Method for controlling stress in substrates during laser deposition

Abstract

To provide a method for controlling stress in a substrate during laser deposition.SOLUTION: The invention relates to a method for controlling stress in a substrate during laser deposition, the method comprising the steps of: providing a laser deposition device 1 in which a target spot 10 is movable relative to a substrate 4 in order to deposit a target material onto a plurality of surface portions of the substrate; defining a plurality of discrete surface portions on the substrate 4; aligning the target spot 10 one after the other with each of the plurality of discrete surface portions and generating a plasma plume 11 to deposit the target material on each of the plurality of discrete surface portions; and adjusting at least one of parameters of the deposition process depending on the discrete surface portion with which the target spot 10 is aligned, the parameters comprising a temperature, a pressure, laser beam pulse duration, laser beam output, a distance of a target 3 to the substrate 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for controlling stress in a thin film on a substrate during laser deposition. [Background technology]

[0002] The fabrication of MEMS (Micro Electro Mechanical Systems) structures and RF (Radio Frequency) acoustic resonators uses substrates with one or more thin piezoelectric layers. These layers can be formed using laser deposition, in which a laser beam is directed at a target spot on the surface of a target material. This results in the formation of a plasma plume of the target material, which is then deposited onto the substrate.

[0003] Particle energy in the plasma plume, deposition rate, film thickness, and physical and chemical incorporation of material induce stress in the layer on the substrate.

[0004] An important aspect of the stress in deposited layers is the intrinsic stress, which is a structural and microstructural related property that arises as a result of the film growth mode, microstructural interactions, and any contamination.

[0005] Because these stresses affect the quality of MEMS structures and RF resonators, it is desirable to control them to obtain substrates with deposited layers in which the stress is uniformly distributed across the surface of the substrate. A uniform stress profile of the deposited layers on the wafer is important for improving the quality and yield of the fabricated MEMS and RF devices and reducing manufacturing costs.

[0006] In some other applications, it may be desirable to have a specific non-uniform stress profile to achieve a particular technological effect in MEMS structures or RF resonators.

[0007] US6156623 describes a technique for reducing stress in layers deposited using physical vapor deposition (PVD) or chemical vapor deposition (CVD). This publication proposes bending the substrate during deposition so that the substrate will bow after the layer is deposited, compensating for the stress introduced by the layer deposition. However, this bending does not allow for local variations in stress, but only allows a preset overall stress to be applied to the layer on the substrate.

[0008] EP2347993 also describes a technique for reducing stress in layers deposited by PVD or CVD. This publication proposes post-treatment of the substrate by locally irradiating the layer on the substrate with a laser beam, thereby locally heating the layer and reducing stress. Although the local heating by the laser beam reduces stress, it may also change the crystalline structure of the layer material.

[0009] WO2007046852 describes a method for providing multiple structures or devices on a single substrate. To this end, regions are defined on the substrate. Sufficient spacing is maintained so that layers in one region do not interdiffuse with layers in adjacent regions.

[0010] The parameters of the process of depositing layers within the regions are fixed and only vary between regions, and the separated regions do not form a continuous surface.

[0011] This publication further discloses that each region can be individually tested for properties such as stress. However, such testing is performed on the entire layer of the region, bounded by the spacing between adjacent layers. Stress differences within the entire layer are not measured or compensated for. Summary of the Invention

[0012] SUMMARY OF THE INVENTION The object of the present invention is to mitigate or obviate the above-mentioned drawbacks.

[0013] This object is, according to the invention, a method for controlling stress in a substrate during laser deposition, comprising the steps of: providing a laser deposition apparatus including a chamber having a target holder with a target, a substrate holder with a substrate facing the target, and a window, the laser deposition apparatus further including a laser beam directed through the window of the chamber to a spot on the target to generate a plasma plume of target material and deposit the target material on a surface portion of the substrate to form a thin film of the target material, the target spot being movable relative to the substrate to deposit the target material on multiple surface portions of the substrate; defining a plurality of discrete surface portions on a substrate; aligning the target spot with each of a plurality of discrete surface portions in turn to generate a plasma plume for depositing target material on each of the plurality of discrete surface portions; and adjusting at least one of the parameters of the deposition process in response to the discrete surface portion on which the target spot is located, the parameters including temperature, pressure, laser beam pulse duration, laser beam power, target-to-substrate distance, spot size, and RF ionization energy.

