JP2013106024A - Silicon substrate, manufacturing method therefor, and semiconductor device manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon substrate suitable for a semiconductor device thin-formed to 50 μm or smaller in a device post-process.SOLUTION: To a device-manufactured silicon substrate, the silicon substrate and the manufacturing method therefor is capable of providing a robust gettering layer by forming the entire rear surface of the silicon substrate, thin-formed in the device post-process by laser irradiation at a predetermined condition, or a portion thereof to be amorphous in a depth direction, or by forming a crystal defect optimized at a predetermined position inside the substrate.

Description

  The present invention relates to a silicon substrate and a manufacturing method thereof, and more particularly to a silicon substrate suitable for a semiconductor device mounted on a multichip package (MCP), a system in package (SiP), and the like and a manufacturing method thereof. The present invention also relates to a silicon substrate and manufacturing method suitable for a structure in which device chips such as MCP and SiP are stacked, and a semiconductor device manufacturing method.

  One problem in the semiconductor process is the mixing of heavy metals into the silicon substrate. When heavy metal diffuses into the device region formed on the surface side of the silicon substrate, device characteristics such as a pause time failure, a retention failure, a junction leak failure, and an oxide dielectric breakdown are significantly adversely affected. For this reason, in order to suppress the heavy metal mixed in the silicon substrate from diffusing into the device region, the gettering method is generally adopted.

  The silicon substrate on which the device is manufactured in the previous process is then transferred to a subsequent process in which the silicon substrate is thinned, dicing, wire bonding, resin sealing, and the like are performed. Even in the post-process, heavy metal contamination is present but has not been particularly emphasized so far. This is because grinding marks including scratches, cracks, and amorphous material generated when the back surface of the silicon substrate is ground and removed in the initial stage of the device post-process had a strong gettering action.

  However, the final chip thickness has been reduced year by year, and in particular, the chip mounted on the MCP is often reduced to 50 μm or less, and depending on the product, it has been reduced to 25 μm or less, and is expected to be 10 μm or less in the future. Yes. However, since the bending strength of the chip is inversely proportional to the square of the chip thickness, the progress of thinning will cause cracking and chipping problems. Further, scratches and cracks in the back surface grinding generate extremely large residual stress in the vicinity of the back surface, which not only increases the warpage of the thinned silicon substrate but also promotes cracks and chips. Accordingly, a method of reducing the residual stress (stress relief) by newly adding a polishing step to remove grinding marks has been adopted.

  However, removal of the grinding traces loses the gettering source, and the thinned silicon substrate has a thin intrinsic gettering (IG) layer, so that a sufficient gettering effect cannot be expected. That is, the chip bending strength and the gettering efficiency are in a trade-off relationship.

  Therefore, in thin semiconductor devices, polishing that does not completely remove the grinding marks after backside grinding to leave slight scratches or cracks, etc. The method of giving is taken. However, even if any method is applied, the gettering effect and the reduction of the residual stress are not sufficient.

  Japanese Patent Laid-Open No. 2003-264194 discloses a gettering method in which a semiconductor silicon substrate is irradiated with laser light to form a modified region including an amorphous region inside the silicon substrate. Japanese Patent Laid-Open Nos. 2010-98107 and 2010-98106 also disclose gettering methods using the same technique.

According to Japanese Patent Laid-Open No. 2003-264194, a method of forming a modified region by multiphoton absorption by irradiating laser light having a long wavelength from one surface of a silicon substrate and aligning the condensing point inside the substrate. The multi-photon absorption is caused under the condition that the laser power density is 1 × 10 ⁸ W / cm ² or more and the pulse width is 1 μm or less. The modified region thus obtained has a gettering effect. On the other hand, Japanese Patent Application Laid-Open No. 2010-98107 also discloses a method of forming a crystal defect by multiphoton absorption in the substrate by irradiating a silicon substrate with a long wavelength laser beam. These laser power density as disclosed in, 100 J / cm ² in JP 2003-264194, which up to now 5100J / cm ² in JP 2010-98107. Accordingly, in any of the methods, the defect region is enlarged with a size of 100 μm or more, and the stress around the crystal defect is inevitably very large. These crystal defects spur out dislocations in order to relieve the stress by heat treatment in the device fabrication process, and the dislocations penetrate to the surface and deteriorate device characteristics. In particular, flash lamp annealing and laser spike annealing processes are frequently used in recent device processes. Since these processes generate enormous stresses near the surface of the silicon substrate, which is the device fabrication surface, dislocations easily penetrate to the device fabrication surface. Degrading device characteristics. Therefore, it is suggested that it cannot be applied to a thin device having a chip thickness of 100 μm or less.

