JP4429995B2 - Manufacturing method of semiconductor wafer - Google Patents

Description

  The present invention relates to a method for manufacturing a semiconductor wafer, and more particularly to a method for adjusting grinding conditions in a grinding process based on a measured value of nanotopography of a wafer surface after the grinding process.

In semiconductor silicon substrate wafers (hereinafter referred to as wafers), the size of the surface waviness component called “nanotopography” has recently become a problem. This nanotopography is obtained by extracting the wavelength component of λ = 0.2 to 20 mm from the surface shape of the wafer, which has a shorter wavelength than “sledge” or “Warp” and a longer wavelength than “surface roughness”. The PV value is a very shallow wave of 0.1 to 0.2 μm or less.
Nanotopography is generally measured by an “optical interference type” measuring device (trade name: Nanomapper (ADE Corp.) or Dynasearch (Raytex Co., Ltd.)). FIG. 10 shows an example of measurement. FIG. 10 (a) is a nanotopography map, and the intensity of nanotopography is qualitatively expressed by the shading. On the other hand, Fig. 10 (b) shows the shape and quantitative intensity of nanotopography on four cross sections (diameters) measured every 45 °. The peaks and valleys in the graph correspond to the shading of the nanotopography map. . FIG. 11 schematically illustrates the correspondence between the nanotopography map and the nanotopography cross-sectional shape.

  This nanotopography is said to affect the yield of STI (Shallow Trench Isolation) process in device manufacturing. Nanotopography is created during the wafer processing process (slicing to polishing) and is strongly influenced by grinding, particularly double-headed grinding.

  An outline of double-head grinding is schematically shown in FIG. As shown in FIG. 12 (a), the raw wafer W (slice wafer) has a gap h between the static pressure pad and the wafer between the static pressure pads 11 and 21, which are the two left and right holding plates. Retained. As shown in FIG. 12 (c), the static pressure pad has lands 13 (bank portions) and pockets 14 (concave portions) on the surface thereof. As shown in FIG. 12 (d), hydrostatic water is supplied to the pocket 14, thereby holding the wafer W rotatably. As shown in FIG. 12 (c), a part of the hydrostatic pad is cut out, and the grinding stones 12 and 22 are inserted therein, and the wafer W and the grinding stones 12 and 22 are inserted as shown in FIG. 12 (b). The wafer W is rotated to grind the wafer W from both the left and right sides simultaneously. During grinding, the wafer W rotates at several tens of rpm, for example, by driving a driving roller against an edge portion or by hooking a notch portion.

  During this double-headed grinding, warped wafers may be warped due to unbalanced cutting loads on both sides of the wafer, and a double-headed grinding method that adjusts the relative position of the wafer and the grindstone to suppress this warpage. It has been proposed (for example, see Patent Document 1). A specific example of the method for adjusting the positional relationship between the wafer W and the grindstones 12 and 22 is shown in FIG. One is called “shift adjustment” and is an adjustment for moving the grindstones 12 and 22 in a direction perpendicular to the wafer surface (FIG. 13A), and the other is called “tilt adjustment”. This adjustment is to change the relative angle between the surface and the grindstones 12 and 22 (FIG. 13B).

  However, adjusting the positional relationship between the wafer and the grinding wheel based on the data obtained by measuring the ground wafer with a commercially available nanotopography measuring machine requires the experience and intuition of skilled workers. However, there is a problem that a long adjustment time and a large number of adjustment dummy wafers are consumed when the grinding apparatus is started up or the setup is changed.

International Publication No. 00/67950 Pamphlet

  The present invention has been made in view of such problems, and provides a method for manufacturing a semiconductor wafer, which allows an unskilled worker to easily and reliably adjust grinding conditions during a semiconductor wafer grinding process. It is intended to do.

  The present invention has been made in order to solve the above-described problem, and is a method for manufacturing a semiconductor wafer, which includes at least a grinding process for grinding a raw material wafer, and nanotopography of the wafer surface ground by the grinding process The average component is obtained by averaging the nanotopography measurement values on a plurality of diameters or radii of the wafer surface, and the residual component is obtained by subtracting the average component from the nanotopography measurement value before the averaging. A method for manufacturing a semiconductor wafer is provided, wherein the grinding condition of the grinding step is adjusted based on the average value component and the residual component.

