waviness remaining there, especially a reaction-controlled acid. The present invention has been completed by contemplating the etching and investigating the processing conditions.

First, the alkali etching will be described in detail. FIG. 1 shows the relationship between the etching allowance and the local deep pit depth of a wafer obtained by lapping an 8-inch wafer with # 1200 lapping abrasive grains, and then performing alkali etching with a 50% NaOH aqueous solution at 85 ° C. . Further, FIG. 2 also shows the relationship with TTV, and FIG. 3 shows the relationship with the surface roughness (Ra).

Here, the local deep pits are the pits formed by the lapping abrasive grains sticking to the wafer surface during lapping, the size and depth of which are increased by alkali etching. When the concentration of alkali is low, the pit depth tends to increase, while when the concentration of alkali is high, the pit depth can be made shallow, but for that purpose, it is necessary to increase the etching allowance. ,ineffective. The depth of this pit is determined by the depth of focus of the optical microscope, but in order to remove this pit, it is necessary to polish it in a mirror polishing step which is a post-step. Therefore, the amount of mirror polishing needs to be equal to or greater than the maximum value of such a deep pit depth, and therefore it is desirable to make the pits as shallow as possible.

TTV [Total Thickness Variation]
(Μm) is a numerical value indicating the difference in thickness between the thickest part and the thinnest part in one wafer, and is an index of the flatness of the wafer. In addition, LTV [Local Thickness Variat
ion] (μm) is a cell (usually 20
X 20 mm or 25 x 25 mm), and the value is the difference in thickness between the thickest part and the thinnest part in the cell, and the LTV of each cell is LTV _cbc , the maximum of one wafer. The value is called LTV _max , which is an index of the flatness of the wafer. Ra (μm) is called center line average roughness and is one of the most commonly used surface roughness parameters.

From FIG. 1, in order to reduce the depth of the local deep pits, an etching allowance of 10 μm or more is required by alkali etching, TTV (FIG. 2) is 1 μm or less, and Ra (FIG. 3) is 0. In order to reduce the thickness to 25 μm or less, the etching allowance is preferably 30 μm or less. Therefore, as a total of these, as an etching allowance for alkali etching, 10 to 30 μm is an appropriate range. Especially, the local deep pit depth is close to the minimum value (about 5 μm),
About 20 μm is a condition that V and Ra do not deteriorate so much.
Is preferred.

Next, the etching allowance of acid etching was examined. FIG. 4 shows that an 8-inch wafer is lapped with lapping abrasive grains of # 1200 and then etched with a mixed acid [50% hydrofluoric acid: 70% nitric acid: 99% acetic acid = 1: 2: 1 (volume ratio)]. Average value and TT after etching
The relationship of the value of V is shown. FIG. 5 shows the etching allowance of a chemical etching wafer by general acid etching,
It shows the ratio of occurrence of defects such as stains due to uneven etching called stain. The presence or absence of stain was visually determined under light collection.

As shown in FIG. 5, in order to avoid stain, an acid etching allowance of at least 5 μm is necessary, and in order to surely eliminate stain, an etching allowance of 10 μm or more is required. On the other hand, from FIG. 4, in order to reduce the TTV to 1 μm or less, the etching allowance is appropriately 20 μm or less. Therefore, as a total of these, as an etching allowance for acid etching, 5 to 20 μm is an appropriate range, and particularly preferably about 10 μm.

As described above, the relationship between the etching allowance of the alkali etching and the acid etching and the etching effect has been clarified separately. In the present invention, these relationships are sufficiently identified, and the alkali etching and the acid etching are used together. By the method of performing alkali etching first and then acid etching, the characteristics of the functions of both etchings could be made to fully function and the etching effect could be sufficiently exhibited.