  Japanese Patent Application Laid-Open No. 2010-98106 describes that a laser beam is irradiated from the back side of a silicon substrate on which a device is manufactured to form defects near the device, and the silicon substrate in a device post-process is thinned to a predetermined temperature. Discloses a method for gettering heavy metals by heat treatment. This method is based on the premise that the thickness of the device chip is 50 μm or less, but crystal defects are formed at the same laser power density as in Japanese Patent Application Laid-Open No. 2010-98107, and the silicon substrate thickness variation is about ± 15 μm. In addition, it is difficult to accurately form crystal defects directly under the device active layer. In the future, it is expected that the device thickness will be reduced to around 10 μm, so it is very difficult to apply this method to mass production. Further, after forming the crystal defects, the silicon substrate is thinned by back grinding, and the temperature is not specifically described. However, since heating in a heat treatment furnace is also performed, the productivity is reduced, the silicon substrate is cracked, Yield reduction due to chipping.

JP 2003-264194 A JP 2010-98107 A JP 2010-98106 A

  An object of the present invention is to provide a silicon substrate and a method of manufacturing the same that can provide a highly reliable device by giving a strong gettering capability to a thin device.

  As a result of diligent studies to solve the above-mentioned problems, the first invention is a predetermined method for condensing a laser beam inside a silicon substrate after making the silicon substrate constant by thinning the silicon substrate manufactured as a device. It is possible to form a crystal defect at the position of the device, and since the defect size is also controlled, it is possible to fabricate a thin device with improved device reliability without forming a crystal defect in the device active layer. The invention provides a powerful gettering capability by thinning the silicon substrate fabricated on the device and then irradiating the back surface of the silicon substrate with a laser beam to make the single crystal silicon amorphous. Further, the stress caused by the back surface processing can be reduced. The present inventors have found that a thin device can be produced and have completed the present invention.

Means for solving the problem

  According to the first aspect of the present invention, after the silicon substrate after device fabrication is made constant in the thickness of the silicon substrate by back surface grinding or polishing, the entire back surface or a part of the back surface is irradiated with laser light from the back surface to be condensed inside the substrate. Thus, a silicon substrate and a manufacturing method are characterized in that crystal defects are formed.

  According to the first aspect of the present invention, the back surface grinding and polishing in the device post-process are made thin while monitoring the thickness of the silicon substrate, so that the thickness variation can be reduced. Since the thickness is constant, the laser beam can be uniformly focused at a specific position inside the silicon substrate, so that it is possible to prevent the formation of crystal defects in the device active layer. In addition, the silicon substrate on which the device is manufactured after the defect is formed is a heavy metal mixed from a material such as a heavy metal or an interposer mixed in a thin process by a subsequent device manufacturing process, a heat treatment after chip stacking, or a heat treatment of a sealing resin. In addition, since gettering is possible, there is no need for additional heat treatment, and the conventional process can be used.

  In addition, since the heat treatment in the device post-process is around 300 ° C., dislocation motion due to crystal defects can be ignored, so that the crystal defect size can be increased and it can act as a powerful gettering source. The crystal defect formation region can be formed on the entire surface or a part of the silicon substrate. In the case of the prior dicing process, since a chip that has been individualized after grinding or polishing is attached to a protective tape for back grinding, crystal defects may be formed by laser irradiation in this state.

  Laser irradiation for crystal defect formation is performed under conditions that allow multiphoton absorption of a minute region inside a silicon substrate as in the prior art. That is, the repetition frequency may be changed from the order of 100 KHz to the order of MHz from the nanosecond order to the femtosecond order, and a wavelength range that can be transmitted through the silicon substrate may be used.

The invention described in claim 2 is a crystal defect formed with a laser light output in the range of 1 μJ / cm ² to 100 μJ / cm ² , and the density is 1 × in the range of the defect size of 0.5 μm to 10 μm. The silicon substrate and the manufacturing method according to claim 1, wherein the range is 10 ⁴ to 1 × 10 ⁸ / cm ² .

  According to the second aspect of the present invention, if a crystal defect size is 10 μm or more with respect to a device chip having a thickness of 50 μm or less, a very large stress is generated around the crystal defect, so that chip cracking is likely to occur. If the size is 0.5 μm or less, there is a limit to the beam diameter of the laser device, and defects having a smaller size cannot be formed. In the future, if the beam diameter is further reduced, it is assumed that even 0.1 μm size has gettering ability. The region where crystal defects are formed may be any region as long as it does not affect the device active layer, and crystal defects are formed entirely or partially. Accordingly, the crystal defect size may be appropriately selected depending on the thickness of the device chip so as to satisfy the stress reduction and the gettering effect.

