JP2014175421A - Gettering semiconductor wafer and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an effective gettering layer without damaging a semiconductor wafer even in the case where the semiconductor wafer is thinned.SOLUTION: A semiconductor wafer includes an oxide layer on its one-side surface. The surface of the semiconductor wafer is irradiated with pulse laser light and consecutive layer light for performing thermal assist, and the semiconductor wafer is molten to the inner layer thereof. In a fast temperature-raising/cooling process in the semiconductor wafer, oxygen is dispersed from the oxide layer to a melting area in the melting step, a high concentration area of oxygen exceeding a solid solution limit concentration is formed in the inner layer in a solidifying step, and a gettering layer is formed for capturing a metal in the semiconductor wafer by means of a crystal defect caused by the high concentration area. Thus, an effective gettering layer can be formed without damaging the semiconductor wafer, and the semiconductor wafer including the gettering layer can be improved in characteristics by improving a flexural strength and capturing metal impurities.

Description

  The present invention relates to a method for manufacturing a gettering semiconductor wafer in which a gettering layer for preventing contamination of metal impurities is formed on a semiconductor wafer by a low temperature process.

Gettering technology (see Non-Patent Document 1) that brings about a gettering effect on a semiconductor wafer is classified into intrinsic gettering (hereinafter referred to as IG) technology and extrinsic gettering (hereinafter referred to as EG) technology. The former has a gettering effect by agglomerating and precipitating oxygen originally contained in a silicon wafer by high-temperature heat treatment to create a defect in the silicon wafer and to form a strain field around it. The latter gives a gettering effect by applying a strain field or chemical action from the outside of the silicon wafer.
Among the EG techniques, there is a laser irradiation method, which uses laser-induced defects as a gettering source. For example, an ultrashort pulse laser (see Patent Document 1), a near-infrared laser (see Patent Document 2), a KrF excimer laser (see Non-Patent Document 1), a Q-switched Nd: YAG laser (see Non-Patent Documents 2 and 3) Attempts have been made to induce a crushing layer (crystal defects) near the surface layer of a Si wafer, trapping (gettering), and removing metal impurities, using as a light source.
Specifically, in Patent Document 1, an ultrashort pulse laser (pulse width: 1.0E-15 to 1.0E-8 sec; wavelength 300 to 1200 nm) is irradiated to getter to a depth of about several tens of μm. Laser gettering techniques for creating layers (including amorphous layers) have been proposed.
Patent Document 2 proposes a laser gettering technique in which a near-infrared laser is irradiated to form a fractured layer having a thickness of less than 1 μm at a certain depth of a silicon wafer having a thickness of less than 100 μm.
Regarding extrinsic gettering (EG) technology, non-patent document 1 introduces gettering technology using KrF excimer laser, and non-patent document 2 and non-patent document 3 describe gettering technology using a Q-switched Nd: YAG laser. It has been introduced.

  According to the technology roadmap for 3D SiP (System in a Package) (Semiconductor Technology of Japan: STRJ), the thickness of silicon wafers is expected to be about 10 μm in recent years. It is necessary to newly form a gettering layer on the back surface so as not to cause thermal damage to the device structure on the surface layer. Therefore, the EG method capable of low-temperature processes has already become mainstream as a gettering technique.

JP 2010-283220 A JP 2007-165706 A

(1) Semiconductor World, January 1987, p. 88-95, “Crystal Defects and Gettering Technology of Ultra LSI Wafers” (2) Y. Hayafuji, T .; Yanada, and Y.J. Aoki: JOUNAL OF THE ELECTROCHEMICAL SOCIETY 128 (1981) p. 1975, “Laser Diameter Getting and Its Application to Lifetime Improvement in Silicon” (3) C.I. W. Pearce and V.M. J. et al. Zaleckas: JOUNAL OF THE ELECTROCHEMICAL SOCIETY 126, No. 8 (1979) p. 1436, “A New Approach to Lattice Damage Gettering”

  In the EG method capable of low temperature processing in the gettering layer forming technology of the three-dimensional structure SiP, the surface side is used as a surface on which the device structure is provided, the back side is ground and thinned, and then laser light irradiation is performed. Yes. However, when the thickness of the silicon wafer is as thin as 10 μm, there is a problem that it is easily broken due to damage applied during grinding.

  The present invention has been made against the background of the above circumstances, and an effective gettering layer can be formed on the back surface of the semiconductor without causing thermal damage to the device structure on the surface of the semiconductor wafer during the gettering process. It is an object of the present invention to provide a semiconductor wafer and a method of manufacturing the same that are less likely to be cracked even when the wafer is thinned.