[0014] The method of the present invention involves dividing the surface of the substrate into a plurality of separate surface portions and then depositing a target material onto the surface portions using specific parameters for each surface portion.

[0015] Since particle energy in the plasma plume, deposition rate, film thickness, and the physical and chemical incorporation of material all affect the stress induced in the layer on the substrate, adjusting at least one parameter of the deposition process can control the stress induced in a particular surface portion of the substrate.

[0016] By adjusting at least one of the parameters of the deposition process according to the discrete surface portions to which the target spots are aligned, a specific deposition pattern can be obtained on the surface of the substrate, which in turn can result in a specific stress pattern on the surface of the substrate, which in turn can result in a more uniform stress pattern.

[0017] It is within the scope of the present invention that when the plasma plume passes over the same discrete surface portion more than once, the parameters of the deposition process may be maintained the same or may be changed for each pass over the discrete surface portion.

[0018] In a preferred embodiment of the method according to the invention, the plurality of discrete surface portions is defined as a two-dimensional grid, for example in longitudinal and lateral or radial and tangential directions.

[0019] Target material is typically deposited on large substrates by moving the substrate in XY directions, i.e., longitudinal and lateral directions, relative to the target spot, or by rotating the substrate and moving the target spot radially, i.e., radially and tangentially, relative to the substrate. Easier control is achieved by defining multiple discrete surface portions in the same direction as the relative movement of the target spot with respect to the substrate.

[0020] A further preferred embodiment of the method according to the present invention further comprises the following steps: measuring the stress of a thin film deposited on a substrate; comparing the stress measurements to a desired stress profile for the thin film; and Adjusting at least one parameter of the deposition process while taking the comparison into consideration.

[0021] By measuring the stress of a thin film on a substrate, the parameters of the deposition process can be more precisely adjusted so that the resulting stress corresponds to a desired stress profile.

[0022] Preferably, the stress of the thin film is measured in situ using a stress measurement device such as a wafer bow meter, which allows direct feedback into adjusting the parameters of the deposition process.

[0023] Another embodiment of the method according to the present invention comprises the following steps. depositing a target material onto a first substrate while holding deposition process parameters constant; measuring ex situ stress of a thin film deposited on a first substrate; calculating an adjustment value for each separate surface portion based on the stress measurements; and Performing the steps of claim 1 on a second substrate and using the calculated adjustment value in the step of adjusting at least one parameter of the deposition process in response to the discrete surface portion to which the target spot is aligned.

[0024] In this embodiment, a first substrate is subjected to deposition of a target material under certain deposition process parameters. The substrate is then removed from the deposition apparatus, and the stress of the thin film deposited on the substrate is measured. Based on the measured stress of the thin film on the first substrate, adjustments to the parameters of each of the separated surface portions are calculated. A second substrate is then subjected to deposition of the target material, and the deposition process parameters are adjusted for each of the separated surface portions according to the calculated adjustments. As a result, the second thin film formed on the substrate has a different stress profile across the surface of the substrate, which more closely corresponds to the desired stress profile. If necessary, the second substrate can be measured outside the deposition apparatus to further enhance the calculated adjustments to the deposition process parameters.

[0025] In another preferred embodiment of the method according to the invention, the temperature of the substrate at the discrete surface portions where the target spots are aligned is controlled by irradiating the substrate with a laser beam.

[0026] Another option is to provide a heater located in the laser deposition apparatus below the substrate with multiple individually controllable heating elements, allowing parts of the substrate to be heated differently.

[0027] It is known that the entire substrate is kept at a constant temperature during deposition. By irradiating the substrate with a laser beam, local temperature changes can be generated, increasing the temperature of the isolated surface area where the target spot is aligned compared to the temperature of the entire substrate.