That is, in the case of alkali etching + acid etching, first, the mechanically processed strained layer is removed by alkali etching while maintaining the flatness after lapping, and then acid etching is performed to leave after the alkali etching. It is possible to make local deep pits and sharp irregularities on the surface into a smooth shape, improve the surface roughness, and suppress the stain occurrence rate. At that time, it is necessary to make the etching allowance of the alkali etching larger than the etching allowance of the acid etching. The main reason is to make the local deep pits remaining after the alkali etching shallower. It is necessary to take a large amount, and this value is larger than the etching amount required for acid etching to reduce the stain generation rate and flatness.

Further, in the present invention, it is preferable to carry out acid etching after immersing the wafer in an aqueous solution of hydrogen peroxide after alkali etching the wafer. This is because the surface of the wafer after alkali etching is active and is hydrophobic, so that foreign matter is easily attached to the wafer and stains easily. Therefore,
If the surface is oxidized with a hydrogen peroxide solution to make it hydrophilic, particles are less likely to adhere and the acid etching solution in the next step is not contaminated with particles. Here, the concentration of the hydrogen peroxide solution used is preferably 0.1 to 30%. If it is less than 0.1%, the surface may not be sufficiently hydrophilic, and if it is 30%, it is sufficient, and if it exceeds this, it is economically disadvantageous.

Next, reaction-controlled acid etching will be described. The reaction rate-determining acid etching solution is, for example, a solution in which silicon is dissolved in a mixed acid aqueous solution of hydrofluoric acid, nitric acid, acetic acid, and water at a concentration of 20 to 30 g / L, and exhibits an action relatively close to that of an alkaline etching solution. It is an acid etching solution. The etching solution is a reaction rate-determining acid etching solution because the reaction rate of a mixed acid aqueous solution, which is a normal acid etching solution, is a diffusion rate-controlling acid, whereas the reaction rate is a rate-controlling acid. . When this reaction-controlled acid etching is performed after alkali etching, first, the mechanically processed strained layer is removed by alkali etching while maintaining the flatness after lapping, and then the reaction-controlled acid etching is performed to remove alkali. Local deep pits remaining after etching and sharp irregularities on the surface are made into a smooth shape, surface roughness is improved, and while the stain generation rate is suppressed, waviness is suppressed compared to diffusion controlled acid etching, Further flattening can be achieved.

Alkaline etching of the present invention described above +
According to the two-step chemical etching of acid etching, a semiconductor wafer having a flatness LTVmax of 0.3 μm or less in a cell size of 20 × 20 mm and a maximum pit depth of 6 μm or less can be easily stabilized. It can be manufactured. Furthermore, it is possible to process a semiconductor wafer having excellent flatness even in a large area having an average waviness of 0.04 μm or less.

[0030]

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. (Example 1) The following etching treatment was performed using a lap wafer (lap abrasive grain count: # 1200) having a diameter of 8 inches. First, in the alkaline etching, the etching allowance was set to 20 μm, and the sample was dipped in a 50 wt% NaOH aqueous solution at 85 ° C. for 450 seconds. Next, as a hydrophilic treatment, after soaking in 0.3% hydrogen peroxide water, finally, 50%
Acid etching was performed with a mixed acid consisting of hydrofluoric acid: 70% nitric acid: 99% acetic acid = 1: 2: 1 (volume ratio) with an etching allowance target of 10 µm. After etching, the flatness, surface roughness, pit depth, and waviness were measured to investigate the effect of etching. The results are shown in Table 1.

The actual results for the target of the etching allowance are as follows. Alkaline etching cost; Target: 20 μm, Number of samples: 51
Number, average value: 20.1 μm, average value ± 3σ: 18.1
22.1 μm. Acid etching charge is 10 μm,
There were 107 particles, 9.8 μm, and 8.3 to 11.3 μm. The flatness (TTV, LTV) is measured by a flatness measuring device (U / G9500, U / S96) manufactured by ADE.
00), and for the surface roughness (Ra) measurement, a universal surface shape measuring instrument (SE-3C type) manufactured by Kosaka Laboratory Ltd. was used.

