A method for optimizing reliability of aluminum nitride copper clad substrate

Abstract

The application discloses a method for optimizing reliability of an aluminum nitride copper-clad substrate and relates to the technical field of semiconductor devices; the method improves the reliability of the aluminum nitride copper-clad substrate through twice baking and residual copper rate compensation; specifically, after a sintered and twisted aluminum nitride copper-clad substrate is baked for the first time, pattern transfer is performed, etching holes are applied at sharp corners of a pattern surface, residual copper rate compensation is performed on a non-pattern surface by applying etching holes / grooves on the non-pattern surface according to a residual copper rate difference between the non-pattern surface and the pattern surface, and the second baking is performed after the pattern transfer. Through the control of the residual copper rates on both sides of the substrate and the twice baking, the stress on both sides is balanced, and the overall reliability is optimized.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of semiconductor devices, and particularly relates to a method for optimizing the reliability of an aluminum nitride copper-clad substrate. BACKGROUND

[0002] The aluminum nitride (AlN) copper-clad substrate is widely applied to high-power electronic devices due to its high thermal conductivity (>=170 W / m*K), but the mechanical strength is low (bending strength <400 MPa), and the ceramic sheet is prone to cracking failure under thermal stress. The existing technology improves the reliability in the following ways:

[0003] 1. Single baking process: thermal stress is released after copper ceramic sintering, but the secondary stress accumulation after pattern transfer cannot be solved;

[0004] 2. Local etching (such as CN202111163775.7): etching holes and grooves at weak places of the copper layer, but the stress balance effect is limited without combining dynamic control of residual copper rate;

[0005] 3. Nitrogen environment annealing: oxidation is inhibited, but the temperature-time parameters are not optimized, and the residual stress still causes warping >0.5 mm.

[0006] Technical difficulties: the existing etching process parameters are single (hole depth / interval fixed), which cannot match the requirements of different substrate sizes and power densities; in addition, the baking and etching do not form a synergistic mechanism, and the ceramic cracking failure cycle is less than 300 times (IEC60749-25 standard). SUMMARY

[0007] The application aims to provide a method for optimizing the reliability of an aluminum nitride copper-clad substrate to solve the problems in the prior art.

[0008] To achieve the above-mentioned purpose, the application provides the following technical scheme:

[0009] A method for optimizing the reliability of an aluminum nitride copper-clad substrate, which improves the reliability by twice baking and residual copper rate compensation of the aluminum nitride copper-clad substrate; specifically, after the sintered aluminum nitride copper-clad substrate is twisted, the first baking is performed, then the pattern transfer is performed, etching holes are applied at the sharp corners of the pattern surface, the residual copper rate difference between the non-pattern surface and the pattern surface of the copper-clad substrate is obtained, and etching holes / grooves are applied on the non-pattern surface for dynamic compensation of the residual copper rate, and then the second baking is performed after the pattern transfer.

[0010] Because the thermal expansion coefficients of copper and ceramic sheet in the aluminum nitride copper-clad substrate are different, the substrate is subjected to tensile stress after sintering, resulting in weak reliability. The surface is directly twisted after sintering of the aluminum nitride copper-clad substrate, so the first baking (referred to as pre-baking) is used to release the stress;

[0011] Preferably, the first baking process parameters include: temperature 75-85℃, time 15-25min, nitrogen concentration ≥99.999%, oxygen content ≤10ppm.