[0028] In yet another embodiment of the method according to the present invention, the laser deposition apparatus further comprises at least one nozzle directed towards the discrete surface portion on which the target spot is aligned, the nozzle being supplied with a controlled gas flow to regulate the pressure for the deposition process.

[0029] Typically, the chamber of a laser deposition system is maintained at a constant pressure, typically near vacuum, allowing the plasma plume to travel unimpeded from the target to the substrate. It is also known to introduce certain types of gases into the chamber to mix with the plasma and enhance deposition.

[0030] In such cases, at least one nozzle aligned with the target can vary the local pressure around the isolated surface area relative to the overall pressure in the chamber, and can also allow for the introduction of other types of gases that mix with the plasma plume to provide different material properties in the deposited layer.

[0031] To adjust the parameters of the deposition process, it is possible to add more plasma plumes, change the spot size on the target, or physically shield portions of the plasma plume. [Brief explanation of the drawings]

[0032] These and other features of the present invention will be explained with reference to the accompanying drawings.

[0033] [Figure 1] 1 is a schematic diagram of a laser deposition apparatus for a method according to the present invention. [Figure 2A] 1 is a schematic top view of one embodiment of a substrate for a method according to the present invention. [Figure 2B] 1 is a schematic top view of another embodiment of a substrate for a method according to the present invention; [Figure 3] 1 is a diagram of a first embodiment of the method according to the invention; [Figure 4] 4 is a diagram of a second embodiment of the method according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] 1 shows a laser deposition apparatus 1 for the method according to the present invention. The laser deposition apparatus 1 has a chamber 2 in which a target holder having a target 3, a substrate holder, and a substrate 4 are arranged. The target 3 can be rotated by a motor 5, and the substrate 4 can be rotated by a motor 6.

[0035] The chamber 2 is provided with a first window 7 through which laser light 8 from a laser 9 is irradiated onto the target 3 at a target spot 10 to generate a plasma plume 11 which deposits on the substrate 4. The laser 9 is radially movable such that the target spot 10 moves radially relative to the substrate 4.

[0036] The substrate 4 is heated by a heater 12 having a separate heating element 13 so that only a portion of the substrate 4 can be heated.

[0037] A drain 14 equipped with a vacuum pump 15 is connected to the chamber 2 to create a low pressure inside the chamber 2. Also, a gas supply unit 16 equipped with a valve 17 is connected to the chamber 2 to create a specific gas atmosphere inside the chamber 2.

[0038] Wafer bow meters 18 and 19 are also provided, and a laser beam 21 is irradiated from a second window of the chamber 2 to measure the bending of the substrate 4, from which the stress of the thin film deposited on the substrate 4 is derived.

[0039] A controller 22 is provided to control the movement of the laser 9, the rotation of the target 3, the rotation of the substrate 4, and to control the vacuum pump 15 and the gas supply 16 in order to carry out the method of the present invention. In addition, measurements from wafer bow meters 18 and 19 are provided to the controller 22 to provide feedback on the stress of the thin film on the substrate 4.

[0040] 2B is a top view of a rectangular substrate 30 defining a grid of separate surface portions 31 in the vertical and horizontal directions. Typically, such a rectangular substrate 30 is moved in the X and Y directions to align each of the separate surface portions 31 with a target spot.

[0041] 2A shows a top view of a disk-shaped substrate 4 defining a grid of radially and tangentially separated surface portions 23. Typically, such a disk-shaped substrate 4 is rotated to move a target spot over each separated surface portion 23.

[0042] Figure 3 shows a diagram 40 of a first embodiment of a method according to the present invention. The diagram 40 begins with step 41, which is providing a laser deposition apparatus as shown in Figure 1. The method then proceeds to step 42, which is defining a plurality of discrete surface portions 23 on a substrate 4, as shown in Figure 2A.

[0043] Next, in step 43 , the target spot 10 is aligned with a discrete surface portion 23 on the substrate 4 and a plasma plume of target material 3 is generated and deposited on the discrete surface portion 23 .