Further, the waviness was measured. The measuring device is
Universal surface profilometer manufactured by Kosaka Laboratory Ltd. (SE-3F
Type) was used. Wafer (diameter 200m
The central portion 60 mm of the surface of m) is traced with a stylus, and only the shape component excluding the fine surface roughness component is measured. Here, the swell (Waviness), as shown in FIG. 6, sets the heights of the measurement start point and the measurement end point to be the origin of the height, and the absolute value Y ₁ of the displacement amount from the origin at intervals of 2 mm. To Y ₂₉ , and the average value Y is defined as the waviness.

[0033]

[Table 1]

Comparative Example 1 First, alkali etching was performed under the same conditions as in Example 1 except that the etching allowance target was 4 μm, and then immediately subjected to acid etching with the etching allowance target being 36 μm. No hydrophilic treatment with hydrogen peroxide solution was performed. The results are also shown in Table 1.

Comparative Example 2 Only 20 .mu.m alkali etching was carried out aiming at the etching margin used in the examples. The results are also shown in Table 1.

As is clear from this table, only with alkali etching (Comparative Example 2), the flatness of the wafer is good, but the surface roughness and especially the depth of the local deep pits become deep, so that acid etching after alkali etching is performed. In the case of (Comparative Example 1), since the acid etching margin is large, on the contrary, the flatness of the wafer is significantly deteriorated. By setting the alkali etching allowance and the acid etching allowance to appropriate values for these (Example 1), the flatness, surface roughness, and local deep pit depth were balanced. Results were obtained. Further, as a result of observing the uneven shape of each surface with a microscope, it was found that Example 1 has an extremely smooth uneven shape as compared with Comparative Example 2, and is at substantially the same level as Comparative Example 1.

Example 2 The following etching treatment was carried out using a lap wafer having an 8 inch diameter (lap abrasive grain count: # 1200). First, in the alkali etching, the etching allowance was set to 20 μm and the concentration of Na was 50% by weight.
It was immersed in an aqueous OH solution at 85 ° C. for 450 seconds. Next, as a hydrophilization treatment, after immersing in 0.3% hydrogen peroxide water, finally, 50% hydrofluoric acid: 70% nitric acid: 99% acetic acid = 1:
Concentration of silicon in mixed acid consisting of 2: 1 (volume ratio) 27.
Reaction-controlled acid etching was carried out with a reaction-controlled acid etching solution dissolved in 5 g / L with an etching allowance of 10 μm. After etching, the flatness, surface roughness, pit depth, and waviness were measured to investigate the effect of etching. The results are also shown in Table 1. The effect of the reaction-controlled acid etching is particularly flat (TTV, LT
Vmax) and undulation are found to be effective.

Example 3 In a lap wafer having a diameter of 8 inches, # 1200 and # 1 were used as lap abrasive grain counts.
Alkaline etching and reaction rate-controlled acid etching were performed under the same conditions as in Example 2 except that 500 was used in combination, and for those that had been etched, flatness, surface roughness, pit depth, and waviness were measured. The effect of etching was investigated, and the results are also shown in Table 1. Again, the effect of the reaction-controlled acid etching is particularly flat (TTV, LT
Vmax) and undulation are clearly effective.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, has substantially the same configuration as the technical idea described in the scope of the claims of the present invention, and has any similar effect to the present invention. It is included in the technical scope of the invention.

For example, an additive such as a surfactant may be added to the alkali etching solution or the acid etching solution in the above embodiment. Specifically, if a nitrite such as NaNO ₂ is added to the alkaline etching solution, the effect of making the pits shallow can be obtained. On the other hand, when a fluorine-based or nonionic surfactant is added to the acid etching solution, the effect of reducing stain can be obtained. Further, as the acid etching solution, a mixed acid aqueous solution consisting of hydrofluoric acid, nitric acid, acetic acid, and water has been exemplified, but hydrofluoric acid, nitric acid, without acetic acid,
Even with an aqueous mixed acid solution containing water, the same effects as those of the present invention can be obtained.

