Patent Description:
In semiconductor devices it is desirable to keep the device from bowing. One approach to prevent bowing has been to deposit material on both opposite sides (major surfaces) of a semiconductor wafer. For example depositing compressive stress material on both front and back major surfaces balances stresses, preventing bowing. However it is not always desirable or practical to deposit material on both major surfaces.

<CIT> discloses a semiconductor device including: a structure comprising at least two heterogeneous layers having different stress levels; and a stress relief layer disposed between the two heterogeneous layers to relive a difference in the stress levels. The stress relief layer may include: a first layer formed over a first heterogeneous layer; a second layer formed over the first layer; and a third layer formed between the second layer and a second heterogeneous layer.

<CIT> discloses a layer stack of different materials deposited on a substrate, the stack comprising multiple alternating layers of compressive and tensile stress with the aim of a total net stress on the substrate close to zero and consequently a prevention of bending or deformation of the substrate, the layer deposition being provided in a single plasma enhanced chemical vapor deposition processing chamber while maintaining a vacuum. A substrate is placed in the processing chamber and a first processing gas is used to form a first layer of a first material on the substrate. A plasma purge and gas purge are performed before a second processing gas is used to form a second layer of a second material on the substrate. The plasma purge and gas purge are repeated and the additional layers of first and second materials are deposited on the layer stack.

<CIT> discloses that the purpose of invention is to prevent the warping of a semiconductor substrate, the disconnection and contact of wiring, and obtain a uniform substrate free from strain, by supplying discharge frequency electric power of different frequencies, forming thin films with different stress directions on a semiconductor substrate, and controlling the total stress by alternately stacking the thin films. By using plasma CVD method and changing discharge frequencies of high frequency power supplies thin films with different stress directions are formed on a semiconductor substrate. A thin film generating compression stress and a thin film generating tensile stress are alternately stacked, thereby controlling stress. When compression stress is generated, the substrate is bent so as to protrude outside. When tensile stress is generated, the substrate is bent so as to protrude inside. Hence, by combining both of the films, the stresses are cancelled, and the semiconductor substrate can be so controlled that external force is not applied. Thereby the generation of warp of the substrate, the disconnection of wiring on the substrate, and the mutual contact of wires can be prevented.

According to an aspect, the present disclosure provides a semiconductor device comprising: a substrate; a tensile layer overlying a major surface of the substrate; and a compressive layer overlying the major surface; and an intermediate layer between the tensile layer and the compressive layer, and in contact with both the tensile layer and the compressive layer, wherein the intermediate layer is an oxidized surface of the compressive layer or the tensile layer; and wherein the tensile layer and the compressive layer both impart forces onto the substrate, to thereby keep the substrate from bowing.

In accordance with the claimed invention, the intermediate layer transmits stresses between the tensile layer and the compressive layer.

According to an embodiment of any paragraph(s) of this summary, the intermediate layer is thinner than the compressive layer and the tensile layer.

According to an embodiment of any paragraph(s) of this summary, the tensile layer is closer than the compressive layer to the substrate.

According to an embodiment of any paragraph(s) of this summary, the tensile layer is a silicon nitride layer.

According to an embodiment of any paragraph(s) of this summary, the compressive layer is a silicon oxide layer.

According to an embodiment of any paragraph(s) of this summary, the intermediate layer is a silicon oxy-nitride layer.

According to an embodiment of any paragraph(s) of this summary, a tensile force of the tensile layer balances out a compressive force of the compressive layer.

According to another aspect, the present disclosure provides a method of making a semiconductor device, the method comprising: depositing a tensile layer overlying a major face of a substrate of the device; and depositing a compressive layer overlying the major face; wherein the tensile layer and the compressive layer both impart forces onto the substrate, to thereby keep the substrate from bowing; and further comprising forming an intermediate layer that is between the tensile layer and the compressive layer, wherein the intermediate layer is an oxidized surface of the compressive layer or the tensile layer, and wherein after the depositing of the tensile layer and the depositing of the compressive layer the intermediate layer is in contact with both the tensile layer and the compressive layer.

According to an embodiment of any paragraph(s) of this summary, depositing the tensile layer occurs before the depositing the compressive layer, with the compressive layer deposited overlying the tensile layer.

According to an embodiment of any paragraph(s) of this summary, the intermediate layer is formed after the depositing of the tensile layer, and before the depositing of the compressive layer.

According to an embodiment of any paragraph(s) of this summary, depositing the tensile layer includes depositing silicon nitride.

According to an embodiment of any paragraph(s) of this summary, depositing the silicon nitride includes depositing the silicon nitride by physical vapor deposition.

According to an embodiment of any paragraph(s) of this summary, depositing the silicon nitride includes columnar deposition of the silicon nitride.

