Process method for improving metal gettering of silicon wafer through wet back damage

Abstract

The invention relates to a process method for improving silicon wafer metal gettering through wet back damage, which belongs to the technical field of silicon wafer processing, and comprises the following operation steps of: 1, dividing silicon wafers into a plurality of experimental groups, firstly chamfering and grinding the silicon wafers, and then carrying out acid corrosion; 2, selecting SIO2 powder with the same particle size under different sand blasting pressure conditions to respectively carry out wet process back soft damage treatment on the silicon wafer; and 3, cleaning after sand blasting, and polishing the back surface of the silicon wafer. And 4, cleaning after polishing. And 5, carrying out metal determination and oxidation induced fault density determination on the silicon wafer. A back soft damage process is adopted, so that the silicon wafer has certain gettering capacity in a high-temperature thermal process of a device, and the metal content in the silicon wafer is reduced. Sand is sprayed and mixed with water, the back face of the silicon wafer is artificially damaged, a large number of dislocations are induced to form faults after high-temperature oxidation of the scars, and the effect of absorbing metal impurities is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of silicon wafer processing, and in particular to a process method for improving metal impurity gettering of silicon wafers through wet back surface damage. Background Art

[0002] Metals exist in silicon wafers mainly in the form of interstitial states and metal precipitates, and have low solubility and fast diffusion rates, which hinder the subsequent application of semiconductor devices.

[0003] Sandblasting is a processing technology used after acid etching in the processing of polished wafers. Its main function is to mechanically damage the back of the silicon wafer to form a metal gettering center. When the silicon wafer reaches a certain temperature, metal atoms such as Fe, Ni, Cr, and Zn that reduce the carrier life will move in the silicon body, and when these atoms encounter a damage point on the back of the silicon wafer, they will be trapped and instinctively move from the inside to the damage point, thereby reducing the heavy metal impurities and lattice defects on the polished surface.

[0004] Sandblasting is a relatively common back-side soft damage process. This process uses a mortar formed by mixing granular materials of a certain particle size (such as Al203) with water, and uses air pressure to drive the mortar to sandblast the silicon wafer on a moving conveyor belt to achieve "soft" damage on the back of the silicon wafer.

[0005] By changing the air pressure, slurry concentration, conveyor speed and spray gun height, the degree of "soft" damage on the back of the silicon wafer can be controlled to achieve the goal of making the silicon wafer have the ability to getter impurities without causing other negative effects due to excessive mechanical damage. Metal ion impurities in silicon wafers will significantly reduce the minority carrier lifetime and further affect the performance of silicon devices. Summary of the invention

[0006] The present invention mainly solves the deficiencies in the prior art and provides a process method for improving metal gettering of silicon wafers by wet back damage. The process adopts a back soft damage process to enable the silicon wafer to have a certain gettering ability in the high temperature thermal process of the device, thereby reducing the metal content in the silicon wafer. Sand material is sprayed and mixed with water to artificially damage the back of the silicon wafer. After high temperature oxidation, these scars will induce a large number of dislocations to form stacking faults, thereby achieving the effect of absorbing metal impurities.

[0007] The above technical problems of the present invention are mainly solved by the following technical solutions:

[0008] A process for improving metal gettering of silicon wafers by wet backside damage comprises the following steps:

[0009] Step 1: Divide the silicon wafers into several experimental groups, first perform chamfering and grinding, and then perform acid etching.

[0010] Step 2: Use SIO2 powder with the same particle size and different sandblasting pressure conditions to perform wet back soft damage treatment on silicon wafers.

[0011] Step 3: Clean and polish the back of the silicon wafer after sandblasting.

[0012] Step 4: Clean after polishing.

[0013] Step 5: Conduct metal measurement and oxidation-induced stacking fault density measurement of silicon wafers.

[0014] Preferably, the silicon wafer is lightly doped with BO, with a doping type of 200.02 um and a crystal orientation of <100>.

[0015] Preferably, the sandblasting pressure is 0.04 MPa to 0.09 MPa, and the sandblasting pressure difference of the silicon wafer in each experimental group is 0.005 MPa.

[0016] As a preference, the particle size of the sandblasting powder is 3.6±0.4um, and the density of the sandblasting powder mixed with water is 1.013g / cm 3 .

[0017] Preferably, the metal content of the silicon wafer is tested by the LTOD hot plate method, the silicon wafer to be tested is placed on a 300° C. hot plate and heated for 2 hours, followed by ICP-MS testing.

[0018] Preferably, the silicon wafer is pretreated first, and the surface of the silicon wafer to be tested is cleaned twice with a 2% HF + 2% H2O2 mixed solution to remove the natural oxide film and dirt on the surface; then the silicon wafer to be tested is placed on a 300°C heating plate and heated for 2 hours; after the temperature is cooled to room temperature, the surface metal elements of the silicon wafer are collected with 2% HF + 2% H2O2 and detected by ICP-MS.

