Diffusion junction depth calculation method

Abstract

The invention relates to the technical field of semiconductor manufacturing. A diffusion junction depth calculation method comprises the following steps that 1, a to-be-tested sample is fixed through a grinding wheel machine clamping plate, and one side of the polishing face of the to-be-tested sample faces a grinding wheel; a testing groove is ground in the surface of the sample to be tested through a grinding wheel, the transverse end face of the testing groove is rectangular, and the longitudinal end face of the testing groove is arc-shaped; step 2, dripping a mixed solution of hydrofluoric acid and nitric acid on the surface layer of the ground test tank, and dyeing for 10-15 seconds; 3, washing the surface of the sample to be detected for 30-40 seconds by using pure water, and wiping and removing water stains on the surface of the sample by using dust-free cloth; and 4, measuring the parameter size of the vertical projection surface of the test groove under the microscope, measuring the outer diameter size of the grinding wheel, and calculating the diffusion junction depth according to the right triangle Pythagorean theorem.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing technology, in particular to a method for calculating diffusion junction depth. Background Art

[0002] Silicon wafers are placed in a furnace at 1250°C using an ion source diffusion process to introduce a certain concentration of impurity ions onto the silicon surface. The impurity ions form a diffusion layer on the silicon surface that has a different conductivity type from the substrate silicon. When the impurity concentration on the silicon surface reaches equilibrium with the impurity concentration within the substrate silicon, a PN junction is formed at this equilibrium point. The diffusion junction depth is the vertical distance from the PN junction to the silicon surface.

[0003] Currently, the most common method for testing diffusion junction depth is to crack the sample, stain it, and then observe it using a scanning electron microscope (SEM). This method requires high integrity of the observed surface after the sample is cracked. If silicon chips or interface damage are present on the observed surface, the position of the PN junction will be significantly affected, requiring multiple sets of duplicate samples. Another method uses a spreading resistance measuring instrument to calculate the curve. This equipment is expensive, and when there are many samples to be tested, the test efficiency cannot meet the timeliness requirements of production and distribution. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for calculating the depth of a diffused junction to solve at least one of the above technical problems.

[0005] In order to achieve the above object, the present invention provides a method for calculating the diffusion junction depth, which is characterized by comprising the following steps:

[0006] Step 1: Fix the sample to be tested with a grinding wheel clamp, with the polished surface of the sample facing the grinding wheel; grind a test groove on the surface of the sample to be tested with the grinding wheel, wherein the transverse end surface of the test groove is rectangular and the longitudinal end surface of the test groove is arc-shaped;

[0007] Step 2: drip a mixed solution of hydrofluoric acid and nitric acid onto the surface of the ground test tank and stain for 10-15 seconds;

[0008] Step 3: Rinse the surface of the sample with pure water for 30-40 seconds, and wipe it with a dust-free cloth to remove any water marks on the surface of the sample;

[0009] Step 4: Measure the parameter dimensions of the vertical projection surface of the test groove under a microscope. At the same time, measure the outer diameter of the grinding wheel and calculate the diffusion junction depth according to the Pythagorean theorem of a right triangle.

[0010] Further preferably, the diffusion layer of the sample to be tested is located on a side of the sample to be tested adjacent to the grinding wheel.

[0011] More preferably, the grinding wheel has a diameter of 40 mm to 35 mm.

[0012] Further preferably, the sample to be tested is a polished wafer with no pattern on the surface, which is made of the same silicon substrate material as the circulating product wafer, is put into and taken out of the same furnace, and is ion-source doped under the same diffusion process conditions.

[0013] Preferably, the test samples are placed at the furnace mouth, center, and tail of the operating furnace tube to monitor the uniformity of ion doping parameters within the entire tube. The diffusion junction depths measured on these samples are used to characterize the process parameter quality of the product wafers in the current process step. The entire testing process is non-destructive to the product wafers.

[0014] Further preferably, in step 2, the mixed solution is prepared by mixing a hydrofluoric acid solution with a mass percentage concentration of 40% and a nitric acid solution with a mass percentage concentration of 65% in a volume ratio of 1:100.

[0015] More preferably, the hydrofluoric acid solution and the nitric acid solution are both of MOS grade.

[0016] Further preferably, the vertical projection surface of the test slot is a first left conductive type area, a second conductive type area, and a first right conductive type area distributed sequentially from left to right;

[0017] The calculation formula for the diffusion junction depth Xj is as follows:

[0018] Xj=c*d / D;

[0019] Wherein, c is the width of the test slot in the left-right direction excluding the first left conductive type region on the vertical projection plane, in μm;

[0020] d is the width of the first left conductive type region and the first right conductive type region in the left-right direction, in μm;

[0021] D is the diameter of the grinding wheel, in μm.

[0022] Further preferably, in step four, the vertical projection surface of the test slot under a microscope is measured to obtain the values of c and d.