A third aspect of the present invention is the silicon according to the first aspect, comprising a crystal-modified layer formed with a laser light output in the range of 1 μJ / cm ² to 100 μJ / cm ² and having a layer width in the range of 1 μm to 10 μm. A substrate and a manufacturing method.

  According to a third aspect of the present invention, there is provided a method for forming a crystalline alteration layer while scanning the surface of a silicon substrate with laser light. Similar to the second aspect, the thickness of the silicon substrate is limited by the limit of the beam diameter of the laser device. The thickness is 0.5 μm or more and 10 μm. The crystal defect layer width with respect to the plane direction is formed entirely or partially. In this case, the width of the crystal defect layer may be appropriately selected depending on the thickness of the device chip so as to satisfy the stress reduction and the gettering effect.

Respect crystal defect size, laser power density of the prior art is a 5100J / cm ² from 100 J / cm ² to reduce the laser power density to control the defect size or crystal defect layer, therefore the laser device cost can be reduced .

  The laser irradiation process may be performed after the thinning process and after the dicing process. For example, after the back grind tape is peeled off, before or after applying the back surface dicing tape, a dicing process may be performed. In particular, in the case of a laser dicing machine that uses a laser with a short pulse width, dicing is performed by injecting laser light from the device fabrication surface. It is also possible to perform laser irradiation. However, since a dicing tape or a die attach film is attached to the back surface of the silicon substrate, dicing and crystal defect formation can be performed by the same apparatus as long as the laser light transmits the film.

  As an improvement of the conventional method, the number of steps increases, but if the laser irradiation conditions of the present invention are applied after measuring the thickness of the silicon substrate after device fabrication, it becomes possible to form a crystal defect layer directly under the device active layer. Also note that it is applicable to the device.

  The invention according to claim 4 is characterized in that the back surface of the silicon substrate after the device fabrication is ground or polished and then irradiated with laser light from the back surface to make the back surface of the silicon substrate amorphous. A substrate and a manufacturing method.

  According to the fourth aspect of the present invention, after the back-grinding protective tape is attached to the surface of the silicon substrate on which the device is manufactured, the back surface of the silicon substrate is ground or polished. Thereafter, the back surface of the silicon is irradiated with laser light under a predetermined condition to amorphize the single crystal silicon on the extreme surface layer. Since amorphous silicon has a high gettering capability, it is possible to reliably getter heavy metals mixed in subsequent device processes and heavy metals mixed during grinding and polishing. Furthermore, the maximum stress is generated in the vicinity of the back surface due to processing, but there is also an advantage that the stress can be reduced because the processing marks on the extreme surface layer are made amorphous.

As laser irradiation conditions, it can be used widely from a short wavelength to a long wavelength. However, in order for amorphization to occur, an extremely short time irradiation with a pulse width of the femtosecond order or less and a high repetition frequency are required, and the laser output is in the range of 1 mJ / cm ² to 1000 mJ / cm ² .

  Invention of Claim 5 is a silicon substrate and manufacturing method of Claim 4 whose thickness of an amorphous layer is the range of 5 nm or more and 200 nm or less.

  According to the invention described in claim 5, when the amorphous layer thickness is 5 nm or less, the gettering effect is low, and when the amorphous layer thickness is 200 nm or more, it takes a long time to change from single crystal silicon to the amorphous layer, resulting in a decrease in productivity. Preferably, if the wavelength of the laser beam is set to the long wavelength side, the growth rate can be increased, leading to an improvement in productivity.

  The present invention will be described more specifically. In the first invention, a backgrinding protective tape is applied to a silicon substrate on which a device is manufactured, and then backside grinding or polishing is performed. Therefore, it is possible to provide a powerful gettering effect by condensing the laser beam inside the substrate to form crystal defects. Compared with the prior art, crystal defects can be formed at a predetermined depth for laser irradiation after the thickness after grinding or polishing is made uniform. Therefore, even in a thinned device, the defects are formed in the active layer. And the crystal defect size is optimized, so that the device characteristics are not deteriorated. Further, since no additional heat treatment is required, the manufacturing cost can be reduced.

  According to a second aspect of the present invention, after back grinding or polishing is performed with a backgrinding protective tape applied to a silicon substrate on which a device is fabricated, a laser beam is applied to the back surface in the femtosecond order by the manufacturing method of the present invention. By irradiating with a short pulse and increasing the repetition frequency, the silicon back surface can be made amorphous, so that a strong gettering effect can be provided. Further, since the stress caused by the back surface processing can be reduced by making the processing mark region amorphous, chip breakage can also be reduced.