  That is, among the methods for manufacturing a gettering semiconductor wafer according to the present invention, the first aspect of the present invention is a continuous laser beam that performs thermal assist with a pulse laser beam on the surface of a semiconductor wafer having an oxide layer on one surface. And the inner layer of the semiconductor wafer is melted to the inner layer of the semiconductor wafer, oxygen is diffused from the oxide layer to the molten region in the melting process in the high temperature heating / cooling process of the semiconductor wafer, and the inner layer is solidified A high concentration region of oxygen exceeding a solid solution limit concentration is formed, and a gettering layer that captures metal in the semiconductor wafer by crystal defects caused by the high concentration region is formed.

  The method for producing a gettering semiconductor wafer according to a second aspect of the present invention is the method according to the first aspect, wherein the pulse laser beam is a green pulse laser beam having a wavelength of 510 to 540 nm, and the continuous laser beam is a wavelength of 780 to 830 nm. It is characterized by being a diode laser beam.

  According to a third aspect of the present invention, there is provided a method for producing a gettering semiconductor wafer, wherein the pulse width of the pulse laser beam is 500 ns or less in the first or second aspect of the present invention.

  A method for producing a gettering semiconductor wafer according to a fourth aspect of the present invention is characterized in that, in any one of the first to third aspects of the present invention, the assist temperature of the continuous laser beam is 200 ° C. or lower.

  The method for producing a gettering semiconductor wafer according to a fifth aspect of the present invention is characterized in that, in any of the first to fourth aspects of the present invention, the melting depth is 1 to 5 μm.

According to a sixth aspect of the present invention, there is provided a method for producing a gettering semiconductor wafer, wherein the semiconductor wafer is a silicon wafer, and the oxide layer is a SiO ₂ film or a SiON film. It consists of one or both.

  According to a seventh aspect of the present invention, there is provided a method for producing a gettering semiconductor wafer according to any one of the first to sixth aspects of the present invention, wherein the optical thickness of the oxide layer is equal to the wavelength of the pulse laser beam during the irradiation. It is characterized by being 1/4 or less.

In the method for producing a gettering semiconductor wafer according to the eighth aspect of the present invention, in any one of the first to seventh aspects, the total amount of oxygen diffused in the melting region is lower than 1.0E + 15 / cm ^2. It is characterized by suppressing.

  A method for manufacturing a gettering semiconductor wafer according to a ninth aspect of the present invention is characterized in that in any one of the first to eighth aspects of the present invention, a device structure is provided on the other surface side.

  The gettering semiconductor wafer of the tenth aspect of the present invention has a high concentration region of oxygen exceeding the solid solution limit concentration at a depth of 1 to 4 μm on one surface side, and a concentration at which oxygen decreases near the liquid phase / solid phase interface. There is a low concentration region of oxygen below the solid solution limit concentration that reaches the other side through the gradient region, and there is a crystal defect in the region from the high concentration region to the concentration gradient region, and the crystal defect exists A gettering layer for capturing metal in the semiconductor wafer is provided in the region to be processed.

The gettering semiconductor wafer of the eleventh aspect of the present invention is characterized in that, in the tenth aspect of the present invention, the total amount of oxygen diffused into the melted region is suppressed to be lower than 1.0E + 15 / cm ^2. .

  A gettering semiconductor wafer according to a twelfth aspect of the present invention is characterized in that, in the tenth or eleventh aspect of the present invention, the thickness is 30 μm or less.

  A gettering semiconductor wafer according to a thirteenth aspect of the present invention is characterized in that, in any of the tenth to twelfth aspects of the present invention, the gettering semiconductor wafer has a device structure on the other surface side.

Below, the effect | action and limitation reason in this invention are demonstrated.
In the present invention, the semiconductor wafer is irradiated with pulsed laser light while receiving the assist heating by the continuous laser light, so that the semiconductor wafer is melted to a sufficient depth without damaging the semiconductor wafer, and the oxygen in the oxide layer. Can be diffused at high speed. Oxygen exceeding the solid solution limit (for example, 2.7E + 18 / cm ³ ) can be dissolved in the semiconductor wafer by rapid cooling peculiar to pulsed laser light, and the oxygen concentration is near the liquid phase / solid phase interface. It is possible to create an oxygen concentration gradient that rapidly decreases and reaches a low concentration region where the oxygen concentration is below the solid solution limit. An oxygen precipitate is generated by supersaturated oxygen solid solution, and a strain field is generated by crystal defects caused by the oxygen precipitate. It should be noted that the total amount of oxygen dissolved in the molten region is suppressed to be lower than, for example, 1.0E + 15 / cm ² , thereby preventing cracks from occurring in the semiconductor wafer due to strain. The total amount of oxygen dissolved in the melting region can be represented by an amount obtained by integrating the oxygen concentration profile from the Si wafer surface to the melting depth. Oxygen in the surface oxide layer is excluded.
The strain metal captures the impurity metal contained in the semiconductor wafer and effectively forms a gettering layer.