According to an embodiment of any paragraph(s) of this summary, forming the intermediate layer includes oxidizing a surface of the silicon nitride, to form silicon oxy-nitride.

According to an embodiment of any paragraph(s) of this summary, oxidizing includes exposing the surface of the silicon nitride to air.

According to an embodiment of any paragraph(s) of this summary, depositing the compressive layer includes depositing silicon oxide on the silicon oxy-nitride.

According to an embodiment of any paragraph(s) of this summary, depositing the silicon oxide includes depositing the silicon oxide by physical vapor deposition.

To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.

The annexed drawings show various aspects of the invention.

A semiconductor device has a substrate with both compressive and tensile layers deposited overlying a single major surface (front face) of the device. The tensile layer may be deposited directly on the substrate of the device, with the compressive layer overlying the tensile layer. A transition material (intermediate layer) is located between the tensile layer and the compressive layer. The transition material is a compound including the components of one or both of the tensile layer and the compressive layer. In a specific embodiment, the tensile material may be a silicon nitride, the compressive layer may be a silicon oxide, and the transition material may be a silicon oxy-nitride, which may be formed by oxidizing the surface of the tensile silicon nitride layer. The materials may be deposited using physical vapor deposition. Conditions for the vapor deposition may be controlled to achieve desired growth rates and/or characteristics of the tensile and compressive layers. By depositing both tensile and compressive layers on the same face of the device the opposite major surface (face) is free for processing.

<FIG> shows a semiconductor device <NUM> that includes a substrate <NUM>, with a tensile layer <NUM> overlying a major surface (front face) <NUM> of the substrate <NUM>, and a compressive layer <NUM> overlying both the tensile layer <NUM> and the front face <NUM>. There is also an intermediate layer (or transition layer) <NUM> between the tensile layer <NUM> and the compressive layer <NUM>. As explained in greater detail below, the intermediate layer <NUM> transmits stresses from the compressive layer <NUM> through to the tensile layer <NUM> and the substrate <NUM>. The intermediate layer <NUM> may be a compound that includes one or more components also in the tensile layer <NUM> and/or the compressive layer <NUM>.

According to the claimed invention, in this embodiment the intermediate layer is an oxidized surface of the tensile layer <NUM>. In other words, the intermediate layer <NUM> is formed by chemical compounding of a surface of the tensile layer <NUM>, by forming an oxide layer on the surface of the tensile layer <NUM>.

The intermediate layer <NUM> may be used to facilitate deposition of the compressive layer <NUM> overlying the tensile layer <NUM>. The intermediate layer <NUM> may make for a more consistent device <NUM> in its performance in terms of being able to prevent bowing of the substrate <NUM>. Toward that end, the intermediate layer <NUM> facilitates consistency in the stresses and in the transmission of stresses from the compressive layer <NUM> to the tensile layer <NUM>. However these possibilities are not exhaustive, and the intermediate layer <NUM> may provide additional benefits to the device <NUM>.

Formation of the tensile layer <NUM> and the compressive layer <NUM> both overlying the front face <NUM> allows operations to be performed on a back face (major surface) <NUM> of the substrate <NUM>. For example it may be possible to reduce thickness of the device <NUM> as needed by removing material along the back face <NUM>. Or it may be important to keep the back side <NUM> available for other purposes, such as for placement of sensitive devices (components), or for bonding to other structures for stacking of wafers or semiconductor devices.

In one embodiment the tensile layer <NUM> is a silicon nitride, the compressive layer <NUM> is a silicon oxide, and the intermediate layer <NUM> is a silicon oxy-nitride. These are only example materials, and other suitable materials are possible as alternatives. The layers may be formed with compositions and thicknesses so as to put a desired stress on the substrate <NUM>, to keep the substrate <NUM> from bowing.

The silicon nitride tensile layer <NUM> may have a thickness from <NUM> to <NUM>, for example having a thickness of <NUM>±<NUM>. The silicon oxide compressive layer <NUM> may have a thickness of less than <NUM>, such as <NUM>±<NUM>. The silicon oxy-nitride intermediate layer <NUM> may have a thickness of about <NUM>Å (<NUM> Angstroms), such as <NUM>±<NUM>Å (<NUM>±<NUM> Angstroms). These values are examples, and should not be construed as limitations. For example a wide varieties of other layer thicknesses may be used, such as while maintaining the general ratios in the thicknesses of the layer. For instance, keeping the ratio of silicon nitride to silicon oxide thicknesses at <NUM>:<NUM> will keep the bow close to zero for thin films on the order of <NUM>-<NUM>.