[0019] ICP-MS, called plasma mass spectrometer, is an analytical instrument that combines inductively coupled plasma (ICP) technology and mass spectrometry.

[0020] Preferably, the oxidation-induced stacking fault density is measured by subjecting the polished silicon wafer to thermal oxidation and preferential etching, and observing and calculating the oxidation-induced stacking faults on the back damaged surface using a microscope.

[0021] Preferably, the silicon wafer is pretreated at 1100° C. for 1 h, and then the silicon wafer is etched in a 2% HF+2% H2O2 mixed solution, and the number of oxidation-induced stacking faults per unit field of view is observed under a microscope, and the corresponding OISF density is calculated according to the following formula: OISF density = number of oxidation-induced stacking faults / unit field of view, unit: number / cm 2 .

[0022] Preferably, the acid etching process sequentially includes a water wheel, a wafer reversing machine, an etching cage, an etching machine, a wafer reversing machine, and an etching cage and a water wheel, and a mixed acid is used to remove the mechanical damage layer on the surface of the silicon wafer to achieve a target thickness of 738±8um and a silicon wafer with no residual mechanical damage layer.

[0023] Preferably, the mixed acid consists of HF solution, HNO3 solution and CH3COOH solution.

[0024] The present invention can achieve the following effects:

[0025] The present invention provides a process for improving metal gettering of silicon wafers by wet back damage. Compared with the prior art, the back soft damage process is adopted to enable the silicon wafer to have a certain gettering ability in the high temperature thermal process of the device, thereby reducing the metal content in the silicon wafer. Sand material is sprayed and mixed with water to artificially damage the back of the silicon wafer. These scars will induce a large number of dislocations to form stacking faults after high temperature oxidation, thereby achieving the effect of absorbing metal impurities.

[0026] By introducing stress or damage on the back side of the silicon wafer, the lattice incompleteness, stress field and stress concentration points formed in the local area can effectively absorb the harmful impurities introduced in the process, so that the harmful metal impurities are deposited at the defects and a clean area is formed on the front surface of the silicon wafer. DETAILED DESCRIPTION

[0027] The technical solution of the invention is further specifically described below through embodiments.

[0028] Embodiment: A process for improving metal gettering of silicon wafers by wet backside damage, comprising the following steps:

[0029] Step 1: Divide the silicon wafers into several experimental groups, first perform chamfering and grinding, and then perform acid etching. The silicon wafers are doped with lightly doped BO, Dia: 200.02um, and crystal orientation <100>.

[0030] The acid etching process is carried out in sequence by water wheel, wafer rewinding machine, etching cage, etching machine, wafer rewinding machine, etching cage and water wheel, and the mechanical damage layer on the surface of the silicon wafer is removed by mixed acid to achieve the target thickness of 738±8um without residual mechanical damage layer of the silicon wafer. The mixed acid is composed of HF solution, HNO3 solution and CH3COOH solution.

[0031] Step 2: Use S1O2 powder of the same particle size and different sandblasting pressure conditions to perform wet back soft damage treatment on silicon wafers. The sandblasting pressure is 0.04Mpa~0.09Mpa, and the sandblasting pressure difference of silicon wafers in each experimental group is 0.005Mpa. The particle size of sandblasting powder is 3.6±0.4um, and the density after sandblasting and water mixing is 1.013g / cm 3 .

[0032] Step 3: Clean and polish the back of the silicon wafer after sandblasting.

[0033] Step 4: Clean after polishing.

[0034] Step 5: Conduct metal measurement and oxidation-induced stacking fault density measurement of silicon wafers.

[0035] The metal content of the silicon wafer was tested by the LTOD hot plate method. The silicon wafer to be tested was placed on a 300°C hot plate and heated for 2 hours, followed by ICP-MS testing.

[0036] First, the silicon wafer was pretreated and the surface of the silicon wafer to be tested was cleaned twice with a 2% HF + 2% H2O2 mixed solution to remove the natural oxide film and dirt on the surface; then the silicon wafer to be tested was placed on a 300°C heating plate and heated for 2 hours; after the temperature was cooled to room temperature, the surface metal elements of the silicon wafer were collected with 2% HF + 2% H2O2 and detected by ICP-MS.

[0037] The density of oxidation-induced stacking faults was determined by subjecting the polished silicon wafer to thermal oxidation and preferential etching, and the oxidation-induced stacking faults on the back damaged surface were observed and calculated using a microscope.

[0038] The silicon wafer was pretreated at 1100°C for 1 hour, and then etched in a 2% HF + 2% H2O2 mixed solution. The number of oxidation-induced stacking faults per unit field of view was observed under a microscope, and the corresponding OISF density was calculated according to the following formula: OISF density = number of oxidation-induced stacking faults / unit field of view, unit: number / cm 2 .