Semiconductor wafer In the present invention, the type of the semiconductor wafer is not particularly limited, but a silicon wafer can be preferably used as the semiconductor wafer. The thickness of the semiconductor wafer is not particularly limited. However, in the present invention, a remarkable effect can be obtained particularly in a semiconductor wafer having a thickness of 30 μm or less.

Oxide layer The semiconductor wafer surface has an oxide layer on at least the side irradiated with laser light. The oxide layer may be intentionally formed or may be naturally generated, or these may be combined. The oxide layer is preferably composed mainly of components of the same material as the semiconductor wafer. For example, when the semiconductor wafer is a silicon wafer, examples of the oxide layer include a Si-based oxide layer, and a SiO ₂ film or a SiON film can be preferably used.
The optical thickness of the oxide layer defined by oxide layer thickness d × refractive index n is preferably ¼ or less of the wavelength of the pulse laser beam. This is because the reflection intensity is minimized and absorption is enhanced to effectively melt. For example, the refractive index of the SiO ₂ film can be expressed as 1.46, and if the wavelength of the pulse laser beam is, for example, 515 nm, the thickness of the SiO ₂ film is desirably 88 nm or less.

Pulse laser light Wavelength In the present invention, the wavelength of the pulsed laser beam is not limited to a specific wavelength, but a wavelength in the green region of, for example, 510 to 540 nm can be used.
Thereby, high output can be obtained in consideration of throughput.

2. Pulse width The pulse width (half width) of the pulse laser beam is not particularly limited in the present invention, but the pulse width is set to 500 ns or less so that the phenomenon of high-speed heating and high-speed cooling can be reliably obtained. Furthermore, it is more desirable to set it to 300 ns or less for the same reason.
When the pulse width is large, the cooling rate is reduced, and it becomes difficult to dissolve oxygen into the semiconductor wafer in a supersaturated state.

3. Repetition frequency Although it does not specifically limit as a repetition frequency of the laser beam of pulsed light, For example, 10-30 kHz can be shown.

Continuous Laser Light Wavelength In the present invention, the wavelength of continuous laser light is not limited to a specific one, but for example, a wavelength of 780 to 830 nm can be used. In the above wavelength range, light absorption with respect to silicon, which is a general semiconductor material, is good, and a light penetration depth deeper than that of the pulse laser beam can be obtained. As a result, the semiconductor surface layer portion is heated to a deep region, and an assist action is effectively obtained. In addition, high output can be easily obtained in the above wavelength range. Furthermore, the continuous laser light is usually preliminarily heated to a deeper depth by setting the wavelength longer than that of the pulsed laser light, so that deep melting is possible.
Note that the temperature adjustment by the assist heating described above can be performed by controlling the power density and scanning speed of the continuous laser beam. As assist temperature, 200 degrees C or less is desirable. When the assist temperature is high, the effect of rapid cooling by irradiation with pulsed laser light cannot be obtained sufficiently, and it becomes difficult to dissolve oxygen into a semiconductor wafer in a supersaturated state.

In the present invention, the pulsed laser beam and the continuous laser beam are irradiated with the pulsed laser beam in the state of being assisted by the continuous laser beam. What is necessary is just to be obtained in combination, and at the same time, the relationship between the irradiation position of the pulse laser beam and the irradiation position of continuous laser light such as near infrared laser light is not limited to a specific one.
Therefore, at the same time, the irradiation area of the continuous laser beam and the irradiation area of the pulse laser beam are partially or entirely overlapped on the surface of the semiconductor wafer, or the positions of the laser beams do not overlap each other. It may be irradiated by shifting. However, if these irradiations are performed completely individually, the effect of the combined irradiation cannot be obtained, and it is necessary to perform irradiation so that the effects of the respective irradiations influence each other.
The irradiation region can be shown as an area where the energy density of pulsed laser light or the power density of continuous laser light is 50% (FWHM) with respect to the peak value on the semiconductor surface.

  However, in order to effectively obtain the assist action, that is, to ensure the melting depth, it is desirable that the irradiation region of the continuous laser beam is larger than the irradiation region of the pulse laser beam, and further, the irradiation region of the continuous laser beam is It is more desirable to cover the irradiation area of the pulse laser beam. Further, in order to obtain a sufficient effect as the assist heating, a part or all of the irradiation region of the continuous laser beam may be positioned beyond the irradiation region of the pulse laser beam at least on the scanning direction side, Furthermore, in order to obtain an effect as post-heating, the irradiation region of the continuous laser beam may exceed the irradiation region of the pulse laser beam on the opposite side in the scanning direction. In addition, it is desirable that the positional relationship between the irradiation areas of both laser beams be symmetric with respect to the scanning direction and the direction orthogonal to the scanning direction. Thus, the same positional relationship can be obtained when the scanning direction is reversed.