As an alternative stoichiometric tantalum nitride and tantalum may be used, with an intermediate transition layer of sub-stoichiometric tantalum nitride. The tantalum nitride is compressive, the tantalum in tensile, and the sub-stoichiometric tantalum nitride allows the tantalum to grow with tensile stress. Another alternative possibility is using a bilayer of tantalum nitride and copper, with an intermediate layer of tantalum oxy-nitride, which may be created by exposing the tantalum nitride film to atmosphere to oxidize.

<FIG> shows a view of the device <NUM> at a later stage in processing, when electronic components <NUM> have been placed on the front face <NUM>, for example engaging conductive traces and/or vias on the substrate <NUM>. Parts of the layers <NUM>, <NUM>, and <NUM> may be removed, such as by selective etching, in order to form or place the components <NUM> on the substrate <NUM>. In other embodiments, the layers <NUM>, <NUM>, and <NUM> may be deposited onto or around existing components and structures. It will be appreciated that the layers <NUM>, <NUM>, and <NUM> may be removed only at certain discrete locations, leaving the remaining parts of the layers <NUM>, <NUM>, and <NUM> as continuous layers that overly large portions of the front face <NUM>.

It is often desirable for the electronic components <NUM> to be electrically isolated from one another. Therefore it is desirable for the materials used in the layers <NUM>, <NUM>, and <NUM> to be dielectrics (electrically insulating). The silicon oxide, silicon nitride, and silicon oxy-nitride materials used in one embodiment of the invention satisfy this condition. In addition silicon nitride has the characteristic of strongly adhering to most substrates used for electronic devices.

The device <NUM> may initially have a wafer for its substrate, with the wafer being subdivided into individual devices. The individual devices may be used in any of a wide variety of products, and may have any of a variety of components, such as conductive traces, switches, capacitors, etc. Devices such as the device <NUM> may be stacked as a part of a larger electronic device, for 3D wafer stacking, for example.

With reference now to <FIG>, steps are shown for a method <NUM> for producing the device <NUM> (<FIG>). The steps shown in <FIG> and described below are only a few of the steps used in forming a final device, with the illustrated steps focused on the process of preventing bowing or other deflection.

In step <NUM> the tensile layer <NUM> (<FIG>) is deposited overlying a major surface (front face) <NUM> of the substrate <NUM>. The deposition may be by physical vapor deposition (PVD), which is a different process than the plasma enhanced chemical vapor deposition (PECVD) that is usually used for depositing this material. Advantages for PVD include facilitating cassette wafer processing, providing a shorter cycle time and higher throughput, a low material consumption rate, and low contamination risk.

The PVD process is performed in a sealed chamber, with the gaseous source materials in a pressure-controlled atmosphere. It has been found that as the chamber pressure increases the tensile film stress of the deposited layer (the tensile layer <NUM> (<FIG>)) increases, but the deposition rate drops. Thus some sort of balance needs to be struck between a desirable tensile stress for the deposited material, and a faster rate of deposition. Additionally the chamber pressure may be selected so as to yield a deposited material that has a similar magnitude of stress as the material of the compressive layer <NUM> (<FIG>), so as to minimize (or reduce) the amount of the tensile material that needs to be deposited. A smaller amount of deposition is preferable because it makes the deposition process proceed faster and at lower cost. In addition, it is possible for deposited silicon nitride to be either compressive or tensile, depending on how it is deposited. For the tensile layer <NUM> of course tensile silicon nitride is desired.

The chamber pressure for the PVD process in step <NUM> may be about <NUM> mTorr, for example being <NUM>±<NUM> mTorr, to give non-limiting example values. The primary source for the chamber pressure may be an inert gas, such as argon. The flow of nitrogen gas may be controlled to prevent poisoning, where material on the target used for deposition accumulates faster than the sputtering process occurs. Temperature in the chamber may be controlled, and/or the processing time may be controlled, to prevent damage to a target for sputtering, and/or to avoid deleterious effects to the substrate (wafer) <NUM> and/or to the deposited material.

Increasing of the pressure in the chamber leads to growth of silicon nitride in columnar structures, which produces a more porous and tensile film. The spacing between columnar grains produces a lower refractive index that the typical stoichiometric silicon nitride (Si<NUM>N<NUM>), although the porous columnar form that may be used for the tensile layer <NUM> may also have the same stoichiometric silicon nitride.

It has been found that silicon nitride yields a wafer bow of -<NUM> for every <NUM> of thickness of the tensile layer <NUM>, to give a single non-limiting example value. The thickness of the layers <NUM> and <NUM> may be selected to balance out tension and compression forces on the substrate <NUM>.