  Thus, based on nanotopography data separated into an average value component and a residual component, even an unskilled worker spends a lot of adjustment time and adjustment dummy wafers on adjustment of grinding conditions This can be done easily and reliably without any problems.

  In this case, it is preferable that the grinding step is a double-headed grinding step.

  Nanotopography is created during the wafer processing process (slicing to polishing), and is particularly affected by double-headed grinding. By adjusting the double-headed grinding process according to the present invention, the nanotopography of the wafer is further improved. be able to.

  The nanotopography measurement values on a plurality of diameters or radii of the wafer surface are preferably nanotopography measurement values on four diameters or radii of the wafer surface or on eight diameters or radii. Item 3).

  As described above, if the nanotopography measurement values on the four diameters or radii on the wafer surface or on the eight diameters or radii are used, the grinding conditions can be adjusted easily and accurately.

  Further, the adjustment of the grinding conditions in the grinding step is preferably performed by shift adjustment for moving the grindstone in a direction perpendicular to the wafer surface and / or tilt adjustment for changing the relative angle between the wafer surface and the grindstone. 4).

  If the grinding conditions are adjusted by shift adjustment and / or tilt adjustment in this way, they have a great influence on nanotopography, the wafer can be ground under appropriate conditions, and the nanotopography of the wafer can be improved. .

  As described above, according to the present invention, the nanotopography measurement value of a wafer after grinding is separated into an average value component and a residual component, so that the apparatus adjustment of the grinding process based on these can be accurately performed. As a result, even an unskilled worker can greatly reduce the adjustment time and the number of dummy wafers for adjustment, and the nanotopography of the wafer can be easily improved.

Hereinafter, although this invention is demonstrated in detail, this invention is not limited to these.
As a result of intensive studies to solve the above problems, the present inventors have separated the nanotopography measurement value of the processed wafer into an average value component and a residual component, and fed back this to the wafer processing conditions. Thus, the inventors have conceived that nanotopography can be easily improved and completed the present invention.

  That is, the semiconductor wafer manufacturing method of the present invention includes at least a grinding process for grinding a raw wafer, measures nanotopography of the wafer surface ground by the grinding process, and has a plurality of diameters or radii on the wafer surface. An average value component is obtained by averaging the nanotopography measurement values, and a residual component is obtained by subtracting the average value component from the nanotopography measurement value before the averaging, and based on the average value component and the residual component This adjusts the grinding conditions in the grinding process.

  In this case, the nanotopography is created during the wafer processing process (slicing to polishing), and the influence of double-head grinding is particularly strong. Therefore, by adjusting the double-head grinding process according to the present invention, the nanotopography of the wafer can be adjusted. It can be improved further.

  An example of the method for separating the nanotopography measurement value into the average value component and the residual component as described above will be described with reference to the flowchart of FIG.

  First, a wafer that has been ground by the grinding process is prepared, the nanotopography of the wafer surface is measured with a measuring machine, and the obtained numerical data is input directly or via a recording medium into a calculation program. (FIG. 1 (a)).

  The nanotopography measuring machine is not particularly limited, and for example, Nanomapper (ADE Corp.) or Dynasearch (Ratex Co., Ltd.) can be used. These devices are optical and measure nanotopography using wafer surface reflections. Nanomapper uses a Michelson interferometer, and the in-plane data of the silicon wafer captured by this interferometer is subjected to processing such as noise removal, then the window size determined by the setting is moved within the wafer plane, By replacing the PV value (maximum value-minimum value) in the window with the center value of the window, the data becomes nanotopography data.

  A nanotopography measurement value on four diameters on the wafer surface, that is, a nanotopography measurement value on eight radii is obtained by the arithmetic program (FIG. 1B).

  Next, the nanotopography measurement values on the eight radii obtained in FIG. 1 (b) are averaged at eight points in each radial position as shown in Table 1 below to obtain an “average value component”. (See FIG. 14 for radial position). Alternatively, the average value component in the radial direction may be folded back in the opposite direction to form a waveform symmetrical to the wafer center point (FIG. 1 (c)).

Next, as shown in Table 1 below, the average value component obtained in FIG. 1 (c) is obtained at each position in the radial direction from the nanotopography measurement values on the eight radii obtained in FIG. 1 (b). Subtract 8 points to obtain the “residual component” (FIG. 1 (d)).