Further, it is desirable that the pulse laser light irradiation and the continuous laser light irradiation be performed simultaneously on the surface of the semiconductor wafer. Therefore, both laser beams may be irradiated to a predetermined position on the surface of the semiconductor wafer at the same time, or both laser beams may be irradiated to a predetermined position on the surface of the semiconductor wafer with a time difference. Good. When there is a time difference, the time difference is set so that the assist action of the continuous laser light can be effectively obtained in the irradiation of the pulsed laser light. That is, if the time difference is too large, the continuous laser beam assist function cannot be sufficiently obtained in the pulse laser beam irradiation. Irradiation having the time difference while maintaining the assist action is also included in the irradiation at the same time.
The relationship between the beam size and the irradiation position described above can be adjusted by an optical system. The optical system includes optical materials such as a homogenizer, a lens, and a mirror, and performs shaping and deflection of laser light.

The surface layer of the semiconductor can be melted deeply by the combined irradiation of the continuous laser light and the pulsed laser light. However, melting too deeply affects the device structure side and may impair transistor characteristics. Therefore, the melting depth is preferably 5 μm or less from the laser light irradiation side.
Further, considering the thickness and effect of the gettering layer, the melting depth is desirably 1 μm or more.
Moreover, since the mechanical strength (bending strength) of the semiconductor wafer is impaired when the melting depth becomes relatively large with respect to the thickness of the semiconductor wafer, the melting depth is 10% or less of the thickness of the semiconductor wafer. Is desirable. The melting depth can be determined by setting the power density of continuous laser light, the pulse energy density of pulsed laser light, and the scanning speed of laser light. The power density of the continuous laser beam and the pulse energy density of the pulse laser beam can be adjusted by adjusting the output of the laser light source and / or adjusting the attenuation rate of the attenuator.

  The thickness of the gettering layer obtained as described above is preferably 1 μm or more and 4 μm or less with the silicon wafer surface as a base point. If the thickness of the gettering layer exceeds 4 μm, the total oxygen concentration in the molten region becomes high, and the strength of the semiconductor wafer may be impaired. For the same reason, the thickness of the gettering layer is preferably 3.5 μm or less, and more preferably 3.0 μm or less.

By irradiation with the pulse laser beam and the continuous laser beam, oxygen can be diffused in the semiconductor wafer at a concentration exceeding the solid solution limit. For example, the solid solution limit of oxygen in a Si wafer is 2.7E + 18 / cm ³ . In order to obtain a sufficient gettering effect, it is desirable to have a region containing oxygen at 2.7E + 18 atoms / cm ³ or more. However, if the concentration of oxygen contained in the semiconductor wafer becomes too high, the bending strength (bending strength) of the semiconductor wafer cannot be secured sufficiently, so that the total oxygen amount in the molten region is from 1.0E + 15 / cm ² . It is desirable to keep it low.

  The semiconductor wafer is provided with a device structure on the side opposite to the side irradiated with the laser beam. The device structure is provided before the laser light irradiation.

  As described above, according to the present invention, an effective gettering layer can be formed without damaging the semiconductor wafer, and the semiconductor wafer having the gettering layer has a good bending strength and a metal impurity. A semiconductor device that is trapped and has excellent characteristics can be obtained.

It is a figure which shows the structure of the laser annealing apparatus used for one Embodiment of this invention. Similarly, it is a figure which shows the time chart of a pulse laser beam and a continuous laser beam. Similarly, it is a figure which shows the heating area | region by the laser beam irradiation in the cross section of a semiconductor, and the irradiation area | region of the pulse laser beam and continuous laser beam on a semiconductor. Similarly, it is a figure which shows the example of a change of the irradiation area | region of the pulse laser beam and continuous laser beam on a semiconductor. Similarly, it is a flowchart which shows the manufacturing process of three-dimensional structure SiP. It is a figure which shows the oxygen concentration distribution (SIMS depth profile) after the laser annealing process in the Example of this invention. Similarly, it is a figure which shows n-type carrier (electron) density | concentration distribution and specific resistance distribution (SR depth profile).