[0039] The experimental results obtained through testing are as follows:

[0040] (1) The bulk metal Cu content of the silicon wafer with back side damaged by sandblasting pressure of 0.07Mpa is as low as 1.12E+09. As the sandblasting pressure decreases, the degree of damage to the back side of the silicon wafer also gradually decreases, and the adsorption capacity of metal gradually weakens.

[0041] (2) At the same time, the oxidation-induced stacking fault density of the silicon wafer under this condition was tested. Due to the strong damage on the back of the silicon wafer, a large number of stacking faults are easily generated on the back of the silicon wafer under the dual effects of stress and heat treatment, forming a clean area on the front of the silicon wafer. The corresponding OISF density will also be higher, 1.1E+06 / cm 2 .

[0042] In summary, the process method of improving metal impurity absorption of silicon wafers through wet back damage explores the process parameters under different sandblasting pressures. The research results show that the metal content of the sandblasting pressure body under 0.07Mpa is lower, and the number of oxidation-induced stacking fault density is better. The back damage of silicon wafers under this condition has a strong ability to absorb metal contamination.

[0043] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are included in the patent scope of the present invention.

Claims

1. A process for improving metal gettering of silicon wafers by wet backside damage, characterized in that The steps are as follows: Step 1: Divide the silicon wafers into several experimental groups, first perform chamfering and grinding, then perform acid etching; Step 2: Use S102 powder with the same particle size and different sandblasting pressure conditions to perform wet back side soft damage treatment on silicon wafers; Step 3: Clean and polish the back of the silicon wafer after sandblasting; Step 4: Clean after polishing; Step 5: Conduct metal measurement and oxidation-induced stacking fault density measurement of silicon wafers.

2. The process for improving metal gettering of silicon wafers by wet back surface damage according to claim 1, characterized in that: The silicon wafer is doped with lightly doped B0, Dia: 200.02umm, and crystal orientation <100>.

3. The process for improving metal gettering of silicon wafers by wet back surface damage according to claim 1, characterized in that: The sandblasting pressure was 0.04 MPa to 0.09 MPa, and the sandblasting pressure difference of the silicon wafer in each experimental group was 0.005 MPa.

4. The process for improving metal gettering of silicon wafers by wet back surface damage according to claim 1, characterized in that: The particle size of sandblasting powder is 3.6±0.4um, and the density of sandblasting powder mixed with water is 1.013g / cm 3 .

5. The process for improving metal gettering of silicon wafers by wet back surface damage according to claim 1, characterized in that: The metal content of the silicon wafer was tested by the LTOD hot plate method. The silicon wafer to be tested was placed on a 300°C hot plate and heated for 2 hours, followed by ICP-MS testing.

6. The process for improving metal gettering of silicon wafers by wet back surface damage according to claim 5, characterized in that: First, the silicon wafer was pretreated and the surface of the silicon wafer to be tested was cleaned twice with a 2% HF + 2% H2O2 mixed solution to remove the natural oxide film and dirt on the surface; then the silicon wafer to be tested was placed on a 300°C heating plate and heated for 2 hours; after the temperature was cooled to room temperature, the surface metal elements of the silicon wafer were collected with 2% HF + 2% H2O2 and detected by ICP-MS.

7. The process for improving metal gettering of silicon wafers by wet back surface damage according to claim 1, characterized in that: The density of oxidation-induced stacking faults was determined by subjecting the polished silicon wafer to thermal oxidation and preferential etching, and the oxidation-induced stacking faults on the back damaged surface were observed and calculated using a microscope.

8. The process for improving metal gettering of silicon wafers by wet back surface damage according to claim 7, characterized in that: The silicon wafer was first pretreated at 1100°C for 1 hour, and then etched in a 2% HF + 2% H2O2 mixed solution. The number of oxidation-induced stacking faults per unit field of view was observed under a microscope, and the corresponding OISF density was calculated according to the following formula: OISF density = number of oxidation-induced stacking faults / unit viewing area, unit: pieces / cm 2 .

9. The process for improving metal gettering of silicon wafers by wet back surface damage according to claim 1, characterized in that: The acid etching process sequentially includes water wheel, wafer rewinding machine, etching cage, etching machine, wafer rewinding machine, etching cage and water wheel. Mixed acid is used to remove the mechanical damage layer on the surface of the silicon wafer to achieve the target thickness of 738±8um silicon wafer with no residual mechanical damage layer.

10. The process for improving metal gettering of silicon wafers by wet back surface damage according to claim 9, characterized in that: The mixed acid consists of HF solution, HNO3 solution and CH3COOH solution.