In step <NUM> the intermediate layer <NUM> (<FIG>) is formed. The intermediate layer <NUM> is formed in accordance with the claimed invention by oxidizing the top of the tensile layer <NUM>, for example oxidizing the surface of the silicon nitride to form oxy-nitride. This may be done by exposing the silicon nitride to air, for a sufficient time to form oxidize the top layers of the silicon nitride, to produce the intermediate layer <NUM>. This forms a film gradient from the silicon nitride tensile layer <NUM> to the silicon oxy-nitride of the intermediate layer <NUM>. This forms a solid base for the subsequent formation of the silicon oxide compression layer <NUM>.

Silicon nitride may be oxidized at room temperature and atmospheric pressure to form a surface layer, such as with a thickness of <NUM>±<NUM> Angstroms of silicon oxy-nitride. The top monolayers of silicon nitride oxidize within the first <NUM>-<NUM> minutes of air exposure.

The deposition of silicon oxide directly on the silicon nitride may produce undesirable and/or unpredictable results. The silicon oxide stress is affected by the surface it grows upon. It is believed that when silicon oxide is deposited (grown) directly on silicon nitride, the porous silicon nitride induces columnar growth in the silicon oxide. This may produce a tensile silicon oxide, for example having a bow of -<NUM> for every <NUM> deposited, when what is desired is for the silicon oxide to be compressive, to provide a force on the substrate <NUM> that counteracts the tensile force of the underlying layer <NUM>. However when the silicon nitride surface is oxidized first, the top oxidized monolayers form a compact film surface that allows the silicon oxide form to grow densely, producing a compressive film. For example the silicon oxide may have a wafer bow of +<NUM> for every <NUM> of silicon oxide thickness. This allows formation of a compressive layer that counteracts the tensile force from the silicon nitride.

The above mechanisms are conjectures for the observed advantageous performance of devices with the intermediate layer <NUM>. It should be appreciated that the actual mechanisms of material growth may be different from those described above, as long as they still fall within the definition of the appended claims.

Finally, in step <NUM> the compressive layer <NUM> (<FIG>) is deposited overlying the tensile layer <NUM>. More specifically, the intermediate layer <NUM> may be used to facilitate deposition of the compressive layer <NUM> overlying the tensile layer <NUM>. The compressive layer <NUM> may be deposited by a PVD or other suitable deposition or formation process. When using PVD, compressive films form at low pressures on the order of <NUM>-<NUM> mTorr. For example, to balance the deflection from a tensile silicon nitride film deposited at <NUM> mTorr, a comprehensive silicon dioxide film may be deposited at <NUM> mTorr. Compressive dielectric films, for example silicon oxide and silicon nitride, may alternatively be deposited using electron beam evaporation. Other material sets of compressive films, typically metals, may be deposited using electroplating. <FIG> shows an alternative arrangement of a semiconductor device <NUM> that has a compressive layer <NUM> overlying a front face <NUM> of a substrate <NUM>. A tensile layer <NUM> overlies the compressive layer <NUM>, with an intermediate layer <NUM> between the layers <NUM> and <NUM>. The device <NUM> may function similarly to the device <NUM> (<FIG>) with regard to resisting bowing or deformation. Certain materials sets, for example tantalum nitride and copper, allow for the compressive film to be deposited first (tantalum nitride) and the tensile film to be deposited on top (copper). In some cases, an intermediate layer of tantalum may be used between the tantalum nitride and copper layers to promote copper adhesion, as long as there is still an intermediate layer <NUM>, formed in accordance with the independent claims.

<FIG> shows another alternative of a semiconductor device <NUM>, not falling within the scope of the claimed invention, that has a tensile layer <NUM> on a front face <NUM> of a substrate <NUM>, and a compressive layer <NUM> is formed directly on the tensile layer <NUM>. The intervening layer <NUM> (<FIG>) is omitted in this alternative example. Although an intermediate layer has advantages, as described above, it may be possible to omit the intermediate layer in some situations, such as with certain materials. As an example, tensile copper may be deposited directly onto compressive tantalum nitride to form a balanced film stack. The two films have complimentary deflections that can cancel out without the aid of an intermediate film.

Claim 1:
A semiconductor device (<NUM>, <NUM>) comprising:
a substrate (<NUM>, <NUM>);
a tensile layer (<NUM>, <NUM>) overlying a major surface (<NUM>, <NUM>) of the substrate; and
a compressive layer (<NUM>, <NUM>) overlying the major surface; and
an intermediate layer (<NUM>, <NUM>) between the tensile layer and the compressive layer, and in contact with both the tensile layer and the compressive layer, wherein the intermediate layer is an oxidized surface of the compressive layer (<NUM>) or the tensile layer (<NUM>);
wherein the tensile layer and the compressive layer both impart forces onto the substrate, to thereby keep the substrate from bowing.