[0044] Next, in step 44, the deposition process parameters are adjusted for the next separated surface portion 23, and then step 43 is repeated. The deposition process parameters can be adjusted by adjusting the substrate temperature with heaters 12, 13, supplying gas with gas supply device 16, or controlling the vacuum with vacuum pump 14. The parameter adjustments can also be controlled by measurements from wafer bow meters 18, 9.

[0045] Figure 4 is a diagram 50 of a second embodiment. In this method 50, a deposition apparatus 1, such as that shown in Figure 1, is provided in step 51. Next, in step 52, a first substrate is provided in the deposition apparatus 1, and in step 53, a plurality of discrete surface portions 23, such as that shown in Figure 2A, are defined thereon.

[0046] In step 54, the target spot is aligned with each of the plurality of discrete surface portions 23 in turn, and a plasma plume is generated to deposit the target material onto each of the plurality of discrete surface portions 23. During deposition on this first substrate, the deposition process parameters are held constant.

[0047] After the deposition process has covered all of the plurality of discrete surface portions 23, the stress of the first substrate is measured in step 55. These measurements are then compared to the desired stress profile, and adjustment parameters are calculated therefrom in step 56 and stored in database 57.

[0048] The deposition process is then repeated for each isolated surface portion 23 using a second substrate in step 58, and after each deposition on an isolated surface portion 23, the parameters of the deposition process are adjusted in step 59 using the parameters stored in database 57. The adjustment and deposition are then repeated for each isolated surface portion 23 to cover the entire second substrate and reduce thin film stress on the substrate.

Claims

1. 1. A method for controlling stress in a thin film on a substrate during laser deposition, comprising: providing a laser deposition apparatus including a chamber having a target holder with a target, a substrate holder with a substrate facing the target, and a window; the laser deposition apparatus further including a laser beam irradiated through the window of the chamber onto a spot on the target to generate a plasma plume of target material and deposit the target material on a surface portion of the substrate, the target spot being movable relative to the substrate to deposit the target material on multiple surface portions of the substrate; defining a plurality of discrete surface portions on a substrate; aligning the target spot with each of a plurality of discrete surface portions in turn and generating a plasma plume for depositing target material on each of the plurality of discrete surface portions; and adjusting at least one parameter of a deposition process according to the separated surface portion to which a target spot is aligned to deposit the target material on the separated surface portion, wherein by adjusting at least one parameter of the deposition process during the laser deposition process, a specific deposition pattern is obtained on the surface of the substrate and the uniformity of the stress of the thin film on the substrate is controlled, thereby controlling bending of the substrate due to stress, the parameters including temperature, pressure, laser beam pulse duration, laser beam power, target-to-substrate distance, spot size, and RF ionization energy.

2. 2. The method of claim 1, wherein the plurality of discrete surface portions are defined as a two-dimensional grid, such as longitudinal and lateral, or radial and tangential.

3. measuring the stress of a thin film deposited on a substrate; comparing the stress measurements to a desired stress profile for the thin film; adjusting at least one parameter of the deposition process in view of the comparison; The method of claim 1 or 2, further comprising:

4. 4. The method according to claim 3, wherein the stress of the thin film is measured in situ using a stress measuring device comprising a wafer bow meter.

5. depositing a target material onto a first substrate while holding deposition process parameters constant; externally measuring the stress of a thin film deposited on a first substrate; calculating an adjustment value for each separate surface portion based on the stress measurements; 2. The method of claim 1, further comprising: performing all of the steps of claim 1 on a second substrate; and using the calculated adjustment value in adjusting at least one parameter of the deposition process in response to the discrete surface portion to which the target spot is aligned.

6. 10. The method of claim 1, wherein the temperature of the substrate at the discrete surface portions where the target spots are aligned is controlled by irradiating the substrate with a laser beam.

7. The method of claim 1, wherein the laser deposition apparatus further includes at least one nozzle directed toward the separated surface portion on which the target spot is aligned, and the nozzle is supplied with a controlled flow of gas to adjust the pressure for the deposition process.

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