FIG. 1 shows an outline of the configuration of the laser processing apparatus 1 and will be described below.
As shown in FIG. 1, the laser processing apparatus 1 includes a processing chamber 2, a scanning device 3 that is movable in the XY direction, and a base 4 on the upper portion. Yes. On the base 4, a target object placement base 5 is provided. At the time of laser light irradiation, the semiconductor wafer 30 to be processed is placed on the processing object placement table 5. The scanning device 3 is driven by a motor (not shown) or the like.

Outside the processing chamber 2, a pulsed laser light source 10 on which a second harmonic of an LD-pumped Yb: YAG laser is mounted is installed. The pulsed laser light 15 that is output after being pulsated by the pulsed laser light source 10 is adjusted in energy density by an attenuator 11 as necessary, and is subjected to beam shaping by an optical system 12 including a lens, a reflecting mirror, a homogenizer, and the like. The deflection is performed and the semiconductor wafer 30 in the processing chamber 2 is irradiated.
The pulsed laser light 15 output from the pulsed laser light source 10 has a pulse waveform with a half width of 500 ns or less, a wavelength of 515 nm, and a repetition frequency of 10 kHz. The pulse laser beam 15 is adjusted to an energy density that melts the surface layer of the semiconductor wafer 30 when the semiconductor wafer 30 is irradiated. The pulse laser beam 15 is shaped by the optical system 12 into an appropriate shape such as a spot shape, a circular shape, a square shape, or a long shape. Preferably, the long shape is desirable in consideration of the throughput.

  In addition, a continuous wave laser light source 20 including an LD laser light source that generates laser light is installed outside the processing chamber 2. The continuous laser beam 25 output from the continuous wave laser light source 20 has a wavelength of 808 nm. The power density of the continuous laser beam 25 is adjusted by an attenuator 21 as necessary, and beam shaping and deflection are performed by an optical system 22 including a lens, a reflection mirror, a homogenizer, and the like, and a semiconductor wafer 30 in the processing chamber 2 is formed. Is irradiated. The continuous laser beam 25 is adjusted to a power density that does not reach the melting point of the semiconductor wafer 30 when the semiconductor wafer 30 is irradiated and scanned. As described above, the continuous laser beam 25 is shaped into, for example, a spot shape by the optical system 22, and the size thereof is adjusted to be larger than the size of the pulse laser beam 15.

  The laser processing apparatus has a control unit 6 that controls the entire laser processing apparatus. The control unit 6 can mainly configure a CPU and a program for operating the CPU. The control unit 6 is controllably connected to a power source 7a for driving the pulse laser light source 10 and a power source 7b for driving the continuous wave laser light source 20, and can set the output of each laser light source. Moreover, the control part 6 is connected to the attenuator 11 and the attenuator 21 in a controllable manner, and can set the respective attenuation rates. The control unit 6 is controllably connected to an XY stage drive circuit 8 that outputs a drive signal to the scanning device 3, and can set a moving speed in the scanning device 3.

  In the laser annealing apparatus, as shown in FIG. 2, a pulsed laser beam 15 and a continuous laser beam 25 are output and are combined and irradiated on the semiconductor wafer 30. At this time, the energy density on the irradiation surface of the pulsed laser beam, the power density on the irradiation surface of the continuous laser beam 25, and the scanning speed of the object placement table 5 are set to predetermined values, so that the semiconductor wafer 30 The surface layer can be melted to a predetermined depth.

The semiconductor wafer 30 is repeatedly and repeatedly irradiated with the pulsed laser light 15 and combined with the continuous laser light 25, whereby the surface layer portion of the semiconductor wafer 30 is melted over a thickness of 1 μm or more. However, it is desirable to set the melt depth so as not to exceed 5 μm.
In addition, as the semiconductor wafer 30, a wafer having a thickness of 30 μm or less can be suitably used, and a device structure is provided on the surface side opposite to the laser light irradiation surface.
The overlapping rate (overlap rate) of the pulse laser beam 15 in the short axis direction and the long axis direction is appropriately selected as necessary (for example, 50 to 90% in the short axis direction, for example, 10% to 50% in the long axis direction). The present invention is not particularly limited. At this time, the semiconductor laser 30 can be scanned with the pulsed laser light 15 and the continuous laser light 25 at a predetermined speed by controlling the moving speed of the object placement table 5 by the scanning device 3. The moving speed of the laser beam in the minor axis direction can be, for example, 30 to 150 mm / second, but is not particularly limited as the present invention.
In addition, the continuous laser light always has a constant power density and may have a discontinuous part. Thereby, the assist heating in the continuous laser beam 25 can be adjusted to adjust the melting depth and the heat load on the surface layer of the semiconductor wafer 30.