[0023] Further preferably, the calculation formula of the diffusion junction depth Xj is calculated as follows:

[0024] According to the Pythagorean theorem of triangles, we get formula 1): ,

[0025] Wherein, a is the distance from the center of the test slot to the outer side of the first left conductive type area or the first right conductive type area;

[0026] b is the distance from the center of the test slot to the connection between the first left conductive type area or the first right conductive type area and the second conductive type area;

[0027] R is the grinding wheel radius;

[0028] Transform Formula 1) to obtain Formula 2): ;

[0029] Formula 2) is calculated to obtain Formula 3): ;

[0030] Further calculations yield Formula 4): ;

[0031] Since the actual grinding wheel radius R in mm is much larger than a in μm, and much larger than b in μm, we can get formula 4): Xj=(a 2 -b 2 ) / (2R);

[0032] Further conversion is obtained, Formula 5): Xj=(ab)*(a+b) / (2R);

[0033] Since (a+b)=c, (ab)=d, we have:

[0034] Xj=c*d / 2R= c*d / D.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] Using the Pythagorean theorem, the previously inaccessible diffusion junction depth Xj can be directly calculated using a formula by measuring the diameter D of the grinding wheel and the distances c and d between the two segments in the dyeing pattern. This ingenious and convenient method is ideal for batch production lines. It ensures accurate determination of process parameters while meeting production and distribution timelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic cross-section of the sample to be tested in specific embodiment 1 of the present invention;

[0038] Figure 2 This is a partial orthographic projection view of the test slot of the sample to be tested in specific embodiment 1 of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to the accompanying drawings.

[0040] See also Figure 1 as well as Figure 2 Specific embodiment 1: A method for calculating the depth of a diffusion junction comprises the following steps:

[0041] Step 1: Fix the sample to be tested with a grinding wheel clamp, with the polished surface of the sample facing the grinding wheel; grind a test groove on the surface of the sample to be tested with the grinding wheel, wherein the transverse end surface of the test groove is rectangular and the longitudinal end surface of the test groove is arc-shaped;

[0042] Step 2: drip a mixed solution of hydrofluoric acid and nitric acid onto the surface of the ground test tank and stain for 10-15 seconds;

[0043] Step 3: Rinse the surface of the sample with pure water for 30-40 seconds, and wipe it with a dust-free cloth to remove any water marks on the surface of the sample;

[0044] Step 4: Measure the parameter dimensions of the vertical projection surface of the test groove under a microscope. At the same time, measure the outer diameter of the grinding wheel and calculate the diffusion junction depth according to the Pythagorean theorem of a right triangle.

[0045] The diffusion layer 11 of the sample to be tested is located on a side of the sample to be tested adjacent to the grinding wheel. Figure 1 The o in the middle is the center of the grinding wheel.

[0046] The diameter of the grinding wheel is 40mm~35mm.

[0047] The sample to be tested is a polished wafer with no pattern on the surface, made of the same silicon substrate material as the circulating product wafer, put into and out of the same furnace, and ion-source doped under the same diffusion process conditions.

[0048] The test samples are placed at the furnace mouth, center, and tail of the operating furnace tube. This allows for monitoring the uniformity of ion doping parameters within the entire tube. The diffusion junction depths measured on these samples are used to characterize the quality of the process parameters of the finished wafers in the current process. The entire testing process is non-destructive to the finished wafers.

[0049] The thickness of the sample to be tested is 625 μm ± 15 μm.

[0050] The grinding method of the grinding wheel in step 1 is that the grinding wheel rotates downward from the surface of the sample to be tested, the grinding wheel descends at a speed of 1 μm / s, the total working time of the grinding wheel is 30 to 45 seconds, and the grinding wheel speed is 1500 to 2500 r / min.

[0051] In step 2, a mixed solution of 40% by weight hydrofluoric acid solution and 65% by weight nitric acid solution is prepared in a volume ratio of 1:100. Both the hydrofluoric acid solution and the nitric acid solution are of MOS grade.

[0052] The vertical projection surface of the test slot includes a first left conductive type area 12 , a second conductive type area 13 , and a first right conductive type area 14 , which are sequentially distributed from left to right.

[0053] When the first left conductive type region and the first right conductive type region are N-type regions, the second conductive type region is a P-type region.

[0054] When the first left conductive type region and the first right conductive type region are P-type regions, the second conductive type region is an N-type region.

[0055] The calculation formula for the diffusion junction depth Xj is as follows:

[0056] Xj=c*d / D;

[0057] Wherein, c is the width of the vertical projection plane of the test slot in the left-right direction excluding the first left conductive type region 12, in μm;

[0058] d is the width of the first left conductive type region 12 and the first right conductive type region 14 in the left-right direction, in μm;

[0059] D is the diameter of the grinding wheel, in μm.