In the above embodiment, the semiconductor wafer has been described by taking the case of semiconductor silicon as an example, but the present invention is not limited to this, and other semiconductor materials such as Ge, GaAs, GaP, The present invention can be similarly applied to a compound semiconductor single crystal such as InP.

[0042]

As described above, according to the present invention,
The flatness of the wafer after lapping can be maintained, the waviness of the wafer surface after etching can be reduced,
It is possible to suppress the occurrence of local deep pits and the deterioration of surface roughness, and it is possible to fabricate a chemical etching wafer that has an etching surface that does not easily cause contamination such as particles and stains, so the stock removal in mirror polishing is reduced. The flatness can be improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the etching allowance of a wafer that has been alkali-etched after lapping and the depth of a local deep pit.

FIG. 2 is a graph showing the relationship between the etching allowance of a wafer that has been alkali-etched after lapping and TTV (flatness).

FIG. 3 is a graph showing a relationship between an etching allowance and a surface roughness (Ra) of a wafer subjected to alkali etching after lapping.

FIG. 4 is a graph showing the relationship between the etching allowance of a wafer subjected to acid etching after lapping and TTV (flatness).

FIG. 5 is a graph showing a relationship between an etching margin due to acid etching and a stain generation rate after lapping.

FIG. 6 is an explanatory diagram showing the definition of waviness on the surface of a wafer.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Seiichi Miyazaki               1393 Yashiro, Osamu, Sarahima-shi, Nagano Naganoden               Child Industry Co., Ltd. (72) Inventor Masahiko Yoshida               1393 Yashiro, Osamu, Sarahima-shi, Nagano Naganoden               Child Industry Co., Ltd. (72) Inventor Hideo Kudo               Odaira, Odakura, Saigo Village, Nishishirakawa-gun, Fukushima Prefecture               No. 150 Shin-Etsu Semiconductor Co., Ltd. Shirakawa               Inside the hall                (56) References Japanese Patent Laid-Open No. 10-92777 (JP, A)                 JP-A-5-291238 (JP, A)                 JP-A-3-1537 (JP, A)

Claims (8)

(57) [Claims] 1. A semiconductor wafer obtained by slicing a single crystal rod is at least chamfered, lapped, etched,
In a semiconductor wafer processing method comprising mirror polishing and washing steps, the etching step is carried out after alkali etching and then acid etching, in which case the etching allowance of the alkali etching is made larger than the etching allowance of the acid etching. The etching allowance is 10 to 30 μm in alkali etching,
The method for processing a semiconductor wafer is characterized in that the acid etching is 5 to 20 μm (excluding about 5 μm). 2. The method of processing a semiconductor wafer according to claim 1, wherein the etching step is performed by immersing in an aqueous solution of hydrogen peroxide after performing alkali etching and then performing acid etching. 3. The etching solution for the alkali etching is a NaOH aqueous solution or a KOH aqueous solution, and the etching solution for the acid etching is a mixed acid aqueous solution containing hydrofluoric acid, nitric acid, acetic acid, and water. The method for processing a semiconductor wafer according to claim 2. 4. The acid etching according to claim 1, wherein the acid etching is reaction-controlled acid etching.
The method for processing a semiconductor wafer according to any one of 1. 5. The etch of the reaction-controlled acid etching
The method for processing a semiconductor wafer according to claim 4, wherein the solution is a solution in which silicon is dissolved in a mixed acid aqueous solution containing hydrofluoric acid, nitric acid, acetic acid, and water at a concentration of 20 to 30 g / L. 6. A semiconductor wafer processed by the method according to any one of claims 1 to 5. 7. A semiconductor wafer chemically etched according to claim 4 , wherein the cell size is 20.
A semiconductor wafer having an LTVmax at × 20 mm of 0.3 μm or less and a maximum pit depth of 6 μm or less. 8. The semiconductor wafer according to claim 7, wherein the average value of the waviness of the semiconductor wafer is 0.04 μm or less.