  In this manner, the nanotopography measurement value can be separated into an average value component and a residual component, but the number of diameters or radii at which the nanotopography measurement values are averaged is not particularly limited. Alternatively, it may be 8 diameters or radii.

The average value component and residual component of the nanotopography measurement values separated by the above method are shown in FIG.
Here, the average value component corresponds to the surface waviness component formed in a ring shape on the wafer surface, that is, it can be said to be a ring-shaped component or a point-symmetric component, and the residual component is a ring-shaped component from a nanotopography measurement value. It can be said that it is a variation component in the excluded wafer surface.

  And it turned out that this ring-shaped component and the dispersion | variation component in a wafer surface are each independent. For example, as in Example 1 and Example 2 in FIG. 3, the variation component (residual component) may be small, but the ring-shaped component (average value component) may be greatly different. Conversely, as in Example 1 and Example 3 in FIG. 3, there are cases where the variation components are greatly different and the ring components are both small. Therefore, it can be seen that these have different causes, and the grinding conditions cannot be improved only from the entire nanotopography.

  Further, it has been found that the ring-shaped component (average value component) can be divided into a double-headed chin, an uneven central portion, an intermediate ring, an outermost ring, and the like depending on the distance from the wafer center, as shown in FIG. In these cases, the cause is not necessarily the same. For example, just because the double-headed thigh is small, the intermediate ring or the like is not necessarily good. Therefore, it is necessary to finely adjust the grinding conditions.

As a result of investigations by the inventors based on this knowledge, the reason why these ring-shaped components (average value components) and in-plane variation components (residual components) are generated is considered as shown in Table 2 below. I found out that

  Therefore, after separating the nanotopography measurement value into an average value component (ring-shaped component) and a residual component (variation component) and ascertaining the component to be improved, grinding conditions according to the component as shown in Table 2 By adjusting this, the nanotopography of the wafer can be improved reliably.

  As shown in Table 2, there are various methods for adjusting the grinding conditions based on the average value component (ring-shaped component) and residual component (variation component) of the nanotopography measurement values, and the grinding wheel is perpendicular to the wafer surface. Shift adjustment that translates the wafer, tilt adjustment that changes the relative angle between the wafer surface and the grindstone, selection of the optimum grindstone (grinding stone characteristics), selection of the static pressure pad of the optimum land pattern, adjustment of the axis deviation of the left and right grindstones If necessary, these can be used alone or in combination to adjust the grinding conditions. Here, shift adjustment and tilt adjustment will be described as an example.

  FIG. 4 shows an example in which the grinding conditions are adjusted by shift adjustment. The ring-shaped component was obtained from the nanotopography measurement value of the wafer measured before the shift adjustment and is shown in the upper part of FIG. Next, each of the shift adjustments was performed as shown in the middle part of FIG. 4, and the ring-shaped component of the nanotopography measurement value of the wafer measured after the shift adjustment is shown in the lower part of FIG. It can be seen that the orientation and size of the nanotopography of the “central unevenness” and “outermost ring” has changed due to the shift adjustment.

  FIGS. 5 and 6 show examples in which the grinding conditions are adjusted by tilt adjustment. As shown in FIG. 5, the ring-shaped component of the nanotopography measurement value of the wafer measured before and after tilt adjustment after tilt adjustment in the vertical and horizontal directions from the neutral position is shown in FIG. It can be seen that the orientation of the nanotopography of the “outermost ring” is changed by the tilt adjustment. As described above, the specific nanotopography component can be changed by performing the shift adjustment and the tilt adjustment.

An example in which adjustment is performed by obtaining a relational expression between a ring-shaped component of a nanotopography measurement value, a shift adjustment value, and a tilt adjustment value will be described below. As described above, the nanotopography measurement value of the wafer after the grinding process is separated into an average value component (ring-shaped component) and a residual component (variation component), and from the ring-shaped component, “amount of unevenness C _{0 at the} center” and “ Read the unevenness E ₀ ”of the outermost ring part (see FIG. 16). The tilt adjustment amount for making the nanotopography after the grinding process as close to zero as possible is ΔX, and the shift adjustment amount is ΔY. The relationship between C ₀ , E ₀ and ΔX, ΔY in an apparatus used for grinding in advance is obtained by experiment to obtain graphs as shown in FIGS. 7 (a) and 7 (b).