Effect of the invention

  According to the silicon substrate and the method of manufacturing the same according to the present invention, a strong gettering source is provided on the surface of the silicon back surface or inside the substrate with respect to the silicon substrate on which the device having a final thickness of 100 μm or less, further 50 μm or less. Since it can be provided, it is possible to suppress deterioration of device characteristics due to heavy metal contamination in the device post-process, and to maintain the quality of the device active layer, so that the yield can be greatly improved.

[Comparative Example 1]
A boron-doped CZ substrate having a diameter of 200 mm, a thickness of 625 μm, an initial oxygen concentration of 1.1 × 10 ¹⁸ atoms / cm ³ , and a specific resistance adjusted from 10 Ω · cm to 20 Ω · cm was prepared. A back grind tape was applied to the surface of these samples and ground from the back side with a # 2000 grindstone. Further, the back side was polished by a depth of 3 μm by CMP to a final thickness of 100 μm. (Sample 1)

[Comparative Example 2]
The pre-heat treatment silicon substrate of Comparative Example 1 was subjected to precipitation nucleation heat treatment at 700 ° C. for 8 hours, and subsequently subjected to precipitate growth heat treatment at 1000 ° C. for 8 hours. A back grind tape was applied to the surface of these samples and ground from the back side with a # 2000 grindstone. Further, the back side was polished by a depth of 3 μm by CMP to a final thickness of 100 μm. (Sample 2)

Using Sample 1, laser light was irradiated from the back side so as to form a cross beam shape at a pitch of 2.5 mm. Laser irradiation conditions were such that the laser beam was condensed at a position of 10 μm in depth from the silicon substrate surface with a wavelength of 1064 nm, an output of 50 μJ / cm ² , and a pulse width of 20 picoseconds. (Sample 3)

Using Sample 1, laser light was irradiated from the back side so as to form a cross beam shape at a pitch of 2.5 mm. Laser irradiation conditions were such that the back surface of the silicon was irradiated with a wavelength of 1053 nm, an output of 150 mJ / cm ² , and a pulse width of 100 femtoseconds. (Sample 4)

[Evaluation 1]
One sample was extracted from each of Sample 2 and Sample 3, and the silicon substrate was cleaved, and then selective etching (Wright Etching) was performed. In sample 2, it was confirmed that oxygen precipitates were formed below 35 μm from the surface, and in sample 3, defects were observed at a depth of 10 μm from the surface. It was confirmed that the defect size was smaller than 10 μm because the defect size was determined by etching evaluation and could not be directly observed, but did not penetrate the device surface.

    Using the sample 4, the cross section of the silicon substrate was observed with a scanning electron microscope. As a result, it was confirmed that amorphous silicon had grown about 45 nm on the back side.

[Evaluation 2]
One sample was extracted from each sample, and an aqueous Cu solution was applied to the back side of the silicon substrate so that the copper contamination concentration was 5.0 × 10 ¹¹ atoms / cm ² . The obtained sample was heated from 250 ° C. for 30 minutes on the hot plate from the back side of the sample, and copper diffused to the silicon substrate surface was evaluated by total reflection X-ray fluorescence. For Sample 1 and Sample 2, the copper concentration of most of the initial contamination concentration was detected. However, Sample 3 had a copper concentration of 4.2 × 10 ¹⁰ atoms / cm ² and Sample 4 had a copper concentration of 2.5 × 10 ¹⁰ atoms / cm ² .

Claims (5)

  It is characterized by concentrating the thickness of the silicon substrate on the silicon substrate after device fabrication by grinding or polishing the back surface, and then condensing laser light from the back surface to the entire back surface or part of the substrate to form crystal defects. A silicon substrate and a manufacturing method. The laser light output is a crystal defect formed in the range of 1 μJ / cm ² to 100 μJ / cm ² , and the density is 1 × 10 ⁴ to 1 × 10 ^{8 in} the range of the defect size of 0.5 μm to 10 μm. The silicon substrate and the manufacturing method according to claim 1, wherein the range is cm ² . ^2. The silicon substrate and the manufacturing method according to claim 1, wherein the laser light output is composed of a crystal modified layer formed in a range of 1 μJ / cm ² to 100 μJ / cm ² , and the layer thickness is in a range of 0.5 μm to 10 μm. .   A silicon substrate and a manufacturing method characterized by amorphizing the back surface of a silicon substrate by irradiating a laser beam from the back surface side after applying stress relief by performing back surface grinding or polishing on a silicon substrate after device fabrication .   The silicon substrate and the manufacturing method according to claim 4, wherein the amorphous layer has a thickness in a range of 5 nm to 200 nm.