JP5203845B2 - Grinding method - Google Patents

Description

  The present invention relates to a grinding method for thinning and grinding a wafer such as a semiconductor wafer.

  In the manufacturing process of a semiconductor device, in order to obtain a desired finish thickness of the device, thinning is performed by using a grinding tool at a stage of a semiconductor wafer which is an aggregate of a large number of devices. In order to grind the finished thickness with high accuracy, for example, a contact type (probe or the like) thickness measuring device described in Patent Document 1 below is used to perform grinding while measuring the residual wafer thickness during grinding. In grinding with a grinding tool, the grinding tool formed with a grindstone is rotated and fed by grinding. At that time, the grindstone wears and grinds the wafer while repeating a self-generated blade that exposes new abrasive grains. . For this reason, the amount of movement of the grinding tool and the actual amount of grinding removal do not exactly match, and a difference corresponding to the amount of wear of the grinding tool occurs. Therefore, the amount of movement of the grinding tool is controlled while measuring the residual thickness until the finished thickness is reached.

  On the other hand, wafers tend to be processed even thinner in response to the recent thinning of devices, and the non-contact type that can measure the thickness without bringing a probe into contact with the wafer does not damage the wafer. This is advantageous in that the bending strength is not lowered. Examples of the non-contact type thickness measuring means include those using laser light. In Patent Document 2 below, a laser beam having a predetermined frequency is irradiated toward a wafer, and the thickness is measured from the waveform of an interference wave between a reflected wave from the front surface of the wafer and a reflected wave from the back surface of the wafer. A non-contact thickness measuring instrument is described. A laser-type non-contact thickness measuring instrument that can measure only the thickness of a silicon wafer in the range of 10 to 400 μm with a laser beam having a wavelength of about 1 μm is sold by Disco Co., Ltd. under the trade name “NCG”. .

JP 2001-009716 A Japanese Patent No. 3491337

  However, there are many cases where it is required to reduce the wafer thickness to 10 μm or less due to a request for further ultrathinning. When grinding to a thickness of 10 μm or less, it is important to measure the thickness in a non-contact manner, but the measurement is impossible because the thickness is outside the measuring range of the measuring instrument. In order to make it possible to measure a thickness below the measurement limit thickness of the measuring instrument in this way, for example, it is necessary to equip the measuring instrument with a complicated optical control system and a variable wavelength laser, which is a significant cost. It becomes high.

  The present invention has been made in view of the above-mentioned fact, and the main technical problem is that it is necessary to provide a separate complicated and expensive measuring instrument in the case of further thinning grinding than the measurement limit thickness of the thickness measuring instrument. And providing a new and improved grinding method capable of performing high-precision grinding.

According to the present invention, as a grinding method for achieving the main technical problem, a desired finishing thickness is obtained by rotating a chuck table holding a wafer, rotating a grinding tool, and gradually moving the grinding tool toward the chuck table. The grinding method is to grind the surface to be ground of the wafer with a grinding tool.
While the residual thickness of the wafer held on the chuck table is continuously measured using a non-contact type thickness measuring device, the residual thickness of the measured wafer is the measurement limit of the non-contact type thickness measuring device. A first grinding step of rotating the chuck table and rotating the grinding tool and moving the grinding tool toward the chuck table to grind the surface to be ground of the wafer until a predetermined thickness equal to or greater than the thickness is reached; ,
After the first grinding step, stop the measurement of the non-contact type thickness measuring device, rotate the chuck table and rotate the grinding tool, and further turn the grinding tool toward the chuck table with the predetermined thickness and finish thickness A second grinding step of grinding the surface to be ground of the wafer by moving the amount corresponding to the difference of
The grinding method characterized by including is provided.

Calculating the correlation between the amount of movement of the grinding tool and the measured residual thickness during the first grinding step;
In the second grinding step, it is preferable to determine the amount of movement of the grinding tool based on the calculated correlation.

  In the grinding method of the present invention, a predetermined thickness equal to or greater than the measurement limit thickness of the non-contact type thickness measuring device (the measurement limit thickness or a thickness as close as possible to this is convenient). Until then, the wafer is ground while continuously measuring the residual thickness of the wafer (first grinding step). When the thickness is further reduced from a predetermined thickness, the wafer is ground by appropriately controlling the moving amount of the grinding tool (second grinding step). The amount of grinding from a predetermined thickness to the desired thickness is very small, and the amount of wear of the grinding tool at this time is very small, so that the desired thickness is sufficiently precise without having to continuously measure the residual thickness of the wafer. Can be ground to thickness. Calculate the correlation between the amount of movement of the grinding tool and the measured residual thickness during the first grinding process, in other words, the correlation between the amount of movement of the grinding tool and the grinding amount. If the amount of movement of the grinding tool is controlled based on the calculated correlation, the desired finished thickness can be made even more precisely.

  Hereinafter, a preferred embodiment of a grinding method configured according to the present invention will be described in more detail with reference to the accompanying drawings.