In this embodiment, as shown in FIG. 3A, the irradiation region 25 a when the semiconductor laser 30 is irradiated with the continuous laser beam 25 is an irradiation region when the pulsed laser beam 15 is irradiated on the semiconductor wafer 30. It is adjusted by the optical systems 12 and 22 so as to cover 15a and to have a size exceeding the entire irradiation area 15a. In the figure, the arrow in the X-axis direction indicates the scanning direction of the laser beam. In this example, the pulse laser beam 15 and the continuous laser beam 25 are irradiated in the same region on the semiconductor wafer 30 without irradiating the irradiation time.
However, in the present invention, the position of the irradiation region of each laser beam is not limited to the above.

FIG. 3B shows a schematic view of thermal diffusion in the depth direction when the semiconductor surface is irradiated with the pulse laser beam and the continuous laser beam.
A temperature assist region is formed in the semiconductor wafer 30 to a deep position of the semiconductor wafer 30 by irradiation with continuous laser light having a light penetration length larger than that of the pulse laser light. For example, with a laser beam having a wavelength of 808 nm, a light penetration length of about 10 μm can be obtained in the depth direction. When pulse laser light is irradiated in this state, heat is diffused mainly in the depth direction (Z-axis direction). In this case, the deep temperature assist region reduces the temperature gradient of the shallow heating region of the pulse laser beam, and as a result, the heat escape is reduced and the semiconductor surface is effectively heated to a deep position. In this case, optimization is performed by adjusting the energy density of the pulsed laser beam, the power density of the continuous laser beam, and the scanning speed, thereby effectively heating the semiconductor surface layer.
When the semiconductor wafer 30 is irradiated with only the pulse laser beam, the temperature gradient in the surface direction and the depth direction is large, and the heat escape is large. For this reason, the heating effect in the depth direction is suppressed, and it becomes difficult to selectively deeply melt the surface layer portion particularly for a thick semiconductor wafer having a large heat capacity.

Next, FIGS. 4A to 4E show examples of changing the irradiation region position of the pulse laser beam and the continuous laser beam.
FIG. 4A shows a rectangular cross section of the pulse at the irradiation position in FIG. 3, and the irradiation region 25a completely covers the irradiation region 15a. FIG. 4B shows that the irradiation region 25a of the continuous laser beam in the major axis direction (Y-axis direction) and the scanning direction (X-axis direction) has a size exceeding the irradiation region 15a of the pulsed laser beam. In the opposite direction, the irradiation areas 15a and 25a overlap and the area ends coincide. In FIG. 4C, the irradiation region 25a does not cover the irradiation region 15a and does not overlap with each other, and the irradiation region 25a is positioned on the scanning direction side of the irradiation region 15a and adjacent irradiation regions. The edges are in contact with each other. In FIG. 4D, the irradiation region 25a is separated without covering the irradiation region 15a and without overlapping. However, both are irradiated near each other on the substrate. FIG. 4E shows an irradiation state outside the present invention, and shows a state where the semiconductor 30 is irradiated with only the pulse laser beam 15 and the semiconductor 30 is processed by the irradiation region 15a. .

  On the semiconductor surface irradiated with the continuous laser beam, the temperature gradually increases immediately after irradiation and becomes a steady state. On the other hand, in the case of pulsed laser light, the temperature rises in a very short time according to the rise time of the pulse (time for the pulse laser intensity to reach 10% to 90%), and the pulse fall time (pulse laser intensity is 90%). The temperature drops in a very short time according to the time from 10% to 10%. The rise time is preferably 160 ns or more, for example, and the fall time is preferably 100 ns or less, for example. When irradiating pulsed laser light, continuous laser light may be irradiated, and the semiconductor laser may be irradiated after the semiconductor surface temperature has reached a steady state. The irradiation timing on the semiconductor surface may be set, for example, by setting a delay time, and after the continuous laser beam irradiation, the pulse laser beam may be irradiated with a delay according to the delay time. It is also possible to change the irradiation timing by scanning the composite laser beam with shifting. 4B, 4C, and 4D, the semiconductor 30 is irradiated with the pulsed laser beam 15 after the irradiation of the continuous laser beam 25.

Next, an example of a semiconductor wafer manufacturing process including the laser light irradiation process will be described with reference to FIG.
First, a semiconductor wafer 30 thicker than the final thickness is prepared, a device layer 300 is provided on one surface of the semiconductor wafer 30, and electrode embedding and bumps 301 are formed on the device layer (FIG. 5A). Next, the back surface side of the semiconductor wafer 30 is ground to reduce the thickness to, for example, about 10 μm (FIG. 5B). Thereafter, an oxide is applied to the ground surface to form an oxide layer 310. Note that the oxide layer 310 may be generated by natural oxidation or may be intentionally formed. As the intentional formation, the oxide layer can be formed by a coating method, a sputtering method, or the like. The optical thickness (refractive index n × film thickness d) of the oxide layer 310 is desirably set to a quarter or less of the pulse laser wavelength.