[0012] At the edge of copper-ceramic combination, stress distribution is uneven, which is the weakest position of reliability; the functions of the two sides of aluminum nitride copper clad plate are different in use, including the pattern surface and the non-pattern surface, and the difference of residual copper rate between the two sides is large, which leads to uneven stress distribution, and this is also the reason for poor reliability, therefore, in the pattern transfer, etching holes are applied at the edge of copper-ceramic combination to release stress, and according to the residual copper rate of the pattern surface and the non-pattern surface, etching grooves / holes are applied on the non-pattern surface to balance the stress of the two sides of the aluminum nitride ceramic sheet;

[0013] Preferably, the aperture calculation formula of the etching hole is: aperture d=0.02×L, L is the side length of the aluminum nitride copper clad plate;

[0014] Preferably, the aperture of the etching hole is 0.5-1.2mm;

[0015] Preferably, the hole spacing of the etching hole is 1.5-2.0 times of the aperture, forming a uniform stress buffer zone;

[0016] Preferably, the groove width of the etching groove is the thickness of the corresponding surface copper layer+(0.2-1.0)mm, and the groove width≤1.0mm;

[0017] Preferably, the length of the etching groove is 20%-100% of the side length of the aluminum nitride copper clad plate;

[0018] Preferably, the groove depth of the etching groove is 40%-100% of the thickness of the corresponding surface copper layer;

[0019] Preferably, the dynamic compensation of residual copper rate is to make the difference ΔR of residual copper rate between the non-pattern surface and the pattern surface ≤3%;

[0020] Because the two surfaces of the aluminum nitride copper clad plate are different in function, the etching holes / grooves added for residual copper rate compensation on the non-pattern surface are generally different from those on the pattern surface:

[0021] The etching holes on the non-pattern surface can release stress and adjust residual copper rate, and can be placed at any position, and the etching groove is also used to adjust residual copper rate, and the groove depth does not necessarily need to be 100% deep;

[0022] The etching holes on the pattern surface are generally used to release stress and placed at the R corner, and the etching groove is used to separate the copper pads and play an insulating role, and the groove depth must be 100% ceramic leakage; unless the drawing is specially required, the pattern surface generally does not increase the groove for adjusting residual copper rate to avoid affecting the space use of the copper pads on the pattern surface;

[0023] Therefore, the stress distribution of the graphic surface and the non-graphic surface is different, so that the substrate is subjected to a second baking (post-baking) after the graphic transfer to release the stress.

[0024] Preferably, the process parameters of the second baking include: the temperature is 100-120℃, the time is 15-25min, and the heating rate is 3℃ / min.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] 1. The reliability of the weak point of the sharp corner is enhanced by increasing the copper etching hole at the weak point.

[0027] 2. The stress balance of the two sides is achieved by controlling the residual copper rate of the two sides and twice baking, and the overall reliability is optimized. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a schematic diagram of the first baking in the present application;

[0029] Figure 2 It is a schematic diagram of the residual copper rate compensation in the present application;

[0030] Figure 3 It is a schematic diagram of increasing the copper etching hole at the weak point of the sharp corner;

[0031] Figure 4 It is the non-graphic surface after the residual copper rate dynamic compensation in Example 1;

[0032] Figure 5 It is the graphic surface after the residual copper rate dynamic compensation in Example 1;

[0033] Figure 6 It is the ultrasonic scanning image of Example 1 after 1000 times of TC cold and hot cycle test;

[0034] Figure 7 It is the graphic surface in Comparative Example 1;

[0035] Figure 8 It is the non-graphic surface in Comparative Example 1;

[0036] Figure 9 It is the ultrasonic scanning image of Comparative Example 1 after 300 times of TC cold and hot cycle test;

[0037] Figure 10 It is the graphic surface after the residual copper rate dynamic compensation in Comparative Example 2;

[0038] Figure 11 It is the non-graphic surface after the residual copper rate dynamic compensation in Comparative Example 2;

[0039] Figure 12The pattern surface of the residual copper rate dynamic compensation in the comparative example 3;

[0040] Figure 13 The non-pattern surface of the residual copper rate dynamic compensation in the comparative example 3;

[0041] Figure 14 The ultrasonic scanning image of the comparative example 3 after 600 times of TC cold and hot cycle test. DETAILED DESCRIPTION

[0042] All other embodiments obtained by the person skilled in the art without creative labor based on the embodiments in the present application belong to the scope of protection of the present application.