  FIG. 1 shows the main part of a grinding apparatus that can be used for carrying out the grinding method of the present invention, that is, the components relating to the finish grinding means. The entire grinding apparatus may be in the form disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-354962, and therefore detailed description thereof is omitted in this specification. As is well known to those skilled in the art, in thinning a semiconductor wafer, the back surface of the wafer is first roughly ground at a relatively high speed, and then finish ground to a desired finish thickness. The following is related to the finish grinding of the wafer. A preferred embodiment of the present invention will be described.

  The illustrated grinding apparatus includes a chuck table 2 for holding a wafer W to be ground, and finish grinding means 4 for grinding the wafer W held on the chuck table 2. The chuck table 2 that is rotationally driven by an appropriate rotational drive source (not shown) has a porous chuck plate, and the wafer W placed on the upper surface of the chuck table 2 is of a well-known form. Good. The finish grinding means 4 arranged facing the chuck table 2 has a casing 6, and a spindle 8 is rotatably mounted on the casing 6. A rotational drive source 10 for rotating the spindle 8 at high speed is also arranged in the casing 6. The rotational drive source 10 can be composed of a pulse motor. A spindle 8 extending substantially perpendicular to the surface of the chuck table 2 protrudes downward beyond the casing 6, and a grinding tool 12 is attached to the lower end of the spindle 6. The grinding tool 12 includes an annular support member 14 and a plurality of arc-shaped grinding wheels 16 fixed to the lower surface of the support member 14. The casing 6 is mounted so as to be movable up and down by an appropriate grinding feed means 18. The grinding feed means 18 may be of a well-known form including a feed mechanism having a rotating ball screw and a servo motor for rotationally driving the ball screw of the feed mechanism.

  The illustrated wafer W has a circuit layer W1 on which a circuit is formed and a silicon layer W2 laminated on the back surface (upper surface in FIG. 1) of the circuit layer W1, and the front surface (lower surface in FIG. 1) of the circuit layer W1. Is attached with a protective tape T formed of an appropriate synthetic resin tape.

  The illustrated grinding apparatus is further equipped with a non-contact type thickness measuring device 20. The measuring instrument 20 is supported by an appropriate support mechanism (not shown) so as to be opposed to the wafer W held on the chuck table 2. A typical example of the non-contact type thickness measuring instrument 20 is a measuring instrument sold under the trade name “NCG” from DISCO Corporation. Such a measuring instrument projects laser light having a wavelength of approximately 1 μm toward the wafer W, and receives interference waves between reflected light reflected from the upper surface of the silicon layer W2 and reflected light reflected from the lower surface of the silicon layer W2. Thus, the thickness of the silicon layer W2 is measured. The nominal measurable range is 10 to 400 μm. The measuring device 20 measures the thickness of the silicon layer W2. Therefore, the wafer W thickness is a value obtained by adding the known thickness of the circuit layer W1 to the measured value of the measuring device 20. The illustrated grinding apparatus is further provided with a calculation means 22 and a control means 24 in association with the non-contact type thickness measuring device 20 and the grinding feed means 18. The calculation means 22 and the control means 24 will be further described later.

  FIG. 2 is a schematic flowchart showing an example of processing control of the grinding operation executed by the control means 24. A predetermined thickness H1 equal to or greater than the measurement limit thickness of the non-contact type thickness measuring device 20 and a desired wafer finish thickness H2 are set in advance for each wafer to be processed. The predetermined thickness H1 is a predetermined thickness that is equal to or greater than the measurement limit thickness of the non-contact type thickness measuring instrument 20, and is a measurement limit thickness or a thickness as close as possible to this. Convenient. Depending on the type of wafer, there may be some error in the measurement thickness when measuring the measurement limit thickness of the non-contact type thickness measuring instrument 20, and in this case, the measurement limit thickness A value that can be stably measured for the above thickness is defined as a predetermined thickness.

  Before starting the grinding operation, the wafer W to be ground is set on the chuck table 2, and then the grinding tool 12 and the chuck table 2 are started to rotate at a predetermined number of revolutions. It is positioned above. When the grinding operation is started, in step S1 of FIG. 2, the pulse motor of the grinding feed means 18 is driven to lower the grinding tool 12 toward the wafer W on the chuck table 2 at a predetermined feed speed. Next, the process proceeds to step S2, and while the lowering of the grinding tool 12 is proceeding at a predetermined feed rate, it is confirmed whether or not the working surface of the grinding tool 12 has contacted the processing surface of the wafer W, and the contact is made. If it confirms, it will progress to step S3 and a grinding operation will be started. Whether or not the working surface of the grinding tool 12 has come into contact with the processing surface of the wafer W can be confirmed, for example, by detecting a minute change in stress acting on the spindle 8.

  In step S4, the measurement of the residual thickness H by the non-contact type thickness measuring device 20 is started. The residual thickness H of the wafer W in the non-contact thickness measuring instrument 20 after the start of the grinding operation in step S3 is sent to the computing means 22 together with the descending amount of the grinding tool 12, that is, the moving amount. When the grinding operation proceeds and it is confirmed in step S5 that the residual wafer thickness H has reached the predetermined thickness H1 of the non-contact thickness measuring instrument 20, the process proceeds to step S6 and the non-contact thickness is reached. Measurement of the measuring instrument 20 is stopped.