[0060] Further preferably, in step four, the vertical projection surface of the test slot under a microscope is measured to obtain the values of c and d.

[0061] Further preferably, the calculation formula of the diffusion junction depth Xj is calculated as follows:

[0062] According to the Pythagorean theorem of triangles, we get formula 1): ,

[0063] Wherein, a is the distance from the center of the test slot to the outer side of the first left conductive type area or the first right conductive type area;

[0064] b is the distance from the center of the test slot to the connection between the first left conductive type area or the first right conductive type area and the second conductive type area;

[0065] R is the grinding wheel radius;

[0066] Transform Formula 1) to obtain Formula 2): ;

[0067] Formula 2) is calculated to obtain Formula 3): ;

[0068] Further calculations yield Formula 4): ;

[0069] Since the actual grinding wheel radius R in mm is much larger than a in μm, and much larger than b in μm, we can get formula 4): Xj=(a 2 -b 2 ) / (2R);

[0070] Further conversion is obtained, Formula 5): Xj=(ab)*(a+b) / (2R);

[0071] Since (a+b)=c, (ab)=d, we have:

[0072] Xj=c*d / 2R= c*d / D.

[0073] The above are only preferred embodiments of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for calculating diffusion junction depth, characterized in that: The steps include: Step 1: Fix the sample to be tested with a grinding wheel clamp, with the polished surface of the sample facing the grinding wheel; grind a test groove on the surface of the sample to be tested with the grinding wheel, wherein the transverse end surface of the test groove is rectangular and the longitudinal end surface of the test groove is arc-shaped; Step 2: drip a mixed solution of hydrofluoric acid and nitric acid onto the surface of the ground test tank and stain for 10-15 seconds; Step 3: Rinse the surface of the sample with pure water for 30-40 seconds, and wipe it with a dust-free cloth to remove any water marks on the surface of the sample; Step 4: Measure the parameter dimensions of the vertical projection surface of the test groove under a microscope. At the same time, measure the outer diameter of the grinding wheel and calculate the diffusion junction depth according to the Pythagorean theorem of a right triangle.

2. The method for calculating the diffusion junction depth according to claim 1, wherein: The diffusion layer of the sample to be tested is located on a side of the sample to be tested adjacent to the grinding wheel.

3. The method for calculating the diffusion junction depth according to claim 1, wherein: The diameter of the grinding wheel is 40 mm to 35 mm.

4. The method for calculating the diffusion junction depth according to claim 1, wherein: The sample to be tested is a polished wafer with no pattern on the surface, made of the same silicon substrate material as the circulating product wafer, put into and out of the same furnace, and ion-source doped under the same diffusion process conditions.

5. The method for calculating the diffusion junction depth according to claim 1, wherein: The samples to be tested are placed at the furnace mouth, furnace middle and furnace tail of the working furnace tube respectively.

6. The method for calculating the diffusion junction depth according to claim 1, wherein: In step 2, the mixed solution is prepared by mixing a hydrofluoric acid solution with a mass percentage concentration of 40% and a nitric acid solution with a mass percentage concentration of 65% in a volume ratio of 1:

100.

7. The method for calculating diffusion junction depth according to claim 1, wherein: The hydrofluoric acid solution and the nitric acid solution are both MOS grade.

8. The method for calculating diffused junction depth according to claim 1, wherein: The vertical projection surface of the test slot is a first left conductive type area, a second conductive type area, and a first right conductive type area distributed sequentially from left to right; The calculation formula for the diffusion junction depth Xj is as follows: Xj=c*d / D; Wherein, c is the width of the test slot in the left-right direction excluding the first left conductive type region on the vertical projection plane, in μm; d is the width of the first left conductive type region and the first right conductive type region in the left-right direction, in μm; D is the diameter of the grinding wheel, in μm.

9. The method for calculating diffused junction depth according to claim 8, wherein: Step 4: Measure the vertical projection surface of the test slot under the microscope to obtain the values of c and d.

10. The method for calculating diffused junction depth according to claim 8, wherein: The calculation formula for the diffusion junction depth Xj is as follows: According to the Pythagorean theorem of triangles, we get formula 1): , Wherein, a is the distance from the center of the test slot to the outer side of the first left conductive type area or the first right conductive type area; b is the distance from the center of the test slot to the connection between the first left conductive type area or the first right conductive type area and the second conductive type area; R is the grinding wheel radius; Transform Formula 1) to obtain Formula 2): ; Formula 2) is calculated to obtain Formula 3): ; Further calculations yield Formula 4): ; Since the actual grinding wheel radius R in mm is much larger than a in μm, and much larger than b in μm, then we get formula 4): Xj=(a 2 -b 2 ) / (2R); Further conversion is obtained, Formula 5): Xj=(ab)*(a+b) / (2R); Since (a+b)=c, (ab)=d, we have: Xj=c*d / 2R= c*d / D.

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