[0043] In the experiment, the specification of the sintered and twisted aluminum nitride copper-clad substrate is 138*190mm, the copper thickness is 0.3mm, the porcelain thickness is 0.635mm, and the copper thickness is 0.3mm;

[0044] Embodiment 1: A method for optimizing the reliability of an aluminum nitride copper-clad substrate, comprising the following steps:

[0045] 1. First baking: the first baking of the sintered and twisted aluminum nitride copper-clad substrate is performed in a nitrogen oven, the baking temperature is 75℃, and the time is 15min;

[0046] 2. In the pattern transfer, the residual copper rate dynamic compensation is performed, as shown in Figure 4 、 5 ,

[0047] 1) According to the pattern, etching holes are applied at the sharp corner weak position of the pattern surface, the diameter of the etching hole is 0.5mm, and the hole spacing is 1.0mm;

[0048] 2) According to the residual copper rate of the pattern surface, strip-shaped etching grooves are applied on the non-pattern surface, the groove width is 0.8mm, the length accounts for 100% of the side length, the groove depth is 100% of the copper layer thickness of the non-pattern surface, and etching holes are applied on both sides of the etching groove, the diameter is 1.0mm, and the hole spacing is 1.5mm;

[0049] 3. Second baking: the second baking of the aluminum nitride copper-clad substrate is performed after the pattern transfer is completed, the temperature is 100℃ in a nitrogen oven, the time is 15min, and the heating rate is 3℃ / min.

[0050] Embodiment 2: A method for optimizing the reliability of an aluminum nitride copper-clad substrate, comprising the following steps:

[0051] 1. First baking: the first baking of the sintered and twisted aluminum nitride copper-clad substrate is performed in a nitrogen oven, the baking temperature is 80℃, and the time is 20min;

[0052] 2. In the pattern transfer, dynamic compensation of residual copper rate is performed:

[0053] 1) According to the pattern, etching holes with a diameter of 0.5 mm and a hole spacing of 1.0 mm are applied on both sides of the etching groove on the pattern surface;

[0054] 2) According to the residual copper rate of the pattern surface, a strip-shaped etching groove with a groove width of 1 mm, a length of 100% of the side length, and a groove depth of 100% of the thickness of the copper layer on the non-pattern surface is applied on the non-pattern surface, and etching holes with a diameter of 1.0 mm and a hole spacing of 1.5 mm are applied on both sides of the etching groove;

[0055] 3. Post-baking: After the pattern transfer is completed, the aluminum nitride copper-clad substrate is subjected to a second baking in a nitrogen oven at a temperature of 110°C for 20 minutes, and the heating rate is 3°C / min.

[0056] Example 3: A method for optimizing the reliability of an aluminum nitride copper-clad substrate, comprising the following steps:

[0057] 1. Pre-baking: The twisted aluminum nitride copper-clad substrate after sintering is subjected to a first baking in a nitrogen oven at a baking temperature of 80°C for 20 minutes;

[0058] 2. In the pattern transfer, dynamic compensation of residual copper rate is performed:

[0059] 1) According to the pattern, etching holes with a diameter of 0.5 mm and a hole spacing of 1.0 mm are applied on both sides of the etching groove on the pattern surface;

[0060] 2) According to the residual copper rate of the pattern surface, a strip-shaped etching groove with a groove width of 0.8 mm, a length of 100% of the side length, and a groove depth of 100% of the thickness of the copper layer on the non-pattern surface is applied on the non-pattern surface, and etching holes with a diameter of 1.2 mm and a hole spacing of 1.5 mm are applied on both sides of the etching groove;

[0061] 3. Post-baking: After the pattern transfer is completed, the aluminum nitride copper-clad substrate is subjected to a second baking in a nitrogen oven at a temperature of 110°C for 20 minutes, and the heating rate is 3°C / min.