Thereafter, the pulse laser beam 15 and the continuous laser beam 25 described above are combined and irradiated from the surface side having the oxide layer 310 in the air, and the surface layer portion of the semiconductor wafer 30 is melted to generate a molten layer 30a ( FIG. 5 (c)). The molten layer 30a has a depth of 1 to 5 μm from the back surface. Oxygen diffuses from the oxide layer 310 on the surface in the liquid phase region (molten layer 30a) melted by this melting to form a high concentration oxygen region. Then, by the pulse-off of the pulsed laser beam 15, an oxygen concentration gradient that rapidly decreases in the vicinity of the liquid phase / solid phase interface is created by rapid cooling, crystal defects caused by oxygen precipitates are generated, and a gettering layer 30b composed of a strain field is formed. Is done.
Next, the process proceeds to a TSV (Through Silicon Via) molding process. First, as TSV molding, an overcoat 320 is formed on the back surface side and a via is opened on the back surface side (FIG. 5D), and then Cu is formed in the via. After embedding and forming the electrode 302 (FIG. 5E), and further grinding the overcoat 320 on the back side, a back bump 303 connected to the electrode 302 is formed (FIG. 5F), and the chip is cut out. . As a result, a gettering semiconductor wafer (for example, 30 μm or less) having the gettering layer 30b on the back surface side is obtained.

According to the present embodiment, the following effects can be obtained.
(1) By using a laser annealing apparatus mainly composed of a short pulse, the oxygen concentration can be increased beyond the solid solution limit by melting the Si wafer coated with the Si-based oxide layer in the air and cooling at high speed. In addition, a steep oxygen concentration gradient is formed in the depth direction, and a strain field due to crystal defects that can capture and exclude heavy metals can be generated in the vicinity thereof.
(2) By controlling the laser irradiation conditions (pulse energy density and number of irradiations), the oxygen diffusion region can be limited to the extreme surface layer of the melting area, and the total oxygen amount in the melting region is 1.0E + 15 that causes cracking The bending strength (bending strength) of the ultra-thin Si wafer can be ensured by keeping it lower than / cm ² .
(3) By using a laser annealing apparatus mainly composed of a short pulse laser, a gettering process at a low temperature (low thermal load) that does not cause thermal damage to the side opposite to the laser irradiation of an ultra-thin Si wafer is performed. It becomes possible.
(4) By applying an oxide layer with a specific thickness on the laser irradiation surface, it is possible to suppress surface roughness due to the supply and melting of oxygen, and also to reduce the energy density of the pulse laser by reducing reflection loss. Can do.

In the laser processing apparatus 1 according to the first embodiment, a solid green laser (wavelength 515 nm) that is a pulse laser beam having a rise time of 160 ns or more and a fall time of 100 ns or less is a near-infrared LD light (wavelength 808 nm) that is continuous laser light. Was used to form a 1-5 μm deep melt layer on a 500 μm thick silicon wafer prepared for testing.
In the silicon wafer, an oxide film having a thickness of 4 to 5 nm was formed on the laser irradiation surface side. This oxide film corresponds to the oxide layer of the present invention. The oxide film was a SiO ₂ layer formed by natural oxidation of silicon. Note that the oxide layer may be intentionally formed as described above.
Silicon when the power density of the near-infrared LD is constant (40 w) and the energy density of the pulse green laser is changed to 14 J / cm ² (A), 18 J / cm ² (B), 20 J / cm ² (C) The diffusion oxygen concentration distribution in the depth direction on the wafer is shown in FIG. The diffusion oxygen concentration distribution was measured by SIMS (Secondary Ion Mass Spectrometry) analysis.

As for the oxygen concentration distribution of the melting area with respect to the energy density of each pulse green laser, there is a high concentration area exceeding the solid solution limit (2.7E + 18 / cm ³ ) in the extreme surface layer (depth of 2 to 3 μm). This produced an oxygen concentration gradient that rapidly decreased near the liquid / solid phase interface. Looking at the correlation between the amount of diffused oxygen and crack generation (inspected with an optical microscope), the total dissolved oxygen amount in the molten region (SIMS oxygen concentration profile was integrated from the Si surface (excluding the natural oxide film) to the melting depth. Since the silicon wafer cracks when the amount is greater than 1.0E + 15 atoms / cm ² , the solid solution oxygen concentration was controlled below the threshold value for cracking by reducing the pulse energy density and the number of irradiations. . Note that the surface has a high oxygen concentration due to the presence of the oxide layer, but is removed by grinding in a later step.