The slope of each regression line is obtained from the graph of FIG. 7 as follows.
Proportional coefficient of “vertical tilt adjustment amount ΔX” and “concavo-convex amount C _{0 at the} center”: −0.0200
Proportional coefficient of “vertical tilt adjustment amount ΔX” and “unevenness amount E ₀ of outermost ring portion”: −0.0161
Proportional coefficient of “shift adjustment amount ΔY” and “concavo-convex amount C _{0 at the} center”: −0.0190
Proportional coefficient of “shift adjustment amount ΔY” and “unevenness amount E ₀ of outermost ring portion”: −0.0087

The proportional coefficient is the amount of change in the unevenness with respect to the vertical tilt adjustment amount or the shift adjustment amount. That is, the following simultaneous equations (1a) are utilized by utilizing the fact that the effects on the unevenness change amounts ΔC ₀ and ΔE _{0 of} the wafer central portion and the outermost ring portion are different between the vertical tilt adjustment amount ΔX and the shift adjustment amount ΔY. And solve (1b). Here, it is assumed that ΔX and ΔY have independent effects on the unevenness variation amounts ΔC ₀ and ΔE ₀ .
ΔC ₀ = −0.0200 ΔX −0.0190 ΔY Equation (1a)
ΔE ₀ = −0.0161 ΔX −0.0087 ΔY Equation (1b)

The simultaneous equations (1a) and (1b) are solved to obtain the following equations (2a) and (2b).

ΔX = (0.0087 ΔC ₀ − 0.0190 ΔE ₀ ) / 1.319 × 10 ⁻⁴ (2a)
ΔY = (−0.0161 ΔC ₀ + 0.0200 ΔE ₀ ) / 1.319 × 10 ⁻⁴ formula (2b)

When the unevenness amounts obtained by measurement are C ₀ and E ₀ , the target unevenness change amounts ΔC ₀ and ΔE ₀ in order to make them zero are −C ₀ and −E ₀ , respectively. Therefore, the following formulas (3a) and (3b) can be derived from the above formulas (2a) and (2b).
ΔX = (−0.0087 C ₀ + 0.0190 E ₀ ) / 1.319 × 10 ⁻⁴ formula (3a)
ΔY = (0.0161 C ₀ − 0.0200 E ₀ ) / 1.319 × 10 ⁻⁴ (3b)

By inputting C ₀ and E ₀ into the above relational expression, ΔX and ΔY can be calculated as shown in the following Table 3 (partially extracted).

そして、上記表に基づいてΔX、ΔYだけチルト調整、シフト調整を手動、ないしはモータ駆動によって自動的に行うことで、非熟練作業員でもナノトポグラフィの改善を的確かつ容易に行うことができる。

Then, by performing tilt adjustment and shift adjustment by ΔX and ΔY automatically or manually by motor drive based on the above table, even non-skilled workers can improve nanotopography accurately and easily.

  Furthermore, as an example of adjusting the grinding conditions, replacement of the grindstone will be described. FIG. 15 shows an example in which the grinding conditions are adjusted by exchanging the grindstone. The variation component was obtained from the nanotopography measurement value of the wafer measured before exchanging the grindstone, and is shown in the upper part of FIG. Next, the whetstone was replaced with a φ3.6 mm small chip whetstone with optimized bonding from a φ6.0 mm large chip whetstone, and the variation component of the wafer nanotopography measurement values measured after the whetstone replacement is shown in the lower part of FIG. Indicated. It can be seen that the nanotopography of the variation component is changed by exchanging the grindstone.

  Moreover, if it is a semiconductor wafer obtained by the said manufacturing method, the nanotopography will be favorable and it can be set as the high quality semiconductor wafer with the good yield of the STI process in device manufacture.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. .
(Example)
A single crystal silicon wafer having a diameter of 300 mm manufactured by the CZ method was used as a sample wafer. The nanotopography of the wafer after the double-sided grinding process is measured with the optical measurement device Nanomapper. As shown in Fig. 8 (a), the nanotopography measurement values on the four diameters of the wafer surface are the average value component and the remaining value. Separated into difference components. Based on the data thus obtained, the left and right grindstones of the double-head grinding apparatus were exchanged, and the grindstone was further subjected to shift adjustment and tilt adjustment as shown in FIG. For the wafer that has been double-ended using the adjusted double-ended grinding machine, nanotopography is measured with Nanomapper in the same way as before adjustment. As shown in FIG. 8 (b), nanotopography on the four diameters of the wafer surface is measured. The measured value was separated into an average value component and a residual component. As can be seen from the figure, after adjustment, the nanotopography map is no longer shaded, and both the average value component and the residual component are improved.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
For example, nanotopography measurement may be performed by a capacitance type measuring machine or a laser type sensor in addition to the optical interference type measuring machine. Moreover, the wafer manufactured by this invention is not restricted to a semiconductor silicon wafer, A compound semiconductor wafer may be sufficient.