[0062] Example 4: A method for optimizing the reliability of an aluminum nitride copper-clad substrate, comprising the following steps:

[0063] 1. Pre-baking: The twisted aluminum nitride copper-clad substrate after sintering is subjected to a first baking in a nitrogen oven at a baking temperature of 80°C for 20 minutes;

[0064] 2. In the pattern transfer, dynamic compensation of residual copper rate is performed:

[0065] 1) Based on the pattern, etch holes are applied to the weak points at the sharp corners of the pattern surface. The diameter of the etch holes is 0.5 mm and the spacing between the holes is 1.0 mm.

[0066] 2) Based on the residual copper ratio of the patterned surface, apply a strip etching groove to the non-patterned surface. The groove width is 1.0 mm, the length is 100% of the side length, and the groove depth is 100% of the copper layer thickness of the non-patterned surface. Also, apply etching holes on both sides of the etching groove with a diameter of 1.2 mm and a hole spacing of 1.8 mm.

[0067] 3. Post-bake: After the pattern transfer is completed, the aluminum nitride copper-clad substrate is baked a second time in a nitrogen oven at 110℃ for 20 minutes at a heating rate of 3℃ / min.

[0068] Example 5: A method for optimizing the reliability of aluminum nitride copper-clad substrates, comprising the following steps:

[0069] 1. First baking: The sintered and twisted aluminum nitride copper-clad substrate is baked for the first time in a nitrogen oven at 80°C for 20 minutes.

[0070] 2. In graphic transfer, perform dynamic compensation for residual copper rate:

[0071] 1) Based on the pattern, etch holes are applied to the weak points of the sharp corners of the pattern surface. The diameter of the etch holes is 0.8 mm and the spacing between the holes is 1.2 mm.

[0072] 2) Based on the residual copper ratio of the patterned surface, apply a strip etching groove to the non-patterned surface. The groove width is 0.5 mm, the length is 100% of the side length, and the groove depth is 60% of the copper layer thickness of the non-patterned surface. Also, apply etching holes on both sides of the etching groove with a diameter of 1.0 mm and a hole spacing of 2.0 mm.

[0073] 3. Post-bake: After the pattern transfer is completed, the aluminum nitride copper-clad substrate is baked a second time in a nitrogen oven at 110℃ for 20 minutes at a heating rate of 3℃ / min.

[0074] Comparative Example 1: As a control experiment for Example 1, no double baking or dynamic compensation for residual copper rate was performed, such as... Figure 7 , 8 As shown.

[0075] Comparative Example 2: As a control experiment for Example 1, no etching grooves or etching holes were applied to the non-patterned surfaces, and no post-bake was performed. The specific steps are as follows:

[0076] 1. First baking: The sintered and twisted aluminum nitride copper-clad substrate is baked for the first time in a nitrogen oven at 80°C for 20 minutes.

[0077] 2. In the pattern transfer, dynamic compensation of residual copper rate is performed: according to the pattern, copper etching holes are applied at the sharp corner weak points of the pattern surface, the diameter of the etching holes is 0.5 mm, and the hole spacing is 1.0 mm; as shown in Figure 10 、 11 .

[0078] Comparative Example 3: As a control experiment of Example 1, etching holes are applied to both the pattern surface and the non-pattern surface, but the non-pattern surface no longer applies etching grooves, as shown in Figure 12 、 13 , and no pre-baking is performed; the specific steps are as follows:

[0079] 1. In the pattern transfer, dynamic compensation of residual copper rate is performed:

[0080] 1) According to the pattern, copper etching holes are applied at the sharp corner weak points of the pattern surface, the diameter of the etching holes is 0.5 mm, and the hole spacing is 1.0 mm;

[0081] 2) According to the residual copper rate of the pattern surface, etching holes are applied on both sides of the etching groove, with a diameter of 1.0 mm and a hole spacing of 1.5 mm;

[0082] 2. Post-baking: After the pattern transfer is completed, the aluminum nitride copper clad substrate is subjected to a second baking, in a nitrogen oven, at a temperature of 110°C for 20 minutes, with a heating rate of 3°C / min.