  At the same time as the measurement by the non-contact type thickness measuring device 20 is stopped, the process proceeds to step S7, where the calculating means 22 correlates the wafer residual thickness H with the movement amount L of the grinding tool 12 and the grinding tool in the second grinding step. 12 movement amounts are calculated (from step 1 to step 7 is the first grinding step).

Here, the calculation process of the calculation means 22 will be described. When the grinding operation in step S3 is started, measurement of the residual thickness H of the wafer W is started in the non-contact type thickness measuring instrument 20, and information on the residual thickness H of the wafer is sent to the computing means 22 (step S4). The residual wafer thickness H is recorded in the calculation means 22 together with information on the movement amount L of the grinding tool 12 from the start of the grinding operation in step S3. Based on the information on the movement amount L1 of the grinding tool 12 when the residual wafer thickness H reaches the predetermined thickness H1 of the non-contact type thickness measuring device 20, the grinding thickness (H0-H1) and the movement amount are calculated. A correlation function is calculated (see FIG. 3). When the original thickness of the wafer W is H0 and the movement amount of the grinding tool 12 up to the desired finished wafer thickness H2 is L2, the following correlation formula A is obtained.
(H1-H0) / L1 = (H2-H1) / (L2-L1)... A
In step S7, the movement amount of the grinding tool 12 from the correlation equation A to the predetermined thickness H1 of the non-contact type thickness measuring device 20 from the predetermined thickness H2, that is, the grinding tool 12 in the second grinding step. The movement amount L2-L1 (μm) is calculated simultaneously.

  In steps S7 and S8, the pulse motor of the grinding feed means 18 is controlled so as to perform grinding according to the movement amount of the grinding tool 12 calculated in step S7 (second grinding step). That is, the grinding operation is further performed at a predetermined feed speed, and after the grinding tool 12 is lowered by L2-L1 (μm), the grinding feed by the grinding feed means 18, that is, the lowering of the grinding tool 12 is stopped (second grinding). Process). Thus, the correlation between the amount of movement of the grinding tool and the measured residual thickness during the first grinding step, in other words, the correlation between the amount of movement of the grinding tool and the amount of grinding is calculated, and the second In the grinding process, if the movement amount of the grinding tool is controlled based on the calculated correlation, the desired finished thickness can be made even more precisely.

  The mode of controlling the movement amount of the grinding tool 12 in the second grinding step based on the correlation between the residual wafer thickness H and the movement amount L of the grinding tool 12 is a predetermined thickness of the non-contact type thickness measuring device 20. When the grinding amount from the height H1 to the desired finish thickness H2 is relatively large, the wear amount of the grinding tool 12 is relatively large, which is particularly effective. On the other hand, when the amount of grinding from the predetermined thickness H1 to the desired finished thickness H2 is small, the amount of wear of the grinding tool at this time is extremely small, and hence the wafer residual thickness H and the amount of movement of the grinding tool 12 are reduced. The wafer W can be ground to a sufficiently precise desired thickness simply by controlling the descending amount of the grinding tool 12 to (H1−H2) μm.

The principal part schematic of the typical example of the grinding apparatus for enforcing the grinding method of this invention. The schematic flowchart which shows the process control example of grinding operation. The conceptual diagram showing the correlation with the wafer residual thickness H and the movement amount L of the grinding tool 12. FIG.

Explanation of symbols

2 Chuck table 4 Grinding means 12 Grinding tool 18 Grinding feed means 20 Non-contact type thickness measuring instrument 22 Calculation means 24 Control means H Residual thickness of semiconductor wafer H1 Predetermined thickness of non-contact type thickness measuring instrument H2 desired Finished wafer thickness L1 Amount of movement of the grinding tool 12 to a predetermined thickness H1 L2 Amount of movement of the grinding tool 12 to a desired finished wafer thickness H2 W Semiconductor wafer W1 Silicon layer W2 Circuit layer

Claims (2)

Grinding by rotating the chuck table holding the wafer and rotating the grinding tool and gradually moving the grinding tool toward the chuck table to grind the surface to be ground of the wafer by the grinding tool to a desired finished thickness In the way
While the residual thickness of the wafer held on the chuck table is continuously measured by using a non-contact type thickness measuring device, the residual thickness of the wafer to be measured is measured by the non-contact type thickness measuring device. The chuck table is rotated and the grinding tool is rotated and the grinding tool is moved toward the chuck table until a predetermined thickness equal to or greater than a measurement limit thickness of A first grinding step of grinding
After the first grinding step, the measurement of the non-contact type thickness measuring device is stopped, the chuck table is rotated and the grinding tool is rotated, and the grinding tool is further predetermined toward the chuck table. A second grinding step of grinding the surface to be ground of the wafer by moving an amount corresponding to the difference between the thickness and the finished thickness;
A grinding method comprising: Calculating a correlation between the amount of movement of the grinding tool and the measured residual thickness during the first grinding step;
The grinding method according to claim 1, wherein in the second grinding step, the amount of movement of the grinding tool is determined based on the calculated correlation.

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