It is a flowchart which shows an example of the method of isolate | separating a nanotopography measurement value into an average value component and a residual component. It is the graph which isolate | separated the nanotopography measurement value into the average value component and the residual component. This is data indicating that the ring-shaped component of the nanotopography measurement value and the in-plane variation component are independent components. It is a graph which shows the change of the average value component of nanotopography at the time of performing shift adjustment. It is a schematic diagram which shows the adjustment method of tilt adjustment. It is a graph which shows the change of the average value component of nanotopography at the time of performing the tilt adjustment of FIG. (a) is a graph showing the relationship between the nanotopography values C ₀ and E ₀ and the tilt adjustment amount ΔX, and (b) is a graph showing the relationship between the nanotopography values C ₀ and E ₀ and the shift adjustment amount ΔY. (a) is the nanotopography data of the wafer before the shift adjustment, the tilt adjustment, etc., and (b) is the nanotopography data after the adjustment. It is the schematic which shows the shift adjustment and the tilt adjustment in an Example. (a) is a nanotopography map that qualitatively expresses the intensity of nanotopography in light and shade, and (b) shows the shape and quantitative intensity of nanotopography on four cross sections (diameters) measured every 45 °. It is a graph. It is the schematic explaining the correspondence of a nanotopography map and nanotopography cross-sectional shape. (a) is a schematic diagram of double-head grinding, (b) is a schematic diagram showing the rotation direction of the wafer and the grindstone, (c) is a photograph showing the land pattern of the hydrostatic pad, and (d) is a static diagram. It is sectional drawing of a pressure pad. (a) is a schematic diagram for explaining the shift adjustment, and (b) is a schematic diagram for explaining the tilt adjustment. It is the schematic which shows the position of a radial direction in the case of using the nanotopography measurement value on eight radiuses of a wafer surface. It is a graph which shows the change of the dispersion | variation component of nanotopography at the time of exchanging a grindstone. In the graph of the mean components of the nanotopography measurement values, indicating the irregularity C ₀ and irregularity E ₀ of the outermost ring of the wafer center.

Explanation of symbols

11 ... Left static pressure pad, 21 ... Right static pressure pad, 12 ... Left grindstone, 22 ... Right grindstone,
13 ... Land, 14 ... Pocket, h ... Gap between static pressure pad and wafer,
W: Wafer, C ₀ ... Unevenness at the center of the wafer surface,
E ₀ ... The amount of irregularities in the outermost ring portion on the wafer surface.

Claims (4)

  A method for manufacturing a semiconductor wafer, comprising at least a grinding step of grinding a raw material wafer, measuring nanotopography of the wafer surface ground by the grinding step, and measuring nanometers on a plurality of diameters or radii of the wafer surface An average value component is obtained by averaging the topography measurement values, a residual component is obtained by subtracting the average value component from the nanotopography measurement value before the averaging, and the grinding step based on the average value component and the residual component A method for producing a semiconductor wafer, characterized by adjusting the grinding conditions.   The method for manufacturing a semiconductor wafer according to claim 1, wherein the grinding step is a double-headed grinding step.   The nanotopography measurement on a plurality of diameters or radii of the wafer surface is a nanotopography measurement on four diameters or radii of the wafer surface or on eight diameters or radii. A method for producing a semiconductor wafer according to claim 1.   2. The grinding condition in the grinding step is adjusted by shift adjustment for moving the grindstone in a direction perpendicular to the wafer surface and / or tilt adjustment for changing the relative angle between the wafer surface and the grindstone. The manufacturing method of the semiconductor wafer of any one of thru | or 3 thru | or 3.

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