[0083] Based on the above, the data of the partially adjusted Examples 1-5 and Comparative Examples 1-3 are listed and arranged as shown in Table 1:

[0084] Table 1

[0085]

[0086] Detection experiment:

[0087] The substrates treated in Examples 1-5 and Comparative Examples 1-3 are subjected to reliability testing (thermal cycle test, TC), and the test conditions are: temperature cycle -55°C-150°C, each cycle of high and low temperature is 15 min, and the conversion time is ≤15 s;

[0088] The test results are shown in Table 2

[0089] Table 2

[0090]

[0091] Conclusion: The ultrasonic scan image of the aluminum nitride copper clad substrate treated in Example 1 after TC thermal cycle is shown in Figure 6 , and it does not fail after 1000 cycles of testing; the ultrasonic scan image of the aluminum nitride copper clad substrate treated in Comparative Example 1 after TC thermal cycle is shown in Figure 9As shown in the figure, the porcelain cracks after 300 cycles of the test; as can be seen from the experimental results of comparative example 1 and comparative example 1, after twice baking and dynamic compensation of residual copper rate, the reliability of the aluminum nitride copper clad substrate is effectively optimized;

[0092] The aluminum nitride copper clad substrate after treatment in comparative example 2 failed after 500 times of TC cold and hot cycle test, with porcelain cracking and copper layer delamination; as can be seen, the compensation of residual copper rate on the non-pattern surface and the post-baking play an indispensable role in optimizing the reliability of the substrate;

[0093] The ultrasonic scanning image of the aluminum nitride copper clad substrate after treatment in comparative example 3 after TC cold and hot cycle test is as shown in the figure Figure 14 As shown in the figure, the copper porcelain delamination fails after 600 cycles of the test; as can be seen, the compensation of etching groove on the non-pattern surface and the pre-baking play an indispensable role in optimizing the reliability of the substrate.

[0094] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the present application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, it still can be modified to the technical solutions recorded in the foregoing embodiments, or equivalent replacement of some technical features. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for optimizing the reliability of aluminum nitride copper-clad substrates, characterized in that, Specifically, after the sintered and twisted aluminum nitride copper-clad substrate is baked for the first time, the pattern is transferred. After applying etching holes at the sharp corners of the patterned surface, etching holes / or etching grooves are applied on the non-patterned surface to dynamically compensate for the residual copper rate based on the difference in residual copper rate between the non-patterned and patterned surfaces of the copper-clad substrate. After transferring the pattern, a second baking is performed. The formula for calculating the aperture of the etched hole is: aperture d = 0.02 × L, where L is the side length of the aluminum nitride copper-clad substrate; The spacing between etched holes is 1.5 to 2.0 times the diameter of the etched holes.

2. The method for optimizing the reliability of aluminum nitride copper-clad substrates according to claim 1, characterized in that, The process parameters for the first baking include: temperature of 75℃~85℃, time of 15min~25min, nitrogen concentration ≥99.999%, and oxygen content ≤10ppm.

3. The method for optimizing the reliability of aluminum nitride copper-clad substrates according to claim 1, characterized in that, The diameter of the etched holes is 0.5mm~1.2mm.

4. The method for optimizing the reliability of aluminum nitride copper-clad substrates according to claim 1, characterized in that, The width of the etching tank is the thickness of the copper clad layer on the corresponding surface plus (0.2~1.0) mm, and the width of the tank is ≤1.0 mm. The length is 20%~100% of the side length of the aluminum nitride copper clad substrate, and the depth of the tank is 40%~100% of the thickness of the copper clad layer on the corresponding surface.

5. The method for optimizing the reliability of aluminum nitride copper-clad substrates according to claim 1, characterized in that, The residual copper rate is dynamically compensated to ΔR≤3%, where ΔR is the difference between the residual copper rate of the non-graphic surface and the residual copper rate of the graphic surface.

6. The method for optimizing the reliability of aluminum nitride copper-clad substrates according to claim 1, characterized in that, The process parameters for the second baking include: temperature of 100℃~120℃, time of 15min~25min, and heating rate of 3℃ / min.

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