Among the above-described examples, SR (Spread Resistance) analysis was performed on a silicon wafer subjected to laser treatment with an energy density of a pulse green laser of 18 J / cm ² . FIG. 7 shows the n-type carrier (electron) concentration distribution and specific resistance distribution in the depth direction obtained from the results. The number of carriers (electrons) is drastically reduced by about 4 digits at the depth near the liquid phase / solid phase interface where the steep oxygen concentration gradient in FIG. 6 occurs, and at the same time, the specific resistance also increases rapidly. This indicates that carriers (electrons) are trapped in a strain field caused by crystal defects, and an effective gettering layer was obtained at a sufficient depth.
Conventional Intrinsic Gettering (IG) technology was only compatible with high-temperature processes, but it was combined with a CW-type near-infrared LD (wavelength 808 nm) mainly composed of a pulse-type solid green laser (wavelength 515 nm). Laser annealing technology using laser annealing equipment can be expected to be applied to three-dimensional stacked SiP that requires gettering technology for low-temperature processes.

  As described above, the present invention has been described based on the above-described embodiment and examples. However, the present invention is not limited to the contents of the above description, and appropriate modifications can be made without departing from the scope of the present invention. It is.

DESCRIPTION OF SYMBOLS 1 Laser processing apparatus 2 Processing chamber 3 Scanning apparatus 4 Base 5 To-be-processed object arrangement | positioning base 6 Control part 8 XY stage drive circuit 10 Pulse laser light source 11 Attenuator 12 Optical system 15 Pulse laser light 15a Irradiation area 20 Continuous oscillation laser light source 21 Attenuator 22 Optical system 25 Continuous laser beam 25a Irradiation area 30 Semiconductor wafer 30a Molten layer
30b Gettering layer 300 Device 301 Front bump 302 Copper electrode 303 Back bump 310 Oxide layer 320 Overcoat

Claims (13)

  The surface of the semiconductor wafer having an oxide layer on one surface side is irradiated with a pulsed laser beam and a continuous laser beam that performs thermal assist to melt the inner layer of the semiconductor wafer, and the semiconductor wafer is heated at a high temperature. In the cooling process, oxygen is diffused from the oxide layer to the melting region in the melting process, and a high concentration region of oxygen exceeding the solid solution limit concentration is formed in the inner layer in the solidification process, resulting from the high concentration region. A method of manufacturing a gettering semiconductor wafer, comprising forming a gettering layer that captures a metal in the semiconductor wafer by crystal defects.   2. The method of manufacturing a gettering semiconductor wafer according to claim 1, wherein the pulse laser beam is a green pulse laser beam having a wavelength of 510 to 540 nm, and the continuous laser beam is a diode laser beam having a wavelength of 780 to 830 nm. .   3. The method for manufacturing a gettering semiconductor wafer according to claim 1, wherein a pulse width of the pulse laser beam is 500 ns or less.   The method of manufacturing a gettering semiconductor wafer according to any one of claims 1 to 3, wherein an assist temperature of the continuous laser beam is 200 ° C or lower.   The method for producing a gettering semiconductor wafer according to claim 1, wherein the melting depth is 1 to 5 μm. It said semiconductor wafer is a silicon wafer production method of gettering semiconductor wafer according to claim 1, wherein the oxide layer is characterized by comprising the one or both of the SiO ₂ film or SiON film.   The method for producing a gettering semiconductor wafer according to claim 1, wherein an optical thickness of the oxide layer is ¼ or less of a wavelength of the pulsed laser beam at the time of irradiation. . The method for manufacturing a gettering semiconductor wafer according to any one of claims 1 to 7, wherein the total amount of oxygen diffused in the melting region is suppressed to be lower than 1.0E + 15 / cm ² .   The method for manufacturing a gettering semiconductor wafer according to claim 1, wherein the other surface side has a device structure.   The solid surface has a high concentration region of oxygen exceeding the solid solution limit concentration at a depth of 1 to 4 μm on one surface side, and reaches the other surface side through a concentration gradient region in which oxygen decreases near the liquid phase / solid phase interface. It has a low concentration region of oxygen below the solubility limit concentration, a crystal defect exists in a region from the high concentration region to the concentration gradient region, and the metal in the semiconductor wafer is captured in the region where the crystal defect exists. A gettering semiconductor wafer provided with a gettering layer. 11. The gettering semiconductor wafer according to claim 10, wherein the total amount of oxygen diffused in the melted region is suppressed to be lower than 1.0E + 15 / cm ² . The gettering semiconductor wafer according to claim 10 or 11, wherein the thickness is 30 µm or less.   The gettering semiconductor wafer according to any one of claims 10 to 12, which has a device structure on the other surface side.

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